Chemical processing with operational step sensitive to feedstream component

This application is a follow-up application to the No. 022136 application filed on March 5, 1987, so the content of the original application can be combined for reference.

The present invention relates to the field of chemical processes, in particular to a chemical process method, which includes an operation step that is very sensitive to at least one component in the processed stream, and also relates to the temporary removal of this harmful component from the stream The method, even if the harmful component bypasses the step sensitive to this component.

In many chemical processes, at least one operation step is sensitive to at least one component contained in the feed stream, or sensitive to a component produced upstream of the sensitive step. Generally speaking, the presence of this step requires the removal of all or most of the harmful components before being introduced into the sensitive operation step.

This sensitive operation step can basically include all unit operations in chemical engineering practice. Therefore, many chemical processes do not allow specific components to be present in the feed stream. For example, the use of membranes to separate methane from natural gas containing condensable pentane and hexane is such a process. Pentane and hexane are harmful to membranes. Similarly, in those chemical reactions that use catalysts, the catalysts are generally sensitive to different chemical components. Such sensitive catalysts include, for example, iron oxide catalysts for the synthesis of ammonia, which are particularly sensitive to carbon oxides. If these harmful components are not removed from the reaction zone, these catalysts will be poisoned and the reaction will not proceed, or will not proceed well, or produce completely unnecessary side reactions.

Chemical reactions are not the only place where the presence of certain components can cause harmful results. For example, when using ion exchange resins, it is often necessary to remove certain components from the stream being treated before the stream enters the ion exchanger. Certain components in the feed stream will seriously interfere with the ion exchange process or completely destroy its use. More specifically, for example, in ion exchange water treatment, potassium ions are used to replace calcium ions. Sodium ions present in the water stream are harmful to the ion exchange process, and sodium ions need to be removed upstream of the process flow.

Even in certain distillation steps, especially during azeotropic distillation, certain components in the treated fluid are harmful to the successful separation of the azeotropic solution. Therefore, it is required to remove these components before the distillation step. This is also effective for other unit operations, such as unidirectional absorption using materials such as zinc oxide.

No matter what kind of sensitive operation step is involved, it is obvious that several steps must and have been taken to remove harmful components in the stream before it enters the sensitive step.

However, in some cases, harmful components are not completely harmful to the final product. Because there is at least one sensitive step in the process flow, some devices must be used to remove this component, usually a large amount of money is spent on the purchase of the required separation equipment, and the overall operating cost has also increased.

In addition, no matter which device is used to remove harmful components in the processed stream, it is necessary to treat the removed components in the separation device. Therefore, when oxide-type solid adsorbents are used to remove harmful components, typically sulfides, such adsorbents are not easy to regenerate. Therefore, it is necessary to frequently replace the adsorbent with considerable expense and dispose of the final waste of oxide laden with sulfide.

When using fluids to remove harmful components, these fluids must be regenerated with other fluids for continued use. This not only increases the cost of the entire process, but also must be adequately supplied with this regenerative fluid. This is the case when using regenerated adsorbents such as molecular sieves. In order to desorb harmful components from the adsorbent, it is necessary to provide sufficient cleaning gas at an appropriate regeneration temperature. In certain plants, this is not always possible. Similarly, once the adsorbent has been regenerated with cleaning gas, the cleaning gas filled with harmful components must also be treated. Combustion of this cleaning gas is not always feasible or desirable.

A particularly common toxic component is sulfur and its compounds. Sulfur is produced in many industrial processes. For various reasons, it is necessary to constantly remove sulfur or sulfur-containing compounds from the process fluid. For example, when a process fluid is burned as a fuel, sulfur must be removed from the fluid to prevent environmental pollution. On the other hand, if a catalyst is used to treat the process fluid, it is often necessary to remove the sulfur to prevent poisoning of the sulfur-sensitive catalyst.

Many methods are suitable for removing sulfur from process fluids, and most of the sulfur removal techniques are gas flow treatments. This technique involves the use of alkaline reagents or amine solutions to remove sulfur or sulfur-containing compounds from the gas stream. On the other hand, molecular sieves or other adsorbents can be used, such as granular oxides, hydrated oxides or hydroxides of aluminum, zinc, iron, nickel, cobalt, etc., which can be used alone, mixed with each other, or with other Additives such as alkali or alkaline earth metal oxides are used together. US3492038 describes a process using this oxide. Another example is the use of molecular sieves as desulfurization adsorbents in patents such as US3024868, 4358297 and 4533529.

However, oxide-based solid adsorbents are usually not easy to regenerate into their original form, and when they are fully vulcanized, they must be completely discarded.

When using molecular sieves, in order to understand the absorption of sulfur and make it regenerate, these molecular sieves must be cleaned with hot air. In many cases, the feasibility of this regeneration is limited by the amount of gas that can be used as a hot purge gas in factories and mines.

A specific industrial process that requires the removal of sulfur and nitrogen compounds from the feed stream due to the use of sulfur-sensitive and nitrogen-sensitive substances in the process is hydrocarbons containing at least 5 carbon atoms (especially light straight-run gasoline or gasoline). Light naphthalene) isomerization of the feed stream. This feed stream generally contains about 200 ppm sulfur sulfur-containing compounds and about 0-10 ppm nitrogen nitrogen-containing compounds. As used herein, the term "sulfur" means to include sulfur and sulfur-containing compounds, and the term "nitrogen" also means to include nitrogen and nitrogen-containing compounds. Such levels of sulfur and/or nitrogen generally adversely affect the performance and life of the isomerization catalyst. Therefore, this feed stream is usually treated by using a hydrodesulfurization step upstream of the isomerization step to remove sulfur and nitrogen from the stream.

This kind of hydrodesulfurization step generally includes a furnace heater for evaporating the feed stream; a hydrogenation reactor for catalytically converting sulfur and nitrogen in the stream into hydrogen sulfide and ammonia; and a hydrogen sulfide reactor that converts 30-40% of the gaseous hydrogen sulfide into hydrogen sulfide and ammonia. A condenser that condenses with ammonia and leaves the remaining hydrogen sulfide and ammonia together with the feed stream from the top of the tower; and a steam stripper to remove the condensed hydrogen sulfide and ammonia in the feed stream. Instead of a steam stripper, hydrogen sulfide and ammonia adsorption beds can also be used, which requires the stream to be cooled to an appropriate temperature before entering the adsorber.

Regardless of whether a steam stripper or an adsorber is used to remove hydrogen sulfide and ammonia, the hydrocarbon stream from which substantially all of the sulfur and nitrogen have been removed must be preheated in order to vaporize it again before entering the isomerization reactor.

This hydrodesulfurization technology to remove sulfur and nitrogen is an effective means for treating the sulfur and nitrogen present, but it is quite expensive. In fact, in common practice, the hydrodesulfurization unit (also called hydrogenation) is operated separately from the isomerization unit, which obviously increases the complexity of the process and the total cost. Similarly, because it is necessary to repeatedly heat and cool the raw material stream, the material undergoes phase change to adapt to different technological processes, which also has an adverse effect on the economic efficiency of the entire technological process.

This is just an example. In this example, there is obviously a need to economically and efficiently remove the at least one harmful component from an industrial process feed stream containing a step that is sensitive to at least one component.

The applicant has developed a process to economically and effectively remove harmful components from the fluid. Even if the harmful components bypass the steps sensitive to the components, all the above-mentioned disadvantages are basically eliminated.

More specifically, the applicants process involves a new and unique method of using adsorbents. In this method, the processed fluid containing a harmful component first passes through an adsorption zone containing solid adsorbents. The adsorbent can selectively adsorb harmful components from each component of the stream under adsorption conditions. The fluid containing low-concentration harmful components enters the subsequent process steps, and finally passes through an operation step sensitive to harmful components to produce a product stream. At least a portion of this product stream (as opposed to any waste stream leaving the sensitive operating steps) is used as purge gas for the regeneration of the adsorbent bed. The adsorption bed has been loaded with harmful components, and a product fluid with a high concentration of harmful components is obtained under desorption conditions.

Therefore, according to the present invention, a chemical process method containing operating steps sensitive to specific components can be realized in a cost-effective manner. Therefore, as long as there is an adsorbent that can selectively remove one or more components from the stream, this adsorbent is used in the method of the present invention without providing a cleaning fluid from the outside, nor is it limited to The waste fluid generated during the regeneration process of the adsorbent is used to regenerate the adsorbent, which avoids the difficulty of sufficient supply and treatment of the regeneration fluid for regeneration purposes. The process method of the present invention provides a good solution. In fact, after the sensitive steps of the process are carried out without the presence of harmful components, the product stream itself is used as a cleaning fluid. This is particularly advantageous in the case of product fluids.

A special case that is very beneficial to the presence of harmful components in the product stream is the process flow for the preparation of acrylic acid. Such a process always includes the reaction of propylene and oxygen in the presence of a sulfur-sensitive catalyst. Since the boiling point of propylene and sulfur-containing compounds (such as hydrogen sulfide, carbonyl sulfide, etc.) are very close, it is always difficult and expensive to remove harmful sulfides. However, according to the present invention, the feed stream containing propylene and sulfide is passed through an adsorbent that is selective for sulfur (relative to propylene). Then, propylene, which is substantially free of sulfides, reacts with oxygen to form an acrylic product fluid. This product fluid is then used to regenerate the adsorbent and desorb the sulfur-containing compounds on the adsorbent. Here is not mixing propylene and sulfide, but acrylic and sulfide. Because acrylic acid and sulfur-containing compounds have a boiling point difference of about 200°F, the two components are easily separated, and the present invention is feasible.

In addition, the present invention has another advantage. Because the sensitive steps in the process always involve high-temperature applications, once the fluid passes through this operation step and no harmful components are present, the discharged fluid is basically at the temperature required for desorption of the adsorbent. Therefore, when the discharged fluid is returned to the adsorption bed to be used as the regenerated cleaning fluid, there is usually no need to increase the cost of heating the fluid, resulting in further savings.

As a practical way, in order to provide the continuity of the adsorption step, at least two adsorption zones must be used, at least one zone for adsorption and at least another zone for desorption. These areas are changed or rotated from time to time during use, so as to prevent the penetration of adsorbed harmful components. In this way, the feed stream containing one or more harmful components continuously flows to the adsorption zone, the fluid discharged from the adsorption zone continuously flows through at least one sensitive step in the process flow, and at least a part continuously passes through the desorption zone. At the appropriate moment, that is, the adsorption zone is basically full of harmful components and before the harmful components penetrate, the adsorption zone is transformed to make it a desorption zone, and the desorption zone is transformed to make it an adsorption zone, together with the streamline of the feedstock. Change accordingly.

It must be understood that in the present invention, it is not necessary for the stream leaving the adsorption step to pass the sensitivity step immediately, nor is it necessary to use the treated fluid immediately after the sensitivity step as a desorption or cleaning medium in whole or in part. In fact, one or more process steps can be completed before the adsorbed discharged fluid enters the sensitive step of the process, and/or the material discharged from the sensitive step can also be completed before being used in whole or in part as a desorption or cleaning medium. Or multiple process steps.

After desorption, if necessary, the product fluid containing harmful components can be treated with ordinary equipment to remove the harmful components.

As the third advantage of the present invention, due to the circulation characteristics of the adsorption bed and the use of the feed stream as a cleaning medium, the applicant has found that the adsorbent can be used under adsorption conditions. Due to the low adsorption capacity of the adsorbent under this condition, this was considered completely impossible in the past.

More precisely, most adsorbents are used for adsorption at low temperatures and regeneration at high temperatures. According to the present invention, the adsorption/desorption operations are cyclically performed at sufficiently frequent time intervals to prevent breakthrough, and the adsorption bed can be operated even at high temperatures that are generally used for regeneration. Since the adsorbent can be used at high or low temperature, it is no longer necessary to provide additional equipment and increase the cost for reducing the temperature of the feed stream to the optimum temperature suitable for the separation characteristics of the adsorbent.

Therefore, in most of its broadest embodiments, the present invention is characterized as follows: a method for treating a fluid containing at least one component, and the resulting product contains said at least one component or its Chemical derivatives, the fluid contains at least one other harmful component in at least one operation step, and the method includes: a) contacting the fluid with an adsorbent under adsorption conditions to selectively adsorb at least one other component Points (relative to the at least one component) to obtain a discharge fluid in the adsorption stage that reduces the concentration of at least one other component;

b) Use the effluent from the adsorption stage in at least one operation to obtain a product fluid; and c) Under desorption conditions, at least a portion of the product fluid is in contact with an adsorbent having at least one other component adsorbed to regenerate the adsorption To obtain a desorption phase discharge containing at least one other component in a high concentration.

In a characteristic embodiment of the present invention, the applicant's process method involves a novel method of using a hydrogen sulfide adsorbent. First, the sulfur in the hydrocarbon feed stream is catalytically converted into hydrogen sulfide, and then the entire feed stream passes through the adsorption zone containing the adsorbent in a high-temperature gas state to selectively adsorb hydrogen sulfide (relative to the hydrocarbon feed stream) to obtain a low-content hydrogen sulfide Hydrocarbon feed stream. The hydrocarbon feed stream with low content of hydrogen sulfide is then passed through a sulfur-sensitive step in the process flow, which is generally a catalytic reaction zone. The resulting hydrocarbon product stream is then used as purge gas to regenerate the sulfur-laden adsorbent bed.

Different from the prior art, the existing hydrogen sulfide adsorption technology is that the hydrocarbon stream containing gas or liquid sulfide passes through the adsorption zone at a relatively low temperature, generally in the range of about 60°-200°F. In the present invention, the gaseous sulfide-containing hydrocarbon feedstock passes through the adsorption zone at a high temperature above the dew point of the feedstock stream , generally 250° to 600°F. This temperature is commonly used in the prior art to use purge gas to desorb hydrogen sulfide from the adsorbent.

Unexpectedly, the applicant found that the raw material can still effectively use hydrogen sulfide adsorbent at high temperature. It is a well-known fact in the art that this kind of hydrogen sulfide adsorbent has a very low ability to remove hydrogen sulfide at such high temperatures. In particular, the applicant has invented that the adsorbent is continuously adsorbed and desorbed, especially when the raw material stream is used as the cleaning medium. In fact, these adsorbents can be used at high temperatures. Therefore, in the usual hydrogen sulfide adsorption step, the adsorption bed can be in the adsorption stage within 8-24 hours. In the present invention, the hydrogen sulfide adsorption only lasts 0.5-6.0 hours before the adsorption bed is converted to the desorption working state.

One of the many advantages of this particular embodiment of the present invention is the ability to desulfurize the feed stream at high temperatures, thereby eliminating the need for gas compressors, heaters and coolers required by prior hydrogen sulfide adsorption technology and the resulting cost. In this regard, the present invention, after converting the sulfur in the feed stream into hydrogen sulfide, immediately passes the feed stream through the adsorption zone and then enters the sulfur-sensitive reaction zone, which generally uses sulfur-sensitive catalysts and usually requires high temperatures. It is obviously economically beneficial to be able to make the feed stream from one operation step to another operation step without condensation.

Moreover, the hydrocarbon product stream is used as a purge gas to desorb the hydrogen sulfide on the adsorbent, and this exhaust fluid is generally already at the high temperature required for desorption. This is because it comes from the sulfur-sensitive reaction step, which eliminates the need to provide heating and sufficient supply of cleaning gas from the outside. Here, since the cleaning gas itself is the raw material stream being processed and is often at the optimal desorption temperature, the supply is always sufficient.

Moreover, because the external cleaning gas is no longer provided to the system, there is no situation in which impurities are brought in by the external cleaning gas to pollute the hydrocarbon feed stream.

Also, according to the present invention, in the adsorption zone, whatever is removed, it is conveniently and efficiently returned to the hydrocarbon fluid. This is particularly advantageous where desulfurization is due only to the presence of one or more sulfur-sensitive operating steps, and not because sulfur is harmful to the final product. Therefore, where sulfur can be allowed to exist in the final product, the special embodiment of the present invention for temporarily removing sulfur can meet the needs of the product, thereby eliminating the need for additional equipment and costs for permanent desulfurization.

In addition, where sulfur is harmful in the final product, sulfur already in the form of hydrogen sulfide can be easily and cheaply removed from the cooled final product.

In general, the present invention has a special embodiment for desulfurization that can be characterized as follows: a process in which hydrocarbons containing hydrogen sulfide are converted in a reaction zone suitable for conversion to produce hydrocarbon products, and the conversion is harmfully affected by hydrogen sulfide, so The process method described is carried out under conditions suitable for conversion, including effectively maintaining the temperature and pressure of hydrocarbons and hydrocarbon products substantially in a gaseous state. The process method includes: (a) At a temperature sufficient to maintain the hydrocarbon containing hydrogen sulfide in a gaseous state , So that it passes into at least one but not all (at least two) adsorption zone, which contains a solid adsorbent selective for hydrogen sulfide adsorption (compared to hydrocarbons);

(B) Discharging hydrocarbons containing a small amount of hydrogen sulfide from at least one adsorption zone that receives hydrocarbons, and passing the hydrocarbons into the reaction zone to produce effluents containing product hydrocarbons;

(C) At a temperature sufficient to maintain the product hydrocarbon-containing stream in a substantially gaseous state, pass at least a portion of the product hydrocarbon-containing effluent to at least one other adsorbent that does not receive hydrocarbons but has adsorbed hydrogen sulfide in step (a) Zone desorbs hydrogen sulfide from the at least one other adsorption zone to regenerate the at least one other adsorption zone;

(D) Discharging an effluent containing hydrogen sulfide and product hydrocarbons from the at least one other adsorption zone;

(E) Stop passing hydrogen sulfide-containing hydrocarbons into at least one adsorption zone, and regenerate the at least one adsorption zone according to step (c), using at least one regenerated adsorption zone as at least one adsorption zone in step (a).

In a more preferred embodiment, a particularly advantageous application of the present invention is the isomerization process flow discussed above. According to the present invention, the hydrodesulfurization section in the process flow can be merged into the isomerization section to obtain a new, simplified, economical and effective process method. This effectively saves a lot of equipment required when the two sections in the entire process operate independently.

Therefore, in this new, simplified and combined isomerization process, the hydrocarbon feed stream containing sulfur-carrying components and/or nitrogen-carrying compounds is first heated to form steam, and then passed through a hydrogenation catalytic reactor, where the sulfur It is converted into hydrogen sulfide, and if nitrogen is present, it is converted into ammonia. The gaseous hydrocarbon feedstock containing sulfur (in the form of hydrogen sulfide) and nitrogen (in the form of ammonia) leaves the hydrogenation reactor at substantially the same temperature as when it was entered. In the adsorption zone of the adsorbent, under the temperature and pressure conditions of the adsorption zone, the adsorbent can selectively adsorb hydrogen sulfide and ammonia from the feed stream. These hydrogen sulfide/ammonia adsorbents can also remove water from the feed stream, and the subsequent isomerization step is beneficial. This is because the sulfur/nitrogen sensitive catalyst used here is also sensitive to water to a lesser extent.

The hydrocarbon feedstock substantially free of hydrogen sulfide and ammonia is then passed to the isomerization reactor. If necessary, after a little heating, the hydrocarbons are isomerized. The isomerized product hydrocarbon effluent is then desorbed in the adsorption bed loaded with hydrogen sulfide and/or ammonia during the previous adsorption process. Due to the pressure drop and temperature rise in the isomerization reactor, the efficiency of isomerized hydrocarbons as purge gas is improved. It must be pointed out, however, that the present invention does not require the isomerization step to immediately follow the adsorption step, and likewise, it does not require the desorption step to immediately follow the isomerization step. Between the adsorption and isomerization steps and/or the isomerization and desorption steps, any number of operating steps can be performed on the hydrocarbon effluent.

The hydrocarbon isomerization product effluent now contains desorbed hydrogen sulfide and/or ammonia. If necessary, it can be condensed to remove excess hydrogen from the cycle, and then flashed or stabilized to remove hydrogen sulfide and/or Or ammonia.

As previously pointed out, the adsorption/desorption steps of the present invention are actually cyclic. When an adsorber is basically full of hydrogen sulfide and ammonia, it starts to enter the desorption operation state, and a newly regenerated bed enters the adsorption operation at the same time, which requires the help of a series of valves to change the flow direction of the hydrocarbon stream.

Due to the relatively short cycle time of adsorption/desorption, the volume of adsorbent required in these beds is much smaller than the volume of the isomerization reactor. Owing to the elimination of expensive equipment in the ordinary hydrodesulfurization/isomerization process, such as furnace heaters, steam strippers and related parts, recirculation compressors, etc., the savings obtained far exceed The cost of adding a relatively small hydrogen sulfide/ammonia adsorption bed.

In the preferred embodiment of the present invention, the need for an ordinary hydrodesulfurization system is eliminated, while at the same time the entire isomerization process is greatly simplified, and the economic benefits are improved, which not only reduces the capital consumption for equipment, but also reduces The operating cost of the entire process is reduced. This is mainly due to reduced equipment and reduced heating and cooling required by common technologies.

The process method of the preferred embodiment of the present invention is characterized as follows: A process method for hydrodesulfurization and isomerization of a feed stream containing a hydrocarbon containing at least four carbon atoms and at least a sulfur and/or nitrogen component, including: (A) Provide a hydrocarbon feed fluid with a certain temperature that contains enough molecular hydrogen to catalytically convert all the sulfur components contained into hydrogen sulfide and all the nitrogen components contained into ammonia, and the temperature is sufficient to ensure the hydrocarbon feed stream Basically in a vapor state;

(B) Circulate the hydrocarbon feedstock heated in step (a) into a catalytic reaction zone containing an effective amount of catalyst. Under the condition that hydrogen sulfide and ammonia are formed, the sulfur and nitrogen in the hydrocarbon feedstream will all form hydrogen sulfide and ammonia. A hydrocarbon feedstock fluid containing hydrogen sulfide and/or ammonia is produced.

(C) Maintaining the temperature of the hydrocarbon feed stream containing hydrogen sulfide and/or ammonia at least sufficient to ensure that the stream is in a vapor state, and passing the fluid to at least one adsorption zone of at least two adsorption zone groups, each of which adsorbs The zones alternately perform adsorption and subsequent desorption, and each adsorption zone contains a solid adsorbent that can selectively adsorb hydrogen sulfide and ammonia, thereby obtaining a hydrocarbon feed fluid containing a low concentration of hydrogen sulfide and/or ammonia;

(D) Discharge a hydrocarbon feed stream containing low concentrations of hydrogen sulfide and/or ammonia from at least one adsorption zone, and pass it to an isomerization reaction zone containing a sufficient amount of isomerization catalyst to produce a stream containing hydrogen sulfide and/or ammonia under isomerization conditions. Emissions of isomers;

(E) Discharge the isomer-containing effluent from the isomerization reaction zone and pass it to another adsorption zone at a temperature sufficient to maintain the stream in a vapor state to desorb hydrogen sulfide and/or ammonia, Obtain an effluent containing hydrogen sulfide and/or ammonia and containing isomers;

(F) Discharging the effluent containing hydrogen sulfide and/or ammonia and containing isomers from another adsorption zone of step (e).

The present invention provides an excellent, simple and ingenious method for temporarily removing harmful components from fluids, so that the harmful components can bypass the operation steps sensitive to the components, which is the most economical and effective way.

Figure 1 is a system flow diagram of the broadest embodiment of the present invention. The figure shows two adsorbers and one process step sensitive to fluid components, and includes a valve control system that can circulate the adsorbent bed.

Figure 2 is a system flow diagram of a preferred embodiment of the present invention, where a hydrocarbon feed stream undergoes an isomerization step.

Figure 3 is a system diagram of another embodiment of the present invention, in which the adsorption zone and the catalytic reaction zone are combined in one vessel.

Referring to Figure 1, it describes the simplest form of the present invention. Only a part of the chemical process is drawn here. It contains a process step that is sensitive to one or more components in the fluid to be treated. The raw material contains at least one component that is harmful to at least one step in the process flow. At least one other component processed in a sensitive process step. The raw material enters the pipeline 200. It can be the raw material of the entire chemical process and already contains harmful components, or it can be the intermediate fluid of the entire process. It has been processed in one or more process steps, and harmful components have been produced. . In both cases, the fluid must be treated to remove one or more harmful components before entering the sensitive step.

After entering the line 200, the raw material stream enters the valve assembly 500 again. In the valve assembly 500, the valves 510 and 514 are open, and the valves 512 and 516 are closed. The stream containing harmful components enters the adsorption bed 518 through the open valve 510.

The adsorbent bed 518 contains an adsorbent that is selective for one or more harmful components in the stream (compared to the remaining components in the stream). The adsorbent is selected according to whether the stream is liquid or vapor and what harmful components are. Appropriate consideration should also be given to the temperature of the feed fluid. The temperature of the feed stream entering the adsorbent should be the most desirable temperature, that is, the temperature that is optimal for the selective removal of harmful components in terms of ease and selectivity of the adsorbent. However, as stated at the beginning, due to the characteristics of the present invention, the adsorbent can be used at a non-optimal temperature due to the rapid cycle of adsorption/desorption.

Those skilled in the field of adsorption technology are well aware that specific adsorbents should be selected according to specific applications. Generally speaking, any adsorbent that can selectively adsorb one or more harmful components in the feed stream and can be regenerated with a fluid medium can be used as an adsorbent in the present invention. Adsorbents such as molecular sieve, silica gel, activated carbon, activated alumina, etc. are all suitable for the present invention. Refer to the book "Zeolite Molecular Sieve" (John Wiley & Sons 1974) by Donald W. Breck, which describes the application and selection of zeolite adsorbents, which can be used as a reference here.

For example, the 3A zeolite adsorbent can be used to adsorb ammonia in the hydrodenitrogenated hydrocarbon fluid, and the process includes steps that are sensitive to nitrogen and its derivatives, such as reforming operations. Similarly, 5A zeolite adsorbent can be used to adsorb carbon monoxide or carbon dioxide in light gas operations like synthetic ammonia and urea production. The presence of CO/CO2 is harmful to the catalysts for synthetic ammonia or urea. For another example, activated carbon can be used to remove condensable components in natural gas. When a membrane is used to separate methane from these gases, these condensable components are harmful to the membrane.

According to different processes and the sensitive steps involved, the adsorbent bed is designed to contain a sufficient amount of adsorbent to substantially remove at least one harmful component. Similarly, according to the allowable number of sensitive steps to determine the allowable penetration of harmful components.

Of course, it should be understood that if none of the harmful components in the feed stream can be selectively removed by a single adsorbent, a mixed adsorbent can be used. This mixture can be in one adsorbent bed or separately in multiple adsorbents. In the bed, the combined effect of these adsorbents can remove all harmful components.

The effluent from the adsorption section discharged from the adsorption bed 518 contains a low concentration of harmful components. The fluid enters line 220 and then passes through the sensitive process steps indicated by 520 in FIG. 1.

The sensitive step may include a chemical reaction step with or without a sensitive catalyst; a distillation step; ion exchange; a non-regenerative sorbent or adsorbent; a membrane separation unit, etc.

After the exhaust fluid of the adsorption stage passes through the sensitive process steps, the product exhaust is obtained. Part of it enters the pipeline 230 and the remainder enters the pipeline 250. The product effluent entering the line 230 must be sufficient to be effectively used as a cleaning medium to regenerate the adsorption bed 522, which is in the desorption stage and was loaded with harmful components in the previous adsorption stage.

Although not shown in Figure 1, sensitive steps can also produce second or waste discharge fluids. Their generation is not the purpose of the entire process flow. The purpose is to produce product effluents that are originally present in the raw material stream and passed through the sensitive steps. Processed components. This component can exist in a purer form or as a reaction product. Therefore, in the reforming operation, the product discharge fluid is the reformed product. According to the present invention, the fluid is used as a cleaning medium for a failed adsorption bed. For example, in the distillation section, the fluid used as the cleaning medium can be a purified product. Similarly, in the isomerization reactor, the isomerized product can also be used as a regeneration medium for the spent adsorbent. Therefore, as used herein, the product effluent contains components originally present in the raw material stream that have been processed in sensitive steps, or reaction products containing such components, and its production is the purpose of the entire process flow. In the process of the present invention, it is this product effluent that is used wholly or partly as the desorption medium for the failed adsorption bed.

Desorption is carried out under desorption conditions that ensure that harmful components can be effectively removed from the adsorbent, and the adsorbent is regenerated for continued use. Generally speaking, if the product effluent is in immediate contact with the adsorbent to be regenerated, the fluid temperature is usually to ensure an appropriate desorption temperature, because the sensitive process steps are carried out under elevated temperature conditions. However, if there is an intervening step between the sensitive step of 520 and the adsorption bed 522, on the other hand, if the temperature is not too high, a heating device (not shown) can be used to increase the temperature of the product discharge to an appropriate desorption temperature.

Those skilled in the adsorption field know the best operating conditions for adsorption and desorption, and they are easy to determine.

After the adsorption bed 522 is regenerated, the exhaust fluid from the desorption section containing high-concentration harmful components leaves the bed through line 240, enters valve assembly 500, and then enters line 300 through valve 514; either as a product or continues throughout the chemical process To process.

After running for a period of time, the adsorption bed 518 will be full of harmful components, and the adsorption bed 522 has been regenerated. At this time, the valve of the valve assembly 500 is adjusted, the valves 510 and 514 are closed, and the valves 512 and 516 are opened. Therefore, the feed stream 200 passes through the system in the reverse direction, flows through the line 240 into the adsorption bed 522 to adsorb harmful components, then enters the sensitive step 520, then enters the regeneration bed 518, and finally leaves the system through the valve 512 and the line 300.

The length of time before the adsorption bed is converted to a desorption section or the desorption section is changed to an adsorption section depends on the specific adsorbent, harmful components, adsorbent capacity and adsorption conditions, and they all change accordingly. In general, the time period for maintaining the adsorption bed in the adsorption zone is less than the time for the harmful components to break through, which is easy to determine for those skilled in the art.

The preferred embodiment of the present invention shown in FIG. 2 is described below. As described above, it is not difficult to understand that the present invention is by no means limited to such an embodiment.

Referring to FIG. 2, the liquid feedstock hydrocarbon containing sulfur, sulfur-containing compounds, nitrogen and/or nitrogen-containing compounds passes through line 10 to pump 102, and the pump is first sent to heat exchanger 104 through line 12.

In the isomerization process, the hydrocarbon feed stream usually contains at least 5 carbon atoms, mainly light straight-run gasoline, light naphthalene, natural gasoline, light hydrocracked product or light reformate, which generally contain 0 -400ppm of sulfur and 0-100ppm, usually 0-10ppm of nitrogen-containing compounds. However, generally speaking, the composition of the feed stream in the present invention is not important, as long as the adsorbent can selectively remove hydrogen sulfide and/or ammonia from the components of the hydrocarbon feed stream.

In the heat exchanger 104, the feed stream is generally heated to 200-500°F, preferably 300-450°F, and then sent to the heater 106 through the line 14 The heater 106 heats the feed fluid to a vapor phase. , To meet the requirements of the following process steps. Generally speaking, the temperature of the feed gas leaving the heater 106 is 500-600°F, preferably 550-600°F, and the pressure is 200/700 psi. The heater 106 is a well-known type and is usually used in hydrodesulfurization/isomerization processes.

The vapor phase raw material from the heater 106 is sent to the hydrogenation reactor 108 through the line 16. Here, the sulfur and sulfur-containing compounds, nitrogen and nitrogen-containing compounds contained in the feed stream react with hydrogen in the presence of a suitable catalyst to generate hydrogen sulfide and ammonia. This hydrogenation reaction is also well known to those skilled in the art, and the typical hydrogenation/isomerization process commonly used has been discussed in, for example, US4533529. Generally speaking, the hydrogenation of sulfur and nitrogen compounds in reactor 108 is carried out at 500-650°F, depending on the conditions selected and the source of hydrogen. The catalyst used is a catalyst containing metals of groups VB, VIB, VIII, and rare earth elements in Mendeleev's periodic table, see "Periodic Table of Elements" published in the fifth edition of "Handbook of Chemical Engineering", Perry and Chilton. The catalyst may or may not have a support, but a catalyst using a refractory inorganic oxide such as silica, bauxite or sillimanite as a support is preferred. These preferred catalysts contain one or more metals added as metal oxides or sulfides, such as cobalt, molybdenum, iron, chromium, vanadium, thorium, nickel, tungsten, and uranium. Typical hydrogenation catalysts include: Shell 344Co/Mo (Shell Chemical Company, Houston, Texas), C20-5, C20-6, C20-7, C20-8 Co/Mo hydrogenation catalysts (United Catalyst Co., Ltd., Louisville, Kentucky) )and many more.

After the sulfur and/or nitrogen in the hydrocarbon feed stream are converted to hydrogen sulfide and ammonia, respectively, the stream in the reactor 108 passes through line 18 at substantially the same temperature as the inlet, and usually immediately enters at least through the valve assembly 110. A hydrogen sulfide/ammonia adsorption zone. However, if necessary, in order to increase the adsorption efficiency, it may be advantageous to cool the hydrocarbon feed fluid containing hydrogen sulfide/ammonia before sending it to the adsorption zone.

The requirement for the valve assembly 110 is that it can appropriately control the hydrocarbon feed fluid flowing into the adsorption beds 118 and 120, according to whether it flows through the adsorption beds in a forward or reverse direction, so that the beds can be adsorbed or desorbed.

It should be noted that although the drawings only show two beds (118 and 120), any number of beds can be used for the adsorption/desorption of this process.

It is generally assumed that the adsorption bed 118 has just been regenerated and is now ready to be adsorbed again. The "A" arrow in the drawing indicates the flow path of the hydrocarbon feed stream. The valves 114 and 117 in the valve assembly are in the open position, and the valves 112 and 116 are in the closed position. The hydrocarbon feed stream containing hydrogen sulfide and/or ammonia enters line 20 through valve 114 and then to the adsorption bed 118, where it flows in a forward direction and the adsorbent selectively removes hydrogen sulfide and/or ammonia from the feed stream. The treated hydrocarbon stream from which substantially all of the hydrogen sulfide and ammonia has been removed passes through line 22 to the isomerization reactor 122. There, in order to obtain high-octane gasoline and form an exhaust fluid containing product hydrocarbons, N-carbon is changed into its corresponding isomer, more precisely, an isomer. This isomer passes through line 24 to the adsorption bed 120, which was loaded with hydrogen sulfide and/or ammonia in the previous adsorption cycle, and the current product hydrocarbon effluent is passed in reverse to regenerate the bed 120, and once again all the initial The amount of hydrogen sulfide and/or ammonia. The product hydrocarbon effluent loaded with hydrogen sulfide and/or ammonia enters the valve assembly 110 again through line 26 and enters line 28 through valve 117.

As already pointed out, the process of the present invention does not require the adsorption effluent to be immediately sent to the sensitive step (in this embodiment, the isomerization reaction), nor does the effluent leaving the sensitive step be used for desorption immediately. bed. Therefore, in the embodiment of FIG. 2, the adsorption exhaust fluid from the adsorption bed 118 may be required to pass through the zinc oxide-containing guard bed (not shown) before entering the isomerization reactor to remove any remaining fluid in the fluid. Trace hydrogen sulfide. Similarly, after leaving the isomerization reactor and before entering the adsorption bed 120 for desorption, the isomers can also be passed through a separator (not shown) such as a distillation column, molecular sieve adsorbent, etc., to separate the isomers with The unisomerized hydrocarbon fluid is separated, and then the isomer fluid is reused to regenerate the adsorption bed 120, and the hydrocarbon fluid is recycled back to the isomerization reactor for further processing.

After the adsorption cycle is completed, generally before the hydrogen sulfide and/or ammonia penetrate the adsorption bed, the bed undergoing adsorption operation is converted to desorption, and the bed undergoing desorption is converted to adsorption operation. As mentioned above, because hydrogen sulfide/ammonia adsorbents are used at high temperatures, which used to be used only for desorption, the capacity of these adsorbents is relatively low. Therefore, in order to still be able to use these adsorbents, the cycle period must be short. The time for the adsorbent bed to maintain continuous adsorption operation is generally about 0.5-6.0 hours, preferably 1.0-2.0 hours. Once the adsorption cycle is completed, it is the time when the bed 118 will desorb and the bed 120 will start the adsorption operation, so the valves 112 and 116 are opened and the valves 114 and 117 are closed at the same time. At this time, the flow line of the raw material flow is shown by the arrow "B" in the figure, that is, the direction of the flow through the adsorption zone and the isomerization reactor is reversed, and it flows forward through the bed 120 for adsorption and countercurrent through the bed for desorption. 118.

Although in this embodiment, the circulation of the adsorbent bed causes the fluid to flow through the isomerization reactor countercurrently, it should be understood that the present invention also includes an embodiment in which the hydrocarbon feed stream can be made to flow through the appropriate arrangement of additional valves (not shown). Continuously flows through the reactor 122 in one direction.

The hydrogen sulfide/ammonia adsorbent used in the adsorption bed must be able to selectively adsorb hydrogen sulfide and/or ammonia in the hydrocarbon stream and be able to withstand the temperature and pressure in the adsorption bed. The general adsorption temperature range is 200°-500°F, preferably 300°-450°F, and the pressure is 00-700 psi.

Although the temperature in the adsorption zone is substantially close to the temperature in the isomerization reactor, it may still be necessary to heat the hydrocarbon feed stream free of hydrogen sulfide and ammonia before being fed into the reactor to meet the appropriate isomerization reaction temperature.

Any adsorbent can be used in this embodiment as long as it can selectively remove hydrogen sulfide and/or ammonia from the remaining components of the fluid. The adsorbents particularly suitable for the process of the preferred embodiment of the present invention and capable of removing hydrogen sulfide and/or ammonia well at the high temperature of the adsorption cycle are 4A zeolite molecular sieve and clinoptilolite.

The term "zeolite" generally refers to a group of natural and synthetic hydrated metal silico-aluminates, many of which are crystalline structures. However, there are obvious differences between various synthetic and natural materials in chemical composition, crystal structure and physical properties, and X-ray powder diffraction patterns.

The structure of crystalline zeolite molecular sieve can describe an open three-dimensional framework of SiO4 and AlO4 tetrahedrons, which are cross-linked by shared oxygen atoms, so that the ratio of the sum of oxygen atoms to aluminum and silicon atoms is 2. The loading valence of aluminum-containing tetrahedrons is balanced by impurities in anionic crystals, such as alkali metal and alkaline earth metal ions, such as sodium, potassium, calcium and magnesium ions. Using ion exchange technology, one cation can be exchanged for another .

It can be activated by removing all the bound water in the zeolite. The space left in the crystal after activation is suitable for the adsorption of adsorbate molecules. This space is only suitable for the adsorption of molecules whose size, shape and energy allow adsorbate molecules to enter the pores of the molecular sieve.

4A zeolite is a sodium cationic type A zeolite with a pore size of about 4 . Its preparation method and its physical and chemical properties are described in detail in US2882243, which can be used as a reference here.

Other adsorbents that are also suitable for use in this preferred embodiment of the invention include a pore size of at least 3.6 (The kinetic energy diameter of hydrogen sulfide) those adsorbents. These adsorbents include 5A zeolite, 13X zeolite, activated carbon and so on. These adsorbents are well known and are generally used for hydrogen sulfide/ammonia adsorption, but in the preferred embodiment of the invention the temperature used is lower.

As a preventive measure, as mentioned above, after the adsorption zone and before the isomerization reactor, a small, simple zinc oxide guard bed (not shown) may also be required to ensure that there is no residual hydrogen sulfide penetration. Possibility of penetration or system malfunction.

The isomerization reactor 122 is a general isomerization reactor well known in the art, and contains a catalytically effective amount of an isomerization catalyst to increase the isomer concentration of the hydrocarbon exhaust stream. The isomerization reaction is generally carried out at 480°-540°F. The temperature of the fluid leaving the reactor is generally slightly higher than the temperature entering the reactor, about 5-40°F higher. Due to the temperature rise and pressure drop in the reactor, the efficiency of the discharged fluid as a cleaning gas is improved.

Although in this preferred embodiment, the process step sensitive to sulfur and nitrogen is the catalyst of the isomerization reactor, the present invention is also applicable to any other process step sensitive to sulfur and/or nitrogen, wherein the specific process steps described above are used. The circulating adsorption system adsorbs sulfur.

The product discharge fluid containing hydrogen sulfide and/or ammonia passes through line 28, is cooled in heat exchanger 104, and then passes through line 30 to separator 124. In the separator 124, an overhead fraction of excess molecular hydrogen and a liquid hydrocarbon isomer condensate are produced. The hydrogen leaves the separator 124 through line 32 and is then divided into two streams through lines 34 and 36.

Line 34 circulates hydrogen to feed line 12 to provide excess molecular hydrogen for the formation reaction of hydrogen sulfide and ammonia. Make-up hydrogen is added through line 52.

As another embodiment of the present invention, line 36 provides hydrogen, which is mixed with isomers through lines 38 or 40, respectively, to enhance the subsequent desorption step. Generally 0-50% (mole) hydrogen is added to the hydrocarbon discharge fluid.

The condensed product hydrocarbon isomer leaving the separator 124 enters the stabilizer 126 through line 42. In the stabilizer 126, the hydrocarbon isomers are flashed to remove all the light end products such as hydrogen sulfide and/or ammonia and C1-C4 gas contained therein, as the overhead fraction, leaving the stabilizer through line 44 . A portion of the overhead fraction is recycled back to the raw material feed pipe 12 via line 46, and the remainder is discharged from the system via line 48. The final isomer product is discharged from the stabilizer 126 through the line 50.

Instead of using a catalytic reactor such as an adsorber and an isomerization reactor separately, as another embodiment of the present invention, these processes in the process flow can also be combined in one vessel, as shown in FIG. 3. Here, the adsorbent is placed in the 11 and 19 zones of the vessel 23, and the catalyst for the sulfur and nitrogen sensitive process steps is placed in the 15 zone of the vessel. The feed stream enters from line 3 or line 5, and the flow lines are shown by arrows A or B, respectively, depending on whether the adsorbent zone is in adsorption operation or desorption operation.

Example 1 The hydrocarbon feed stream to be isomerized contains 70 ppmw sulfur (in various sulfur-containing compounds) and 3 ppmw nitrogen (in various nitrogen-containing compounds). 40CC of feed per minute (density 0.65g/CC, equivalent to 26g/min) is fed into the hydrogenation bed with 300g C20-8Co/Mo hydrogenation catalyst, the weight hourly space velocity (WHSV) of the hydrogenation reaction Is 5.2.

The fluid that now contains hydrogen sulfide and ammonia is then fed to 400 grams of 4A zeolite (with a pore size of about 4 ) Inside the adsorber. Use high-sensitivity gas chromatography (capable of distinguishing sulfur below 0.1ppmv) to monitor the trajectory of sulfur in the system. The sampling ports are arranged at the inlet and outlet of the adsorption bed.

After heating the fluid to 500°F, it is sent to the isomerization reactor. The isomerization reactor was equipped with 945 grams of HS-10 isomerization catalyst (Union Carbide, Danbury, CT), and the resulting weight hourly space velocity was 1.65 [feed weight/catalyst weight·hour]. The isomer leaving the reactor at a temperature of 500°F then enters the desorption bed.

In this embodiment, a moderate temperature shift is used to improve the adsorption performance. The system parameters are as follows: system pressure 350 psig (gauge pressure) hydrogenation temperature 575°F adsorption temperature 350°F desorption temperature 500°FH2/hydrocarbon (mole) 1.0 total cycle time (adsorption + desorption) 2 hours hydrogenator The measurement of the sulfur and nitrogen content in the effluent proves that all the sulfur in the raw material has become hydrogen sulfide and all the nitrogen has become ammonia. During the adsorption period of the cycle, the sulfur (hydrogen sulfide) or nitrogen (ammonia) in the discharge fluid of the adsorber can no longer be detected.

After the cycle is switched to desorption, the hydrogen sulfide and ammonia content in the desorption effluent is measured. The integration of sulfur and nitrogen content over time is performed for both the adsorption feed and the desorption effluent. The comparison proves that all the sulfur and nitrogen brought in with the adsorption feed leave with the desorption effluent, and it can be determined that no unstable phenomenon occurs.

Example 2 A reforming operation was performed on a hydrocarbon feedstock containing 410 ppmw sulfur (among various sulfur compounds). The raw material of 40CC/min (density 0.65g/CC, equivalent to 26g/min) is fed into the hydrogenation bed equipped with 300g C20-8Co/Mo hydrogenation catalyst, and the weight hourly space velocity of the hydrogenation reaction is 5.2.

The fluid containing hydrogen sulfide is then fed into 400g of 4A zeolite (with a pore size of about 4 ) Inside the adsorber. Use high-sensitivity gas chromatography (which can resolve sulfur below 0.1ppmv) to monitor the trajectory of sulfur in the system. The sampling ports are arranged at the inlet and outlet of the adsorption bed.

After the fluid is heated to 900°F, it enters the reformer and still leaves the reformer at that temperature.

In this embodiment, the naturally occurring temperature is used to improve the adsorption performance. The system parameters are as follows: system pressure 350 psig (gauge pressure) hydrogenation temperature 575°F adsorption temperature 575°F desorption temperature 900°F H2/hydrocarbon (mole) 1.0 total cycle time (adsorption + desorption) 2 hours hydrogenator The determination of the sulfur content in the effluent proves that all the sulfur in the raw material is converted into hydrogen sulfide. During the adsorption period of the cycle, the presence of sulfur (hydrogen sulfide) in the adsorber discharge stream cannot be monitored.

After switching the cycle to desorption, monitor the hydrogen sulfide content of the desorption effluent. The integration of sulfur content versus time is performed on both the adsorption feed and the desorption effluent. The comparison proves that all the sulfur brought in with the adsorption feed exits with the desorption effluent, confirming that no unstable phenomenon occurs.

Example 3 reacts one pound of ammonia synthesis gas per hour to form ammonia. The composition of the synthesis gas is as follows: N224.9% (mole) H274.9% (mole) CO 500ppmvCO2500ppmv Use an adsorber containing 1 pound (Cbs) 5A molecular sieve. Keep it at 100°F, which is the outlet temperature of the bulk CO2 removal stage before ammonia synthesis. Under this condition, the capacity of 5A molecular sieve to adsorb carbon oxides is 0.1% by weight. The total flow of carbon oxides into the bed is 0.0043 lbs/hr. Therefore, the bed circulates 5 times per hour and has sufficient capacity to process this content of carbon oxide feedstock. After the carbon oxides are saturated, the bed is purged at 300°F with ammonia product that has not been cooled and sent to storage.