Abstract: Para-xylene (PX) is a fundamental chemical raw material that is utilized in the production of polyester fibers, dyes, and pesticides. It often existed in mixtures with meta-xylene (MX) and ortho-xylene (OX). Separating PX from xylene mixtures is essential for its chemical application. Due to their highly similar physicochemical properties, the separation and purification of xylene isomers have always been a significant challenge. Among the separation processes, melt crystallization is an effective technology to obtain high-purity PX based on the difference in the melting points of each xylene isomer. It is more efficient and environmentally friendly than other methods. However, the presence of eutectic points necessitates the separation of mixed xylene isomers at significantly low temperatures. The complex-melting crystallization method combines complexation with crystallization processes, which improves the melting points of the isomers to be separated. In this research, the bimetallic halide CuAlCl4 was used as a complexing agent, forming complexes with the three xylene isomers. The complex system had higher melting points and eutectic temperatures than pure xylene system, and the temperature required for crystallization operation was closer to normal temperature. A xylene mixture with a PX content of 74.60% was used as feedstock, and the operating conditions of the complex-melting crystallization process were optimized. In the first crystallization stage, crystallization time was 1.0 h, final crystallization temperature was 5℃, cooling rate was 0.15℃/min, sweating temperature was 36℃, and sweating rate was 1.0℃/min. In the second crystallization stage, final crystallization temperature was 15℃, sweating temperature was 38℃. Through the implementation of two-stage melting crystallization, the purity of PX was successfully increased from 74.60% to over 99.50%, and the yield of PX reached 43.12%. Compared with the pure mixed xylene isomers system, the operating temperature was increased by 20℃ at a similar yield. The results demonstrated that CuAlCl4 was able to separate PX from xylene mixtures and significantly decrease the refrigeration energy consumption during the crystallization process.

Key words: bimetallic halides, para-xylene, π complexation, complex crystallization, melting crystallization

摘要： 对二甲苯(PX)是一种基础的化工原料，通常与间二甲苯(MX)和邻二甲苯(OX)以混合物的形式存在，将其从二甲苯混合物中分离是生产高价值精细化学品的前提。络合-熔融结晶法通过生成新的络合物，可显著提升待分离体系的熔点。本研究使用双金属卤化物CuAlCl4作为络合剂与二甲苯进行络合。研究发现，所得络合物的混合体系与纯物质混合体系均为低共熔体系，但络合物的熔点和低共熔温度均高于纯物质，使得结晶操作所需温度更趋于常温。实验以PX含量为74.60%的混合二甲苯为原料，考察了络合-熔融结晶过程中的各项操作条件。通过二级熔融结晶工艺，成功将PX的纯度提升至99.50%以上，收率达到43.12%。与纯物质体系相比，在相近收率的情况下，本方法的操作温度可提高20℃。本研究结果表明，CuAlCl4能够成功分离混合二甲苯中的对二甲苯，同时在结晶过程中可大幅降低制冷能耗。

关键词: 双金属卤化物, 对二甲苯, π络合, 络合结晶, 熔融结晶