Vapor accumulation in ethanol to jet fuel process

Abstract

An ethanol dehydration process is provided in which the ratio of steam to ethanol is between 1.0 wt / wt and 2.0 wt / wt, and preferably 1.5 wt / wt. Steam may be input from outside the dehydration process, such as from oligomerization or dimerization reactions.

Description

[0001] Priority declaration

[0002] This patent application claims priority to Indian provisional patent application 202211049526 filed on August 30, 2022. Technical Field

[0003] The present invention relates to a process for dehydrating ethanol. More particularly, the present invention relates to generating steam from oligomerization and hydrogenation reaction steam accumulation throughout the ethanol to jet fuel process. Background Art

[0004] Oil and gas refineries around the world are exploring methods and routes to reduce their carbon footprint 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 end 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 main 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 paraffins. Summary of the invention

[0006] A method for dehydrating ethanol is provided, the method comprising adding an amount of steam to an ethanol feed stream, wherein the ratio of steam to ethanol is between 1.0 wt / wt and 2.0 wt / wt, and reacting the ethanol feed stream in the presence of a catalyst under reaction conditions to produce an ethylene effluent stream. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic process flow diagram of the present disclosure.

[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] 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.

[0023] Fresh ethanol feed is combined with unconverted ethanol and split into two equal streams entering parallel combined feed exchangers. A split reactor configuration is contemplated because a desired steam to ethanol ratio is maintained at the reactor inlet to maintain

[0024] Reactor endothermicity and ensure catalyst stability. In order to minimize the combined feed rate to the reactor, it is necessary to reduce the intake of steam. The ethanol dehydration reaction leads to the generation of water as a byproduct. The ethanol dehydration method needs to inject steam in the method to obtain the desired catalyst life and maintain the operation below the maximum endothermic in the adiabatic system. It has been confirmed that the optimal ratio of steam to ethanol should be between 1.0wt / wt and 2.0wt / wt (preferably 1.5). In addition, some towers in the unit (including feed purification towers and wastewater stripping towers) can also be reboiled with steam. Since the ethanol dehydration reactor is operated in the gas phase, it may be energy intensive to generate steam from product water (product water condenses and evaporates). In order to overcome this problem, it has been concluded that it is preferred to import steam (~100psig) from the outside of the dehydration boundary. Exothermic oligomerization and hydrogenation reactions may be a good source for generating steam, and there is a good accumulation opportunity to meet the steam demand.

[0025] The oligomerization step of the ethanol to jet fuel process uses a high temperature reactor in the front end position. Steam generation can be used to achieve inter-bed temperature control. The steam level can be set to 100 psig to cool the hot effluent to a minimum of 370°F (187°C). The convection section of the jet fractionator reboiler can also be a good source of steam generation.

[0026] For a 300 MMGPY ethanol unit, the combined flow rate of steam is estimated to be ~140 k lb / hr, which can meet the injection requirements of ethanol dehydration steam.

[0027] In Figure 1, a method 10 for treating an oxygenate feedstock is shown according to an exemplary embodiment. The oxygenate feedstock may contain an alcohol, and preferably contains ethanol. The feedstock may contain primarily ethanol and may be aqueous. Preferably, the oxygenate feedstock is a biorenewable feedstock.

[0028] Feed line 12 delivers the oxygenate stream of the oxygenate feedstock to a feed pretreatment section 14. The 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 the feed line 12. The feed pretreatment section 14 may include an additional vessel 18 having the same adsorbent bed for further removing metals from the oxygenate stream. The vessels 16, 18 may be arranged in series or in a lead-lag type arrangement to allow regeneration of spent adsorbent. Line 17 delivers a partially pretreated oxygenate stream from the outlet of vessel 16 to the inlet of vessel 18. The pretreated oxygenate stream flows out of the feed pretreatment section 14 from the outlet of the additional vessel 18 in line 20 and is fed to a purification tower 22. The feed pretreatment section 14 may be operated at a temperature of 32°C to 104°C and a pressure of atmospheric pressure to 670 kPa(g).

[0029] 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 recycled 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).

[0030] 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.

[0031] 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.

[0032] 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.

[0033] The dehydration catalyst may be an alumina based catalyst.

[0034] 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.

[0035] 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, the vent stream being delivered to the wastewater stripper 80 via a control valve on the wastewater stripper. A first portion of the quench recycle stream is air cooled in product condenser 69 and circulated as a first lower cooling water stream in line 70 via a control valve on that line, 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. Quench tower 68 may be operated utilizing a bottoms temperature of 37°C (100°F) to 104°C (220°F) and an overhead pressure of 280 kPa(g) (40 psig) to 490 kPa(g) (70 psig).

[0036] The quenched ethylene stream in line 74 is fed to a first stage suction drum 86. In the first stage suction drum, ethylene flows from an overhead line 88 to a first stage compressor 90, while residual water flows from the bottom of the drum in line 92 through a control valve on the drum and may be sent to a wastewater stripper 80 through line 78. The first stage compressor 90 compresses the ethylene stream to a first pressure of 350 kPa (gauge) (50 psig) to 1225 kPa (gauge) (175 psig), and the effluent in line 91 is cooled in a first stage effluent cooler 93 and a first stage trim cooler 94.

[0037] The cooled compressed ethylene stream from the first stage trim cooler 94 is fed to the first stage discharge drum 96. Ethylene flows out of the first stage discharge 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 the control valve on the drum 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 discharge in line 101 is cooled in the second stage discharge cooler 103 and the second stage trim cooler 104.

[0038] The secondary cooled compressed ethylene stream from the second stage trim cooler 104 is fed to the second stage discharge drum 106. Ethylene flows out of the second stage discharge 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 on the drum and may be sent to a waste water stripper 80 via line 102, line 92, and line 78.

[0039] In the water scrubber 110, the secondary cooled, compressed ethylene stream is counter-currently scrubbed with cooled, treated water in line 118 from the wastewater stripper 80 to absorb additional oxygenates, thereby producing a washed ethylene stream flowing out in an overhead line 120 and a wash water stream in a bottom line 122. The washed ethylene stream in the overhead 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 on the water stripper. 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).

[0040] 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 a caustic 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 a caustic 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 line 142 and supplemented with a fresh water stream from line 144 to provide a wash water stream in line 134 and pumped to the top of the water wash section 124 to contact 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(g) to 2975 kPa(g).

[0041] 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 the 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 using a temperature of 32° C. (90° F.) to 49° C. (120° F.) and a pressure of 2758 kPa (gauge) (400 psig) to 3102 kPa (gauge) (450 psig).

[0042] 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 .

[0043] The dryer outlet stream in line 162 can be fed to a heavy oxygenate removal column 170 to separate a tower top stream containing mainly ethylene but possibly containing higher olefins from heavy ketones and ethers. 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 (gauge) (400 psig) to 7000 kPa (gauge) (1000 psig) in the compressor discharge line 176 can be provided to the dimerization reaction section. The heavy oxygenate removal column 170 can be operated at a tower bottom temperature of -20°F to 250°F and a tower top pressure of 350 psig to 450 psig).

[0044] The water streams containing oxygenates and volatiles in lines 92, 102, 112, 122, 150, 164 can be fed to a wastewater stripper 80, where the volatiles and oxygenates are vaporized to provide an 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 wash tower 110. The wastewater stripper 80 can be operated using a bottom temperature of 93°C (200°F) to 121°C (250°F) and a top pressure of 34 kPa (gauge) (5 psig) to 138 kPa (gauge) (20 psig).

[0045] 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 via line 24 to feed buffer tank 26 in line 27.

Claims

1. A process for the dehydration of ethanol, the process comprising adding an amount of steam to an ethanol feed stream, wherein the ratio of steam to ethanol is between 1.0 wt / wt and 2.0 wt / wt, and reacting the ethanol feed stream in the presence of a catalyst under reaction conditions to produce an ethylene effluent stream.

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

5.

3. The method according to claim 1, wherein a portion of the steam is input from outside the ethanol dehydration process.

4. The process of claim 1, wherein the amount of steam is from an oligomerization or hydrogenation reaction.

5. The process according to claim 1, wherein a portion of the steam is generated by a wastewater stripper and then heated in the oligomerization stage.

6. The method of claim 5, wherein a portion of the water is removed to minimize accumulation of impurities.

7. The method of claim 1, wherein the steam is generated in a dedicated steam generator.

8. The process of claim 7, wherein the steam is further heated by heat exchange with the olefin separator bottoms in a steam superheater.

9. The method of claim 1, wherein at least five steam generators are used to generate the steam.

10. The method of claim 1, wherein the circulating steam generator cools hot diesel from the flash steam stripper feed to the circulating oil exchanger.

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