Study On The Esterification Of Cyclohexene With Formic Acid Over Carbon-based Solid Acid And Its Kinetics

Cyclohexanol is an important chemical intermediate.The synthesis of cyclohexanol via cyclohexyl formate using cyclohexene as raw material is a clean route,and it can improve the efficiency of the direct hydration of cyclohexene which is used in the chemical industry.In this study,a kind of peanut shell-derived carbon-based solid acid catalyst?PSCSA?was prepared for the esterification of cyclohexene with formic acid,which is the first step of the indirect hydration of cyclohexene to cyclohexanol.The PSCSA was characterized and evaluated for its catalytic performance for the esterification.And then,the kinetics was studied over PSCSA and HZSM-5 catalyst.First,PSCSA was prepared from peanut shell,a agricultural waste,by partially carbonization and sulfonation.The PSCSA was characterized and its acidity was also analyzed.Then it was used as catalyst for the esterification of cyclohexene with formic acid and the reaction conditions were optimized.At a 3:1 molar ratio of formic acid to cyclohexene,a catalyst loading of 0.07 g/mL of cyclohexene,and a reaction time of 1 h at140?,cyclohexene conversion was 88.4%with 97.3%selectivity to cyclohexyl formate.Moreover,the carbon-based solid acid catalyst also showed higher reusability than HZSM-5because of its large-size pores that were minimally affected by the accumulation of oligomerized cyclohexene,which resulted in the deactivation of HZSM-5.Its catalytic activity decreased in a certain at the first two recycles due to the leaching of polycyclic aromatic hydrocarbon containing-SO₃H groups.Then it remained constant in the following reuse.Second,the kinetic study of the esterification of cyclohexene with formic acid over HZSM-5 and PSCSA were conducted respectively.Based on the Langmuir-Hinshelwood-Hougen-Watson?LHHW?mechanism and Eley-Rideal?ER?mechanism,three heterogeneous models were proposed to discriminate the reaction mechanisms over the two catalysts.The results of kinetic study showed that the heterogeneous models gave a more satisfactory agreement with the experimental data that the pseudo-homogeneous model.According to the kinetic results,it is suggested that the esterification of cyclohexene with formic acid catalyzed by HZSM-5 belongs to the LHHW mechanism.The activation energy obtained is 58.6 kJ/mol,and the adsorption constants of cyclohexene,formic acid and cyclohexyl formate are determined to be 5.262,128.5 and 56.9.While,the esterification over PSCSA belongs to the ER mechanism,and cyclohexene is adsorbed on the active sites during the reaction.The activation energy obtained is 51.2 kJ/mol,and the adsorption constants of cyclohexene and cyclohexyl formate are determined to be 2.568 and 72.5.