Ethanol to ethylene process

Abstract

A process for ethanol dehydration to produce ethylene is provided. Ethanol is dehydrated to produce ethylene, which is subsequently converted to longer-chain olefins, which are then hydrogenated to produce long-chain alkanes. In some embodiments, separate feeds are employed to improve efficiency and omit an alkaline tower. Advantages of the process include lower demand for steam and 30%-40% combined reactor volume reduction when using two reactors compared to a single reactor.

Description

[0001] Cross-references

[0002] This patent application claims priority to Indian provisional patent applications 202211049527, 202211049520 and 202211049523 filed on August 30, 2022. Technical Field

[0003] This relates to a process for the dehydration of ethanol to produce ethylene. More specifically, the invention relates to a flow chart of an ethanol dehydration process in some cases without a caustic scrubber. In other cases, the flow chart has a split feed configuration to allow the use of less steam and reduce the size of the reactor section. Background Art

[0004] Oil and gas refineries worldwide are exploring ways and routes to reduce their carbon footprint and are moving towards sustainable processes. The method of converting bioethanol into green ethylene is one such sustainable method.

[0005] The present disclosure relates to the processing of ethylene.

[0006] Advantages have been found in dehydrating ethanol to produce ethylene by operating a split stream and / or not using a caustic scrubber in the process. The ethylene is produced for further processing into olefin feedstocks, for example for ethylene oligomerization. Summary of the invention

[0007] A method for converting an ethanol feed stream to ethylene is provided, the method comprising dividing the ethanol feed stream into a first portion and a second portion; passing the first portion to a reactor through a feed heater; mixing steam with the first portion at the feed heater and passing the ethanol / steam mixture to the reactor; subjecting the ethanol / steam mixture to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water; mixing the effluent with the second portion to form an effluent / second portion mixture, and passing the mixture to a second reactor for reaction to produce a product effluent comprising ethylene and water, wherein the reactor section is reduced in volume by 30%-40% compared to a process comprising a caustic scrubber, and wherein the first reactor and the second reactor contain less steam compared to a process having a single reactor.

[0008] In another embodiment, a method for converting an ethanol feed stream into ethylene is provided, the method comprising dividing the ethanol feed stream into a first portion and a second portion for delivery to a reactor section comprising a first reactor and a second reactor, wherein the combination of the first reactor and the second reactor has a reactor volume of about 60%-70% of the volume of a single reactor system; delivering the first portion to the first reactor through a feed heater; mixing steam with the first portion at the feed heater and delivering the ethanol / steam mixture to the first reactor; subjecting the ethanol / steam mixture to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water; mixing the effluent with the second portion to form an effluent / second portion mixture, and delivering the effluent / second portion mixture to the second reactor for reaction to produce a product effluent comprising ethylene and water. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings provide views of flow charts. DETAILED DESCRIPTION

[0010] The ethanol dehydration treatment unit is divided into six sections: feed pretreatment section, feed purification section, reactor section, ethylene compression section and water washing section.

[0011] In the feed ethanol pretreatment section, metals can be removed by using an ion exchange resin guard bed. It is configured in a lead / lag flow scheme so that one vessel can be offline and reloaded while one vessel is online. The ion exchange resin supplier recommends a regenerable system using HCl or sulfuric acid as the regenerant. HCl regenerant is not appropriate because the unit has stainless steel metallurgy.

[0012] The demetallized product leaving the feed ethanol pretreatment section is sent to the feed purification tower (FPC) by the tube side of the new feed-tower top vapor exchanger. The tower is designed to remove the heavier molecules through the bottom of the tower together with the ethanol feed. The heavier molecules may include but are not limited to components such as C3+ alcohols, acetals, hexadecanoic acid, octadecanoic acid, isoamyl acetate, cyclohexanol, cyclopentanol, phenol, cresols, acetals, etc. Some of these heavier molecules can be converted into ketones in the reactor and tend to accumulate without leaving the process, and therefore need to be removed or minimized before the feed can be sent to the reactor section. The tower bottom purge stream is expected to be <1.0% of the total feed, which is composed of concentrated heavy substances such as acetic acid, acetals, cresols, phenol, free fatty acids such as hexadecanoic acid and octadecanoic acid, some heavy alcohols, etc.

[0013] Since there are no expected dissolved light fractions in the ethanol feed raw material, a total condensing system is suitable for this tower. The receiver pressure controlled by the nitrogen push-pull system is set to allow the use of MP steam as the reboiling medium for the tower. The vapor from the overhead distillate is first condensed on the shell side of the new feed-tower top vapor exchanger and then condensed on the feed purification column overhead condenser before entering the feed purification column receiver. The receiver liquid at its bubble point is pumped by the feed purification column net tower top pump and further supercooled in the feed purification column net tower top cooler. The supercooled material is mixed with the liquid ethanol circulating stream and cooled in the DEE absorber feed cooler before entering the DEE absorber on the tower top tray or feed buffer tank.

[0014] The DEE absorber floats with the dehydration separator vapor stream which enters below the bottom tray of the DEE absorber and provides for the removal of ether from the dehydration separator vapor. The DEE absorber bottoms sump is designed to provide a 15 minute residence time for the liquid feed entering the reactor section.

[0015] The reactor section includes the following elements. The feed surge tank liquid or the DEE absorber bottom liquid stream is pumped to the reactor section by a dehydration feed pump. The discharge stream is first preheated in an ethanol-treated water exchanger. The preheated ethanol is divided into two streams during flow control. The first branch of the feed stream is heated and evaporated in the first ethanol steam heater before entering the cold side (tube side) of the combined feed exchanger 1 (CFE1) and then enters the feed heater. Before entering CFE1, the vaporized feed is mixed with steam generated in the steam generator. The combined stream is heated to the desired reaction temperature in the feed heater and fed to the first reactor.

[0016] The second split of the feed stream is heated and evaporated before entering the cold side (tube side) of the second combined feed exchanger (CFE2). At the cold side outlet of CFE2, the feed stream is mixed with the first reaction effluent and sent to the first intermediate heater, where the stream is further heated to the desired reaction temperature. Steam does not participate in the reaction (except for some minor side reactions), but the steam added to the reactor serves the dual purpose of controlling the heat absorption across the reactor and maintaining catalyst stability (reducing coking). Minimizing the temperature drop across the reactor is critical because the formation of diethyl ether is more significant at a lower reactor outlet temperature. In order to ensure that the formation of diethyl ether is limited, the second reactor effluent is passed through the second intermediate heater and heated to the desired reactor temperature again before entering the third reactor. The third reactor is a finishing reactor that ensures that diethyl ether is converted into useful ethylene together with unconverted ethanol. The third reactor effluent is separated and passes through the hot side (shell side) of CFE1 and CFE2. The hot side outlet of the combined feed exchanger is further cooled and condensed in the wastewater stripper reboiler and subsequently in the dehydrated product condenser before entering the dehydration separator.

[0017] The dehydration separator liquid stream is primarily water with some dissolved oxygenates and is sent to a low pressure wastewater stripper, while the vapor stream is essentially ethylene product. As described above, the dehydration separator vapor is sent to the DEE absorber.

[0018] The fired heaters used in the reactor section are designed as natural draft furnaces with the primary process heating occurring in the radiant section, while the convection section of these fired heaters is designed to produce high pressure steam

[0019] The ethylene compression section involves the following factors. The pressure requirement for the vapor product stream of the downstream oligomerization unit exceeds 1000 psig, which is achieved by a four-stage or five-stage compressor system. A reciprocating machine may have four stages, while a centrifugal machine may have five stages. In one embodiment, there will be a four-stage reciprocating machine with one run and one standby. The number of stages can be based on the downstream unit pressure requirements and limiting the compressor discharge temperature to less than 90°C.

[0020] The vapor from the water scrubber is mixed with the first-stage ethylene compressor overflow before entering the first-stage ethylene compressor suction tank to separate any entrained liquid. The vapor from the tank is compressed in the first-stage ethylene compressor, and the compressor discharge is cooled in the first-stage discharge cooler and the first-stage discharge trim cooler, and the cooling stream is further mixed with the second-stage ethylene compressor overflow and enters the first-stage ethylene compressor discharge tank. The vapor from the first-stage ethylene compressor discharge tank is divided into two streams, the first stream is the overflow of the first-stage ethylene compressor, and the second stream is the net vapor stream entering the second-stage ethylene compressor. The vapor is further compressed in the second-stage ethylene compressor, and the compressor discharge is cooled in the second-stage discharge cooler and the second-stage discharge trim cooler; the cooling stream is further mixed with the third-stage ethylene compressor overflow and enters the second-stage ethylene compressor discharge tank. The vapor from the second-stage ethylene compressor discharge tank is divided into two streams, the first stream is the overflow of the second-stage ethylene compressor, and the second stream is the net vapor stream entering the third-stage ethylene compressor. The vapor is further compressed in the third stage ethylene compressor, and the compressor discharge is cooled in the third stage discharge cooler and the third stage discharge trim cooler before entering the third stage ethylene compressor discharge tank. The vapor from the third stage ethylene compressor discharge tank is divided into two streams, the first stream is the third stage ethylene compressor overflow, and the second stream is the net vapor product entering the ethylene dryer to remove saturated water.

[0021] The dry vapor from the ethylene dryer is mixed with the fourth stage ethylene compressor overflow and enters the fourth stage ethylene compressor suction tank. The vapor is compressed in the fourth stage ethylene compressor before entering the fourth stage ethylene compressor discharge tank. The fourth stage ethylene compressor discharge tank vapor is divided into two streams, the first stream is the fourth stage ethylene compressor overflow, and the second stream is the net vapor product sent to the oligomerization unit. Unlike the upstream level, the fourth stage ethylene compressor discharge is not cooled, and the hot vapor stream is directly sent to the oligomerization unit. In order to ensure that the fourth stage ethylene compressor discharge temperature does not exceed the recommended temperature limit, a fourth stage cooler is added to the compressor overflow line.

[0022] The saturated water in the vapor from the water scrubber is partially separated in the first stage ethylene compressor suction tank and discharge tank and the second and third stage ethylene compressor discharge tank. The separated liquid is mostly water, and this condensation is caused by the increase in pressure and the decrease in intermediate temperature. The separation tank liquid is sent to the wastewater stripping tower.

[0023] Two ethylene dryers loaded with molecular sieves are designated to remove moisture from the ethylene vapor product, and these dryers are operated in lead-lag mode. Once the lead dryer molecular sieve is saturated with water, the dryer needs to be regenerated to restore the screening capacity. The dry ethylene vapor from the lag dryer is used as the regenerant medium. The slipstream from the lag dryer outlet is sent to the regenerant superheater, in which the regenerant is heated to the required regeneration temperature before entering the regenerant dryer. Before entering the regenerant coalescer, the waste regenerant from the regenerant dryer is cooled and condensed in the regenerant condenser, and the waste regenerant carries the desorbed moisture leaving the molecular sieve. The regenerant coalescer separates water from the waste regenerant (i.e., ethylene), and the ethylene vapor is sent back to the first stage ethylene compressor suction tank under pressure control, and the waste water is sent to the wastewater stripping tower.

[0024] The wastewater section consists of a wastewater stripper and a water scrubber. Liquids from the dehydration separator, water scrubber bottoms, regenerator coalescer (intermittent), and separated liquids from the ethylene compressor section knockout drum are directed through the shell side of the wastewater stripper feed-bottoms exchanger before entering the top tray of the wastewater stripper. The wastewater stripper is designed to strip out oxygenates that enter as overhead vapor product with the feed, while recovering process water in the bottoms.

[0025] The wastewater stripper is operated at 5psig-10psig, and the overhead vapor is cooled and condensed in the waste gas condenser before entering the waste gas knockout drum. The waste gas knockout drum liquid has most of the alcohol carryover from the DEE absorber vapor, unconverted alcohol from the reactor, water, and other non-selective oxygenates formed in the reactor such as acetaldehyde, ether, acetic acid, etc., which are recycled and mixed with new feed and sent to the reactor section through the feed buffer tank or the bottom of the DEE absorber. The waste gas knockout drum steam is a small purge stream, which is a mixture of olefins (dissolved in the dehydration separator and water scrubber liquids) and oxygenates. The wastewater stripper has two reboiler systems. The wastewater stripper auxiliary reboiler uses low-pressure steam as the reboiling medium, and the wastewater stripper reboiler is a process heat integrated with the hot dehydration reactor effluent upstream of the dehydration product condenser. The wastewater stripper net bottoms are pumped by a process water pump through the tube side of the wastewater stripper feed bottoms exchanger and divided into three streams downstream. The first stream is the process water used to wash the vapor product oxygenates in the water scrubber. This stream is sent to the water scrubber through an ethanol treated water exchanger, a treated water cooler and a treated water trim cooler.

[0026] The second stream is the amount of process water corresponding to the steam injected into the dehydration reactor plus 5% blowdown. This stream is sent to the steam generator. The steam produced is sent to the dehydration reactor to meet the steam to ethanol ratio requirements. The continuous blowdown from the steam generator is sent directly to the wastewater treatment plant. This stream is split upstream of the water exchanger treated with ethanol.

[0027] The third stream is net process water resulting from the various reactions occurring in the reactor section and is sent to a wastewater treatment facility and is taken downstream of the process water trim cooler.

[0028] As mentioned before, the dehydrator steam can be sent to the DEE absorber or water scrubber. The dehydrator steam has certain impurities / oxygenates, such as acetaldehyde, diethyl ether, dimethyl ether, water, unconverted alcohol, etc., which may need to be removed depending on the further use of the ethylene product.

[0029] With the DEE absorber, the diethyl ether in the separator vapor is absorbed into the bottom liquid along with some other oxygenates. Since the ethanol feed is used to wash the separator vapor, there is some ethanol feed left over in the DEE absorber vapor. The DEE absorber overhead vapor is sent to below the bottom tray of the water scrubber. The water scrubber is designed to use the treated water from the bottom of the wastewater stripper to wash away oxygenates, such as acetaldehyde, unconverted alcohol from the reactor section, ethanol carryover from the DEE absorber vapor, acetic acid, etc. The treated water enters the top tray of the water scrubber, and the absorption of oxygenates occurs in a countercurrent direction on multiple trays. The washed water scrubber overhead vapor is sent to the downstream ethylene compression section, and the liquid bottoms stream with all dissolved oxygenates / alcohols is sent to the wastewater stripper.

[0030] The following table shows the expected process conditions and conversion and selectivity based on dry ethanol feed.

[0031] surface

[0032] parameter value Feed rate, MMGPY 300.0 Steam to ethanol (dry basis) mass ratio 1.5 Reactor inlet temperature, °C 450 Lag reactor outlet pressure, psig kPa (g) 450 <![CDATA[LHSV (based on dry ethanol in the fresh feed) hr -1 > 1.0 Total ethanol conversion % 99.9 Ethylene selectivity, weight % 97+ Olefin selectivity, weight % 99+ Oxygenated compounds and other by-products Ppm Level BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In Figure 1, a method 10 for treating an oxygenate feedstock is shown according to an exemplary embodiment. The oxygenate feedstock may contain an alcohol, and preferably contains ethanol. The feedstock may contain primarily ethanol and may be aqueous. Preferably, the oxygenate feedstock is a biorenewable feedstock.

[0035] Feed line 12 conveys the oxygenate stream of the oxygenate feedstock to a feed pretreatment section 14. Feed pretreatment section 14 includes a vessel 16 containing a cation exchange resin adsorbent bed for removing metal contaminants, such as sodium, zinc, phosphate, copper and calcium, from the oxygenate stream in feed line 12. Feed pretreatment section 14 may include an additional vessel 18 having the same adsorbent bed for further removing metals from the oxygenate stream. Vessels 16, 18 may be arranged in series or in a lead-lag type to allow regeneration of spent adsorbent. Line 17 conveys a partially pretreated oxygenate stream from the outlet of vessel 16 to the inlet of vessel 18. The pretreated oxygenate stream flows out of feed pretreatment section 14 from the outlet of additional vessel 18 in line 20 and is fed to purification tower 22. Feed pretreatment section 14 may be operated at a temperature of about 32° C. to about 105° C. and a pressure of about 2800 kPa(g) to about 3100 kPa(g).

[0036] In the purification tower 22, the pretreated oxygenate stream is fractionated to separate ethanol from heavier oxygenates (also known as fusel oils, such as cyclohexanol, cyclopentanol, and heavier acids). The purification tower 22 is operated to minimize ethanol, not exceeding 1% of the feed in the bottom stream of the pipeline 26. The heavy oxygenate stream in the bottom pipeline 26 flows out from the bottom of the purification tower 22 for heavy oxygenate treatment. The purification tower 22 can be reboiled by heat exchange with a suitable hot stream such as steam to provide the heat required for distillation. The purification tower 22 provides a gaseous overhead stream of purified ethanol in the top pipeline 24, which can be cooled in the air cooler 25 and fed to the feed buffer tank 26 together with the circulating ethanol stream in the pipeline 27. The purification tower 22 can be operated with a bottom temperature between about 82°C and about 121°C and a top pressure of about 35kPa(g) to about 140kPa(g).

[0037] The ethanol in the feed buffer tank 26 can be covered with nitrogen. Feed pump 29 pumps the ethanol feed stream in pipeline 28 into the two feed streams. The first feed stream in pipeline 30 is heat exchanged with the first dehydration exchange stream in pipeline 32, mixed with steam in pipeline 33 and fed to the first feed heater 34. The first feed heater 34 can be a flame heater and can heat the first feed stream to about 400°C to about 550°C. The first heated feed stream obtained in pipeline 36 is added to the first dehydration reactor 40. In the first dehydration reactor 40, the ethanol feed is converted into ethylene and water over a dehydration catalyst at a pressure of about 455kPa(g) to about 630kPa(g). The first dehydration stream is discharged from the first dehydration reactor 40 via pipeline 42.

[0038] The second feed stream in line 44 is heat exchanged with the second dehydration exchange stream in line 46, mixed with the first dehydration stream in line 42 and fed to the second feed heater 48. The second feed heater 48 can be a fired heater and can heat the second feed stream to about 400°C to about 550°C. The resulting second heated feed stream in line 50 is added to the second dehydration reactor 52. In the second dehydration reactor 52, the ethanol feed is converted to ethylene and water over a dehydration catalyst at a pressure of about 420 kPa (g) to about 700 kPa (g). The second dehydration stream is discharged from the second dehydration reactor 52 via line 54.

[0039] The second dehydrated stream in line 54 is fed to an intermediate heater 56. The intermediate heater 56 can be a fired heater and can heat the second dehydrated stream to about 400°C to about 550°C. The resulting third heated feed stream in line 58 is fed to a third dehydration reactor 60. In the third dehydration reactor 60, the residual ethanol feed is converted to ethylene and water over a dehydration catalyst at a pressure of about 420 kPa(g) to about 700 kPa(g). The third dehydrated stream is discharged from the third dehydration reactor 60 via line 62.

[0040] The dehydration catalyst is an alumina based catalyst.

[0041] The third dehydrated stream is split between the first dehydrated exchange stream in line 32 and the second dehydrated exchange stream in line 46. The first dehydrated exchange stream in line 32 is heat exchanged with the first feed stream in line 30, and the second dehydrated exchange stream in line 46 is heat exchanged with the second feed stream in line 44, and the cooled dehydrated streams are recombined in line 64.

[0042] The cooled dehydrated stream in line 64 is fed to a quench tower 68 where it is quenched by direct contact with water from a first cooling water stream in line 70 and a second cooling water stream in line 72. A quenched ethylene stream exits in a quench tower overhead line 74, and a bottoms water stream exits the bottom of the tower in line 76. The bottoms water stream is split between a vent stream in line 78 and a quench recycle stream in line 82, and the vent stream can be sent to a wastewater stripper 80 via a control valve thereon. A first portion of the quench recycle stream is air cooled in a product condenser 69 and circulated as a first lower cooling water stream in line 70 via a control valve thereon, and a second portion of the quench recycle stream is heat exchanged in a trim condenser 71 and circulated to the quench tower 68 as a second higher cooling water stream in line 72. The quench tower 68 may be operated at a bottom temperature of about 37°C to about 104°C and a top pressure of about 280 kPa(g) to about 490 kPa(g).

[0043] The quenched ethylene stream in line 74 is fed to the first stage suction drum 86. In the first stage suction drum, ethylene flows out from the top line 88 to the first stage compressor 90, while residual water flows out from the bottom of the drum in line 92 through a control valve thereon and may be sent to the wastewater stripper 80 through line 78. The first stage compressor 90 compresses the ethylene stream to a first pressure of about 350 kPa(g) to about 1225 kPa(g), and the discharge in line 91 is cooled in the first stage discharge cooler 93 and the first stage trim cooler 94.

[0044] The cooled compressed ethylene stream from the first stage trim cooler 94 is fed to the first stage bleed drum 96. Ethylene flows from the first stage bleed drum 96 in overhead line 98 to the second stage compressor 100, while residual water flows from the bottom of the drum in line 102 through a control valve thereon and may be sent to the wastewater stripper 80 via line 92 and line 78. The second stage compressor compresses the ethylene stream to a second pressure of about 455 kPa(g) to about 3220 kPa(g), and the effluent in line 101 is cooled in the second stage bleed cooler 103 and the second stage trim cooler 104.

[0045] The secondary cooled compressed ethylene stream from the second stage trim cooler 104 is fed to the second stage take-off drum 106. Ethylene flows out of the second stage take-off drum 106 in overhead line 108 and is sent to a water scrubber 110, while a residual water stream flows out of the bottom of the drum in line 112 through a control valve thereon and may be sent to a waste water stripper 80 via line 102, line 92 and line 78.

[0046] In the water scrubber 110, the secondary cooled, compressed ethylene stream is countercurrently washed with cooled, treated water in line 118 from the wastewater stripper 80 to absorb additional oxygenates, thereby producing a washed ethylene stream flowing out in an overhead line 120 and a wash water stream in a bottoms line 122. The wash ethylene stream in the overhead line 120 is conveyed to the product dryer section 140. The wash water stream in line 122 is conveyed back to the water stripper 80 via a control valve thereon. The wash water 110 can be operated at a bottoms temperature of about 16°C to about 82°C and a top pressure of about 2800 kPa(g) to about 3500 kPa(g).

[0047] In other flow charts different from the current flow chart, the washed ethylene stream can be sent to the caustic scrubber section to remove oxygenates. However, it has been found that the method can be successfully operated without the use of a caustic scrubber under certain operating conditions, and ethylene is produced for further processing as an olefin feedstock, such as for the ethylene oligomerization section. On the contrary, as described below, the wastewater stripping tower bottom stream is sent to the top tray of the water scrubber, and the steam from the second stage compressor discharge port is sent to the bottom tray of the water scrubber. The purpose is to wash the steam rich in ethylene and remove oxygenates as much as possible from the product stream. The ethylene-rich steam with ppm trace CO and ppm level CO2 is directly sent to a group of molecular sieve-containing dryers in the lead-lag system to remove moisture in the steam stream, and further sent to a cryogenic distillation unit. The steam from the cryogenic distillation unit is further compressed in the third stage of the ethylene compressor to meet the downstream unit cell limit pressure requirements.

[0048] In the product dryer section 140, the washed, scrubbed ethylene stream in line 120 is fed to a first dryer inlet knockout drum 146 to remove residual water and provide a dryer inlet stream in line 148 and a separated water stream in a bottoms line 150, which is fed to the wastewater stripping tower 80 via line 122. The dryer inlet stream is fed to a first product dryer 152 via line 148. The first product dryer 152 contains an adsorbent for adsorbing water from the ethylene in the dryer inlet stream in line 148 to provide a dry ethylene stream. The adsorbent may be a molecular sieve material having a pore size of 2A-4A. The first product dryer 152 may be operated in an upflow mode. The product dryer section 140 may include a second product dryer 156 operating as the first product dryer 142. The two product dryers may be operated in series, but are preferably arranged in a lead-lag mode of operation to facilitate regeneration during continuous operation. Similar to the first product dryer 152, the second product dryer 156 contains an adsorbent for adsorbing water from ethylene. The dried ethylene stream exits the product dryer section 140 as a dried ethylene stream in line 158. The product dryer section 140 may be operated at a temperature of about 32° C. to about 105° C. and a pressure of about 2800 kPa(g) to about 3100 kPa(g).

[0049] The dried ethylene stream in line 158 is fed to a dryer outlet knockout drum 160 to remove residual water and provide a dryer outlet stream in line 162 and a second separated water stream in bottoms line 164 which may be fed to wastewater stripper 80 via lines 150 and 122 .

[0050] The dryer outlet stream in line 162 can be fed to a heavy oxygenate removal tower 170 to separate a tower top stream containing mainly ethylene but possibly containing higher olefins from heavy ketones and diethyl ether. Olefins are produced in the tower top line 172 and fed to the third stage compressor 174, and a tower bottom heavy oxygenate stream is produced in the tower bottom line 176. The heavy oxygenate purge stream can be subjected to heavy oxygenate treatment in line 178, while the reboiler portion is reboiled and fed back to the tower 170. A compressed ethylene stream at a pressure of about 2800 kPa (g) to about 7000 kPa (g) in the compressor discharge line 176 can be provided to the dimerization reaction section. The heavy oxygenate 170 can be operated at a tower bottom temperature of about -30°C to about 120°C and a tower top pressure of about 2415 kPa (g) to about 3100 kPa (g).

[0051] The water streams containing oxygenates and volatiles in lines 92, 102, 112, 122, 150, and 164 can be fed to a wastewater stripper 80, where the volatiles and oxygenates are vaporized to provide a tower overhead volatile stream in line 182 and a stripping water stream in line 184. A portion of the stripping water stream can be reboiled and sent back to the tower to provide the necessary heat. The treated water stream in line 186 can be pumped to a water outlet in line 188, which includes a cooled treated water stream in line 118 for the water scrubber 110. The wastewater stripper 80 can be operated at a tower bottom temperature of about 90° C. to about 120° C. and a tower top pressure of about 35 kPa(g) to about 140 kPa(g).

[0052] The overhead volatile stream in line 182 may be cooled in air cooler 189 and fed to off-gas knockout drum 190. The overhead stream in line 192 from knockout drum 190 may be sent to a flare while the ethanol recycle stream may be pumped through line 24 to feed buffer tank 26 in line 27.

[0053] While the following is described in conjunction with specific embodiments, it should be understood that this description is intended to illustrate and not to limit the scope of the foregoing description and the appended claims.

[0054] Although there is no further detailed description, it is believed that those skilled in the art can utilize the present invention to the greatest extent by using the foregoing description and can easily determine the essential characteristics of the present invention without departing from the spirit and scope of the present invention to make various changes and modifications of the present invention and adapt it to various usages and conditions. Therefore, the aforementioned preferred specific embodiments should be understood as merely illustrative and not to limit the rest of the present disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0055] In the foregoing, all temperatures are given in degrees Celsius, all pressures are given in kPa (g), and all parts and percentages are by weight unless otherwise indicated, and wherein n is an integer from 20 to 2000.

[0056] A first embodiment is a process for treating a stream comprising ethylene and oxygenates comprising sending the stream to a water wash column and sending the resulting ethylene-rich vapor stream directly to a dryer without first being sent to a caustic wash section.

[0057] A second embodiment is a method of converting an ethanol feed stream to ethylene, the method comprising dividing the ethanol feed stream into a first portion and a second portion; passing the first portion to a reactor through a feed heater; mixing steam with the first portion at the feed heater and passing the ethanol / steam mixture to the reactor;

[0058] The ethanol / steam mixture is subjected to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water; the effluent is mixed with the second portion to form an effluent / second portion mixture, and the mixture is sent to a second reactor for reaction to produce a product effluent comprising ethylene and water. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the first portion or the second portion comprises a mixture of ethanol and water. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph up to the first embodiment in this paragraph, wherein the water is circulated and mixed with the ethanol feed stream.

[0059] A third embodiment of the present invention is a method for converting an ethanol feed stream into ethylene, the method comprising dividing the ethanol feed stream into a first portion and a second portion to be sent to a reactor section including a first reactor and a second reactor; sending the first portion to the first reactor through a feed heater; mixing steam with the first portion at the feed heater and sending the ethanol / steam mixture to the first reactor; subjecting the ethanol / steam mixture to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water; mixing the effluent with the second portion to form an effluent / second portion mixture, and sending the effluent / second portion mixture to the second reactor for reaction to produce a product effluent comprising ethylene and water. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the first portion or the second portion comprises a mixture of ethanol and water. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the water is circulated and mixed with the ethanol feed stream. One embodiment of the present invention is one, any or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the reactor section is about 30%-40% smaller in volume than the dehydration method in which the ethanol feed stream is maintained as a single stream. An embodiment of the present invention is one, any or all of the first embodiment in this paragraph to the previous embodiments in this paragraph, wherein the reactor section also includes a third reaction vessel. An embodiment of the present invention is one, any or all of the first embodiment in this paragraph to the previous embodiments in this paragraph, wherein the oxygenate feedstock is pretreated to remove contaminants, and then the pretreated oxygenate stream is sent to the reactor section. An embodiment of the present invention is one, any or all of the first embodiment in this paragraph to the previous embodiments in this paragraph, wherein the pretreated oxygenate stream is fractionated to separate ethanol from heavier oxygenates, and then the ethanol is the ethanol feed stream. An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the ethanol feed stream sent to the first reactor is heated to about 400°C to about 550°C and converted to ethylene over a dehydration catalyst at about 455kPa to about 630kPa(g). An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the effluent / second portion mixture is heated to about 400°C to about 550°C and converted to ethylene over a dehydration catalyst at about 420kPa(g) to about 700kPa(g).An embodiment of the present invention is one, any or all of the first embodiment of this paragraph to the previous embodiment of this paragraph, wherein the product effluent from the second reactor is sent to an intermediate heater, and the heated product effluent is then sent to a third reactor. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the product effluent of the third reactor does not contain measurable ether. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the first reactor and the second reactor contain less steam than when all the ethanol feed streams are sent to a single reactor, wherein the first reactor and the second reactor operate at an increased endothermic level. An embodiment of the present invention is one, any or all of the previous embodiments in this paragraph to the first embodiment in this paragraph, wherein the product effluent is not sent to the caustic wash section.

Claims

1. A method for converting an ethanol feed stream into ethylene, the method comprising a. dividing the ethanol feed stream into a first portion and a second portion; b. delivering the first portion to the reactor through a feed heater; c. mixing steam with the first portion at the feed heater and delivering the ethanol / steam mixture to the reactor; d. subjecting the ethanol / steam mixture to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water; e. mixing the effluent with the second portion to form an effluent / second portion mixture, and sending the mixture to a second reactor for reaction to produce a product effluent comprising ethylene and water, wherein the reactor section is reduced in volume by 30%-40% compared to a process comprising a caustic scrubber, and wherein the first reactor and the second reactor contain less steam than a process having a single reactor.

2. The method of claim 2, wherein the first part or the second part comprises a mixture of ethanol and water.

3. The process of claim 2, wherein the water is recycled and mixed with the ethanol feed stream.

4. A method for converting an ethanol feed stream into ethylene, the method comprising a. dividing the ethanol feed stream into a first portion and a second portion to be sent to a reactor section comprising a first reactor and a second reactor, wherein the combination of the first reactor and the second reactor has a reactor volume of about 60% to 70% of the volume of a single reactor system; b. delivering the first portion to the first reactor through a feed heater; c. mixing steam with the first portion at the feed heater and sending the ethanol / steam mixture to the first reactor; d. subjecting the ethanol / steam mixture to sufficient conditions to dehydrate the ethanol to produce an effluent comprising ethylene and water; e. combining the effluent with the second portion to form an effluent / second portion mixture, and sending the effluent / second portion mixture to the second reactor for reaction to produce a product effluent comprising ethylene and water.

5. The process of claim 4, wherein the oxygenate feedstock is pretreated to remove contaminants and the pretreated oxygenate stream is then fed to the reactor section.

6. The process of claim 5, wherein the pretreated oxygenate stream is fractionated to separate ethanol from heavier oxygenates and the ethanol is then the ethanol feed stream.

7. The process of claim 4, wherein the ethanol feed stream to the first reactor is heated to about 400°C to about 550°C and converted to ethylene over a dehydration catalyst at about 455 kPa(g) to about 630 kPa(g).

8. The process of claim 4, wherein the product effluent from the second reactor is sent to an intermediate heater and the heated product effluent is then sent to a third reactor.

9. The process of claim 4 wherein the first and second reactors contain less steam than when all of the ethanol feed stream is sent to a single reactor, wherein the first and second reactors are operated at an increased endothermic level.

10. The process of claim 4, wherein the product effluent is not sent to a caustic wash stage.

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