The effect of propylene pressure on shape-selective isopropylation of biphenyl over H-mordenite

Abstract The effect of propylene pressure on the isopropylation of biphenyl was investigated over highly dealuminated H-mordenite. The selectivity of 4,4′-diisopropylbiphenyl (4,4′-DIPB) in liquid phase products was achieved up to 90% under a high propylene pressure of 0.8 MPa, whereas the decrease of the selectivity of 4,4′-DIPB by the isomerization to 3,4′-DIPB was observed under low pressure of 0.1 MPa. However, the formation of IPBP isomers was not influenced by the pressure. The yield of 4-isopropylbiphenyl (4-IPBP) reached a maximum at 50–60% conversion of biphenyl, whereas that of 3-IPBP increased monotonously. The isomerization of 4,4′-DIPB occurred extensively under low propylene pressure, but decreased with the increase of the pressure. No significant isopropylation of 4,4′-DIPB was observed even under high pressure. The selectivities of 4,4′-DIPB encapsulated in the catalysts were more than 90% in both cases for the isopropylation of biphenyl and for the isomerization of 4,4′-DIPB under every pressure. These results of the isopropylation and the isomerization suggest that selective formation of 4,4′-DIPB occurred in the pores, and that high selectivity under high pressures is due to the prevention of the adsorption of 4,4′-DIPB at external acid sites because of preferential adsorption of propylene. The isomerization of 4,4′-DIPB under low pressures occurred on external acid sites where no propylene was adsorbed.