CO_2-[emim][Tf_2N]二元混合体系超额混合焓的预测

Prediction of Molar Excess Enthalpies in Binary Solution of CO_2-[emim][Tf_2N]

针对传统制冷工质对存在诸如氢氟烃的环境问题、氨水的毒性和精馏问题,以及溴化锂制冷温度高和腐蚀结晶等问题,提出一种对环境友好的以CO2为制冷剂与以离子液体[emim][Tf2N]为吸收剂的新型吸收制冷工质对。为了研究CO2-[emim][Tf2N]吸收制冷系统性能,以WS混合规则为桥梁,结合PR状态方程和NRTL活度系数模型,建立GE-EOS热力学模型,得到CO2和离子液体二元混合体系在高温高压下的超额混合焓。计算结果表明:CO2液相摩尔分数大于0.43时,二元混合体系的超额混合焓均为负值,混合为放热过程,说明二元混合体系具有成为吸收制冷工质对溶液的基本特征。同时,利用CO2-[emim][Tf2N]吸收制冷系统进行初步实验研究,实验结果表明,系统制冷系数平均相对误差为16.3%,验证了模型具有较好的计算精度。

In view of the facts that traditional refrigerants may cause some problems, e. g. , hydroflurocarbon results in environmental problems; ammonia water has toxicity and needs distillation; lithium bromide-water solution has the problems of corrosion and crystallization and its refrigeration temperature is relatively high etc. , a new absorption refrigeration working pair has been developed. To study the performances of this absorption refrigeration system, NRTL model and PR state equation are combined using WS mixing rule as the link to develop a GE-EOS thermodynamic model in the paper. The molar excess enthalpies of the binary solution were obtained at high pressure and temperature. The calculation results showed that the excess molar enthalpies in the binary solution are negative when the CO2 mole fraction in the liquid phase is higher than 0. 43, so the mixing process of CO2 and [-emim][Tf2N] is exothermic, which indicates that the binary solution has the basic properties of absorption refrigeration working pair. Meanwhile, experimental study was performed using an [emim][Tf2N] absorption refrigeration system. The experimental results showed that the relative deviations were 16.3%,verifying the calculation accuracy of this model.