ACIDIC CS-TUNGSTOPHOSPHORIC ACID AS SOLID CATALYSTS FOR ISOBUTANE(, NH4+, AND K+ SALTS OF 12)2-BUTENE ALKYLATION/

The caesium, ammonium, and potassium salts of 12-tungstophosphoric aci d (HPW) have been prepared with different stoichiometries (1 less than or equal to x less than or equal to 3), and their catalytic behavior measured for the liquid phase alkylation of isobutane with 2-butene at 80 degrees C. The salts with a cation content of 2.5 less than or equ al to x less than or equal to 3, and that of Cs+ with x = 2, showed a much higher surface area than the parent acid, which is partially due to the formation of micropores, The micropores presented a fairly homo geneous distribution, with an average diameter in the range of 6-11 An gstrom, depending on the type of cation and cation content. The activi ty of the heteropoly acid and their monovalent type B salts for isobut ane alkylation could be correlated with the surface acidify of the sol ids, Thus, the initial (1 min TOS) olefin conversion went through a ma ximum for the NH4+ and K+ salts with a cation content of x = 2.5, and in the range of 2 less than or equal to x less than or equal to 2.5 in the case of the Cs+ compounds. (NH4)(2.5)PW showed a very high initia l cracking activity (ca. 72 wt% C-5-C-7 in C-5+), suggesting the prese nce of surface acid sites of a higher acid strength in the ammonium sa lt, as compared to the caesium and potassium salts with similar compos ition, In all cases the desired trimethylpentanes (TMPs) were the pred ominant compounds in the C-8 fraction formed in the initial reaction s tages. The deactivation rate also depended on the nature of the cation exchanged in the heteropoly salts. (C) 1996 Academic Press, Inc.