Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2000-01-26
2001-03-13
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C521S025000, C521S028000
Reexamination Certificate
active
06200924
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to solid acid catalysts and more particularly relates to a porous highly fluorinated acidic polymer catalyst and a process for its manufacture.
BACKGROUND OF THE INVENTION
Perfluorinated sulfonic acid polymer is known for use as an acid catalyst in a variety of chemical reactions (F. J. Waller, et al.
Chemtech,
July 1982, pp. 438-441). The polymer is used in a variety of physical forms, including powder, particles and pellets in a range of sizes and shapes, films, and tubes. High surface area is generally desirable to facilitate contact of the polymer with the material or materials with which it interacts, and to make most efficient use of the polymer. Surface area can be increased by more finely dividing the solid polymer, or by using the polymer on or in a substrate as described in U.S. Pat. Nos. 5,430,212 and 5,824,622. Finely divided polymer can pack and obstruct flow in continuous processes in which reactants pass through a catalyst bed. Carry-over of fines and resulting down-stream contamination is also a problem. Cleaning spent polymer is complicated by these same factors. By combining the polymer with a substrate, high surface area may be achieved without finely dividing the polymer. However, the substrate can interact with the strongly acid polymer and affects its activity. Separation of polymer from the substrate, and attrition of the substrate during use are also problems.
New forms of perfluorinated sulfonic acid catalyst are needed which have high surface area but avoid the problems inherent in finely divided polymer or polymer-on-substrate forms of catalyst.
SUMMARY OF THE INVENTION
In accordance with the invention, a solid acid catalyst is provided which comprises porous highly fluorinated acidic polymer. The catalyst is comprised of at least about 90 wt. % highly fluorinated acidic polymer and has a surface area of about 0.01 m
2
/g to about 5 m
2
/g. Preferably, the catalyst is substantially free of pores having a size of about 1.7 to about 300 nm as measured by the BET absorption method. Preferably, the highly fluorinated acidic polymer is highly fluorinated sulfonic acid polymer.
In accordance with a process for making a solid acid catalyst in accordance with the invention, highly fluorinated acidic polymer or precursor thereof is exposed to a pressurized fluid to produce fluid-swelled polymer or polymer precursor. The fluid-swelled polymer or polymer precursor is heated to a temperature above the softening point of said fluid-swelled polymer or precursor. The pressure of the pressurizing fluid is then reduced sufficiently quickly that gases escape from said fluid-swelled polymer and the escaping gases expand said polymer or polymer precursor into a porous structure. The polymer or polymer precursor is cooled to at least partially retain the porous structure.
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Francis J. Waller et al., Catalysis with Nafion,Chemtech, pp. 438-441, Jul. 1987.
Howard, Jr. Edward George
Lloyd Ralph Birchard
E. I. Du Pont de Nemours and Company
Wood Elizabeth D.
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