Process for preparing an olefin stream for oligomerization with dimethyl ether removal - Patent Application 20070122997

Abstract

A method for preparing a hydrocarbon stream for oligomerization is provided. The method uses a stripping column to strip dimethyl ether from an olefin stream. Lighter olefins, such as C3-olefins, are also removed. The C4+ olefins can then be sent for further processing, including selective hydrogenation followed by oligomerization.

Description

[Technical Field]

[0001] The field is the conversion of olefins to distillates. The field may particularly relate to the preparation of olefins for oligomerization into distillate fuels. [Background technology]

[0002] Molecular sieves, such as microporous crystalline zeolites, and non-zeolitic catalysts, particularly silicoaluminophosphate (SAPO), are known to promote the conversion of oxygenates, such as methanol, to light olefins. Highly efficient methanol to olefin (MTO) processes can convert oxygenates to light olefins that have typically been considered for plastics production. Light olefins produced from the MTO process are concentrated in ethylene and propylene, but also contain C4 to C8 olefins.

[0003] Ethylene can be oligomerized to olefins such as C4, C6, and C8 olefins. Propylene can be oligomerized to olefins such as C6, C9, and C12 olefins. Larger MTO olefins can also be oligomerized. Olefin oligomerization is a process by which smaller olefins can be oligomerized to larger olefins. More specifically, olefins can be converted to carbon-long molecules in the distillate range, including jet fuel and diesel range products. The oligomerized distillate can be saturated for use as transportation fuel.

[0004] Jet fuel is one of the few petroleum fuels that cannot be easily substituted in electric motor systems because fueling an airplane requires a high energy output that cannot be provided by an electric motor. Jet fuel has an end boiling point specification of less than 300 °C using ASTM D86. In certain regions, significant tax incentives are currently available for renewable jet fuel.

[0005] The product olefin stream from an MTO unit contains water and oxygenates, which must be removed before encountering the oligomerization catalyst. Additionally, the product olefin stream may contain diolefins and acetylenes that can polymerize in the oligomerization reactor, fouling the process, requiring cleaning, and significantly reducing selectivity to distillate range fuels. An efficient method for preparing a renewable olefin feed stream for oligomerization to distillate range fuels is desired. Summary of the Invention

[0006] The present inventors have devised a method for preparing an olefin stream for oligomerization that involves stripping dimethyl ether from the olefin stream using a stripping column. Lighter olefins, such as C3-olefins, are also removed. The C4+ olefins can then be sent for further processing, including selective hydrogenation followed by oligomerization. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram of the olefin feed preparation process and apparatus of the present disclosure. [Figure 2] FIG. 1 is a schematic diagram of the oligomerization feed preparation method and apparatus of the present disclosure. [Figure 3] FIG. 2 is a schematic diagram of another embodiment of the oligomerization feed preparation method and apparatus of the present disclosure. [Figure 4] FIG. 2 is a schematic diagram of yet another embodiment of the oligomerization feed preparation process and apparatus of the present disclosure.

[0008] definition The term "communication" means that fluid flow is operably permitted between the listed components, which may be characterized as "fluid communication."

[0009] The term "downstream communication" means that at least a portion of the fluid flowing to an object in downstream communication can operatively flow from the object in fluid communication.

[0010] The term "upstream communication" means that at least a portion of the fluid flowing from the object with which it is in upstream communication can operatively flow to the object with which it is in fluid communication.

[0011] The term "direct communication" means that fluid flow from an upstream component enters a downstream component without passing through any other intervening vessel.

[0012] The term "indirect communication" means that fluid flow from an upstream component passes through an intervening vessel before entering a downstream component.

[0013] The term "bypass" means that an object is out of downstream communication with a bypass subject, at least to the extent that it bypasses.

[0014] As used herein, the term "predominant" or "majority" means more than 50%, suitably more than 75%, preferably more than 90%.

[0015] 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 overhead of the column to condense and reflux a portion of the overhead stream that returns to the top of the column, and a reboiler at the bottom of the column to vaporize a portion of the bottom stream and return 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 stripping column may omit the reboiler at the bottom of the column and instead provide the heating requirements and separation driving force from a fluidized inert medium such as steam. A stripping column typically feeds the top tray and removes the main product from the bottom. Column may also refer to an extraction column for separating one or more components from a stream into an extract stream via liquid-liquid contact, or an absorption column for separating one or more components from a gas stream into a liquid solvent stream.

[0016] As used herein, the term "separator" means a vessel having an inlet and at least an overhead vapor outlet and a bottom 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. As used herein, the term "boiling point temperature" means the atmospheric equivalent boiling point (AEBP) calculated from the observed boiling point and distillation pressure, calculated using the formula provided in ASTM D1160 Appendix A7, entitled "Practice for Converting Observed Vapor Temperatures to Atmospheric Equivalent Temperatures."

[0017] As used herein, the term "True Boiling Point" (TBP) refers to a test method for determining the boiling point of a substance, which test method corresponds to ASTM D-2892 for producing liquefied gases, distillate fractions, and residual oils of standardized quality for which analytical data can be obtained, and for determining the yield of said fractions by both mass and volume, where a graph of temperature versus mass % distilled is produced using 15 theoretical plates in a column with a reflux ratio of 5:1.

[0018] As used herein, the terms "T5," "T10," "T90," or "T95" refer to the temperature at which 5 percent, 10 percent, 90 percent, or, as the case may be, 95 percent by weight of a sample boils, respectively, using ASTM D-86 or TBP, as the case may be.

[0019] As used herein, the term "initial boiling point" (IBP) means the temperature at which a sample begins to boil using ASTM D-7169, ASTM D-86, or TBP, as the case may be.

[0020] As used herein, the term "end point" (EP) means the temperature at which the sample has completely evaporated using ASTM D-7169, ASTM D-86, or TBP, as the case may be.

[0021] As used herein, the term "diesel" refers to hydrocarbons boiling within a range of "diesel cut points" including an IBP of about 125°C (257°F) to about 175°C (347°F) or a T5 of about 150°C (302°F) to about 200°C (392°F), and a T95 of about 343°C (650°F) to about 399°C (750°F) using the TBP distillation method or a T90 of 280°C (536°F) to about 340°C (644°F) using ASTM D-86. The term "green diesel" or "renewable diesel" refers to diesel containing hydrocarbons not derived from fossil fuels.

[0022] As used herein, the term "jet fuel" means hydrocarbons boiling in the range of about 190°C (374°F) to about 215°C (419°F) T10 and about 290°C (554°F) to about 310°C (590°F). The terms "green jet fuel" or "renewable jet fuel" mean jet fuel containing hydrocarbons not derived from fossil fuels.

[0023] 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, and preferably than all other streams withdrawn from the vessel.

[0024] As used herein, the term "component lean stream" means that the lean stream exiting the vessel has a lower concentration of components than the feed to the vessel and preferably than all other streams withdrawn from the vessel. DETAILED DESCRIPTION OF THE INVENTION

[0025] The disclosed method and apparatus involve treating an olefin reactor product produced by the reaction of methanol over a catalyst to serve as a feedstock for oligomerization utilizing a zeolite catalyst. The zeolite catalysts used in the oligomerization of olefinic hydrocarbons are sensitive to a variety of contaminants, including CO, ethers, ketones, aldehydes, dienes, acetylenes, sulfur, and nitriles. Finding a suitable feedstock can be difficult because these contaminants can cause permanent or temporary catalyst deactivation at ppm levels.

[0026] The olefin product from the reaction of methanol over the catalyst is a highly olefinic material and an excellent feedstock for oligomerization using a zeolite catalyst. However, the olefin product also contains various contaminants that must be removed for the zeolite catalyst to be effective. The olefin reactor effluent may contain CO in the range of about 100 to about 1000 wppm, CO2 in the range of about 50 to about 500 wppm, dimethyl ether (DME) in the range of about 1 to about 1.5 wt%, acetylene in the range of about 20 to about 50 wppm, and dienes in the range of about 1000 to about 3000 wppm, all of which must be addressed before being sent to the oligomerization reactor. The olefin reactor effluent may also contain unreacted methanol.

[0027] The process and apparatus may include an olefin recovery section 10 shown in FIG. 1 and an oligomerization feed preparation section 110 shown in FIG.

[0028] Referring to the method and apparatus 10 of Figure 1, a superheated feed stream in line 12 is supplied to an oxygenate conversion reactor 16, which reacts oxygenates, such as methanol or dimethyl ether (DME), with a fluidized catalyst. A hot steam reactor effluent stream in line 14 is removed from the oxygenate conversion reactor 16, which periodically or continuously recycles the fluidized catalyst to a regeneration zone 18 in a conventional manner to maintain the desired selectivity and conversion. The oxygenate conversion reactor 16 is maintained at conditions effective to convert the oxygenates to produce light olefin products and oxygenate by-products. The hot steam reactor effluent stream may include light olefins, water, and oxygenates. The oxygenate conversion reactor 16 may be operated to produce a significant portion or a majority of propylene.

[0029] The hot vapor reactor effluent stream in line 14 may be pre-cooled in reactor effluent heat exchanger 15 to recover heat before being sent to quench tower 20. In quench tower 20, the vapor reactor effluent is directly contacted with a water stream provided in line 19, which may be derived from the stripped water stream in line 21, to reduce superheat, neutralize organic acids, and remove catalyst fines. After quenching, a first olefin stream comprising C2 to C8 olefins in line 22 exits quench tower 20 and is provided to product separator column 24. The first olefin stream in line 22 may also contain methane, CO, CO2, hydrogen, and other oxygenates. Product separator column 24 may be in downstream communication with oxygenate conversion reactor 16.

[0030] Product separator column 24 includes two sections for separating the reactor effluent stream into a product second olefin stream in overhead line 40, an intermediate liquid stream in intermediate line 28, and a product water stream in bottoms line 26. The first, or lower, section receives the first olefin stream in line 22. The lower section removes most of the heat from the first olefin stream while partially condensing the water in the first olefin stream to produce a product water stream in bottoms line 26 containing some of the oxygenate by-products in the first olefin stream in line 22. A portion of the product water stream is cooled and pumped around the top of the first section of product separator column 24 to cool the first olefin stream in line 22. A second portion of the product water stream in bottoms line 26 is sent to water stripper column 30. A water return stream containing oxygenate by-products from compression section 80 in return line 32 may also be sent to water stripper column 30. A water stripper column 30 may be in downstream communication with the product separator column 24 .

[0031] The vapor stream from the first section of product separator column 24 is sent to the second (i.e., upper) section of the product separator. An intermediate stream in line 28 containing hydrocarbons, oxygenate by-products, and water in the liquid phase is withdrawn at the bottom of the upper section. A portion of the intermediate stream in line 28 is cooled and sent as a pumparound to the top of the second section of product separator column 24. The remainder of the intermediate stream in line 28 is sent to coalescer 29 to separate a hydrocarbon overhead stream from an aqueous stream in line 34, which is returned to the product water stream in line 36 and sent to water stripper column 30. The overhead product stream, i.e., the second olefin stream containing C2-C8 olefins and dimethyl ether in line 40 from product separation column 24 in line 40, is sent to compression section 80.

[0032] The product water stream in line 36 contains dilute hydrocarbon oxygenates such as DME, methanol, acetaldehyde, acetone, and methyl ethyl ketone (MEK). Water stripper column 30 separates or strips the oxygenates into a methanol and oxygenate-rich stream enriched in both methanol and at least another oxygenate in overhead line 49 and an oxygenate-lean water stream in bottoms line 46. A first portion of the oxygenate-lean water stream in line 46 is recycled to the process via the stripped water stream in line 21. A second portion may be discharged to a wastewater stream in line 23.

[0033] In one embodiment, water stripper column 30 may be operated at a temperature of from about 115°C (239°F) to 200°C (392°F) at the bottom of the water stripper column and a pressure of from about 70 kPa(g) (10 psig) to about 830 kPa(g) (120 psig) at the top of the water stripper column 30.

[0034] In one embodiment, the second olefin stream in line 40 is a product olefin stream from product separation column 24. The product olefin stream in product overhead line 40 carries a valuable olefin product that must be recovered. Compression section 80 increases the pressure of the product olefin stream necessary for downstream processing, such as that used in conventional light olefin recovery units. Compression section 80 may include a first knockout drum 82 that separates the product olefin stream into a pressurized first olefin-rich stream in overhead line 83 at a temperature of from about 20°C (68°F) to about 60°C (140°F) and a pressure of from about 150 kPa(g) (22 psig) to about 280 kPa(g) (41 psig), and an oxygenate-rich first aqueous stream in bottoms line 84. The olefin-rich stream in overhead line 83 may be fed to compressor 85, cooled, and directed to second knockout drum 86. The aqueous stream in bottoms line 84 is pumped via manifold line 76 to return line 32 which, along with the product water stream in product separator bottoms line 36 , returns the water stream to water stripper column 30 .

[0035] Compression section 80 may include a second knockout drum 86 that separates the pressurized first olefin-rich stream into a second pressurized olefin-rich stream in overhead line 87 at a pressure of about 300 kPa(g) (44 psig) to about 400 kPa(g) (58 psig) and a temperature of about 20°C (68°F) to about 60°C (140°F), and a second oxygenate-rich aqueous stream in bottoms line 88. The second olefin-rich stream in overhead line 87 may be fed to compressor 89, cooled, and directed to third knockout drum 90. The aqueous stream in bottoms line 88 is pumped via manifold line 76 to return line 32, which returns the water stream to water stripper column 30 along with the product water stream in product separator bottoms line 36.

[0036] Compression section 80 may include a third knockout drum 90 that separates the pressurized second olefin-rich stream into a third pressurized olefin-rich stream in overhead line 91 and a third oxygenate-rich aqueous stream in bottoms line 92. The third olefin-rich stream in overhead line 91 may be fed to oxygenate absorption column 50. The aqueous stream in bottoms line 92 is sent via manifold line 76 to return line 32, which returns the water stream to water stripper column 30 along with the product water stream in product separator bottoms line 36.

[0037] Suitable compressor types may include centrifugal, positive displacement, piston, diaphragm, screw, etc. In one embodiment, compressors 85, 89 in compression section 80 are centrifugal compressors. The final discharge pressure may be from about 1.0 MPa(g) (145 psig) to about 2.1 MPa(g) (305 psig). The compressor discharge may be cooled to about ambient temperature using conventional heat transfer methods.

[0038] 1, in accordance with a preferred embodiment, at least a portion of the compressed product stream via overhead line 91 is contacted in oxygenate absorber column 50 with a cooled lean water stream in line 102 under conditions effective to absorb at least a quantity of effluent oxygenates, such that water is not removed directly from product separator column 24 without prior removal of oxygenates. Contact in oxygenate absorber column 50 produces an absorbed olefin-rich stream in overhead line 54 and an absorbed water-rich stream containing a quantity of effluent oxygenates in bottoms line 52. Oxygenate absorber column 50 may have operating conditions including a bottoms temperature range of about 30°C (86°F) to about 60°C (140°F) and an overhead pressure range of about 700 kPa(g) (101 psig) to about 1 MPa(g) (145 psig).

[0039] The absorption olefin-rich stream in overhead line 54 can be fed to third stage knockout drum 60, where a gaseous olefin stream is taken overhead line 61 to third compressor 62, while water and oxygenates are taken in bottoms line 59 to manifold line 76. Third stage knockout drum 60 can operate at about the same pressure as the oxygenate absorber overhead and at a temperature of from about 32°C (90°F) to about 52°C (125°F). The gaseous olefin stream in line 61 is compressed in third compressor 62 to form a compressed gaseous olefin stream in line 63, which is then combined with a stream in stripper overhead line 71, partially condensed by cooling in feed cooler 64, and fed in line 65 to stripper separator 66. Stripper separator 66 separates an aqueous stream containing oxygenates in the boot in line 67 which feeds manifold line 76, a light olefin vapor stream in overhead line 68 containing C3- olefins, and a heavy olefin liquid stream containing C4+ olefins in line 69. The heavy olefin liquid stream in line 69 is stripped in DME stripper column 70 to remove C3 and lower vapors in stripper overhead line 71 from the heavy olefin liquid stream in stripper bottoms line 168. In one embodiment, a reboil stream may be taken from the heavy olefin liquid stream in stripper bottoms line 168, reboiled in DME stripper reboiler 167, and returned to DME stripper column 70. Most of the oxygenates are separated as they are stripped into stripper overhead line 71 and recycled to stripper separator 66 after cooling. The bottoms stream leaving DME stripper column 70 may be sent through line 168 to selective hydrogenation reactor 170 via line 169, as shown in Figure 2. This stream contains primarily C4+ olefins, but also diolefins that interfere with the oligomerization catalyst requiring selective hydrogenation. DME stripper column 70 may operate at an overhead temperature of from about 60°C (140°F) to about 82°C (180°F) and a column bottoms pressure of from about 1.8 MPa(g) (260 psig) to about 2.2 MPa(g) (320 psig).Stripper separator 66 may operate at a temperature of about 10°C (50°F) to about 60°C (140°F) and a pressure of about 1.7 MPa(g) (250 psig) to about 2.1 MPa(g) (300 psig). The light olefin vapor stream in overhead line 68 is scrubbed in caustic scrubber 73 by countercurrent contact with a caustic solution in line 42 to absorb acid gases, such as carbon dioxide, from the light olefin vapors exiting caustic scrubber 73 in overhead line 74. The acid gas-rich caustic solution exits caustic scrubber 73 in line 44. Caustic scrubber 73 may operate at an overhead temperature of about 32°C (90°F) to about 54°C (130°F) and a pressure of about 1.7 MPa(g) (250 psig) to about 2.0 MPa(g) (290 psig).

[0040] The scrubbed light olefins vapor stream in overhead line 74 may be refrigerated by propylene refrigerant in dryer feed cooler 75 to liquefy a portion of the light olefins vapor stream and provide a cooled scrubbed first vapor olefins stream in line 33. The cooled scrubbed first vapor olefins stream in line 33 is separated in dry separator 45 to provide an aqueous stream from the boot in line 47 that is removed in manifold line 76, a vaporous light olefins stream comprising C3− hydrocarbons and gases in overhead line 77, and a liquid light olefins stream in bottoms line 78 comprising C3+ hydrocarbons. The vaporous light olefins stream in overhead line 77 is dried in dryer 79a to provide a vaporous product olefins stream in line 112. The liquid light olefins stream in bottoms line 78 is pumped to dryer 79b and dried to provide a liquid product olefins stream in line 114. The product olefin streams in lines 112 and 114 are processed in oligomerization feed preparation section 110 of FIG.

[0041] Referring to oligomerization feed preparation section 110 of Figure 2, a vaporous product olefin stream in line 112 is fed to fractionation section 108. The vaporous product olefin stream in line 112 comprises a C2-olefin stream and may comprise primarily ethylene. In one embodiment, a liquid product olefin stream in line 114 may be fed to fractionation section 108. The liquid product olefin stream in line 114 comprises a C3+ olefin stream and may comprise primarily propylene. The C3 olefin stream may also comprise C4-C8 olefins. In the fractionation section, the vaporous product olefin stream in line 112 and / or the liquid product olefin stream in line 114 are fractionated to provide a light gas stream in line 120 and an olefin-rich stream in line 122.

[0042] In one embodiment, the vaporous product olefin stream in line 112 may be fed to demethanizer fractionation column 116. The vaporous product olefin stream in line 112 may be fed to the top half of demethanizer fractionation column 116. In one aspect, the vaporous product olefin stream in line 112 may be sent to first suction drum 113 and then compressed in first compressor 133. The vaporous product olefin stream may be taken from first compressor 133 in line 115 and sent to first heat exchanger 107. The cooled vaporous product olefin stream is taken from heat exchanger 107 in line 117 and sent to demethanizer fractionation column 116.

[0043] In one embodiment, the liquid product olefin stream in line 114 may be fed to a demethanizer fractionation column 116. The liquid product olefin stream in line 114 may be fed to the bottom half of the demethanizer fractionation column 116. In one aspect, the liquid product olefin stream in line 114 may be sent to a second heat exchanger 109. The cooled liquid product olefin stream is taken from the heat exchanger 109 in line 119 and sent to the demethanizer fractionation column 116. The vaporous product olefin stream and the liquid product olefin stream may be fractionated together in the demethanizer fractionation column 116.

[0044] In one embodiment, the vaporous product olefin stream in line 115 and the liquid product olefin stream in line 114 may be combined and sent to a combined heat exchanger (not shown). The combined heat exchanged streams may be separated in a demethanizer fractionation column 116.

[0045] The vaporous product olefin stream and / or liquid product olefins are preferably fractionated together in demethanizer fractionation column 116 to provide an overhead light gas stream in overhead lights line 118 and an olefin-rich bottoms stream in bottoms line 122, which can be considered a demethanized olefin-rich stream. The overhead light gas stream in line 118 can contain methane lights and lighter gases such as carbon monoxide, carbon dioxide, methane, nitrogen, and hydrogen. Essentially all of the carbon monoxide exits in the overhead lights stream in line 118. The overhead lights stream in line 118 is condensed in demethanizer condenser 123 and fed to demethanizer receiver 124. The condensed lights are refluxed from demethanizer receiver 124 to column 116 in reflux line 121, while the lights stream is taken in net overhead line 120. A reactor purge gas stream in line 126 may be taken from the light gas stream to the oxygenate conversion reactor 16 and a fuel gas stream may be taken in line 127 .

[0046] An olefin-rich stream containing C2+ olefins, typically C2 to C8 olefins, in demethanizer bottoms line 122 is reboiled in demethanizer reboiler 111 and may be split into a reboil stream in line 128 returned to the column and a net olefin-rich stream in net bottoms line 130. The demethanizer bottoms temperature may be from about 0°C (32°F) to about 45°C (113°F), and the pressure may be from about 2.4 MPa(g) (350 psig) to about 3.5 MPa(g) (500 psig). Alternatively, the demethanizer bottoms temperature may be from about -40°C (-40°F) to about 10°C (50°F), and the bottoms pressure may be from about 0.7 MPa(g) (102 psig) to about 2.1 MPa(g) (305 psig).

[0047] The olefin-rich stream contains significant levels of dienes, acetylene, dimethyl ether, and other oxygenates, all of which are poisonous to the oligomerization catalyst. In one embodiment, the olefin-rich stream may be further fractionated to separately prepare ethylene and propylene. If ethylene is sent to selective hydrogenation reactor 150, it may become completely saturated with ethane, which would render it inactive in the oligomerization reactor and unable to oligomerize, adversely affecting jet fuel yield. Therefore, the net olefin-rich stream in line 130 may be further fractionated in deethanizer column 132.

[0048] The net olefin-rich stream in line 130 is deethanized by fractionation in deethanizer column 132 to provide an ethylene stream in net overhead line 134 and a fractionated olefin-rich stream in net deethanized bottoms line 136. The fractionated olefin-rich stream can be considered a deethanized olefin-rich stream. Deethanizer column 130 can operate at a bottoms temperature of from about 43°C (110°F) to about 104°C (220°F) and an overhead pressure of from about 1.8 MPa (260 psig) to about 3.2 MPa (460 psig).

[0049] The ethylene overhead stream in overhead line 138 is condensed in deethanizer condenser 139 and separated in deethanizer receiver 140. Liquid from deethanizer receiver 140 may be refluxed from the bottom of deethanizer receiver 140 back to deethanizer column 132 in reflux line 141. The net overhead vapor stream from deethanizer receiver 140 in line 134 is sent to acetylene feed effluent exchanger 143 where it may be heated by heat exchange with a concentrated ethylene stream in line 212 and combined with a hydrogen stream from line 214 to provide the acetylene converter feed in line 216. The acetylene converter feed stream in line 216 may be further heated in acetylene converter feed heater 145 to provide a heated acetylene converter feed stream in line 217, which is charged to acetylene conversion reactor 210. In acetylene conversion reactor 210, acetylene is converted to ethylene over an acetylene conversion catalyst in the presence of hydrogen, thereby producing a concentrated ethylene stream in line 212. The concentrated ethylene stream in line 212 is cooled in acetylene feed effluent heat exchanger 143 by heat exchange with a net overhead vapor stream in line 134 to provide an ethylene stream in line 213. The deethanized stream in bottoms line 142 may be split between a reboil stream in line 144, which is reboiled in deethanizer reboiler 147 and boiled back to deethanizer column 132 to provide the heating requirements. The acetylene conversion catalyst may be a palladium and silver on aluminum oxide catalyst. Acetylene conversion conditions may include pressures of from about 1.4 MPa(g) (200 psig) to about 2.8 MPa(g) (400 psig) and temperatures of from about 38°C (100°F) to about 93°C (200°F).

[0050] The fractionated olefin-rich stream in net bottoms line 136 may contain oxygenates such as dimethyl ether, methanol, and acetaldehyde in concentrations that poison the selective hydrogenation catalyst. Therefore, the olefin-rich stream in line 136 is sent to a water wash column 150 to absorb oxygenates such as dimethyl ether, methanol, and acetaldehyde from the fractionated olefin-rich stream to provide an oxygenate-rich water wash stream and a washed olefin-rich stream. The washed olefin-rich stream may be oligomerized.

[0051] In water wash column 150, the water wash stream from DME wash water stripper column 160 is sent in cooled stripped wash water line 152 to the upper third of the water wash column and countercurrently contacted with the fractionated olefin-rich stream in net bottoms line 136 that feeds the lower third of the water wash column. Countercurrent contact of the fractionated olefin-rich stream with the water wash stream results in absorption of oxygenates, including DME, from the fractionated olefin-rich stream into the water wash stream. The absorption produces a washed olefin-rich stream in overhead line 154 and an oxygenate-rich water wash stream in bottoms line 156. The washed olefin-rich stream in overhead line 154 has a total oxygenate concentration of 1000 wppm or less, which is acceptable for the selective hydrogenation catalyst in selective hydrogenation reactor 170. Suitably, the washed olefin-rich stream in overhead line 154 has a total oxygenate concentration of 500 wppm or less to accommodate the adsorbent bed size in oxygenate removal unit 180. Preferably, the washed olefin-rich stream in overhead line 154 has a total oxygenate concentration of 50 wppm or less. Wash water column 150 may operate at a bottoms temperature of from about 10°C (50°F) to about 66°C (150°F) and an overhead pressure of from about 2.4 MPa(g) (350 psig) to about 3.2 MPa(g) (450 psig).

[0052] The oxygenate-rich water wash stream in bottoms line 156 is heated in DME wash water exchanger 149 to produce a heated oxygenate-rich water wash stream in line 157, which is fed to DME wash water stripper column 160 to strip DME and other oxygenates. In DME wash water stripper column 160, DME and oxygenates are stripped from the oxygenate-rich water wash stream to produce a recycled DME stream in line 162, which also contains other oxygenates that may be recycled to oxygenate conversion reactor 16 in FIG. 1. A stripped water wash stream is produced in bottoms line 164. A reboil stream in line 166 is removed from the stripped water wash stream in bottoms line 164, reboiled in DME wash stripper reboiler 161, and returned to DME wash water stripper column 160. A cooled stripped wash water stream is taken from the stripped water wash stream in bottoms line 164 and cooled in DME wash water exchanger 149, possibly followed by wash water cooler 151, to produce a cooled stripped wash water stream in line 152 which is recycled to water wash column 150, possibly after being supplemented with a make-up water stream in line 158. In another embodiment, the make-up water stream in line 158 may be sent directly to DME wash water stripper column 160.

[0053] The washed olefin-rich stream in line 154 may be oligomerized, possibly in the liquid phase, in oligomerization reactor 200. However, the washed olefin-rich stream in water wash overhead line 154, which contains C3-C8 olefins, also contains diolefins, which can cause cross-linking polymerization in the oligomerization reactor. Therefore, it may be selectively hydrogenated to convert the diolefins and acetylenes to monoolefins before sending it to the oligomerization reactor. The C4+ olefins in DME stripping line 168 from FIG. 1 may also contain diolefins and therefore benefit from selective hydrogenation prior to oligomerization. The washed olefin-rich stream in water wash overhead line 154 may be combined with the heavy olefin stream in line 168 to provide a combined olefin stream in combined line 169. The combined olefin stream in combined line 169 may be mixed with hydrogen from line 155, possibly heated by heat exchange with a mono-olefin stream in line 174 in heat exchanger 171, and input to selective hydrogenation reactor 170 in selective hydrogenation reactor input line 172. In selective hydrogenation reactor 170, di-olefins and residual acetylene are converted to mono-olefins to provide a mono-olefin stream in line 174. Selective hydrogenation just minimizes the hydrogenation of mono-olefins to paraffins.

[0054] The selective hydrogenation reactor 170 typically operates under relatively mild hydrogenation conditions. These conditions typically result in hydrocarbons existing as liquid phase materials. The reactants are typically maintained under a minimum pressure sufficient to maintain the reactants as liquid phase hydrocarbons. Suitable operating pressures include from about 2.3 MPa(g) (330 psig) to about 3.1 MPa(g) (450 psig). Relatively moderate temperatures of from about 20°C (68°F) to about 100°C (212°F) are typically used. The liquid hourly space velocity of the reactants over the selective hydrogenation catalyst is about 1.0 hr -1 Exceeding 35.0 hours -1To avoid undesirable saturation of significant amounts of monoolefinic hydrocarbons, the molar ratio of hydrogen to diolefinic hydrocarbons in the selective hydrogenation reactor input line 172 entering the bed of selective hydrogenation catalyst is maintained between 1:1 and 4.5:1.

[0055] Suitable selective hydrogenation catalysts include, but are not limited to, catalysts comprising copper and at least one other metal, such as titanium, vanadium, chromium, manganese, cobalt, nickel, zinc, molybdenum, palladium, and cadmium, or mixtures thereof. The metal is preferably supported on an inorganic oxide support, such as, for example, silica and alumina. A monoolefin stream can exit the reactor in line 174 having a higher concentration of monoolefins and a lower concentration of acetylenes and dienes than the selective hydrogenation reactor input stream in line 172. The monoolefin stream in line 174 can have an acetylene and diolefin concentration of about 50 to about 80 wppm or less.

[0056] The mono-olefin stream in line 174 may be oligomerized in oligomerization reactor 200, possibly in mixed or liquid phase. However, the mono-olefin stream still has a high concentration of oxygenates that may suppress oligomerization catalyst activity. Therefore, the selectively hydrogenated stream in line 174 may be transported to oxygenate removal unit 180 for adsorption of DME, water, and other trace oxygenates and residual oxygenates, including water. Oxygenate removal unit 180 may include one or more adsorber vessels 182, 184, such that one or more adsorber vessels 182 or 184 may be fed with the mono-olefin stream in line 174 via appropriate valve control to adsorb oxygenates therefrom, while the other one of adsorber vessels 184 or 182 may be fed with a regenerant stream via line 188 via appropriate valve control to undergo regeneration. The mono-olefin stream in line 174 may flow upwardly through adsorber vessels 182, 184, although downward flow is also preferred. Three adsorber vessels may be used in the oxygenate removal unit. A deoxygenated olefin stream may be recovered from oxygenate removal unit 180 in line 186. An oxygenated regenerant stream may be recovered from oxygenate removal unit 180 in line 190. The deoxygenated olefin stream in line 186 contains C3-C8 olefins and less than 1 wppm of oxygenates, including DME and water.

[0057] When adsorber vessels 182, 184 require regeneration, they may be taken off stream with the selectively hydrogenated stream in line 174 and contacted with heated vaporous regenerant from line 188, through appropriate valve control, in a direction opposite to the normal flow of the olefinic selectively hydrogenated stream. The regenerant may be a clean, inert gas such as nitrogen, hydrogen, natural gas, or light paraffins such as propane, butane, and pentane. The regenerant may fully restore the capacity of the adsorbent in the regenerated vessels 182, 184. Spent regenerant may leave the oxygenate removal unit 180 in spent regenerant line 190. The oxygenate removal unit may operate at an inlet temperature of about 26°C (50°F) to about 66°C (150°F) and an inlet pressure of about 2.3 MPa(g) (330 psig) to about 3 MPa(g) (430 psig). The adsorbent in oxygenate removal unit 180 may be a large pore molecular sieve such as 13X.

[0058] The deoxygenated olefin stream in line 186 can provide an oligomerization input stream in line 198 that can be input to oligomerization reactor 200. Alternatively, or cumulatively, the concentrated ethylene stream in line 213 can be compressed to a higher pressure in compressor 157 and input to one or more oligomerization reactors 200 in the oligomerization input stream in line 198. Oligomerization reactor 200 can include a two-stage reactor system, and each stage can include multiple beds.

[0059] The oligomerization input stream in line 198 may contact an oligomerization catalyst in oligomerization reactor 200 to oligomerize ethylene and propylene and C4+ olefins into oligomers. A third stream containing unreacted C3+ olefins in recycle line 199 may be sent to oligomerization reactor 200. In one embodiment, the third stream in line 199 may be combined with the oligomerization input stream in line 198 and sent to oligomerization reactor 200. The oligomerization reaction generates a large exotherm. As a result, this large exotherm must be managed. To manage the exotherm, the input olefin stream may be diluted with a diluent stream in line 202 to provide a diluted olefin stream to absorb the exotherm. The diluent stream may include a paraffin stream. Additionally, the input olefin stream may be split and fed to multiple oligomerization reactors 200. The oligomerization reaction temperature may be from about 110°C (230°F) to about 260°C (500°F), and the oligomerization pressure may be from about 3.5 MPa(g) (500 psig) to about 8.4 MPa(g) (1200 psig). The input olefin stream in line 198 may be cooled before entering oligomerization reactor 200. The oligomerized stream may be discharged from oligomerization reactor 200 in line 204.

[0060] Figure 3 shows an embodiment in which the deethanizer column and acetylene converter are omitted. Many of the elements in Figure 3 have the same configuration and have the same reference numbers as in Figure 2. Elements in Figure 3 that correspond to elements in Figure 2 but have a different configuration have the same reference numbers as in Figure 2 but with a prime symbol (') appended.

[0061] In the embodiment of Figure 3, fractionation section 108' includes only demethanizer fractionation column 116. The olefin-rich stream in demethanizer net bottoms line 130' is transported directly to water wash column 150. Water wash column 150 absorbs oxygenates from the olefin-rich stream into a cooled, stripped wash water stream in line 152 to provide an oxygenate-rich water wash stream in line 156 and a washed olefin-rich stream in line 154, which can be selectively hydrogenated in selective hydrogenation reactor 170 and / or have oxygenates removed in oxygenate removal unit 180 to provide an input stream in line 198' to oligomerization reactor 200. With the exceptions noted above, Figure 3 is configured and operates like the embodiment shown in Figure 2.

[0062] FIG. 4 illustrates an embodiment in which the deethanizer column 132'' and acetylene converter are moved downstream of the water wash column 150''. Many of the elements in FIG. 4 have the same configuration and have the same reference numbers as in FIG. 2. Elements in FIG. 4 that correspond to elements in FIG. 2 but have a different configuration have the same reference numbers as in FIG. 2 but are prefixed with a double prime symbol ('').

[0063] In the embodiment of FIG. 4 , in fractionation section 108″, the olefin-rich stream in demethanizer net bottoms line 130″ is transported directly to water wash column 150″. Water wash column 150″ absorbs oxygenates from the olefin-rich stream into a cooled, stripped wash water stream in line 152 to provide an oxygenate-rich water wash stream in line 156 and a washed olefin-rich stream in line 154″. The washed olefin-rich stream in line 154″ is dried in dryer 163 to provide a dried washed olefin-rich stream in line 165. The dried washed olefin-rich stream in line 165 is then deethanized in deethanizer fractionation column 132″ to provide a fractionated deethanized olefin-rich stream in deethanizer net bottoms line 136″ and an ethylene stream in deethanizer overhead line 138″. The fractionated de-ethanized olefin-rich stream in deethanizer net bottoms line 136" can be selectively hydrogenated in selective hydrogenation reactor 170 and / or have oxygenates removed in oxygenate removal unit 180 to provide an input stream in line 198" to oligomerization reactor 200. The ethylene stream in deethanizer overhead line 138" can be converted to acetylene in acetylene conversion reactor 210" to produce an enriched ethylene stream in line 134". The enriched ethylene stream can be combined with the mono-olefin stream in line 174 or the deoxygenated olefin stream in line 186 to provide an oligomerization input stream in line 198" that can be oligomerized in oligomerization reactor 200. With the exceptions noted above, FIG. 4 is configured and operates like the embodiment shown in FIG. 2. [Example]

[0064] To demonstrate its effectiveness in removing dienes from an olefin stream, the inventors simulated a selective hydrogenation reactor, where approximately 2400 wppm of dienes was present in the feed to the selective hydrogenation reactor, but less than 65 wppm of dienes was present in the selective hydrogenation product.

[0065] Specific Embodiments While the following will be described in conjunction with specific embodiments, it will be understood that this description is illustrative, but not intended to limit the scope of the preceding description and appended claims.

[0066] A first embodiment of the present disclosure is a method for preparing a hydrocarbon stream for oligomerization, the method comprising: producing a first olefin stream comprising C2-C8 olefins, water, methanol, and dimethyl ether; separating water from the first olefin stream to provide a water-rich stream and a second olefin stream comprising C2-C8 olefins and dimethyl ether; stripping the second olefin stream to provide a first vapor olefin stream comprising C4-olefins and a first liquid olefin stream comprising C4+ olefins; and selectively hydrogenating the first liquid olefin stream. An embodiment of the present disclosure is one, any, or all of the preceding through first embodiments of this paragraph, wherein the stripping of the second olefin stream is performed in a dimethyl ether stripping column. An embodiment of the present disclosure is one, any, or all of the preceding through first embodiments of this paragraph, wherein the first vapor olefin stream comprises dimethyl ether. An embodiment of the present disclosure is one, any, or all of the previous embodiments through the first embodiment of this paragraph, further comprising scrubbing the first vapor olefin stream with caustic in a caustic scrubber to provide a scrubbed first vapor olefin stream. An embodiment of the present disclosure is one, any, or all of the previous embodiments through the first embodiment of this paragraph, wherein the scrubbed first vapor olefin stream is cooled after exiting the caustic scrubber to produce a cooled scrubbed first vapor olefin stream. An embodiment of the present disclosure is one, any, or all of the previous embodiments through the first embodiment of this paragraph, wherein the cooled scrubbed first vapor olefin stream is separated into a second liquid olefin stream and a second vapor olefin stream. An embodiment of the present disclosure is one, any, or all of the previous embodiments through the first embodiment of this paragraph, wherein the second liquid olefin stream and the second vapor olefin stream are dried. An embodiment of the present disclosure is one, any, or all of the preceding embodiment of this paragraph through the first embodiment of this paragraph, further comprising a second oxygenate stripper column upstream of the dimethyl ether stripping column.An embodiment of the present disclosure is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, further comprising oligomerizing the hydrogenated olefin stream to produce an oligomerized stream. An embodiment of the present disclosure is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein the first olefin stream is withdrawn from an oxygenate conversion reactor. An embodiment of the present disclosure is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, further comprising fractionating the first vapor olefin stream to provide a fractionated olefin-rich stream, and absorbing oxygenates from the fractionated olefin-rich stream in a water wash stream to provide an oxygenate-rich water wash stream and a washed olefin-rich stream. An embodiment of the present disclosure is one, any, or all of the preceding embodiments through the first embodiment of this paragraph, wherein the water wash stream is withdrawn from a dimethyl ether wash water stripper column. An embodiment of the present disclosure is one, any, or all of the preceding through first embodiments of this paragraph, further comprising selectively hydrogenating the washed olefin-rich stream and the first liquid olefin stream. An embodiment of the present disclosure is one, any, or all of the preceding through first embodiments of this paragraph, wherein the fractionated olefin-rich stream is a demethanized olefin-rich stream.

[0067] A second embodiment of the present disclosure is a method for preparing a hydrocarbon stream for oligomerization, the method comprising: producing a first olefin stream comprising C2-C8 olefins, water, methanol, and dimethyl ether from an oxygenate conversion reactor; separating water from the first olefin stream to provide a water-rich stream and a second olefin stream comprising C2-C8 olefins and dimethyl ether; stripping the second olefin stream to provide a first vapor olefin stream comprising C4- olefins and a first liquid olefin stream comprising C4+ olefins; selectively hydrogenating the first liquid olefin stream; and oligomerizing the hydrogenated olefin stream to produce an oligomerized stream. One embodiment of the present disclosure is one, any, or all of the previous embodiment through the second embodiment of this paragraph, wherein stripping of the second olefin stream is performed in a dimethyl ether stripping column. An embodiment of the present disclosure is one, any, or all of the previous through second embodiments of this paragraph, further comprising fractionating the first vaporous olefin stream to provide a fractionated olefin-rich stream, and absorbing oxygenates from the fractionated olefin-rich stream in a water wash stream to provide an oxygenate-rich water wash stream and a washed olefin-rich stream. An embodiment of the present disclosure is one, any, or all of the previous through second embodiments of this paragraph, wherein the water wash stream is removed from a dimethyl ether wash water stripper column.

[0068] A third embodiment of the present disclosure is a method for preparing a hydrocarbon stream for oligomerization, the method comprising: producing a first olefin stream comprising C2 to C8 olefins, water, methanol, and dimethyl ether; separating water from the first olefin stream to provide a water-rich stream and a second olefin stream comprising C2 to C8 olefins and dimethyl ether; stripping the second olefin stream to provide a first vapor olefin stream comprising C4- olefins and a first liquid olefin stream comprising C4+ olefins; selectively hydrogenating the first liquid olefin stream and a fractionated olefin-rich stream removed from the first vapor olefin stream; and oligomerizing the hydrogenated olefin stream to produce an oligomerized stream. One embodiment of the present invention is one, any, or all of the previous embodiment of this paragraph through the third embodiment of this paragraph, further comprising: fractionating the first vaporous olefin stream to provide a fractionated olefin-rich stream; absorbing oxygenates from the fractionated olefin-rich stream in a water wash stream to provide an oxygenate-rich water wash stream and a washed olefin-rich stream; and selectively hydrogenating the first liquid olefin stream and the washed olefin-rich stream.

[0069] Without further elaboration, it is believed that, using the preceding description, one skilled in the art can utilize the present disclosure to its fullest extent and easily ascertain the essential characteristics of the present disclosure, and can make various changes and modifications to the present disclosure to adapt it to various uses and conditions, without departing from the spirit and scope of the present disclosure. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way, and are intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

[0070] Above, all temperatures are set forth in degrees Celsius and all parts and percentages are by weight unless otherwise indicated.

Claims

1. 1. A process for preparing a hydrocarbon stream for oligomerization, comprising: Producing a first olefin stream comprising C2 to C8 olefins, water, methanol, and dimethyl ether; separating water from the first olefin stream to provide a water-rich stream and a second olefin stream comprising C2 to C8 olefins and dimethyl ether; stripping the second olefin stream to provide a first vaporous olefin stream comprising C4- olefins and a first liquid olefin stream comprising C4+ olefins; and selectively hydrogenating said first liquid olefin stream.

2. 10. The process of claim 1, wherein said stripping of said second olefin stream occurs in a dimethyl ether stripping column.

3. 3. The method of claim 2, wherein the first vaporous olefin stream comprises dimethyl ether.

4. 3. The method of claim 2, further comprising scrubbing the first vapor olefin stream with caustic in a caustic scrubber to provide a scrubbed first vapor olefin stream.

5. 5. The method of claim 4, wherein the scrubbed first vapor olefin stream is cooled after exiting the caustic scrubber to produce a cooled scrubbed first vapor olefin stream.

6. 6. The method of claim 5, wherein the cooled scrubbed first vapor olefin stream is separated into a second liquid olefin stream and a second vapor olefin stream.

7. 7. The method of claim 6, wherein the second liquid olefin stream and the second vapor olefin stream are dried.

8. 10. The process of claim 1 further comprising a second oxygenate stripper column upstream of the dimethyl ether stripping column.

9. 10. The process of claim 1, further comprising oligomerizing the hydrogenated olefin stream to produce an oligomerized stream.

10. 10. The process of claim 1, wherein the first olefin stream is removed from an oxygenate conversion reactor.

Images