Abstract
AbstractThe reaction of trimethylbenzene (TMB) over alumina‐pillared montmorillonite (Al‐PM) had been investigated in a fixed‐bed flow reactor at 300 °C and atmospheric pressure. Al‐PM calcined in the range 300‐500 °C exhibited decreased layer distance, surface area and acid amount. The strong acid sites of Al‐PM calcined at 500 °C were greatly diminished according to measurements of ammonia temperature‐programmed desorption. Under our conditions the reaction proceeded mainly via isomerization and disproportionation with little dealkylation. The conversion of reactant decreased in the order 1,2,3‐TMB ≥ 1,2,4‐TMB > 1,3,5‐TMB and the selectivity of isomerization in the order 1,2,3‐TMB > 1,3,5‐TMB > 1,2,4‐TMB, corresponding to the order of diminishing thermal instability. Both the catalytic activity and the selectivity ratio of disproportionation to isomerization decreased with increased calcined temperature and time‐on‐stream. o‐Xylene content in the total xylene produced from 1,2,4‐TMB or 1,2,3‐TMB greatly exceeded the composition at thermodynamic equilibrium. These results arc consistent with the decrease of both the strong acid sites and the pore size of Al‐PM which exhibits the restricted transition state selectivity.
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