Process for removing light components from an ethylene stream

[0001] The present invention is a process for removing light components from an ethylene stream. Optionally, pollutants containing oxygen are also removed.

[0002] Olefins are traditionally produced from petroleum-based raw materials in catalytic or steam cracking processes. In such cracking processes, especially steam cracking, a light (s) olefin (s), such as ethylene and / or propylene, is made from a variety of hydrocarbon feedstocks. Ethylene and propylene are important commercial petrochemicals useful in many processes for the production of plastics and other chemical compounds. Limited supplies and the rising price of crude oil accelerated research into alternative ways of producing hydrocarbon products.

[0003] Olefins can be made by dehydrating the corresponding alcohol. Ethanol can be obtained by fermentation of carbohydrates, synthesis gas, a mixture of CO and H2 or any other method. Biomass, composed of organic matter from living organisms, is a leading global renewable energy source. The effluent obtained by ethanol dehydration contains substantially unconverted ethanol, water, ethylene, acetaldehyde, as well as light components. Ethanol is removed and can be recycled to the dehydration reactor. It remains a stream containing essentially ethylene, ethane, CO, CO2, H2, CH4, C3 + hydrocarbons and possibly oxygenates. In an embodiment, said stream essentially comprises ethylene, ethane, CO, CO2, H2, CH4, C3 + hydrocarbons as well as up to 1 wt.%. oxygenates. The weight ratio of ethane + CO + CO2 + H2 + CH4 + C3 + hydrocarbons to ethylene is mostly below 20/80 for most of the time. The removal of light components, CO, H2 and CH4, can result in loss of ethylene.

[0004] Among oxygenates, acetaldehyde can cause problems in ethylene recovery operations, so it would be desirable to remove said oxygenate if present.

[Background of the Invention] [0005] In the ethylene process, the stream to be purified, essentially containing ethylene, ethane, CO, CO2, H2, CH4, C3 + hydrocarbons, as well as oxygenates, is sent to a stripping tower (also referred to as a tower for methane stripping) to produce a overhead stream containing essentially CO, H2 and CH4 and a bottom stream containing substantially ethylene, oxygenates, ethane, CO2 and C3 + hydrocarbons. The separation of light components depends on their ratio in the stream. If the proportion of light components is relatively high, a very low temperature will be necessary to separate them from the ethylene stream, and therefore a cold stream will be necessary.

[0006] The following prior art documents have already described the purification of olefins, but in order to remove oxygenates, they require a scrubber with corrosive substance or washing columns, or both.

[0007] US 20030098281 A1 describes a method for controlling the water and / or oxygenate concentration of an olefin stream. The method comprises contacting an olefin stream with a liquid absorbent. The liquid absorbent is selected from the group consisting of a polyol, an amine, an amide, a nitrile, a nitrogen-containing heterocyclic compound and mixtures thereof. A gaseous stream containing essentially water vapor, ethylene, propylene and less than 2 wt.%. oxygenates are condensed in the cooling tower. The top of said cooling tower is washed with a caustic solution to remove CO2, and then contacted with a liquid absorbent to remove oxygenates.

[0008] WO 03 020670 A1 provides a method for removing oxygen-containing compounds, such as acetaldehyde, CO2 and / or water, from an olefin stream. It is explained that removal of such oxygen-containing compounds is desirable because they can poison catalysts that are used in the further process of olefin compositions. In addition, the presence of certain oxygen-containing compounds, such as acetaldehyde, may cause fouling in other olefin purification units, e.g. acid gas treatment units. The method includes providing an olefin stream comprising ethylene, propylene, C4 + olefins and acetaldehyde. The olefin stream is separated into a first fraction and a second fraction, the first fraction comprising at least the majority of ethylene and / or propylene present in the olefin stream, and the second fraction contains at least the majority of C4 + olefins and acetic aldehyde present in the olefin stream. The first fraction is then subjected to treatment with acidic gas treated with sodium hydroxide or potassium hydroxide. The olefin stream is separated by distillation, preferably distillation is extractive distillation using an extractant. The preferred extractant is a polar composition with an average boiling point of at least 38 ° C at 1 atm. (0.1 MPa). Methanol is one type of beneficial extractant. The preferred extractant is a polar composition with an average boiling point of at least 38 ° C at 1 atm. (0.1 MPa). Methanol is one type of beneficial extractant. The preferred extractant is a polar composition with an average boiling point of at least 38 ° C at 1 atm. (0.1 MPa). Methanol is one type of beneficial extractant.

[0009] WO 03 020672 A1 describes a process for removing dimethyl ether from a stream comprising ethylene and / or propylene. The olefin stream is passed to a water absorption column, where methanol is used as a water absorbent. The methanol and water contained therein, as well as some of the oxygen-containing hydrocarbon, are recovered as the bottom stream from said water absorption column, the olefin top stream is recovered and sent to the distillation column. The distillation column is separated by ethylene and propylene, as well as lower boiling components from dimethyl ether and higher boiling components, including C4 + components and methanol remaining from the methanol washing. Additional methanol is added to the distillation column to reduce the formation of clathrate and / or free water in the distillation column. The stream containing ethylene and propylene leaves the distillation column as a peak, and the higher boiling components, which include dimethyl ether and C4 + components, leave the distillation column as bottom streams. Ethylene and propylene then flow to the wash column with a caustic substance. [0010] WO 03 033438 A1 describes a process for treating an olefin stream comprising oxygenates and water, comprising: providing an olefin stream containing oxygenates and water; olefin stream dehydration; compressing the dehydrated olefin stream; washing the olefin stream with methanol to remove at least some of the oxygenate from the olefin stream; contacting methanol washed olefin stream with water; and fractionation of the olefin stream in contact with water. The recovered olefin stream (washed with methanol, followed by water) is further sent for alkaline washing and for the drying step. The olefin stream containing oxygenates and water is a drain from the MTO process.

[0011] EP 0 669 389 describes a cryogenic recovery system of ethylene in which a feed gas containing ethylene is cooled and condensed before fractionation. In particular, this document writes an improved method that uses a combination of one or more partial condensers followed by one or more deflegmators. In this document, purification is carried out using two methane stripping towers. The top stream of the first tower 117 for stripping methane passes directly into the second tower 119 for stripping methane without any other treatment.

[0012] US6444869 describes a process for the production of ethylene from the effluent stream from oxygenate conversion. The leachate from the oxygenate conversion contains hydrogen, methane, ethylene, ethane, propylene, propane and C4 + olefins. The effluent is compressed, treated to remove oxygenates, sent to a carbon dioxide removal zone, in which carbon dioxide is absorbed by contact with the caustic solution or by contacting the amine solution in combination with the caustic solution in the usual manner to remove the carbon dioxide. carbon dioxide, dried, then fractionation is carried out through a tower for stripping ethane and a tower for stripping methane. [0013] Document US 2005-0283038 A1 describes a method for producing an olefin stream from a first steam effluent stream from an oxygenate to olefin conversion reaction, wherein said first steam effluent stream comprises C2 and C3 olefins, C4 hydrocarbons and from C2 to C6 carbonyl compounds. In the process, the temperature and pressure of the first steam effluent stream are adjusted to produce a second steam effluent stream with a pressure in the range of about 100 psig to about 350 psig (from 790 to 2514 kPa) and a temperature in the range of about 70 ° F to about 120 ° F (from 21 to 49 ° C), wherein said second steam effluent stream contains about 50% by weight or more C4 hydrocarbons expressed as total C4 hydrocarbons in the first stream of vapor. The second steam effluent stream is then rinsed with a liquid stream containing alcohol to obtain a third stream of vapor, whereupon the third steam effluent stream is rinsed with liquid water to provide a fourth effluent stream of steam containing C2 and C3 olefins and about 1.0 wt.%. or less from C2 to C6 carbonyl compounds. In one embodiment of such a recovery method, at least a portion of the fourth vapor-effluent stream is contacted with a basic component, such as a caustic or amine, to remove most of the carbon dioxide therefrom (and thus remove the "acid gas" from the fourth effluent stream) ), then the CO2-free stream is dried.

[Brief Summary of the Invention] [0014] The present invention relates to a process for removing light components from an ethylene stream, comprising:

a) providing a stream (A) of dried ethylene containing essentially ethylene, ethane, CO,

CO2, H2, CH4, C3 + hydrocarbons and possibly oxygenates,

b) sending said stream (A) to a stripping tower (also referred to as a methane stripping tower) to produce a top stream containing essentially ethylene, CO, H2 and CH4, a bottom stream containing substantially ethylene, ethane, CO2, C3 + hydrocarbons and optionally oxygenates, wherein the gas phase at the top of the stripper is condensed in a heat exchanger cooled by a refrigerant stream to obtain a first gas phase and a first liquid phase, in a preferred embodiment the refrigerant stream consists of one or more C3 or C4 hydrocarbons it preferably consists of liquid and propane gas or propylene, the first gas phase is condensed in a heat exchanger cooled by liquid ethane or liquid ethylene to obtain a second gas phase,referred to as the overhead stream, essentially comprising ethylene, CO, H2 and CH4, and a second liquid phase, the first and second liquid phases are the reflux of the stripper.

[0015] It has been found that when the proportion of light components in the stream to be purified is low enough, the cooling source of the condenser at the top of the stripper can be liquid propane or liquid propylene and only a small amount of ethylene escapes with the light components. When the proportion of light components in the stream to be purified is higher, liquid propane or propylene is not cold enough, most of the ethylene escapes with the light components. A colder cooling source is necessary. Instead of using a cooling source that is colder than propane or propylene to liquefy the entire top of the stripper column, it has been found in particular that a liquid propane-cooled condenser or liquid propylene should be maintained and insert a further condenser using liquid ethane or liquid ethylene as a cooling source.

[0016] Optionally, the method of the present invention comprises an additional device for removing oxygenates as well as CO2, and obtaining substantially pure ethylene, preferably ethylene, for the production of polymer (polymer grade). In the aforementioned method, no abrasive cleaner for removing CO2 is present, or a washing column for removing oxygenates.

[0017] Said method is referred to as a basic process.

[0018] The liquid ethane or liquid ethylene is in fact a liquid and gas mixture, the refrigerant stream is in fact a mixture of liquid and gas, such as a mixture of liquid and gaseous C3 or C4 hydrocarbons. Preferably, it consists of liquid and propane gas or propylene.

[0019] The use of a propan-propylene mixture instead of propane or propylene would not deviate from the invention.

[0020] The pressure of the liquid propane or liquid propylene is preferably from 0.3 to 2 barg (from 30 kPag to 200 kPag).

[0021] The pressure of the liquid ethane or liquid ethylene is preferably from 0.3 to 5 barg (from 30 kPag to 500 kPag).

[0022] The pressure of the liquid iso-butane is preferably from 0.3 bar to 0.7 bar (from 30 kPa to 70 kPaa).

[0023] The gas phase condensers at the top of the stripper can be arranged in a variety of ways, provided that the gas phase substantially containing CO, H2 and CH4 ethyl is cooled with liquid ethane or liquid ethylene before the final exit of the stripper zone.

[0024] The condenser cooled by liquid propane or liquid propylene (the first condenser) and the condenser cooled by liquid ethane or liquid ethylene (second condenser) can be arranged in series, the gas phase starting from the first one going into the other one. They can be arranged in the same jacket, having two sets of tubes, one for each coolant.

[0025] The first condenser may be traditionally arranged with a reversal drum and the second condenser is at the outlet of the reel to cool the gas phase substantially comprising ethylene, CO, H2 and CH4 through liquid ethane or liquid ethylene before the final exit of the stripper zone.

[0026] Fig 1 describes an embodiment of the above method. Stream 2 of dried ethylene containing essentially ethylene, ethane, CO, CO2, H2, CH4, C3 + hydrocarbons and possibly oxygenates is sent to the stripper. The bottom stream 4 containing essentially ethylene, ethane, CO 2, C 3 + hydrocarbons and possibly oxygenates is recovered and optionally sent for further purification. The gas phase at the top of the stripper is condensed in a heat exchanger cooled by liquid propane or liquid propylene to obtain a first gas phase and a first liquid phase recovered in a tumbler, the first gas phase being condensed in a heat exchanger cooled by liquid ethane or liquid ethylene 7 to obtain a second gas phase 3, referred to as a top stream essentially comprising ethylene, CO,

In one embodiment, the bottom stripper stream, essentially comprising ethylene, ethane, CO 2, C3 + hydrocarbons and optionally oxygenates, is further purified to remove any possible oxygenates as well as CO 2, and to obtain substantially pure ethylene, preferably ethylene for the production of polymers . Preferably, a portion of the ethylene is expanded to yield liquid ethylene and said liquid ethylene is sent as a cooling fluid to condense the first gas phase at the top of the stripper. Preferably ethylene is expanded to a pressure in the range of 0.3 to 5 barg (from 30 kPag to 500 kPag) to obtain a colder gas and liquid mixture. During condensation of the first gas phase at the top of the stripper, ethylene returns to the gas phase and is preferably recycled.

[0028] In a first embodiment, the basic process further comprises (i)

c) transferring said bottom stream from step b) to the ethane stripper to produce a bottom stream containing essentially ethane, C3 + hydrocarbons and possibly oxygenates, • a top stream consisting essentially of ethylene and CO2,

d) transmitting said peak stream from step c) to a CO2 adsorption zone with a fixed bed for recovering an essentially CO2-free ethylene stream, or (ii) c1) transmitting said bottom stream from step b) to a CO2 adsorption zone with a fixed bed in order to recover; recovering the stream substantially free of CO2, and then transferring said stream to the ethane stripper to produce a bottom stream containing essentially ethane, C3 + hydrocarbons and optionally oxygenates, a top stream consisting essentially of ethylene substantially free of CO2. The above method is referred to as embodiment 1.

[0029] Preferably, in said embodiment 1, a portion of the liquid ethylene in the tumbler (also known as a decanter) of the ethane stripper is expanded and sent as a cooling fluid to condense the first gas phase at the top of the stripper.

[0030] In an embodiment, the weight ratio of ethane + CO + CO2 + H2 + CH4 + C3 + hydrocarbons to ethylene in (A) is less than 10/90.

[0031] In an embodiment, the weight ratio of ethane + CO + CO2 + H2 + CH4 + C3 + hydrocarbons to ethylene in (A) is below 10/90 and above 0.1 / 99.9.

[0032] In an embodiment, the weight ratio of ethane + CO + CO2 + H2 + CH4 + C3 + hydrocarbons to ethylene in (A) is less than 5/95.

[0033] In an embodiment, the proportion of oxygenates in (A) is from 50 ppm by weight. up to 10,000 ppm by weight

[0034] In an embodiment, the proportion of oxygenates in (A) is up to 3000 ppm by weight.

[0035] In an embodiment, the proportion of oxygenates in (A) is up to 2000 ppm by weight.

In one embodiment, the proportion of H 2 in (A) is up to 2% by weight.

[0037] In an embodiment, the proportion of H 2 in (A) is up to 1% by weight.

[0038] In an embodiment, the proportion of H2 in (A) is up to 0.5 wt%.

[0039] In an embodiment, the proportion of H2 in (A) is up to 0.1 wt%.

[0040] In an embodiment, the proportion of CO2 in (A) is up to 400 ppm vol.

[0041] Suitably, the "dried ethylene stream" in step a) means a water content below 5 ppm by weight, advantageously below 3ppm by weight, and preferably below 1 ppm by weight.

In an embodiment of the invention, when the dried ethylene stream (A) has been produced by ethanol dehydration, said stream (A) is substantially free of acetylene.

[0043] The ethylene treated in accordance with the present invention is particularly suitable as a raw material for the production of alpha-olefins, ethylbenzene / styrene, ethylene oxide / ethylene glycol, ethylene dichloride and suitable polymers such as homo or polyethylene copolymer (PE, EPR, EPDM etc. .), polystyrene (PS), copolymers of styrene with butadiene, isoprene, acrylonitrile or combinations (SBS, SIS, SBR, ABS, SAN), polyesters (PET) and poly (vinyl chlorides) (PVC).

[0044] In another embodiment, the invention relates to a process for removing light components from an ethylene stream, comprising:

a) providing a stream (A) of dried ethylene comprising ethylene, ethane, CO, CO2, H2, CH4, C3 + hydrocarbons and optionally oxygenates, b) separating said ethylene stream (A) using a separation agent, which is preferably a tower for methane stripping or stripper stream (g) of a gaseous stream containing ethylene, CO, H2 and CH4, • lower stream (C) containing ethylene, ethane, CO2, C3 + hydrocarbons and possibly oxygenates,

c) cooling the gas peak (B) to a temperature in the range of -10 ° C to -45 ° C to obtain the first (D) gas stream and the first liquid stream (E),

d) cooling the first (D) gaseous stream to a temperature in the range of -10 ° C to -45 ° C, lower than the temperature from step c) to obtain a second gaseous stream (F) containing ethylene, CO, H2 and CH4, and a second stream (G) liquid,

e) transmitting the first and second liquid streams (E) and (G) to said separation agent as reflux.

In another embodiment, said method is noteworthy in that the cooling of step c) is carried out using a coolant stream that contains a mixture of liquid and optionally gaseous hydrocarbons, from C3 to C4, more preferably liquid and optionally gaseous propane and and / or liquid and optionally gaseous propylene at a pressure ranging from 30 kPag to 200 kPag.

[0046] In another embodiment, said method is noteworthy in that the cooling from step d) is carried out using liquid ethane or liquid ethylene at a pressure ranging from 30 kPag to 500 kPag.

In another embodiment, said method is noteworthy in that the bottom stream (C), essentially comprising ethylene, ethane, CO 2, C3 + hydrocarbons and possibly oxygenates, is further purified to remove oxygenates as well as CO2, and recover a stream (H) of substantially pure ethylene, which is preferably ethylene for the production of polymers.

In another embodiment, said method is notable in that a part of said stream (H) of substantially pure ethylene is expanded, preferably to a pressure in the range of 0.3 to 5 barg (from 30 kPag to 500 kPag ), in order to obtain a cold mixture of liquid and optionally gas, said liquid ethylene being used as a refrigerant stream to cool the top gas stream (B).

In another embodiment, said method is noteworthy in that during the cooling of the top stream (B) the ethylene gas from said stream (H) of substantially pure ethylene returns to the gaseous phase and is recycled.

[0050] In another embodiment, the invention relates to a device for implementing the above methods:

• a first separation unit, which is preferably a methane stripping tower or stripper, for extracting from the stream (A) the top gas stream (B) and lower stream (C) • a second separation unit, preferably a return drum or stripping column, for separating the first (C) gas stream from the first liquid stream (D) - a first cooling unit, preferably a heat exchanger, for cooling the gas flow peak (B) - a second cooling unit, preferably a heat exchanger, for cooling the first stream (C) gaseous means for transferring the stream (A) of the dried ethylene to the first separation unit, means for transferring the gas peak (B) to the first cooling unit,means for transferring the first (D) gas stream to the second cooling unit and means for transferring the first and second liquid stream (E) and (G) to said first separation unit

All embodiments described above are interconnected and should be considered in combination with each other.

[Detailed Description of the Invention] [0051] With respect to oxygen-containing pollutants, also referred to as oxygenates, there may be mentioned methanol, ethanol, C3 alcohols; ethers, such as diethyl ether and methyl ethyl ether and dimethyl ether; carboxylic acids, such as acetic acid; aldehydes, such as acetaldehyde; ketones, such as acetone; and esters, such as methyl esters; and vinyl derivatives. Oxygen-containing polluting substances, especially those causing problems in alcohol dehydration, are aldehydes.

[0052] With reference to the ethylene stream (A) in step a), it may originate from ethanol dehydration. Said dewatering may be carried out in one or more ethanol dehydration reactors. With regard to alcohol dehydration, such a method is described in documents WO-2009-098262, WO-2009-098267, WO-2009-098268 and WO-2009-098269. The present invention is very efficient in the purification of ethylene produced by ethanol dehydration.

[0053] The outlet stream from said dehydration reactor comprises ethylene and steam as well as small amounts of oxygenates, ethane, CO, CO2, H2, CH4 and C3 + hydrocarbons. "Low quantities" means that the weight ratio of ethane + CO + CO2 + H2 + CH4 + C3 + hydrocarbons to ethylene is below 20/80, and most often below 10/90.

[0054] Said outlet stream from the dehydration reactor is initially cooled, typically in a cooling tower using water as the cooling medium. In the cooling tower, most of the water contained in the outlet stream of the dehydration reactor condenses and is removed from the bottom of the tower as a bottom stream of liquid water. A part of said lower water stream is cooled in a heat exchanger and recycled as a cooling agent to the top of the cooling tower. The portion of the bottom water stream that is not recycled as a cooling agent may contain a portion of oxygenates and mostly unconverted ethanol, if present. Said stream may be treated in a stripper to recover a stream of clean water. Ethylene, oxygenates, ethane, CO, CO2, H2, CH4 and C3 + hydrocarbons are removed from the top of the cooling tower usually under pressure, such as from 1 to 16 absolute bars (from 0.1 MPaa to 1.6 MPaa), and are directed as a stream of contaminated ethylene. Suitably, said contaminated ethylene stream is successively compressed and cooled in one or more steps to remove the major part of the water, then introduced into the fixed bed drying zone and finally into the process according to the invention.

[0055] In the previous compression stages, the recovered water contains part of the contaminant containing oxygen and dissolved hydrocarbons. The polluted hydrocarbon stream can also be cooled before the first compression step and recover water. In an embodiment of the invention, the water recovered after each cooling subsequent to the compression step and after cooling, if present, before the first compression step, is sent to the stripping tower to provide a top stream comprising, essentially, pollutants containing oxygen and hydrocarbons, and a bottom stream of substantially pure water . The overhead stream is optionally burned to destroy oxygen-containing pollutants and recover heat.

[0056] After the compression steps, the contaminated ethylene stream is then introduced into the fixed bed drying zone and finally into the process according to the invention. The drying zone with a fixed bed is known as such.

[0057] With regard to the stripping column, the task of said stripping column is to recover the overhead stream containing essentially H2, CH4 and CO. This is preferably a distillation column.

[0058] With respect to operating conditions, a skilled person in the field of hydrocarbon distillation can select operating conditions due to the contribution of light feed components to the stripper column with ethylene and the thermodynamic properties of the cooling liquids. The basis of the present method is mainly the use of propane or propylene to condense the top of the stripper and "complete" condensation by cooling with ethane or ethylene to reduce the amount of ethylene that escapes with the light components in the bottom stream of the stripper. Preferably, a portion of the cooling energy in the second condenser, the latter fed by ethane or ethylene, at the top of the stripper is up to 10% of the total cooling energy required at the top of the stripper. [0059] The stripper column must be pressurized high enough to operate at temperatures that are not too low for using predominantly liquid propane or liquid propylene as the coolant at the top. A stripper for recovery of the top stream containing H2, CH4 and CO and essentially liquid ethylene at the bottom operating at 40 barg (4 MPag) has a peak flow temperature of about 0 to -10 ° C and a bottom temperature of about 0 ° C. . The same stripper operating at 21 barg (2.1 MPaag) has a peak flow temperature of -30 ° C and a bottom temperature of about containing H2, CH4 and CO and essentially liquid ethylene at the bottom, operating at 40 barg (4 MPag) has a peak head temperature of about 0 to -10 ° C and a bottom temperature of about 0 ° C. The same stripper operating at 21 barg (2.1 MPaag) has a peak flow temperature of -30 ° C and a bottom temperature of about containing H2, CH4 and CO and essentially liquid ethylene at the bottom, operating at 40 barg (4 MPag) has a peak head temperature of about 0 to -10 ° C and a bottom temperature of about 0 ° C. The same stripper operating at 21 barg (2.1 MPaag) has a peak flow temperature of -30 ° C and a bottom temperature of about

-24 ° C. These temperatures and pressures are a function of the ratio of H2, CH4 and CO in the (ethylene) stream and mainly the H2 ratio.

[0060] With reference to the temperature of the stream (D) i.e. the temperature at the top of the stripper and after the first condenser, it is in the range of -5 ° C, -10 ° C or -15 ° C to -45 ° C, - 40 ° C or -35 ° C. With reference to the temperature of the coolant stream from step c), it is in the range of -10 ° C; -15 ° C or -20 ° C to -50 ° C, -45 ° C or -40 ° C. With respect to the temperature of the liquid ethane or ethylene used in step d), it is in the range of -60 ° C; -65 ° C or -70 ° C to 80 ° C, -85 ° C or -90 ° C.

[0061] With respect to the first embodiment and the CO2 adsorption zone with a fixed bed, this can be any element capable of selectively removing CO2. For example, it is commercially available fixed bed adsorption (PSA for pressure swing adsorption or TSA for variable temperature adsorption) using molecular sieves or basic oxides, basic oxides on a support, large surface carbons, organic metal framework components (MOF) or mixtures thereof . The molecular sieves are preferably zeolites with a low silica content, containing 8- (among them zeolite A) or 12-membered (including X zeolite) rings and exchanged with alkali, alkaline earth or lanthanide cations. Other molecular sieves are crystalline titanium silicates (materials from the ETS family). The basic oxides on the support are preferably oxides of alkali metals, alkaline earths or lanthanides deposited on high surface area coals, alumina, silica, zirconium oxide or titanium oxide, clays. CO2 removal can be carried out using a liquid stream or a gaseous ethylene stream, depending on the pressure and temperature. A stream essentially free of CO2 is recovered. Since only traces of CO2 need to be removed from ethylene, a preferred process cycle is temperature-change adsorption (TSA). CO2 adsorption can be carried out on two or more fixed bed adsorbers. Said fixed bed adsorbent, after CO2 saturation, can be regenerated while the main stream is treated on another adsorbent bed or any combination. During the regeneration as a result of desorption, a stream is obtained that can be processed anywhere. In the TSA process cycle, regeneration is carried out by sweeping the saturated adsorbent with an inert gas by raising the temperature until CO2 desorption occurs. Finally, the saturated adsorbent can be replaced with a new adsorbent and the saturated adsorbent can either be removed or regenerated ex-situ for further use. The term "substantially" should be interpreted in the light of the continued use of ethylene. If the ethylene is to be polymerized or oligomerised, the CO2 content should be 1 ppm vol. or less, preferably 0.5 ppm vol. or less. In the TSA process cycle, regeneration is carried out by sweeping the saturated adsorbent with an inert gas by raising the temperature until CO2 desorption occurs. Finally, the saturated adsorbent can be replaced with a new adsorbent and the saturated adsorbent can either be removed or regenerated ex-situ for further use. The term "substantially" should be interpreted in the light of the continued use of ethylene. If the ethylene is to be polymerized or oligomerised, the CO2 content should be 1 ppm vol. or less, preferably 0.5 ppm vol. or less. In the TSA process cycle, regeneration is carried out by sweeping the saturated adsorbent with an inert gas by raising the temperature until CO2 desorption occurs. Finally, the saturated adsorbent can be replaced with a new adsorbent and the saturated adsorbent can either be removed or regenerated ex-situ for further use. The term "substantially" should be interpreted in the light of the continued use of ethylene. If the ethylene is to be polymerized or oligomerised, the CO2 content should be 1 ppm vol. or less, preferably 0.5 ppm vol. or less. should be interpreted in the light of the further use of ethylene. If the ethylene is to be polymerized or oligomerised, the CO2 content should be 1 ppm vol. or less, preferably 0.5 ppm vol. or less. should be interpreted in the light of the further use of ethylene. If the ethylene is to be polymerized or oligomerised, the CO2 content should be 1 ppm vol. or less, preferably 0.5 ppm vol. or less.

[0062] In an embodiment of the invention, the pressure in the C2 fractionation column, also referred to as the ethane strip tower, is chosen so as to achieve this temperature at the bottom of the C2 fractioning column / ethane tower so that no oligomerization or polymerization of the oxygenates will take place. For example, said temperature should not exceed 150 ° C and preferably not exceed 100 ° C. This temperature is a function of the pressure and contribution of oxygenates in the blend of + ethane + C3 + hydrocarbons. The higher the proportion of oxygenates, the higher the temperature. The higher the pressure, the higher the temperature. The C2 fractionation column / tower for stripping the ethane is preferably a distillation column.

wherein said top stream of the ethane stripping tower is sent to the CO2 adsorption zone with a fixed bed in order to recover a substantially ethylene-free ethylene stream. A portion of the liquid ethylene in the reverse drum (also known as a decanter) of the ethane stripper tower is expanded and sent as a cooling fluid to condense the first gas phase at the top of the stripper.

[0064] In an embodiment, the stripper (methane stripping tower) and C2 splitter / ethane stripping tower operate at the same pressure except for the pressure drop between the methane stripper tower and the C2 fractionator column / ethane strip for fluid flow . Preferably the pressure is in the range of 15 to 45 barg (from 1.5 MPaag to

4.5 MPag).

In a specific example, the pressure in the stripper is from about 15 to 35 barg (from

1.5 MPag to 3.5 MPag), and the pressure in the ethane stripping tower and CO2 adsorbers is about 1 or 2 barg (from 0.1 MPag to 0.2 MPag) less, corresponding to the pressure drop caused by pipes and equipment. In this pressure range, the temperature at the top of the stripper and after the first condenser is in the range of -20 to -30 ° C, with the bottom temperature of the stripper being in the range of -15 to -25 ° C, the temperature at the top of the tower for stripping ethane and after the condenser is in the range from -30 to -20 ° C, and the temperature at the bottom of the tower for stripping ethane is in the range from 75 to 85 ° C.

In a specific example, the stripper pressure is 20 to 25 barg (from 2.0 MPa to 2.5 MPa) and the pressure in the ethane stripper and CO2 adsorbents is about 1 or 2 barg (from 0.1 MPag to 0.2 MPag) less, corresponding to the pressure drop caused by pipes and equipment. In this pressure range, the temperature at the top of the stripper and after the condenser is in the range -22 to -26 ° C, with the bottom temperature of the stripper being in the range of -20 to -24 ° C, the temperature at the top of the tower to The ethane stripping and after the condenser is in the range from -27 to -22 ° C, and the temperature at the bottom of the ethane stripper tower is in the range of up to 82 ° C.

In another specific example, the stripper pressure is from 30 to 45 barg (from 3.0 MPaq to 4.5 MPaag) and the pressure in the ethane stripper and CO2 adsorbers is from about

5 to 25 barg (from 0.5 MPag to 2.5 MPag) less. Preferably the pressure in the ethane stripper is in the range from 15 to 30 barg (from 1.5 MPa0 to 3.0 MPaag). In this pressure range, the peak of the stripping column is condensed at a temperature in the range of -20 to -45 ° C, the temperature at the bottom of the stripper is in the range of -5 to 5 ° C, the temperature at the top of the tower for stripping the ethane is in the range of -25 to -35 ° C, condensed at a temperature in the range from -25 to -35 ° C, and the temperature at the bottom of the tower for stripping the ethane is in the range from 75 to 85 ° C.

[0068] Preferably, the stripper pressure is in the range of 25 to 35 barg (from 2.5 MPag to 3.5 MPag) and the pressure of the ethane stripping tower and the CO2 adsorbers is in the range of 20 to 25 barg (from 2.0 MPag to 2.5 MPag). In this pressure range, the peak of the stripping column is condensed at a temperature ranging from -10 to -35 ° C, the temperature at the bottom of the stripper is in the range of -5 to -25 ° C, the temperature at the top of the tower to strip the ethane is in the range of -28 to -32 ° C, it is condensed at a temperature in the range of -28 to -32 ° C and the temperature at the bottom of the tower to strip the ethane is in the range of 50 to 80 ° C. [Examples]

Example 1, according to the invention.

[0069] The process according to figs 2-3 is carried out. The results are shown in the following table 1:

Table 1

<td></td><td colspan="7">stream number</td>

<td></td><td>1</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td>

<td>Flow rate kg / h</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>H2</td><td>12</td><td>12</td><td>12</td><td>0</td><td>0</td><td>0</td><td>0</td>

<td>WHAT</td><td>2</td><td>2</td><td>2</td><td>0</td><td>0</td><td>0</td><td>0</td>

<td>METHANE</td><td>1</td><td>1</td><td>1</td><td>0</td><td>0</td><td>0</td><td>0</td>

<td>ETHYLENE</td><td>25119</td><td>25954</td><td>73</td><td>25881</td><td>24987</td><td>59</td><td>835</td>

<td>ETHANE</td><td>15</td><td>15</td><td></td><td>15</td><td>14</td><td>0</td><td>1</td>

<td>CO2</td><td>8</td><td>8</td><td></td><td>8</td><td></td><td>0</td><td></td>

<td>C3 +</td><td>767</td><td>720</td><td></td><td>720</td><td></td><td>720</td><td></td>

<td>H2O</td><td>197</td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>TOGETHER</td><td>26121</td><td>26712</td><td>88</td><td>26624</td><td>25001</td><td>779</td><td>836</td>

[0070] Stream 1 is the starting stream from the cooling that follows the dewatering of ethanol, stream 7 is recycled in the compression zone between cooling and the stripper as shown in figure 3.

[0071] 25119 kg of C2H4 are produced, 73 kg are lost in stream 3 and 59 kg are lost in stream 6, meaning that about 0.5% is lost.

Example 2, comparative.

[0072] The process according to fig 4 is carried out. The results are shown in the following table 2.

Table 2

<td>stream number on Fig. 4</td><td></td><td>1</td><td>2</td><td>3</td>

<td></td><td></td><td>Feeding the stripping column</td><td>Bottom of the column stripper</td><td>Blow from column stripper</td>

<td>Temperature</td><td>° C</td><td>15</td><td>-20</td><td>-24</td>

<td>Pressure</td><td>bar g</td><td>22</td><td>22</td><td>22</td>

<td>H2</td><td>kg / h</td><td>0.1</td><td></td><td>0.1</td>

<td>WHAT</td><td>kg / h</td><td>1</td><td></td><td>1</td>

<td>CO2</td><td>kg / h</td><td>1</td><td>1</td><td></td>

<td>ethane</td><td>kg / h</td><td>5</td><td>5</td><td></td>

<td>ethylene</td><td>kg / h</td><td>25091</td><td>25013</td><td>78</td>

<td>acetaldehyde</td><td>kg / h</td><td>18</td><td>18</td><td></td>

<td>C3 +</td><td>kg / h</td><td>325</td><td>325</td><td></td>

<td>Together</td><td>kg / h</td><td>25,441.1</td><td>25362</td><td>79.1</td>

Table 2 continues

<td>stream number in Figure 4</td><td></td><td>4</td><td>5</td><td>6</td>

<td></td><td></td><td>Bottom of the tower to stripping ethane</td><td>The distillate of the steam from the tower for stripping ethane</td><td>Product, ethylene</td>

<td>Temperature</td><td>° C</td><td>80</td><td>-24</td><td>20</td>

<td>Pressure</td><td>bar g</td><td>21</td><td>21</td><td>20</td>

<td>H2</td><td>kg / h</td><td></td><td></td><td></td>

<td>WHAT</td><td>kg / h</td><td></td><td></td><td></td>

<td>CO2</td><td>kg / h</td><td></td><td>1</td><td></td>

<td>ethane</td><td>kg / h</td><td></td><td>5</td><td>5</td>

<td>ethylene</td><td>kg / h</td><td>18</td><td>24995</td><td>24995</td>

<td>acetaldehyde</td><td>kg / h</td><td>18</td><td></td><td></td>

<td>C3 +</td><td>kg / h</td><td>325</td><td></td><td></td>

<td>Together</td><td>kg / h</td><td>361</td><td>25001</td><td>25000</td>

[0073] By comparison with example 1, the feedstock of the stripper contains much less light components, as a result of which it is sufficient to cool the condenser to -24 ° C. To obtain -24 ° C on the process side, the coolant may be liquid propane at a pressure of 0.5 bar. The loss of C2H4 in the overhead stream from the stripping column is 78 kg / h. In the example

1 to obtain a loss C2H4 of 73 kg / hr in the bottom strip stream from the stripper, it is required to supply a second condenser with liquid ethylene at -65 ° C.

[0074] 25091 kg of C2H4 are produced, 78 kg are lost in stream 3 and 18 kg are lost in stream 4, meaning that about 0.5% is lost.

Total Research &amp; Technology Feluy Plenipotentiary:

PL-PAT-2012-923

EP 2 931 688 B1