加盐萃取-精馏耦合分离甲醇-甲苯的工艺研究

Separation of methanol-toluene by combined process of extraction with salt and distillation

研究了加盐萃取分离甲醇-甲苯共沸体系,考察了盐水种类、用量、质量分数及萃取温度等因素对萃取效果的影响,计算了在各种萃取条件下甲醇和甲苯的分配系数。实验结果表明:CaCl2水溶液的萃取效果最好,在CaCl2水溶液质量分数为0.35、萃取温度40℃、溶剂比(体积比)1.5∶1的条件下,甲醇的分配系数为2.32,选择性系数为18 200。基于以上实验数据,回归得到了萃取液液相平衡常数与萃取温度关联式的模型参数。在此基础上,提出了加盐萃取-精馏耦合分离甲醇-甲苯3塔工艺流程,并利用Aspen Plus软件中的Extract模拟萃取塔、RadFrac模拟精馏塔,选用NRTL-HOC和ELECNRTL热力学模型,对提出的工艺进行模拟计算,得到了合适的工艺操作条件。模拟结果表明:当萃取塔理论板数为5块;甲醇回收塔理论板数为21块、回流比为1.8;甲苯回收塔理论板数为28块、回流比为2.4时,分离得到的甲醇和甲苯的质量分数分别为0.996和0.997。

The extraction with salt was applied to separate methanol from toluene. The effects of different salt solution,volume,mass fraction and temperature on extraction were studied,and the partition coefficients for methanol and toluene were calculated. The experimental results show that the best extractant is the CaCl2salt solution,the partition coefficient and the selectivity coefficient of methanol reach up to 2. 32 and 18 200 respectively at 40 ℃,salt solution mass fraction 0. 35,and the volume ratio of salt solution to feed 1. 5 ∶ 1. Based on the experimental results,the parameters of the liquid-liquid phase equilibrium comparison expression were determined. The scheme for separating methanol-toluene by combined process of extraction with salt and distillation was put forward. The simulations for the process were performed by Aspen Plus,in which Extrac. module and RadFrac. module were used to simulate extraction column and rectification column respectively. Based on the NRTL-HOC and ELECNRTL thermodynamic models,the suitable operating parameters were obtained. The simulation results show that the mass fraction of methanol and toluene can reach up to 0. 996 and 0. 997 respectively,under the operating conditions of the theoretical plate of extraction column 5,the theoretical plate of methanol column 21 with a reflux ratio of 1. 8,and the theoretical plate of toluene column 28 with a reflux ratio of 2. 4.