Chemistry of hydrocarbon compounds – Unsaturated compound synthesis – By addition of entire unsaturated molecules – e.g.,...
Reexamination Certificate
2002-05-22
2003-11-18
Dang, Thuan D. (Department: 1764)
Chemistry of hydrocarbon compounds
Unsaturated compound synthesis
By addition of entire unsaturated molecules, e.g.,...
C585S514000, C585S531000
Reexamination Certificate
active
06649802
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the oligomerization of olefins (e.g. propylene) to higher value products (e.g. hexene) using a molecular sieve catalyst. In such a process, acid washing of the molecular sieve prior to use results in increased selectivity of the oligomerization reaction to the desired product. More specifically, the catalyst is a layered catalyst with an outer layer of a molecular sieve bonded to an inner core, and the inner core made of an inert material.
BACKGROUND OF THE INVENTION
Processes for the oligomerization of light olefins (e.g. ethylene, propylene, and butylene) to produce higher carbon number olefin products (e.g. C
6
+
olefins) are well known. Oligomerization processes have been employed to produce high quality motor fuel components as well as petrochemicals from ethylene, propylene, and butylene. These oligomerization processes are also referred to as catalytic condensation and polymerization, with the resulting motor fuel often referred to as polymer gasoline. In the refining area, methods have been continually sought to improve the octane number of the gasoline boiling range oligomerization products. This octane enhancement is generally realized through the improvement of the oligomerization reaction selectivity to enhance the representation of high octane blending components (e.g. branched olefins) in the product slate. The ability of the process to better target specific carbon number species is also a primary consideration when highly purified chemical grade products are desired. In any case, the enrichment of product slate to the targeted species, in addition to providing a higher quality and quantity of useable products, also benefits catalyst life. This is due to the reduction in non-selective heavy oligomers that condense into coke which ultimately covers the catalyst.
Known catalysts for effecting the oligomerization reaction include heterogeneous catalysts such as solid acids and homogeneous catalysts, in particular boron trifluoride as described, for example, in U.S. Pat. No. 3,981,941. Other catalysts fall within the description of mild protonic acids, generally having a Hammett acidity function of less than−5.0. Particularly preferred among these are solid phosphoric acid (SPA) catalysts having as a principal ingredient an acid of phosphorous such as ortho, pyro, or tetraphosphoric acid. Details of SPA catalysts are provided in the prior art, for example in U.S. Pat. No. 5,895,830.
The use of zeolites, particularly those of the medium pore consideration, as oligomerization catalysts is also described, along with various catalyst treatment methods designed to improve performance. U.S. Pat. No. 4,547,613 discloses the use of a ZSM−5 type catalyst that has been conditioned by treatment with a light hydrocarbon gas at low pressure and elevated temperature. U.S. Pat. No. 4,520,221 describes a process for providing high yields of lubricating oils from the conversion of light olefins such as propylene using ZSM−5 catalyst. The results are achieved through removing the surface acidity of the catalyst by treatment with a bulky amine. U.S. Pat. No. 4,642,404 is directed to the conversion of C
2
+
olefins to C
5
+
olefins over a catalyst of a bound, high silica zeolite having a constraint index of 1-12. The catalyst is modified, while it is at least partially in the hydrogen form, by steaming to improve activity.
Finally, U.S. Pat. No. 5,284,989 discusses the use of a constrained intermediate pore siliceous acidic zeolite (e.g. ZSM−22, −23, or −35) having Brönsted acid activity and wherein the zeolite surface is rendered substantially inactive for acidic reactions. The zeolite can be inactivated by contact with dicarboxylic acid (e.g. oxalic acid). The reference states that treatments with strong acids such as HCl, HNO
3
, and H
2
SO
4
“are limited, in many cases, . . . by the onset of crystal degradation and loss of sorption capacity.”
In contrast to the prior art, and specifically the teachings of the '989 patent, the present invention is based on the realization that treatment of solid oligomerization catalysts with a strong acid provides significant benefits in terms of product selectivity and yield. The unexpected improvements in process performance associated with the present invention are believed to directly result from changes in catalyst surface properties stemming from the acid treatment.
SUMMARY OF THE INVENTION
In a broad embodiment, the process is for oligomerizing an olefinic feed in the liquid phase. The process comprises contacting the olefinic feed with a catalyst at oligomerization conditions. The catalyst is a layered structure comprising an inner inert core, and a thin outer layer bonded to the inner core and comprising an acidic molecular sieve. The outer layer of sufficient thinness is to control amounts of oligomerization and to provide selective control over the amounts of specific oligomerization products in the liquid phase.
In a more specific embodiment of the invention, the molecular sieve comprises a crystalline silicoaluminate or metalloaluminophosphate characterized by a 3-dimensional framework structure and having a chemical composition on an anhydrous basis expressed by an empirical formula of:
(EL
x
Al
Y
P
z
)O
2,
The EL is an element selected from the group consisting of silicon, magnesium, zinc, iron, cobalt, nickel, manganese, chromium and mixtures thereof. The mole fraction of EL is “x” and has a value of at least 0.005, the mole fraction of Al is “y” and has a value of at least 0.01, and the mole fraction of P is “z” and has a value from 0 to about 0.6.
This and other objects, and embodiments of the present invention will become apparent to those skilled in the art in the following detailed description of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to the use of a layered catalyst composition for the oligomerization of an olefinic feed stream. The layered catalyst composition comprises an inner core composed of an inert material. The inert material is non-reactive to the olefins in the feed stream, and preferably is made of an impermeable material. The layered catalyst further comprises an outer layer composed of a molecular sieve having a composition providing acidic sites for the oligomerization reactions to proceed. The layered catalyst is contacted with a light olefinic feed for oligomerization to a higher olefin product. This provides a benefit for controlling the amount of oligomerization of the lighter olefins, and provides a method of economically producing the catalyst.
The feed for the process of the present invention generally comprises light olefin components, typically C
2
to C
5
olefins, although olefins with higher carbon numbers may also be used. Sources of the olefin feeds normally include: light gas streams recovered from the gas separation section of a refinery fluid catalytic cracking (FCC) process, C
4
streams from steam cracking and coker off gas, or the effluents from light paraffin (e.g. LPG) dehydrogenation zones. In most operations, the combined C
3
and C
4
olefins will account for at least 50% by weight of the total feed olefins. Certain situations may also warrant the oligomerization of feeds having, with respect to their olefin content, exclusively ethylene, propylene, or butylene (either pure isomers or mixed normal and branched isomers) to obtain relatively high yields of a given carbon number product. If a feed comprising predominantly propylene (or predominantly propylene with an inert diluent such as propane) is processed, the dimer (hexene) and trimer (nonene) are generally the desired products and their yields can be maximized using the acid-washed molecular sieve catalyst of the present invention, combined with optimizing the reaction conditions. Likewise, a butylene feed may be incorporated to target primarily an octene product or a product containing octenes as well as dodecenes.
The layered catalyst composition provides excep
Abrevaya Hayim
Frame Robert R.
Jan Den-Yang
Dang Thuan D.
Gooding Arthur E.
Molinaro Frank S.
Tolomei John G.
UOP LLC
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