Study On Preparation Of Cyclohexanol From Hydration Of Cyclohexene Catalyzed By Acid-Modified HZSM-5

Cyclohexanol is an important intermediate for the production of caprolactam,adipic acid,polyamide and other organic products.Industrial production methods mainly include cyclohexane oxidation,phenol hydrogenation,cyclohexene hydration and other methods,but at present most industrial production of cyclohexanol adopts cyclohexane oxidation.Although the technology of this method is relatively mature,it still has the disadvantages of low conversion of cyclohexane and low yield of cyclohexanol and cyclohexanone.With the rise and development of green chemical industry,researchers are paying more and more attention to the preparation of cyclohexanol from cyclohexene hydration.Due to the fact that the reaction is carried out in an aqueous phase and low solubility of cyclohexene in water,low catalyst activity,which results in the low hydration conversion and cyclohexanol yield.Therefore,it is urgent to develop a new hydration process to improve the efficiency of this process.In this work,the commercial HZSM-5?Si/Al=38?molecular sieve catalyst was modified,and new hydration conditions were explored to improve the conversion of cyclohexene and the yield of cyclohexanol.The main conclusions are as follows:Firstly,the effects of different types of molecular sieves and some acidic catalysts on the hydration of cyclohexene were investigated.It was found that HZSM-5 with good hydrothermal stability showed good catalytic performance for the reaction.Moreover,the influence of HZSM-5 with different Si/Al ratio on hydration reaction was further investigated.The results show that HZSM-5 with Si/Al ratio of38 has better catalytic performance.Then the hydration reaction conditions were optimized over HZSM-5 with a Si/Al ratio of 38.The results showed that the optimal reaction conditions were that the reaction temperature was 130 ^oC,reaction time was3 h,reaction pressure was 0.5 MPa,mass fraction of catalyst was 20%,cyclohexene and water ratio was 2:5?v:v?and stirring speed was 900 rpm.The conversion of cyclohexene was 9.0%with 99.5%of selectivity to cyclohexanol,and the catalyst exhibited better stability.The microstructures of HZSM-5 were revealed by XRD,SEM,BET,Py-FTIR,NH₃-TPD,FT-IR,TG-DTG and other characterization methods,and the possible hydration mechanism was also suggested.Secondly,in order to further improve the reaction efficiency of this process,HZSM-5?Si/Al=38?was modified by acid.The effects of different acids and acid concentrations on the modification of molecular sieves were emphatically investigated.The experimental results showed that the catalyst modified with HNO₃displayed better catalytic performance.Furthermore,the effects of HZSM-5 with different Si/Al ratios modified by HNO₃ were also studied.It was found that HZSM-5with Si/Al ratio of 38 exhibited better catalytic performance.Finally,the influence of modification conditions?such as HNO₃ concentration,treatment temperature,treatment time,etc.?on the catalytic performance of HZSM-5 was further investigated.The results showed that the cyclohexene conversion could reach to 12.2%with 100%of the selectivity to cyclohexanol under the optimal reaction conditions.The microstructures of HZSM-5 modified by nitric acid were characterized by XRD,SEM,BET,Py-FTIR,NH₃-TPD,FT-IR,and TG-DTG.This work affords a new cyclohexene hydration approach for improving the cyclohexanol yield,and has important theoretical significance and application prospect for realizing the synthesis of caprolactam from benzene.