福馬林及甲醇直接生產聚甲氧基二甲醚之製程探討

OME Production Directly from Formalin and Methanol

艾子傑(Tsu-Chieh Ai)

指導教授 ： 錢義隆

國立臺灣大學/工學院/化學工程學研究所/碩士(2017年)

https://doi.org/10.6342/NTU201701834

摘要

聚甲氧基二甲醚擁有極高的發展性，尤其是汽柴油需求量日益增長同時追求
環境永續發展的世代，傳統汽柴油使用上有諸多缺陷，燃燒不完全又伴隨煙塵排放，都讓傳統柴油地位受到挑戰，開發新型柴油勢在必行。聚甲氧基二甲醚(OME3-5)可作為添加劑與傳統柴油混合，改善煙塵問題、加強燃燒效率，且其與柴油互溶性高、性質接近，可以直接使用不須額外的引擎改裝。在安全考量上，鏈長低於3 之聚甲氧基二甲醚有閃燃點過低的問題，鏈長高於5 的聚甲氧基二甲醚則是黏滯性過高而不利使用。
聚甲氧基二甲醚的生產製程可分為兩種路徑，第一種路徑由甲醇生產甲醛，在合成兩中間產物三聚甲醛與甲縮醛，最後兩中間產物反應得到聚甲氧基二甲醚產品，此路徑至少需要四座工廠較為繁複，而第二種路徑由甲醇產製甲醛後，以甲醛、甲醇、水的混合物直接生成聚甲氧基二甲醚，僅有兩個生產步驟，大幅簡化工廠數目，而系統內水與其他化合物之間存在許多共沸物，使得分離純化不易進行。
在本研究將聚焦於利用甲醛、甲醇、水的混合物直接生成聚甲氧基二甲醚的部分，整廠程序可分為上游段與下游段，上游段為反應器及剩餘反應物回流，下游段得到純化後達到99.95 wt%的OME 產品及高純度的水，並以最小化的年度總成本為目標函數進行穩態程序設計，然後以動態模擬擾動進入程序時所需的控制策略，最後因為基礎架構中的再混合效應，以隔牆塔進行節能改善穩態設計。

關鍵字

柴油添加劑 ； 聚甲氧基二甲醚 ； 程序最適化 ； 隔牆塔程序 ； 動態控制

並列摘要

Diesel fuel is highly demanded in recent years. However, there are many drawbacks for conventional diesel fuel, such as smog production and low combustion efficiency. In order to solve these problems, blending them with the conventional dissel fuels may be a feasible way. Among different diesel additives, poly(oxymethylene) dimethyl ethers(OME3-5) are the promising ones that can enhance the oxygenation of diesel fuel. The properties of OME3-5 are close to conventional diesel fuel, so there is no need of modifications for those original diesel fuel engines. For OMEs chain outside the range of 3 to 5, there may be some safety concerns, because the flash points of shorter OMEn (n<3) are too low, and the viscosity of longer OMEn (n>5) are too high.
There are two routes for the manufacture of OMEs. The most common route is through methanol and formaldehyde forming the two intermediates, trioxane and methylal, then reacting to the target OME product (named as route 1). The alternative route is directly from formaldehyde and methanol in aqueous solution (named as route 2). However, the complex azeotropes among the reactants and the products make it difficult to get target OME3-5 product.
In this work, a production process of OME3-5 is designed through the route 2 is rigorously studied. The overall process includes an upstream reaction section and a downstream product purification section. The upstream process includes a CSTR, two distillation columns and the downstream process is a one-decanter-two-stripper system with a methanol purge. After the steady-state model is established, it is optimized by minimizing total annual cost. Then, a proper control strategy is developed for the optimal process to reject the process disturbances. Last but not least, the dividing-wall-column configuration can be used to relieve the remixing effect of the distillation columns, and can improve the separation efficiency.

並列關鍵字

Diesel additives ； POMDME ； Optimization ； Dividing-wall column ； Dynamic control

參考文獻

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[4] Burger, J.; Strofer, E.; Hasse, H. Chemical equilibrium and reaction kinetics of the heterogeneously catalyzed formation of poly(oxymethylene) dimethyl ethers from methylal and trioxane. Industrial and Engineering Chemistry Research, 2012, 51, 12751-12761.

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