Experimental Study Of Solubility Of Ethylene Glycol In Supercritical Carbon Dioxide

Polyethylene terephthalate （PET） is a large amount condensation polymer with a wide range of application. The traditional melt phase poly-condensation process （MPP） of high-temperature, high-vacuum and high viscosity has to overcome the following two disadvantages: （1） Side reactions, including degradation reaction and colored-body generating reaction, etc, caused by high temperature; （2） In final phase of the polycondensation, devolatilization is the key step, and the efficiency of traditional devolatilization methods approaches to limits and condensation products contain more residues. Therefore, it becomes more difficult to meet the higher standards of food, medicine and other products. So, more effective methods of devolatilization are necessary. Swelling agents are added to improve the reaction conditions and enhance the rate of melt polycondensation in the MPP. In order to protect environment, organic swelling agent should be avoided to be used. Therefore, melt/solid-phase polycondensation based on supercritical fluid technology becomes more interesting, and has become spotlight in the research of green polymerization. In order to reveal the enhancing mechanism of the high viscosity melt/solid-phase polycondensation process with SC-CO2, it is necessary to study the thermodynamics of the process. Research of Solubility of volatiles/EG in SC-CO₂ is one of very important content.In this study, a high pressure apparatus is used to measure the solubility of EG in the SC-CO₂ with static method. The solubility is measured under the following conditions: temperature range is from 40℃to 80℃and the pressure range is from 7 MPa to 19 MPa. The data of three isothemal lines are measured twice, which are measured at the temperatures of 40℃, 50℃and 60℃respectively. And its precision is not more than 10%. The literature data of the solubility of EG in the SC-CO₂ has yet been reported.The experimental results show: （1） the solubility of EG in the SC-CO₂ is with tendency of increase under increasing pressure; （2） the change of solubility of EG with temperature is complex. When pressure is less than the transition pressure （about 16MPa）, temperature is higher, the solubility is less. When the pressure is higher than the transition pressure, temperature is higher, the solubility is more.Experimental data are correlated with state equations of PR, SRK, RK and association model. The results show that: （1） the effect of association model is better than that of the state equations with the average absolute deviation of 4.13% and the maximum deviation of -10.36%; （2） PR is the best correlation state equation with the average absolute deviation of 4.36% and the maximum deviation of -12.98%; SRK is the second one with an average absolute deviation of 7.44 % and the maximum deviation of -24.60%; RK is the worst one with an average absolute deviation of 11.47% and the maximum deviation of -25.77%.