溶析结晶法提纯龙脑的热力学研究

Thermodynamic properties of borneol with anti-solvent crystallization

采用激光合成法测定了龙脑在不同比例乙醇水溶液中的溶解度,并分别采用多项式经验模型、modified Apelblat模型对溶解度数据进行拟合,拟合系数R^2均在0.999 0以上,总平均相对偏差均小于1%,取得了较好的关联效果,建立了理想的溶解度模型。在此基础上,计算了龙脑在乙醇/水混合溶剂中溶解的热力学函数,讨论了焓熵补偿现象,证明龙脑的溶解过程为非自发熵驱动的吸热过程,且焓变对吉布斯自由能变的贡献最大。在不同的工艺条件下测定了龙脑在乙醇水溶液中结晶的介稳区宽度,得出乙醇/水体系溶析结晶的工艺参数:结晶温度15—25℃,搅拌转速不大于150 r/min,溶剂比w(水/乙醇)控制在0.5以内。这些工艺参数为乙醇/水溶析结晶工艺的优化奠定了理论基础。

The solubility of borneol was measured in different ratio of ethanol and water with a He-Ne laser method.The data were well correlated with the empirical model and the modified Apelblat equation,respectively. All the correlation coefficients R-2 of the regression are no less than 0. 999 0,and both of the overall ARD（ average relative deviations） are within 1%,which means the regression has much better results. The ideal solubility models were set up. Furthermore,the thermodynamic functions were deduced by means of van＇ t Hoff equation,indicating that the dissolution of borneol is endothermic,entropy-driven and nonspontaneous in all cases,and enthalpy is the main contributor to the Gibbs energy. Meanwhile,the enthalpy-entropy compensation phenomenon was also discussed based on the calculated results. In the end,the metastable zone width（ MSZW） was obtained at specific conditions. Therefore,the anti-solvent crystallization process parameters are demonstrated as follows： crystallization temperature is within 15-25 ℃,the agitation speed is less than 150 r / min; solvent mixture ratio w（ water / ethanol）is no more than 0. 5. These parameters can provide the theoretical guidance to the anti-solvent crystallization process optimization of borneol with ethanol / water solvent mixture.