ALKANES AND ALKENES CONVERSION TO HIGH OCTANE GASOLINE

Abstract: Lower molecular weight paraffins and olefins are converted to high octane gasoline, rich in alkylated aromatics, in a two-stage process catalysed by an intermediate pore zeolite. A high-temperature first stage (110) is followed by a lower temperature second stage (120), the ratio of olefins to paraffins in the first stage being maintained at a level sufficient to maintain essentially isothermal reaction conditions. The preferred means for effecting the conversion include a transport riser reactor (210) and turbulent bed reactor (220) combination.

Description: ALKANES AND ALKENES CONVERSION TO HIGH OCTANE GASOLINE This invention relates to the conversion of light paraffins and olefins to high octane gasoline. US-A-3,960,978 and 4,021,502 disclose conversion of gaseous olefins in the range of ethylene to pentene, either alone or in admixture with paraffins, into an olefinic gasoline blending stock by contact with ZSM-5 or a related zeolite. US-A-3,827,968 discloses a two stage operation wherein a mixed feed containing paraffins and olefins is upgraded in the absence of added hydrogen to a highly aromatic gasoline' product. In a first stage oligo erisation reaction, olefins are upgraded, under relatively mild conditions with a catalyst having the structure of ZSM-5, to higher molecular weight liquid hydrocarbons, which are converted to an aromatic product in a second stage. A gas phase highly paraffinic stream is withdrawn as by-product from the first stage. We have now discovered that mixtures of alkanes and alkenes can be converted to high octane gasoline rich in alkylated aromatics, with high alkene conversion, by combining an initial high temperature aromatisation step with a subsequent lower temperature oligomerisation and alkylation step, provided that the alkene content in the initial step is sufficiently high to provide a heat of reaction which will balance the endothermic reaction of the alkanes while maintaining the overall reaction at a high temperature. The reaction in both conversion steps is catalysed by an acidic, medium pore, crystalline metallosilicate zeolite. Uniquely, aromatics formed in the first reaction zone are alkylated and alkenes oligomerised to produce high octane gasoline. More particularly, the invention comprises an improved process for the conversion of lower alkane and alkene hydrocarbons to high octane gasoline comprising: (a) contacting a hydrocarbon feedstock comprising lower alkanes and alkenes with a fluidised bed of acidic, shape selective metallosilicate catalyst in a first conversion zone under high temperature alkane conversion conditions wherein said feedstock contains an amount of lower alkene sufficient to provide an exotherm sufficient to maintain near isothermal reaction conditions whereby an effluent stream is produced comprising higher aliphatic hydrocarbons rich in aromatics; (b) contacting said effluent stream and, optionally, an alkene feedstock with a fluidised bed of acidic, metallosilicate catalyst in a second conversion zone at low temperature under oligomerisation and alkylation conditions whereby a C5+ gasoline boiling range product is produced rich in alkylated aromatics. The present invention may be implemented in a novel reactor system for the conversion of alkanes and alkenes to C5+ gasoline boiling range hydrocarbons rich in aromatics, comprising in combination: first reaction means for containing a fluidised bed of metallosilicate catalyst and hydrocarbon feedstock at high temperature reaction conditions; heater means operatively connected to said first reactor for receiving and preheating a portion of said hydrocarbon feedstock; second reactor means for containing a fluidised bed of metallosilicate catalyst at low temperature operatively connected to said first reactor means to receive effluent therefrom; heat exchange means for cooling first reactor effluent receivably connected to said first reactor and in communication with said second reactor; catalyst regenerator reactor means operatively connected to said first and second reactor means for regenerating spent catalyst therefrom; separator means operatively connected to said second reactor to receive effluent therefrom and separate product. £lief_De^cription_of_the_ rawi_Q3S Fig. 1 is a schematic drawing of a prior art ("MOG") process design for the conversion of olefins to gasoline. Fig. 2 is a schematic drawing of a process design for the present invention. Fig. 3 is a schematic drawing of a process design for the present invention, illustrating a novel configuration for catalyst regeneration and fuel gas conversion with C3 hydrocarbons. Fig. 4 is a schematic drawing of a process design for the present invention illustrating novel reactor configuration for C4- conversion. Fig. 5 is a schematic drawing of a process design for the present invention illustrating novel reactor configuration for fuel gas conversion. Fig. 6 is a schematic drawing showing the integration of an MOG process into an unsaturated gas plant in accordance with the present invention. From one aspect the present invention may be regarded as improving the prior art "MOG" process, to produce high olefin conversion as part of a unique process for high octane gasoline production. The MOG process is a well-known, continuous process for upgrading light olefins, such as FCC product components, to liquid hydrocarbons including fuel products, by oligomerising olefinic components. The preferred MOG feedstock contains about 10 to 90 wt% C2-C4 alkenes, with non-deleterious components, such as methane and other paraffins and inert gases, optionally present. A particularly useful feedstock is the light gas by-product of FCC gas oil cracking, containing typically 10-40 mole % C2-C4 olefins and 5-35 mole % H2 with varying amounts of C1-C3 paraffins and inert gas, such as 2. The process may be tolerant of a wide range of lower alkanes, from 0 to 90%. Preferred feedstocks contain more than 50 wt% C1-C4 lower aliphatic hydrocarbons, and contain sufficient olefins to provide total olefinic partial pressure of at least 50 kPa. Conversion of lower olefins, especially ethene, propene and butenes, over HZSM-5 is effective at moderately elevated temperatures and pressures, as disclosed in US-A-4,456,779, 4,497,968 and 4,433,185. Catalysts useful in the MOG process, and also in the process of the present invention, include a unique group of zeolites, of intermediate pore size (between 0.5 and 0.7 hm) . Most prominent among these is zeolite ZSM-5, which is usually synthesised with a metal such as Al, B, Ga, or Fe in tetrahedral coordination in the zeolitic framework, but such metals are not necessarily present, as shown in CA-A-1,121,975 which discloses zeolite ZSM-5 consisting essentially of silica. The oligomerisation catalyst preferred for use in the process of the present invention includes the intermediate pore zeolites having a silica to alumina ratio of about 20:1 or greater, a constraint index of about 1-12, and acid cracking activity (alpha value) of about 2-200. Representative zeolites are ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38 and ZSM-48, defined respectively by the x-ray data set forth in US-A- 3,702,886, 3,709,979, 3,832,449, 4,076,979, 4,076,842, 4,016,245, 4,046,859 and 4,375,573. While suitable zeolites having a non-silica metal oxide to silica molar ratio of 20:1 to 200:1 or higher may be used, it is advantageous to employ ZSM-5 having a silica alumina molar ratio of about 25:1 to 70:1, suitably modified. A typical catalyst for use in the present invention comprises alu inosilicate ZSM-5 zeolite with 5 to 95 wt% silica, clay and/or alumina binder. The zeolite may be employed in the acid form, ion exchanged or impregnated with one or more suitable metals, such as Ga, Pd, Zn, Ni, Co and/or other metals of Periodic Groups III to VIII. Ni-exchanged or impregnated catalyst is particularly useful in converting ethene under low severity conditions. The zeolite may include other components, generally one or more metals of Group IV, IIB, IIIB, VA, VIA or VIIIA of the Periodic Table (IDPAC) . Useful hydrogenation components include the noble metals of Group VIIIA, especially platinum, but other noble metals, such as palladium, gold, silver, rhenium or rhodium, may also be used. Base metal hydrogenation components may also be used, especially nickel, cobalt, molybdenum, tungsten, copper or zinc. The catalyst may include two or more catalytic components, such as a metallic oligomerisation component (eg, ionic Ni + 2) and a shape-selective medium pore acidic oligomerisation catalyst (such as ZSM-5 zeolite) , which components may be present in admixture or combined in a unitary bifunctional solid particle. A favoured Ni-ZSM-5 ethylene conversion catalyst is described in USSN 893,522 dated 4 August 1986. ZSM-5 type zeolites are particularly useful in the process of the invention because of their regenerability, long life and stability under extreme conditions of operation. Usually the zeolite is of crystal size from 0.01 to 2/*m, preferably In Fig. 1 an olefin-rich feedstock 10 is preheated in heater 11 and passed to reactor 12 containing a fluidised bed of acidic, shape selective metallosilicate catalyst, preferably ZSM-5. The catalyst may have an acid cracking value of about 2 to 35, preferably about 2-5. The feedstock is preheated to a temperature of 65-175°C and the reactor operating conditions comprise temperatures of about 215-535°C and pressures of about 50-2000 kPa and a weight hourly space velocity (WHSV) based on active catalyst of about 0.5-10. The reactor effluent 13 is cooled, optionally in indirect heat exchange with feedstock 14 and cooling water 22 and separated in separator 15 to produce liquid C5+ gasoline 16 and vapour product 17. Spent catalyst is passed to regenerator vessel 18 via line 19 for oxidative regeneration with air 23 and regenerated catalyst is recycled to reactor 12 through line 20. Under these conditions greater than 80% of the lower olefins in the feedstock are converted to higher hydrocarbons. The conversion of paraffins to aromatics is a highly endothermic reaction which occurs at high temperature. In the MOG process conversion of paraffins is negligible. According to the present invention paraffin conversion is achieved by the use of a dual reactor zone system employing a first, high-temperature zone containing paraffins and olefins in a ratio sufficient to provide enough heat of reaction from olefin conversion to balance the paraffins' endothermic conversion reaction and maintain the overall reaction at near isothermal conditions. Reactions occurring in the first zone are primarily dehydrocyclisation reactions to produce aromatics. The effluent is passed to a second reaction zone, optionally in conjunction with additional olefin feed. The second zone is operated at lower temperature, typically MOG conversion conditions, which favour olefin oligomerisation and alkylation of aromatics produced in the first conversion zone. Accordingly, product separated from the second reaction zone includes C5+ gasoline having a motor octane of about 90+, compared to 85 for prior art product. Catalyst employed in the first and second fluidised bed reaction zones is preferably a Gallium-containing ZSM-5. The feed to the first reactor zone is advantageously preheated to a temperature of about 510°C or greater. Operating conditions for the first zone comprise a ratio of paraffins to olefins in the feedstock of between .1 and 5, preferably .3 to 2; temperature between 510 and 800°C, preferably 550 to 650°C; pressure between 100 and 2000 kPa, preferably 1150 to 1450 kPa; WHSV between 0.4 and 400, preferably 0.7 to 3. In the second reaction zone, suitable operating conditions include a temperature of 215 to 535°C, pressure of 50 to 2000 kPa and WHSV of 0.5 to 10; an operating temperature of about 360 to 440°C is preferred to enhance alkylation of benzene in the effluent from the first reaction zone. Referring to Fig. 2, the major components comprise feedstock preheater 105, high temperature first fluidised bed reactor vessel 110, second lower temperature fluidised bed reactor vessel 120, catalyst regenerator vessel 130 and product separator 140. Feedstock 102 is passed to preheater 105, preferably through indirect heat exchanger 103. Preheated feedstock is then passed to reactor 110 where under high temperature conditions in contact with zeolite catalyst paraffins and olefins are converted to aromatics and higher hydrocarbons. The effluent is passed via line 115 to fluidised bed reactor 120, preferably following indirect heat exchange with feedstock through heat exchanger 103. In reactor 120 the effluent is converted to C5+ gasoline boiling range hydrocarbons and alkylated aromatics plus lighter hydrocarbons and inerts in contact with zeolite catalyst at relatively lower temperature. Spent catalyst from reactors 110 and 120 is passed to oxidative regenerator vessel 130 via lines 121 and 122 and regenerated catalyst is recycled to the reactors via lines 123 and 124. Effluent from reactor 120 after cooling is passed via line 130 to separator 140. In separator 140, liquid product 150 comprising C5+ high octane gasoline is separated as well as gaseous products comprising C4- hydrocarbon and inerts 160. Referring to Fig. 3, major system components include transport riser reactor 210, turbulent fluidised bed MOG reactor 220, catalyst regenerator vessel 230, preheater 240 and separator 250. C3 hydrocarbon feedstock is passed 205 to riser reactor 210 through preheater 240 for paraffins and olefins conversion, preferably following indirect heat exchange in reactor 220. Fuel gas as feedstock is passed 206 to reactor 220 and, optionally, passed 207 to reactor 210. Effluent from reactor 210 is passed 208 for conversion in reactor 220, the product of which is passed 209 to product separator 250 for product recovery as described to MOG gasoline 260 and vapour product 270. Catalyst regeneration is accomplished by passing 231 a portion of spent catalyst from reactor 220 to oxidative regenerator 230 while another portion is recycled 232 to reactor 210 in conjunction with regenerated catalyst recycled via line 233. Referring to Fig. 4, major components include a single reactor vessel 310 containing separate fluidised bed reactor zones 311 and 312, catalyst regenerator 320, preheater 330 and separator 340. C3-C4 hydrocarbons are passed 305 to high temperature reactor zone 311 through heater 330 optionally in conjunction with a portion of fuel gas feedstock 304, preferably after indirect heat exchange in reactor zone 312. At least a major portion of fuel gas feedstock is passed to reactor 311 directly via line 306, optionally in conjunction with reformate or crackate feed 303. Following conversion of the feedstock in zones 311 and 312, vessel effluent 307 is cooled and separated in separator 340 to produce C5+ high octane gasoline 350 as previously described and vapour product. Catalyst regeneration is accomplished by passing 308 and 308A spent catalyst from zones 312 and 311 to regenerator 320 and recycling 309 and 309A regenerated catalyst to zones 311 and 312. Figure 5 presents an alternative novel process configuration of the present invention particularly applicable to fuel gas conversion as provided to the process via line 405. In this configuration spent catalyst from high temperature fluidised bed reactor 410 is passed 415 to catalyst regenerator 420 and regenerated catalyst therefrom is recycled 416 to reactor 410. A portion of spent catalyst from reactor 410 is also passed 425 to fluidised bed reactor 430 and spent catalyst therefrom is recycled 435 to reactor 410 or optionally passed 460 to regenerator 420. Product effluent 450 is recovered as previously described as MOG gasoline 455 and vapour product 458.- Optional feeds to reactor 430 include benzene/methanol 457 and LSR or other paraffins 58. The process of the present invention is readily integrated as an MOG reaction section 500 with unsaturated gas plant to realise significant cost savings as depicted in Figure 6. Feeds to the plant comprise FCC wild gasoline 510, FCC C3 hydrocarbons 511, gas and liquid feeds 512 and 513 processed in deethaniser, debutaniser and depropaniser 520, 525 and 530 to provide FCC and MOG gasoline 535, FCC and MOG C4-S 540 and C3-S 545. The FCC C3 feedstream 511 is combined with effluent 551 from amine absorber 550 as feedstream to the MOG reaction section 500. The MOG effluent is cooled and treated in sponge absorber 560 with lean oil 561 to provide off gas 562, MOG product and rich oil recycle 563 to FCC main column.

Claims: 1. A process for the conversion of a feedstock comprising lower alkane and alkene hydrocarbons to high octane gasoline, comprising contacting said feedstock in a first conversion zone with a fluidised bed of a catalyst comprising an acidic, intermediate-pore zeolite under high temperature alkane conversion conditions, said feedstock containing an amount of lower alkene sufficient, by exothermic reaction, to maintain near isothermal reaction conditions in said zone, to produce an effluent stream comprising higher aliphatic hydrocarbons rich in aromatics, and contacting said effluent stream in a second conversion zone with a fluidised bed of a catalyst comprising an acidic, intermediate-pore zeolite at moderate temperature under oligomerisation and alkylation conditions to produce a C5+ gasoline boiling range product rich in alkylated aromatics. 2. A process according to claim 1 wherein said feedstock is preheated before passing to said first conversion zone. 3. A process according to claim 1 or claim 2 wherein said hydrocarbon feedstock is preheated to a temperature between 480 and 800°C. 4. A process according to any preceding claim wherein the ratio of alkane to alkene in said feedstock is 0.2 to 5. 5. A process according to any preceding claim wherein the temperature of said first conversion zone is 510 to 800°C. 6. A process according to any preceding claim wherein the pressure in said first conversion zone is 100 to 2000 Pa. 7. A process according to any preceding claim wherein the first conversion zone operates at weight hourly space velocity, based on active catalyst, of 0.4 to 400. 8. A process according to any preceding claim wherein the weight hourly space velocity in the first conversion zone is 0.7 to 3 and the alkane/alkene ratio is 0.3 to 2. 9. A process according to any preceding claim wherein the temperature in the second conversion zone is between 315 and 480°C. 10. A process according to claim 9 wherein said temperature is 360 to 400°C. 11. A process according to any preceding claim wherein said first conversion zone is a transport riser fluidised bed conversion zone and said second conversion zone is a turbulent fluidised bed conversion zone. 12. A process according to any preceding claim wherein said alkane and/or alkene feedstock components comprise C2-C4 hydrocarbons. 13. A process according to any preceding claim wherein the alkane component of said feedstock comprises fuel gas. 14. A process according to any preceding claim wherein spent catalyst from said first and/or second conversion zone is passed to a catalyst regeneration zone, regenerated, and recycled to said first and/or second conversion zones. 15. A process according to claim 14 wherein the regeneration is conducted in a common regeneration zone under oxidative conditions. 16. A process according to claim 14 or claim 15 wherein a first portion of spent catalyst from said second conversion zone is passed to said regeneration zone and a second portion thereof is passed to a transport riser first conversion zone together with regenerated catalyst from said regeneration zone. 17. A process according to claim 14 or claim 15 wherein a first portion of spent catalyst from said first conversion zone is passed to said regeneration zone and a second portion thereof is passed to said second conversion zone and regenerated catalyst is recycled to said first conversion zone together with spent catalyst from said second conversion zone. 18. A process according to any preceding claim wherein said zeolite has the structure of ZSM-5. 19. A process according to any preceding claim wherein said zeolite contains gallium. 20. A process according to any preceding claim wherein the catalyst contains nickel. 21. A process according to any preceding claim wherein the effluent stream from the first conversion zone is co-fed to the second zone together with added alkene.

Inventors: HARANDI MOHSEN NADIMI, OWEN HARTLEY, HARANDI, MOHSEN, NADIMI, OWEN, HARTLEY
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1989
Main classification: C07C2
IPC codes: C07C2, C10G11, C10G35, C10G50