Theoretical Calculations Of The Chemical Reaction Equilibrium/Vapor–liquid Equilibrium Of Solutions Containing Formaldehyde Based On The Conductor-like Screening Model For Real Solvents

The chemical reactive equilibria and vapor-liquid equilibria?VLE?of solutions containing formaldehyde are the basis of formaldehyde production,trixoane synthesis and related systems separation process design and optimization.There are oligomerization reactions in the formaldehyde aqueous solution,forming H?CH₂O?_nOH?n=1,2,3,…?,so VLE of solution containing formaldehyde with full concentration range is related with decomposition reaction equilibria of soluble acetal oligomers in the liquid phase and phase equilibiria of formaldehyde in the gas phase,that is,compositions of this special systems in the liquis and gas phase are different.Acetal oligomerization is extremely complex.Plus,acetal oligomers are easy to form intermolecular hydrogen bonds and intramolecular hydrogen bonds.What's more,with the increasing of polymerization degree,oligomers'solubility in water will reduce to form paraformaldehyde solids.In view of the decomposition rate of paraformaldehyde solid is extremely slow,causing difficulty in reliably experimental measuring VLE of high concentration of formaldehyde experiment.On the other side,the distribution of the oligoacetal molecules and the formation of the paraformaldehyde solid are closely related to the formaldehyde overall concentration and temperature.While,we must handle acetal distribution and gas comopition at different temperatures when modling the chemical reaction/phase equilibrium of solutions containing formaldehyde.Although the NMR technique can generally test the acetal distribution of formaldehyde aqueous solution under normal temperature conditions,the confessed data is about polymerization degree n<10.These data are far from enough for phase equilibrium theory modeling.At present,the experimental technology has not yet reached the breakthrough;the most suitable way to study the gas-liquid equilibrium of formaldehyde water system is to use molecular simulation technology according to the existing experimental data and empirical data.Therefore,to develop the theoretical calculation of reaction/phase equilibrium of solution containing formaldehyde is not only has important academic value,but also has important engineering application significance.With the development of quantum theory,quantum chemistry has gradually become the theoretical basis of chemical structure,chemical reaction performance.Theoretical calculation can work together with experimental science to explore the nature of the chemical system.Conduct-like Screening Model for Real solvents?COSMO-RS?has been widely concerned and developed in all directions as a quantitative method for describing the thermodynamic properties of fluids.In this paper,based on collecting literature experimental data,the COSMO-RS method was used to theritical calculation of chemical reaction and vapor liquid phase equilibriaaboutformaldehyde-water/methanol,formaldehyde-water-methanol,formaldehyde-water/methanol-trioxone,formaldehyde-water-methanol-trioxone,form-aldehyde-water-dioxalane,formaldehyde-water/methanol-methylaldehyde,formald ehy-de-water-methanol-methylal system were studied.The COSMO-RS theory was used to study the chemical equilibrium and phase equilibrium of formaldehyde-water system,and then we give vapor-liquid phase equilibria of the regular characteristics of the theoretical analysis and interpretation.The reaction properties of formaldehyde-containing water system and gas-liquid equilibrium are the basic parameters of the synthesis and separation of trioxane?TOX?.Therefore,the reaction with formaldehyde aqueous solution and VLE experimental study is very important.At the same time,as a result of aqueous solution containing formaldehyde solution and VLE experimental measurement difficult and some components difficult to be separated,the theoretical calculation of reaction/phase equilibrium with formaldehyde water system was carried out.Not only has important academic value,but also has important engineering application significance.COSMO-RS,as a quantitative method for describing the thermodynamic properties of flow phase,is being widely concerned and developed,and is increasingly being used by ASPEN Plus users.1.Our research successfully linked the activity coefficients module in COSMOtherm and the chemical reaction equilibrium constants and mass balance equations with the help of the MATLAB program,which is the key process for using COSMO-RS method in formaldehyde-containing water reactivity system.For this study,calculation of each piece of experimental data required about 5s,and the computational process have been smoothly run for hundreds of times,shows very good stability.2.Based on the construction of the method of theoretical calculation of the reaction/phase equilibrium of formaldehyde-containing water system,chemical reaction equilibrium constant were re-fitted by combining the activity coefficients of the reaction product molecules calculated by COSMO-RS and the component content of formaldehyde solution determined by NMR.On this basis,the acetal distribution and gas-liquid equilibrium data in formaldehyde-water solution were calculated.The calculated results are in good agreement with the experimental data,the results of formaldehyde content in the liquid phase are better than those in the UNIQUAC model,the calculation accuracy of pressure is higher than that of UNIFAC model.3.COSMO-RS method was successfully employed for predicting and interpreting the thermodynamic behavior of formaldehyde–water–methanol reactive fluids.From the?-profile and?-potential of the species,the hydrogen-bonding interaction and hydrophobic effect essentially affect the intermolecular interaction in this complicated multicomponent mixture.The vapor pressures of MG and HF were predicted by COSMOtherm implementation:the higher vapor pressure of HF was observed from the more symmetrical?-profiles of MG than that of HF.As compared to the experimental data obtained from species distribution,from those predicted by the revised COSMO-RS model indicate average relative deviations of no greater than 10%for MG_1-3-3 and HF_1-3.The calculated vapor–liquid equilibrium?VLE?result shows good agreement with the experimental data.Based on the quantitative and qualitative analysis of species,the maximum partition coefficient for formaldehyde in a diluted formaldehyde–water–methanol mixture at low temperature is attributed to the interchange from MG to HF.The COSMO-RS model is proven to provide a better understanding of the intermolecular interaction in such a complicated formaldehyde-containing system.4.The COSMO-RS model was applied to predict the vapor-liquid equilibrium?VLE?of the formaldehyde-water-?Trioxane,Dioxolane,Methyl acetal?system.The agreement between the experimental and predicted results was very good.Moreover,comparison of the results showed that the quantum chemical calculation model was more accurate than the previously reported UNIFAC method.Furthermore,our present COSMO-RS model can be applied to other multicomponent systems,and can be used to guide the rational design of trioxane and dioxolane synthesis and the separation processes for formaldehyde-containing mixtures.