Process for the production of a crystallized product

The disclosure relates generally to methods for separating solids from a solid-liquid slurry, for example, in separation processes during melt crystallization and purification processes. More specifically, the disclosure relates to separation and purification processes that, under certain operating conditions, preferably prevent entry into molecular oxygen processes. The processes are, therefore, more effective than and at least as safe as conventional processes for separating solids from a solid-liquid slurry.

Brief description of related technology [0002] Solid-liquid separation methods are important in a variety of industries, including, but not limited to, the chemical industry, the pharmaceutical industry, and the wastewater industry. Such solid-liquid separation methods are different and may include, but are not limited to, vacuum or pressure filtration, centrifugation, sedimentation and clarification. In many chemical processes, these solid-liquid separation methods often play an important role in the production of specific chemical intermediates. For example, para-xylene (p-xylene or pX) is a chemical intermediate that, after purification, is useful for the production of terephthalic acid. Purification of para-xylene by crystallization includes the required centrifugation for several years to obtain para-xylene purity levels of around 99.7%.

[0003] The para-xylene purification process is usually part of a much larger process for producing paraxylene from a hydrocarbon feed containing mixed C8 aromatic hydrocarbons. In this larger process, the hydrated charge is usually dewatered in the distillation tower. The oxygen present in the distillation batch usually exits from the top of the steam tower. The dry charge, of course, does not have to undergo a dewatering step. After dehydrating the batch (if it leads) dry C8 aromatic hydrocarbons are purified in a process using different unit operations. The smaller para-xylene stream produced in this purification process contains ortho-xylene (o-xylene or oX), meta-xylene (m-xylene or mX), ethylbenzene and other ingredients.

[0004] It has been found that the introduction of oxygen into the process adversely affects part of the isomerisation process. For example, the presence of oxygen in the charge into the isomerisation reactor leads to reactor overgrowth and lower parts of the heat exchangers. As a result, the length of the cycle is reduced. At the end of the cycle, the process must be interrupted to regenerate the catalyst and remove the deposits in the heat exchangers. The presence of oxygen may be negligible in other processes in which solid-liquid separators could be used. In the process for the production of para-xylene from a mixed batch of C8 aromatic hydrocarbons, however, it has been found that the absence or minimization of oxygen is important for an efficient process operation.

[0005] The purification of para-xylene usually begins with a batch of mainly C8 aromatic hydrocarbons, which usually include a mixture of ortho-, meta- and para-xylene isomers, ethylbenzene, some non-aromatic hydrocarbons and some C9 + aromatic hydrocarbons. Typical C8 aromatic hydrocarbon mixtures generally contain about 22 wt. para-xylene, about 21 wt. ortho-xylene, about 47 wt. meta-xylene and about 10 wt. other components (mainly ethylbenzene). Methods for the separation of these xylene isomers include low temperature crystallization, fractionated distillation and adsorption.

[0006] While the usual techniques for separation by distillation (based on different boiling points of the mixture components) and adsorption (based on different affinities of the constituents of the mixture to a solid adsorbent) are often suitable for generic liquid-liquid mixtures, no adsorbent is required for crystallization. , is more tolerant of different raw material compositions and usually does not require expensive pre-treatment of the raw material. During the separation of para-xylene from the C8 aromatic hydrocarbon feed, for example, crystallization is more advantageous than adsorption and distillation, because crystallization does not require an expensive adsorbent (as in adsorption processes) and because the xylene and ethylbenzene isomers have similar boiling points, which is undesirable ( makes distillation difficult), but completely different melting points. Pure para-xylene freezes at 56 ° F (13 ° C), pure meta-xylene freezes at -54 ° F (48 ° C), pure ortho-xylene freezes at -13 ° F (-25 ° C), and pure ethylbenzene freezes at -139 ° F (-95 ° C). Since para-xylene is present in these mixed feed streams at low concentrations, low temperatures are generally required for the efficient recovery of para-xylene from these feed streams by crystallization.

[0007] As in any chemical process, the capital and operating costs will influence the decisions that specific operational units should make to obtain satisfactory products and by-products. These decisions, of course, can be difficult and limited by the physical properties of products and by-products. In addition, these decisions can be difficult when, for example, the process is to be designed and carried out to avoid the introduction (or production) of contaminants. For the recovery and purification of para-xylene by crystallization, it is important to consider, for example, operating costs associated with obtaining low freezing temperature and capital costs associated with devices distributing the body of the constant body. In addition, as explained in more detail here, in the processes of para-xylene production, oxygen is considered an impurity because oxygen reduces the efficiency of processes. Oxygen can also be considered an impurity in other manufacturing processes using solid-liquid separation methods and purification.

T he T he T he T he T he T he T he T he T he he he he he he he he he he he he he he he he he he he he T he T he he T T he T T he T T T T he T T T T T T T he T T T T T he T T T T T he T T T T T he T T T T he 00 In addition, effective solid-liquid separation and purification methods are needed, which also minimize or completely eliminate the entry of oxygen into the unit operations responsible for separation and purification. In a given context for the production of para-xylene, effective methods for recovering and purifying para-xylene are needed, which also remove oxygen from the unit operations responsible for the separation and purification of para-xylene. He T he T he T he T he T he T he T he T he T he T he T he T he T he T he T he T he T he T he T he he T he T he T he T he T T T he T T T he T T T he T T T he T T T he T T 35

[0009] US 2005/0056599 discloses a method for separating solids from liquids in a filtration zone defined by a zone with a higher concentration and a zone of lower concentration that are separated by a filter.

[0010] US 2007/0225539 discloses a filter column type device comprising a filtration zone and a reslurry zone and a method for separating at least a portion of at least one substantially solid component from a solid-liquid stream comprising a substantially solid component. and at least one substantially liquid component.

SUMMARY OF THE INVENTION [0011] As indicated above, the absence or minimization of oxygen is important for an efficient operation in the para-xylene production process.

[0012] Separation of para-xylene from other C8 aromatic compounds were (and are) commonly used separation devices (e.g., centrifuges). Even the use of centrifuges, however, can still lead to the entry of oxygen. Filter centrifuges, for example, work under a slight overpressure. Despite this condition, the spinning operation to clean the xylenes, for example, will create a negative pressure at the junction between the centrifuge feeding tube and the rotating member of the centrifuge. The presence of gaps in the joint will lead to the air centrifuge (and oxygen in it).

[0013] It has been found that the use of a purification (or separation) process in accordance with the invention limits the entry of molecular oxygen into various process streams, such as, for example, those streams that supply further reactors for the production of para-xylene. isomerization. Thus, it has been found that certain separation steps (e.g., using filter columns) can be used in accordance with the invention in para-xylene production processes without compromising the safety and efficiency that the method currently provides. The reduction of molecular oxygen provides various advantages so far unachievable in the production of para-xylene. For example, this reduction will improve the operation of the device located behind the separation devices, such as an isomerisation reactor and any heat exchanger placed between the separation devices and the isomerization reactor. This decrease will result in a decrease in contamination in case of fouling and clogging of the reactor as well as in the coalification of the catalyst in the reactor. The decrease will also result in less frequent catalyst regeneration and reactor downtime. In addition, shrinkage and clogging of the heat exchangers that are located between the separation devices and the isomerisation reactor are likely to be avoided by this reduction. These benefits will be seen in the cost efficiency and improved process efficiency of para-xylene. This decrease will result in a decrease in contamination in case of fouling and clogging of the reactor as well as in the coalification of the catalyst in the reactor. The decrease will also result in less frequent catalyst regeneration and reactor downtime. In addition, shrinkage and clogging of the heat exchangers that are located between the separation devices and the isomerisation reactor are likely to be avoided by this reduction. These benefits will be seen in the cost efficiency and improved process efficiency of para-xylene. This decrease will result in a decrease in contamination in case of fouling and clogging of the reactor as well as in the coalification of the catalyst in the reactor. The decrease will also result in less frequent catalyst regeneration and reactor downtime. In addition, shrinkage and clogging of the heat exchangers that are located between the separation devices and the isomerisation reactor are likely to be avoided by this reduction. These benefits will be seen in the cost efficiency and improved process efficiency of para-xylene. which are located between the separation devices and the isomerisation reactor. These benefits will be seen in the cost efficiency and improved process efficiency of para-xylene. which are located between the separation devices and the isomerisation reactor. These benefits will be seen in the cost efficiency and improved process efficiency of para-xylene.

[0014] The disclosure generally relates to a process involving the separation of para-xylene and molecular oxygen from a suspension containing them and containing other xylene isomers under conditions that prevent molecular oxygen from entering the process. The para-xylene and molecular oxygen are preferably separated from the suspension in a filter column under conditions that prevent molecular oxygen entering the process to form a para-xylene filter cake and forming a filtrate containing a liquid product component comprising a para-xylene poor product.

[0015] In another embodiment, the process is a separation process that involves purifying para-xylene from a slurry containing it and containing other xylene isomers under conditions that prevent molecular oxygen from entering the separation process to form a para-xylene poor product and isomerizing the lean in the para-xylene of the separation product. The para-xylene is preferably purified from the suspension in the filter column under conditions that protect it against the entry of compound oxygen into the separation process to form a filter cake containing para-xylene and a filtrate containing a liquid product component comprising a para-xylene-poor product.

[0016] It has been found that the filter column, operating under the conditions specified herein, will minimize the content of molecular oxygen in the filtrate, which in turn will help to prevent undesired carbonizing of the catalyst and overgrowing and clogging of the isomerisation device. For example, and as described in more detail below, a filtration column operating at least at ambient pressure, and preferably at a pressure above ambient pressure (e.g., about 2 pounds per square inch (psig) to about 30 psig), will minimize the molecular oxygen content of the filtrate. In a very advantageous operation, the filter column operates at an elevated pressure of about 0.5 pounds per square inch (psi) above ambient pressure (i.e., at least about 0.5 psig), even more preferably at least about 1.5 psi above ambient pressure , even more

Preferably, at least about 3 psi is above ambient pressure, even more preferably at least about 5 psi above ambient pressure, even more preferably at least about 10 psi above ambient pressure, and even more preferably at least about 15 psi above ambient pressure. A very advantageous pressure range for the work of the filtration column is about 1.5 psi to about 3 psi above ambient pressure (i.e., about 1.5 psig to about 3 psig). Although the pressure exceeding the ambient pressure is a prerequisite for ensuring minimal or no entry of molecular oxygen, a pressure much higher than the ambient pressure will undesirably increase the operational costs of the process to a level where the economic benefits of the process are lost. Also,the tank used to carry out the separation will not have exceeded the rated pressure, which is effectively set to the upper limit of the operating pressure, which, in most cases, will not be achieved, although it is appropriate. Thus, careful observation of pressure should be maintained to obtain many of the benefits possible due to the findings set forth herein.

[0017] In order to further avoid the harmful effect of molecular oxygen on the method of producing paraxylene, the feed stream of the separation devices (e.g., the filter column) should be substantially free of molecular oxygen. As used herein, the stream is substantially free of molecular oxygen if it does not contain an amount of molecular oxygen (e.g., O2 dissolved in a liquid stream, O2 gas in a gaseous stream) which, if transferred to a filtrate (specifically to a liquid secondary filtrate component) will adversely affect the operation of the further device (e.g., in the isomerisation device or in a heat exchanger placed between the isomerization and separation devices). E.g, each feed stream of the filter column preferably contains about 5 parts by weight (ppm) or less (more preferably about 2 ppm or less, and even more preferably about 1 ppm or less) of molecular oxygen, based on the total weight of the stream, and individual streams they can be simply free of molecular oxygen. Thus, the concentration of molecular oxygen in the liquid secondary component of the filtrate from the filtration column is less than that in the feed stream, and is preferably about 2 ppm by weight or less (more preferably about 0.7 ppm by weight or less, and even more preferably about 0.4 ppm by weight or less), based on the total weight of the filtrate from the filtration column. and even more preferably about 1 ppm or less) of molecular oxygen, based on the total weight of the stream, and the individual streams can be simply molecular oxygen-free. Thus, the concentration of molecular oxygen in the liquid secondary component of the filtrate from the filtration column is less than that in the feed stream, and is preferably about 2 ppm by weight or less (more preferably about 0.7 ppm by weight or less, and even more preferably about 0.4 ppm by weight or less), based on the total weight of the filtrate from the filtration column. and even more preferably about 1 ppm or less) of molecular oxygen, based on the total weight of the stream, and the individual streams can be simply molecular oxygen-free. Thus, the concentration of molecular oxygen in the liquid secondary component of the filtrate from the filtration column is less than that in the feed stream, and is preferably about 2 ppm by weight or less (more preferably about 0.7 ppm by weight or less, and even more preferably about 0.4 ppm by weight or less), based on the total weight of the filtrate from the filtration column.

[0018] The use of filter columns in accordance with the process conditions presented here further improves the efficiency of the process regarding both the recovery of the product component and the operating costs. For example, in the crystallization / production of a secondary slurry using filtration columns for purification and recovery of para-xylene, the yield and reduced operating costs associated with the cooling power during crystallization and the re-isomerisation cycle can be increased.

[0019] Additional embodiments of the method are also disclosed herein. For example, in one such embodiment, the method of purifying a solid product from a slurry stream comprises administering a slurry and displacing the fluid to the filtration column. The slurry contains solid product components and a liquid secondary component, wherein the slurry and the displacing fluid are substantially free of molecular oxygen. The filter column at least partially separates the solid product components and the liquid secondary component of the suspension to form a filtrate (including a secondary secondary component and at least a portion of the displacing fluid) and a filter cake (including solid product components) such that the concentration of molecular oxygen in the filtrate is equal to or less than the concentration of molecular oxygen in the suspension. preferably,

Less, or even more preferably, about 0.4 ppm by weight or less. Preferably, the displacing fluid is substantially free of molecular oxygen and includes a gas and / or liquid, both non-reactive towards the component crystals, e.g. nitrogen (most preferred), carbon dioxide, hydrogen, methane, ethane, natural gas, helium. , xenon, argon, neon and their combinations. Optional process steps include feeding the washing liquid to the filtration column (where the washing liquid is also substantially free of molecular oxygen) and / or converting at least a portion of the liquid secondary filtrate component into a product component in the liquid phase in a further chemical reactor.

[0020] In another embodiment, the method of crystallizing the product comprises first crystallizing a liquid feed stream comprising a liquid secondary component and a liquid product component having a melting point higher than the liquid secondary component. The liquid feed stream crystallizes in a crystallizer operating at a temperature sufficient to crystallize at least a portion of the liquid product component to form a slurry of suspension comprising the product component crystals and the liquid secondary component. The product component crystals and the secondary secondary component in the slurry leakage are then at least partially separated in a filtration column to form a filtrate that includes a secondary liquid component and a filter cake that includes the product component crystals.

Both the enriched product stream and the diluent for resuspending (comprising the liquid product component and the liquid secondary component) are fed (included) into the secondary suspension forming barrel containing the product component crystals. The crystals of the product component are then equilibrated with the liquid product and the secondary secondary components in the secondary suspension drum for a sufficient time to produce a leak of the secondary suspension containing and the product component crystals and the secondary liquid component.

[0022] In another embodiment, the method of preparing the crystalline product comprises performing further two- or more-than-two-stage crystallization processes, wherein each stepwise crystallization process comprises first crystallizing a liquid feed stream comprising a secondary liquid component and a liquid product component that has a melting temperature. higher than the melting point of the liquid secondary component. The liquid feed stream crystallizes in a crystallizer operating at a temperature sufficient to crystallize at least a portion of the liquid product component to form a slurry of suspension comprising the product component crystals and the liquid secondary component. The product component crystals and the secondary liquid component in the slurry leakage are then partially separated in a filter column, a wash column or a centrifuge (although at least one filter column is used) to form a filtrate containing a liquid product component and a liquid secondary component and an enriched product stream comprising component crystals product. The liquid feed stream at any crystallization stage, other than the first crystallization stage, contains the filtrate from the previous prior crystallization step. a washing column or centrifuge (although at least one filtration column is used) to form a filtrate comprising a liquid product component and a liquid secondary component and an enriched product stream comprising the product component crystals. The liquid feed stream at any crystallization stage, other than the first crystallization stage, contains the filtrate from the previous prior crystallization step. a washing column or centrifuge (although at least one filtration column is used) to form a filtrate comprising a liquid product component and a liquid secondary component and an enriched product stream comprising the product component crystals. The liquid feed stream at any crystallization stage, other than the first crystallization stage, contains the filtrate from the previous prior crystallization step.

[0023] In yet another embodiment, the method of recovering the solid product from the filtrate after centrifugation first comprises at least partially separating in the centrifuge the feed stream of liquid containing suspension and dispersed solids to form at least a high solids filtrate and cake from the centrifuge. . The high solids filtrate contains liquid and dispersed solids, wherein the weight concentration of the dispersed solids in the high solids filtrate is about 5 wt%. up to about 50 wt.%, based on the total weight of the high solids filtrate and the centrifuge cake contains liquid and dispersed solids, wherein the weight concentration of the dispersed solids in the cake from the centrifuge is greater than 50 wt%, based on the total weight of the cake from the centrifuge. The dispersed solids and liquid in the high solids filtrate are then at least partially separated in a filtration column to form a filtrate from a filtration column containing liquid and cake from a filtration column containing dispersed solids, the cake from the filtration column having a weight concentration of dispersed solids. larger than the filtrate from the filtration column.

[0024] Each of the above-described embodiments can be used to isolate and purify para-xylene (which can be crystallized in solid form) from C8 aromatic hydrocarbons, including ortho-xylene, meta-xylene and / or ethylbenzene. As evident from the above summary, the method disclosed is not simply limited to purifying para-xylene from a mixture of xylene isomers, but is also suitable for use in a solid-liquid separation process in which molecular oxygen is considered an undesirable process contamination. . .

[0025] Additional features of the invention will become apparent to those skilled in the art from the review of the following detailed description together with the drawings, examples and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the disclosure, reference should be made to the following detailed description and attached drawings, in which:

Figure 1 is a flow chart illustrating the process of crystallization / post-suspension (reconstitution) using a two-step recycle and filtration columns to recover a solid (crystalline) product component;

Figure 2 is a process flow diagram illustrating a crystallization / re-enrichment process using any number of resoluring steps and filtration columns for recovering a solid (crystalline) product component;

Figure 3 is a flow chart illustrating a series array of crystallizers and filter columns for recovering a solid (crystalline) product component, and Figure 4 is a process diagram illustrating a series system of centrifuges and filter columns for recovering a solid (crystalline) product component from a centrifuge filtrate.

[0027] Although the methods disclosed may have different embodiments, specific embodiments are illustrated in the drawings (and will be further described), it being understood that the disclosure is intended to be illustrative only and is not intended to limit the invention to the specific embodiments described and illustrated herein.

DETAILED DESCRIPTION OF THE INVENTION [0028] Processes capable of separating solids from a solid-liquid slurry are disclosed herein under conditions in which protection against entry of molecular oxygen is required for a process in which the presence of molecular oxygen (O2) can adversely affect the effectiveness of , process safety

EP 2 238 853 B1 and / or product yield. Thus, in the exemplary general embodiment of the process according to the invention, para-xylene and molecular oxygen are separated from the suspension containing them, which also contains other xylene isomers under conditions that prevent the entry of molecular oxygen into the process. The para-xylene and molecular oxygen are preferably separated from the suspension in the filter column under conditions that prevent the entry of molecular oxygen into the process to form a para-xylene containing filter cake to form a filtrate containing a liquid product component that includes a para-xylene-poor product.

[0029] In another general exemplary embodiment, the method is a separation process that involves purifying para-xylene from a slurry containing it that also contains other xylene isomers under conditions that prevent molecular oxygen from entering the separation process to produce a low-para product. -exylene and isomerization of a para-xylene-poor product from separation. The para-xylene is preferably purified from the suspension in the filter column under conditions that prevent the entry of molecular oxygen into the separation process to form a para-xylene filter cake and a filtrate containing a liquid product component that includes a para-xylene poor product.

[0030] According to these exemplary embodiments, the filtrate may further comprise a displacing fluid.

Preferably, at least one of the filter cake and the displacing fluid comprise at least part of the molecular oxygen introduced into the process. As used herein, the term "at least a portion of the molecular oxygen introduced into the process" means at least about 40%, preferably at least about 45% and more preferably at least about 50% of the molecular oxygen introduced into the process. In addition, at least one of the filter cake and the displacing fluid in the filtrate preferably contains substantially all of the molecular oxygen introduced into the process. The term "substantially all of the molecular oxygen incorporated into the process" as used herein means at least about 80%, preferably at least about 90% and more preferably at least about 95% of the molecular oxygen introduced into the process.

[0031] Within various other embodiments disclosed herein are processes involving the use of filter columns for solids separation from a solid-liquid slurry, for example in purification processes by melt crystallization, under conditions that ensure that molecular oxygen does not cross into streams. process. The processes utilize several unit operations generally described below. One such embodiment includes the work of the filtration column in a manner that limits the entry of molecular oxygen into the filtrate from the filtration column. Another embodiment of the disclosure includes the use of filter columns in combination with a crystallization / secondary suspension process with specific embodiments, wherein subcombinations include a crystallizer and a filtration column or a drum for producing a secondary slurry and a filtration column. The additional implementation includes the use of filter columns in combination with a serial array of crystallizers. Another embodiment involves the use of a filtration column in combination with a centrifuge to recover residual solids passing through the centrifuge into the filtrate. The test and simulation data indicate that the processes in which the filter columns of the disclosure are used are effective in reducing molecular oxygen access and further improving the efficiency of the process. Another embodiment involves the use of a filtration column in combination with a centrifuge to recover residual solids passing through the centrifuge into the filtrate. The test and simulation data indicate that the processes in which the filter columns of the disclosure are used are effective in reducing molecular oxygen access and further improving the efficiency of the process. Another embodiment involves the use of a filtration column in combination with a centrifuge to recover residual solids passing through the centrifuge into the filtrate. The test and simulation data indicate that the processes in which the filter columns of the disclosure are used are effective in reducing molecular oxygen access and further improving the efficiency of the process.

One preferred embodiment of the disclosure includes a process for purifying a solid product from a given slurry under process conditions that reduce or prevent the entry of molecular oxygen into the streams flowing through the process (e.g., to one or more streams exiting unit operations responsible for purifying the solid product). An example of this embodiment is a process that may include a first administration of a solid / liquid slurry comprising the components to be separated, a displacing fluid and, optionally, a rinsing fluid for the filtration column, all three streams being substantially free of molecular oxygen.

[0033] The solid / liquid slurry feed comprises solid product components to be separated / recovered in the filter column and the liquid secondary component to be removed from the slurry feed. The disclosed purification method is suitable for separating solid product components dispersed in suspension with a secondary liquid component. When the purification process is carried out in conjunction with a crystallization and / or secondary suspension, the two components to be separated have different melting points and the solid component of the product may be the crystals of the product component produced in the earlier crystallization step and / or secondary suspension production. by crystallizing the product component in the liquid phase. In a preferred embodiment, the disclosed processes (including those described below) are used to separate and purify para-xylene from other hydrocarbons, and the product component (in liquid or solid / crystalline form) preferably contains para-xylene. Similarly, the liquid secondary component preferably contains ortho-xylene, meta-xylene and / or ethylbenzene. The term "liquid secondary component" is used herein in its singular, but may refer to either one chemical compound or a collection of chemical compounds that can be separated from a particular product component using the disclosed methods. the liquid secondary component preferably contains ortho-xylene, meta-xylene and / or ethylbenzene. The term "liquid secondary component" is used herein in its singular, but may refer to either one chemical compound or a collection of chemical compounds that can be separated from a particular product component using the disclosed methods. the liquid secondary component preferably contains ortho-xylene, meta-xylene and / or ethylbenzene. The term "liquid secondary component" is used herein in its singular, but may refer to either one chemical compound or a collection of chemical compounds that can be separated from a particular product component using the disclosed methods.

[0034] The filter column is a solid-liquid separating apparatus for concentrating the suspension. Examples of suitable filter columns are disclosed in US Patent Application Publication Nos. 2005/0056599 and

2007/0225539, the disclosures of which are hereby incorporated herein by reference. A suitable filter column includes a hollow cylinder in which there is one or more pipes of a defined outside diameter and extending in the axial direction in the hollow cylinder. In the wall of each pipe there is at least one filter, which creates only a direct connection between the inside of the pipe and the interior of the hollow cylinder. The filter column separates the solid from the liquid in a solid-liquid slurry (e.g., a solid product component suspended in the mother liquor) by directing the slurry to the first end of the filtration column. The displacer fluid (e.g., a gas or liquid immiscible with the liquid in the slurry) exerts a back pressure on the other end of the filter column, helping to push a portion of the slurry liquid through the filter into the tube, which is to be taken out of the filtration column pipes as a filtrate (e.g. mother liquor), thereby producing a concentrated suspension (i.e., bed) of solids in the hollow cylinder and around the tubes. The concentrated solids suspension is withdrawn from the second end of the filtration column through the product overflow channel, e.g. in the form of a concentrated product cake containing a small amount of liquid suspension (e.g., mother liquor) and / or a displacement fluid.

[0035] Optionally, a washing fluid is fed into the product gutter to clean the product gutter from blockages. Preferably, when a washing fluid is used, the product gutter also includes a re-suspension tank, for example when the washing liquid contains the liquid suspension (mother liquor) and / or the liquid component of the product. In this embodiment of the secondary suspension filter column, the re-suspension zone tank functions as a separate secondary suspension drum (see below). Analogously to the secondary slurry drum, the leakage of the slurry containing the product component crystals dispersed in the liquid comprising the secondary secondary component and part of the non-crystallized liquid product component exits the secondary slurry filter column through the outlet at the first end of the secondary slurry filtration column.

Gravity to move the filter cake and it must be on a raised surface). The term & quot; filter column & quot; as used herein refers to both the general embodiment described above and the embodiment of the re-suspending zone tank and the washing fluid.

In general, the pushing fluid may comprise a gas and / or a liquid, each preferably inert, incompatible and / or insoluble with respect to the product component (e.g., the solid / crystalline component is not soluble in the displacer fluid and the liquid product components / secondary) they are not miscible with the displacement fluid). When the product component contains para-xylene, the displacing fluid is substantially free of molecular oxygen (e.g., O 2 dissolved in the liquid displacer fluid, O 2 gas in the propellant displacement fluid). When the product component contains para-xylene, the displacing fluid is preferably a gas selected from the group consisting of nitrogen, carbon dioxide, hydrogen, methane, ethane, natural gas or one or more noble gases (e.g., helium, xenon, argon, neon) and their mixtures. Nitrogen is a particularly preferred displacement fluid. Nitrogen gas is effective to remove the oxygen present in the charge and ensures that the filtrate contains less oxygen than in the feed. In case the gaseous nitrogen is recycled, the oxygen present in it can be removed before reuse of recycled nitrogen gas; however, additional costs would be associated with this procedure.

[0037] When the slurry feed, the displacing fluid and (optionally) washing liquid are introduced into the filter column, the solid product component and the liquid slurry secondary component are separated in a filter column to form a filtrate and a filter cake. The filtrate contains a liquid secondary component and a displacing fluid and may further comprise a small, residual amount of the product component (e.g., through the filter of the filtration column may pass the liquid product component initially in the slurry feed and / or very fine solid product component). The filter cake is mainly composed of solid product components, but will generally also contain a residual liquid secondary component that does not pass through the filter to the filtrate. In the para-xylene purification process, the filter cake generally has a moisture content of about 15% by weight. to about 20 wt.%, meaning that the filter cake contains about 80 wt.%. up to about 85 wt.% solid para-xylene crystals and about 15 wt.% up to about 20 wt.% mixed C8 hydrocarbons in liquid form. [0038] It has been found that operation in a filtration column in this way can provide advantages in the process regarding the absence (or protection against introduction) of molecular oxygen in the flow streams in the process (e.g., in the filtrate from the filtration column). It has been found that when the filter column works according to the process conditions disclosed herein, it minimizes the content of molecular oxygen in the filtrate helping to protect against undesired charring and clogging in the isomerisation device (in the reactor). Unlike other solid-liquid separators (e.g. in some centrifuges), the filter column operates according to the process conditions described herein, ensuring that the concentration of molecular oxygen in the filtrate is equal to or less than the concentration of molecular oxygen in the slurry feed. Accordingly, the filter columns should operate at least at ambient pressure, and preferably at pressures above ambient pressure (e.g., about 2 psig to about 30 psig) to minimize the content of molecular oxygen in the filtrate. In a very advantageous operation, the filter column is operated at a pressure of at least about 0.5 psi above ambient pressure (e.g., at least about 0.5 psig), even more preferably at least about 1.5 psi, above ambient pressure, even more preferably at least about 3 psi of ambient pressure, even more preferably at least about 5 psi of ambient pressure, even more preferably at least about 10 psi of ambient pressure and even more preferably at least about 15 psi of excess pressure environment. A very advantageous pressure range for the operation of the filtration column is the pressure from

About 1.5 psi to about 3 psi in excess of ambient pressure (i.e., about 0.5 psig to about 3 psig). However, pressure above ambient pressure is a prerequisite for being sure that no molecular oxygen will enter, too much pressure will exceed the ambient pressure unnecessarily increase the operating cost of the process to the level at which the economic benefits of the process will be lost. In addition, the tank used to carry out the separation will not have exceeded the rated pressure, which is actually set as the upper limit of the operating pressure, which, in most cases, will not be reached, although it is, however, appropriate. Thus, careful observation of pressure should be maintained to obtain many of the benefits possible due to the findings set forth herein.

The present reference to the operating pressure in the separation step (or to the pressures in the filtration column described in the previous paragraph) relates to the lowest plurality of pressures under which the various parts (interior, feed inlets and outlets) of the separation device can be operated. For example, when the separation device is a filter column, it is understood that it is not an isobaric column and that it is practically based on pressure gradients. The pressure at the inlet of the suspension is the highest of three. The second highest of the three pressures is the pressure at the inlet of the displacement fluid. The lowest of the three pressures is the pressure at which the displacement fluid and filtrate exit the column. The pressure anywhere in the column is limited by the highest and lowest of these pressures. Accordingly, as long as the pressure, where the displacement fluid and filtrate exit from the column is higher than the atmospheric pressure (ambient), it can still be considered that the pressure anywhere in the column is higher than the atmospheric (ambient) pressure. Furthermore, as long as the pressure in the column (separation device) exceeds atmospheric (ambient) pressure, the oxygen inlet may not be possible.

[0040] In general, the amount of molecular oxygen present in a stream poor in a product (e.g., paroxylene-poor) exiting the separation device is associated with the amount of such oxygen entering the device through the supply and removed by the displacing fluid. The feed streams of the filter column should be substantially free of molecular oxygen. According to the process conditions disclosed herein, the filter column operates at a pressure above atmospheric pressure and there are no moving parts. As used herein, the stream is substantially free of molecular oxygen if it does not contain an amount of molecular oxygen (e.g., O2 dissolved in a liquid stream, O2 gas in a gaseous stream), which, if it is transferred to the filtrate (in particular to its secondary liquid component) it will adversely affect the operation of the further device (e.g., in an isomerisation device or in a heat exchanger placed between the isomerization device and the separation device). For example, each of the feeds of the filter column preferably contains about 5 parts by weight (ppm) or less (more preferably about 2 ppm or less, and even more preferably about 1 ppm or less) of molecular oxygen, based on the total weight of the stream. and a single stream can simply be free of molecular oxygen. Working in this way, the filtration column will not allow molecular oxygen to penetrate from the ambient air into a unit operation and contamination of process streams flowing through it. Suitably, the concentration of molecular oxygen in the filtrate from the filtration column is preferably about 2 ppm by weight or less (more preferably about 0.7 ppm by weight or less, even more preferably about 0.4 ppm by weight) based on the total weight of the filtrate from the filtration column.

[0041] As mentioned previously, the low level of molecular oxygen is particularly advantageous when the filtrate (specifically its liquid secondary component) is fed to the chemical reactor to convert the liquid secondary component into a product component, e.g. to a catalytic device

Isomerization, which converts ortho-xylene, meta-xylene and ethylbenzene to para-xylene (described in more detail below). Molecular oxygen in the feed stream of the isomerisation device is a contamination causing the charring and clogging of the catalytic reactor and / or the reactor heater.

See, e.g., WT Koetsier and J. van Leenen, "Oxygen Induced Fouling in a Xylene Isomerization Reactor Bed,"

Catalyst Deactivation, 1987 (G. Delmon and GF Froment, eds.).

[0042] Figure 1 illustrates the crystallization process / secondary dispersion 100 using the crystallization degree 105, followed by the first step of producing the secondary slurry 125 and the second step of producing the secondary slurry 145 in combination with at least one filter column to recover the solid (crystalline) product component from a liquid multicomponent stream, the solid component of the product can then be melted to produce a substantially pure liquid component of the product. The crystallization step 105 includes a crystallizer 110 and a separation device 120. After the crystallization step 105, the first step of producing a secondary slurry 125 takes place, which includes a secondary slurry 130 and a separation device 140. After the first step of producing the secondary slurry 125, the second (or "

Alternatively, the crystallization process / secondary slurry 100 may be run as a series of one or more separation / post slurry steps preceded by a crystallizer 110 (which feeds the first separation / secondary slurry step) followed by a separation device 160 (which cleans the leak product from the final separation / secondary slurry step). This is illustrated in Figure 1 through the two separation / slurry steps 115 and 135, although the general crystallization / secondary slurry process 100 could involve only one separation / secondary slurry step or more than two separation / secondary slurry steps. The separation / secondary slurry step 115 includes a separation device 120 and a drum for the secondary slurry 130, followed by a separation / secondary slurry step 135, respectively,

[0044] The crystallization vessel (crystallizer) cools the previous liquid charge, which contains at least two mixing components, to recover one of these liquid components. A suitable example of a purification process by melt crystallization is disclosed in US Pat. No. 3,177,265, which disclosure is incorporated herein by reference. The liquid feed includes a liquid component of the product to be separated from the feed and a liquid secondary component that should not be recovered from the liquid component of the product, and is fed to the crystallizer. The liquid component of the product has a melting point higher than the melting point of the liquid secondary component. The crystallizer cools the liquid feed stream to a temperature sufficient to crystallize at least a portion of the liquid component of the product. For a given liquid charge, the temperature can be limited by the eutectic temperature of the supply system. Thus, the crystallizer preferably operates at a temperature above the eutectic temperature defined by the mixture of product and secondary components to avoid co-crystallization of the secondary component with the product component. The crystallizer preferably has sufficient capacity / residence time to crystallize the major part of the liquid product component in the liquid charge. The slurry leak (i.e., solid-liquid slurry) exits the crystallizer through the outlet. The slurry leak essentially comprises pure crystals of a product component dispersed in a liquid that mainly contains a liquid secondary component, but can also include a portion of the non-crystallized liquid component of the product.

[0045] In a bowl for producing a secondary slurry, a previously prepared product filter cake of a product component with a typically warmer diluent stream containing an additional (liquid) component of the product is balanced to provide a slurry suitable for further processing. A suitable drum for producing a secondary suspension is described in US Pat. No. 6,565,653, which disclosure is incorporated herein by reference. A solid crystal cake of the product component and a liquid diluent containing the liquid product and the secondary components are fed to the inlet of a suitable drum for producing a secondary slurry. The solid cake and liquid diluent can be added to the drum for producing the secondary slurry separately (i.e. through two different feed lines) or can be a mixed stream before the drum for producing a secondary slurry and added to it via a single feed line. The secondary suspension drum is a reservoir containing the crystals of the product component and has sufficient capacity / residence time to allow the crystals of the product component to be balanced with the liquid component of the product in the reservoir. During balancing the content of the drum for producing the secondary slurry is preferably mixed. The slurry leak (i.e., solid-liquid slurry) exits the drum through the outlet. The slurry leak contains the crystals of the product component dispersed in the liquid containing the secondary liquid component and part of the non-crystallized liquid product component. The secondary suspension drum is a reservoir containing the crystals of the product component and has sufficient capacity / residence time to allow the crystals of the product component to be balanced with the liquid component of the product in the reservoir. During balancing the content of the drum for producing the secondary slurry is preferably mixed. The slurry leak (i.e., solid-liquid slurry) exits the drum through the outlet. The slurry leak contains the crystals of the product component dispersed in the liquid containing the secondary liquid component and part of the non-crystallized liquid product component. The secondary suspension drum is a reservoir containing the crystals of the product component and has sufficient capacity / residence time to allow the crystals of the product component to be balanced with the liquid component of the product in the reservoir. During balancing the content of the drum for producing the secondary slurry is preferably mixed. The slurry leak (i.e., solid-liquid slurry) exits the drum through the outlet. The slurry leak contains the crystals of the product component dispersed in the liquid containing the secondary liquid component and part of the non-crystallized liquid product component. During balancing the content of the drum for producing the secondary slurry is preferably mixed. The slurry leak (i.e., solid-liquid slurry) exits the drum through the outlet. The slurry leak contains the crystals of the product component dispersed in the liquid containing the secondary liquid component and part of the non-crystallized liquid product component. During balancing the content of the drum for producing the secondary slurry is preferably mixed. The slurry leak (i.e., solid-liquid slurry) exits the drum through the outlet. The slurry leak contains the crystals of the product component dispersed in the liquid containing the secondary liquid component and part of the non-crystallized liquid product component.

[0046] Typically, a single separation device may be a filter column, a wash column or a centrifuge (described herein), or another type of solid-liquid separator known in the art. In the embodiments of the present disclosure, at least one of the separation devices may be a filter column and preferably the filter column is used in at least one step of producing a secondary suspension not in the product (non-final) step. For example, in the embodiment illustrated in Figure 1, at least one of the separation devices 120, 140 and 160 is a filter column and preferably the filter column is used as one or both separation devices 120 and 140. In contrast, the separation device 160 is preferably not a column filtration, for example, is a wash column or a centrifuge.

[0047] Filter columns are advantageous separation devices used at an earlier stage (i.e., not at the product stage), based on the various efficiencies they produce. For example, in relation to centrifuges, they do not have any rotating parts (thus simplifying construction and maintenance), they give less mechanical energy to process fluids (thus reducing cooling costs and product losses caused by melting the product crystals in the cake from the centrifuge) and give higher recovery than centrifuges based on lower solids content in the filtrate. Additionally, in the filter columns it is possible to easily adjust the moisture of the filter cake by changing the amount of displacer fluid and they can be used to obtain processes more spatially compact and / or to increase the capacity of the processes by replacing centrifuges with filter columns. It has also been found that in the operating conditions disclosed herein, filtration columns eliminate the entry of oxygen into the process streams. In comparison with the washing columns, the absence of rotating parts is also advantageous because the wash columns usually have either rotating parts or rotating parts are omitted in them at relatively low cost per unit volume of the wash column. Additionally,

[0048] In contrast, non-filtration columns are preferably used as separation devices at the product steps in the process. Typically, wash columns and centrifuges give a higher purity of the product streams relative to the filter columns, and therefore product streams require less additional treatment before subsequent storage or use. While the filter column recovers the larger part

The filter column also recovers the major part of the secondary liquid component in the product stream.

[0049] The wash column (or hydraulic wash column) is a solid-liquid separation apparatus for concentrating the suspension. Examples of suitable washing columns are disclosed in US Pat. No. 4,734,102 and 4,735,781, which disclosure is incorporated herein by reference. The washing column comprises a hollow cylinder in which there is one or more tubes of a given outer diameter and extending in the axial direction in the hollow cylinder. In the wall of each pipe there is at least one filter, which creates only a direct connection between the inside of the pipe and the interior of the hollow cylinder. The wash column separates solids from liquids in a solid-liquid slurry (e.g., a solid component of the product suspended in the mother liquor) by directing the slurry to the first end of the wash column, and a washing liquid to the other end of the wash column in countercurrent flow to the slurry, thereby forming a bed in the hollow cylinder and around the tubes. The filtrate (e.g., mother liquor) from the slurry) escapes through the filter tube filters and is discharged from the wash column into the interior of the tubes and then discharged from the wash column (e.g. from the first end of the wash column). The concentrated suspension of the solid product component is discharged from the other end of the wash column. The wash liquid introduced at the other end of the washing column produces a secondary suspension of a concentrated solids suspension and may melt some of the solids recovered. When the wash column is used to separate / purify the slurry from the melt crystallization process,

[0050] Centrifuges that are suitable for use as solid-liquid separators are not particularly limited and include generally known in the art, such as, for example, filter centrifuges, in particular centrifuges with a perforated drum, sedimentation and / or with a piston pulsating. A suitable centrifuge generally comprises an inlet for a solid-liquid slurry (e.g., a solid product component suspended in the mother liquor) to be separated, a first outlet for a concentrated solid suspension (e.g., product filter cake) and a second outlet for a filtered liquid (e.g. a mother liquor) from the inlet suspension. In some embodiments (e.g., when using a centrifuge with a perforated drum) the centrifuge comprises a third outlet for the filtered liquid from the inlet slurry, wherein the second and third outlet streams differ in the relative amounts of solids (e.g., residual, unrecovered component of the product) contained in each stream. In such embodiments, the second outlet may be for a low solids filtrate stream, and the third outlet may be for a high solids filtrate stream. [0051] In the embodiment illustrated in Figure 1, the product component purification and recovery process begins with feeding the liquid feed stream 204 to the crystallizer 110. As described above, the feed stream 204 comprises a liquid product component and a liquid secondary component, the liquid product component having a temperature melting higher than the liquid secondary component. Although in the feed stream 204, the decomposition of the liquid secondary components of the product may usually be desired, the preferred feed stream 204 for purifying para-xylene contains about 10 wt. up to about 30 wt.% (more preferably about 15 wt% to about 25 wt%) para-xylene. The crystallizer 110 operates at a temperature sufficient to crystallize at least a portion of the liquid product component from the liquid feed stream 204 to produce a slurry 208 that contains both the product component crystals and the secondary secondary component. For example, when the feed stream 204 contains about 22 wt. up to about 23 wt.% para-xylene, the corresponding crystallization temperature at atmospheric pressure is about -89 ° F (-67 ° C) or about a preferred feed stream 204 for purifying para-xylene contains about 10 wt. up to about 30 wt.% (more preferably about 15 wt% to about 25 wt%) para-xylene. The crystallizer 110 operates at a temperature sufficient to crystallize at least a portion of the liquid product component from the liquid feed stream 204 to produce a slurry 208 that contains both the product component crystals and the secondary secondary component. For example, when the feed stream 204 contains about 22 wt. up to about 23 wt.% para-xylene, the corresponding crystallization temperature at atmospheric pressure is about -89 ° F (-67 ° C) or about a preferred feed stream 204 for purifying para-xylene contains about 10 wt. up to about 30 wt.% (more preferably about 15 wt% to about 25 wt%) para-xylene. The crystallizer 110 operates at a temperature sufficient to crystallize at least a portion of the liquid product component from the liquid feed stream 204 to produce a slurry 208 that contains both the product component crystals and the secondary secondary component. For example, when the feed stream 204 contains about 22 wt. up to about 23 wt.% para-xylene, the corresponding crystallization temperature at atmospheric pressure is about -89 ° F (-67 ° C) or about The crystallizer 110 operates at a temperature sufficient to crystallize at least a portion of the liquid product component from the liquid feed stream 204 to produce a slurry 208 that contains both the product component crystals and the secondary secondary component. For example, when the feed stream 204 contains about 22 wt. up to about 23 wt.% para-xylene, the corresponding crystallization temperature at atmospheric pressure is about -89 ° F (-67 ° C) or about The crystallizer 110 operates at a temperature sufficient to crystallize at least a portion of the liquid product component from the liquid feed stream 204 to produce a slurry 208 that contains both the product component crystals and the secondary secondary component. For example, when the feed stream 204 contains about 22 wt. up to about 23 wt.% para-xylene, the corresponding crystallization temperature at atmospheric pressure is about -89 ° F (-67 ° C) or about

EP-2328853B1EN ° F (1.1 ° C) more than a binary eutectic temperature around -91 ° F (-68 ° C). The crystallization temperature will usually vary depending on the amount of para-xylene present in the streams recycled to the feed stream 204. In a continuous para-xylene purification process, the residence time in the crystallizer 110 is preferably sufficient to crystallize a substantial portion of the liquid product component from the liquid feed stream 204 , e.g. at least about 50 wt.%. (more preferably at least about 70 wt.%) of the liquid product component in the feed stream 204.

[0052] The leakage of the slurry 208 is then fed to the separation device 120, which is a filtration column in a preferred embodiment, but it can also be a washing column or a centrifuge. The filter column 120 at least partially separates the product component crystals and the secondary secondary component from the slurry leak 208 to form the filter cake 212 and the filtrate 216. The filter cake 212 is mainly a solid crystal of the product component. Preferably, substantially all of the product component crystals from slurry spillage 208 are recovered in filter cake 212, and the weight concentration of the product component (i.e., total liquid and solids) in filter cake 212 is greater than the concentration in filtrate 216. Filter cake 212 also contains a small the amount of liquid, usually comprising and a liquid secondary component and a liquid component of the product. Specifically, the filter cake preferably contains about 50 wt. up to about 99% by weight (more preferably about 75 wt% to about 88 wt%) of the crystals of the product component, based on the total weight of the filter cake, including any liquid. The filtrate 216 is mainly a liquid stream of the secondary secondary component, and preferably substantially all of the secondary secondary component from the slurry leak 208 is recovered in the filtrate 216. However, the filtrate 216 may contain a small amount of the liquid product component and / or the product component crystals. In general, the filtrate 216 can either be rejected as a reject stream or, preferably, recycled for further processing.

[0053] The filter cake 212 and the diluent for the secondary slurry 240 are then fed to the first slurry for producing a secondary slurry 130 in stream 220. The diluent for the secondary slurry 240 is a liquid stream containing both a liquid product component and a liquid secondary component. As illustrated in Figure 1, the filter cake 212 and the secondary slurry solvent 240 are mixed before the first melt-producing secondary drum 130 and then fed in one stream

220. In an alternative embodiment (not shown), however, the filter cake 212 and the secondary slurry solvent 240 may be fed into the first secondary suspension forming drum 130 as two separate streams.

[0054] In a further embodiment (not shown) the prior separation device 120 may be a centrifuge. In this case, the effluent from the centrifuge, which is fed to the first slurry 130, is similar to the filter cake 212 (i.e. mainly the solid crystal cake component of the product with a small amount of the liquid secondary component and the liquid product component).

[0055] The drum for producing the secondary slurry 130 is a tank containing a slurry of a solid body, including the crystals of the product component and the liquid component of the product. In the secondary suspension drum 130, the crystals of the product component are equilibrated with the liquid product and secondary components in sufficient time to produce a secondary leak of the slurry 224. During balancing, the secondary effluent becomes warmer with respect to the temperature of the filter cake 212. In the continuous process, the capacity

The slurry for the secondary slurry 130 and the feed rate of the filter cake 212 and the diluent to the secondary slurry 240 can be selected so as to obtain a residence time sufficient to balance. [0056] The leakage of the secondary slurry 224 is then fed to the separation device 140, which works in the same way as the separation device 120. The separation device 140 can be a filter column, a wash column or a centrifuge. Preferably, the separation device 140 is a filter column. The filter column 140 works similarly to the filter column 120, producing a filter cake

228 with content analogous to filter cake 212, and filtrate 232, containing both the liquid component of the product and the liquid secondary component. Although filtrate 232 may or may be rejected as a reject stream, it is preferably recycled to further processing. As illustrated in Figure 1, portion 236 of filtrate 232 is returned to the secondary slurry 130 as a diluent for secondary slurry 240 (in which case filtrate 232 contains at least a portion of the liquid product component) and filtrate portion 244 is recycled to crystallizer 110 as part of the liquid feed stream 204. The diluent for the secondary slurry 240 may be heated using a diluent heater 242 providing the thermal load so selected,

The filter cake 228 and the secondary slurry dispenser 272 are then fed to the second slurry suspension 150 in stream 248. The second slurry for the secondary slurry 150 works in analogy to the first slurry secondary drum 130 to produce a slurry leaking 252 containing the component crystals product, a liquid component of the product and a liquid secondary component.

[0058] The leakage of the secondary slurry 252 is then fed to the final separation device 160 in the embodiment illustrated in Figure 1. The final separation device 160 preferably is a solid-liquid separator other than a filter column, for example, a wash column or a centrifuge. The separation device 160 comprises a filtrate 268 (similar to the other previous filtrates 216 and 232) as the first batch. Filtrate 268 is a liquid stream containing both a liquid component of the product and a liquid secondary component, although it may contain a small amount of crystals of the product component. Although filtrate 268 may be rejected as a reject stream, it is preferably recycled for further processing. As illustrated in Figure 1, a part of the filtrate 268 is recycled to the second slurry for the secondary slurry 150 as a diluent for the secondary slurry 272, and part 276 of the filtrate 268 is recycled to the first slurry secondary drum 130 as part of the slurry to the secondary slurry 240. The diluent for the secondary slurry 272 can be heated from using a diluter heater 274 providing a thermal load so selected that the resulting solid-liquid slurry temperature in the secondary slurry drum 150 is brought to the desired value. The separation device 160 also includes a product stream 256. The product stream 256 may comprise mainly the crystals of the product component together with a portion of the liquid product component (e.g., a washed filter cake formed when the centrifuge device 160 is a centrifuge), or may contain a substantial portion of both the crystals of the product component and the liquid product component (e.g., the outgoing washed suspension formed when the separation device 160 is the washing column). The heater 170 is preferably used to melt the crystals of the product component remaining in the product stream 256. A portion of the product melt stream 256 is preferably recycled to the separation device 160 as washing liquid 260 and the portion is received as the final product stream 264 which is a purified liquid component stream product. Preferably, the washing liquid 260 and / or the final product stream 264 contain the liquid component of the product in wt when the separation device 160 is a washing column). The heater 170 is preferably used to melt the crystals of the product component remaining in the product stream 256. A portion of the product melt stream 256 is preferably recycled to the separation device 160 as washing liquid 260 and the portion is received as the final product stream 264 which is a purified liquid component stream product. Preferably, the washing liquid 260 and / or the final product stream 264 contain the liquid component of the product in wt when the separation device 160 is a washing column). The heater 170 is preferably used to melt the crystals of the product component remaining in the product stream 256. A portion of the product melt stream 256 is preferably recycled to the separation device 160 as washing liquid 260 and the portion is received as the final product stream 264 which is a purified liquid component stream product. Preferably, the washing liquid 260 and / or the final product stream 264 contain the liquid component of the product in wt A portion of the product melt stream 256 is preferably recycled to the separation device 160 as washing liquid 260, and the portion is received as the final product stream 264, which is a purified stream of the product liquid stream. Preferably, the washing liquid 260 and / or the final product stream 264 contain the liquid component of the product in wt A portion of the product melt stream 256 is preferably recycled to the separation device 160 as washing liquid 260, and the portion is received as the final product stream 264, which is a purified stream of the product liquid stream. Preferably, the washing liquid 260 and / or the final product stream 264 contain the liquid component of the product in wt

At least about 99.5 wt.% (Preferably at least about 99.7 wt.%, More preferably at least about

99.8 wt%, e.g., about 99.9 wt%).

meta-xylene and / or ethylbenzene in para-xylene and a distillation device to separate the aromatic C8 hydrocarbon stream into heavier and lighter components. The details of isomerization and distillation are known in the art, e.g. as described in US Pat. No. 5,284,992, the disclosure of which is hereby incorporated by reference.

[0060] As illustrated in Figure 1, para-xylene depleted para- xylene (or para-xylene) filter 216 (e.g. containing up to about 15 wt% para-xylene) and hydrocarbon feed 280 are fed into the 180 isomerisation unit. Adjectives "depleted in para-xylene," "para-xylene-poor" and their various variants, when used in connection with the description of the unit operating stream, refer to a stream coming out of a unit operation that contains less para-xylene than contained in the stream the batch for this unit operation. The catalytic reaction in the isomerization device 180 converts the inlet ortho-xylene, meta-xylene and / or ethyl-benzene into para-xylene, and also produces heavier and lighter hydrocarbon components. The reaction products are separated in the distillation part of the isomerization device 180 to form a waste stream of lighter hydrocarbons 288 (e.g. including C1 to C7 hydrocarbons, aliphatic and aromatic), stream of heavier hydrocarbons 290 (e.g. including C9 and higher aliphatic and aromatic hydrocarbons) and isomerate 284 The isomerate stream 284 typically contains the following mixture of C8 aromatic hydrocarbons: about 20 wt. up to about 25 wt.% (e.g., about 22 wt.%) para-xylene, about 15 wt.%. up to about 30 wt.% ortho-xylene, about 40 wt. up to about 55 wt.% meta-xylene and about 5 wt. up to about 15 wt.% ethylbenzene. As illustrated in Figure 1, the isomeric stream 284 and the mixed feed of xylene 292 combine to form the feed of the crystallization step 296.

[0061] Although the described embodiment of the crystallization process / secondary slurry using the filter columns illustrated in Figure 1 comprises a crystallization step followed by two successive stages of the secondary slurry production, the disclosed method is not limited thereto. Figure 2 illustrates a generic crystallization process / secondary slurry using filter columns including the crystallization step 305, followed by any number n intermediate steps for producing a secondary slurry 325 and the final step of producing a secondary slurry 345. Any number of intermediate steps for producing a secondary slurry is possible 325, including zero (i.e., n> 0, when n = 0 means one process for producing a secondary slurry), so that the minimum number of purification / separation steps are two steps: crystallization step 305 followed by the final stage of the secondary slurry 345. One advantage of the increased number of secondary slurry production steps is the possibility of obtaining a given product purity in a more energy-efficient manner, or alternatively the possibility of obtaining a higher product purity with an equivalent energy load. Other than

The potential difference in the number of secondary slurry production steps, similarly numbered unit operations and streams in Figures 1 and 2, have analogous functions and are not described in further detail hereinafter.

[0062] For example, in the crystallization step 305, the crystallizer 310 in Figure 2 has an analogous function as the above-described crystallizer 110 in Figure 1, has a feed stream 404 and a slurry leak 408. The slurry leak 408 is then fed to the separation device 320 (preferably to filtration column) in which the crystals of the product component and the secondary secondary component are separated from the leakage of the slurry 408 to at least partially produce a filter cake 412 and filtrate 416.

[0063] As illustrated in Figure 2, the feed stream for the secondary slurry for each step of producing the secondary slurry 325n comprises an enriched stream of product from an earlier purification step or a secondary slurry. This can be easily visualized in the following way, taking into account the process in which n = 3 and considering the different process streams in the middle of the three stages of secondary suspension production, i.e. the secondary suspension stage 3252. In this middle stage of producing the secondary suspension 3252, the feed 4202 to the drum for producing the secondary slurry 3302 contains the proportion of the previous filter cake 4281. At this middle stage of the secondary slurry production 3252, leakage of the secondary slurry 4242 is then added to the separation device 3402 (preferably the filter column) to form the next filter cake 4282 and the filtrate 4322. Most generally, the feed 420 for the secondary slurry bowl 330 is considered to be 330 at the n-th stage of the secondary slurry 325 comprises the proportion of a previously produced filter cake (i.e., filter cake 412 when n = 1), the enriched product stream is a stream coming from the crystallization step 305 or a previously produced filter cake 428 when n> 2 and enriched the product stream is a stream coming from the (n-1) stage of the secondary slurry 325). At this stage of producing the secondary suspension 325, leakage of the secondary slurry 424 is then fed to a separation device 340 (preferably a filtration column) to form a filter cake 428 and filtrate 432. Preferably, the secondary slurry suspension in each step of the secondary slurry production comprises a recycled portion of the filtrate from at least one same production step a secondary suspension and a further subsequent step of producing a secondary slurry. By illustrating the process in which n = 3 and considering the different process streams in the middle of the three stages of secondary slurry production (i.e., in the secondary slurry step 3252), part 4362 of filtrate 4322 is returned to the secondary slurry drum 3302 as a diluent for the secondary slurry 4402 (on an example heated by a secondary slurry heater 4422) in the middle stage of the secondary slurry 3252.

At the final stage of producing the secondary slurry 345 the filter cake 428 from the preceding intermediate step of producing the secondary slurry 325 and the diluent of the secondary slurry 472 are fed to the secondary slurry drum 350 via stream 448. The leakage of the secondary slurry 452 from the secondary slurry drum 350 is then fed to a separation device 360 ​​(preferably to a wash column or centrifuge) to produce product stream 456 and filtrate 468. Preferably, a portion of the filtrate 468 is returned to the secondary slurry drum 350 as a diluent of the secondary slurry 472 (e.g. heated by

A secondary slurry heater 474) and the filtrate portion 468 is returned to the previous intermediate stage of the secondary slurry 325 as part of the slurry secondary slurry 440. The heater 370 is preferably used to melt the crystals of the product component remaining in the product stream 456. Part of the molten product stream 456 is preferably recycled to the separation device 360 ​​as the washing liquid 460, and the part is taken as the final product stream 464, which is a purified stream of the liquid product component.

[0065] Figure 3 illustrates an additional embodiment of the disclosure that includes a multistage crystallization process 500. Process 500 includes a series system of at least two degrees of crystallization, e.g., first crystallization stage 505 followed by a second crystallization stage 525 in combination with filter columns to recovering a solid (crystalline) product component from a liquid multi-component feedstock (e.g., to separate and purify para-xylene from ortho-xylene, meta-xylene and / or ethylbenzene).

The first crystallization stage 505 comprises a crystallizer 510 and a separation device 520. Likewise, the second crystallization stage 525 comprises a crystallizer 530 and a separation device 540. At least one of the separation devices 520 and 540 is a filter column. In other steps, there may be a filtration column or there may be something other than a filter column, such as a wash column or a centrifuge.

Similarly to the embodiment in Figure 1, the product component purification and recovery process begins by feeding the liquid feed stream 604 to the crystallizer 510. The liquid feed stream 604 comprises a liquid product component and a liquid secondary component, wherein the liquid product component has a melting point higher than that of the crystallizer. liquid secondary component. Similar to the crystallizer 110, the crystallizer 510 is operated at a temperature sufficient to crystallize at least a portion of the liquid product component from the liquid feed stream 604 to produce a slurry of suspension 608 comprising the product component crystals and the secondary liquid component.

[0067] The leakage of the slurry 608 is then fed to the filter column 520 to at least partially separate the crystals of the product component and the secondary liquid component from the slurry leak 608 to form a filter cake 612 and filtrate 616. The filter cake 612 is mainly a solid crystal of the product component. Preferably, substantially all of the crystals of the product component from the slurry leak 608 are recovered in the filter cake 612, wherein the weight concentration of the product component (i.e., comprising the liquid and solid) in the filter cake 612 is greater than in the filtrate 616. The filter cake 612 can be picked up from process 500 as a product stream or can be further purified if indicated. Filtrate 616 is mainly a liquid stream of a secondary liquid component,

[0068] In the second crystallization stage 525 (and any other subsequent crystallization stage), the liquid feed stream comprises the filtrate from the previous prior degree of crystallization. Thus, as illustrated, the filtrate 616 is fed to the crystallizer 530 to produce a slurry of suspension 620, which is separated in the filter column 540 into filter cake 624 and filtrate 628.

[0069] The advantage of using a filtration column instead of a centrifuge in a crystallizer array (or in the crystallization / preparation of the secondary suspension described above) is that the filter column adds significantly less energy (heat) to the filtrate than the centrifuge. Specifically, the mechanical action of the centrifuge during distribution separates the thermal energy of the crystals of the product component, causing some of the crystals to melt and thereby reduce the recovery efficiency of the product component crystals in the filter cake from the centrifuge. In contrast, during normal operation in the filter column it produces

Not much heat is produced or not produced at all, which prevents loss by melting and improves the recovery efficiency of the product component crystals. In addition, as explained in detail above, it has been found that in certain separation steps (e.g. using filter columns) carried out under the conditions disclosed herein, in the para-xylene production processes it is advantageous and desirable to limit the entry of molecular oxygen into the various process streams.

Figure 4 further illustrates an additional embodiment of the disclosure that includes a multi-stage solid-liquid separation process 700. The process 700 includes a system with a centrifuge 710 behind which a filter column 720 is in series. In this additional embodiment, the filter column 720 may increase part recovery solids that would otherwise be lost in the filtrate stream from the centrifuge.

[0071] In Figure 4, the slurry feed 804 containing liquid and dispersed solids is fed into the centrifuge 710 (e.g., centrifuges with a perforated drum). Centrifuge 710 at least partially separates the slurry feed components 804, producing the following three outgoing streams: centrifugal cake 808 containing liquid and more than 50 wt.%. dispersed solids, a filtrate with low solids content

812 containing about 5 wt. or less dispersed solids and a high solids filtrate 816 comprising a liquid and about 5 wt.%. up to about 50 wt.% (e.g., at least about 10 wt.%) of dispersed solids. The high solids filtrate 816 is then fed to the filtration column 720 to produce a cake from a filtration column 820 containing dispersed solids and a filtrate with a liquid-containing filtration column 824. The cake from the filtration column 820 has a weight concentration of dispersed solids greater than the filtrate from the filtration column 824.

[0072] In general, the cake from the centrifuge 808 and the cake from the filtration column 820 can be taken as a product stream and can go into further processing (e.g., for purification, melting, storage). The filtrate with low solids content 812 and the filtrate from the filtration column 824 can be collected as waste streams or further processed. For example, when the embodiment of Figure 4 is used for the para-xylene separation and purification process (i.e., the dispersed solid is para-xylene and the liquid is a mixture of C8 hydrocarbons including liquid para-xylene), the filtrates 812 and 824 are relatively poor in para-xylene, can be sent to the isomerization device to produce additional para-xylene and then recycled to the separation / purification process (e.g., as described above).

[0073] In the disclosed process (and its various embodiments), it is important for the skilled artisans to understand the need for appropriate equipment and process control. Such equipment includes, but is not limited to, suitable piping, valves, equipment for unit operations (e.g., reaction vessels with appropriate inlets and outlets, heat exchangers, separation devices, etc.), associated process control equipment and equipment quality control. Furthermore, those skilled in the art will readily understand that the main unit operations described herein, such as, for example, in Figure 1, can be carried out with similar equipment in parallel: separation devices 120, 140 and 160; heaters 170, 242 and 274; and drums for producing a secondary slurry 130 and 150. Other process equipment is specified herein,

EXAMPLES [0074] The following examples are given to illustrate the invention, but are not intended to limit its scope.

EP-2328853B1PL

Example 1 [0075] Investigations of a slurry stream and liquid secondary component streams in the filtrate coming from different solid-liquid separators were carried out to measure the effect of separators on the molecular oxygen content in the process streams to the separator. Oxygen measurements were carried out with the ORBISPHERE Model 2611E oxygen analyzer (available from Hach Ultra, Geneva, Switzerland), which was calibrated using air containing 20.9% oxygen. Samples were heated to 25 ° C before oxygen measurement, and in all tests a closed sample system (i.e. completely isolated from atmospheric oxygen) was used.

[0076] A filter column was tested in which nitrogen was used as a displacer fluid operating as a separation device in the first stage (i.e., analogous to the separation device 120 in Figure 1) in a para-xylene purification process. The slurry feed into the filtration column and the filtrate were analyzed for the content of molecular oxygen over a period of about one day. Data from the test period (summarized in Table 1) indicate that no oxygen enters the filtration column. The data indicates that the filter column strips a portion of the oxygen that was present in the batch so that the liquid secondary component of the filtrate from the filtration column has a lower oxygen level than the batch. Specifically, the feed contained approximately 1.5 parts by weight per million (ppm) oxygen, while the liquid secondary filtrate component contained less than about 0.4 ppm oxygen. The relatively low oxygen content in the liquid secondary component of the filtrate causes the liquid secondary component of the filtrate to be particularly suitable for recycling to the isomerisation device to further produce para-xylene. Pressure measurements in the filtration column were recorded in pounds per square inch (psig) pressure units, thus avoiding the need to record atmospheric pressure / ambient.

Table 1 - The content of molecular oxygen in the streams to the filtration column and the operating pressure in the filter column

<td></td><td colspan="2">O2 in the filtration column (ppm)</td><td colspan="3">Pressure in the filtration column (psig)</td>

<td>Time measurement</td><td>Batch</td><td>Filtrate</td><td>Slurry feed Intake</td><td>N2 Inlet</td><td>Filtrat and N2 Outlet</td>

<td>0.00 hours</td><td>1.84</td><td>0.38</td><td>-150</td><td>-50</td><td>-2.5</td>

<td>19.67 Hours</td><td>1.41</td><td>0.30</td><td>-100</td><td>-40</td><td>-2</td>

<td>25.25 Hours</td><td>1.7</td><td>0.30</td><td>-100</td><td>-55</td><td>-2</td>

[0077] For comparison, a traditional centrifuge operating as a separation device in the first stage was also tested (i.e. analogous to the separation device 120 in Figure 1) in a paraxylene purification process. The slurry feed and filtrate from the two centrifuges were analyzed for the content of molecular oxygen. Traditional high-speed centrifuges allow oxygen to be added to the process, both during steady-state operation and when they are periodically open to the atmosphere for maintenance and repair. In contrast to the filtration column, the data (summarized in Table 2) illustrates that oxygen is introduced through traditional centrifuges. Specifically, the oxygen content rises from 0.15 ppm in the centrifuge charge to more than about 0.7 ppm (e.g.

about 0.8 ppm to about 1.5 ppm) in the centrifuge filtrate. Since the oxygen content in the filtrate is increased in relation to the content in the filtration column, feeding the filtrate from the centrifuge to the isomerization unit to produce para-xylene, without further oxygen reduction steps, could lead to significant carbonization and / or clogging of the isomerization device and its pre-heater.

EP-2328853B1PL

Table 2 - The content of molecular oxygen in streams from the centrifuge

<td>Centrifuge #</td><td>O2 in the centrifuge charge (ppm)</td><td>O2 in the filtrate from the centrifuge (ppm)</td>

<td>1</td><td>0.15</td><td>0.76</td>

<td>2</td><td>0.15</td><td>1.51</td>

Example 2 [0078] A crystallization / twice production of a secondary slurry for purifying para-xylene (i.e. as illustrated in Figure 1) was performed to compare the efficiency of the process associated with using filter columns as separation devices instead of centrifuges. Table 3 shows the mass balance information for the process of Figure 1, wherein the two separation devices 120 and 140 are filter columns, and the separation device 160 is a washing column. Table 4 shows the mass balance information for the process of Figure 1, in which all separation devices 120, 140 and 160 are centrifuges. In Tables 3 and 4, the "stream number" refers to the streams as indicated in Figure 1. The word "composition" includes a given proportion of the solid and / or liquid phase component present in the stream. The term "other C8" includes ortho-xylene, meta-xylene, ethylbenzene and any other residual aliphatic and aromatic hydrocarbons. Each process generally generates streams of increasing purity of para-xylene at each of the starting stages (e.g., up to a para-xylene purity of 99.9 wt% in stream 264 in a filtration column process) and produces a filtrate stream 216 relatively rich in meta-xylene, ortho-xylene and ethylbenzene.

Table 3 - Steam-xylene purification process using filter columns

<td colspan="2">Stream number</td><td>296</td><td>216</td><td>264</td><td>292</td>

<td>Temperature</td><td>(° =)</td><td>97.5</td><td>74.6</td><td>80.0</td><td></td>

<td>Flow rate</td><td>(Lb / hr).</td><td></td><td></td><td></td><td></td>

<td></td><td>Clean stream</td><td>710.9</td><td>610.9</td><td>100.0</td><td>130.4</td>

<td></td><td>p-Xylene</td><td>148.6</td><td>48.9</td><td>99.9</td><td>23.2</td>

<td>Composition</td><td>(wt%)</td><td></td><td></td><td></td><td></td>

<td></td><td>p-Xylene</td><td>20.9</td><td>8.0</td><td>99.9</td><td>17.8</td>

<td></td><td>Other</td><td>79.1</td><td>92.0</td><td>0.1</td><td>82.2</td>

Table 4 - Steam-xylene purification process using centrifuges

<td colspan="2">Stream number</td><td>296</td><td>216</td><td>264</td><td>292</td>

<td>Temperature</td><td>(° =)</td><td>97.5</td><td>73.1</td><td>80.0</td><td></td>

<td>Flow rate</td><td>(Lb / hr).</td><td></td><td></td><td></td><td></td>

<td></td><td>Clean stream</td><td>732.3</td><td>632.3</td><td>100.0</td><td>130.7</td>

<td></td><td>p-Xylene</td><td>153.1</td><td>53.1</td><td>99.85</td><td>23.3</td>

<td>Composition</td><td>(wt%)</td><td></td><td></td><td></td><td></td>

<td></td><td>p-Xylene</td><td>20.9</td><td>8.4</td><td>99.85</td><td>17.8</td>

<td></td><td>Other</td><td>79.1</td><td>91.6</td><td>0.15</td><td>82.2</td>

[0079] The values ​​in Tables 3 and 4 were calculated on the basis of 100 pounds / hour. para-xylene produced in the final product stream 264 based on the mass balance principle. The distribution of feed streams into various solid-liquid separation devices 120, 140 and 160 can be (and was) determined based on a predetermined proportion of solid body weight going to the filter cake and filtrate for each case.

EP-2328853B1GB separation device. The formation of the solid part (i.e., by para-xylene crystallization) in the crystallizer 110 and the drums for producing the secondary slurry 130 and 150 is based on the assumption of thermal equilibrium.

[0080] Table 5 shows a comparison of the general characteristics of the process between the process and the filtration column (Table 3) and the centrifugation process (Table 4). As the efficiency parameters of the process, "purity" refers to the concentration of para-xylene in the final product stream 264, "recovery" refers to the amount of para-xylene in the final product stream 264 relative to the amount of para-xylene in the feed to the crystallization step 296, and "yield" refers to the amount of para-xylene in the final product stream 264 relative to the amount of hydrocarbons in the mixed xylene feed 292. The "feed to the isomerisation device" refers to the total amount of hydrocarbon feed into the isomerisation device 180 through the filtrate 216 at a para-xylene unit produced in the final product stream 264. "Crystallizer Power" crystallizer duty) indicates cooling capacity in a unit operation in a crystallizer. Both "charge to the isomerisation device" and "crystallizer power" are dimensionless values ​​normalized by charge / power calculated for the case with a centrifuge. The binary eutectic temperatures relating to the compositions administered to the crystallizer 110 are also indicated in Table 5.

Table 5 - Comparison of para-xylene purification processes

<td>Process parameter</td><td></td><td>Filter column</td><td>creamer</td><td>% Difference</td>

<td>The efficiency of p-xylene</td><td>(wt%)</td><td></td><td></td><td></td>

<td colspan="2">P-xylene purity</td><td>99.9</td><td>99.85</td><td></td>

<td colspan="2">Recovery of p-xylene for the transition</td><td>67.2</td><td>65.2</td><td></td>

<td colspan="2">The yield of p-xylene</td><td>76.6</td><td>76.4</td><td></td>

<td>Feed into the isomerization device</td><td>(-)</td><td>0.966</td><td>1,000</td><td>-3.4%</td>

<td>Crystallizer power</td><td>(-)</td><td>0.973</td><td>1,000</td><td>-2.7%</td>

<td>Binary eutectic</td><td>(° =)</td><td>-90.9</td><td>-90.9</td><td></td>

[0081] The data in Table 5 shows the advantages of a process using filtration and washing columns in a para-xylene purification process according to the process conditions disclosed herein, compared to a similar process using traditional solid-liquid separation technology in the centrifuge. Generally, a filtration column process operated under the conditions disclosed herein (e.g., a process in a filtration column) is more efficient giving higher purity of the final para-xylene product, higher recovery and yield. The process with the filter column also significantly reduces the power required by the isomerization device 180. The concentration of para-xylene in filtrate 216 is higher in the process with a centrifuge of 0.4 wt%. para-xylene, in the sense that the larger para-xylene fraction is not recovered and it is not necessary to recycle in the centrifuge process (i.e. about 8.6% more para-xylene is recycled compared to the process in the filter column). This loss can be caused, for example, by mechanically generated heat in the centrifuge, which can melt part of the solid para-xylene crystallized in the crystallizer 110, thus forming a part of para-xylene which passes into filtrate 216 and is not recovered in Filter cake 212.

The reduced flow rate of the recycled material to the isomerization device 180, when filtering columns are used (i.e., reduced by 3.4%) under the conditions disclosed herein, leads to reduced operating costs for the isomerisation device 180. The filtration column process is also more efficient energy, because cooling power is lower (ie by 2.7% less). This efficiency prevails

It is a disadvantage of the filter column that it usually produces a more moist cake product compared to a centrifuge.

[0082] Since other modifications and variations accommodating specific requirements and operating conditions will be apparent to a person skilled in the art, the invention is not limited to the example selected for disclosure and includes all changes and modifications that do not deviate from the scope of the invention.

[0083] Therefore, the above description is given only for clarity of understanding and no limitations should be drawn on this basis, since modifications within the scope of the invention may be apparent to those skilled in the art.

Throughout the description, where the compositions, processes or apparatus are described to include components, steps or materials, it is contemplated that the compositions, processes or apparatuses may also comprise, consist essentially of or consist of any combination of the listed components or materials unless otherwise stated. Component combinations are believed to include homogeneous and / or heterogeneous mixtures, as would be understood by one of skill in the art in view of the above disclosure.