Gas Phase Acetoxylation Of Toluene Over Pd-Sn-K/HY-W Catalyst

Benzyl acetate is a versatile fine chemical product. It is widely used in perfumery, food and chemical industries. Direct synthesis of benzyl acetate for gas phase acetoxylation of toluene, which possesses advantages of mild reaction conditions, simple experimental procedure, environmental friendliness, has good development and applied prospects.The catalysts were prepared by multi-step incipient wetness method and the gas phase acetoxylation of toluene to produce benzyl acetate in a single step over the Pd-Sn-K/Support catalyst was investigated in an integral reactor.Activity of the catalyst influeneced by the composition of catalyst was studied. It was found that the Pd-Sn-K/HY-W(0.09) catalyst optimized in composition behaved better catalytic performance both at 200℃and 220℃. The presence of Sn component was very important to the Pd-Sn-K/HY-W catalyst for the gas phase acetoxylation of toluene. With the Sn/support mass ratio increasing from 0 to 0.09, the selectivity to benzyl acetate increased at a same toluene conversion.The influences of the reaction temperature, mole ratio of oxygen to toluene and that of acetic acid to toluene on gas phase acetoxylation of toluene over the Pd-Sn-K/HY-W(0.09) catalyst were investigated. The results indicated that temperature had a great effect on the reaction in the range of 180～220℃. At 200℃, the mole ratios of both oxygen to toluene and acetic acid to toluene holding at 1 are favorable to the reaction. By comparing the reaction results obtained in different reaction conditions, we suggested that although increasing the reaction temperature and the mole ratio of O₂ to toluene could significantly increase the conversion of toluene, both of them led to much lower benzyl acetate formation selectivity compared to that obtained by decreasing the gas hourly space velocity of the reaction at the same toluene conversion level.The influence of water on the reaction of toluene acetoxylation in gas phase was studied. It was found that a small quantity of water(with 0.3 mole ratio to toluene) presented in reaction system could promote the selectivity to benzyl acetate of the reaction.The catalytic stability of Pd-Sn-K/HY-W(0.09) for the reaction of toluene acetoxylation in gas phase was investigated. It revealed that this catalyst was stable enough to withstand the effect caused by the possible stop and start of the reaction during real the reaction processes. It was found that coke deposition could be removed by flowing oxygen and nitrogen through the catalyst in the raising temperature process of the reation, and activity of the catalyst could be thus regenerated.Dynamics of gas phase acetoxylation of toluene over Pd-Sn-K/HY-W(0.09) catalyst was studied, and the power function model was employed to describe the rate of the reaction. Kinetic parameters of the reaction at 200℃over the catalyst were obtained as follows: reaction orders with respect to toluene, acetic acid and oxygen were 0.57, 0.29, 0.43, respectively, and the activation energy was 109.4 kJ/mol for the reaction over the catalyst. The dynamic equation for the toluene acetoxylation was validated by the experimental data.