Thermodynamics And Physicochemical Properties Calculations Of Polyoxymethylene Monomer Containing Formaldehyde Based On COSMO-RS

The technical bottleneck named that domestic weak research in thermodynamics properties of formaldehye solution,1,3,5-trioxane?TOX?and POM post-process and foreign monopoly status,resulted in embarrassing situation of insufficient production capatcity and poor product quality when importing high quality POM product,although domestic POM industry has developed 20 years.Considering the sensitive and volatile chemical reactions in the solution,complex substance species,hence,experimental research is time-consuming and money consuming.On the other side,the group contribution method cannot give a better description of complex molecular structures and interactions.While one of feasible solutions is molecular simulation.Hence,Thermodynamic properties of formaldehyde solution and POM monomers using quantum chemistry theory COSMO-RS have been carried out.This work aims to achieve progress in the molecular interaction and system energy;enrich the present method research on the formaldehyde solution and TOX systems for the promoting the COSMO-RS method application in thermodynamics properties of chemical engineering reactive system.1).This paper shows all the molecular screening charge distribution?-profile of all the oligomers in the solution formaldehyde using the COSMO-RS method,and then gives conformation computation of each oligomer molecule.Based on above work,a cosmo profiles database of oligomers existing formaldehyde solution were built,which consist of 158 molecular conformations for 18 kinds of molecules.2).Based on previous work that linked activity coefficients produced in the module of COSMO-RS and chemical equilibria and mass balance,we proposed a new substance distribution and VLE model for the reactive fluids containing formaldehyde using COSMO-RS theory considering all the conformers of oligomers.The substance equilibrium concentration and VLE of FA-W and FA-W-Me OH system were calculatedand compared with experimental data and other calculated results based on our modified model.It illustrated that the quantum chemical calculation model can provide good quantitative of VLE and can show a better description of substance distribution than the previously reported UNIFAC and UNIQUAC method.Furthermore,substance distribution law and VLE behavior were interpreted reasonably and scientifically by?-profiles and energy analysis.It laid a good foundation for further study of the other thermodynamic properties of chemical reactive solution by the COSMO-RS model.3).Density and viscosity data for the binary system?FA-W?and ternary system?FA-W-Me OH?were measured with an SVM 3000 Stabinger developed by Anton Parr Company.The density and viscosity data of binary and ternary system were improved.Then,solution density and viscosity model were built respectively via the density and viscosity data of each oligomers calculated by COSMOtherm software combining with substance equilibrium concentration described in 2).Our COSMO-RS can re-produce all the experimental density data very well,while the calculated viscosity data were less accurate than calculated density.Besides,excess molar volume(1properties of the binary and ternary system together with the effect of methanol on(1were observed based on COSMO-RS theoretical calculation.The results demonstrated that small amounts of methanol had a great influence on the excess molar properties of formaldehyde solution,interpreting the reason based on nature of molecular structure and system energy.4).In the production of polyoxymethylene?POM?,tiny amount of water,methanol,methyl formate?MF?and by-product dimethoxymethane?DMM?may enter into the1,3,5-trioxane?TOX?cooling crystallization process through the feed stream.Considering the effect of impurities in the TOX freeze crystallization efficiency,the solubility model of TOX in different solvents were obtained by correlating experimental solubility data and COSMO-RS calculating results.The solubility behavior and key component parameters of TOX were predicted and analyzed.Furthermore,solubility of POM in water and methanol solvent were calculated using COSMO-RS,providing a new technical guidance for the post-process optimization of POM polymer powder materials in POM plant with a methanol solution method.