Alkylation of isobutane by the butane–butene fraction catalyzed by a superacidic ionic liquid

Abstract

The effect of the catalytic activity of a superacidic ionic liquid on the selectivity of formation of C 8 isomers and the yield of alkylation gasoline in the alkylation of industrially produced isobutene and butane-butene fractions was studied.Currently there are two basic methods for the production of alkylation gasoline -alkylation of isobutane with olefins over sulfuric or hydrofluoric acids, and also over their mixture with additives of other acids [1]. The complexity of exploitation of homogeneous acid catalysts -corrosion, consumption of the catalyst, difficulty in their regeneration -has led, starting from the 60s of the last century, to the search for new heterogeneous alkylation catalysts.Heterogeneous catalysts containing SbF 5 , FSO 3 H-SbF 5 , HF-SbF 5 [2, 3] on carriers have been widely studied, as well as ion-exchange resins and sulfated zirconium oxide [4].Sulfated zirconium oxide (SZO) is characterized by the strongest acidic centers in a series of known heterogeneous superacids and it has high activity in the alkylation of isobutane with C 2 -C 4 olefins [5]. However recently the view has been expressed on the lack of success in attempts to create effective industrial samples based on SZO, connected to reduction reaction of the sulfate sulfur, which is the starting of the chain process which accompanies the generation of tert-butyl cations [6].The most promising direction for the development of the technology for the preparation of alkylation gasoline on heterogeneous catalysts is the use of zeolites of the faujasite type (FAU structural type) [7,8].Most promising direction in the development of technology for alkylation gasoline on heterogeneous catalysts is the use of zeolites such as faujasite.The principal drawbacks of all the heterogeneous catalysts for the alkylation of isobutane with olefins are: the small number of active sites calculated for 1 g of catalyst, the short life-time of the catalysts dye to rapid coking with formation of products which are difficult to desorb (polyalkyl bicyclic olefins with 12-28 carbon atoms) on the surface of catalyst, and diffusion complications in the pores of the catalyst caused by high rate of alkylation of isobutane [9].In this connection the authors examined catalytic media, which combined with the properties of the liquid acids, but would be environmentally friendly. One such direction -ionic liquids (IL) -are substances which are liquid at temperatures below 100°C and consist of organic cations and inorganic anions, independent on the degree of dissociation. Investigations [10,11] have shown in principle the possibility of carrying out the alkylation of isobutane based on IL, however the alkylating agent used was only butene-2, which does not illustrate the complete picture on the potential of using industrial sources. In paper [12] it was proposed that a Brønsted acid, namely HCl, should be included additionally in the composition of the IL. For