PROCESS FOR UPGRADING PROPENE-ETHENE MIXTURES IN A TURBULENT FLUIDIZED CATALYST BED REACTOR

Abstract: A fluidized bed catalytic process for conversion of propene-rich light olefinic gas feedstock comprising at least 2 mol % ethene and having a C3:C2 molar ratio of at least 2:1 to produce hydrocarbons rich in C4<+> aliphatics and aromatics. In the preferred embodiments the process includes: maintaining a turbulent fluidized bed in a reactor operating at a moderate pressure in the range from 400 to 2500 kPa, and temperature of 315 to 510 DEG C. In a typical turbulent regime fluidized bed reactor system the catalyst has an apparent particle density of 0.9 to 1.6 g/ml<3>, a size range of 1 to 150 mu m, and average catalyst particle size of 20 to 100 mu m containing 10 to 25 weight percent of fine particles having a particle size less than 32 mu m. The reaction is controlled by passing hot feedstock vapor upwardly through the fluidized catalyst bed; while maintaining turbulent fluidized bed conditions through the reactor bed between transition velocity and transport velocity at a superficial fluid velocity of 0.3 to 2 meters per second. Hydrocarbon product is recovered containing a major amount of C5<+> hydrocarbons and containing C3-C5 alkanes and alkenes in the ratio of 0.1:1 to 200:1 and preferably at a reaction severity index (R.I.) of 0.2:1 to 5:1.

Description: -I. PROCESS FOR UPGRADING PROPENE- E1HENE MIXTURES IN A TURBULENT FLUIDIZED CATALYST BED REACTCR This invention relates to a catalytic technique for upgrading light olefin gas to heavier hydrocarbons. In particular, it provides a continuous process for oligomerizing ethene/prcpene-containi g olefinic light gas feedstock, optionally containing paraffins, such as propane, or other lower alkanes. The inventive process is employed advantageously in conjunction with light hydrocarbon gas recovery operations associated with FCC (fluid catalytic cracking) refinery units to produce C. hydrocarbons, such as olefinic licμid fuels, isobutane, aromatics and other useful products. Propene (propylene, C,H^) and ethene (ethylene, C H.) -containing gases, such as petroleum cracking offgas, are useful feedstocks herein. Developments in zeolite catalysis and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks for producing Cr gasoline, diesel fuel, etc. In addition to basic chemical reactions promoted by ZSM-5 type zeolite catalysts, a nunber of discoveries have contributed to the development of new industrial processes. Thesv. are safe, environmentally acceptable processes for utilizing feedstocks that contain lower olef ins, especially C2~C 4 alkenes. Conversion of lower olef ins, especially prcpene and butenes, overHZSM-5 is effective at moderately elevated temperatures and pressures. The conversion products are sought as licμid fuels, especially the 0.. aliphatic and aromatic hydrocarbons. Product distribution for licμid hydrocarbons can be varied by controlling process conditions, such as temperature, pressure and space velocity. Gasoline is readily formed at elevated temperature (e.g., up to 400°C) and moderate pressure from ambient to 5500 kPa, preferably 250 to 2900 kPa. Olefinic gasoline can be produced in good yield and may be recovered pressure reactor system for further conversion to heavier distillate-range products. Distillate mode operation can be eπployed to maximize production of C. 0 aliphatics by reacting the lower and intermediate olefins at high pressure and moderate temperature. Operating details for typical "MDGD' (Mobil Olef in to Gasoline and Distillate) oligo eriza ion units are disclosed in U.S. Patents 4,456,779; 4,497,968 (Owen et al.) and 4,433,185 (Tabak). At moderate teπperature and relatively high pressure, the conversion conditions favor distillate-range product having a normal boiling point of at least 165°C (330°F) . Lover olefinic feedstocks containing C^-C,- alkenes may be converted selectively; however, the low severity distillate mode conditions do not convert a major fraction of ethene. While prqpene, butene-1, and others may be converted to the extent of 50 to 95% in the lower severity moderate teπperature distillate mode, only 10% to 30% of the ethene component will be converted using HZSM-5 or similar acid zeolites. Many feedstocks of commercial interest, such as FCC offgas, dehydrogenat ion products, ethane cracking byproduct, etc., contain both ethene and hydrogen along with. H^S and light aliphatics. Ethene can also be converted at moderate temperature with a bifunctional nictel catalyst. It has been found that propenerrich olefinic light gas, particularly prcpene -enriched ethylenic fuel gas, can be upgraded to licμid hydrocarbons rich in olefinic gasoline, isobutane and aromatics by catalytic conversion in a turbulent fiuidized bed of solid acid zeolite catalyst under high severity reaction conditions in a single pass or with recycle of gas product. This tech icμe is particularly useful for upgrading FCC light gas, which usually contains significant amounts of ethene, prqpene, C 2 -C. paraffins and hydrogen produced in cracking heavy petroleum oils or the like. By upgrading the by-product light gas, gasoline yield of FCC units can be significantly increased. An improvement has been discovered in the process for continuous conversion of ethene -containing light hydrocarbon feedstock to heavier hydrocarbon products wherein the feedstock is contacted at elevated temperature with a fiuidized bed of zeolite catalyst under conversion conditions while maintaining the fiuidized catalyst bed in a vertical reactor column having a turbulent reaction zone by passing feedstock gas upwardly through the reaction zone at a velocity greater than dense bed transition velocity to a turbulent regime and less than transport velocity for the average catalyst particle. A portion of coked catalyst withdrawn from the reaction zone is oxidatively regenerated catalyst and returned to the reaction zone at a rate to control catalyst activity whereby C- j -C 5 alkane:alkene weight ratio in the hydrocarbon product is maintained at 0.1:1 to 200:1 under conditions of reaction severity to effect feedstock conversion. The present improvement comprises enriching olefinic feedstock with a prop ene -propane mixture to provide a molar ratio of propene: ethene of at least 2:1, thereby obtaining increased throughput, gasoline yield and C.+ hydrocarbon product. In the drawings, FIG. 1 is a schematic view of a fiuidized bed reactor system according to the present invention; FIG. 2 is a graphic plot showing product yields vs. reaction temperature; FIG. 3 shows corresponding licμid product octane vs temperature; FIG. 4 shows yields for various mixtures of propene and ethene in feedstock olefin; and FIG. 5 is a semilog plot comparing C..-C,- alkane : lkene. Description of Catalysts Recent developments in zeolite techology have provided a group of medium pore siliceous materials having similar pore geometry. Most prominent among these intermediate pore size zeolites is ZS -5, which is usually synthesized with Bronsted acid active sites by incorporating a tetrahedrally coordinated metal, such as Al, Ga, B or Fe, within the zeolitic framework. These medium pore zeolites are favored for acid catalysis; however, the advantages of ZStA-5 structures may be utilized by employing highly siliceous materials or crystalline metal losilicate having one or more tetrahedral species having varying degrees of acidity. ZSM-5 crystalline structure is readily recognized by its X-ray diffraction pattern, which is described in U.S. Patent No. 3,702,866 (Argauer, et al.) , incorporated by reference. The oligomerization catalysts preferred for use herein include the medium pore (i.e., 5-7 x 10 ~ mm) shqpe- selective crystalline aluminosilicate zeolites having a silica-to-alumina ratio of at least 12, a constraint index of 1 to 12 and acid cracking activity of 10-250. In the fiuidized bed reactor the coked catalyst may have an apparent activity (alpha value) of 10 to 80 under the process conditions to achieve the recμired degree of reaction severity. Represen ative of the ZS -5 type zeolites are ZSM-5, ZSM-11, ZSf-12, Z3 -22, Z9 -23, ZSM-35 aixi ZSM-48. ZS -5 is disclosed in U.S. Patent No. 3,702,886 and U.S. Patent No. Re. 29,948. Other suitable zeolites are disclosed in U.S. Patents 3,709,979; 3,832,449; 4,076,979; 4,076,842; 4,046,839; and 4,579,999. While suitable zeolites having a coordinated metal α ide to silica molar ratio of 20:1 to 200:1 or higher may be used, it is advantageous to eπploy a standard ZSM-5 having a silica alumina molar ratio of 25:1 to 70:1, suitably modified. A typical zeolite catalyst conponent having Bronsted acid sites may consist essentially of aluminosilicate ZSM-5 zeolite with 5 to 95 wt. % silica and/or alumina binder. These siliceous zeolites may be em loyed in their acid forms ion exchaηged 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. The zeolite may include a hydrcgenation-dehydrogena ion coπponent (sometimes referred to as a hydrogenation coπponent) which is generally one or more metals of group IB, IIB, IIIB, VA, VIA or VIIIA of the Periodic Table (IUPAC) , especially aromatization metals, such as Ga, Pd, etc. Useful hydrogenation coπponeπts 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 coπponents may also be used, especially nickel, cobalt, molybdenum, tungsten, copper or zinc. The catalyst materials may include two or more catalytic coπponents, such as a metallic oligomerization component (e.g., ionic Ni , and a shape-selective medium pore acidic oligomerization catalyst, such as ZSM-5 zeolite) which coπponeπts may be present in admixture or combined in a unitary bif unctional solid particle. It is possible to utilize an ethene dimerization metal or oligomerization agent to effectively convert feedstock ethene in a continuous reaction zone. Certain of the ZSM-S type medium pore shφe selective catalysts are sometimes known as pentasils. In addition to the preferred aluπi no silicates, the borosilicate, ferrosilicate and "silicalite" materials may be eπplσyed. It is advantageous to eπploy a standard ZS -5 having a silica : alumina molar ratio of 25:1 to 70:1 with an apparatus alpha value of 3-80 to convert 60 to 100 percent, preferably at least 70%, of the olefins in the feedstock. ZSM-5 type pentasil zeolites are particularly useful in the process because of their regenerability, long life and stability under the extreme conditions of operation. Usually the zeolite crystals have a crystal size from 0.01 to over 2 jim or no re, with 0.02-1 tm being preferred. In order to obtain the desired particle size for fluidization in the turbulent regime, the zeolite catalyst crystals are bound with a suitable inorganic oxide, sich as silica, alumina, etc. to provide a zeolite concentration of 5 to 95 wt. %. In the description of preferred embodiments a 25% H-ZSM-5 catalyst contained within a si lie a -alumina matrix and having a fresh alpha value of 80 is eπplσyed unless otherwise stated. Particle size distribution can be a significant factor in achieving overall homogeneity in turbulent regime fluidization. It is desired to operate the process with particles that will mix well throughout the bed. Large particles having a particle size greater than 250jum should be avoided, and it is advantageous to eπploy a particle size range consisting essentially of 1 to 150^m. Average particle size is usually 20 to 100 £m, preferably 40 to 80 ^ . Particle distribution may be enhanced by having a mixture of larger and smaller particles within the operative range, and it is particularly desirable to have a significant amount of fines. Close control of distribution can be maintained to keep 10 to 25 wt. % of the total catalyst in the reaction zone in the size range less than 32 JJLIH. This class of fluidizable particles is classified as Geldart Group A. Accordingly, the fluidization regime is controlled to assure ope ration between the transition velocity and transport velocity. Fluidization conditions are substantially different from those ound in non-turbulent dense beds or transport beds. Process Operation In this description, metric units and parts by weight are eπplσyed unless otherwise stated. The preferred feedstock contains alkenes (mono-olefin) including at least 2 mole % ethene, wherein the total C2-C3 alkenes are in the range of 10 to 100 wt% . Non-deleterious coπponents, such as methane and other paraffins and inert gases, may be present. Some of the paraffins in the feed will also conv rt to C.+ hydrocarbons, dep ending on reaction conditions and the catalyst eπployed. A particularly use ul feedstock is a light gas by-product of FCC gas oil cracking units containing typically 10-60 mol % C 2 -C. olef ins and 5-35 mol % H 2 with varying amounts of C-^-C- j paraffins and inert gas, such as N 2 . The process may be tolerant of a wide range σf lower alkanes, from 0 to 90%. Feedstocks may contain more than 50 wt. % C,-C. lower aliphatic hydrocarbons, but should contain sufficient olefins to provide total olefinic partial pressure of at least 50 kPa. Under the reaction severity conditions employed in the present invention, lower alkanes, such as propane optionally cof ed with propene from FCC light gas recovery, may be partially converted to C. products. The desired products are C. to C q hydrocarbons, which will comprise at least 50 wt. % of the recovered product, preferably 80% or more. While olefins may be a predominant fraction of the C. reaction effluent, up to 45% butenes, pentenes, hexenes, heptenes, octenes, nonenes and their isomers, it is desired to upgrade the feedstock to high octane gasoline containing aromatics, preferably at least 10% by weight. The reaction severity conditions can be controlled to optimize yield of C^-Cg aliphatic hydrocarbons. It is understood that aromatics and light paraffin production is promoted by those zeolite catalysts having a high concentration of Bronsted acid reaction sites. Accordingly, an iπportant criterion is selecting and maintaining catalyst inventory to provide either fresh catalyst having acid activity or by controlling catalyst deacti ation and regeneration rates to provide an apparent average alpha value of 3 to 80. Reaction teπperatures and contact time are also significant factors in the reaction severity, and the process parameters are followed to give a substantially steady state condition wherein the reaction severity index (R.I.) is maintained within those e rating conditions which yield a desired weight ratio of propane to prφene. While this index may vary greatly in the presence of added propane in the feedstock, eg -from 0.1 to 200, it is preferred to φerate the steady state fiuidized bed unit to hold the R.I. at 0.2:1 to 5:1, when measured in the substantial absence of added prφane. While reaction severity is advantageously determined by the weight ratio of prφane: prφene in the gaseous phase, it may also be approximated by the analogous ratios of butanes :butenes, pentanes:pentenes, or the average of total reactor effluent alkanes:alkenes in the C,-Cr range, as depicted graphically in Fig. 5. FIG. 5 shows the close relationship between R.I. value for C,, C. and Cr aliphatics and total alkane:alkene ratio. These values are shown in the range of 0.1 to 50 with typical C 2 -C-τ olefinic feedstock in the substantial absence of added prφane in the feedstock. The optimium value will dφend upon tie exact catalyst coπposition, feedstock and reaction conditions; however, the typical ethene/propene-rich light gas mixtures used in the exaπples herein and similar cracking process off -gas can be φtionally upgraded to the desired aliphatic-rich gasoline by keφing the R.I. at 1. The olefinic feedstream may be enriched by addition of prφane to increase the production of C. product. Prφane containing streams, such as C,-C. IPG and various refinery fractions can be eπployed to supplement the olefinic feedstock. Suitable C 2 ~C. aliphatic mixtures containing 20 to 85 wt. % propane may enhance olefinic feedstocks of 15 to 80% raono-alkene. Since prφane conversion is incoπplete under ordinary φerating conditions, this addition can raise the apparent C, R.I. value above 50:1. The use of fiuidized bed catalysis permits the conversion system to be φe rated at low pressure drφ, which in an economically practical φeration can provide a total φerating pressure of 200 to 2500 kPa, preferably at least 400 kPa. Another iπportant advantage is tie close teπperature control that is made possible by turbulent regime φeration, wherein the uniformity of conversion teπperature can be maintained within close tolerances, often less than 25°C. Except for a snail zone ad acent the bottom gas inlet, the midpoint measurement is representative of tie entire bed, due to the thorough mixing achieved. In a typical process, the olefinic feedstock is converted in a catalytic reactor under oligomerization conditions and moderate pressure (i.e., 400 to 2000 kPa) to produce at least 6% isobutane and a predominantly licμid product consisting essentially of C. hydrocarbons rich in gasoline-range olefins and aromatics. Referring now to FIG. 1, feed gas rich in C 2 -C 3 olefins passes under pressure through conduit 10, with the main flow being directed through the bottom inlet of reactor vessel 20 for distribution through grid plate 22 into the fluidization zone 24. Here the feed gas contacts the turbulent bed of finely divided catalyst particles. Reactor vessel 20 is shown provided with heat exchange tubes 26, which may be arranged as several sφaiate heat exchaηge tube bundles so that teπperature control can be sφarately exercised over different portions of the fluid catalyst bed. The bottoms of the tubes are spaced above feed distributor grid 22 sufficien ly to be free of jet action by the charged feed through the small diameter holes in the grid. Alternativ ly, reaction heat can be partially or coπpletely removed by using cold feed. Baffles may be added to control radial and axial mixing. Although depicted without baffles, the vertical reaction zone can contain φen end tubes above the grid for maintaining hydraulic constraints, as disclosed in US Pat. 4,251,484 (E&viduk and Haddad). Heat released from the reaction can be controlled by adjusting feed teπperature in a known manner. Catalyst outlet means 28 is provided for withdrawing catalyst from above bed 24 and passed for catalyst regeneration in vessel 30 via control valve 29. The partially deactivated catalyst is oxidatively regenerated by controlled contact with air or other regeneration gas at elevated teπperature in a fiuidized regene ration zone to remove carbonaceous deposits and restore acid acitivity. The catalyst particles are entrained in a lift gas and transported via riser tube 32 to a tφ portion of vessel 30. Air is distributed at the bottom of the bed to effect fluidization, with oxidation byproducts being carried out of the regeneration zone through cyclone separator 34, which returns any entrained solids to the bed. Flue gas is withdrawn via top conduit 36 for diφosal; however, a portion of the flue gas may be recirculated via heat excharger 38, separator 40, and compressor 42 for return to the vessel with fresh oxidation gas via line 44 and as lift gas for the catalyst in riser 32. Regenerated catalyst is passed to the main reactor 20 through conduit 46 provided with flow control valve 48. The regenerated catalyst may be lifted to the catalyst bed with pressurized feed gas through catalyst return riser conduit 50. Since the amount of regenerated catalyst passed to tie reactor is relatively snail, the teπperature of the regen rated catalyst does not upset the teπperature constraints of the reactor φerations in a significant amount. A series of seφentially connected cyclone separators 52, 54 are provided with dip legs 52A, 54A to return any entrained catalyst fines to the lower bed. These sφarators are positioned in an upper portion of the reactor vessel coπprising di ersed catalyst phase 24. Filters, such as sintered metal plate filters, can be used alone or in conjunction with cyclones. The product ef luent sφarated from catalyst particles in the cyclone sφarating system is then withdrawn from the reactor vessel 20 through top gas outlet means 56. The recov red hydrocarbon product comprising Cς olefins and/or aromatics, paraffins and naphthenes is thereafter processed as re ired to provide a desired gasoline or higher boiling product. Under φtimized process conditions the turbulent bed has a sφerf icial vφor velocity of 0.3 to 2 meters per second (m/s) . At higher velocities, entrai ment of fine particles may become excessive and beyond 3 m/s the entire bed may be tranφorted out of the reaction zone. At lower velocities, the formation of large bubbles or gas voids can be detrimental to conversion. Even fine particles cannot be maintained effectively in a turbulent bed below 0.1 m/sec. A convenient measure of turbulent fluidization is the bed density. A typical turbulent bed has an φerating density of 100 to 500 kg/ 3 , preferably 300 to 500 kg/m 3 , measured at the bottom of the reaction zone, becoming less dense toward the top of the reaction zone, due to pressure drop and particle size differentiation. This density is generally between the catalyst concentration eπplσyed in dense beds and the dispersed transport systems. Pressure differential between two vertically aced points in th? reactor column can be measured to obtain the av rage bed density at such portion of the reaction zone. For instance, in a fiuidized bed system employing ZSM-5 particles having an apparent packed density of 750 kg/m and real density of 2430 kg/m , an average fiuidized bed density of 300 to 500 kg/m is satisfactory. By virtue of the turbulence experienced in the turbulent regime, gas-solid contact in the catalytic reactor is improved, providing high ethene/propene conversion in the range of 70-95+%, enhanced selectivity and teπperature unifoπnity. One main advantage of this technicμe is the inherent control of bubble size and characteristic bubble lifetime. Bubbles of the gaseous reaction mixture are small, random and short-lived, thus resulting in good contact between the gaseous reactan s and the solid catalyst particles. A significant difference between the process of this invention and conversion processes of the prior art is that φeration in the turbulent fluidization regime is optimized to produce high octane Cr liφid in good yield. The weight hourly space velocity and uniform contact provides a close control of contact time between vφor and solid phases, typically 3 to 15 seconds. Another advantage of operating in such a mode is the control of bubble size and life an, thus avoiding large scale gas by -pas sing in the reactor. As the sφerficial gas velocity is increased in the dense bed, eventually slugging conditions occur and with a further increase in the sψerficial gas velocity the slug flow breaks down into a turbulent regime. The transition velocity at which this turbulent regime occurs appears to decrease with particle size. The turbulent regime extends from the transition velocity to the so-called transport velocity, as described by Avidan et al in U.S. Patent 4,547,616. As the transport velocity is approached, there is a sharp increase in the rate of particle carryover, and in the absence of solid recycle, the bed could eπpty quickly. Several useful parameters contribute to fluidization in the turbulent regime in accordance with the process of the present invention. When eπplσying a ZS -5 type zeolite catalyst in fine powder form such a catalyst should comprise the zeolite suitably bound or impregnated on a suitable support with a solid density (weight of a representative individual particle divided by its apparent "outside" volume) in the range from 0.6-2 g/ml, preferably 0.9-1.6 g/ml. The catalyst particles can be in a wide range of particle sizes up to 250 jj.ii., with an average particle size between 20 and lOO^m, preferably between 40 and 80^m. When these solid particles are placed in a fiuidized bed where the sφerf icial fluid velocity is 0.3-2 m/s, operation in the turbulent regime is obtained. Those skilled in the art will appreciate that at higher pressures, a lower gas velocity may be eπployed to ensure operation in the turbulent fluidization regime. The reactor can assume any technically feasible con guration, but several iπportant criteria should be considered. The bed of catalyst in the reactor can be at least 5-20 meters in height, preferably 7-9 meters. Fine particles may be included in the bed, especially due to attrition, and the fines may be entrained in the product gas stream. A typical turbulent bed may have a catalyst carryover rate to 1.5 times the reaction zone inventory per hair. If the fraction of fines becomes large, a portion of the carryover can be removed from the system and rep laced by larger particles. It is feasible to have a fine particle sφarator, such as a cyclone and/or filter means, disposed within or outside the reactor shell to recover catalyst carryov r and return this fraction continuously to the bottom of the reaction zone for recirculation at a rate of one catalyst inventory per hour. Optionally, fine particles carried from the reactor vessel entrained with effluent gas can be recovered by a high φerating tenperature sintered metal filter. This process can be used with any process stream which contains sufficient light olefins and paraffins. For ecaπple, it can be used to process FCC by-product fuel gas, which typically contains 10 to 40 wt. % total ethene, and is enriched to contain at least 3 parts by weight of propene per part of ethene (ie-2:l to 40:1 molar ratio). Experimental runs are performed using a ZS -5 catalyst to demonstrate the inventive process. The fiuidized bed unit can be φe rated over a wide range of process variables and catalyst activity. Reactor Operation A typical reactor unit employs a teπperature- controlled catalyst zone with indirect heat exchange and/or adjustable gas quench, whereby the reaction exotherm can be carefully controlled to prevent excessive teπperature above the usual φerating range of 315°C to 510°C, preferably at average reactor teπperature of 315°C to 430°C. Energy conservation in the system may utilize at least a portion of the reactor exotherm heat value by exchanging hot reactor effluent with feedstock and/or recycle streams. Optional heat exchangers may recover heat from the effluent stream prior to fractionation. Part of all of the reaction heat can be reiroved from the reactor without using the indirect heat exchange tubes by using cold feed, whereby reactor teπperature can be controlled by adjusting feed teπperature. The internal heat exchange tubes can still be used as internal baf les which lower reactor hydraulic diameter, and axial and radial mixing. The weight hourly space velocity (WHSV, based on total olefins in the fresh feedstock is 0.1-5 WH5V. Typical product fractionation systems are described in U.S. Patents 4,456,779 and 4,504,693 (Owen, et al.) . Typical results of ethene-rich catalysis obtained in a fluid bed reactor are shown in Ecaπples 1-3. EXAMPLE 1 Reactor Conditions: Teπperature 370°C Pressure 410 kPa Olefin-WHSV 0.5 No Recycle Feed Composition, wt. % Hyd rog en 10.7 Ethene 89.3 Product Yields, wt. % Methane 0.1 Ethane 1.9 Ethene 11.7 Prφane 7.3 Propene 5.0 Isobutane 10.6 n-Butane 4.4 Butenes 7.6 C Hydrocarbons 51.4 r Hydrocarbon Properties R+O Octane 93.2 Specific Gravity 0.74 EXAMPLE 2 Reactor Conditions: Teπperature 370°C Pressure 1200 kPa Olefin-WHSV 0.4 No Recycle Feed Composition, wt. % Nitrogen 65.8 Hydrogen 0.8 Ethene 14.7 P rφene 18.7 Product Yields, wt. % Methane 0.1 Ethane 1.4 Ethene 3.6 rφane 8.9 Propene 2.8 Isobutane 12.8 n-Butane 6.0 Butenes 5.7 C,. Hydrocarbons 58.7 C j . Hydrocarbon Properties R+O Octane 93.2 Specific Gravity 0.74 EXAMPLE 3 Reactor Conditions: Teπperature 370°C Pressure 1200 kPa Olefin-WHSV 0.4 Recycle ratio, MolMole 1.4 Feed Composition, wt. % Nitrogen 65.8 Hydrogen 0.8 Ethene 14.7 Prφene 18.7 Product Yields, wt. % Methane 0.1 Ethane 0.7 Ethene 6.0 Prφane 4.7 Propene 3.0 Isobutane 9.9 n-Butane 3.6 Butenes 6.3 C_ Hydrocarbons 65.7 C_ Hydrocarbon Properties R+O Octane 90.3 Specific Gravity 0.73 Eca ple 1 is for a feed containing only ethene and hydrogen. Examp le 2 is for a feed containing nit rogen, hydrogen, ethene and propene. C . yields will be highe r, as some of the alkanes conve rt. Examp le 3 is similar to Examp le 2 , but a substantial portion of the C . product is recycled back to the reactor. C ς yields are higher and catalyst makeup recμirements are lower for Example 3 compared to Example 2. Higher isobutane yields, and higher gasoline octane numbers a re possible at higher temperatures, lower pressures, and higher catalyst activity. The produced isobutane, usually mo re than 5 wt. % , may have signif icant iπpact on potent ial alkylate yield, dφending on the supply situation of isobutane in a petroleum refinery. The maximum yield (Cr plus alkylates ) may be achieved at a conve rsion teπperature between 360 to 415° C. The flexibility of the fluid bed for controlling the reactor teπperatu re under exothe rmic reaction conditions allows an easy adjustment for achieving the optimal yield structure. The prφosed fuel gas conversion unit can f it into an existing FCC gas plant, with appropriate amine scrubbing to remove most of the deleterious sulfur compounds, such as H 2 S. Example 4 To demonstrate the effect of prφene enrichment, a continuous fluid-bed olef in upgrading unit is operated with a feed which contains a minor amount ethylene and pa rt or all of the C. prφane/prcpylene stream from a refinery cracki ng complex. The C, may be the only feed or may be mixed with the cracki ng complex fuel gas st ream. The propylene converts quite readily at M3G conditons (315-510°C, 1344 kPa (180 psig) , and 0.8 WHSV, for example) to produce mainly C g + gasoline, with octane ranging from 90 to 100 R+0 , dφending on the reactor teπperature. Gasoline yield is typ ically 2 -5 wt. % liigher than for fuel gas f eed alone in the substantial absence of C, coπponents, while the octane quality is the same under similar φerati ng conditions . Typical feedstock is a dilute ethylene stream, usually the fuel gas from the re inery cracking coπplex. This stream will normally contain some prφylene in addition to ethylene. Typical weight ratios of ethylene to propylene are 3:1 to 1:1. The prφylene present in this stream converts readily. The present invention involves adding additional propylene, typically from the refinery cracking coπplex C, stream, to bring the ethylene -propylene weight ratio down to 1:3 to 1:4, which may be expressed as a C j :C 2 molar ratio greater than 2:1. Reactor space velocity (WHSV on total ole ins) in feed can be at least doubled by adding additional prφylene without significan ly affecting the conv rsion of ethylene present in the fuel gas. Table 4 shows results from a fluid- bed upgrading plant for adding addi tonal propylene to a simulated fuel gas mixture. In this exaπple, the reactor teπperature, fuel gas feed rate, and catalyst inventory are held constant. Adding the propylene (simulating a commercial C, stream), results in a doubling of the WHSV on feed olefins. Despite this increase in WHSV, ethylene conv rsion only decreases by 1%, and gasoline yield increased by 4% without a chaηge in the gasoline octane quality. The effect of adding the C-- stream to the fuel gas feed at various teπperatures is showi in Figures 2 and 3. As shown in Figure 2, the additional propylene results in a 2-5% increase in gasoline yield, and the yield for both feeds decreases with increasing teπperature. Product octane increases with teπperature; therefore, the most desirable φerating point will d end on the relative value c£ yield versus octane in the refinery. Table 4 Effect of Prφene Addition Fuel Gas Fuel Gas ■ Feed Oily Prφene Ethene/Propene Weight Ratio 47/53 23/77 W BV on Total Olefins, Hr "1 0.36 0.74 WHSV on Ethene, Hr -1 0.17 0.17 Reactor Temp., °C(T) 427(800) 427(800) Avg. Reactor Vel., m/s 0.83 1.0 Partial Pressures, psia Ethene 24.5 19.8 Inc re men al Prφene 17.0 39.6 Yield on Added Conve sions, wt. % Propene, wt% Ethene 95.2 94.3 - Prop ene 92.1 96.0 97.9 Yields on Olef in Feed, Wt. % Methane 0.2 0.1 0.0 Ethane 0.7 0.4 0.1 Ethylene 2.3 1.3 0.4 Pr ane 8.5 7.6 6.7 Propene 4.2 3.1 2.1 n-Butane 5.6 6.0 6.4 i -Butane 12.3 11.8 11.3 Butenes 6.1 5.3 4.5 Cr Gasoline 60.1 64.4 68.5 C,. Gasoline Properties RCN+0 96.7 96.8 MON+O 84.0 83.7 Specific Gravity 0.751 0.748 RVP 7.3 7.3 Fig. 4 dφicts graphically the synergism in yields for mixtures of ethene and propene. A binary mixture containing 75-80 wt. % prφene gives the optimum yield, correφonding to a molar ratio of C,:C 2 of 2:1 to 3:1. This proportion is approximately that of a typical mixture of FCC fuel gas and C, streams. The use of a fluid- bed reactor in this process offers several advantages over a fixed-bed reactor. Due to continuous catalyst regeneration, fluid-bed reactor φeration will not be adversely affected by oxygenate, sulfur ai /oτ nitrogen containing contaminants presented in FCC fuel gas. In addition, the high isobutane yield in a fluid-bed reactor φeration could be a significant advantage in isobutane short refineries. The reaction teπperature can be controlled by adjusting the feed teπperature so that the enthalphy charge balances the heat of reaction. The feed teπperature can be adjusted by a feed pre heater, heat excharge between the feed and the product, or a combination of both. Once the feed and product coπpositions are determined using, for exaπple, an on-line gas chromatograph, the feed teπperature needed to maintain the desired reactor teπperature, and conseφent olef in conversion, can be easily calculated from a heat balance of the system. In a commercial unit this can be done automatically by state-of-the-art control techniφes. While the invention has been shown by describing preferred embodiments of the process, there is no intent to limit the inventive concφt, excφt as set forth in the following claims.

Claims: CIAIMS: 1. A process for continuous conversion of ethe e -containing light hydrocarbon feedstock to heavier hydrocarbon products wherein the feedstock is contacted at elevated teπperature with a fiuidized bed of zeolite catalyst under conversion conditions while maintaining the fiuidized catalyst bed in a vertical reactor colunn having a turbulent reaction zone by passing feedstock gas upwardly through the reaction zone at a velocity greater than dense bed transition velocity to a turbulent regime and less than transport velocity for the average catalyst particle, and withdrawing a portion of coked catalyst from the reaction zone, σxidatively regenerating the withdrawn catalyst and returning regenerated catalyst to the reaction zone at a rate to control catalyst activity whereby C,-Cr alkane:alkene weight ratio in the hydrocarbon product is maintained at 0.1:1 to 200:1 under conditions of reaction severity to effect feedstock conversion; characterized in that: the olefinic feedstock is enriched with a prop ene -prop ane mixture to provide a molar ratio of prφene:ethene of at least 2:1, thereby increasing yields of isobutane and C gasoline. 2. The process of claim 1 wherein the catalyst comprises a siliceous metallosilicate acid zeolite having the structure of Z5M-5 zeolite and a si lie a: alumina ratio in the range from 25:1 to 70:1. 3. The process of claim 1 wherein the feedstock consists essentially of light cracking gas comprising at least 75 to 80 weight percent propene and 2 to 25 wt. % ethene. 4. The process of claim 1 wherein the active catalyst consists essentially of pore pentasil zeolite having an apparent alpha value of 3 to 80, and average particle size of 20 to 100 μ.m , and tie reactor catalyst inventory includes at least 10 weight percent fine particles having a particle size less than yijjn. 5. The process of claim 1 wherein the catalyst particles comprise 5 to 95 weight percent aluminosilicate ZSM-5 zeolite in which the silica:alumina molar ratio is in the range from 20:1 to 200:1 and have a crystal size of 0.02 -2 fj . 6. The process of claim 1 wherein the sφerficial feedstock vφor velocity is 0.3-2 m/sec; the reaction temperature is 315 to 510°C; the weight hourly feedstock space velocity (based on olef in eψivalent and total reactor catalyst inventory) is 0.1 to 5. 7. The process of claim 1 wherein the catalyst consists essentially of a medium pore pentasil zeolite having an apparent alpha value of 3 to 80, am av rage particle size of 20 to 100 tm, the reactor catalyst inventory includes at least 10 weight percent fine particles having a particle size less than 32^m. 8. The process of claim 1 wherein the feedstock consists essentially of C,-C 4 light hydrocarbon cracking gas, and wherein olef in partial pressure in the feedstock is at least 50 kPa. 9. The process of claim 1 wherein C.- hydrocarbon product is sφa rated from the Cr+ product and is recycled back to the reactor at a recycle ratio of 0.1:1 to 5:1 mol/mol to fresh feed. 10. The process of claim 1 wherein the reactor colunn contains vertical, horizontal, or a combination of vertical and horizontal heat exchanger tubes to remove reaction heat and control reaction temperature. 11. The process of claim 1 wherein the heat excharge tubes reduce ef ective reactor hydraulic diameter, decrease radial and axial mixing in the reactor, and improve reactor efficiency, whereby heat of reaction removal and reactor teπperature control are enhanced by controlling feed tenperature by heat excharge with reactor e luent and/or a sφplemental heater. 12. The process of claim 1 wherein the feedstock comprises ethylenic FCC fuel gas enriched with a prop ane -propylene FCC byproduct stream and wherein hydrocarbon gas product is measured to determine prop ane : prop ene ratio and reaction severity conditions are adjusted to maintain the prφane:prφene weight ratio from 0.2:1 to 5:1 a ter a counting for added propane. 13. The process of claim 1 wherein the catalyst consists essentially of siliceous aluminosilicate acid zeolite having the structure of ZSM-5 zeolite and a silica: alumina ratio in the rarge from 25:1 to 70:1.

Inventors: AVIDAN AMON ANDREW, JOHNSON DAVID LEE, SOTO JORGE LUIS, AVIDAN, AMON, ANDREW, JOHNSON, DAVID, LEE, SOTO, JORGE, LUIS
Applicants: MOBIL OIL CORP, MOBIL OIL CORPORATION
Application year: 1989
Main classification: C07C2
IPC codes: B01J8, B01J29, C07B61, C07C2, C07C9, C10G35