Study Of Solubility Of Water In Supercritical Carbon Dioxide

The preparation of high molecular weight nylon often use the Solid State Polycondensation/SSP, but the existing SSP process has the following two insurmountable shortcomings:(1) Polycondensation reaction rate is low;(2) The efficiency of devolatilization (removal of small molecules in polycondensation reaction) is close to the limit, restricting the increasing of molecular weight in the SSP process. Thus we must seek new technology and new methods to enhance the SSP process. Adding the swelling agent to the SSP process can improve the reaction conditions, the rate of polycondensation reaction and the efficiency of devolatilization, but considering the environmental security, we should avoid to use organic swelling agent. Therefore, SSP based on the technology of supercritical fluid has become a hot research topic. Supercritical carbon dioxide(SCCO2) is nontoxic, cheap, non-combustible, inert and has special physical and chemical properties, so that it becomes the preferred and most commonly used cleaning solvent in supercritical fluid technology platform. SCCO2is not only used as a medium to enhance the SSP process, but also can effectively remove the polycondensate(such as water or other small molecule polymer), promoting the reaction. Therefore, the determination of water solubility in SCCO2has a great significance for the research of SSP process enhanced by SCCO2.In this work, we use a melt phase poly condensation/devolatilization equipment to determine the solubility of water in SCCO2at temperatures ranging from313.15to373.15K and pressures from8.0to18.0MPa by the static+Gas chromatography method, and explore the effect of temperature and pressure on the solubility. The experimental results show that:(1)At constant temperature, the solubility of water in SCCO2increases as the pressure rises;(2) At constant pressure, the solubility of water in SCCO2increases as the temperature rises.Finally, we use the PR equation of state and Chrastil modified model to correlate and calculate the experimental data. The results show that:PR equation of state and Chrastil modified model both can correlate and calculate the experimental data well with average absolute relative deviation (AARD)4.63%and5.89%, respectively.