Removal of phosphorus-containing compounds from an olefin...

Details Removal of phosphorus-containing compounds from an olefin... Removal of phosphorus-containing compounds from an olefin...

2000-05-08

2002-12-10

Barts, Samuel (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

Reexamination Certificate

active

06492568

ABSTRACT:

FIELD OF THE INVENTION
The invention pertains to a process of removing contaminants from olefin feedstocks using a sorbent comprising a metal. The contaminants removed preferably are phosphorus-containing compounds, most preferably organophosphines and/or organophosphine oxides. Preferred olefin feedstocks are made by oligomerizing ethylene to linear olefins having from about 6 to about 36 carbon atoms, preferably from about 11 to about 20 carbon atoms, and most preferably from about 14 to about 18 carbon atoms.
BACKGROUND OF THE INVENTION
Depending upon the method of their production, olefin feedstocks may comprise a variety of impurities. Impurities found in olefins that are produced by oligomerization of ethylene units include phosphorus-containing impurities, including but not necessarily limited to organophosphines and organophosphine oxides. These phosphorus-containing compounds are largely removed from many olefin streams during the process of distillation to separate various “cuts” of olefins. Unfortunately, the organophosphines and organophosphine oxides found in C
14
-C
18
streams tend to co-distill with the C
14
-C
18
in the product, making it difficult, if not impossible to remove these phosphine impurities by simple distillation.
C
6
-C
36
olefins have utility in the fields of paper and pulp processing, drilling fluids, and machine or metal working oils. Alcohols of such olefins have commercial importance in a variety of applications, including detergents, soaps, surfactants, and freeze point depressants in lubricating oils. These alcohols are produced by a number of commercial processes, such as by oxo or hydroformylation of long chain olefins. In many of these applications, the olefin feedstocks are treated using acid catalysts.
Unfortunately, any phosphorus-containing compounds in these olefin feedstocks will negatively affect acid catalysts. The phosphorus-containing moieties are basic in nature and will neutralize the active acid sites of the catalyst, which lowers catalyst activity and performance. The organophosphine moeities may even cause the olefins to oligomerize into undesirable forms.
Methods are needed to reduce the phosphorus-content of olefin feedstocks.
SUMMARY OF THE INVENTION
The present invention provides a method for purifying an olefin feed comprising a content of phosphorus-containing compounds. The method comprises contacting the olefin feed with a sorbent comprising a metal under conditions and for a time effective to reduce the content of phosphorus-containing compounds, producing a purified olefin feed.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a process and sorbents which efficiently and effectively reduce the content of phosphorus-containing compounds in olefin streams. In a preferred embodiment, the content is reduced to about 1 ppm or less, preferably about 0.5 ppm or less, most preferably to about 0.1 ppm or less. Given sufficient run time, the sorbents reduce the content of phosphorus-containing compounds in the olefin stream to parts per billion (ppb) levels.
The invention may be used to treat substantially any olefin stream. Preferred olefin streams are linear olefin streams made by oligomerizing ethylene. Some of the known processes for oligomerizing ethylene use organophosphorus compounds that result in phosphorus as a contaminant in the resulting olefin stream. A preferred commercially available olefin feed for the treatment of the present invention is the product marketed in the United States by Shell Chemical Company under the trademark NEODENE®. In a preferred embodiment, the olefin feedstock is treated before exposure to an acid catalyst, or before exposure to other conditions which would be adversely affected by the basic nature of phosphorus-containing contaminants.
In a most preferred embodiment, the olefin stream is the feedstock for the skeletal isomerization catalyst used in the method described in U.S. Pat. No. 5,849,960, which has been incorporated herein by reference. The olefins used in the feed to this skeletal isomerization catalyst are mono-olefins having at least 6 carbon atoms, preferably having from about 11 to about 20 carbon atoms, and most preferably having from about 14 to about 18 carbon atoms.
In general, the olefins in the feed to the skeletal isomerization catalyst are predominately linear. While the olefin feed can contain some branched olefins, the olefin feed processed for skeletal isomerization preferably contains greater than about 50 percent, more preferably greater than about 70 percent, and most preferably greater than about 80 mole percent or more of linear olefin molecules.
The olefin feed to the skeletal isomerization catalyst does not consist of 100% olefins, and usually contains a distribution of mono-olefins having different carbon lengths, with at least 50 wt. % of the olefins being within the stated carbon chain range or digit, however specified. Preferably, the olefin feed will contain greater than 70 wt. %, more preferably about 80 wt. % or more of mono-olefins in a specified carbon number range, the remainder of the product being olefins of other carbon number or carbon structure, diolefins, paraffins, aromatics, and other impurities resulting from the synthesis process. The location of the double bond is not limited. The olefin feed composition may comprise alpha olefins, internal olefins, or a mixture thereof.
The sorbent of the present invention comprises a suitable metal, preferably comprising metal oxide, on a suitable support. Preferred metals are transition metals, including but not necessarily limited to those selected from Groups 3-12 of the Periodic Table of the Elements. When the Periodic Table of the Elements is referred to herein, the source of the Periodic Table is: F. Cotton et al.
Advanced Inorganic Chemistry
(5th Ed. 1988). Suitable metals include, but are not necessarily limited to Sc, V, Cr, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mn, Ag and combinations thereof. Preferred metals are Fe, Co, Ni, Mn, Ag and Cu. In a preferred embodiment, the metal is silver or copper, preferably in the form of oxides. The sorbent suitably comprises from about 0.1 wt. % to about 50 wt. % of the metal oxide of the foregoing metals, preferably copper. Preferably, the sorbent comprises from about 1 wt. % to about 20 wt. %, more preferably from about 5 wt. % to about 15 wt. %, and most preferably from about 8 wt. % to about 10 wt. % of the metal oxide.
The metal oxide resides on a suitable support material. Although the surface area of the support is not a critical feature, the surface area preferably is at least about 10 m
2
/g in order to provide sufficient contact between the sorbent and the olefin stream. In a preferred embodiment, the support has a surface area of from about 100 m
2
/g to about 900 m
2
/g. Acidic supports are more advantageous than basic supports. Suitable support materials are acidic or neutral, most preferably acidic. Suitable support materials include, but are not necessarily limited to alumina, silica, molecular sieves, such as zeolites, activated carbon, aluminosilicate clays, amorphous silicoaluminas, and the like. Where the support material surface is porous, the pores preferably are sufficiently large to permit entry of bulky phosphorus containing compounds in the feed. A most preferred support material for copper is an acidic or neutral alumina. A most preferred support material for silver is X-zeolite. A commercially available sorbent that is suitable for use in the present invention is SELEXSORB AS™, which is commercially available from Alcoa Industrial Chemicals.
It is preferred for the particles of supported sorbent to be as small as possible; however, if the size of the particles is too small, the pressure drop through the bed becomes too large. Very small particles also are difficult to retain in the sorbent bed. SELEXSORB AS™ is purchased in the form of ⅛ inch spheres, and may be used in the process as purchased. However, spheres are not the most efficient particle shape for purposes of maximizing particle surface to vo

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