| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 11.01.2000 |
| 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. DETAILED DESCRIPTION OF THE INVENTION In each of the above-mentioned aspects of the invention, the selected element is advantageously aluminium. The elements selected for the core and for the outer layer are advantageously, but not necessarily, the same. For example, a gallium-containing outer layer may surround an aluminium-containing core. Advantageously, the resulting crystalline product is ion exchanged with ammonium ions or protons, and calcined to yield the acid form of the molecular sieve. Advantageously, calcination takes place at a temperature of at most 600.degree. C., preferably at most 500.degree. C. Certain features of the process for the manufacture of the molecular sieve of the present invention are shared with processes known in the art as commonly practised or as described in the literature. These may be described briefly, as follows: ______________________________________ Propene up to 50% Propane up to 10% C .sub.4.sup.+ up to 95% Polyunsaturates up to 1.5% ______________________________________ (As used herein, the term polyunsaturates includes compounds having two or more unsaturated carbon to carbon bonds, whether double or triple, and also compounds other than acetylene which contain one triple bond, e.g., propyne.) Higher boiling components, especially C.sub.5.sup.+ hydrocarbons, may be removed from such a feedstream source as a desirable product, e.g., naphtha from fluid bed catalytic cracking, as a result of processing or to avoid further handling of by-products. For example, the tar formed from steam cracking of vacuum gas oil may be removed as an undesirable by-product in the primary fractionation of the process gas, while the C.sub.5.sup.+ component of the product from steam cracking of ethane may be removed during the quench and process gas compression stages immediately following cracking. Intermediate boiling components (C.sub.3.sup.+) of a feedstream source may also be removed from the dilute olefin stream as a desired co-product or to avoid further handling of by-products. For example, propene may be removed from the process gas effluent of cracked naphtha for use as a chemical feedstock. production of the crystalline framework the organic compound acts as a template around which the crystalline framework grows, or which causes the crystallization to be directed to form a particular crystalline framework. Preferred agents for the manufacture of ZSM-22 sieves are mono- and di-aminoalkanes having up to 12 carbon atoms, particularly 4, 6, 8, 10 or 12 carbon atoms, e.g. 1,6-diaminohexane (which is preferred), diethylamine, 1-aminobutane or 2,2'-diaminodiethylamine; arylamines containing up to 8 carbon atoms, heterocyclic organic compounds, e.g., as N-ethylpyridinium; polyalkylenepolyamines, e.g. triethylene tetramine or tetraethylene pentamine, and alkanolamines, e.g. ethanolamine or diethanolamine. A preferred quantity of template R, based on the preferred template of 1,6-diaminohexane, is a molar ratio of R/SiO.sub.2 in the synthesis mixture of 0.025 to 0.4. The SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in the synthesis mixture is generally at least 150:1, preferably at least 250:1, and may be as high as 1500:1. Ratios between 300:1 and 900:1, especially between 300:1 and 600:1, are especially preferred. The SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in the zeolite layer after crystallization may be up to 30% lower than the molar ratio in the synthesis mixture; this reduction may be taken into account in selecting the proportions of components in the synthesis mixture, to ensure the required relationship between core and outer layer ratios. The SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio in the core crystals dispersed in the synthesis mixture is advantageously at most 120:1, is more advantageously in the range 40:1 to 120:1, and preferably in the range 60 to 100:1. The proportions of reactants in the synthesis mixture are generally lower than in the normal synthesis mixture, i.e., in addition to the lower aluminium content, the synthesis mixture should be highly diluted, for example, with water. The synthesis mixture including the core material may contain, for example, up to 85%, advantageously from 50 to 80% by weight, of diluent, especially water. Advantageously, crystallization is effected at 120 to 180.degree. C., preferably 140 to 170.degree. C. The crystallization time may be from 10 to 72 hours, typically 15 to 48 hours. After crystallization the zeolite may be washed with deionized water or with acidified water, and then, optionally after a drying or calcining step, ion exchanged to yield the acidic form. The zeolite is preferably exchanged with ammonium ions and subjected to conditions under which the ammonium ions decompose, with the formation of ammonia and a proton, thus producing the acidic form of the zeolite. Alternatively the acid form may be obtained by acid exchange with, for example, hydrochloric acid. The exchange with ammonium ions may be carried out by any suitable method, for example, by treating the crystals with an aqueous solution of ammonium chloride, ammonium nitrate or ammonium hydroxide. Exchange with protons is advantageously carried out by contacting the crystals with a dilute acid solution, e.g., HCl. After exchange with ammonium ions or protons, the crystals may be calcined, advantageously at a temperature of from 120.degree. to 600.degree. C., preferably from 150.degree. to 500.degree. C. Suitable calcination times range from 1 hour to several days, the temperatures in the upper part of the specified temperature range corresponding to the shorter heating times and the temperatures in the lower part of the specified temperature range corresponding to the longer heating times. Thus, for example, crystals may be calcined at a temperature of 400.degree. C. for from 1 to 20 hours. At a temperature of 120.degree. C., longer calcination times of at least 2 days and preferably from 3 to 5 days will generally be necessary to achieve adequate voiding of the pores. The sieve may be post-treated, as by steaming, or may be caused to contain other cations either by incorporation during preparation or by subsequent ion-exchange, examples of suitable cations being Ni, Cd, Cu, Zn, Pd, Ca, B and Ti and rare earth metals. Advantageously, the molecular sieve of the invention has a refined constraint index (as hereinafter defined) greater than 2, and advantageously greater than 10. The refined constraint index, CI.degree., is defined in J. A. Martens, M. Tielen, P. A. Jacobs and J. Weitkamp, Zeolites, 1984, p. 98, and P. A. Jacobs & J. A. Martens, Pure and Applied Chem., 1986, Vol. 58, p. 1329, as the ratio of 2-methylnonane to 5-methylnonane produced at 5% conversion in the hydro-isomerization of n-decane. Examples of molecular sieves having a CI.degree. between 2 and 10 include ZSM-5, 11, 12, 35, 38, 48, and 57, SAPO-11, MCM-22 and erionite, those having a CI.degree. between 5 and 10 presently being preferred. Examples of molecular sieves having a CI.degree. greater than 10, and accordingly most preferred, include ZSM-22, ZSM-23, and certain ferrierites. It is within the scope of the oligomerization process of the invention to employ mixtures containing two or more molecular sieves. The molecular sieve or zeolite catalyst is advantageously ZSM-22, described in U.S. Pat. No. 4,556,477 and in WO 93/25475, the disclosures of which are incorporated herein by reference. A molecular sieve crystallite size advantageously up to 5 .mu.m, preferably within the range of from 0.05 to 5 .mu.m, more especially from 0.05 to 2 .mu.m, and most preferably from 0.1 to 1.0 .mu.m, may be employed. The proportion by weight represented by the surface layer, based on the total weight of the molecular sieve of the invention, may, for example, be within the range of 5% to 20%, conveniently from 8% to 15%, after calcination. The molecular sieve may be used in the form of granules, powder or other shaped form, e.g., an extrudate. The extrudate advantageously contains the molecular sieve, and a binder, for example alumina, silica, an aluminosilicate, or clay, advantageously in a proportion of from 10:90 to 90:10, preferably 20:80 to 80:20, by weight of sieve to binder. The sieve and binder may be composited by, for example, intimately mixing them together in the presence of water, and extruding or otherwise shaping, e.g., by pelletizing. The feed olefin advantageously contains from 2 to 12 carbon atoms, and preferably from 2 to 6 carbon atoms; more preferably, the olefin feed advantageously contains propene, butenes and/or pentenes. Reaction conditions for the oligomerization process of the invention may be, with the exception of the use of the novel catalyst, in accordance with conditions operative for prior art processes oligomerizing the same olefin. The olefin may, for example, be fed to the catalyst in admixture with an inert diluent, e.g., a saturated hydrocarbon, in the liquid or, preferably, the gaseous, phase. For a feed comprising propene, a suitable diluent is propane, advantageously in proportions of propene:propane from 90:10 to 10:90, preferably from 10:90 to 60:40, especially about 50:50 by weight. Correspondingly, for a butene feed, a suitable diluent is butane, advantageously in proportions from 90:10 to 10:90, preferably from 75:25 to 50:50, especially about 2:1, by weight olefin:saturate. The feed is advantageously hydrated; preferably it contains from 0.05% to 2% by weight water. The desired proportion of water may be incorporated by saturating the feed at an appropriate temperature, e.g., from 25 to 60.degree. C., or by injecting water through a pump. The oligomerization may take place at a temperature advantageously in the range of from 160.degree. C. to 300.degree. C., preferably from 170.degree. C. to 260.degree. C., and most preferably from 180.degree. C. to 260.degree. C., at a pressure advantageously in the range of from 5 to 10 MPa, preferably from 6 to 8 MPa, and at an olefin hourly space velocity advantageously in the range 0.1 to 20, preferably from 0.5 to 10, and most preferably 0.75 to 3.5, whsv. In olefin oligomerizations employing a normal prior art catalyst, e.g., ZSM-22, it was found that with a decrease in conversion rate, selectivity to dimer, e.g., from butene to octene, increased but the degree of branching increased also. Using the catalyst of the present invention, however, it has surprisingly been found that, at lower conversion rates, the selectivity to dimer is retained and is accompanied by a decrease in the degree of branching. Accordingly, oligomerization may be carried out at a lower conversion rate, unreacted monomer separated from oligomer, and recycled, resulting in a high dimer selectivity without loss of linearity in the product. Further, the catalyst of the present invention has the additional advantage over the bulky-amine treated material of the prior art that it may readily be regenerated, as by calcining, without requiring a subsequent amine treatment. The catalyst of the present invention will moreover not differ on regeneration in its ability to oligomerize olefins to a less highly branched product from the catalyst of the invention as originally prepared . |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
|
Want more information ? Interested in the hidden information ? Click here and do your request. |