Isopentane disproportionation

#The conversion of isopentanes to alkanes (paraffins) containing fewer carbon atoms per molecule and alkanes containing more carbon atoms per molecule (i.e., the disproportionation of isopentanes) in the presence of hydrogen fluoride as a catalyst is known and has been described in U.S. Pat. Nos. 2,403,649, 2,403,650 and 3,679,771. This process has recently gained importance because of governmental regulations requiring the reduction of the amount of volatile C.sub.4 and C.sub.5 alkanes in gasoline. Thus, there is an incentive to convert isopentanes to higher isoalkanes, especially isoheptanes and isooctanes which are valuable high-octane motor fuels, and to isobutane which is a feedstock for the alkylation with olefins and also for the production of MTBE (via isobutylene). The present invention is directed to an improvement of the HF-catalyzed disproportionation of isopentane.

#It is an object of this invention to improve the disproportionation of isopentanes (2-methylbutane and/or 2,2-dimethylpropane) to isobutane and C.sub.6 + alkanes. Other objects and advantages of the present invention will be apparent from the detailed description and the appended claims.

#In accordance with this invention, in a process for disproportionating isopentanes in the presence of hydrogen fluoride as the catalyst at effective disproportionation conditions, the improvement comprises adding at least one higher isoalkane additive containing 6-18 (in particular 6-10) carbon atoms per molecule to a liquid feed comprising at least one isopentane so as to increase the conversion of said at least one isopentane to isobutane and to higher product alkanes which contain at least 6 carbon atoms per molecule. Preferably, the formed disproportionation product is then subjected to a separation process, wherein hydrogen fluoride, unconverted isopentane and at least one unconverted isoalkane additive are separated from the remainder of the disproportionation product (primarily isobutane and C.sub.6 + product alkanes) and are then recycled to the disproportionation reaction zone.

#The following example is presented to further illustrate this invention and is not to be construed as unduly limiting the scope of the invention.

#A Monel autoclave reactor (volume: 300 ml), which was equipped with a mechanical stirrer, a thermocouple, a pressure gauge and various valves, was filled with about 150 grams (about 161 ml) of anhydrous hydrogen fluoride (HF). The reactor content was slowly stirred, and its temperature was raised from room temperature to about 190.degree. F. (about 88.degree. C.). Thereafter, the stir rate was increased to about 1500 rpm, and 75 mL isopentane was charged to the reactor via a feed sight gauge by means of pressurized nitrogen gas.

#After a reaction time of about 30 minutes, at a N.sub.2 pressure of about 250 psig (i.e., about 17.2 atm. gauge) and a reaction temperature ranging from about 182.degree. F. (about 83.degree. C.) to about 202.degree. F. (about 94.degree. C.), the stirring of the reactor was stopped, and the product was withdrawn from the reactor. First, the product was allowed to settle in a sight gauge settler for about 30 seconds, and then it was passed through a column of alumina beads (1/4 inch diameter) so as to remove soluble HF from the product. The product was analyzed by means of a gas chromatograph.