Study On The Kinetic Of Non-catalytic Esterification To Produce Benzyl Benzoate And The Application In Benzoic Acid Purification

Benzyl benzoate, an important chemical raw material, is used for a variety of floral essences as styling agent and correction fragrance, and also has many applications in the food flavor. In addition, the product is widely used as plasticizers or solvents. In medicine field, it can be used for preparation of whooping cough medicine, asthma treatment drug, with the effect of expanding blood vessels and relieving spasm.Benzyl benzoate was easily produced by the esterification reaction of benzoic acid and by-products benzyl alcohol in the preparation of benzoic acid and benzaldehyde by toluene liquid-phase oxidation method, and it was difficult to be separated from the products due to its high boiling point. Thus, it is valuable for waste reduction and economic improvement to inhibit the esterification reaction or enrich benzyl benzoate via the study on the principles of esterification reaction.In this paper, the synthesis process of benzyl benzoate from benzoic acid and benzyl alcohol under non-catalyst was investigated, as well as the conversion of benzyl alcohol as a function of the reaction temperature, the ratio of benzoic acid and benzyl alcohol, the speed of agitator and the reaction time. Results showed that the esterification reaction could be promoted at following conditions: the reaction temperature was below 200℃, the ratio of benzoic acid and benzyl alcohol was 3:1, and the speed of agitator was 300 r/min. On the contrary, the inhibition of benzyl benzoate in the benzoic purification could be reached at the temperature of 160℃and decompression operation.In addition, the synthesis kinetics of benzyl benzoate from benzoic acid and benzyl alcohol under non-catalyst was also investigated. The dynamics equation was established using the power series model, and the parameters were figured out by the initial velocity method in order to obtain the rate equation under different conditions. It showed that the esterification reaction of benzoic acid and benzyl alcohol was reversible and endothermic. The positive reaction was a second-order reaction, and the reverse reaction was a one-order reaction. The equilibrium constant could be increased with the increasing temperature. Meanwhile, the relationship between reaction rate constant and temperature was determined by calculating the rate constants and activation energy of positive and reverse reaction under different temperatures. The dynamics calculation results were in good agreement with the experimental values. The coincidence was the highest at 200℃and 160℃,and the rational ratio of benzoic acid to benzyl alcohol were 3:1.The benzoic acid distillation column was simulated with Aspen Plus by appropriate model and kinetic regulations. The effect of the flow rate of water vapor, the liquid holdup of column plate or packing and the operating pressure for the concentration of benzyl benzoate and benzyl alcohol were studied. The results showed that benzyl benzoate was converted to benzoic acid and benzyl alcohol completely when operating pressure was dropped from 100KPa to 50KPa and the consumption of water vapor was decreased by 42.1% , and the purpose for inhibiting the occurrence of benzyl benzoate was achieved.