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Selection and evaluation of alternative solvents for caprolactam extraction

机译：己内酰胺萃取替代溶剂的选择和评估

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Because of the strict legislation for currently applied solvents in the industrial extraction of caprolactam,being benzene,toluene and chlorinated hydrocarbons,a need exists for alternative,environmentally benign solvents.An experimental screening procedure consisting of several steps was used to determine a suitable replacement solvent.(1) The distribution ratio of caprolactam was investigated at 293 K for an initial 10mass% aqueous caprolactam solution;(2) the capacity and mutual solvent solubility were determined as function of the aqueous caprolactam concentration at equilibrium for solvents or solvent mixtures showing favourable capacities compared to benzene and toluene;(3) the equilibrium phase compositions for conditions covering the full industrial range were determined and correlated using the NRTL model for solvents or mixtures showing favourable characteristics compared to benzene and toluene;(4) the physical properties,being density and viscosity data of the separate phases and interfacial tension data of the liquid-liquid systems were determined and correlated for the remaining candidate solvents.It was found that the caprolactam distribution ratio increased with increasing solvent (mixture) polarity,characterized by a more polar active group (ether,ester,ketone and alcohol),decreasing carbon chain length of the polar solvent (C_(12)-c_6) or increasing polar solvent fraction in the mixture.Based on a high capacity,a low mutual solvent solubility and beneficial physical properties the solvent mixture of 40 mass% heptanol in heptane was finally selected as replacement solvent.Calculating the solvent to feed ratio (S/F) and the number of theoretical stages (NTS) needed to reach the industrially required raffinate concentrations,it was found that in the forward extraction the S/F is 3.0 for the mixed solvent and benzene,whereas the NTS is 5 and 9,respectively.In the back-extraction the S/F is 0.67 whereas the NTS is 10 and 5 for the solvent mixture and benzene,respectively.
机译：由于对己内酰胺的工业萃取中目前使用的溶剂（包括苯，甲苯和氯代烃）有严格的立法规定，因此需要替代的，对环境有益的溶剂。采用了由几步组成的实验筛选程序，以确定合适的替代溶剂（1）研究了己内酰胺在初始质量为10％的水溶液中在293 K时的分布比例;（2）确定了容量和互溶性与己内酰胺水溶液在平衡状态下对水溶液或混合溶剂浓度的函数关系，显示出良好的与苯和甲苯相比具有较高的容量;（3）使用NRTL模型确定了涵盖整个工业范围的条件下的平衡相组成，并将其与溶剂或混合物相比具有相关性;与苯和甲苯相比，溶剂或混合物具有良好的特性;（4）物理性质分离相的密度和粘度数据确定了液-液系统的界面张力和界面张力数据，并对剩余的候选溶剂进行了相关分析。发现己内酰胺的分配比随溶剂（混合物）极性的增加而增加，其特征是极性更大的活性基团（醚，酯，酮和醇），减少极性溶剂（C_（12）-c_6）的碳链长度或增加混合物中的极性溶剂分数。基于高容量，低互溶剂溶解度和有益的物理性能，溶剂混合物40最后选择质量分数为庚烷的庚醇作为替代溶剂。计算溶剂进料比（S / F）和达到工业要求的提余液浓度所需的理论级数（NTS），发现在正向萃取中混合溶剂和苯的S / F为3.0，而NTS分别为5和9.在反萃取中，溶剂混合物和苯的S / F为0.67，而NTS为10和5分别为zene。

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