熱整合反應蒸餾塔應用於乙酸甲酯水解系統

Heat Integrated Reactive Distillation Column Applied to Hydrolysis of Methyl Acetate System

李奕成(Yi-Chen Lee)

指導教授 ： 黃孝平

國立臺灣大學/工學院/化學工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.01312

摘要

本論文將介紹兩種利用加壓技術的熱整合反應蒸餾塔：內部熱整合反應蒸餾塔（r-HIDiC），與雙效熱整合反應蒸餾塔(r-FS)，並實際應用於乙酸甲酯水解反應蒸餾系統（林禹德 2006）。在加壓的操作下，將可以使得反應蒸餾塔發生內部或外部的熱傳，進而達到熱整合的效果；乙酸甲酯水解係微吸熱反應，在操作壓力、溫度提高的條件下，亦加快系統的反應速率（reaction rate），並提升平衡常數（equilibrium constant），使得反應轉化率變好，而系統所需的觸媒量亦可以減少。

在最適化的設計下，r-HIDiC約有27 %的節能效果而r-FS則有38 %。但由於r-HIDiC必須使用價格昂貴的設備裝置-氣體壓縮機且其耗費61.9 %的總設備成本與31.3 %的總水電、蒸氣費用，使得r-HIDiC之年總成本（TAC）高出傳統反應蒸餾塔約33 %，因此就經濟層面來看，r-HIDiC並無好處。相較之下，r-FS有較好的經濟效益並可以節省15.2 %的操作成本以及6.4 %的TAC；雖然r-FS是由兩根反應蒸餾塔所組成，但在加壓與進料負載量減半的操作下，每根反應蒸餾塔都較原來的小，所以其設備成本與傳統反應蒸餾塔相去不遠。

經由節能效益與經濟面的分析，對乙酸甲酯水解反應系統而言，r-FS係為較好的熱整合架構。因此，我們將探討r-FS的動態控制策略，其控制架構將有三種：CS1~CS3。為了達到產物的規格，我們將第二根分離塔底液位視為系統內水庫存量的大小，用來控制新鮮水入料流量，以滿足化學計量平衡。在溫度控制下將造成產品組成偏差；但是其偏差很小，亦在可以接受的範圍內。這些控制架構在進料組成擾動皆有良好的排除效果；此外，控制架構CS3在進料流量擾動的排除效果優於CS1與CS2。

關鍵詞：反應蒸餾塔、內部熱整合、雙效熱整合、乙酸甲酯水解、節能技術、壓力轉移。

關鍵字

反應蒸餾塔 ； 內部熱整合 ； 雙效熱整合 ； 乙酸甲酯水解 ； 節能技術 ； 壓力轉移

並列摘要

In this paper, two designs of heat-integrated reactive distillation for the hydrolysis of methyl acetate are studied. The first one employs internal heat-integrated reactive distillation column (r-HIDIC) and the other utilizes feed-split reactive distillation column (r-FS). The savings in energy consumption and total annual costs are focused on the reactive column only. The reference base case for comparison is the RD column in the work of Lin et al. (2006). In both cases, part of the reactive distillation utilizes a higher pressure. This is because a higher pressure makes heat transfers in the system possible. In fact, this higher pressure benefits the reaction taking place. Because, the hydrolysis reaction of methyl acetate is slightly endothermic, a higher operating pressure implies higher temperatures, faster reaction rates, and better equilibrium constants in the reaction part which, in turn, results in less catalyst requirement.

The energy conservation studies show that r-HIDIC can reduce energy saving up to 27%, and r-FS had 38% saving when the process conditions are both optimized. Nevertheless, as far as economic aspect is concerned, r-HIDIC has no benefit, because of 33% more total annual cost (TAC) than the original RD column is required. This is due to an expensive gas compressor which takes 61.9% total capital cost and 31.3% utility costs. On the other hand, r-FS has a better economical efficiency with 6.4% and 15.2% savings on TAC and operating cost. Although r-FS consisted of two columns, each column is smaller than original one under the higher operating pressure and half loading conditions. Thus, the capital cost of r-FS is almost same as RD.

Based on the energy conservation ability and economical analysis, r-FS is the better heat-integrated structure than r-HIDiC for hydrolysis of Methyl acetate reactive distillation system. Then, the issue of control strategies for r-FS is studied. There are three control strategies (CS1 to CS3) to be considered. The system should keep stoichiometric balance for satisfying both product specifications. Therefore, in the control structure, fresh water feed is controlled by the liquid level of the second separation column. Since offsets in product composition may result in temperature control, the deviations are small and under acceptable range. These schemes all have good results for feed composition disturbance rejections. Beside, CS3 has a better result for feed flow rate disturbance rejections than CS1 and CS2.

Keywords: reactive distillation, internally heat-integrated distillation column (HIDiC), feed-split columns, hydrolysis of methyl acetate, energy saving, pressure swing.

並列關鍵字

reactive distillation ； internally heat-integrated distillation(HIDiC) ； feed-split columns ； hydrolysis of methyl acetate ； energy saving ； pressure swing

參考文獻

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