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碳酸二甲酯（DMC）作为一种优良的绿色溶剂和化工中间体，是煤化工、甲醇（MeOH）化工以及CO2应用下游产业链的重要延伸。但其生产过程中面临着与MeOH形成共沸、分离能耗高、操作复杂的技术难题，极大地制约了其工业化经济效益。离子液体（ILs）是一种新兴的绿色溶剂，具有结构可设计、蒸汽压低、分离回收简便等优良性质，可通过空间结构调配以及官能团功能化设计，实现与共沸物各分子间选择性的键合及分离，使其在分离共沸物方面具有广阔的应用前景。本文针对ILs用于萃取精馏分离MeOH-DMC共沸物开展了相平衡实验及分离性能研究，并分别针对ILs萃取精馏工艺与传统MeOH-DMC分离工艺进行了过程模拟与系统集成优化研究。论文主要创新工作及成果如下：1. 筛选了空间结构取向不同、阴阳离子极性相异的三种咪唑类离子液体[Bmim][Tf2N]、[Emim][Tf2N]和[Emim][PF6]作为萃取剂，开展了IL- MeOH-DMC体系相平衡研究。实验结果显示，三种ILs的分离性能强弱顺序分别是：[Bmim][Tf2N] > [Emim][Tf2N] > [Emim][PF6]；阳离子侧链较长以及阴离子极性较大的离子液体[Bmim][Tf2N]分离效果最佳，其摩尔分数达到0.05时即可消除体系共沸点；计算了阴、阳离子分别与MeOH和DMC之间的相互作用能，阳离子与共沸物分子间的键能高于阴离子的作用，但不同阳离子对两组分间的作用相差较小，因而确定了阴离子与共沸物分子间的键合作用强弱是实现共沸物高效分离的关键；阴、阳离子与共沸物分子间的键能强弱次序分别为[PF6]- < [Tf2N]-，[Emim]+ < [Bmim]+，验证了[Bmim][Tf2N]拥有最好的分离效果。2. 系统地开展了ILs萃取精馏技术与传统碳酸乙烯酯（EC）萃取精馏技术、乙二醇（EG）萃取精馏技术以及变压精馏技术四种共沸物分离过程的模拟与参数优化。通过构建酯交换制备DMC工艺模拟系统模型，采用全局灵敏度分析方法，确定工艺过程的约束条件包括：（1）EC转化率99.8%；（2）循环MeOH浓度90wt%；（3）DMC产品质量≥99.5wt%；（4）EG产品纯度≥99wt%。以系统能耗为控制目标，对分离过程的参数进行了优化，在相同约束条件下，工艺能耗大小顺序依次为：EG萃取精馏技术 > EC萃取精馏技术 > ILs萃取精馏技术 > 变压精馏技术。3. 利用?分析手段对变压工艺过程中的有效能流构成进行了探索研究，结果显示：共沸物分离过程中的内部循环物流?是输入?的1.55倍，循环过程建立初始阶段需要耗费更高的有效能，稳态过程不易建立；变压精馏共沸物分离过程的?损为7.9%，占全流程总损失量的80%以上；分析并确定制备DMC过程的?损症结是不同品位的能量未能有效利用；通过梯级利用方法对系统进行能量集成，变压精馏分离共沸物过程的能耗降低至4.16 t/tDMC，能耗降低幅度达27%以上。;As a kind of green solvent and chemical intermediate, dimethyl carbonate (DMC) is an important extension of the downstream industrial chain of coal chemical industry, methanol (MeOH) chemical industry and CO2 chemical industry. However, the MeOH-DMC azeotrope separation with many disadvantages like high energy consumption, complicated operation has greatly restricted its industrialization economic benefits. Ionic liquids (ILs), as novel solvents, have excellent properties such as structure designable, low vapor pressure, easy separation and resuable. ILs can achieve selective bonding and separation with MeOH-DMC azeotrope through varing their spatial structures and functional groups, which enables it a wide application prospect in azeotrope separation. In this paper, the vapor-liquid phase equilibrium of MeOH-DMC with ionic liquid was studied, and the process and system integration of DMC production process was simulated and optimized. The main innovative work and achievements were as follows:1. A study on phase equilibria of IL-MEOH-DMC system was carried out with three kinds of imidazole ionic liquids (i.e. [Bmim][Tf2N], [Emim][Tf2N] and [Emim][PF6]) as extractants, comprising different spatial orientations and polarity of anions and cations. The results showed that the order of interacting effects between three ionic liquids and azeotropes followed by [Bmim][Tf2N] > [Emim][Tf2N] > [Emim][PF6]. [Bmim][Tf2N] with longer chain cation and larger polar anion showed a better separation performance. And the azeotrope point could be eliminated when the molar ratio of [Bmim][Tf2N] was 0.05. Furthermore, the interaction energy of anion and cation with MeOH and DMC were calculated. The results showed that the interaction of cations and azeotrope molecules was higher than that of anions, but the effects of different cations were near the same, so the bond cooperation between anions and azeotrope molecules was the key to achieve high efficiency separation of azeotropic system. The order of the interaction energy between cation or anion and the azeotrope components was [PF6]- < [Tf2N]-，[Emim]+ < [Bmim]+ respectively, [Bmim][Tf2N] was proved to have the best separation performance.2. The process simulation and optimization of four kinds of azeotropic separation processes (i.e. ILs extractive distillation, ethylene carbonate (EC) extractive distillation, ethylene glycol (EG) extractive distillation and pressure swing distillation) were systematically carried out. The global sensitivity analysis method was used to determine the constraint conditions of the process with co-production of DMC, which were as follows: EC conversion > 99.8%, recycled MeOH purity > 90wt%, DMC purity > 99.5wt% and EG purity > 99wt%. The order of products energy consumption in azeotrope separation processes was: EG extractive distillation > EC extractive distillation > ILs extractive distillation > pressure swing distillation.3. The system integration of effective energy flow in the DMC production process was comprehensively studied with exergy analysis method. The results showed that the internal circulation exergy of azeotrope separation process was 1.55 times larger than that in the input total exergy, which means higher energy was needed to establish the initial cycle process and the steady state process was not easy to achieve. Also, the exergy loss in azeotrope mixture separation process was about 7.9%, which occupying more than 80% of total flow exergy loss. The integrated utilization of different grade heat energy played an important role in reducing the exergy loss. With the energy integration, the energy consumption of the pressure swing distillation method was reduced by more than 27% to 4.16 t/tDMC.
|陈嵩嵩. 甲醇-碳酸二甲酯共沸物分离工艺系统集成研究[D]. 中国科学院研究生院,2018.|
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