Study On The Capture Of Methanol And Methylal By Using Ionic Liquid

Polymethoxy dimethyl ether(DMMn,the same below)is a promising diesel additive.In the production process,the presence of formaldehyde will affect the separation and purification of DMMn products,which can be obtained by catalytic hydrogenation.Conversion to methanol,but will cause a large amount of methanol entrained in hydrogen and another product,methyl acetal,affecting the recycling of hydrogen and causing equipment loss,so it is necessary to capture methanol and methylal in the gas as much as possible.In this paper,the suitable ionic liquid was screened by molecular simulation method as the absorbent of methanol and methylal in the trapping gas.The thermodynamic model was established and verified,and the reasonable process flow was designed to achieve the removal effect under the premise of green energy saving.First,this study used COSMOthermX software to calculate the Henry's constant of gas,methanol and methylal in 240 ionic liquids,and calculated the selectivity of hydrogen/methanol and hydrogen/methylal in ionic liquids.Analysis of the effect of ionic liquid species on methanol and methylal in trapped gases and comprehensively consider other physical properties and economy of ionic liquid,and finally choose 1-ethyl-3-methyl-imidazole tetrafluoroborate([EMIM][BF4])is an absorbent for methanol and methylal in the trap gas.After screening and determining the absorbent,the mechanism of methanol and methylal in the[EMIM][BF4]trapping gas was analyzed from the molecular level by calculating the surface shielding charge density distribution,mixed enthalpy,binding energy and weak interaction.Second,after screening the absorbent,the vapor-liquid equilibrium data of[EMIM][BF4]+methanol,[EMIM[BF4]+methylal at different temperatures and different compositions were obtained by saturated vapor pressure experiments.The model parameters of ionic liquids and methanol and methylal were obtained by consulting the relevant literature and fitting the experimental values using the UNIFAC model.Comparing the experimental results with the predicted values of the UNIFAC model,it is found that the relative deviation between the predicted values and the experimental values is small,which proves that the UNIFAC model can effectively predict methanol and methylal in the ionic liquid trapping gas.Thirdly,a laboratory experiment was carried out on a small test of methanol and methylal in an ionic liquid trapping gas to investigate the effect of ionic liquid flow on the experimental results.In the Aspen Plus software,the mathematical model of the absorption tower corresponding to the experiment is established.The UNIFAC model is selected and the relevant model parameters are input to carry out the process simulation.The experimental results were compared with the simulated results to verify the reliability of the UNIFAC model for methanol and methylal in ionic liquid trapping gases.Fourth,based on the premise of the reliability of the UNIFAC model,the process of amplifying methanol and methylal in the ionic liquid trapping gas is designed to be an industrial scale process.Through the Aspen Plus software simulation calculation,the design parameters and operating parameters of the absorption tower and the flash tank in the process are optimized,and the optimal process conditions are determined by comprehensively considering various factors.Exploring the feasibility of ionic liquids for trapping methanol and methylal in gases provides a basis for industrial use of ionic liquids to capture volatile organic compounds.