Olefin oligomerization catalyst, process for preparing the same, and olefin oligomerization process using the same

Abstract: An olefin oligomerization catalyst comprises at least one oxide selected from alumina and silica·alumina having a sulfate ion supported thereon. The amount of the sulfate ion contained in the catalyst is desirably in the range of 0.3 to 60 % by weight based on the total weight of the alumina and/or silica·alumina and the sulfate ion. The olefin oligomerization catalyst can be readily prepared by bringing a sulfuric acid aqueous solution or an ammonium sulfate aqueous solution into contact with at least one compound selected from alumina, silica alumina and their precursors, followed by drying and calcining. Further, an olefin oligomerization catalyst comprises at least one oxide selected from alumina and silica·alumina on which a transition metal oxide is further supported in addition to the sulfate ion. By the use of the catalyst, a lower olefin produced in, for example, a petroleum refining process can be converted into an oligomer of high value added.

Description: FIELD OF THE INVENTION The present invention relates to an olefin oligomerization catalyst, a process for preparing the catalyst and an olefin oligomerization process using the catalyst. More particularly, the invention relates to an olefin oligomerization catalyst capable of converting a lower olefin produced by, for example, petroleum refining into an oligomer of high value added such as gasoline, kerosine or gas oil, and also relates to a process for preparing the catalyst and an olefin oligomerization process using the catalyst. BACKGROUND OF THE INVENTION As solid catalysts for olefin oligomerization, there are known solid acid catalysts, such as solid phosphoric acid, silica alumina and zeolite, and catalysts wherein a transition metal is supported on silica, alumina, silica-alumina or active carbon (see: "Industrial Catalyst Reaction I", Catalyst Course Vol. 8, 1985, published by Kodansha, "Catalyst Reaction (3), Polymerization", Catalyst Industrial Course Vol. 8, 1977, published by Chijinshokan). Catalysts comprising sulfate ions supported on alumina or silica-alumina, and also containing a transition metal, are widely known, as for example from EP-A-272,970 and US-A-4,423,267, -5,182,247, -2,794,842 and -3,959,400; in which the catalyst is prepared by treating the support with nickel sulfate, or with a source of nickel followed by a source of sulfate. Examples of olefin oligomerization processes using catalysts having alumina or silica-alumina as a carrier include: a process using a catalyst wherein nickel sulfide is supported on a carrier of silica, alumina or silica·alumina, as described in Japanese Patent Publication No. 3489/1974; a process using a catalyst wherein nickel oxide and cobalt sulfate and/or magnesium sulfate are supported on alumina, as described in Japanese Patent Publication No. 30044/1975; a process using a nickel oxide-aluminum phosphate catalyst containing a small amount of alumina, silica or silica·alumina, as described in Japanese Patent Publication No. 30046/1975; and a process using a catalyst obtained by allowing a carrier of alumina, silica or silica-alumina to support thereon a nickel compound capable of being converted into nickel oxide by calcining and any of nitrate, sulfate and halide of a metal selected from Ca, Mg, Cd, Co, Zn, Al, Fe, Zr and Mn, or sulfate or halide of Ni, followed by calcining at 300 to 700 °C, as described in Japanese Patent Laid-Open Publication No. 85506/1973. Further, there have been proposed the following processes: an olefin oligomerization process using a catalyst wherein Ni 2+ cation is introduced into silica-alumina by means of cation exchange, as described in Japanese Patent Laid-Open Publication No. 143830/1985; and a C 2-6 olefin oligomerization process using a catalyst obtained by treating a supported composition wherein an oxide of a transition metal (M) selected from Ni, Co, Cr and Pd is supported on an acid oxide (e.g., alumina, silica·alumina, zeolite, diatomaceous earth, silica·titania and silica·magnesia), with a halogen-containing alkylaluminum compound, the atomic ratio of Al derived from the aluminum compound to the transition metal M (Al/M) being 0.5 to 10, as described in Japanese Patent Laid-Open Publication No. 151136/1986. Furthermore, there are known other olefin oligomerization processes, such as a process in which a C 4-10 olefin-containing raw material is brought into contact with amorphous silica-alumina having an alumina content of 10 to 50 % by weight, a surface area of 50 to 600 m 2 /g and a mean pore diameter of 10 to 100 Å under the reaction conditions of a temperature of 150 to 400 °C and a pressure of 30 to 100 kg/cm 2 -G, as described in Japanese Patent Publication No. 434/1993; a process in which a C 4-10 olefin-containing raw material is brought into contact with a catalyst having 0.1 to 5.0 % by weight of a rare earth metal supported on amorphous silica·alumina, as described in Japanese Patent Publication No. 39412/1994; and a process in which a material containing a C 4 olefin of normal structure as its main component is subjected to a reaction by the use of a nickel oxide support type catalyst obtained by impregnating silica-alumina, which has been preliminarily heat treated at not lower than 600 °C, with a nickel salt solution to allow the silica-alumina to support 3 to 15 % by weight (in terms of Ni) of nickel oxide, under the reaction conditions of a temperature of 50 to 200 °C, a pressure of 20 to 100 kg/cm 2 -G and LHSV of 0.1 to 5.0 hr -1 , to obtain a C 8 olefin having a degree of branching of not higher than 1.5, as described in Japanese Patent Laid-Open Publication No. 287227/1994. These conventional catalysts, however, are not always satisfactory in oligomerization of an olefin due to their poor selectivity of dimerization and low activity. In addition, when an olefin oligomer is used, for example, as material for a phthalic acid plasticizer to be blended with polymer such as polyvinyl chloride, the olefin oligomer is desired to have a low degree of branching, i.e., few side chains. The above conventional process, however, are not always successful in obtaining a desired olefin oligomer having a sufficiently low degree of branching. OBJECT OF THE INVENTION The present invention has been made in the light of the prior arts as mentioned above, and it is an object of the invention to provide an olefin oligomerization catalyst which is capable of causing oligomerization of a lower olefin with prominently high activity and is excellent in selectivity of the degree of oligomerization such as dimerization, trimerization, tetramerization and pentamerization, and an olefin oligomerization catalyst which is further capable of obtaining with excellent selectivity an olefin oligomer having a low degree of branching which is useful as a material for a plasticizer. It is another object of the invention to provide a process for preparing the catalyst and an olefin oligomerization process using the catalyst. According to the present invention there is provided an olefin oligomerization catalyst comprising alumina and/or silica-alumina, sulfate ion and nickel oxide, said catalyst being obtainable by a process comprising the steps of: a) bringing a sulfuric acid aqueous solution or an ammonium sulfate aqueous solution into contact with at least one oxide selected from alumina and silica-alumina.; b) calcining the thus-contacted oxide at a temperature at which sulfate ion is not decomposed; c) supporting a nickel compound, capable of being converted into nickel oxide by calcination, on the calcined oxide; and d) calcining at a temperature at which a sulfate ion is not decomposed, the sulfate ion being present in the product of (d) in the amount of 0.3 to 60% by weight (in terms of SO 4 ) of the total weight of alumina, silica-alumina and sulfate ion. The nickel oxide preferably constitutes 0.1 to 40% by weight (in terms of nickel) of the total weight of the catalyst. Advantageously the catalyst further comprises aluminum oxide supported on the alumina and/or silica-alumina, and is obtainable by supporting an aluminum compound, capable of being converted into aluminum oxide by calcination, on said calcined oxide either simultaneously with or subsequent to the supporting of the nickel compound in step (c) and before step (d). The aluminum oxide typically constitutes 0.1 to 20% by weight (in terms of aluminum) of the total weight of the catalyst. In the olefin oligomerization catalyst of the invention, it is desired that the sulfate ion is contained in an amount preferably 0.5 to 45% by weight in terms of SO 4 , based on the total weight of the alumina and/or the silica-alumina and the sulfate ion. The invention also comprehends a process for preparing an olefin oligomerization catalyst, comprising the steps of: a) bringing a sulfuric acid aqueous solution or an ammonium sulfate aqueous solution into contact with at least one oxide selected from alumina and silica-alumina.; b) calcining the thus-contacted oxide at a temperature at which sulfate ion is not decomposed; c) bringing the calcined product into contact with a nickel compound capable of being converted into nickel oxide by calcination; and d) calcining the nickel-contacted product at a temperature at which sulfate ion is not decomposed. Advantageously, in step (c) the calcined product is brought into contact with an aluminum compound capable of being converted into aluminum oxide by calcining, either together with the nickel compound or after bringing the calcined product into contact with the nickel compound. In the olefin oligomerization process according to the present invention, an oligomerization raw material containing an olefin is subjected to an oligomerization reaction in the presence of the above-described olefin oligomerization catalyst. This olefin is preferably at least an olefin of 2 to 10 carbon atoms. As the oligomerization raw material containing an olefin, a low-boiling fraction obtained in a petroleum refining process or an ethylene plant can be employed. In the present invention, the olefin is preferably subjected to an oligomerization reaction under the conditions of a reaction temperature of 0 to 400 °C, a reaction pressure of 0 to 100 kg/cm 2 -G and LHSV (Liquid Hourly Space Velocity) of 0.1 to 50 hr -1 . In the invention, it is preferred that the olefin is subjected to an oligomerization reaction so as to obtain a substance selected from gasoline, kerosine and gas oil. BRIEF DESCRIPTION OF THE DRAWING Fig. 1 is a view showing a relationship between a content of the sulfate ion in the alumina carrier and a butene conversion. In the olefin oligomerization catalyst of the invention, the sulfate ion is first supported on the alumina and/or the silica·alumina as described above, so that an olefin can undergo oligomerization with high activity. For reference, a catalyst wherein a metal sulfate such as cobalt sulfate or magnesium sulfate is supported on alumina or silica·alumina (aforesaid JP-30044/1975 and JP-85506/1973) only exhibits low activity in the olefin oligomerization process. Thus, the catalyst of the invention wherein the sulfate ion is first supported on alumina and/or silica·alumina shows prominently high activity in the olefin oligomerization process, while the conventional catalysts wherein the metal sulfate is supported on alumina or silica·alumina shows only low activity, as is apparent from the later-described invention examples and comparative examples. That is, the action and effect of the olefin oligomerization catalyst of the invention are fundamentally different from those of the conventional catalysts due to their morphological (structural) difference. As for the olefin oligomerization catalyst of the invention, it is presumed that when the sulfate ion is first supported on the alumina or the silica-alumina, the sulfate ion is generated in the form of a bidentate ligand which is linked to the Al atom present on the surface of the alumina or the silica-alumina to form an extremely strong acid site, so that the olefin oligomerization catalyst of the invention exhibits high activity, though the reason is not clear. There is no specific limitation on the olefin oligomerization catalyst of the invention, so long as a sulfate ion per se (not a metal sulfate) is first supported on the alumina and/or the silica-alumina. The alumina and/or the silica-alumina having the sulfate ion supported thereon may be used after diluted with substances inert to the reaction or other inorganic oxides. In the present invention, also preferred is an olefin oligomerization catalyst wherein, in addition to nickel oxide aluminum oxide is further supported on the alumina and/or the silica·alumina having the sulfate ion supported thereon. The nickel oxide is desirably supported in an amount of 0.1 to 40 % by weight, preferably 1 to 30 % by weight, in terms of a transition metal, based on the total weight of the catalyst. The aluminum oxide is desirably supported in an amount of 0.1 to 20 % by weight, preferably 0.3 to 15 % by weight, in terms of aluminum, based on the total weight of the catalyst. By the use of the olefin oligomerization catalyst of the invention an olefin can undergo oligomerization with high activity as mentioned above, and oligomers of high value added, such as a dimer, a trimer, a tetramer and a pentamer of olefin, can be prepared in high yields, and an oligomer having few side chains, namely, a low degree of branching can be selectively prepared. The olefin oligomerization catalyst wherein both nickel oxide and aluminum oxide are present is much more improved in the selectivity of the low degree of branching, and particularly, an oligomerization reaction at a high temperature can be carried out with excellent selectivity of the low degree of branching. The term "degree of branching" as used herein means a number of the chain hydrocarbon groups (methyl, ethyl) branched from the main hydrocarbon chain of the α-olefin structure. For example, in the case of an olefin of 8 carbon atoms (i.e., dimer of butene), normal octene has a degree of branching of 0, methylheptene has that of 1, dimethylhexene has that of 2, and trimethylpentene has that of 3. The term "average degree of branching" as used herein means an average value of the degrees of branching of the mixed olefins. The alumina and silica·alumina may be used in the form of precursors such as alumina hydrate, aluminum hydroxide and silica·alumina gel, in preparing the caralyst. In more detail, the catalyst of the present invention can be prepared by a process comprising the steps of treating the alumina and/or the silica-alumina with a sulfuric acid aqueous solution or an ammonium sulfate aqueous solution by means of impregnation, immersion, kneading or the like so as to allow the alumina and/or the silica·alumina to support the sulfate ion, followed by drying and calcining. The calcining temperature is in the range of 300 to 800 °C, preferably 400 to 700 °C. As the alumina or the silica-alumina, commercially available ones are employable. Aluminum hydrate, aluminum hydroxide or a silica·alumina gel is also employable by treating it with the sulfuric acid aqueous solution or the ammonium sulfate aqueous solution. The catalyst wherein the nickel oxide is supported can be prepared by bringing the alumina and/or the silica-alumina, on which the sulfate ion is preliminarily supported, into contact with a nickel oxide-forming material, i.e., a compound capable of being converted into nickel oxide by calcining or decomposition in an inert gas such as nitrogen or in air. Examples of the oxide-forming materials include inorganic salts such as nitrates, carbonates and halides of transition metals, organic salts such as oxalates and acetates, and ammonia complex salts. Examples of aluminum oxide-forming materials include aluminum nitrate, aluminum sulfate and aluminum halides. For allowing the alumina and/or silica-alumina having the sulfate ion supported thereon to support the nickel and possibly aluminium oxide the alumina and/or silica·alumina containing the sulfate ion is treated with the metallic salt aqueous solution or ammonia complex salt aqueous solution serving as the oxide-forming material by a method conventionally used for the catalyst preparation, such as impregnation, immersion, co-deposition, deposition or kneading, and then the thus treated product is dried and calcined (decomposed). In this method, the calcining temperature is a temperature at which the oxide-forming material is decomposed in an inert gas or air to produce a transition metal oxide, and it is in the range of usually 300 to 800 °C, preferably 400 to 700 °C. The nickel oxide and the aluminum oxide may be simultaneously supported on the alumina and/or silica-alumina having the sulfate ion supported thereon, or the aluminum oxide may be supported before or after the nickel oxide is supported. However, the simultaneous supporting is economically advantageous. The morphology of the aluminum oxide thus supported on the alumina and/or silica·alumina having the sulfate ion supported thereon is not clear, but it is presumed that the aluminum oxide serves to stabilize oxidation state of the nickel. The catalyst wherein the nickel oxide and the aluminum oxide are further supported on the alumina and/or the silica·alumina in addition to the sulfate ion may be used after diluted with substances inert to the reaction or other inorganic oxides, or other ingredients may be added to the catalyst to use. It is preferred that the catalyst wherein the sulfate ion is supported on the alumina and/or the silica·alumina and the catalyst wherein the nickel oxide and the aluminum oxide are further supported on the alumina and/or the silica·alumina in addition to the sulfate ion are dried under heating in an inert gas before they are used for the olefin oligomerization reaction. The catalyst is appropriately used in the form of a powder or a molded product in accordance with the reaction type. Olefin oligomerization process In the olefin oligomerization process according to the invention, an oligomerization raw material containing an olefin is subjected to an oligomerization reaction in the presence of the olefin oligomerization catalyst described above. The olefin is preferably at least an olefin of 2 to 10 carbon atoms. In the present invention, one kind of an olefin may be subjected to an oligomerization reaction or two or more kinds of olefins may be subjected to the reaction. The olefin used herein is, for example, a low-boiling fraction obtained in a petroleum refining process or an ethylene plant. Specifically, an olefin fraction produced in a FCC apparatus or an olefin fraction produced in an ethylene cracker or a coker can be employed. These fractions may be used in combination. In the present invention, only an olefin may be used as the oligomerization raw materiel containing an olefin, but it is preferred that the olefin is diluted with an inert substance such as saturated hydrocarbon, because the temperature rise caused by heat of reaction can be suppressed. The olefin oligomerization of the invention may be carried out in accordance with any reaction systems such as batchwise system, fixed bed system and fluidized bed system. The reaction temperature varies depending on the reactivity of the olefin, but it is in the range of usually 0 to 400 °C, preferably 0 to 300 °C. According to the invention, a higher olefin conversion can be realized at a relatively low temperature as compared with the case of using the conventional catalysts. The reaction can be carried out at atmospheric pressure or under pressure by any of a liquid phase process and a gas phase process. For example, when an olefin of 3 to 4 carbon atoms is mainly used, it is preferred that the reaction temperature is in the range of 0 to 300 °C and the reaction pressure is in the range of 5 to 100 kg/cm 2 -G. The contact time is in the range of 0.1 to 50 hr -1 , preferably 0.1 to 15 hr -1 , in terms of LHSV. In the invention, by conducting oligomerization of an olefin, an oligomer of high value added, such as gasoline, kerosine or gas oil, can be obtained in a high yield. Further, in the invention, an olefin oligomer having a low degree of branching which is useful as a material of a plasticizer, can be obtained with excellent selectivity of the low degree of branching. EFFECT OF THE INVENTION According to the catalyst of the invention, alumina or silica-alumina which is a stable and inexpensive solid acid is used as a carrier, so that the production cost is low. Further, the sulfate ion supported on the alumina or the silica·alumina is stably present, so that a problem of apparatus corrosion or separation does not take place. Moreover, when the catalyst is used in an olefin oligomerization process, the equipment cost and the operation cost can be decreased, and an oligomer of high value added can be selectively obtained in a high yield due to the catalyst having prominently high activity. By the use of the catalyst wherein nickel oxide is supported on the alumina or the silica-alumina in addition to the sulfate ion, an olefin having a low degree of branching can be selectively obtained in a high yield. EXAMPLE The present invention will be further described with reference to the following examples, but it should be construed that the invention is in no way limited to those examples. Example 1 A sulfuric acid (special grade chemical, > 96 %, available from Wako Pure Chemical Industries, Ltd.) was diluted with distilled water to give a sulfuric acid aqueous solution having a concentration of 11.2 g/100 ml. Then, a commercially available alumina carrier (DC-2282, γ-Al 2 O 3 , available from Mitsubishi Chemical Corporation) was impregnated with 66 ml of the sulfuric acid aqueous solution per 100 g of the carrier. The quantity of the impregnation solution corresponded to a water absorption of the alumina carrier. After the impregnation, the thus treated alumina carrier was dried at 110 °C overnight and calcined at 500 °C for 3 hours in an air stream, to obtain a sulfate ion-containing alumina carrier (sulfate ion content: 6.9 % by weight in terms of SO 4 ). The sulfate ion-containing alumina carrier was further impregnated with a nickel nitrate aqueous solution, then dried and calcined at 500 °C for 3 hours in an air stream, to prepare catalyst I wherein NiO was supported in an amount of 10 % by weight in terms of Ni, based on the total weight of the catalyst (weight of sulfate ion-containing alumina + weight of nickel oxide) (sulfate ion content based on total weight of catalyst after supporting of nickel oxide: 6.0 % by weight in terms of SO 4 ). Similarly, catalyst J wherein nickel oxide was further supported after supporting of the sulfate ion on a silica·alumina carrier (IS-28, available from Catalysts & Chemicals Industries Co., Ltd.), catalyst K wherein nickel oxide was supported on untreated alumina containing no sulfate ion (DC-2282, available from Mitsubishi Chemical Corporation) and catalyst L wherein nickel oxide was supported on untreated silica·alumina containing no sulfate ion were prepared. Examples 2 and 3, Comparative Examples 1 and 2 A fixed bed flow type reactor having an inner diameter of 16 mm was charged with 10 ml of catalyst I, J, K or L. To the reactor, ethylene was fed at a feed rate of 3,000 ml/hr to perform oligomerization reaction at a reaction temperature of 200 °C and at atmosphere. The results obtained after 5 hours from the initiation of the reaction are set forth in Table 1. Example Comparative example 2 3 1 2 Catalyst I J K L Carrier Alumina Silica alumina Alumina Silica alumina Content of SO 4 (%) 6.9 6.9 -- -- Content of SO 4 based on total amount of catalyst (%) 6.0 6.0 -- -- Amount of Ni supported (%) 10 10 10 10 Reaction temperature (°C) 200 200 200 200 Ethylene conversion (%) 53 38 0.5 3 Selectivity of n-butene (%) 86 85 As is evident from Table 1, the catalysts I and J wherein nickel oxide was supported on the sulfate ion-containing alumina and the sulfate ion-containing silica-alumina, respectively, were superior in both the ethylene conversion and the selectivity of n-butene to catalysts K and L wherein the nickel oxide was supported on the alumina containing no sulfate ion and the silica-alumina containing no sulfate ion, respectively. Examples 4 and 5, Comparative Examples 3 and 4 A fixed bed flow type reactor having an inner diameter of 16 mm was charged with 60 ml of each catalyst having a composition shown in Table 2. To the reactor, a propane-propylene mixed material containing 79.7 % by weight of propylene was fed to perform oligomerization reaction under the conditions of a reaction pressure of 60 kg/cm 2 -G and LHSV of 1.0 hr -1 . The results obtained after 24 hours from the initiation of the reaction are set forth in Table 2. Example Comparative example 4 5 3 4 Catalyst I J K L Carrier Alumina Silica alumina Alumina Silica alumina Content of SO 4 (%) *1 6.9 6.9 -- -- Content of SO 4 based on total amount of catalyst (%) *2 6.0 6.0 -- -- Amount of Ni supported (%) 10 10 10 10 Reaction temperature (°C) 50 100 50 100 Propylene conversion (%) 83 62 0.6 45 Selectivity of C 6 olefin (%) 76 73 19 Selectivity of C 9 olefin (%) 17 14 36 Average degree of branching of C 6 olefin 0.61 0.86 1.44 *1 and *2 : See remarks of Table 1 As is evident from Table 2, catalysts I and J wherein nickel oxide was supported on the sulfate ion-containing alumina and the sulfate ion-containing silica·alumina, respectively, were superior in both the propylene conversion and the selectivity of C 6 olefin to catalysts K and L wherein the nickel oxide was supported on the alumina containing no sulfate ion or the silica·alumina containing no sulfate ion, respectively. Further, a C 6 olefin having a low degree of branching was obtained by the use of catalyst I or J. Example 6 The alumina carrier containing 6.9 % by weight of the sulfate ion, which was obtained in Example 1, was impregnated with a nickel nitrate aqueous solution in the same manner as in Example 1 except for varying the concentration of the nickel nitrate aqueous solution, then dried and calcined, to obtain catalysts M and N wherein nickel oxide was supported. Separately, the alumina carrier containing 6.9 % by weight of the sulfate ion was pulverized into grains of 100 mesh under and then introduced into a nickel nitrate aqueous solution having a concentration of 1 mol/l. To the resulting mixture was dropwise added an ammonium carbonate aqueous solution having a concentration of 1 mol/l with stirring at 35 °C, to adjust pH of the mixture to 7. The mixture was then filtered, dried and calcined at 500 °C for 3 hr, to prepare catalyst O wherein NiO was supported in an amount of 25 % by weight in terms of Ni. Further, the alumina carrier containing 6.9 % by weight of the sulfate ion was impregnated with a mixture of a nickel nitrate aqueous solution and an aluminum nitrate aqueous solution, then dried and calcined at 500 °C for 3 hours in air, to prepare a catalyst P wherein NiO was supported in an amount of 8 % by weight in terms of Ni and aluminum oxide was supported in an amount of 3 % by weight in terms of Al. Examples 7 - 12, Comparative Examples 5 and 6 A fixed bed flow type reactor was charged with 60 ml of catalyst I, M, N, O, P, L or K in a manner similar to that of Example 4. To the reactor, a C 4 fraction material containing a C 4 olefin of a composition shown in Table 3 was fed, to perform butene oligomerization reaction under the conditions of a reaction pressure of 50 kg/cm 2 -G and LHSV of 1.0 hr -1 . The results obtained after 24 hours from the initiation of the reaction are set forth in Tables 4 and 5. i-Butane 40.0 % by weight n-Butane 12.0 % by weight i-Butene 0.5 % by weight 1-Butene 7.0 % by weight 2-Butene 40.5 % by weight Example 7 8 9 10 Catalyst I M N O Carrier Alumina Alumina Alumina Alumina Content of SO 4 (%) *1 6.9 6.9 6.9 6.9 Content of SO 4 based on total amount of catalyst (%) *2 6.0 6.5 6.9 3.2 Amount of Ni supported (%) 10 5 1.0 25 Reaction temperature (°C) 50 100 150 50 50 100 Butene conversion (%) 75 72 65 72 74 58 Selectivity of C 8 olefin (%) 82 79 80 81 78 78 Average degree of branching of C 8 olefin 1.14 1.04 1.11 1.18 1.48 1.14 *1 and *2 : See remarks of Table 1 Example Comp. Example 11 12 5 6 Catalyst P J K L Carrier Alumina Silica alumina Alumina Silica alumina Content of SO 4 (%) 6.9 6.9 -- -- Content of SO 4 based on total amount of catalyst (%) 5.4 6.0 -- -- Amount of Ni supported (%) 8 10 10 10 Amount of Al supported (%) 3 -- -- -- Reaction temperature (°C) 100 150 175 100 100 100 Butene conversion (%) 71 64 61 75 1 61 Selectivity of C 8 olefin (%) 80 81 79 80 70 Average degree of branching of C 8 olefin (%) 1.04 1.04 1.19 1.17 1.71 The catalyst of the invention wherein nickel oxide was supported on the sulfate ion-containing alumina or silica-alumina carrier had a higher butene conversion as compared with the catalyst which was alumina or silica·alumina containing no sulfate ion, and a C 8 olefin having a low degree of branching was selectively obtained. Further, the catalyst of the invention showed a high butene conversion even at a low temperature, and a C 8 olefin having a low degree of branching was selectively obtained. Furthermore, it was confirmed that the degree of branching of the C 8 olefin was decreased particularly in the oligomerization reaction at a high temperature by the use of the catalyst obtained by allowing the sulfate ion-containing carrier to further support aluminum oxide in addition to the nickel oxide. Example 13 An alumina hydrate was prepared by neutralization reaction of a sodium aluminate and aluminum sulfate in accordance with a method described in "Catalyst Preparation Chemistry" p. 207, by Ozaki, et al., published by Kodansha, 1980. To the amorphous and pseudo-boehmite alumina hydrate powder obtained by drying the alumina hydrate at 110 °C was dropwise added a sulfuric acid aqueous solution. Then, the mixture was kneaded, then adjusted in its water content and extrusion molded. The molded product was dried at 110 °C overnight by means of a dryer and calcined at 550 °C for 3 hours in an air stream, to obtain a sulfate ion-containing γ-alumina carrier. The content of the sulfate ion in the alumina was 8.4 % by weight in terms of SO 4 . The sulfate ion-containing alumina carrier was impregnated with a nickel nitrate aqueous solution in a manner similar to that in the preparation of catalyst I, then dried at 110 °C and calcined at 500 °C for 3 hours in an air stream, to obtain a catalyst wherein NiO was supported in an amount of 10 % by weight in terms of Ni (sulfate ion content based on total weight of catalyst after supporting of nickel oxide: 7.2 % by weight in terms of SO 4 ). Then, a butene oligomerization reaction was carried out under the same conditions as in Example 7. The results are set forth in Table 6. Reaction temperature 50 °C Butene conversion 74 % Selectivity of C 8 olefin 82 % Average degree of branching of C 8 olefin 1.15 Comparative Example 7 An alumina carrier was impregnated with a mixture of a nickel nitrate aqueous solution and a cobalt sulfate aqueous solution, then calcined at 500 °C for 3 hours in an air stream and allowed to stand at the same temperature for 2 hours in an nitrogen stream, to obtain a catalyst. The content of NiO in the catalyst was 1.6 % by weight in terms of Ni, and the content of CoSO 4 in the catalyst was 9.5 % by weight. Using a material containing a C 4 olefin of a composition shown in Table 3, an oligomerization reaction was carried out under the same conditions as in Example 7. The results are set forth in Table 7. The thus obtained catalyst having the metal sulfate of the sulfate group supported on the carrier (conventional catalyst wherein cobalt sulfate was supported on alumina carrier, prepared by methods of Japanese Patent Publication No. 30044/1975 and Japanese Patent Laid-Open Publication No. 85506/1973) had an extremely lower butene conversion, as compared with the catalysts of the invention wherein the sulfate ion per se (not the metal sulfate) was supported on alumina (Examples 7 to 11 in Tables 4 and 5). Further, the average degree of branching of the resulting C 8 olefin was very high. Reaction temperature 50 °C Butene conversion 14 % Selectivity of C 8 Olefin 93 % Average degree of branching of C 8 olefin 1.98

Claims: An olefin oligomerization catalyst comprising alumina and/or silica-alumina, sulfate ion and nickel oxide, said catalyst being obtainable by a process comprising the steps of: a) bringing a sulfuric acid aqueous solution or an ammonium sulfate aqueous solution into contact with at least one oxide selected from alumina and silica-alumina.; b) calcining the thus-contacted oxide at a temperature at which sulfate ion is not decomposed; c) supporting a nickel compound, capable of being converted into nickel oxide by calcination, on the calcined oxide; and d) calcining at a temperature at which a sulfate ion is not decomposed, the sulfate ion being present in the product of (d) in the amount of 0.3 to 60% by weight (in terms of SO 4 ) of the total weight of alumina, silica-alumina and sulfate ion. A catalyst as claimed in claim 1, whereof the nickel oxide constitutes 0.1 to 40% by weight (in terms of nickel) of the total weight of the catalyst. A catalyst as claimed in claim 1 or claim 2 which further comprises aluminum oxide supported on the alumina and/or silica-alumina, obtainable by supporting an aluminum compound, capable of being converted into aluminum oxide by calcination, on said calcined oxide either simultaneously with or subsequent to the supporting of the nickel compound in step (c) and before step (d). A catalyst as claimed in claim 3, whereof the aluminum oxide constitutes 0.1 to 20% by weight (in terms of aluminum) of the total weight of the catalyst. A catalyst as claimed in any preceding claim wherein the calcining temperature in the steps (b) and (d) is in the range 300 to 800°C. A catalyst as claimed in claim 5 wherein said calcining temperature is in the range 400 to 700°C. A process for preparing an olefin oligomerization catalyst comprising the steps of: a) bringing a sulfuric acid aqueous solution or an ammonium sulfate aqueous solution into contact with at least one oxide selected from alumina and silica-alumina.; b) calcining the thus-contacted oxide at a temperature at which sulfate ion is not decomposed; c) bringing the calcined product into contact with a nickel compound capable of being converted into nickel oxide by calcination; and d) calcining the nickel-contacted product at a temperature at which sulfate ion is not decomposed. A process according to claim 7 wherein in step (c), the calcined product is brought into contact with an aluminum compound capable of being converted into aluminum oxide by calcining, together with the nickel compound or after bringing the calcined product into contact with the nickel compound. A process as claimed in claim 7 or claim 8 wherein the calcining temperature in the steps (b) and (d) is in the range 300 to 800°C. A process as claimed in claim 9 wherein said calcining temperature is in the range 400 to 700°C. An olefin oligomerization process comprising subjecting an oligomerization raw material containing an olefin to an oligomerization reaction in the presence of an olefin oligomerization catalyst according to any one of claims 1 to 6. A process as claimed in claim 11 wherein the olefin contains 2 to 10 carbon atoms. A process as claimed in claim 11 or claim 12 wherein said oligomerization raw material is a low-boiling fraction obtained in a petroleum refining process or an ethylene plant. A process as claimed in any of claims 11 to 13 which is carried out at a temperature of 0 to 400°C, a reaction pressure of 0 to 100 kg/cm 2 -G and LHSV of 0.1 to 50 hr -1 . A process as claimed in any one of claims 11 to 14 wherein the olefin is subjected to an oligomerization reaction so as to produce gasoline, kerosine and/or gas oil.

Inventors: FUJIE HIROKAZU, IMURA KOZO, MATSUMOTO HIDEYUKI, NAKANISHI KAZUHISA, NOH TAKAYUKI, FUJIE, HIROKAZU, IMURA, KOZO, MATSUMOTO, HIDEYUKI, NAKANISHI, KAZUHISA, NOH, TAKAYUKI
Applicants: KOA OIL CO LTD, KOA OIL COMPANY, LIMITED
Application year: 1996
Main classification: B01J27
IPC codes: C07C2, C10G50, B01J27