Study On The Hydrolyzation Of Cyclohexyl Acetate Catalyzed By Acidic Zeolites

Cyclohexanol is an important chemical product that are widely used in chemical industry.The synthesis of cyclohexanol from cyclohexene via cyclohexyl carboxylate is a clean route with high efficiency.However,when cyclohexyl acetate was used,cyclohexanol selectivity was very low because of the pyrolysis of cyclohexyl acetate to cyclohexene and acetic acid.In this study,inorganic salts were used as co-catalyst and the effect on hydrolyzation of cyclohexyl acetate catalyzed by HZSM-5 was investigated.Moreover,study on hydrolyzation of cyclohexyl acetate over NaHSO₄ or H?was also explored.First,it was found that the inorganic salts,such as NaBr,ZnSO₄ and NaHSO₄,could restrict the pyrolysis of cyclohexyl acetate and then increased the selectivity of cyclohexanol by hydrolyzation.However,NaBr and ZnSO₄ could destroy the Brosted acid sites on the surface of HZSM-5 by ion exchange and dealumination and decrease its catalytic activity.Though NaHSO₄ could also damage the acid sites,it could accelerate the hydrolyzation of cyclohexyl acetate because of the acidity of NaHSO₄ itself.Then,hydrolyzation of cyclohexyl acetate catalyzed by NaHSO₄ was investigated.Under the optimized conditions,cyclohexyl acetate conversion was 63.8%with 90.9%cyclohexanol selectivity and the results were far better that those over HZSM-5.When the aqueous solution of NaHSO₄ was separated and reused for this reaction,cyclohexanol selectivity changed unobviously and cyclohexyl acetate conversion decreased gradually.This was due to the accumulation of acetic acid in the reaction system which would in favor of the proceeding of the reverse reaction and therefore lower the cyclohexyl acetate conversion.Thirdly,hydrolyzation of cyclohexyl acetate catalyzed by H?was investigated.Under the optimized conditions,cyclohexyl acetate conversion was 47.0%with 88.1%cyclohexanol selectivity.Comparison of catalytic performance of H?with HZSM-5 was conducted.It was thought that the Brosted acid sites on zeolites were capable of promote the pyrolysis of cyclohexyl acetate to cyclohexene.Because there are more acid sites,especially Brosted type acid sites,on HZSM-5 than H?,HZSM-5 exhibited high catalytic activity and low selectivity for the hydrolyzation of cyclohexyl acetate.Lastly,in-situ FT-IR technique was used to investigate the adsorption of reactants and pyrolysis process on the surface of HZSM-5 and H?zeolites.It was found that there were more strong acid sites,bridging hydroxyl,on HZSM-5 than H?.And most of acid sites on H?were weak acid sites,silanol.Therefore,H?showed a low activity and high cyclohexanol selectivity for the hydrolyzation of cyclohexyl acetate.