| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | January 11, 2000 |
| PATENT TITLE |
Catalyst having a core and surface layer and use of same in olefin oligomerization |
| PATENT ABSTRACT |
A molecular sieve comprising a core having deposited thereon a surface layer, wherein the surface layer has a higher Si:Al ratio than that of the core, provides for lower branching in olefin oligomerization products. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | October 27, 1997 |
| PATENT CT FILE DATE | January 29, 1996 |
| PATENT CT NUMBER | This data is not available for free |
| PATENT CT PUB NUMBER | This data is not available for free |
| PATENT CT PUB DATE | August 15, 1996 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT CLAIMS |
We claim: 1. A particulate molecular sieve, each particle of the molecular sieve comprising a core having deposited thereon a surface layer, the core comprising a zeolite containing silicon and aluminium, and the surface layer comprising a zeolite containing silicon and aluminium, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:aluminium ratio than that of the core. 2. The particulate molecular sieve according to claim 1, wherein the Si:Al ratio in the surface layer is in the range 300:1 to 1500:1. 3. The particulate molecular sieve according to claim 1, wherein the molecular sieve has a CI.degree. of at least 10. 4. A process for the oligomerization of an olefin, which comprises contacting under oligomerization conditions a feed comprising at least one olefin with an olefin oligomerization catalyst comprising a particulate molecular sieve comprising a core having deposited thereon a surface layer, the core comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, and the surface layer comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:selected element ratio than that of the core. 5. The process according to claim 4, wherein the silicon:selected element ratio of the core is at most 120:1. 6. The process according to claim 4, wherein the silicon:selected element ratio of the core is in range 60:1 to 100:1. 7. The process according to claim 4, wherein the silicon:selected element ratio in the surface layer is at least 150:1. 8. The process according to claim 4, wherein the silicon:selected element ratio in the surface layer is in the range 300:1 to 1500:1. 9. The process according to claim 4, wherein the molecular sieve has a CI.degree. of at least 2. 10. The process according to claim 4, wherein the molecular sieve has a CI.degree. of at least 10. 11. The process according to claim 4, wherein the molecular sieve is ZSM-22. 12. The process according to claim 4, wherein the selected element is aluminium. 13. The process according to claim 4, wherein the olefin contains from 2 to 12 carbon atoms. 14. The process according to claim 4, wherein the olefin contains from 2 to 6 carbon atoms. 15. The process according to claim 4, wherein said process is carried out at a temperature within the range of from 160.degree. C. to 300.degree. C. 16. The process according to claim 4, whereby an oligomer having a reduced degree of branching is formed. 17. A process for the manufacture of a particulate molecular sieve, which comprises heating an aqueous synthesis mixture comprising a source of silicon, a source of aluminium, a source of monovalent inorganic cations, the synthesis mixture having dispersed therein crystals of a molecular sieve containing silicon and aluminium, the molar ratio of silicon to aluminium in the crystals being lower than the molar ratio of silicon to aluminium in their respective sources in the synthesis mixture, to cause crystallization of a molecular sieve layer from the synthesis mixture onto the surfaces of the crystals. 18. The process according to claim 17, wherein said aqueous synthesis mixture further comprises an organic structure directing agent. |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to the treatment of hydrocarbons, especially olefinic hydrocarbons, to effect oligomerization, and to catalysts for use in such treatment. BACKGROUND OF THE INVENTION Olefinic hydrocarbons are employed as starting materials in the hydroformylation, or oxo, process, for the eventual manufacture of numerous valuable products, e.g., alcohols, esters and ethers derived therefrom, aldehydes, and acids. In many of these end uses, linear or lightly branched hydrocarbon chains have advantages compared with more heavily branched chains. In the oxo process itself, moreover, olefins with heavily branched chains are less reactive than those with linear or lightly branched structures and, for a given degree of branching, certain isomers are less reactive than others. Olefinic feedstocks, especially in the C.sub.4 to C.sub.20, and more particularly in the C.sub.6 to C.sub.15 range, are frequently produced by oligomerization of lower molecular weight original starting materials, a process that, because of rearrangements that take place during the reaction, may produce an undesirably high proportion of multiply branched olefins, even if the original materials are linear. Also, the locations of the branches, at sites close to each other on the hydrocarbon chain, or in the central region of the chain, or both, resulting from the oligomerization further reduce the reactivity of the molecules in the oxo reaction. There are other areas in which a less highly branched hydrocarbon has advantages; these include the alkylation of aromatic hydrocarbons by reaction with olefins in the manufacture of surfactants and polyolefin stabilizers. There is accordingly a need to provide a method to produce an olefin oligomer having a reduced degree of branching of a hydrocarbon material. U.S. Pat. No. 5,284,989 (Apelian, et al, assigned to Mobil Oil Corporation) describes the use of a medium pore size shape-selective acid crystalline zeolite in the catalytic oligomerization of olefinic hydrocarbons, and discusses the factors influencing the linearity or degree of branching of the products. Acid activity at the zeolite particle surface is said to favour the production of branched products, and reference is made to de-alumination of zeolite surfaces to reduce surface acidity, or the ratio of surface acidity to intracrystalline acid site activity. Other reduction methods mentioned in an extensive prior art review in the patent include the use of bulky amines to inactivate acid sites; the invention to which the patent is directed is the use of a dicarboxylic acid to inactivate the surface acid sites. In U.S. Pat. No. 5,250,484 (Beck et al., also assigned to Mobil), surface acidity is reduced by contacting the catalyst with an ammonia-borane solution and calcining to form an inactive ceramic layer on the surface. In U.S. Pat. No. 4,788,374 (Chu et al., also assigned to Mobil), surface acidity is reduced by forming a silica shell on a metallosilicate core by crystallizing silica on the surface of the core in the presence of fluoride. SUMMARY OF THE INVENTION The present invention provides a process for the oligomerization of an olefin, which comprises contacting under oligomerization conditions a feed comprising at least one olefin with an olefin oligomerization catalyst comprising a particulate molecular sieve, each particle of the molecular sieve comprising a core having deposited thereon a surface layer, the core comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, and the surface layer comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:selected element ratio than that of the core. The invention also provides a particulate molecular sieve, capable of catalysing olefin oligomerization, each particle of the molecular sieve comprising a core having deposited thereon a surface layer, the core comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, and the surface layer comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:selected element ratio than that of the core. The invention further provides the use of a particulate molecular sieve, each particle of the molecular sieve comprising a core having deposited thereon a surface layer, the core comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, and the surface layer comprising a zeolite containing silicon and at least one element selected from aluminium, gallium and iron, the zeolite of the surface layer being of the same crystalline structure as the core and having a higher silicon:selected element ratio than that of the core, as an olefin oligomerization catalyst to reduce the degree of branching of the oligomer product. The invention still further provides a process for the manufacture of a particulate molecular sieve, which comprises heating an aqueous synthesis mixture comprising a source of silicon, a source of an element selected from aluminium, gallium and iron, a source of monovalent inorganic cations, and, if desired or required, an organic structure directing agent, the synthesis mixture having dispersed therein crystals of a molecular sieve containing silicon and an element selected from aluminium, gallium, and iron, the molar ratio of silicon to selected element in the crystals being lower than the molar ratio of silicon to selected element in their respective sources in the synthesis mixture, to cause crystallization of a molecular sieve layer from the synthesis mixture onto the surfaces of the crystals |
| PATENT EXAMPLES | Available on request |
| PATENT PHOTOCOPY | Available on request |
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