Thermodynamic And Kinetic Studies On The Esterification Reactions Catalyzed By Cation Exchange Resins

Ester compounds exist widely in nature and are closely related to our life.For example,low-carbon atomic esters are colorless and fruit-flavored liquids found in flowers or fruits;many esters of branched-chain alcohols are excellent lubricants;esters are also widely used in perfumes,fragrances,cosmetics,soaps and pharmaceutical products.At present,the traditional preparation methods of ester compounds often use sulfuric acid as catalyst,but it has many disadvantages,such as side reactions,easy corrosion of equipment,and difficulty in separating the catalyst from the production process.Compared with homogeneous catalysts,cation exchange resins can provide better selectivity and reusability.In this paper,hexanoic acid and isoamyl alcohol,myristic acid and methanol were selected as raw materials,and the cation exchange resin Amberlyst39 WET was used as solid acid to catalyze esterification reaction to prepare isoamyl hexanoate and methyl myristate respectively.Considering that the reaction solution is a non-ideal system,it is necessary to introduce the activity coefficient to correct the concentration of the solution components.UNIFAC group contribution method is used to calculate the activity coefficient of the solution components within the reaction temperature range,and then calculate the equilibrium constant.According to the enthalpy change ΔrH0 whether change with temperature,the thermodynamic parameters of the reaction were calculated by two methods respectively.The PH model,E-R model and LHHW model were used to fit the kinetic process of esterification reaction respectively,and the corresponding kinetic parameters were obtained,which provided experimental reference and theoretical basis for industrial simulation design and factory production scaling up.The progress made in this research is as follows:1.Synthesis of isoamyl hexanoate catalyzed by cation exchange resinUsing cation exchange resin Amberlyst39 WET as catalyst,and hexanoic acid and isoamyl alcohol as raw materials,the synthesis of isoamyl hexanoate was studied.The optimal conditions were as follows:catalyst type was Amberlyst39 WET;catalyst dosage was 15wt%;the reaction stirring rate was 400rpm;the initial molar ratio of reaction material was hexanoic acid:isoamyl alcohol=1:1.8;the reaction temperature was 343.15K.After correcting the non-ideality of the reaction system by the UNIFAC group contribution method,the relationship between the equilibrium constant K and the temperature T within the experimental temperature range was expressed as:K=exp(896.46/T+1.72)According to the enthalpy change ΔrH0 whether change with temperature,using two different methods to calculate hexanoic acid and isoamyl alcohol esterification reaction enthalpy change ΔrH0,entropy change ΔrS0,Gibbs free energy ΔrG0:(1)within the scope of the experimental temperature,the ΔrH0 does not change with temperature,calculated enthalpy change ΔrH0 is-7.45 kJ·mol-1,ΔrS0 is 14.30 J·moI·-1·K-1,the ΔrG0 is-11.72 kJ·mol-1;(2)within the scope of the experimental temperature,the ΔrH0 is changing with temperature,calculated enthalpy change ΔrH0 is-7.10 kJ·mol-1,ΔrS0 is 15.43 J·moI-1·K1,the ΔrG0 is-11.70 kJ·mol-1;The results of enthalpy change ΔrH0,entropy change ΔrS0 and Gibbs free energyΔrG0 obtained by the two methods have little difference,indicating that the change of enthalpy with temperature can be ignored basically,and the reaction system is close to an ideal state.After eliminating the effect of internal and external diffusion on the mass transfer of the reaction,the PH model and E-R model were used to simulate the kinetic process of the reaction between hexanoic acid and isoamyl alcohol.E-R model can describe the kinetic process more accurately.The kinetic equation based on E-R model is as follows:(?) Where(?)(?)(?)(?)2.Synthesis of methyl myristate catalyzed by cation exchange resinUsing cation exchange resin as catalyst to catalyze the reaction of myristic acid and with methanol,the optimal experimental conditions were as follows:catalyst type was Amberlyst39 WET;the dosage of catalyst is 20%of the total weight of the reaction liquid;the reaction stirring rate was set at 400rpm;the initial molar ratio of reaction materials was myristic acid:methanol=1:3;the optimum reaction temperature was 333.15K.UNIFAC group contribution method was used to correct the solution,and the relationship between the reaction equilibrium constant and temperature was obtained as follows:K=exp(915.63)+1.50According to the enthalpy change ΔrH0 whether change with temperature,using two different methods to calculate myristic acid and methanol esterification reaction enthalpy change ΔrH0,entropy change ΔrS0,Gibbs free energy ΔrG0:(1)within the scope of the experimental temperature,the ΔrH0 does not change with temperature,calculated enthalpy change ΔrH0 is-7.61 kJ·mol-1,ΔrS0 is 12.46 J·moI-1·K-1,the ΔrG0 is-11.33 kJ·mol-1;(2)within the scope of the experimental temperature,the ΔrH0 is changing with temperature,calculated enthalpy change ΔrH0 is-8.04 kJ·mol-1,ΔrS0 is 11.09 J·moI-1·K1,the ΔrG0 is-11.35 kJ·mol-1;The results of enthalpy change ΔrH0,entropy change ΔrS0 and Gibbs free energyΔrG0 obtained by the two methods have little difference.After eliminating the influence of internal and external diffusion on the mass transfer of the reaction,the PH model and the LHHW model were respectively used to simulate the kinetic process of the reaction between myristic acid and methanol.The LHHW model can more accurately describe the kinetic process of the reaction.The kinetic equation based on the LHHW model is as follows:(?) Where(?)...