ABSTRACT
There is a considerable industrial demand for para-xylene because of its importance as raw material for the manufacture of terphthalic acid, which a major component in the production of polyester fibers, polyethylene terephthalate resins, vitamins and other pharmaceuticals. In this work, H-ZSM-5 zeolite was hydrofluorinated to modify its acid sites number and strength. This zeolite, before and after HF treatment was tested as a catalyst for the alkylation of toluene with methanol at reaction temperatures of 300-500oC, molar ratio of methanol to toluene of 2.5 and liquid hourly space velocity of 2.6v/v/h. HF acid concentrations between 1.0 and 4.0wt% were also examined. The reaction selectivity for para-xylene production has been found to reach an optimum at an HF concentration of 3.0wt%. The catalysts were characterized by temperature programmed desorption (TPD) of ammonia for acid sites distribution analysis. The BET surface area and pore volume for each catalyst were also estimated. Higher concentrations of HF have been found to cause leaching of the structural aluminium of the zeolite, causing fluoro-alumino debris that results in blocking of the channels of this zeolite and giving higher values of Thiele modulus (ФL) and hence lower values of effectiveness factor (η). The simple kinetic evaluation of the reaction rate constant, k, and apparent activation energy were carried out.