Cresol Isomerization on HZSM-5

Abstract

The cresol transformation was investigated on HZSM-5 at 380°C. Isomerization and disproportionation products were observed. Isomerization was the main reaction. The cresol isomerization rates on HZSM-5 increased fromortho- tometa- topara-isomer with decreasing molecular kinetic diameter. The initial conversion rates were in a ratiorp:rm:ro=20:3:1. The isomerization product selectivity favoured molecules with the smallest kinetic molecular diameter at the onset of the reaction, and as reaction proceeded, the reaction product composition was determined thermodynamically. Forortho-cresol, at low conversion them/pratio slightly decreased with conversion, and at higher conversions the selectivity became insensitive to the degree of conversion, giving am/pratio equal to 3. Formeta-cresol isomerization, thep/oratio decreased steadily with conversion, and the initialparaselectivity was associated to both transition state and product shape/size selectivity. The isomer equilibrium composition obtained was 36%ortho-, 48%meta-, and 16%para-cresol, in disagreement with the thermodynamically calculated composition. The isomerization rates were always greater than disproportionation rates. The isomerization rates followed the sequencerI(p)>rI(m)>rI(o), while the disproportionation rate sequence wasrD(p)>rD(m)≅rD(o). The initialI/Dselectivities were in a ratio (I/D)p:(I/D)m:(I/D)o=100:30:8.