Novel nonmetal catalyst of supported tetraphenylphosphonium bromide for acetylene hydrochlorination

Tetraphenylphosphonium bromide (TPPB) ionic liquid-supported catalysts were synthesized and evaluated for the acetylene hydrochlorination reaction for the development of highly efficient nonmetal catalysts as substitutes for the currently used industrial mercuric catalyst in the production of vinyl chloride (VCM). The optimal 15% TPPB/SAC catalyst exhibited favorable catalytic activity and stability, with the highest acetylene conversion of 97.1% and the selectivity for VCM above 99.5% under the conditions of 220 degrees C, an acetylene gas hourly space velocity (GHSV) = 30 h(-1) and V-HCl/VC2H2 = 1.15. Characterized by TPD, FTIR, XPS, etc., TPPB exhibits strong adsorption toward HCl but very weak adsorption toward C2H2 and VCM; in particular, the adsorbed HCl can change the conformational structure of TPPB. DFT calculations suggest that over the active catalytic site of TPPB, the activation energy of acetylene hydrochlorination is 21.15 kcal mol(-1), which is much lower than that without catalyst (44.29 kcal mol(-1)). During the reaction, the H-Cl bond is preferentially activated through accepting the electrons transferred from the anion of TPPB, and then the C2H2 is activated to complete the addition reaction of H and Cl. Such unique preferential activation toward the H-Cl bond as well as the weak adsorption to the product VCM promotes the catalytic activity and the stability of the supported TPPB catalysts. The amount of carbon deposition on the 15% TPPB/SAC catalyst is as low as 2.99%, even after 300 h of reaction. The high activity and stability of the 15% TPPB/SAC catalyst indicate great promise for its application as a nonmetal catalyst for acetylene hydrochlorination.