High temperature final dehydration reactor for preventing diethyl ether production during dehydration

Abstract

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

Description

[0001] Priority declaration

[0002] This application claims priority to Indian provisional patent application No. 202211049529 filed on August 30, 2022. Technical Field

[0003] The field is the conversion of alcohols to olefins. The field may particularly relate to the dehydration of ethanol to produce ethylene and the subsequent conversion of ethylene to long chain olefins and the hydrogenation of long chain olefins to produce paraffins, and more particularly to the use of a high temperature final dehydration reactor to prevent the production of diethyl ether. Background Art

[0004] Oil and gas refineries around the world are exploring methods and routes to reduce carbon footprints and are moving towards sustainable processes. The ethanol to jet fuel process is one of the routes that promises to minimize or eliminate the consumer's carbon footprint. The final products of the process are jet fuel and diesel fuel produced from bioethanol. Jet fuel is a sustainable aviation fuel and is intended to replace jet fuel produced from conventional sources such as crude oil.

[0005] There are generally three major steps in the process of converting ethanol to jet fuel. The first step is to dehydrate the ethanol to produce ethylene. Next the ethylene is converted to long chain olefins, which are then hydrogenated to produce paraffins. The present disclosure is primarily concerned with the conversion of an ethanol feed stream to ethylene and the significant reduction in the production of diethyl ether impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic process flow diagram of the present disclosure. Summary of the invention

[0007] 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; 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; 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, 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 400°C-500°C.

[0008] definition

[0009] The term "communication" means operatively allowing material flow between enumerated components.

[0010] The term "downstream communication" means that at least a portion of the material flowing to the body in the downstream communication can operatively flow from the object in communication therewith.

[0011] The term "upstream communication" means that at least a portion of the material flowing out of the body in the upstream communication can be operatively flowed to an object in communication therewith.

[0012] The term "direct communication" means that a stream from an upstream component enters a downstream component without passing through a fractionation or conversion unit and without undergoing a composition change due to physical fractionation or chemical conversion.

[0013] The term "indirect communication" means that a stream from an upstream component passes through a fractionation or conversion unit and enters a downstream component where it undergoes a composition change due to physical fractionation or chemical conversion.

[0014] The term "bypass" means that the object loses downstream communication with the bypassed body at least within the scope of the bypass.

[0015] The term "tower" means one or more distillation towers for separating one or more components with different volatilities. Unless otherwise specified, each tower includes a condenser on the top of the tower for condensing a portion of the overhead stream and refluxing it back to the top of the tower, and a reboiler at the bottom of the tower for vaporizing a portion of the bottom stream and sending it back to the bottom of the tower. The feed to the tower can be preheated. The top pressure is the pressure of the overhead vapor at the vapor outlet of the tower. The bottom temperature is the liquid bottom outlet temperature. The top line and the bottom line refer to the net line from any reflux or reboil to the tower downstream. The stripping tower can omit the reboiler at the bottom of the tower, but provide heating requirements and separation power for the liquefied inert medium (such as steam). The stripping tower is usually fed from the top tray and the main product is taken out from the bottom.

[0016] As used herein, the term "component-rich stream" refers to a rich stream exiting a vessel having a greater concentration of a component than the feed to the vessel.

[0017] As used herein, the term "component-lean stream" means that the lean stream exiting a vessel has a lesser concentration of a component than the feed to the vessel.

[0018] As used herein, the term "separator" means a vessel having an inlet and at least one overhead vapor outlet and one bottom liquid outlet, and may also have an outlet for an aqueous stream from a boot. A flash tank is a type of separator that may be connected downstream to a separator that may operate at a higher pressure.

[0019] As used herein, the term "predominantly" or "majority" means greater than 50%, suitably greater than 75%, and preferably greater than 90%.

[0020] As used herein, the term “C x " is understood to refer to molecules having the number of carbon atoms indicated by the subscript "x". Similarly, the term "C x -" refers to molecules containing less than or equal to x, and preferably x and fewer carbon atoms. The term "C x +" refers to molecules having greater than or equal to x, and preferably x and more carbon atoms.

[0021] As used herein, the term "carbon number" refers to the number of carbon atoms per hydrocarbon molecule, and typically a paraffin molecule. DETAILED DESCRIPTION

[0022] 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.

[0023] 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 scheme so that one vessel can be offline and reloaded while one vessel is online. Ion exchange resin suppliers recommend a regenerable system using HCl or sulfuric acid as the regenerator. HCl regenerator is not appropriate because the unit has stainless steel metallurgy. A regenerable system with sulfuric acid would need to be fully reviewed and reviewed if implemented. Ion exchange resins will have the highest capacity. At present, feed pretreatment is not considered necessary for metal levels below <1.0wppm.

[0024] The demetallized product leaving the feed 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 bottom discharge material is expected to be <1.0% of the total feed, which is composed of concentrated heavy materials such as acetic acid, acetals, cresols, phenol, free fatty acids such as hexadecanoic acid and octadecanoic acid, some heavy alcohols, etc., and the bottom storage tank can be swaged and designed to keep the heavier discharge material usually 24 hours, and discharged into the ethanol waste liquid tank.

[0025] Since there are no expected dissolved light ends 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 of 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 (see discussion below).

[0026] The diethyl ether (DEE) absorber floats with the dehydration separator vapor stream, which enters below the bottom tray of the DEE absorber, and the tower 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. If the DEE absorber is not considered part of the design, a feed surge tank with a 15 minute residence time should be provided, and the FPC net overhead liquid mixed with the recycled ethanol will enter the feed surge tank instead of the DEE absorber. If the FPC is not included as part of the design, the new ethanol feed plus the recycled ethanol stream can be sent to the DEE absorber (if it is considered part of the specific design) or the feed surge tank.

[0027] 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. Before entering the cold side (tube side) of the combined feed exchanger 1 (CFE1), the first branch of the feed stream is heated and vaporized in the ethanol-jet product exchanger, the ethanol-hydrogenation reactor feed exchanger (both of which are located in the oligomerization unit) and the first ethanol steam heater, and then enters the feed heater. Before entering CFE1, the vaporized feed is mixed with steam produced in a steam generator placed in a downstream oligomerization unit. The combined stream is heated to the desired reaction temperature in the feed heater and sent to the first reactor.

[0028] The ethanol dehydration reaction is endothermic in nature. Water is a byproduct of the dehydration reaction, and the water produced in the first reactor satisfies the steam demand in the downstream reactor. Before entering the cold side (tube side) of the second combined feed exchanger (CFE2), the second split of the feed stream is heated and evaporated in the ethanol-second stage oligomerization lag reactor feed exchanger, the ethanol-second stage oligomerization advance reactor feed exchanger (these two exchangers are both located in the oligomerization unit) and the second ethanol steam heater. 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 required reaction temperature. Steam does not participate in the reaction (except that there may be some minor side reactions), but the steam added to the reactor plays a 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 at a lower reactor outlet temperature, the formation of diethyl ether is more significant. In order to ensure that the formation of diethyl ether is restricted, the second reactor effluent is passed through the second intermediate heater and is heated to the required reactor temperature again before entering the third reactor. The third reactor is a finishing reactor, which ensures that diethyl ether is converted into useful ethylene together with unconverted ethanol. The third reactor effluent is split and passed 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 then in the dehydration product condenser before entering the dehydration separator.

[0029] 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 the ethylene product. As described above, the dehydration separator vapor is sent to the DEE absorber. If the DEE absorber is not considered part of the design, the separator vapor is sent to a water scrubber.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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 overflow cooler is added to the compressor overflow line.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] The wastewater stripper operates 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 (if the DEE absorber is part of the design), 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 DEE absorber bottom (if included as part of the design). The waste gas knockout drum vapor is a small purge stream, which is a mixture of olefins (dissolved in the dehydration separator and water scrubber liquids) and oxygenates. This purge gas stream is mixed with the low-pressure waste gas stream produced in the downstream oligomerization unit and further compressed in the waste gas compressor to the required fuel gas knockout drum pressure and then burned in the complex combustion heater. The wastewater stripper has two reboiler systems. One reboiler, i.e., the wastewater stripper auxiliary reboiler, utilizes low pressure steam as the reboiling medium (expected to be operated at startup and as an auxiliary standby reboiler), while the other reboiler, i.e., 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 a process water pump through the tube side of the wastewater stripper feed bottoms exchanger, and the downstream is divided into three streams. The first stream is the process water for washing the vapor product oxygenates in the water scrubber. The stream is sent to the water scrubber through an ethanol treated water exchanger, a treated water cooler, and a treated water tempering cooler.

[0038] 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 a steam generator placed in the downstream oligomerization unit reactor section for heat recovery. The steam produced is recycled 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 treated water exchanger.

[0039] 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.

[0040] As previously mentioned, the dehydrator vapor can be sent to a DEE absorber (if included as part of the design) or a water scrubber. The dehydrator vapor has certain impurities / oxygenates, such as acetaldehyde, diethyl ether, dimethyl ether, water, unconverted alcohol, etc., which need to be removed before sending the vapor product stream to the downstream oligomerization unit.

[0041] 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.

[0042] Ethanol feed comes from wet grinding or dry grinding process. These ethanol feeds may contain a variety of pollutants, such as higher alcohols, metals, acetaldehyde, ethyl acetate, etc. In addition, dry grinding feed may also contain fusel oil (heavier alcohols and acids). Ethanol feed can be treated to remove metal contaminants by using a resin processor. Heavy hydrocarbons from fresh feed can be separated in a feed purification tower.

[0043] Currently in the ethanol dehydration process unit, the feed to the reactor section is split into two parallel reactors. This is done to minimize the steam demand of the unit. At lower steam levels, the parallel reactors absorb heat very high, resulting in reactor outlet temperatures in the range of 300°C to 340°C. At such low outlet temperatures, the ethanol in the reactor may form undesirable diethyl ether. The present invention aims to reduce the formation of diethyl ether, which is a non-selective component and causes selectivity loss. Since the first two parallel reactors have process outlet temperatures in the range of 300°C-340°C, it is possible to form diethyl ether in the reactor, mainly in the cooler sections of these reactors. Pilot plant data show that ether is formed at lower temperatures. In order to ensure that diethyl ether is not formed, a third reactor (refining reactor) with an intermediate heater is added at the outlet of the parallel reactors. The inlet of the third reactor has very little unconverted ethanol, and the inlet temperature is kept high enough, in the range of 400°C-500°C, to avoid any ether formation. Additionally, due to the lower ethanol concentration at the inlet of the 3rd reactor, the expected endotherm in the 3rd reactor is smaller, which prevents any possibility of ether formation.

[0044] Fresh ethanol feed is combined with unconverted ethanol and divided into two equal streams entering parallel combined feed exchangers. Split reactor configuration is considered because the desired steam to ethanol ratio is maintained at the reactor inlet to maintain reactor endothermicity and ensure catalyst stability. In order to minimize the combined feed rate to the reactor, it becomes necessary to reduce the intake of steam. The ethanol dehydration reaction results in the generation of water as a by-product.

[0045] The new feed entering the reactor section can be divided equally by two combined feed exchangers. The feed from CFE1 (what does CFE1 stand for?) is sent to reactor 1 through a feed heater. Steam is mixed with the new feed at the inlet of the feed heater. Since only half of the feed passes through reactor 1, the required steam level is only half of the required steam level. Moisture is produced from the dehydration reaction in reactor 1, and the reactor 1 effluent is mixed with the new feed entering reactor No 2 through CFE 2 and intermediate heater No 1. The water produced in reactor No 1 meets the requirements of the ratio of steam to ethanol in the reactor. Through the present invention, the steam demand is reduced by 50%, thereby reducing the combined feeding capacity of the entire reactor by 30%-40%. As another additional item for the feed section, diluted ethanol feed can also be processed in the reactor section. When a more diluted ethanol feed is processed in the dehydration section, the amount of steam required is reduced. Diluting the ethanol feed has the benefit of reducing power consumption in the upstream ethanol production unit. Diluting the ethanol feed to less than 90% does not produce significant power savings.

[0046] As already explained, 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 fed to reactor no 1 at the inlet of CFE 1. The recycled water is divided into two streams. One stream passes through the fired heater convection section (50-60%) to produce steam, and the remaining water stream is mixed with the fresh feed at the inlet of CFE1. This creates a unique problem because the evaporation of liquid water with ethanol must occur on the cold side of CFE1. Assuming that the cold side is at a higher pressure and is boiling, while the hot side is at a lower pressure and is condensing, the available methods are significantly reduced, making the CFE design impractical. In order to ensure that there are enough methods available in CFE1, the cold side pressure needs to be reduced or the hot side pressure needs to be increased. This is achieved by including an inter-reactor compressor at the outlet of reactor No 1. The reactor No 1 outlet operates at a lower pressure, thereby reducing the CFE1 cold side inlet pressure. The reactor 1 effluent is compressed and mixed with the fresh feed entering reactor no2. This option provides a unique opportunity to improve energy recovery from the reactor effluent in the combined feed exchanger, thereby reducing power in the feed heater as well as the product condenser.

[0047] A second option for the reactor section design can be considered, the inter-reactor compressor is a large piece of equipment, and even though it helps reduce power consumption, it is expensive and difficult to design. One of the main reasons for using such a compressor is to ensure that the circulating water is evaporated efficiently. This embodiment was developed to eliminate this water circulation. Instead, the steam demand of the dehydration reactor is met by the steam produced in the downstream oligomerization / hydrogenation unit. Part of the steam can also be produced in the fired heater convection section using BFW. Now the reactor effluent is only used to vaporize the ethanol feed in this option, and an inter-reactor compressor is not required. Without an inter-reactor compressor, the load on the product condenser increases by 20%-30%. However, this option provides an easier design.

[0048] Combined Feed Exchangers - Both combined feed exchangers are contemplated to be vertical exchangers.

[0049] Reactor - Considering that the reactor section operates at very low pressure, high temperature, and the gas molecular weight varies between 20-30, the volume flow rate through the reactor is very large, which results in excessive bed pressure drop when using conventional fixed bed downflow reactors. The pressure drop problem can be alleviated by designing a fixed bed radial flow design or a compartment reactor design.

[0050] Fired Heaters - Fired heaters are contemplated to be box furnaces with process heating in the radiant section. A convection section may be utilized to generate steam that may be used in the dehydration process.

[0051] The reactor effluent from the CFE may be sent to a separator via a product condenser / product trim condenser, or may be sent through a quench column. The separator design is conventional and will not be discussed further.

[0052] The quench tower is a unique design where the hot effluent from the CFE is conveyed below the bottom tray of the tower. The liquid effluent is separated and the hot vapor effluent is re-contacted with circulating water. The heat in the reactor effluent is absorbed by the circulating water stream which is cooled in the product condenser / trim condenser. 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 scrubber to remove oxygenates.

[0053] The clean wastewater from the quench tower bottom / separator bottom has unconverted ethanol and other dissolved oxygenates. This stream is sent to the wastewater stripper. The wastewater stripper is steam reboiled to recover dissolved oxygenates and unconverted ethanol as vapor product. The vapor from the wastewater stripper is condensed and sent to a knockout tank to recover unconverted ethanol. This unconverted ethanol along with some other dissolved oxygenates is pumped back to the reactor section for further conversion.

[0054] The wastewater stripper bottoms are now 99.9mol% pure water and can be used as a scrubbing medium to scrub oxygenates from the ethylene vapor stream of the second-stage ethylene compressor from the water scrubber. In addition to using the wastewater stripper overhead as a scrubbing medium in the water scrubber, a clean water discharge is also taken out from the process. This water can be used for the electrolyzer unit that produces green hydrogen, or can be further treated to remove oxygenates at the ppm level before being used to generate steam. The wastewater stripper bottoms 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 of the water scrubber tray. The purpose is to wash the ethylene-rich steam and remove as many oxygenates as possible from the product stream. Some oxygenates are not effectively removed, such as ethers (dimethyl ether and diethyl ether), carbon dioxide and carbon monoxide. Carbon dioxide can be removed in a two-stage caustic wash process, and oxygenates can be further removed in a cryogenic distillation unit.

[0055] The vapor from the above treatment is further passed through a set of dryers to remove moisture from the vapor stream and sent to the cryogenic distillation unit. The vapor from the cryogenic distillation unit is further compressed in the third stage of the ethylene compressor to meet the downstream unit cell ultimate pressure requirements.

[0056] exist Figure 1 In the present invention, 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 mainly ethanol and may be aqueous. Preferably, the oxygenate feedstock is a biorenewable feedstock.

[0057] 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 32°C to 104°F and a pressure of about atmospheric to 670 kPa(g) psig).

[0058] 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 alcohols and 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 82°C and 121°C and a top pressure of 35kPa(g) to 140kPa(g).

[0059] 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 400°C to 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 on a dehydration catalyst at a pressure of 455kPa(g) to 630kPa(g). The first dehydration stream is discharged from the first dehydration reactor 40 via pipeline 42.

[0060] 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 400° C. to 550° C. The resulting second heated feed stream in line 50 is fed to the second dehydration reactor 52. In the second dehydration reactor 52, the ethanol feed is converted into 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 via line 54.

[0061] The second dehydrated stream in line 54 is fed to an intermediate heater 56. The intermediate heater 56 may be a fired heater and may heat the second dehydrated stream to 400° C. to 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 420 kPa(g) to 700 kPa(g). The third dehydrated stream is discharged from the third dehydration reactor 60 via line 62.

[0062] The dehydration catalyst is an alumina based catalyst.

[0063] 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.

[0064] 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 tower bottom temperature of 37° C. to 104° C. and a tower top pressure of 280 kPa(g) to 490 kPa(g).

[0065] 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 tower top line 88 to the first stage compressor 90, and residual water flows out from the bottom of the drum in line 92 through the 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 350 kPa (g) to 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.

[0066] The cooled compressed ethylene stream from the first stage trim cooler 94 is fed to the first stage bleed drum 96. Ethylene flows out of the first stage bleed drum 96 in the overhead line 98 to the second stage compressor 100, while residual water flows out of the bottom of the drum in line 102 through a control valve thereon and may be sent to the wastewater stripper 80 through line 92 and line 78. The second stage compressor compresses the ethylene stream to a second pressure of 455 kPa(g) to 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.

[0067] 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.

[0068] In the water scrubber 110, the secondary cooled, compressed ethylene stream is counter-currently 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 the top line 120 and a wash water stream in the bottom line 122. The washed ethylene stream in the top line 120 is conveyed to the caustic scrubber 116. The wash water stream in line 122 is conveyed back to the water stripper 80 through a control valve thereon. The water scrubber 110 can be operated at a bottom temperature of 16° C. to 82° C. and a top pressure of 2800 kPa(g) to 3500 kPa(g).

[0069] The caustic scrubber 116 has a lower caustic scrubber section 124 and an upper water scrubber section 132. In the lower caustic scrubber section 124, the scrubbed ethylene stream in line 120 is scrubbed with an alkaline water stream from line 126 to absorb acidic gases such as carbon dioxide from the scrubbed ethylene stream. Spent caustic is pumped from the bottom of the lower section in line 128 to the periphery and replenished with new caustic in line 130 to provide an alkaline water stream 126. The scrubbed gaseous ethylene stream depleted of acidic gases rises from the caustic scrubber section 124 to the upper water scrubber section 132 through a steam inlet. In the water scrubber section 132, the scrubbed ethylene stream contacts the scrubber water stream from line 134. The scrubbed, scrubbed gaseous ethylene stream flows out of the tower top of the water scrubber section 132 in line 136 and is fed to the product dryer section 140. The waste water stream is discharged from the bottom of the water wash section 132 in the liquid storage tank in pipeline 142 and supplemented with a fresh water stream from pipeline 144 to provide a wash water stream in pipeline 134 and pumped to the top of the water wash section 124 to contact with the scrubbed gaseous ethylene stream. The caustic scrubber can be operated at a bottom temperature of 38° C. to 43° C. and a top pressure of 2800 kPa (gauge) to 2975 kPa (g).

[0070] In the product dryer section 140, the washed, scrubbed ethylene stream in line 136 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 may be fed to a wastewater stripper 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 32° C. to 49° C. and a pressure of 2758 kPa(g) to 3310 kPa(g).

[0071] 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 .

[0072] 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 2800 kPa (g) to 7000 kPa (g) in the compressor discharge line 176 can be provided to the dimerization reaction section. The heavy oxygenate removal tower 170 can be operated at a tower bottom temperature of -29°C) to (121°C) and a tower top pressure of 2410 kPa (g) to 2380 kPa (g).

[0073] 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 93° C. to 121° C. and a tower top pressure of 34 kPa(g) to 138 kPa(g).

[0074] 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.

[0075] In the comparison of the two-reactor system and 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 total steam injection has been reduced. The formation of diethyl ether is more obvious at the lower reactor temperature, as shown in the following table:

[0076] Table 1

[0077] unit Split 2 reactors 2 reactors in series Feed rate Lb / Hr 230530 230530 Oxygenated compounds in vapor products MOLPPM 151.9 35.1 Diethyl ether in the vapor product MOLPPM 137.8 1.3 Reactor 1 inlet temperature F 842 842 Reactor 1 outlet temperature DEG F 528 526 Reactor 1 absorbs heat DEG F 314 316 Reactor 2 inlet temperature DEG F 842 842 Reactor 2 outlet temperature F 592 835 Reactor 2 absorbs heat F 250 7.0

[0078] In order to eliminate the concern of diethyl ether formation, a second intermediate heater and a third reactor were added. As shown in Table 2, without the third reactor, the expected diethyl ether in the vapor product was 130 mol ppm-50 mol ppm, while with the third reactor, it dropped to less than 5 mol ppm.

[0079] Table 2

[0080]

[0081]

[0082] Since the last reactor inlet only had unconverted ethanol, ethylene and water from reactor 2, a more detailed test was performed to check if there was sufficient diethyl ether conversion in the third reactor at a steam to ethanol ratio of 65:1. The process conditions included a catalyst amount of 19 g (40 cc), 75% dilute ethanol and water plus diethyl ether (300 cc / hr), and the results using a high temperature third reactor are shown in Table 3, where 98% ethylene selectivity was observed, complete conversion of diethyl ether, and some increase in the formation of acetaldehyde, butanone, and acetic acid was observed. No butene was formed.

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. combining the effluent with the second part to form an effluent / second part mixture, and sending the mixture to a second reactor for reaction to produce a product effluent comprising ethylene and water, and sending the product effluents from the first reactor and the second reactor to a third reactor, wherein the inlet temperature of the third reactor is 400°C-500°C.

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

3. The method according to claim 1, wherein the selectivity to ethylene is 98% to 99%.

4. The process of claim 1 wherein 0.00% butene is produced.

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

100.

6. The method of claim 1, wherein the ratio of ethanol to steam is 1:50-1:

75.

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

66.

8. The method according to claim 1, wherein the inlet temperature is 440°C-460°C.

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

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

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