Study Of Vapor-liquid Equilibrium And Excess Properties Of Rosin And Turpentine System Using COSMO-RS Model

Pine gum is a highly viscous resin secreted by pine trees and is usually collected from live pine trees in an open environment under sun and rain.The more volatile components of turpentine,such asα-pinene,camphene,β-pinene,limonene and p-cymene will continuously volatilize during turpentine harvesting,resulting in the loss of turpentine.The research of the vapor-liquid equilibrium（VLE）of components of turpentine and rosin can provide more basic data for the collection of pine gum,the design of process and distillation of separation and purification of turpentine and rosin and their components.The main research of this study is as follows:（1）The VLE data of three binary systems,α-pinene（1）+camphene（2）,α-pinene（1）+limonene（2）andα-pinene（1）+longifolene（2）at 313.2,333.2 and358.2 K,were determined by headspace gas chromatography.The VLE data for the three binary systems at 313.2,333.2 and 358.2 K were calculated using the NRTL,PR Eo S and COSMO-RS models,respectively,and the results showed that the calculated results of the NRTL and COSMO-RS models exhibited better agreement with the experimental values than the PR Eo S.In the absence of resin acids,the activity coefficients ofα-pinene gradually decreased for all three binary systems in the three temperatures,while those of other components gradually increased;the excess enthalpy and excess Gibbs free energy both showed an increasing and then decreasing trend.（2）Headspace gas chromatography was used to determine the VLE data for the five-elements systems ofα-pinene（1）+camphene（2）+（abietic acid+palustric acid+neoabietic acid）,α-pinene（1）+limonene（2）+（abietic acid+palustric acid+neoabietic acid）（3）andα-pinene（1）+longifolene（2）+（abietic acid+palustric acid+neoabietic acid）（3）（x₃=0,0.06,0.12）at 313.2,333.2 and358.2 K and showed good agreement with the COSMO-RS model calculations.The addition of resin acids decreased the pressure and significantly increased the excess enthalpy and excess Gibbs free energy for all systems.However,unlike the systems ofα-pinene（1）+camphene（2）andα-pinene（1）+limonene（2）,the excess Gibbs free energy ofα-pinene（1）+longifolene（2）system was less than zero and showed a decreasing and then increasing trend.After the addition of the three resin acids,H^E（HB）all contributed the most to H^E.（3）Headspace gas chromatography was used to determine the VLE data for the six-elements systems ofα-pinene（1）+camphene（2）+limonene（3）+（abietic acid+palustric acid+neoabietic acid）（4）andα-pinene（1）+camphene（2）+longifolene（3）+（abietic acid+palustric acid+neoabietic acid）（4）（x₄=0,0.06,0.12）at 313.2,333.2 and 358.2 K and showed good agreement with the COSMO-RS model calculations.After adding the three resin acids,the activity coefficients all gradually increased,the pressure decreased,and the excess enthalpy and excess Gibbs free energy were positive and significantly increased of the systems.In addition,H^E（VDW）was negative after the molar fraction of resin acids was increased to 0.12,indicating that the increase of resin acid content had a significant enhancement of molecular forces.（4）Headspace gas chromatography was used to determine the VLE data of the turpentine+rosin system at 313.2 K and 333.2 K were measured.The results showed that the total and partial pressures of the system increased with the molar fraction of rosin and temperature;the activity coefficients of all the components of turpentine except longifolene exceeded 1;the excess enthalpy and excess Gibbs free energy were also positive.Theσ-profiles distribution plots showed that there was heterogeneity between the components of turpentine and rosin,making H^E（VDW）negative.And also observed that H^E（HB）has the largest contribution to the excess enthalpy H^E.（5）The most stable structures and interactions binding energies ofα-pinene+camphene/camphene/longifolene+abietic acid/palustric acid/neoabietic acid,α-pinene+camphene+limonene/longifolene+abietic acid/palustric acid/neoabietic acid were calculated using density flooding theory（DFT）,and no false frequency phenomenon was observed in the most stable structures.Meanwhile,the contribution of hydrogen bonding forces to the excess enthalpy was also verified.