ALKYLATION CATALYSTS AND PROCESSES

Abstract: A process for treating a molecular sieve-containing alkylation catalyst to increase its selectivity for monoalkylation in which the alkylation catalyst is contacted with a feedstock comprising at least one organic compound under conditions such that a sufficient amount of carbon­ aceous material evenly deposits on the alkylation catalyst to substantially suppress its alkylation activity. The carbon-containing catalyst particles are then subjected to combustion by contacting them with a gaseous oxidizing agent at an elevated temperature to remove at least a portion of the carbonaceous material, preferably subs­ tantially all of the carbonaceous material, thereby increasing the selectivity of the catalyst for monoaklyl­ ation by at least about 1.0 percentage point. The resulting alkylation catalyst can be used to alkylate benzene and other aromatic compounds with ethylene, propylene or other olefins to produce high yields of ethylbenzene, cumene and other alkylated products. Preferably, the alkylation catalyst contains an ammonium-exchanged and steam stabilized Y zeolite.

Description: This invention relates to the alkylation of aromatic compounds and is particularly concerned with (1) a process for increasing the selectivity of an alkylation catalyst for monoalkylation, (2) alkylation catalysts that have been treated in such a manner as to improve their selectivity for monoalkylation and (3) alkylation processes using such catalysts of improved selectivity for monoalkylation. In the past it has been common practice to alkylate aromatic molecules such as benzene, toluene and xylene with ethylene, propylene and other olefins using acidic Friedel-Crafts type catalysts or heterogeneous acidic silica-alumina catalysts. Such processes have several disadvantages including corrosion problems caused by Friedel-Crafts type catalysts and the control of the product distribution obtained from the alkylation reactions. Normally, the desired product is the monoalkylate rather than the di- or trialkylate. In an effort to avoid a large production of di- and trialkylate products, it is conventional practice to use a large excess of the aromatic compound. To avoid some of the problems associated with earlier commercial alkylation processes, solid zeolite-containing catalysts have been used in recent years to promote the alkylation of aromatic compounds with olefins and other alkylating agents, especially the alkylation of benzene with ethylene. Normally, these catalysts are used in a fixed bed reactor through which the reactants are continuously passed. Although such fixed bed processes using zeolite-containing catalysts have advantages over earlier commercial processes, the selectivity and activity maintenance for monoalkylation, especially when producing cumene by reacting propylene with benzene, is not as high as desired and is often unsatisfactory. Accordingly, it is one of the objects of the present invention to provide a process for increasing the selectivity and maintaining the activity of alkylation catalysts containing zeolites selected from Y zeolites, fluorided Y zeolites and zeolite beta. It is another object of the invention to provide an alkylation catalyst containing such a zeolite and having an increased selectivity for monoalkylation and a process for alkylating an aromatic compound to form an alkylated aromatic using a catalyst having an increased selectivity for monoalkylation. These and other objects of the invention will become more apparent in view of the following description of the invention. In accordance with the invention it has now been found that the selectivity of an alkylation catalyst containing a zeolite selected from Y zeolites, fluorided Y zeolites and zeolite beta and a porous, unorganic refractory oxide can be increased by at least about 1.0 percentage point while maintaining a relatively high activity by depositing carbonaceous material on the catalyst to suppress its alkylation activity, and then contacting the resultant carbon-containing catalyst particles with a gaseous oxidizing agent at an elevated temperature to remove at least a portion of the carbonaceous material. The carbon deposition step is normally carried out by contacting the alkylation catalyst with a feed-stock comprising at least one organic compound under conditions such that a sufficient amount of carbonaceous material deposits relatively evenly on the alkylation catalyst to suppress its alkylation activity. The carbon-containing catalyst particles are then treated with a gaseous oxidizing agent at an elevated temperature to remove at least a portion, normally greater than about 95 weight percent, of the carbonaceous material. The resulting alkylation catalyst exhibits a much higher selectivity for monoalkylation than it did prior to its treatment in accordance with above-described process of the invention. As used herein the term "selectivity" refers to the ratio multiplied by 100 of the molar amount of the desired monoalkylated product and the molar amount of all products derived from the alkylating agent. In addition to exhibiting a high selectivity, the treated catalyst will possess an activity maintenance at least about 95 percent, typically about 100 percent, that of the catalyst prior to treatment in accordance with the invention. The invention is to be contrasted with US-A-4 001 346 that discloses a process for the selective production of para-xylene by methylating toluene in the presence of a modified catalyst comprising a crystalline aluminosilicate zeolite, such as a ZSM-5 type zeolite, having a silica-to-alumina mole ratio of at least about 12 and a constraint index of from 1 to 12. The catalyst is modified by depositing thereon a coating of coke produced by the decomposition of hydrocarbons, to provide the catalyst with a coke content between about 15 and about 75 weight percent. Generally, the precoking of the catalyst is accomplished by initially using the uncoked catalyst in the reaction of interest, i.e., methylation of toluene, such that coke is deposited on the catalyst surface. Thereafter, the catalyst is periodically regenerated by exposing it to an oxygen-containing atmosphere at an elevated temperature such that the coke content of the catalyst is reduced to a value between 15 and 75 weight percent. The regenerated catalyst is then employed for further use in the selective production of para-xylene. In a preferred embodiment of the invention, the feedstock with which the alkylation catalyst is contacted is a hydrocarbon feedstock, preferably one comprising a mixture of benzene and propylene. The alkylation catalyst is normally present in the contacting zone in the form of a fixed bed and the catalyst is typically contacted with the hydrocarbon feedstock until the reaction exotherm zone has passed through the fixed bed of catalyst, thereby indicating that the catalyst has been deactivated by the relatively uniform deposition of carbonaceous material on the catalyst particles. The carbon-containing catalyst particles are then preferably treated with a gaseous oxidizing agent in two stages. First, the catalyst particles are contacted with a gas comprising between 0.05 and 5.0 volume percent oxygen, preferably between 0.2 and 1.0 volume percent, as the temperature is gradually increased from at least ambient temperature, preferably from a temperature between -4°C (25°F) and 38°C (100°F) to a temperature in the range between 400°C (750°F) and 595°C (1100°F), preferably between 400°C (750°F) and 510°C (950°F), and most preferably between 425°C (800°F) and 470°C (875°F) to remove a portion but not all of the carbonaceous material via combustion. After combustion in this first stage ceases, the oxygen concentration of the gas is increased at least about 0.01 percentage point, preferably at least 0.05 percentage point, and the temperature is gradually increased to a value between 455°C (850°F) and 650°C (1200°F), preferably between 480°C (900°F) and 540°C (1000°F), while contacting is continued until substantially all of the carbonaceous material is combusted. The resulting alkylation catalyst has been found to have a substantially higher selectivity for monoalkylation than the catalyst originally placed in the fixed bed contacting zone. In a preferred embodiment of the invention, the molecular sieve-containing alkylation catalyst subjected to the process of the invention contains a Y zeolite, preferably a steam treated and stabilized zeolite known as LZY-82 zeolite. Tests indicate that the process of the invention can increase the selectivity of such a catalyst for the alkylation of benzene with propylene to form cumene from about 94.6 percent to about 97.6 percent. The molecular sieve-containing alkylation catalysts that can be treated in accordance with the process of the invention to increase their selectivity for monoalkylation comprise a zeolitic molecular sieve component selected from Y zeolites, fluorided Y zeolites and zeolite beta composited with a porous, inorganic refractory oxide matrix or binder. Examples of porous, inorganic refractory oxide comonents which can be used as the binder or matrix include alumina, gallia, thallia, titania, zirconia, beryllia, silica, silica-alumina, silica-magnesia, magnesia, silica-titania, other such combinations and the like. In general, the alkylation catalyst will contain between 2 and 98 weight percent molecular sieve, preferably between 50 and 95 weight percent, while the amount of binder or matrix in the catalyst will range between 2 and 98 weight percent, preferably between 5 and 50 weight percent. The most preferred molecular sieves for use as the active alkylation component of the catalysts which may be treated in accordance with the process of the invention are Y zeolites. US-A-3 130 007 describes Y-type zeolites having an overall silica-to-alumina mole ratio between 3.0 and 6.0, with a typical Y zeolite having an overall silica-to-alumina mole ratio of about 5.0. It is also known that Y-type zeolites can be produced, normally by dealumination, having an overall silica-to-alumina mole ratio above 6.0. Thus, for the purposes of this invention, a Y zeolite is one having the characteristic crystal structure of a Y zeolite, as indicated by the essential X-ray powder diffraction pattern of Y zeolite, and an overall silica-to-alumina mole ratio above 3.0, and includes Y-type zeolites having an overall silica-to-alumina mole ratio above 6.0. A preferred Y zeolite for use as the molecular sieve component of the alkylation catalysts which may be treated in accordance with the process of the invention is one produced by (1) first ammonium-exchanging a Y zeolite to a sodium content between 0.6 and 5.0 weight percent, calculated as Na₂0; (2) calcining the ammonium-exchanged zeolite at a temperature between 315°C (600°F) and 900°C (1650°F) in the presence of steam at a water vapor partial pressure of at least 1.4 kPa (0.2 p.s.i.a), preferably above about 14 kPa (2.0 p.s.i.a.), and most preferably between 34.5 and 103 kPa (5.0 and 15 p.s.i.a.), to reduce the unit cell size of the ammonium-exchanged zeolite to a value in the range between 2.440 and 2.464 nm, and then (3) ammonium-exchanging the steam calcined zeolite to replace at least 25 percent of the residual sodium ions and obtain a zeolite product of less than about 1.0 weight percent sodium, preferably less than about 0.6 weight percent sodium, and most preferably below about 0.2 weight percent sodium, calculated as Na₂0. Such a Y zeolite is highly stable and maintains a high activity. The zeolite is described in detail in US-A-3 929 672. The same or a substantially similar zeolite is sold by the UOP as LZY-82 zeolite. The alkylation catalyst which is subjected to the process of the invention can be either a fresh catalyst, i.e., one that has not previously been used to alkylate an aromatic compound, or a deactivated or partially deactivated alkylation catalyst, i.e., one that has already been used to at least some degree for promoting the alkylation of an aromatic compound. Since the process of the invention is quite effective in increasing the selectivity of a fresh alkylation catalyst, it may be desirable to subject a fresh catalyst to the process of the invention before it is used commercially to alkylate aromatic compounds. The alkylation catalyst is subjected to the process of the invention by first contacting the catalyst with a feedstock comprising at least one organic compound under conditions such that carbonaceous material deposits relatively evenly on the catalyst, thereby suppressing its alkylation activity. The feedstock utilized is preferably a hydrocarbon feedstock. As used herein "hydrocarbon" refers to any compound which comprises hydrogen and carbon and "hydrocarbon feedstock" refers to any charge stock which contains a mixture of hydrocarbon compounds and comprises greater than about 70 weight percent carbon and hydrogen, preferably greater than about 80 weight percent, calculated as the elements. Examples of hydrocarbon feedstocks that may be used in the process of the invention include nonpolar aromatic compounds such as benzene, toluene, ethylbenzene and xylene, unsaturated aliphatic hydrocarbons such as alkenes and alkynes, preferably C₂-C₁₅ alkenes or alkynes, and polar aliphatic hydrocarbons such as alcohols and alkyl halides. The preferred hydrocarbon feedstocks will normally comprise a mixture of an aromatic compound such as benzene and an unsaturated aliphatic hydrocarbon such as ethylene or propylene. In order to effectively suppress the alkylation activity of the catalyst, the hydrocarbon feedstock is contacted with the catalyst, normally by passing the feedstock through a fixed bed of the catalyst, under conditions such that carbonaceous material deposits on the alkylation catalyst. When a mixture of a nonpolar aromatic compound such as benzene or toluene and an unsaturated aliphatic hydrocarbon, preferably an olefin, is used as the hydrocarbon feedstock, the temperature at which the feedstock and catalyst are contacted will normally range between 120°C (250°F) and 425°C (800°F), preferably between 175°C (350°F) and 260°C (500°F). The pressure in the contacting zone will typically range between 10 bar (150 p.s.i.g.) and 138 bar (2000 p.s.i.g.). The mole ratio of the olefin to the aromatic compound in the feedstock will normally range from 0.01 to 10.0. In general, the conditions in the contacting zone are held relatively constant until the reaction exotherm zone, i.e., the exotherm caused by the reaction of the aromatic compound with the olefin, passes through the entire catalyst bed. The passage of the exotherm zone through the bed can be monitored by following the catalyst bed temperature profile. Passage of the exotherm zone through the entire catalyst bed is indicative of the fact that tars, i.e. carbonaceous material comprising condensed aromatics and olefin polymers, have been deposited over the alkylation catalyst to suppress its alkylation activity. After the alkylation catalyst has been treated in accordance with the procedure discussed above, the carbon-containing catalyst particles are subjected to a combustion step by contacting the particles with a gaseous oxidizing agent at a temperature between 290°C (550°F) and 595°C (1100°F), preferably between 425°C (800°F) and 510°C (950°F), to remove at least a portion of the deposited carbonaceous material. It has been surprisingly found that the resultant carbon-depleted material has an activity maintenance and a selectivity that are, respectively, at least 95 percent of and at least about 1.0 percentage point greater than the activity maintenance and selectivity of the fresh, deactivated or partially deactivated alkylation catalyst which is subjected to treatment in accordance with the process of the invention. It is normally preferred to carry out the combustion step under conditions such that greater than about 95 percent, preferably greater than about 98 weight percent, of the carbonaceous material is removed from the catalyst. It is most preferred that the combustion step be carried out under conditions such that substantially all of the carbonaceous material is removed from the catalyst. The above-described combustion step is typically carried out in situ in a fixed bed alkylation reactor by passing the gaseous oxidizing agent through the particles of carbon-containing catalyst. It will be understood, however, that the combustion step can be conducted in a separate vessel which can be a fixed bed or fluidized bed combustor, a rotary calciner, a moving belt combustor and the like. The gaseous oxidizing agent may be oxygen, air, carbon dioxide, steam, nitrogen dioxide, nitric oxide, nitrous oxide, and mixtures thereof. Preferably, however, the gaseous oxidizing agent comprises oxygen in amounts ranging between 0.05 and 60 volume percent, preferably between 0.05 and 5.0 volume percent. The most preferred gaseous oxidizing agent is air diluted with nitrogen, a combustion gas or steam so that the oxygen content of the resultant gas is between 0.2 and 1.0 volume percent. In a preferred embodiment of the combustion step, the carbonaceous material is burned from the treated catalyst particles in two stages. In the first stage the carbon-containing catalyst particles are contacted with a gaseous oxidizing agent comprising between 0.05 and 5.0 volume percent oxygen, preferably between 0.2 and 1.0 volume percent, as the temperature is gradually increased from at least ambient temperature, preferably from a temperature between -4°C (25°F) and 38°C (100°F) to a temperature between 400°C (750°F) and 595°C (1100°F), preferably between 400°C (750°F) and 510°C (950°F), and most preferably between 425°C (800°F) and 470°C (875°F), to remove a portion but but not all of the carbonaceous material on catalyst particles. After combustion in this first stage ceases, the oxygen concentration of the gas is increased at least about 0.01 percentage point, preferably at least about 0.05 percentage point, and the temperature is gradually increased to a value between 455°C (850°F) and 650°C (1200°F), preferably between 480°C (900°F) and 540°C (1000°F), while contacting is continued until substantially all of the carbonaceous material is combusted. In both stages of contacting, the temperature increase is limited such that the exothermic temperature rise caused by combustion of carbon on the catalyst particles does not exceed 110°C (200°F), preferably 55°C (100°F), and most preferably 14°C (25°F). During the combustion step it is necessary to avoid extremely high temperatures so that the crystallinity of the molecular sieve component of the alkylation catalyst is not destroyed. Preferably, the combustion step is carried out under conditions such that there is substantially no decrease in the crystallinity of the molecular sieve, i.e., the molecular sieve is collapsed during the combustion step by less than about 10 percent as compared to the crystallinity of the molecular sieve in the alkylation catalyst subjected to the process of the invention, preferably less than about 5 percent, as measured by X-ray diffraction. In the embodiment of the invention described above, a fresh, partially deactivated or completely deactivated alkylation catalyst is first contacted with a hydrocarbon feedstock under conditions such that the activity of the catalyst is suppressed by the uniform deposition of carbonaceous material and then subjected to combustion to remove the deposited carbonaceous material. The resultant alkylation catalyst has a higher selectivity for monoalkylation than the original catalyst prior to treatment in accordance with the invention. It will be understood that the first step in the process of the invention may not be necessary when treating a completely deactivated alkylation catalyst if the catalyst has been used in an alkylation process under conditions such that its activity was suppressed by the uniform distribution of carbonaceous material throughout the catalyst bed. If this is the case, it may only be necessary to subject the deactivated catalyst to the combustion step described above in order to significantly increase its selectivity for monoalkylation. The catalyst of the invention, which is produced in accordance with the process described above, will have a marked increase in selectivity for monoalkylation. This increase will normally be at least 1.0 percentage point higher than that obtained with a catalyst of the same composition which has not been treated in accordance with process of the invention, typically at least about 2.0 percentage points higher, and in many cases at least about 3.0 percentage points higher. In a specific case, it has been found that the selectivity of a catalyst containing 90 weight percent LZY-82 zeolite and 10 weight percent Catapal alumina for producing cumene from benzene and propylene was 94.6 percent while the cumene selectivity for the same catalyst treated in accordance with the process of the invention was 97.6 percent, an increase of 3 percentage points. The shape of the catalyst of the invention is essentially the same as the shape of the catalyst subjected to the process of the invention. Although the catalyst may be cylindrical in shape, it is normally preferred that the catalyst be in the shape of three-leaf clovers similar to the shape shown in Figures 8 and 8A of U.S. Patent No. 4,028,227. It is normally desired that the catalyst particles have a surface-to-volume ratio greater than that of particles in the shape of a cylinder and preferably in the range between 216 (85) and 406 (160) reciprocal centimeters (inches). Normally, the length of the catalyst particles ranges between 0.0254 (0.01) and 0.635 cm (0.25 inch) and the diameter between 0.0762 (0.03) and 0.2032 cm (0.08 inch). The preferred shapes of the catalyst particles are described in detail in U.S. Patent No. 4,185,040. The catalyst of the invention may be used to increase the selectivity for monoalkylation when alkylating an aromatic compound with an alkylating agent in any conventional manner. The aromatic compound that is alkylated may be a monocyclic aromatic compound such as benzene or toluene, a polycyclic aromatic compound such as naphthalene, methyl naphthalene or anthracene, and nonpolar substituted derivatives of such monocyclic and polycyclic aromatic compounds. The alkylating agent used may be any aliphatic compound capable of reacting with the aromatic compound used. Normally, the alkylating agent will be a C₂-C₃₅ olefin, preferably a C₂-C₂₅ olefin, most preferably ethylene, propylene, isobutene or n-butene. Usually a monoalkylated product is desired, but polyalkylated products can also be produced by, for instance, using toluene as the aromatic compound and ethylene as the alkylating agent. The process of the invention, however, is preferably used to produce ethylbenzene from benzene and ethylene, most preferably to produce cumene from benzene and propylene. Regardless of what aromatic compound or alkylating agent is utilized, use of the catalyst of the invention will result in a significantly increased selectivity for monoalkylation of the aromatic compound to the desired product whether it be a monoalkylated product or a polyalkylated product. The alkylation process of the invention is typically carried out by passing the reactants through one or more fixed beds of the catalyst of the invention. An excess of the aromatic compound is utilized in order to minimize the formation of polymers of the alkylating agent and undesired polyalkylated products. The alkylating agent is essentially completely consumed in the process and the reactor effluent is fractionated to recover the unreacted aromatic compound for recycle, the desired alkylated product, and any minor proportion of undesired polyalkylated product which may be recycled to the alkylation reactor to suppress any net production of undesired polyalkylated compounds. In some cases it may be desired to use a multistage system of alkylation reactors in lieu of a single reactor. The alkylation process is normally carried out at a temperature between 95°C (200°F) and 480°C (900°F), preferably between 150°C (300°F) and 315°C (600°F). The pressure utilized in the process ranges between 10 bar (150 p.s.i.g.) and 138 bar (2000 p.s.i.g.), preferably between 27.5 bar (400 p.s.i.g.) and 103 bar (1500 p.s.i.g.). The weight hourly space velocity typically ranges between 2 and 2000, preferably between 4 and 100 reciprocal hours. The mole ratio of the alkylating agent to the aromatic compound used typically ranges between 0.01 and 1.0, preferably between 0.02 and 0.1. The nature and objects of the invention are further illustrated by the following example which is provided for illustrative purposes only and not to limit the invention as defined by the claims. The example demonstrates that the selectivity for monoalkylation of an alkylation catalyst can be significantly increased by first depositing carbonaceous material on the catalyst to suppress its alkylation activity and subsequently removing the carbonaceous material from the catalyst by combustion. EXAMPLE Fifty grams of a fresh alkylation catalyst are placed in the form of a fixed bed in a pilot plant size reactor vessel. The catalyst is in the shape of 1.6mm (1/16 inch) cloverleaf pellets containing 90 weight percent LZY-82 zeolite and 10 weight pecen Catapal alumina. Benzene and propylene are passed upwardly through the bed at ambient temperature and at a rate of 51 grams per hour and 6.9 grams per hour respectively. The temperature in the reactor vessel is raised to 163°C (325°F) while the flows of benzene and propylene are continued at constant rates. The pressure in the reactor is maintained at about 34.5 bar (500 p.s.i.g.) and the weight hourly space velocity is 1.14 reciprocal hours. The temperature profile of the catalyst bed is monitored on a daily basis. The initial exotherm temperature at the inlet of the bed ranges between 170°C (338°F) and 172°C (342°F) while the average bed temperature is about 163°C (325°F). The process conditions for the remainder of the run are set forth below in Table 1. The product from the reactor is analysed at periodic intervals to determine when complete propylene conversion terminates. Movement of the reaction exotherm zone through the bed is used to monitor for deactivation. After about 700 hours the exotherm zone passes through the bed and propylene is present in the product mixture confirming that the catalyst is essentially deactivated. After the catalyst is deactivated as described above benzene is purged from the catalyst bed, and the catalyst is removed from the pilot plant reactor and transferred to a pilot plant size fixed bed apparatus. Here the deactivated catalyst is contacted at a temperature of 454°C (850°F) with a gas stream prepared by blending air and nitrogen in a ratio such that the resultant gas contains about 0.5 volume percent oxygen. The oxygen concentration of the gas is then increased to 2.0 volume percent and the contacting continued until breakthrough of oxygen is detected. The catalyst bed is grey in colour after the above treatment indicating an incomplete removal of carbon. To obtain complete removal of carbon, the temperature in the fluidized bed unit is raised to 510°C (950°F) and contacting of the catalyst with the gas containing 2.0 volume percent oxygen is continued until the colour of the catalyst particles becomes a light tan. The physical properties of the fresh catalyst are compared with those of the catalyst treated in the above-described fashion in Table 2 below. The selectivity of the fresh catalyst as compared to the treated catalyst is determined as described below. Ten grams of the catalyst treated as discussed above are placed in the form of a fixed bed in the pilot plant size reactor vessel utilized to deactivate the fresh catalyst. Propylene and benzene are passed upwardly through the catalyst bed in a molar ratio of 0.033, propylene to benzene, at a temperature of 163° C (325° F) and a pressure of 34.5 bar (500 p.s.i.g.). The weight hourly space velocity is 10. Liquid and vapor samples from the outlet of the reactor are analyzed periodically over the length of the run. The run is terminated after 900 hours as no decline in activity or change in selectivity of the catalyst is noted. The product at the end of the run is analyzed and the cumene selectivity calculated. The resultant data are set forth below in Table 3 and compared with similar data obtained under identical conditions when using the fresh catalyst instead of the treated catalyst. As can be seen from Table 3, the yield of cumene is significantly higher using the treated catalyst as opposed to the fresh catalyst. The cumene selectivity is 97.6% for the treated catalyst as compared to 94.6% for the fresh catalyst, an increase of 3 percentage points. Such an increase in selectivity is quite significant when commercial operations for the production of cumene by the alkylation of benzene with propylene are considered. The higher selectivity for cumene is due to a marked reduction in the formation of 1,3 and 1,4 diisopropyl benzene. It is theorized that the decrease in the production of the dialkylated product may be caused by passivation of active acid sites, the generation of new sites with a net lower acidity or a reduction in the ability of the catalyst to adsorb cumene.

Claims: A process for treating an alkylation catalyst comprising a molecular sieve having catalytic activity for alkylation, said molecular sieve being selected from Y zeolites, fluorided Y zeolites and zeolite beta, and a porous, inorganic refractory oxide, said alkylation catalyst being substantially devoid of hydrogenation metal components, to increase the selectivity of said aklylation catalyst for monoalkylation, which process comprises (a) depositing carbonaceous material on said catalyst in such a manner as to suppress the alkylation activity of said catalyst; and (b) contacting the carbon-containing catalyst particles formed in step (a) with a gaseous oxidizing agent at an elevated temperature to remove at least a portion of said carbonaceous material so as to increase the selectivity of said alkylation catalyst for monoalkylation by at least about 1.0 percentage point. A process according to claim 1, wherein said carbonaceous material is deposited on said catalyst by contacting said alkylation catalyst in a contacting zone with a feedstock comprising at least one organic compound. A process according to claim 2, wherein said feedstock comprises a hydrocarbon feedstock. A process according to claim 3, wherein said hydrocarbon feedstock comprises a C₂-C₁₅ alkene or alkyne. A process according to claim 3, wherein said hydrocarbon feedstock comprises a mixture of an aromatic compound and an olefin and said alkylation catalyst is contacted with said feedstock under conditions such that said aromatic compound reacts with said olefin. A process according to any one of claims 1 to 5, wherein said gaseous oxidizing agent consists essentially of air and nitrogen or air and carbon dioxide. A process according to any one of claims 1 to 6, wherein said gaseous oxidizing agent comprises between 0.05 volume percent and 5.0 volume percent oxygen. A process according to any preceding claim, wherein the carbon-containing catalyst particles formed in step (a) are first contacted with a gaseous oxidizing agent comprising between 0.05 and 5.0 volume percent oxygen at a temperature between 400°C (750°F) and 595°C (1100°F) to remove a portion of said carbonaceous material and produce catalyst particles of reduced carbon content, whereafter the oxygen content of said gaseous oxidizing agent is increased at least about 0.01 percentage point, and the catalyst particles of reduced carbon content are contacted with said gaseous oxidizing agent of increased oxygen content at a temperature between 455°C (850°F) and 650°C (1200°F) until substantially all of said carbonaceous material is removed. A process according to any preceding claim, wherein greater than about 95 weight percent of said carbonaceous material is removed in step (b). A process according to any preceding claim, wherein said alkylation catalyst is a fresh catalyst and is treated in accordance with steps (a) and (b) prior to being used to produce alkylated aromatics. A process according to claim 2 or any claim dependent thereon, wherein said alkylation catalyst forms a fixed bed in said contacting zone and is contacted with said feedstock until the reaction exotherm zone has passed through said fixed bed of catalyst. A process for treating an alkylation catalyst comprising a molecular sieve having catalytic activity for alkylation, said molecular sieve being selected from Y zeolites, fluorided Y zeolites and zeolite beta, and a porous, inorganic refractory oxide, said alkylation catalyst being substantially devoid of hydrogenation metal components, to increase the selectivity of said alkylation catalyst for monoalkylation, the alkylation activity of said catalyst having been suppressed by the deposition of carbonaceous material thereon to form carbon-containing catalyst particles, which process comprises contacting said carbon-containing catalyst particles with a gaseous oxidizing agent at an elevated temperature to remove at least a portion of said carbonaceous material so as to increase the selectivity of said alkylation catalyst for monoalkylation by at least about 1.0 percentage point. A process according to claim 12, wherein said zeolitic molecular sieve comprises a Y zeolite. A process according to claim 13, wherein said Y zeolite comprises LZY-82 zeolite. A process according to claim 13, wherein said molecular sieve having catalytic activity for alkylation comprises a Y zeolite prepared by the process comprising: (a) ammonium-exchanging a Y zeolite to a sodium content between 0.6 and 5.0 weight percent, calculated as Na₂O; (b) calcining the ammonium-exchanged zeolite at a temperature between 315°C (600°F) and 900°C (1650°F) in the presence of steam at a water vapor partial pressure greater than about 1.4 kPa (2.0 p.s.i.a.) to reduce the unit cell size of the ammonium-exchanged zeolite to a value in the range between 2.440 and 2.464 nm; and (c) ammonium-exchanging the steam-calcined zeolite to replace at least 25 percent of the residual sodium ions and obtain a zeolite product of less than about 0.6 weight percent sodium, calculated as Na₂O. A process according to claim 12 or any claim dependent thereon, wherein said carbon-containing catalyst particles are (1) contacted with a gaseous oxidizing agent comprising between 0.05 and 5.0 volume percent oxygen at a temperature between 400°C (750°F) and 595°C (1100°F) to remove a portion of said carbonaceous material and produce a first set of catalyst particles having a reduced carbon content; (2) the oxygen content of said gaseous oxidizing agent is increased by at least about 0.05 percentage point; (3) said first set of catalyst particles having a reduced carbon content is contacted with said gaseous oxidizing agent of increased oxygen content at about the temperature utilized in step (1) to remove a further portion of said carbonaceous material and produce a second set of catalyst particles having a reduced carbon content as compared with said first set of catalyst particles; and (4) said second set of catalyst particles is contacted with said gaseous oxidizing agent at a temperature, between 455°C (850°F) and 650°C (1200°F), that is higher than the temperature used in step (1) while the oxygen concentration in said gaseous oxidizing agent is maintained at about the value used in step (3) until substantially all of said carbonaceous material is removed from said catalyst particles. A process according to any preceding claim, wherein there is substantially no decrease in the crystallinity of said molecular sieve while said carbon-containing catalyst particles are contacted with said gaseous oxidising agent. A process according to any preceding claim, wherein said porous, inorganic refractory oxide comprises alumina. A process for alkylating an aromatic compound to form an alkylated aromatic, which comprises contacting said aromatic compound with an alkylating agent under alkylation conditions in the presence of a molecular sieve-containing alkylation catalyst that has been treated to increase its selectivity in accordance with the process of any one of claims 1 to 18. A process according to claim 19, wherein said aromatic compound is selected from monocyclic aromatic compounds, polycyclic aromatic compounds and nonpolar substituted derivatives thereof. A process according to claim 20, wherein said aromatic compound comprises benzene or toluene. A process according to claim 19, 20 or 21, wherein said alkylating agent comprises a C₂-C₂₅ olefin. A process according to claim 22, wherein said alkylating agent comprises ethylene or propylene. A process according to claim 19, wherein said aromatic compound comprises benzene, said alkylating agent comprises propylene, said alkylation catalyst comprises a Y zeolite, and said alkylated aromatic comprises cumene.

Inventors: RATCLIFFE, CHARLES T., WARD, JOHN W.
Applicants: UNION OIL COMPANY OF CALIFORNIA
Application year: 1987
Main classification: B01J29
IPC codes: C07B61, B01J29, B01J21, C07C2, B01J37, C07C67, C07C1, C07C15