High-temperature final dehydration reactor in dehydration process to prevent diethyl ether formation

Abstract

A process for converting an ethanol feed stream to ethylene, comprising passing a portion of said ethanol feed stream to two reactors in parallel and then passing the combined product to a third reactor operated at a higher temperature to prevent the formation of ethers such as diethyl ether.

Description

[Technical Field]

[0001] (Priority statement) CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to Indian Provisional Patent Application No. 202211049529 filed on August 30, 2022.

[0002] FIELD OF THE INVENTION The field is the conversion of alcohols to olefins. The field particularly relates to the dehydration of ethanol to produce ethylene and the subsequent conversion of ethylene to long chain olefins and hydrogenation of the long chain olefins to produce paraffins, and may more particularly relate to the use of a high temperature final dehydration reactor to prevent the production of diethyl ether. [Background technology]

[0003] Oil and gas refiners worldwide are exploring methodologies and pathways to reduce their carbon dioxide emissions and are moving toward sustainable processes. The ethanol-to-jet fuel process is one promising pathway to minimize or eliminate customers' carbon dioxide emissions. The end product of this process is jet fuel and diesel fuel produced from bioethanol. Jet fuel is a sustainable aviation fuel and is intended to replace jet fuel produced from traditional sources such as crude oil.

[0004] Generally, the process of converting ethanol to jet fuel has three main steps. First, the ethanol is dehydrated to produce ethylene. Next, the ethylene is converted to long-chain olefins, which are then hydrogenated to produce paraffins. This disclosure is primarily concerned with the conversion of ethanol feedstreams to ethylene and significantly reducing the production of diethyl ether impurities. Summary of the Invention

[0005] overview 1. A process for converting an ethanol feed stream into ethylene, comprising: dividing said 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, passing the mixture to a second reactor for reaction to produce a product effluent comprising ethylene and water; and passing the product effluent from the first reactor and the second reactor to a third reactor, wherein the inlet temperature of the third reactor is 400-500°C.

[0006] definition The term "communication" means operatively permitting the flow of materials between the listed components.

[0007] The term "downstream communication" means that at least a portion of the material flowing to the object in the downstream communication can operatively flow from the object in communication.

[0008] The term "upstream communication" means that at least a portion of the material flowing from the object in the upstream communication can operatively flow to the communicating object.

[0009] The term "direct communication" means that the stream from the upstream component enters the downstream component without passing through a fractionation or conversion unit and undergoing a change in composition by physical fractionation or chemical conversion.

[0010] The term "indirect communication" means that a stream from an upstream component enters a downstream component after passing through a fractionation or conversion unit and undergoing a change in composition by physical fractionation or chemical conversion.

[0011] The term "bypass" means that an object is out of downstream communication with a bypass subject, at least to the extent that it bypasses.

[0012] The term "column" refers to a distillation column or columns for separating one or more components of different volatility. Unless otherwise indicated, each column includes a condenser at the top of the column for condensing and refluxing a portion of the overhead stream that returns to the top of the column, and a reboiler at the bottom of the column for vaporizing a portion of the bottom stream and returning it to the bottom of the column. The feed to the column may be preheated. The top pressure is the pressure of the overhead vapor at the vapor outlet of the column. The bottom temperature is the liquid bottom outlet temperature. The overhead and bottom lines refer to the net lines from column to column downstream of any reflux or reboil. A stripper column may omit the reboiler at the bottom of the column and instead provide the required heat and driving force for separation from a fluidized inert medium such as steam. A stripping column typically feeds the feed to the top tray and removes the main product from the bottom.

[0013] As used herein, the term "component-rich stream" means that the rich stream exiting the vessel has a higher concentration of the component than the feed to the vessel.

[0014] As used herein, the term "component lean stream" means that the lean stream exiting the vessel has a lower concentration of the component than the feedstock to the vessel.

[0015] As used herein, the term "separator" means a vessel having an inlet and at least an overhead vapor outlet and a bottoms liquid outlet, and may also have an aqueous outlet from a boot. A flash drum is a type of separator that may be in downstream communication with a separator that may be operated at a higher pressure.

[0016] As used herein, the term "predominant" or "predominantly" means more than 50%, suitably more than 75%, and preferably more than 90%.

[0017] As used herein, "C x " should be understood to refer to a molecule having the number of carbon atoms represented by the "x" subscript. x The term "-" refers to a molecule containing less than or equal to x, preferably x and less, carbon atoms. x The term "+" refers to a molecule having more than or equal to x, preferably x and more, carbon atoms.

[0018] As used herein, the term "carbon number" refers to the number of carbon atoms per hydrocarbon molecule, typically a paraffin molecule. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic process flow diagram of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0020] 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.

[0021] In the feed 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 recharged while the other vessel is online. The ion exchange resin supplier recommends a regenerable system using HCl or sulfuric acid as the regenerant. Because the unit has stainless steel metallurgy, HCl regenerants are not suitable. A regenerable system using sulfuric acid, if implemented, would need to be thoroughly vetted and considered. Ion exchange resins would have the highest capacity. Currently, feed pretreatment is not considered necessary for metal contents below 1.0 wppm.

[0022] The demetallized product from the feed pretreatment section is sent through the tube side of a fresh feed-to-overhead vapor exchanger to a feed purification column (FPC). This column is designed to purge heavier molecules that accompany the ethanol feed passing 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, acetals, etc. Some of these heavier molecules may be converted to ketones within the reactor and tend to accumulate without exiting the process, and therefore 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 and octadecanoic acids, and some heavy alcohols; the column bottoms sump is swaged and designed to hold the heavy purge material for typically 24 hours, which can be purged to an ethanol slop tank.

[0023] 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 (see discussion below).

[0024] A diethyl ether (DEE) absorber is provided to remove diethyl ether from the dehydration separator vapor stream, floating below the bottom tray of the DEE absorber. The DEE absorber bottom sump is designed to provide a 15-minute residence time for the liquid feed entering the reactor section. If the DEE absorber is not considered part of the design, a feed surge drum with a 15-minute residence time should be provided, and the net overhead liquid of the FPC mixed with recycled ethanol would enter the feed surge drum instead of the DEE absorber. If the FPC is not included as part of the design, the fresh ethanol feed and recycled ethanol stream can be sent to either the DEE absorber (if considered part of the particular design) or the feed surge drum.

[0025] The reactor section includes 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 discharge 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 an ethanol-jet product exchanger, an ethanol-hydrogenation reactor feed exchanger (both of which are located in the oligomerization unit), and a first ethanol steam heater before entering the cold side (tube side) of Combined Feed Exchanger 1 (CFE1) and then the charge heater. Before entering CFE1, the vaporized feed is mixed with steam generated in a steam generator located in the downstream oligomerization unit. The combined stream is heated to the required reaction temperature in the charge heater and sent to the first reactor.

[0026] The ethanol dehydration reaction is endothermic in nature. Water is a by-product of the dehydration reaction, and the water produced in the first reactor satisfies the steam requirements of downstream reactors. The second split of the feed stream is heated and vaporized in the ethanol-second-stage oligomerization lag reactor feed exchanger, the ethanol-second-stage oligomerization lead reactor feed exchanger (both located in the oligomerization unit), and the second ethanol steam heater before entering the cold side (tube side) of the second combined feed exchanger (CFE2). At the cold side exit 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), steam added to the reactor serves the dual purpose of controlling the overall reactor endotherm 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 passes through a second intermediate heater and is reheated to the required reactor temperature before being sent to the third reactor, a polishing reactor that ensures that the 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.

[0027] 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 a DEE absorber. If a DEE absorber is not considered part of the design, the separator vapor is sent to a water wash tower.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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 spillback cooler is added to the compressor spillback line.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] The wastewater stripper operates at 5 to 10 psig, and the overhead vapor is cooled and condensed in an 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 (if a DEE absorber is part of the design), 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 a feed surge drum or the bottom of the DEE absorber (if included as part of the design). 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. This purge gas stream is mixed with the low-pressure off-gas stream produced in the downstream oligomerization unit and further compressed in a waste off-gas compressor to the required fuel gas knockout drum pressure before being combusted in a combined-fired heater. The wastewater stripper has two reboiler systems. One reboiler, the wastewater stripper auxiliary reboiler, utilizes low-pressure steam as the reboiling medium (expected to operate during start-up and as an auxiliary backup), while the other reboiler, 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.

[0036] The second stream is process water equivalent to the steam injected into the dehydration reactor plus 5% blowdown. This stream is sent to a steam generator located in the downstream oligomerization unit reactor section for heat recovery. The generated steam is recycled back 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 facility. This stream is split upstream of the ethanol process water exchanger.

[0037] 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.

[0038] As previously mentioned, the dehydration separator vapor may be sent to a DEE absorber (if included as part of the design) or a water wash tower. The dehydration separator vapor has certain impurities / oxygenates such as acetaldehyde, diethyl ether, dimethyl ether, water, unconverted alcohols, etc. that need to be removed before the vapor product stream is sent to the downstream oligomerization unit.

[0039] 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.

[0040] Ethanol feeds are obtained from either wet mill or dry mill processes. These ethanol feedstocks may contain various contaminants such as higher alcohols, metals, acetaldehyde, ethyl acetate, etc. In addition, dry mill feedstocks may also contain fusel oils (heavier alcohols and acids). Ethanol feedstocks may be treated to remove metal contaminants by the use of resin treaters. Heavy hydrocarbons from the fresh feedstock may be knocked out in feed purification columns.

[0041] Currently, the ethanol dehydration process unit uses a reactor The feed to this section is split between two parallel reactors. This is done to minimize the steam requirements of the unit. At the lower vapor level, the parallel reactor endotherm is very high, resulting in reactor outlet temperatures in the 300-340°C range. At such low outlet temperatures, ethanol in the reactors can form undesirable diethyl ether. This invention aims to mitigate diethyl ether formation, which is a nonselective component and results in selectivity loss. Because the first two parallel reactors have process outlet temperatures in the 300-340°C range, diethyl ether can form within the reactors, primarily in the cooler sections of these reactors. Pilot plant data also indicates ether formation at lower temperatures. To ensure that diethyl ether does not form, a third reactor (polishing reactor) with an intermediate heater is added to the outlet of the parallel reactors. The third reactor inlet has very little unconverted ethanol, and the inlet temperature is maintained high enough, in the 400-500°C range, to avoid any ether formation. Also, since the ethanol concentration at the inlet of the third reactor is lower, the expected endotherm in the third reactor is small, which prevents any possibility of ether formation.

[0042] Fresh ethanol feedstock is mixed with unconverted ethanol and split into two equal streams entering a parallel mixed feed exchanger. A split reactor configuration is considered if the desired steam-to-ethanol ratio is maintained at the reactor inlet. This is to maintain the endothermicity of the reactor as well as ensure catalyst stability. It is essential to reduce steam entrapment in order to minimize the combined feed rates to the reactor. The ethanol dehydration reaction results in the generation of water as a by-product.

[0043] The fresh feed to the reactor section can be split equally through two combined feed exchangers. The feed from CFE1 (what does CFE1 stand for?) is sent to Reactor 1 through a charge heater. Steam is mixed with the fresh feed at the charge heater inlet. Because only half of the feed is sent through Reactor 1, the steam level required is exactly half of the required steam. Water is produced from the dehydration reaction in Reactor 1, and the effluent of Reactor 1 is mixed with the fresh feed sent to Reactor 2 through CFE2 and Intermediate Heater No. 1. The water produced in Reactor No. 1 satisfies the steam-to-ethanol ratio requirements in the reactor. This innovation reduces steam requirements by 50%, thereby reducing the total reactor feed capacity by 30-40%. As an additional item to the feed section, a diluted ethanol feed can be processed in the reactor section. If a more diluted ethanol feed is processed in the dehydration section, the amount of steam required decreases. Diluting the ethanol feed has the advantage of reducing utility consumption in upstream ethanol product units. Diluting the ethanol feed below 90% does not result in significant utility savings.

[0044] As previously discussed, water is produced as a by-product from the ethanol dehydration reaction. A portion of the water produced in the process is recycled and mixed with the fresh feed sent to Reactor No. 1 at the CFE 1 inlet. The recycled water is split into two streams. One stream is sent through a fired heater convection section (50-60%) to generate steam, and the remaining water is mixed with the fresh feed at the CFE 1 inlet. This poses a unique problem because evaporation of the liquid water along with the ethanol must occur on the cold side of CFE 1. Assuming the cold side is at a higher pressure and boiling, and the hot side is condensing at a lower pressure, the available energy is significantly reduced, making the CFE design impractical. To ensure sufficient energy is available in CFE 1, either the cold-side pressure must be reduced or the hot-side pressure must be increased. This is accomplished by including an inter-reactor compressor at the Reactor No. 1 outlet. Reactor No. 1 outlet is operated at a lower pressure by reducing the CFE 1 cold-side inlet pressure. The effluent of reactor 1 is compressed and mixed with the fresh feed entering reactor no. 2. This option presents a unique opportunity to improve energy recovery from the reactor effluent in a combined feed exchanger, thereby reducing utility in the charge heater as well as the product condenser.

[0045] A second option for reactor section design can be considered: the inter-reactor compressor is a large piece of equipment and, even though it helps reduce utility consumption, is expensive and difficult to design. One of the main reasons for having this compressor is to ensure that the recycled water is effectively vaporized. This embodiment is developed to eliminate this water recycle. Instead, the steam requirements for the dehydration reactor are met by steam generated in the downstream oligomerization / hydrogenation unit. In part, steam can also be generated using BFW in the fired heater convection section. The reactor effluent in this option is An inter-reactor compressor is not required; it is utilized only to vaporize the ethanol feed. Without an inter-reactor compressor, the product condenser duty would increase by 20-30%. However, this option presents a much easier design.

[0046] Combined Feed Exchangers - Both combined feed exchangers are expected to be vertical exchangers.

[0047] Considering that the reactor section operates at very low pressures, high temperatures, and gas molecular weights vary from 20 to 30, the volumetric flow rate through the reactor is very large, resulting in excessive bed pressure drop using a conventional fixed-bed downflow reactor. The pressure drop problem can be mitigated by designing either a fixed-bed radial flow design or a compartment reactor design.

[0048] Fired Heater - The fired heater is expected to be a box furnace with process heating in the radiant section. The convection section may be utilized to generate steam that may be used in the dehydration process.

[0049] The reactor effluent from the CFE can be sent either to a separator via a product condenser / product trim condenser or through a quench tower. The separator design is conventional and will not be discussed further.

[0050] The quench tower is a unique design in which the hot effluent from the CFE is routed below the bottom tray. The liquid effluent is separated and the hot vapor effluent is re-contacted with recycled water. The heat in the reactor effluent is absorbed by the recycled water stream, which is cooled in the product / trim condenser.

[0051] The cooled vapor from the quench tower / separator is compressed in a two-stage compressor. An intercooler / trim cooler is present to maintain the process gas temperature. The ethylene-rich vapor leaving the compressor is sent to a water wash tower for oxygenate removal.

[0052] The net wastewater from the quench tower bottom / separator bottom contains unconverted ethanol and other dissolved oxygenates. This stream is sent to the wastewater stripper, which is steam reboiled to recover the dissolved oxygenates and unconverted ethanol as a vapor product. Vapors from the wastewater stripper are condensed and sent to a knockout pot for unconverted ethanol recovery. This unconverted ethanol, along with any other dissolved oxygenates, is pumped back to the reactor section for further conversion.

[0053] The wastewater stripper bottoms, now 99.9 mol% pure water, can be used as a wash medium in a water wash tower to scrub oxygenates from the ethylene vapor stream coming from the second-stage ethylene compressor. Aside from using the wastewater stripper bottoms as a wash medium in the water wash tower, a net water draw is also removed from the process. This water can be used in an electrolyzer unit for green hydrogen generation or sent to further processing for ppm-level oxygenate removal before being used for steam generation. The wastewater stripper bottoms stream is sent to the top tray of the water wash tower, while the vapor from the second-stage compressor discharge is sent below the bottom tray of the water wash tower. The intention is to scrub the ethylene-rich vapor stream and remove as many oxygenates as possible from the product stream. Some oxygenates, such as ethers (dimethyl ether and diethyl ether), carbon dioxide, and carbon monoxide, are not effectively removed. Carbon dioxide can be removed in a two-stage caustic scrub process, while oxygenates can be further removed in a cryogenic distillation unit.

[0054] The vapor from the above process is further passed through a set of dryers to remove moisture from the vapor stream and then sent to a cryogenic distillation unit. The vapor from the cryogenic distillation unit is further compressed in a third stage of the ethylene compressor to meet downstream unit cell limit pressure requirements.

[0055] 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.

[0056] 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 32°C to 104°C and a pressure of approximately 670 kPa (g) psig (approximately 670 kPa (g) psig) atmospheric pressure.

[0057] 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 alcohols and 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 82°C to 121°C and an overhead pressure of 35 kPa(g) to 140 kPa(g).

[0058] 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 fired heater and may heat the first charge stream to 400°C to 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 455 kPa(g) to 630 kPa(g). The first dehydration stream is discharged from the first dehydration reactor 40 in line 42.

[0059] The second charge 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 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 400°C to 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 420 kPa(g) to 700 kPa(g). The second dehydration stream is discharged from the second dehydration reactor 52 in line 54.

[0060] The second dehydrated stream in line 54 is supplied to an intermediate heater 56, which may be a fired heater and may heat the second dehydrated stream to between 400°C and 550°C. The resulting third heated charge stream in line 58 is supplied to a third dehydration reactor 60, where the residual ethanol feedstock is converted to ethylene and water over a dehydration catalyst at a pressure between 420 kPa(g) and 700 kPa(g). The third dehydrated stream is discharged from the third dehydration reactor 60 in line 62.

[0061] The dehydration catalyst is an alumina-based catalyst.

[0062] 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.

[0063] 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. The quench column 68 may be operated with a bottom temperature between 37°C and 104°C and a pressure at the top between 280 kPa(g) and 490 kPa(g).

[0064] 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 350 kPa(g) to 1225 kPa(g), and the effluent in line 91 is cooled in first-stage effluent cooler 93 and first-stage trim cooler 94.

[0065] 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, 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 between 455 kPa(g) and 3220 kPa(g), and the effluent in line 101 is cooled in second-stage effluent cooler 103 and second-stage trim cooler 104.

[0066] 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.

[0067] In water wash tower 110, the twice-cooled and compressed ethylene stream is washed countercurrently with cooled, treated water in line 118 from wastewater 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 caustic scrubber column 116. 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 16°C to 82°C and an overhead pressure of 2800 kPa(g) to 3500 kPa(g).

[0068] Caustic scrubber column 116 has a lower caustic wash section 124 and an upper water wash section 132. In lower caustic wash section 124, the washed ethylene stream in line 120 is scrubbed with an aqueous caustic stream from line 126 to absorb acid gases, such as carbon dioxide, from the washed ethylene stream. Spent caustic is pumped from the bottom of the lower section in line 128 and replenished with fresh caustic in line 130 to provide aqueous caustic stream 126. The scrubbed vapor ethylene stream, with acid gases removed, ascends from caustic wash section 124 through a steam inlet to upper water wash section 132. In water wash section 132, the scrubbed ethylene stream is contacted with a wash water stream from line 134. The washed, scrubbed vapor ethylene stream exits the top of water wash section 132 in line 136 and is fed to product dryer section 140. A spent water stream is removed from the bottom of water wash section 132 from the liquid sump in line 142 and is supplemented with a fresh water stream from line 144 to provide a wash water stream in line 134 which is pumped to the top of water wash section 124 for contact with the scrubbed vapor ethylene stream. The caustic scrubber column may be operated at a bottom temperature of 38°C to 43°C and an overhead pressure of 2800 kPa (gauge) to 2975 kPa(g).

[0069] In product dryer section 140, the washed and scrubbed ethylene stream in line 136 is fed to a first dryer inlet knockout drum 146 to remove residual water, providing a dryer inlet stream in line 148 and, possibly, a knockout water stream in a bottoms line 150 that is fed to wastewater stripper column 80 via line 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 Å. 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 between 32° C. and 49° C. and a pressure between 2758 kPa(g) and 3310 kPa(g).

[0070] 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.

[0071] 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 2800 kPa(g) to 7000 kPa(g), may be provided to the dimerization section. Heavy oxygenate removal column 170 It can be operated at a bottom temperature of -29°C to 121°C and a pressure at the top of the column of 2410 kPa(g) to 2380 kPa(g).

[0072] The water streams containing oxygenates and volatiles in lines 92, 102, 112, 122, 150, and 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 93° C. to 121° C. and an overhead pressure of from 34 kPa(g) to 138 kPa(g).

[0073] 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.

[0074] In the two reactor system compared to the three reactor system in the split reactor configuration, the effluent temperature of the second reactor is lower compared to the series reactor configuration because the overall steam injection is reduced. At lower reactor temperatures, diethyl ether formation is more pronounced as can be seen in the table below:

[0075] [Table 1]

[0076] To eliminate the concern of diethyl ether formation, a second intermediate heater and a third reactor were added. Without the third reactor, the expected diethyl ether in the vapor product would be 130-50 molar ppm, but this drops to less than 5 molar ppm with the third reactor, as seen in Table 2.

[0077] [Table 2]

[0078] Because the final reactor inlet had only unconverted ethanol, ethylene, and water coming from Reactor 2, a more detailed test was performed to determine whether there was sufficient diethyl ether conversion in the third reactor at a steam-to-ethanol ratio of 65:1. Process conditions included a catalyst load of 19 g (40 cc), 75% diluted ethanol + water + diethyl ether (300 cc / hr). Results using the high temperature third reactor are shown in Table 3; 98% ethylene selectivity was observed, with complete conversion of diethyl ether and some increase in acetaldehyde, butanone, and acetic acid formation. No butene formation was observed.

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; combining the effluent with the second portion to form an effluent / second portion mixture, passing the mixture to a second reactor to react and produce a product effluent comprising ethylene and water, and passing the product effluents from the first reactor and the second reactor to a third reactor, wherein the inlet temperature of the third reactor is between 400 and 500°C.

2. 10. The process of claim 1, wherein the selectivity to ethylene is 98%.

3. 10. The process of claim 1, wherein the selectivity to ethylene is 98-99%.

4. 10. The process of claim 1 wherein 0.00% butenes are produced.

5. 10. The process of claim 1, wherein the ratio of ethanol to steam is from 1:30 to 1:

100.

6. 10. The process of claim 1, wherein the ratio of ethanol to steam is from 1:50 to 1:

75.

7. 10. The process of claim 1, wherein the ratio of ethanol to steam is 1:

66.

8. 2. The process of claim 1, wherein the inlet temperature is 440 to 460°C.

9. 2. The process of claim 1, wherein the inlet temperature is 450 to 454°C.

10. 10. The process of claim 1, wherein the product effluent from the third reactor contains less than 5 molar ppm diethyl ether.

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