Abstract: Adsorption separation of mixed xylene can obtain p-xylene,but it still contains a small amount of toluene. A new separation process of p-xylene and toluene by melt crystallization was proposed. The solid-liquid equilibrium phase diagram of p-xylene and toluene was measured by differential scanning calorimetry (DSC). The experimental data showed that the binary system presented a eutectic point. On the basis of the solid-liquid equilibrium,liquid film crystallization experiments were carried out. It can obtain p-xylene products with the purity over 99.5%. The results indicated that it was feasible to separate p-xylene and toluene by melt crystallization. According to the experimental process,the dynamic mathematical model of liquid film crystallization was established. The model values agreed well with the experimental data,which verified the accuracy of the model. With the model optimization of operating conditions,the appropriate spray density and cooling rate can weaken the problem of uneven crystal layer growth. Cost accounting about melt crystallization and distillation separation processes was carried out respectively. The results showed that the fixed investment of crystallization was much lower than the distillation and operation conditions were stable. Crystallization was easy to get high purity products,but its energy consumption was slightly higher than distillation. Thus,the crystallization was suitable for small batch production,and the distillation was appropriate for high-volume production.

Key words: melt crystallization, p-xylene, solid-liquid equilibrium, modeling, cost accounting

摘要： 针对混合二甲苯吸附分离后得到的对二甲苯中含有少量甲苯物系，提出熔融结晶法分离对二甲苯与甲苯的新工艺。采用差示扫描量热法（DSC）测量了对二甲苯与甲苯之间的固液平衡相图，实验数据表明该二元物系为低共熔型物系，在此基础上进行液膜结晶实验，可分离得到对二甲苯纯度为99.5%以上的产品，证明采用熔融结晶法分离对二甲苯与甲苯是可行的。根据实验过程建立了液膜结晶动态过程的数学模型，由模型计算得到的结果与实验数据很好的吻合，验证了模型的准确性，并用模型优化操作条件，得到适当的喷淋密度与降温速率可改善晶层生长不均的结论。分别对熔融结晶和精馏分离过程进行成本核算，结果表明结晶过程固定投资相比精馏低很多，且操作工况稳定，易于得到高纯产品，但能耗略高，因此结晶适用于小批量生产，精馏适用于大批量生产。

关键词: 熔融结晶, 对二甲苯, 固液平衡, 建模, 成本核算