Solubility enhancement in supercritical carbon dioxide by fluorination effect

本研究通过测定含氟化合物在超临界二氧化碳中的溶解度，考察超临界二氧化碳对含氟化合物溶解度的影响。进一步，通过分子模拟对增溶机理进行了探讨，得到了如下结果：测定了作为加氢裂化催化剂的Rh配合物在超临界CO2中的溶解度。作为配体，采用三苯基膦（TTP）和三（对三氟甲基苯基）膦（TTFMPP）。通过红外吸收测定溶解度。结果表明，与未氟化的TPP和Rh-TPP相比，含氟的TTFMPP和Rh-TTFMPP的溶解度均有所提高。以含氟化合物2，3-三氟甲基苯甲酸为模型物质，测定了其升华压力。将样品置于平衡池中，通过UV吸光度测定气相浓度。用理想气体状态方程确定了升华压力。根据本实验方法可以获得可靠的升华压力数据。2-，3-三氟甲基苯甲酸的升华压力在314 K附近有一个交叉点。研究了2-、3-、4-、三氟甲基苯甲酸和2-、3-、4-甲基苯甲酸。结果表明，CO2分子在三氟甲基周围发生了溶剂化作用，这是CO2分子在超临界CO2中溶解度增加的原因，而CO2分子在三氟甲基周围的溶剂化作用是CO2分子在超临界CO2中溶解度增加的主要原因。

In this study, solubilities of fluorinated compounds were measured to examine the fluorination effect on the solubility in supercritical carbon dioxide. Further, the mechanism of solubility enhancement was discussed by a molecular simulation and the following results were obtained.The solubilities of Rh complexes, which are used as catalysts for hydroformylation, in supercritical carbon dioxide were measured. As a ligand, triphenylphosphine (TTP) and tris (p-Trifluoromethylphenyl) phosphine (TTFMPP) were adopted. The solubilities were determined by IR absorbance. It is found that the solubilities of the ligand and the complex fluorinated, TTFMPP and Rh-TTFMPP, can be enhanced compared to non-fluorinated TPP and Rh-TPP.2-,3-trifluoromethyl benzoic acids, which are fluorinated compounds, were adopted as model substances and its sublimation pressures were measured. The sample was set in an equilibrium cell and the vapor phase concentration was determined by UV absorbance. The sublimation pressures were determined by using the equation of state for ideal gas. Reliable sublimation pressure data can be obtained based on the present experimental procedure. The sublimation pressures of 2-,3-trifuloromethyl benzoic acids show the cross point near 314K.MD simulation was performed for the supercritical carbon dioxide + fluorinated compounds mixtures. 2-,3-,4-,trifluoromethyl benzoic acids and 2-,3-,4-methyl benzoic acids were studied. It is found that carbon dioxide molecules are solvated around trifluoromethyl group and this fact is the reason for the solubility enhancement.As mentioned above, fluorination is effective to enhance the solubility in supercritical carbon dioxide and the mechanism is due to solvation.