Structure Optimal Regulation Of Dimethyl Adipate Hydrogenation Catalysts And Multi-scale Simulation Of The Reaction Process

1,6-Hexanediol(HDOL)is an important chemical intermediate that is widely used in the synthesis of special chemicals and a variety of polymers,polyesters,polyurethanes and coatings.Hydrogenation of DMA to HDOL with relatively simple process and high selectivity,that can be reckoned as a most feasible way for the industrial production of HDOL.Our previous studies showed that Cu-ZnO-Al2O3 catalyst had excellent catalytic activity in DMA hydrogenation,but the stability was a great challenge for industrial application.In this paper,the structure of Cu-ZnO-Al2O3 catalyst was optimized according to the characteristics of DMA hydrogenation reaction to improve its catalytic stability.The thermodynamics and kinetics of the reaction were systematically studied,and multi-scale numerical simulation of the reaction process was carried out to provide reference to the design of DMA hydrogenation catalyst for industrial application.In order to explore the deactivation mechanism of Cu-based catalysts in DMA hydrogenation and the relationship between structure and catalytic stability,Cu-ZnO and Cu-Al2O3 binary catalysts with different copper contents were prepared by co-precipitation method,and the influence mechanism of zinc and aluminium components on catalyst structure and stability was investigated.Significant deactivation of Cu-ZnO and Cu-Al2O3 catalysts was observed.The deactivation mechanism of the two catalysts were different due to their different structures.Sintering was the main reason for the decrease of catalytic activity of Cu-ZnO catalysts,cause of the lower dispersion of copper in the catalysts and the relatively weak interaction between copper particles and ZnO.While the leading case for the rapid deactivation of Cu-Al2O3 catalysts was carbon deposition,due to the smaller pore diameter of the catalysts.The key to improve the catalytic stability of Cu-based catalysts in DMA hydrogenation was to improve the anti-sintering property and enlarge the pore size.Comparing the characterization results of Cu-ZnO and Cu-Al2O3 catalysts,the addition of zinc component was conducive to the formation of larger pore and then reduce the amount of carbon deposition,while the addition of aluminium component could significantly improve the dispersion of copper and that was contribute to the improvement of anti-sintering property of catalysts.Based on the above results,the structure and morphology of Cu-ZnO-Al2O3 catalysts can be controlled by changing the content of ZnO and Al2O3,and CZA30-1 catalyst with excellent catalytic stability and thermal stability was obtained.Furthermore,it was found that ZnO could act as a barrier to restrict the migration of copper particles and further improve the anti-sintering property as well as enlarge the pore size of the catalyst.In order to explore the influence of operation conditions on the equilibrium of the DMA hydrogenation reaction,thermodynamic calculation and analysis of the reaction system were carried out.Firstly,thermodynamics properties such as standard molar enthalpy of formation,standard entropy and constant pressure heat capacity of DMA,6-hydroxyhexanoic acid methyl ester(1C6MEol,intermediate product)and HDOL were estimated by using of Benson group contribution method.Both Joback group contribution method and Constantinou-Gani(C-G)group contribution method were applied to estimate the critical properties and the estimated results were compared with available literature values.It was found that Joback method was more suitable for the estimation of critical properties of DMA hydrogenation.Vapor pressures of pure DMA and HDOL were measured by a modified Othmer still,and the eccentric factor and the molar enthalpy of evaporation were calculated.Besides,the estimation method of eccentric factor of 1C6MEol was optimized based on the calculated results of DMA and HDOL.The molar volume of saturated liquid of chemicals were estimated by the contrast method.The state of mixtures under different conditions were analyzed by Soave-Redlish-Kwang(RKS)state equation,and the results indicated that no liquid was formed during the reaction.Additionally,thermodynamic analysis on hydrogenation of DMA was carried out on the basis of the above calculation results,and the effects of temperature,pressure and molar ratio of hydrogen to ester on the reaction equilibrium were investigated.Kinetics study of DMA hydrogenation catalyzed by CZA30-1 catalyst was carried out in a high pressure fixed bed reactor,and the kinetics data were obtained under the following reaction conditions:T=473～513 K,p=2～6 MPa,H2/DMA=150～270,liquid hourly space velocity(LHSV)=1.28～2.55 h-1.According to the expression of Langmuir-Hinshelwood-Hougen-Watsont(LHHW)theory,35 kinds of hyperbolic kinetic models were assumed.Optimized the parameters of kinetic models by using of the experimental data,and the better equation was screened out.The optimal kinetic model is represented as:r=(k1KDMApDMAKHpH-k2KHDOLpHDOLKMeOHpMeOH)/(1+KHpH+KDMApDMA+KHDOLpHDOL+KMeOHpMeOH)2 A synergy mechanism was established in which hydrogen and the ester adsorb on the active sites in molecular state,surface reaction of reaction 1 is the rate-determing step.Furthermore,the kinetics equation in power function form which is more simple and convenient for engineering application was established.The parameters of kinetics equation were fitted by the classical fourth-order Runge-Kutta method,and the statistical test results showed that the obtained equation with high significance and adaptability.The obtained kinetics equation was:r=87.05exp(-63.55 ×103/Rt)pDMA0.63pH0.40Based on the above research,three-dimensional models of CZA30-1 catalyst pellets with different geometric structures were established for reaction-diffusion simulation,and the distributions of concentration and temperature under typical conditions were obtained.The 5-hole cylindrical catalyst pellet(Φ5×5 mm)was selected for industrial production of HDOL by taking the internal diffusion effective factor as index.The effects of reaction conditions such as reaction temperature,pressure and molar ratio of hydrogen to ester on the internal diffusion efficiency factor of catalyst were obtained,which provided a basic reference for the design of industrial reactor.Additionally,a model of adiabatic fixed bed reactor(Φ2000×8000 mm)was established and the effects of feed temperature,pressure,molar ratio of hydrogen to ester and LHSV on the performance of the reactor were investigated.