SHAPE-SELECTIVE ALKYLATION OF POLYNUCLEAR AROMATIC-HYDROCARBONS OVER H-MORDENITES

Liquid phase alkylation of polynuclear aromatic hydrocarbons, such as biphenyl and naphthalene, over H-mordenite (HM) was studied. Selective formation of the narrowest products, 4,4'-diisopropylbiphenyl (4,4'-D IPB) and 2,6-diisopropylnaphthalene (2,6-DIPN) occurred only over HM a mong the zeolites with twelve-membered pore openings. These shape-sele ctive catalysis are ascribed to steric restriction of transition state and to entrance of bulky substrates into the pores. Catalytic activit y and shape-selectivity are governed by coke-deposition on the acid si tes inside the pores. Dealumination of HM enhanced catalytic activity and the selectivity of 4,4'-DIPB and 2,6-DIPN because of the decrease of coke-deposition, while the activity and the selectivity were low ov er HM with the low SiO2/Al2O3 ratio. Non-regioselective catalysis occu rs on external acid sites because the acid sites inside the pores an d eactivated by blocking pores due to severe coke-deposition. Selectivit y of DIPB isomers was changed with propylene pressure. Selective forma tion of 4,4'-DIPB occurred under high propylene pressure (<0.3 MPa), w hile the selectivity of 4,4'-DIPB decreased with the conversion under such low propylene pressure as 0.2 MPa because of isomerization of 4,4 '-DIPB to 3,4'-DIPB. 4,4'-DIPB was almost exclusive isomer in the enca psulated DIPB isomers inside the ports under all pressures. preferenti al adsorption of propylene prevents isomerization of 4,4'-DIPB under h igh pressures. Isomerization of 4,4'-DIPB occurs on the external acid sites under low pressures. Selectivity of 4,4'-diethylbiphenyl (4,4'-D EBP) in ethylation of biphenyl was much lower than that in isopropylat ion. Among the BEEP isomers, 4,4'-DEBP has the highest reactivity for ethylation to higher ethylates inside the pores, whereas isopropylatio n of 4,4'-DIPB was negligibly low inside the pores. These differences are ascribed to the difference in steric restriction at the transition state composed of substrate, propylene, and acid sites inside the por es. Deactivation of external acid sites of HM was examined to reduce n on-regioselective alkylation and isomerization. External acid sites we re deactivated by calcination after impregnation of cerium on HM witho ut the decrease in pore radii. Selectivities of 2,6-DIPB and 4,4'-DIPB were improved in the isopropylation of naphthalene and biphenyl becau se of the suppression of non-regioselective alkylation and isomerizati on at the external surface.