Continuous Synthesis Of P-methoxycyclohexanone And It’s CFD Simulation

The catalytic hydrogenation reaction is a dangerous hydrogen-involving process.Traditional stirred-tank reactor hydrogenation process has defects such as long reaction time,low safety,severe catalyst wear,and difficulty in achieving automatic control.If the reaction is transferred to a three-phase trickle bed reactor operated continuously,the larger gas-liquid-solid three-phase contact area can effectively solve the problems of small mass transfer area and low macroscopic reaction rate in the stirred-tank reactor hydrogenation process,which can promote realizing the goal of continuous,safe,automatic,efficient,and economical reaction.In this paper,the catalytic hydrogenation kinetics of P-methoxyphenol were studied in a stirred-tank reactor,a small gas-liquid-solid trickle bed reactor was designed,and the continuous synthesis of P-methoxycyclohexanone by catalytic hydrogenation of P-methoxyphenol was explored.The fluid flow conditions in the trickle bed reactor are also investigated by simulating the fluid mechanics of the gas-liquid-solid three-phase flow in the drip bed reactor.The main elements are as follows:1.The macroscopic kinetic model of catalytic hydrogenation of P-methoxyphenol was established,and the kinetic equation was fitted by experimental data.The results show that the macroscopic reaction rate of catalytic hydrogenation of P-methoxyphenol can be expressed by power function kinetic equation in the stirred-tank reactor,and the reaction orders of P-methoxyphenol concentration and hydrogen are 0.48 and 0.37,respectively.The reaction activation energy is 26.38 kJ/mol,and the pre-exponential factor is 48.91(mol0.52/MPa0.37·L0.52·min).Verification analysis shows that this kinetic equation has high credibility.2.A small trickle bed reactor was designed,and the continuous synthesis of P-methoxycyclohexanone by catalytic hydrogenation of P-methoxyphenol was carried out to explore the effects of solvent,space-time,temperature,pressure,concentration,catalyst particle size,and loaded promoter on the reaction conversion and selectivity.The results show that the best process conditions were obtained using a self-made Ca supported alkaline earth metal and Pd/C-3 catalysts added with Lewis acid:space-time of 13 min,temperature of 150℃,pressure of 0.2 MPa,and concentration of 0.05 g/mL,with 68%conversion of P-methoxyphenol and 70%selectivity of P-methoxycyclohexanone.3.A physical model of gas-liquid-solid three-phase flow in a trickle bed reactor was established,and the fluid flow conditions in the trickle bed reactor were studied by simulation with Fluent software in CFD(Computational Fluid Dynamics).The results show that,from the perspective of reaction rate and production efficiency,the space-time should be controlled between 3～16 min,and the catalyst particle size should be larger than 0.3 mm;the higher the catalyst bed,the larger the space-time of fluid flow through the bed,which is beneficial to improve the conversion rate.Increasing the diameter of an industrial-scale trickle bed reactor can reduce the wall effect on the catalyst bed inlet,and the larger the diameter of the reactor,the more uniform the distribution of fluid velocity inside the catalyst bed.