Abstract:

Dimethyl carbonate (DMC), methyl formate and methylal etc. are co-products which are not well separated and discharged as waste materials in many coal-to-ethylene glycol plant. As DMC is a valuable and useful raw material in many fields, proper process is needed for DMC rectifying because DMC and methanol forms stable azeotrope and they cannot be completely separated by conventional distillation methods. Pressure swing distillation is chosen after comparing methods of DMC-methanol separation. Three improved process schemes are discussed and designed to be used in the recovery and purification of dimethyl carbonate from the co-product residual liquid, which contain methanol, dimethyl carbonate and methyl formate etc. in coal-to-ethylene glycol plant, to obtain high purity (over 99.9%) DMC product. Those three process schemes are suitable for feeding DMC composition lower than high pressure azeotropic composition, higher than normal pressure azeotropic composition and more than 90% DMC content, respectively, in which the lower energy consumption and high DMC purity can be achieved.

Key words: dimethyl carbonate, methanol, rectifying, divided wall column, heat integration

摘要：

在煤制乙二醇的生产过程中，会副产碳酸二甲酯（DMC）、甲酸甲酯、甲缩醛等，目前煤制乙二醇联产残液大都未进行有效分离和纯化，只能作为低纯度碳酸二甲酯或廉价杂醇处理，这样不仅造成甲醇损耗，而且降低了装置应有的经济性，因此经济合理地回收碳酸二甲酯具有重要的意义。由于甲醇与DMC形成二元共沸物，常规精馏方法无法将二者彻底分离。本文总结了各种DMC-甲醇分离方法，并优选采用变压精馏技术进行甲醇与DMC分离。利用煤制乙二醇中富含碳酸二甲酯以及甲醇、甲酸甲酯等杂质的副产残液为原料，提出3种改进工艺，获得99.9%以上高纯度DMC产品。计算结果表明，3种工艺方法分别适用于含量低于高压共沸组成、高于常压共沸组成、90%以上浓度DMC物料的分离，实现以更低能耗、更优化流程获得高纯度DMC产品。

关键词: 碳酸二甲酯, 甲醇, 精馏, 隔板塔, 热集成