Para-Selective Chlorination of Chlorobenzene on Modified Y-Type Zeolites

Para-selective liquid-phase chlorination of chlorobenzene was investigated on modified Y-type zeolites. It was indicated that chlorination occurred in the pore of zeolites. Less acidic Na-Y revealed to present higher para-dichlorobenzene selectivity than H-Y. In order to modify catalyst properties of Na-Y, Na-Y was impregnated with sodium chloride solution. Thus obtained NaCl-impregnated Na-Y showed about 5-6% higher para-selectivity than the original Na-Y. This improvement was explained by salt-bearing effect and salt-modification effect. ESCA showed electron transfer from chloride anion to aluminum and 27 Al MAS NMR indicated that sodium at S II moved to the direction of the center of sodalite cage. Thus, it was strongly suggested that acid strength of active site was weakened by salt-bearing and as a result para-selectivity increased. Although salt-modification effect is not clear yet, it was considered that NaCl blocked less selective active site on the outer surface or that NaCl influenced the active site on the surface somehow. When salt-bearing Y-type zeolites of various silica to alumina ratios(3.6-5.5) were studied, higher para-selectivity was obtained for each of the catalysts than their originals. The zeolite of silica/alumina ratio 4.6 gave the highest para-selectivity. Dependence of para-selectivity on silica/alumina ratio was explained by acid strength and the number of active site.