Process for preparing an olefin stream for oligomerization by selective hydrogenation - Patent Application 20070122997

Abstract

A method for preparing an olefin stream for oligomerization includes fractionating an olefin stream to provide a light gas stream and an olefin-enriched stream, which is selectively hydrogenated to convert diolefins to monoolefins to provide a monoolefin stream, and oligomerizing the monoolefin stream over an oligomerization catalyst to provide an oligomerized stream.

Description

[Technical Field]

[0001] The field is the conversion of olefins into fractions. The field may in particular 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 silicoaluminophosphates (SAPOs), are known to promote the conversion of oxygenates, such as methanol, to light olefins. The highly efficient methanol to olefin (MTO) process can convert oxygenates to light olefins, which have typically been considered for plastic production. Light olefins produced from the MTO process are primarily 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 a range of fractions, including jet fuel and diesel range products. The oligomerized fractions can be saturated for use as transportation fuels.

[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 electric motors cannot provide. Jet fuel has an end boiling point specification of less than 300 °C using ASTM D86. Currently, significant incentives are available in certain regions for renewable jet fuel.

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

[0006] The present inventors have devised a method for preparing an olefin stream for oligomerization which comprises fractionating the olefin stream to provide a light gas stream and an olefin-enriched stream. The diolefin stream is selectively hydrogenated to convert diolefins to monoolefins to provide a monoolefin stream, and the monoolefin stream is oligomerized over an oligomerization catalyst to provide an oligomerized stream. [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 process and apparatus of the present disclosure. [Figure 3] FIG. 2 is a schematic diagram of an alternative embodiment of the oligomerization feed preparation method and apparatus of the present disclosure. [Figure 4] FIG. 2 is a schematic diagram of a further alternative embodiment of the oligomerization feed preparation method 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 the subject in downstream communication can operatively flow from the object in fluid communication.

[0010] The term "upstream communication" means that at least a portion of a fluid flowing from a main body side in upstream communication can operatively flow to an object side 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 the object side is out of downstream communication with the subject side that it bypasses, at least within the extent of the bypass.

[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 top of the column to condense and reflux a portion of the overhead stream back 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 top and bottom lines refer to the net lines from the column to the 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. Stripping columns typically feed to a top tray and remove the main product from the bottom. A tower may also refer to an extraction tower for separating one or more components from a stream into an extract stream by liquid-liquid contact. A tower may also refer to an absorption tower 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 a top 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 yields of said fractions by both mass and volume, in which a graph of temperature versus mass % distilled is generated 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 sometimes 95 percent by weight of a sample boils using ASTM D-86 or TBP, respectively.

[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 terms "green diesel" or "renewable jet fuel" refer to diesel containing hydrocarbons not derived from fossil fuel sources.

[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-enriched stream" means that the enriched stream exiting the vessel has a higher concentration of the component than the feed to the vessel, and preferably than all other streams removed 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 the component than the feed to the vessel, and preferably than all other streams removed 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 olefin hydrocarbons are susceptible 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 about 100 to about 1000 wppm CO, about 50 to about 500 wppm CO, about 1 to about 1.5 wt.% dimethyl ether (DME), about 20 to about 50 wppm acetylene, and about 1000 to about 3000 wppm dienes, all of which must be addressed before being sent to the oligomerization reactor. The olefin reactor effluent may also contain unreacted methanol.

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

[0028] Referring to the process and apparatus 10 of FIG. 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 vaporous reactor effluent stream in line 14 is removed from the oxygenate conversion reactor 16, which periodically or continuously circulates 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 for the conversion of oxygenates to produce light olefin products and oxygenate-containing by-products. The hot vaporous reactor effluent stream may include light olefins, water, and oxygenates. The oxygenate conversion reactor 16 may be operated to produce substantial or predominantly propylene.

[0029] The hot vaporous reactor effluent 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 vaporous reactor effluent is desuperheated, organic acids are neutralized, and catalyst fines are removed by direct contact with a water stream provided in line 19 (which may be obtained from the stripped water stream in line 21). The quenched reactor effluent in line 22 leaves quench tower 20 and is provided to product separation tower 24, which may be in downstream communication with oxygenate conversion reactor 16.

[0030] Product separation column 24 includes two sections for separating the reactor effluent into a product olefin stream in top line 40, an intermediate liquid stream in middle line 28, and a product water stream in bottom line 26. The first, or lower, section receives the quenched reactor effluent in line 22. In the lower section, most of the heat is removed from the quenched reactor effluent while partially condensing the water in the quenched reactor effluent to produce a product water stream in bottom line 26 containing a portion of the oxygenate by-products in the quenched reactor effluent in line 22. A portion of the product water stream is cooled and pumped back to the top of the first section of product separation column 24 to cool the quenched reactor effluent in line 22. A second portion of the product water stream in bottom 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 can also be sent to water stripper column 30. A water stripper column 30 may be in downstream communication with product separation column 24 .

[0031] The vapor stream from the first section of product separation column 24 is sent to the second, or upper, section of the product separator. An intermediate stream in line 28 containing hydrocarbons, oxygenate by-products, and water in a liquid phase is removed at the bottom of the upper section. A portion of the intermediate stream in line 28 is cooled and sent as a recycle stream to the top of the second section of product separation column 24. The remainder of the intermediate stream in line 28 is sent to coalescer 29 to separate a hydrocarbon overhead stream from the 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 in line 40 containing olefins from product separation column 24 is sent to compression section 80.

[0032] The product water stream in line 36 contains lean 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 in top line 49 that is rich in both methanol and at least another oxygenate, and an oxygenate-lean water stream in bottom 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 is discharged to the waste water stream in line 23.

[0033] In one embodiment, water stripper column 30 may operate 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 water stripper column 30.

[0034] The product olefins stream in product overhead line 40 carries valuable olefin product that needs to be recovered. Compression section 80 increases the pressure of the product olefins stream necessary for downstream processing such as that used in conventional light olefins recovery units. Compression section 80 may include a first knockout drum 82 that separates the product olefins stream into a first pressurized olefins-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 a first oxygenate-rich aqueous stream in bottoms line 84. The olefins-rich stream in overhead line 83 may be fed to compressor 85, cooled, and sent to second knockout drum 86. The aqueous stream in bottoms line 84 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 .

[0035] Compression section 80 may include a second knockout drum 86 that separates the first pressurized olefin-rich stream into a second pressurized olefin-rich stream in an upper line 87 at a pressure of from about 300 KPa(g) (44 psig) to about 400 KPa(g) (58 psig) and a temperature of from about 20° C. (68° F.) to about 60° C. (140° F.), and a second oxygenate-rich aqueous stream in a bottoms line 88. The second olefin-rich stream in upper line 87 may be fed to a compressor 89, cooled, and sent to a 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 second pressurized olefin-rich stream into a third pressurized olefin-rich stream in top line 91 and a third oxygenate-rich aqueous stream in bottom line 92. The third olefin-rich stream in top line 91 may be fed to oxygenate absorber 50. The aqueous stream in bottom line 92 is sent via manifold line 76 to return line 32, which returns the aqueous 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. Final discharge pressures may range from about 1.0 MPa(g) (145 psig) to about 2.1 MPa(g) (305 psig). The compressor discharge streams may be cooled to about ambient temperature by conventional heat transfer methods.

[0038] 1 , in accordance with a preferred embodiment, at least a portion of the compressed product stream via top line 91 is contacted in oxygenate absorber 50 with a cooled lean water stream in line 102 under conditions effective to absorb at least a portion of the oxygenates in the effluent stream, without directly removing water from product separation column 24 prior to oxygenate removal. Contact in oxygenate absorber 50 produces an absorbed olefins-rich stream in top line 54 and an absorbed water-rich stream in bottoms line 52, the absorbed water stream having a portion of the oxygenates in the effluent stream. Oxygenate absorber 50 may have operating conditions including a bottoms temperature range of about 30° C. (86° F.) to about 60° C. (140° F.) and a top pressure range of about 700 KPa(g) (101 psig) to about 1 MPa(g) (145 psig).

[0039] The absorption olefin-rich stream in top line 54 may be fed to third-stage knockout drum 60, where a gaseous olefin stream is taken in top line 61 to third compressor 62, while water and oxygenates are taken in bottom line 59 to manifold line 76. Third-stage knockout drum 60 may be operated at about the same pressure as the top of the oxygenate absorber 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 from stripper top line 71, partially condensed by cooling in feed chiller 64, and fed in line 65 to stripper separator 66. The stripper separator 66 separates an oxygenate-containing aqueous stream in the boot portion of line 67, which is fed to manifold line 76, a light olefin vapor stream containing C3- olefins in top line 68, 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 lighter vapors in stripper top line 71 from the heavy olefin liquid stream in stripper bottom line 168. In one embodiment, a reboil stream may be taken from the heavy olefin liquid stream in stripper bottom line 168, which is reboiled in DME stripper reboiler 167 and returned to the DME stripper column 70. Most of the oxygenates are stripped in stripper top line 71 and recycled to the stripper separator 66 for separation after cooling. The bottoms stream exiting DME stripper column 70 can be sent through line 168 and via line 169 to selective hydrogenation reactor 170, as shown in Figure 2. This stream contains mostly C4+ olefins, but also diolefins that will inhibit the oligomerization catalyst requiring selective hydrogenation. DME stripper column 70 can be operated at a top temperature of from about 60°C (140°F) to about 82°C (180°F) and a bottoms pressure of from about 1.8 MPa(g) (260 psig) to about 2.2 MPa(g) (320 psig).Stripper separator 66 may be operated 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 upper line 68 is scrubbed in caustic scrubber 73 by countercurrent contact with caustic solution in line 42 to absorb acid gases, such as carbon dioxide, from the light olefin vapors exiting caustic scrubber 73 in upper line 74. The acid gas-enriched caustic solution exits caustic scrubber 73 in line 44. Caustic scrubber 73 may be operated at an upper 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 upper line 74 can be cooled by propylene refrigerant in dry feed chiller 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 a vaporous light olefins stream comprising C3− hydrocarbons and gases in upper line 77 and a liquid light olefins stream comprising C3+ hydrocarbons in bottom line 78, with an aqueous stream from the boot in line 47 sent to manifold line 76. The vaporous light olefins stream in upper line 77 is dried in dryer 79a to provide a vaporous product olefins stream in line 112. The liquid light olefins stream in bottom line 78 is pumped to dryer 79b to be dried and 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 may comprise 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 may comprise a C3+ olefin stream and may comprise primarily propylene. The C3 olefin stream may also comprise C4 to 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-enriched stream in line 122.

[0042] In one embodiment, the vaporous product olefin stream in line 112 may be fed to demethanizer fractionator 116. The vaporous product olefin stream in line 112 may be fed to the top half of demethanizer fractionator 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 removed from first compressor 133 in line 115 and sent to first heat exchanger 107. The cooled vaporous product olefin stream is removed from heat exchanger 107 in line 117 and sent to demethanizer fractionator 116.

[0043] In one embodiment, the liquid product olefin stream in line 114 may be fed to demethanizer fractionator 116. The liquid product olefin stream in line 114 may be fed to the bottom half of demethanizer fractionator 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 removed from heat exchanger 109 in line 119 and sent to demethanizer fractionator 116. The vaporous product olefin stream and the liquid product olefin stream may be fractionated together in demethanizer fractionator 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 exchange streams may be separated in demethanizer fractionator 116.

[0045] The vaporous product olefin stream and / or liquid product olefins are preferably co-fractionated in demethanizer fractionator 116 to provide an upper light gas stream in upper light gas line 118 and an olefin-rich bottoms stream in bottoms line 122, which may be considered a demethanized olefin-rich stream. The upper light gas stream in line 118 may include methane light gases and lighter gases such as carbon monoxide, carbon dioxide, methane, nitrogen, and hydrogen. Essentially all of the carbon monoxide is removed from the upper light gas stream in line 118. The upper light gas stream in line 118 is condensed in demethanizer condenser 123 and fed to demethanizer receiver 124. The condensed light gases are refluxed from demethanizer receiver 124 to column 116 in reflux line 121, while the light gas stream is removed in net tops 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 can be split into a reboil stream in line 128 that is reboiled in demethanizer reboiler 111 and returned to the column, and a net olefin-rich stream in net bottoms line 130. The demethanizer bottoms temperature can be from about 0°C (32°F) to about 45°C (113°F), and the pressure can be from about 2.4 MPa(g) (350 psig) to about 3.5 MPa(g) (500 psig). Alternatively, the demethanizer bottoms temperature can be from about -40°C (-40°F) to about 10°C (50°F), and the bottoms pressure can be from about 0.7 MPa(g) (102 psig) to about 2.1 MPa(g) (305 psig).

[0047] The olefin-rich stream contains significant amounts of dienes, acetylene, dimethyl ether, and other oxygenates that are poisonous to the oligomerization catalyst. In one embodiment, the olefin-rich stream can be further fractionated to separately prepare ethylene and propylene. If the ethylene is sent to the selective hydrogenation reactor 170, it may become completely saturated with ethane, become inactive in the oligomerization reactor, and be unable to oligomerize, adversely affecting jet fuel yield. Therefore, the net olefin-rich stream in line 130 can be further fractionated in a deethanizer 132.

[0048] The net olefin-rich stream in line 130 is deethanized by fractionation in deethanizer 132 to provide an ethylene stream in net tops line 134 and a fractionated olefin-rich stream in deethanizer net bottoms line 136. The fractionated olefin-rich stream can be considered a deethanized olefin-rich stream. Deethanizer 132 can be operated at a bottoms temperature of from about 43°C (110°F) to about 104°C (220°F) and a top pressure of from about 1.8 MPa(g) (260 psig) to about 3.2 MPa(g) (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 through reflux line 141 to deethanizer 132. 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 in line 214 to provide an acetylene conversion reactor feed stream in line 216. The acetylene conversion reactor feed stream in line 216 may be further heated in acetylene conversion reactor feed heater 145 to provide a heated acetylene conversion reactor 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 exchanger 143 by heat exchange with the 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 into a reboiler stream in line 144. This reboiler stream is reboiled in deethanizer reboiler 147 and boiled back to deethanizer 132 to meet the tower heat requirements. The acetylene conversion catalyst may be a palladium and silver on aluminum oxide catalyst. Acetylene conversion conditions can 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 and the oligomerization 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 tower 150, the water wash stream from DME wash water stripper tower 160 is sent to the top third of the water wash tower in cooled stripped wash water line 152 for countercurrent contact with the fractionated olefin-rich stream in net bottoms line 136, which is fed to the bottom third of the water wash tower. Countercurrent contact between the fractionated olefin-rich stream and the water wash stream results in absorption of oxygenates, including DME, from the fractionated olefin-rich stream into the water wash stream. Absorption produces a washed olefin-rich stream in top line 154 and an oxygenate-rich water wash stream in bottoms line 156. The washed olefin-rich stream in top 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 top line 154 has a total oxygenate concentration of 500 wppm or less to accommodate a reasonable adsorbent bed size in oxygenate removal unit 180. Preferably, the washed olefin-rich stream in top line 154 has a total oxygenate concentration of 50 wppm or less. Water wash column 150 may be operated at a bottom temperature of from about 10°C (50°F) to about 66°C (150°F) and a top pressure of from about 2.4 MPa(g) (350 psig) to about 3.2 MPa(g) (450 psig).

[0052] The oxygenate-rich wash stream in bottoms line 156 is heated in DME wash water exchanger 149 to produce a heated oxygenate-rich 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 wash stream to produce a recycled DME stream in line 162, which also contains other oxygenates that can be recycled to oxygenate conversion reactor 16 of FIG. 1. A stripped water wash stream is produced in bottoms line 164. A reboiler stream in line 166 is removed from the stripped water wash stream in bottoms line 164, reboiled in DME wash water 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, optionally 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 after being supplemented, as needed, with a make-up water stream in line 158. In an alternative embodiment, the make-up water stream in line 158 can be sent directly to DME wash water stripper column 160.

[0053] The washed olefin-rich stream in line 154 may be oligomerized in the liquid phase in oligomerization reactor 200, if desired. However, the washed olefin-rich stream in water wash top line 154, which contains C3-C8 olefins, also contains diolefins, which can cause cross-polymerization in the oligomerization reactor. Therefore, it can be selectively hydrogenated to convert the diolefins and acetylenes to monoolefins before sending it to the oligomerization reactor. The C4+ olefins in DME-stripped line 168 from FIG. 1 may also contain diolefins and may also advantageously be subjected to selective hydrogenation before oligomerization. The washed olefin-rich stream in water wash top line 154 may be combined with a heavy olefin stream in line 168 to provide a combined olefin stream in combination line 169. The combined olefin stream in combination line 169 can be mixed with hydrogen from line 155, optionally heated in heat exchanger 171 by heat exchange with a mono-olefin stream in line 174, 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 provides just minimal hydrogenation of mono-olefins to paraffins.

[0054] The selective hydrogenation reactor 170 typically operates under relatively mild hydrogenation conditions. These conditions typically result in the 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 Over 35.0 hours -1To avoid undesired saturation of significant amounts of monoolefin hydrocarbons, the molar ratio of hydrogen to diolefin hydrocarbons in the selective hydrogenation reactor input line 172 entering the selective hydrogenation catalyst bed 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 contain 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, optionally in mixed phase or liquid phase. However, the mono-olefin stream still has a high concentration of oxygenates that may inhibit oligomerization catalyst activity. Therefore, the selectively hydrogenated stream in line 174 may be transported to oxygenate removal unit 180 for adsorption of residual oxygenates, including DME, water, and other trace oxygenates. Oxygenate removal unit 180 may comprise one or more adsorption vessels 182, 184, such that one or more of adsorption vessels 182 or 184 may be fed with the mono-olefin stream in line 174 and adsorb oxygenates therefrom by appropriate valve control, while one of the other adsorption vessels 184 or 182 may be fed with a regeneration stream from line 188 and undergo regeneration by appropriate valve control. The mono-olefin stream in line 174 may flow upward through adsorption vessels 182, 184, although downward flow is also suitable. Three adsorption vessels may be used in the oxygenate removal unit. An oxygenate-depleted olefin stream may be withdrawn from oxygenate removal unit 180 in line 186. A recycle stream containing oxygenates may be withdrawn from oxygenate removal unit 180 in line 190. The oxygenate-depleted olefin stream in line 186 comprises C3-C8 olefins and up to 1 wppm of oxygenates including DME and water.

[0057] When regeneration of the adsorption vessels 182, 184 is required, the adsorption vessels can be removed from flow with the selectively hydrogenated stream in line 174 by appropriate valve control and contacted with heated vaporous regeneration fluid from line 188 in a direction opposite to the normal flow of the selectively hydrogenated olefin stream. The regeneration fluid can be a clean inert gas such as nitrogen, hydrogen, natural gas, or light paraffins such as propane, butane, and pentane. The regeneration fluid can fully restore the capacity of the adsorbent in the regenerated vessels 182, 184. Spent regeneration fluid can exit the oxygenate removal unit 180 in spent regeneration fluid line 190. The oxygenate removal unit can be operated at an inlet temperature of about 10°C (50°F) to about 66°C (150°F) and an inlet pressure of about 2.3 MPa (gauge) (330 psig) to about 3 MPa (gauge) (430 psig). The adsorbent in oxygenate removal unit 180 can be a large pore molecular sieve such as 13X.

[0058] The oxygenate-depleted olefin stream in line 186 can provide an oligomerization feed stream in line 198 that can be charged 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 charged to one or more oligomerization reactors 200 in the oligomerization feed 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 can be contacted with an oligomerization catalyst in oligomerization reactor 200 to oligomerize ethylene, propylene, and C4+ olefins into oligomers. A third stream containing unreacted C3+ olefins in recycle line 199 can be sent to oligomerization reactor 200. In one embodiment, the third stream in line 199 can 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 can be diluted with a dilution stream in line 202 to provide a dilute olefin stream that absorbs the exotherm. The dilution stream can include a paraffin stream. Additionally, the input olefin stream can be split and fed to multiple oligomerization reactors 200. The oligomerization reaction temperature can be from about 110°C (230°F) to about 260°C (500°F), and the oligomerization pressure can be from about 3.5 MPag (500 psig) to about 8.4 MPag (1200 psig). The input olefin stream in line 198 can be cooled before entering oligomerization reactor 200. The oligomerization stream can be discharged from oligomerization reactor 200 in line 204.

[0060] Figure 3 shows an embodiment in which the deethanizer and acetylene shift reactor are omitted. Many of the elements in Figure 3 are configured the same as in Figure 2 and are numbered the same. Elements in Figure 3 that correspond to elements in Figure 2 but are configured differently are numbered the same as in Figure 2 but with a prime symbol (').

[0061] In the embodiment of Figure 3, fractionation section 108' comprises only demethanizer fractionator 116. The olefin-rich stream in demethanizer net bottoms line 130' is transported directly to water wash tower 150, which 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 olefins stream in line 154, which is selectively hydrogenated in selective hydrogenation reactor 170 and / or has 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 132'' and acetylene conversion reactor are moved downstream of the water wash column 150''. Many of the elements in FIG. 4 are configured the same as in FIG. 2 and are numbered the same. Elements in FIG. 4 that correspond to elements in FIG. 2 but are configured differently are numbered the same as in FIG. 2 but 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 olefins stream in line 154″. The washed olefins stream in line 154″ is dried in dryer 163 to provide a dried, washed olefins stream in line 165. The dried, washed olefins stream in line 165 is then deethanized in deethanizer fractionator 132″ to provide a fractionated olefins-rich stream in deethanizer net bottoms line 136″ and an ethylene stream in deethanizer tops line 138″. The fractionated olefin-rich stream in deethanizer net bottoms line 136" can be selectively hydrogenated in selective hydrogenation reactor 170 and / or subjected to oxygenate removal in oxygenate removal unit 180 to provide an input stream in line 198" to oligomerization reactor 200. The ethylene stream in deethanizer overheads line 138" can be subjected to acetylene conversion in acetylene conversion reactor 210" to produce an enriched ethylene stream in line 134". The enriched ethylene stream can be combined with the mono-olefins stream in line 174 or the oxygenate-depleted olefins 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] The operation of an acetylene shift reactor was simulated. More than 150 molar ppm of acetylene was present in the acetylene shift reactor feed stream to the acetylene shift reactor. Hydrogen was added to the acetylene shift reactor feed stream and heated. After hydrogenation in the reactor, the acetylene shift reactor product had less than 50 molar ppm of acetylene.

[0065] Specific Embodiments While the following will be described in conjunction with specific embodiments, it should 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 treating an olefin stream, comprising: fractionating the olefin stream to provide a light gas stream and an olefin-enriched stream; selectively hydrogenating the olefin-enriched stream to convert diolefins to mono-olefins and provide a mono-olefin stream; and oligomerizing the mono-olefin stream over an oligomerization catalyst to provide an oligomerized stream. One embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, further comprising absorbing oxygenates from the olefin-enriched stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-enriched stream, wherein the selectively hydrogenated olefin-enriched stream is the washed olefin-enriched stream. One embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the fractionation step comprises demethanizing the olefin stream to provide a light gas stream and an olefin-enriched stream. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments in this section up to the first embodiment of this section, further comprising fractionating the olefin-enriched stream to provide a fractionated olefin-enriched stream and an ethylene stream. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments in this section up to the first embodiment of this section, further comprising absorbing oxygenates from the fractionated olefin-enriched stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-enriched stream, wherein the olefin-enriched stream that is selectively hydrogenated is the washed olefin-enriched stream. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments in this section up to the first embodiment of this section, further comprising absorbing oxygenates from the fractionated olefin-enriched stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-enriched stream, wherein the olefin-enriched stream that is selectively hydrogenated is the washed olefin-enriched stream. An embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, further comprising absorbing oxygenates from the mono-olefin stream prior to oligomerizing the mono-olefin stream.

[0014] An embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, further comprising converting acetylene in the ethylene stream to ethylene in the presence of hydrogen to provide an enriched ethylene stream.

[0015] An embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, further comprising oligomerizing the enriched ethylene stream.

[0016] An embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, further comprising co-oligomerizing the enriched ethylene stream and a mono-olefin stream.

[0017] An embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, further comprising compressing the product olefin stream to provide a compressed product olefin stream; stripping the compressed product olefin stream to provide a light olefin stream and a heavy olefin stream; and selectively hydrogenating the heavy olefin stream with the olefin-rich stream to convert di-olefins to mono-olefins to provide a mono-olefin stream. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the olefin-rich stream is a demethanized olefin-rich stream. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the olefin stream is removed from an oxygenate conversion reactor. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the oxygenates absorbed from the olefin-rich stream comprise one or more of dimethyl ether, methanol, and acetaldehyde. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the olefin-rich stream is a demethanized olefin-rich stream comprising C2 to C8 olefins. An embodiment of the present disclosure is any one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the olefin-rich stream comprises C3 to C8 olefins.An embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section through the first embodiment of this section, wherein the lighter gas stream comprises carbon monoxide, carbon dioxide, nitrogen, hydrogen, and methane.

[0067] A second embodiment of the present disclosure is a method for treating an olefin stream, comprising: fractionating the olefin stream to provide a light gas stream and an olefin-enriched stream; absorbing oxygenates from the olefin-enriched stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-enriched stream; selectively hydrogenating the washed olefin-enriched stream to convert diolefins to monoolefins and provide a mono-olefin stream; and oligomerizing the mono-olefin stream over an oligomerization catalyst to provide an oligomerized stream. One embodiment of the present disclosure is one, any, or all of the preceding embodiments of this section up to the second embodiment of this section, further comprising compressing the product olefin stream to provide a compressed product olefin stream; stripping the compressed product olefin stream to provide a light olefin stream and a heavy olefin stream; and selectively hydrogenating the heavy olefin stream with the washed demethanized olefin-enriched stream to convert diolefins to mono-olefins and provide a mono-olefin stream.

[0068] A third embodiment of the present disclosure is a method for treating an olefin stream, the method comprising: fractionating a vaporous olefin stream and a liquid olefin stream to provide a light gas stream and an olefin-enriched stream; selectively hydrogenating the olefin-enriched stream to convert diolefins to mono-olefins and provide a mono-olefin stream; and oligomerizing the mono-olefin stream over an oligomerization catalyst to provide an oligomerized 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 method for treating an olefin stream, comprising: fractionating the olefin stream to provide a light gas stream and an olefin-enriched stream; selectively hydrogenating the olefin-rich stream to convert diolefins to monoolefins and provide a monoolefin stream; and oligomerizing said monoolefin stream over an oligomerization catalyst to provide an oligomerized stream.

2. 10. The process of claim 1, further comprising absorbing oxygenates from the olefin-rich stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-rich stream, wherein the olefin-rich stream to be selectively hydrogenated is the washed olefin-rich stream.

3. 10. The process of claim 1, wherein said fractionation step comprises demethanizing said olefin stream to provide said light gas stream and said olefin-enriched stream.

4. 4. The process of claim 3, further comprising fractionating the olefin-rich stream to provide a fractionated olefin-rich stream and an ethylene stream.

5. 5. The process of claim 4, further comprising absorbing oxygenates from the fractionated olefin-rich stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-rich stream, wherein the olefin-rich stream to be selectively hydrogenated is the washed olefin-rich stream.

6. 4. The process of claim 3, further comprising absorbing oxygenates from the fractionated olefin-rich stream into a water wash stream to provide an oxygenate-enriched water wash stream and a washed olefin-rich stream, wherein the olefin-rich stream to be selectively hydrogenated is the washed olefin-rich stream.

7. 10. The process of claim 1, further comprising absorbing oxygenates from said monoolefin stream prior to oligomerizing said monoolefin stream.

8. 5. The method of claim 4, further comprising converting acetylene in the ethylene stream to ethylene in the presence of hydrogen to provide a concentrated ethylene stream.

9. 9. The method of claim 8, further comprising oligomerizing the concentrated ethylene stream.

10. 10. The process of claim 9, further comprising co-oligomerizing said enriched ethylene stream and said monoolefin stream.

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