Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
1999-11-08
2001-10-09
Tran, Hien (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C502S067000, C502S071000, C502S077000
Reexamination Certificate
active
06300536
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the treatment of hydro-carbons, especially olefinic hydrocarbons, to effect oligomerization, and to catalysts for use in such treatment.
BACDGROUND 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
4
to C
20
, and more particularly in the C
6
to C
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 dealumination 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° C., preferably at most 500° 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
4
+
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
5
+
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
5
+
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
3
+
) 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 fr
Martens Luc Roger Marc
Verduijn Johannes Petrus
Verrelst Wim Herman
Dang Thuan D.
Exxon Mobil Chemical Patents Inc.
Tran Hien
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