Ethanol to Ethylene Process

Abstract

A process for dehydrating ethanol to produce ethylene is provided. The ethanol is dehydrated to produce ethylene, which is subsequently converted to longer-chain olefins, which are then hydrogenated to produce long-chain paraffins. In some embodiments, a split feed is used to improve efficiency, eliminating the caustic wash column. Advantages of the process include lower steam requirements and a 30-40% reduction in combined reactor volume when using two reactors compared to a single reactor.

Description

[Technical Field]

[0001] (cross reference) This application claims priority to Indian Provisional Patent Applications Nos. 202211049527, 202211049520, and 202211049523, filed on August 30, 2022.

[0002] FIELD OF THE INVENTION This relates to an ethanol dehydration process to produce ethylene. More particularly, this relates to a flow system for an ethanol dehydration process, optionally without a caustic scrubber. In another example, the flow system has a split feed configuration to allow for less steam use and reduced reactor section size. [Background technology]

[0003] Oil and gas refineries around the world are exploring methodologies and pathways to reduce their carbon footprint and moving towards sustainable processes. The process of converting bioethanol into green ethylene is one such sustainable process.

[0004] The present disclosure relates to the processing of ethylene.

[0005] In the dehydration of ethanol to produce ethylene, advantages have been found by operating a split stream and / or eliminating the use of a caustic scrubber in the process, for example, to produce ethylene for further processing as an olefin feedstock for ethylene oligomerization. Summary of the Invention

[0006] 1. A process for converting an ethanol feed stream to ethylene, comprising: splitting the ethanol feed stream into a first portion and a second portion; passing the first portion through a charge heater to a reactor; mixing steam with the first portion in the charge heater and passing the ethanol / steam mixture to the reactor; subjecting the ethanol / steam mixture to conditions sufficient to dehydrate the ethanol to produce an effluent comprising ethylene and water; combining 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 has a 30-40% reduction in volume compared to a process including a caustic scrubber, and the first and second reactors contain less steam than a process having a single reactor.

[0007] In another embodiment, a process for converting an ethanol feed stream to ethylene is provided, comprising: splitting the ethanol feed stream into a first portion and a second portion that are fed to a reactor section comprising a first reactor and a second reactor, the first reactor and the second reactor combined comprising a reactor volume that is about 60-70% of the volume of a single reactor system; feeding the first portion to the first reactor through a charge heater; mixing steam with the first portion in the charge heater and feeding an ethanol / steam mixture to the first reactor; subjecting the ethanol / steam mixture to conditions sufficient to dehydrate the ethanol to produce an effluent comprising ethylene and water; combining the effluent with the second portion to form an effluent / second portion mixture; and feeding the effluent / second portion mixture to the second reactor for reaction to produce a product effluent comprising ethylene and water. [Brief explanation of the drawings]

[0008] [Figure 1] A diagram of the flow scheme is provided. DETAILED DESCRIPTION OF THE INVENTION

[0009] The ethanol dehydration process unit is divided into six major sections: feed pretreatment section, feed purification section, reactor section, ethylene compression section, and water wash section.

[0010] 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 mode so that one vessel can be taken offline and reloaded while the other vessel is online. The ion exchange resin supplier recommends a regenerative system using HCl or sulfuric acid as a regenerant. Because the unit has stainless steel metallurgy, HCl regenerant is not suitable.

[0011] The demetallized product from the ethanol pretreatment section is sent to the feed purification column (FPC) through the tube side of the fresh feed-to-overhead vapor exchanger. This column is designed to purge heavier molecules that accompany the ethanol feed through the bottom of the column. The heavier molecules may consist of components such as, but not limited to, C3+ alcohols, acetals, hexadecanoic acid, octadecanoic acid, isopentyl acetate, cyclohexanol, cyclopentanol, phenol, cresols, and acetals. Some of these heavier molecules may be converted to ketones in the reactor and tend to accumulate without exiting the process; therefore, they need to be removed or minimized before the feed can be sent to the reactor section. The bottoms purge is expected to be <1.0% of the total feed, consisting of concentrated heavies such as acetic acid, acetals, cresols, phenols, free fatty acids such as hexadecanoic acid and octadecanoic acid, and some heavy alcohols.

[0012] Because no dissolved light ends are expected in the ethanol feed, a full condensation system is suitable for this column. The receiver pressure, controlled by a nitrogen push-pull system, is set to allow MP vapor to be used as the reboil medium for the column. Vapor from the column overhead is first condensed in the shell side of the fresh feed overhead vapor exchanger, followed by condensation in the feed purification column overhead condenser before entering the feed purification column receiver. The receiver liquid is pumped at its bubble point by the feed purification column net overhead pump and further subcooled in the feed purification column net overhead cooler. The subcooled material is mixed with the liquid ethanol recycle stream and cooled in the DEE absorber feed cooler before entering the DEE absorber on the top tray or feed surge drum.

[0013] The DEE absorber is suspended with the dehydration separator vapor stream entering below the bottom tray of the DEE absorber, and this column is provided to remove diethyl ether from the dehydration separator vapor. The DEE absorber bottom sump is designed to provide a 15 minute residence time for the liquid feed entering the reactor section.

[0014] The reactor section contains the following elements: The feed surge drum liquid or DEE absorber bottoms liquid stream is pumped to the reactor section via a dehydration charge pump. The effluent stream is first preheated in an ethanol process water exchanger. The preheated ethanol is split into two streams with flow control. The first split of the feed stream is heated and vaporized in a first ethanol vapor heater before entering the cold side (tube side) of Combined Feed Exchanger 1 (CFE1) and subsequently the charge heater. Before entering CFE1, the vaporized feed is mixed with steam generated in a steam generator. The combined stream is heated to the required reaction temperature in the charge heater and sent to the first reactor.

[0015] The second split feed stream is heated and vaporized 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 reactor effluent and sent to the first intermediate heater, where the stream is further heated to the required reaction temperature. While steam does not participate in the reaction (except for some minor side reactions), the steam added to the reactor serves the dual purpose of controlling the overall reactor heat absorption and maintaining catalyst stability (reducing coke laydown). Because diethyl ether formation is more pronounced at lower reactor outlet temperatures, it is important to minimize the temperature drop across the reactor. To ensure limited diethyl ether formation, the second reactor effluent is passed through a second intermediate heater and reheated to the required reactor temperature before being sent to the third reactor. The third reactor is a polishing reactor, which ensures that diethyl ether, along with unconverted ethanol, is converted to useful ethylene. The third reactor effluent is split and passes through the hot side (shell side) of CFE1 and CFE2. The hot side outlet from the combined feed exchanger is further cooled and condensed in a wastewater stripper reboiler followed by a dehydration product condenser before entering the dehydration separator.

[0016] The dehydration separator liquid stream is primarily water with some dissolved oxygenates, and this stream is sent to a low-pressure wastewater stripper, while the vapor stream is essentially ethylene product. As noted above, the dehydration separator vapor is sent to the DEE absorber.

[0017] The fired heaters used in the reactor section are designed as natural draft furnaces, with the primary process heating occurring in the radiant section and the convection section of these fired heaters designed to generate high pressure steam.

[0018] The ethylene compression section includes the following components: The pressure requirement for the vapor product stream to the downstream oligomerization unit is greater than 1000 psig, which is achieved by a four-stage or five-stage compressor system. Four stages may be specified for reciprocating machines, and five stages for centrifugal machines. In one embodiment, there is a four-stage reciprocating machine, one in operation and one on standby. The number of stages is based on downstream unit pressure requirements, and the compressor discharge temperature may be limited to less than 90°C.

[0019] The vapor from the water wash tower mixes with the first-stage ethylene compressor spillback to knock out any entrained liquid before entering the first-stage ethylene compressor suction drum. The vapor from the drum is compressed in the first-stage ethylene compressor, and the compressor discharge is cooled in the first-stage discharge cooler and first-stage discharge trim cooler. The cooled stream further mixes with the second-stage ethylene compressor spillback and enters the first-stage ethylene compressor discharge drum. The vapor from the first-stage ethylene compressor discharge drum is split into two streams: the first stream is the first-stage ethylene compressor spillback and the second stream is the net vapor flow 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 second-stage discharge trim cooler. The cooled stream further mixes with the third-stage ethylene compressor spillback and enters the second-stage ethylene compressor discharge drum. The vapor from the second-stage ethylene compressor discharge drum is split into two streams: the first stream is the second-stage ethylene compressor spillback and the second stream is the net vapor flow entering the third-stage ethylene compressor. The vapor is further compressed in the third-stage ethylene compressor, and the compressor discharge is cooled in a third-stage discharge cooler and a third-stage discharge trim cooler before entering the third-stage ethylene compressor discharge drum. The vapor from the third-stage ethylene compressor discharge drum is split into two streams: the first stream is the third-stage ethylene compressor spillback and the second stream is the net vapor product entering an ethylene dryer to remove saturated moisture.

[0020] Dry vapor from the ethylene dryer is mixed with the fourth-stage ethylene compressor spillback and enters the fourth-stage ethylene compressor suction drum. The vapor is compressed in the fourth-stage ethylene compressor before entering the fourth-stage ethylene compressor discharge drum. The fourth-stage ethylene compressor discharge drum vapor is split into two streams: the first stream is the fourth-stage ethylene compressor spillback, and the second stream is the net vapor product sent to the oligomerization unit. Unlike the upstream stage, the fourth-stage ethylene compressor discharge is not cooled; the hot vapor stream is sent directly to the oligomerization unit. To ensure that the fourth-stage ethylene compressor discharge temperature does not exceed recommended limits, a fourth-stage cooler is added on the compressor spillback line.

[0021] The saturated water in the vapor from the water wash tower is partially knocked out in the first-stage ethylene compressor suction and discharge drums and the second- and third-stage ethylene compressor discharge drums. The knocked-out liquid is mostly water, and this condensation occurs due to the increase in pressure and decrease in intermediate temperature. The knock-out drum liquid is sent to the wastewater stripper.

[0022] Two ethylene dryers loaded with molecular sieves are designated for moisture removal from the ethylene vapor product and are operated in lead-lag mode. When the lead dryer molecular sieves become saturated with moisture, the dryer must be regenerated to restore sieve capacity. The dried ethylene vapor from the lag dryer is used as the regenerant medium. The slip stream from the lag dryer outlet is sent to a regenerant superheater, where the regenerant is heated to the required regeneration temperature before entering the dryer under regeneration. Under regeneration, the spent regenerant, carrying moisture desorbed from the molecular sieves from the dryer, is cooled and condensed in a regenerant condenser before entering the regenerant coalescer. The regenerant coalescer separates the water from the spent regenerant, i.e., ethylene. This ethylene vapor is pressure-controlled returned to the first-stage ethylene compressor suction drum, and the spent water is sent to the wastewater stripper.

[0023] The wastewater section consists of a wastewater stripper and a water wash tower. Liquid from the dehydration separator, water wash tower bottoms, regenerant coalescer (intermittent), and knocked-out liquid from the ethylene compressor section knockout drum are routed 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 remove oxygenates entering with the feed as an overhead vapor product while recovering process water in the bottoms.

[0024] The wastewater stripper operates at 5-10 psig, and the overhead vapor is cooled and condensed in the off-gas condenser before entering the off-gas knockout drum. The off-gas knockout drum liquid contains water, along with most of the alcohol carried from the DEE absorber vapor, unconverted alcohol from the reactor, and other non-selective oxygenates formed in the reactor, such as acetaldehyde, ethers, and acetic acid. These are recycled, mixed with fresh feed, and sent to the reactor section through the feed surge drum or the bottom of the DEE absorber. The off-gas knockout drum vapor is a small purge stream that is a mixture of olefins (dissolved in the dehydration separator and water wash column liquid) and oxygenates. The wastewater stripper has two reboiler systems. The wastewater stripper auxiliary reboiler utilizes low-pressure steam as the reboiling medium, while the wastewater stripper reboiler is process heat integrated with the hot dehydration reactor effluent upstream of the dehydration product condenser. The wastewater stripper net bottoms are pumped by the process water pump through the tube side of the wastewater stripper feed-bottoms exchanger and split downstream into three streams. The first stream is process water used to wash the vapor product oxygenate in the water wash tower. This stream is sent to the water wash tower via the ethanol process water exchanger, process water cooler, and process water trim cooler.

[0025] The second stream is a volume of process water equivalent to the steam injected into the dehydration reactor plus 5% blowdown. This stream is sent to a steam generator. The generated steam 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 ethanol process water exchanger.

[0026] The third stream is the net process water produced from the various reactions occurring in the reactor section and is sent to a wastewater treatment facility; this stream is removed downstream of the process water trim cooler.

[0027] As previously mentioned, the dehydration separator vapor may be sent to a DEE absorber or a water wash tower. The dehydration separator vapor has certain impurities / oxygenates, such as acetaldehyde, diethyl ether, dimethyl ether, water, unconverted alcohol, etc., that may need to be removed depending on further uses of the ethylene product.

[0028] In the DEE absorber, diethyl ether in the separator vapor is absorbed into the bottom liquid along with some other oxygenates. Because ethanol feed is used to wash the separator vapor, there is some carryover of ethanol feed into the DEE absorber vapor. The DEE absorber overhead vapor is sent below the bottom tray of the water wash tower. The water wash tower is designed to wash away oxygenates such as acetaldehyde, unconverted alcohol from the reactor section, ethanol carryover from the DEE absorber vapor, and acetic acid using process water from the wastewater stripper bottom. Process water enters the top tray of the water wash tower, and oxygenate absorption occurs countercurrently across multiple trays. The washed water wash overhead vapor is sent to the downstream ethylene compression section, while the liquid bottom stream, containing all dissolved oxygenates / alcohols, is sent to the wastewater stripper.

[0029] The expected process conditions and conversions and selectivities based on dry ethanol feedstock are shown in the table below.

[0030] [Table 1]

[0031] DESCRIPTION OF THE DRAWINGS 1 illustrates a process 10 for treating an oxygenate feedstock according to one exemplary embodiment. The oxygenate feedstock may include an alcohol, preferably ethanol. The feedstock may include ethanol as a primary component and may be aqueous. Preferably, the oxygenate feedstock is a biorenewable feedstock.

[0032] Feed line 12 transports the oxygenate stream of the oxygenate feedstock to feed pretreatment section 14. Feed pretreatment section 14 includes vessel 16 containing a bed of cation exchange resin adsorbent 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 containing a bed of the same adsorbent for further removal of metals from the oxygenate stream. Vessels 16, 18 may be in a series or lead-lag configuration to allow for regeneration of spent adsorbent. Line 17 transports the partially pretreated oxygenate stream from the outlet of vessel 16 to the inlet of vessel 18. The pretreated oxygenate stream exits feed pretreatment section 14 from the outlet of additional vessel 18 in line 20 and is fed to purification column 22. Feed pretreatment section 14 may be operated at a temperature of from about 32° C. to about 105° C. and a pressure of from about 2800 kPa(g) to about 3100 kPa(g).

[0033] In refinery column 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. Refinery column 22 is operated to minimize ethanol to 1% or less of the feed in a bottoms stream in line 26. A heavy oxygenate stream in bottoms line 26 is removed from the bottom of refinery column 22 to heavy oxygenate processing. Refinery column 22 may be reboiled by heat exchange with a suitable high-temperature stream, such as steam, to provide the heat necessary for distillation. Refinery column 22 provides an overhead gas stream of purified ethanol in overhead line 24 that may be cooled in air cooler 25 and fed to feed surge drum 26 along with a recycled ethanol stream in line 27. Refinery column 22 may be operated at a bottoms temperature of about 82°C to about 121°C and an overhead pressure of about 35 kPa(g) to about 140 kPa(g).

[0034] The ethanol in the feed surge drum 26 may be blanketed with nitrogen. A charge pump 29 pumps the ethanol charge stream in line 28 into two charge streams. The first charge stream in line 30 is heat exchanged with a first dehydration exchange stream in line 32, mixed with steam in line 33, and supplied to a first charge heater 34. The first charge heater 34 may be a combustion heater and may heat the first charge stream to about 400°C to about 550°C. The resulting first heated charge stream in line 36 is supplied to a first dehydration reactor 40. In the first dehydration reactor 40, the ethanol feedstock is converted to ethylene and water over a dehydration catalyst at a pressure of about 455 kPa(g) to about 630 kPa(g). The first dehydration stream is discharged from the first dehydration reactor 40 in line 42.

[0035] The second charge stream in line 44 is heat exchanged with a second dehydration exchange stream in line 46, mixed with the first dehydration stream in line 42, and supplied to a second charge heater 48. The second charge heater 48 may be a combustion heater and may heat the second charge stream to a temperature of from about 400°C to about 550°C. The resulting heated second charge stream in line 50 is supplied to a second dehydration reactor 52. In the second dehydration reactor 52, the ethanol feedstock is converted to ethylene and water over a dehydration catalyst at a pressure of from about 420 kPa(g) to about 700 kPa(g). The second dehydration stream is discharged from the second dehydration reactor 52 in line 54.

[0036] The second dehydrated stream in line 54 is supplied to an intermediate heater 56. The intermediate heater 56 may be a combustion heater and may heat the second dehydrated stream to between about 400°C and about 550°C. The resulting third heated charge stream in line 58 is supplied to a third dehydration reactor 60. In the third dehydration reactor 60, the residual ethanol feedstock is converted to ethylene and water over a dehydration catalyst at a pressure of between about 420 kPa(g) and about 700 kPa(g). The third dehydrated stream is discharged from the third dehydration reactor 60 in line 62.

[0037] The dehydration catalyst is an alumina-based catalyst.

[0038] The third dehydrated stream is split into a first dehydrated exchange stream in line 32 and a second dehydrated exchange stream in line 46. The first dehydrated exchange stream in line 32 exchanges heat with the first charge stream in line 30, the second dehydrated exchange stream in line 46 exchanges heat with the second charge stream in line 44, and the cooled dehydrated streams are recombined in line 64.

[0039] The cooled dehydrated stream in line 64 is fed to 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 through quench tower overhead line 74, and a bottoms stream exits the bottoms in line 76. The bottoms stream is split into a drain stream in line 78 which can be transported to a waste water stripper column 80 via a control valve thereon, and a quench recycle stream in line 82. A first portion of the quench recycle stream is air cooled in product condenser 69 and recycled through a control valve thereon as a first lower cooled water stream in line 70, and a second portion of the quench recycle stream is heat exchanged in trim condenser 71 and recycled to quench tower 68 as a second higher cooled water stream in line 72. Quench column 68 may be operated at a bottom temperature of about 37° C. to about 104° C. and an overhead pressure of about 280 kPa(g) to about 490 kPa(g).

[0040] The quenched ethylene stream in line 74 is fed to first-stage suction drum 86. In the first-stage suction drum, ethylene exits overhead line 88 to first-stage compressor 90, while residual water exits the bottom of the drum in line 92 through a control valve thereon and is transported to wastewater stripper column 80, possibly via line 78. First-stage compressor 90 compresses the ethylene stream to a first pressure of from about 350 kPa(g) to about 1225 kPa(g), and the effluent in line 91 is cooled in first-stage effluent cooler 93 and first-stage trim cooler 94.

[0041] The cooled, compressed ethylene stream from first-stage trim cooler 94 is fed to first-stage discharge drum 96. From first-stage discharge drum 96, the ethylene exits overhead line 98 to second-stage compressor 100, while residual water exits the bottom of the drum in line 102 through a control valve thereon and is transported to wastewater stripper column 80, possibly via lines 92 and 78. The second-stage compressor compresses the ethylene stream to a second pressure of from about 455 kPa(g) to about 3220 kPa(g), and the effluent in line 101 is cooled in second-stage effluent cooler 103 and second-stage trim cooler 104.

[0042] The twice-cooled, compressed ethylene stream from second-stage trim cooler 104 is fed to second-stage discharge drum 106. From second-stage discharge drum 106, ethylene exits overhead line 108 and is transported to water wash column 110, while a residual water stream exits the bottom of the drum in line 112 through a control valve thereon and is transported to wastewater stripper column 80, possibly via lines 102, 92, and 78.

[0043] In water wash tower 110, the twice-cooled and compressed ethylene stream is washed countercurrently with cooled, treated water in line 118 from waste water stripper column 80 to absorb additional oxygenates and produce a washed ethylene stream exiting in overhead line 120 and a wash water stream in bottoms line 122. The washed ethylene stream in overhead line 120 is transported to product dryer section 140. The wash water stream in line 122 is returned to water stripper column 80 through a control valve thereon. Wash water 110 may be operated at a bottoms temperature of from about 16° C. to about 82° C. and an overhead pressure of from about 2800 kPa(g) to about 3500 kPa(g).

[0044] In other flow schemes, the scrubbed ethylene stream can be sent to a caustic scrubber section to remove oxygenates. However, it has been discovered that the process can be successfully operated under certain operating conditions without the use of a caustic scrubber, producing ethylene for further processing as an olefin feedstock, e.g., for ethylene oligomerization. Instead, as described below, the wastewater stripper bottoms stream is sent to the top tray of a water wash tower, while the vapor from the second-stage compressor discharge is sent below the bottom tray of the water wash tower. The intent is to scrub the ethylene-rich vapor stream and remove as many oxygenates as possible from the product stream. The ethylene-rich vapor, with traces of CO and ppm-level CO2, is sent directly to a series of dryers containing molecular sieves in a lead-lag system to remove moisture from the vapor stream before being sent to a cryogenic distillation unit. The vapor from the cryogenic distillation unit is further compressed in the third stage of the ethylene compressor to meet downstream unit cell limit pressure requirements.

[0045] In product dryer section 140, the washed and scrubbed ethylene stream in line 120 is fed to a first dryer inlet knockout drum 146 to remove residual water, providing a dryer inlet stream in line 148 and a knockout water stream in bottoms line 150 that is fed to wastewater stripper column 80 via 122. The dryer inlet stream is fed in line 148 to a first product dryer 152. First product dryer 152 contains an adsorbent for adsorbing water from the ethylene in the dryer inlet stream in line 148 to provide a dried ethylene stream. The adsorbent may be a molecular sieve material having a pore size of 2 to 4 A. First product dryer 152 may be operated in an upflow mode. Product dryer section 140 may include a second product dryer 156 that operates as first product dryer 142. The two product dryers may be operated in series, but are preferably arranged in lead-lag operation to facilitate regeneration during continuous operation. Second product dryer 156, like first product dryer 152, includes an adsorbent for adsorbing water from the ethylene. A dry ethylene stream exits product dryer section 140 in line 158. Product dryer section 140 may be operated at a temperature of from about 32° C. to about 105° C. and a pressure of from about 2800 kPa(g) to about 3100 kPa(g).

[0046] 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 knockout water stream in bottoms line 164 which is possibly fed to wastewater stripper column 80 via lines 150 and 122.

[0047] The dryer effluent stream in line 162 may be fed to a heavy oxygenate removal column 170 to separate an overhead stream containing primarily ethylene, but possibly higher olefins, from heavy ketones and diethyl ether. Olefins are produced in overhead line 172 and fed to a third-stage compressor 174, and a bottom heavy oxygenate stream is produced in bottoms line 176. A heavy oxygenate purge stream may be taken to heavy oxygenate processing in line 178, while the reboil portion is reboiled and returned to column 170. The compressed ethylene stream in compressor discharge line 176, at a pressure of from about 2800 kPa(g) to about 7000 kPa(g), may be provided to the dimerization section. Heavy oxygenates removal column 170 may be operated at a bottom temperature of from about −30° C. to about 120° C. and an overhead pressure of from about 2415 kPa(g) to about 3100 kPa(g).

[0048] The water stream containing oxygenates and volatiles in lines 92, 102, 112, 122, 150, 164 may be fed to wastewater stripper column 80, where the volatiles and oxygenates are boiled off to provide an overhead volatiles stream in line 182 and a stripped water stream in line 184. A portion of the stripped water stream may be reboiled and returned to the column to provide the necessary heat. The treated water stream in line 186 may be pumped to a water outlet in line 188 containing the cooled, treated water stream in line 118 for water wash tower 110. Wastewater stripper column 80 may be operated at a bottom temperature of from about 90° C. to about 120° C. and an overhead pressure of from about 35 kPa(g) to about 140 kPa(g).

[0049] The overhead volatiles stream in line 182 may be cooled in air cooler 189 and fed to off-gas knockout drum 190. The overhead stream from knockout drum 190 in line 192 may be sent to a flare, while the ethanol recycle stream is pumped to feed surge drum 26 in line 27, possibly via line 24.

[0050] While the following will be described in conjunction with specific embodiments, it will be understood that this description is illustrative, but not intended to limit the scope of the preceding description and appended claims.

[0051] Without further elaboration, it is believed that, using the preceding description, one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of the present invention, and can make various changes and modifications to the present invention to adapt it to various uses and conditions, without departing from the spirit and scope of the present invention. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0052] In the above, unless otherwise indicated, all temperatures are listed in degrees Celsius, all pressures are in kPa (g), and all parts and percentages are by weight, where n is an integer from 20 to 2000.

[0053] A first embodiment is a process for treating a stream comprising ethylene and oxygenates, comprising passing said stream to a water wash tower and passing the resulting ethylene-rich vapor stream directly to a dryer without first passing it to a caustic wash section.

[0054] A second embodiment is a process for converting an ethanol feed stream to ethylene, comprising: splitting the ethanol feed stream into a first portion and a second portion; passing the first portion through a charge heater to a reactor; mixing steam with the first portion in the charge heater and passing the ethanol / steam mixture to the reactor; subjecting the ethanol / steam mixture to conditions sufficient to dehydrate the ethanol to produce an effluent comprising ethylene and water; and combining 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. One embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein the first portion or the second portion comprises a mixture of ethanol and water. One embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein the water is recycled and combined with the ethanol feed stream.

[0055] A third embodiment of the present invention is a process for converting an ethanol feed stream to ethylene, comprising: splitting the ethanol feed stream into a first portion and a second portion fed to a reactor section comprising a first reactor and a second reactor; feeding the first portion through a charge heater to the first reactor; mixing steam with the first portion in the charge heater and feeding the ethanol / steam mixture to the first reactor; subjecting the ethanol / steam mixture to conditions sufficient to dehydrate the ethanol to produce an effluent comprising ethylene and water; combining the effluent with the second portion to form an effluent / second portion mixture; and feeding the effluent / second portion mixture to the second reactor for reaction to produce a product effluent comprising ethylene and water. One embodiment of the present invention is one, any, or all of the previous embodiment through the first embodiment of 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 preceding embodiments through the first embodiment of this paragraph, in which the water is recycled and combined with the ethanol feed stream. An embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, in which the reactor section is approximately 30-40% smaller in volume than a dehydration process in which the ethanol feed stream remains a single stream. An embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, in which the reactor section further comprises a third reactor vessel. An embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, in which an oxygenate feedstock is pretreated to remove contaminants and then the pretreated oxygenate stream is sent to the reactor section. One embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the first embodiment of this paragraph, wherein said pretreated oxygenate stream is fractionated to separate ethanol from heavier oxygenates, and said ethanol is then said ethanol feed stream.An embodiment of the present invention is any one, any, or all of the preceding through first embodiments of this paragraph, in which 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 455 kPa(g) to about 630 kPa(g). An embodiment of the present invention is any one, any, or all of the preceding through first embodiments of this paragraph, in which 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 420 kPa(g) to about 700 kPa(g). An embodiment of the present invention is any one, any, or all of the preceding through first embodiments of this paragraph, in which the product effluent from the second reactor is sent to an intermediate heater, and then the heated product effluent is sent to a third reactor. An embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein the product effluent of said third reactor does not contain measurable diethyl ether. An embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein said first and second reactors contain less steam than if all of said ethanol feed streams were sent to a single reactor and said first and second reactors were operating at an increased endothermic level. An embodiment of the present invention is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein said product effluent is not sent to a caustic wash section.

Claims

1. 1. A process for converting an ethanol feedstream into ethylene, comprising: a. dividing the ethanol feed stream into a first portion and a second portion; b. passing the first portion through a charge heater and into a reactor; c) mixing steam with the first portion in the charge heater and delivering the ethanol / steam mixture to the reactor; d. subjecting the ethanol / steam mixture to conditions sufficient 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 passing the mixture to a second reactor to react and produce a product effluent comprising ethylene and water, wherein the reactor section has a 30-40% reduction in volume compared to a process containing a caustic scrubber and the first and second reactors contain less steam than a process having a single reactor.

2. 3. The process of claim 2, wherein the first portion or the second portion comprises a mixture of ethanol and water.

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

4. 1. A process for converting an ethanol feedstream into ethylene, comprising: a. dividing the ethanol feed stream into a first portion and a second portion that are sent to a reactor section comprising a first reactor and a second reactor, the first reactor and the second reactor combined comprising a reactor volume that is about 60-70% of the volume of a single reactor system; b. passing the first portion through a charge heater into the first reactor; c) mixing steam with the first portion in the charge heater and delivering an ethanol / steam mixture to the first reactor; d. subjecting the ethanol / steam mixture to conditions sufficient 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 passing the effluent / second portion mixture to the second reactor to react and produce a product effluent comprising ethylene and water.

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

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

7. 5. The process of claim 4, 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 455 kPa(g) to about 630 kPa(g).

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

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

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

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