包含不純物收集之批次反應蒸餾系統的設計、操作與最適化

Design, Operation and Optimization of Batch Reactive Distillation with Off-Cut

高玉龍(Yu-Lung Kao)

指導教授 ： 吳哲夫

國立臺灣大學/工學院/化學工程學研究所/博士(2015年)

https://doi.org/10.6342/NTU201600304

摘要

批次反應蒸餾為一整合程序，其結合了反應蒸餾的優點及批次程序操作的適應性，在批次蒸餾程序中，不純物收集為一常見運用於改進程序表現之操作策略，然而此項操作策略卻非常少見於批次反應蒸餾的文獻中。本論文將探討包含不純物收集之批次反應蒸餾的設計與操作的幾個面向，首先藉由一先前考慮過之理想四成份反應系統 (Kao, Y. L. Effect of Relative Volatility Ranking on the Design and Operation of Batch Reactive Distillation System. Master Thesis. National Taiwan University, Taipei, Taiwan, 2010)，建立包含不純物收集之最適化操作程序，並探討改變產物純度與反應平衡常數對程序之影響，和先前的結果比較，新的結果顯示，利用不純物收集能改善批次反應系統之生產力因子(batch capacity)，特別是當系統中兩反應物的沸點介於另外兩產物中間時，或是當產物的純度要求較高時，亦或是當反應平衡常數較小時，除此之外，一真實反應系統，乳酸甲酯的水解反應也被研究以補充理想系統之不足，並印證理想系統之結論。
雖然不純物收集能夠改善批次反應蒸餾程序，但是它的使用效力在部份的反應系統中，因為反應物與產物間的沸點排序而受到限制，因此本研究進而提出兩種改善不純物收集之方法，其一是利用中槽式批次蒸餾塔架構，另一種則是利用過量反應之設計，此兩種改善方法利用三個真實反應系統做為說明，分別為乳酸甲酯的水解反應、甲酸酯化反應以及1,1-二甲氧乙烷的生成反應。結果顯示，對於此三個研究系統，運用適當的不純物收集改善方法，生產力因子平均進步幅度為百分之41.9。
接著，本研究探討收集到之不純物回收課題，其策略為將目前批次所收集到之不純物，全部回收至下一批次做為部份之進料，這樣的操作將會使原本的單一批次操作問題，轉換成批次與批次間(batch-to-batch)的操作問題，本研究利用偽穩態(pseudo-steady-state)之概念，來簡化最適化操作問題，並利用相同於前一段所提及之三個真實系統加以說明。研究結果顯示，比較包含不純物收集並回收之批次操作，與僅有包含不純物收集之批次操作，兩種批次操作的最適化操作策略(operating recipe)和生產力因子相似，除此之外，包含不純物收集並回收之批次操作的生產力因子，平均約是不包含不純物收集之批次操作的生產力因子的兩倍(高出93.3%)。
最後，本研究探討同時考慮設備設計和程序操作之最適化問題，利用乳酸甲酯水解反應和甲酸酯化反應，來說明最小化年總成本(total annual cost)之問題，批次反應蒸餾程序中，不同設計與操作變數對年總成本之影響，被逐一討論。最適化的結果建議:恆組成蒸餾液之收集策略能充分表現最適化操作；蒸餾塔的塔板數要足夠，應設計於藉由增加板數使生產力因子增加不顯著的範圍；蒸氣沸騰率的設計，應該要能最充分運用可使用的操作時間；再者，催化劑的填充量主要影響最適化的蒸氣沸騰率；藉由洞悉這些變數的影響，本研究發展出一有效同時考慮設備設計與程序操作之最適化運算法則。

關鍵字

批次 ； 反應蒸餾 ； 設計 ； 最適化

並列摘要

Batch reactive distillation (BREAD) is an integrated process which combines the advantages of reactive distillation and the flexibility of batch processes. Off-cut is commonly applied in non-reactive batch distillation to improve the performance. However, reports of the application of off-cut for BREAD are quite rare. In this thesis, several aspects of design and operation of BREAD processes with off-cut are studied. A hypothetical reaction system considered previously (Kao, Y. L. Effect of Relative Volatility Ranking on the Design and Operation of Batch Reactive Distillation System. Master Thesis. National Taiwan University, Taipei, Taiwan, 2010) is used to develop the optimal operation policy without off-cut. In addition, the effect of changing product purity specifications and reaction equilibrium constants is also investigated. Compared with the previous results, the new results show that using off-cut can improve performance in terms of batch capacity (CAP), especially when both reactants have boiling points between those of the two products, when the product purity is high, and when the reaction equilibrium constant is low. A real case study, hydrolysis of methyl lactate, is also investigated to validate the results from the ideal system study.
Next, methods for improving the operation of BREAD with off-cut are presented. Although off-cut can improve the operation of batch reactive distillation, its usefulness is limited in some cases due to the relative volatility ranking of reactants and products. In these cases, performance can be improved by using a middle vessel column or by using an excess of one reactant. These methods are demonstrated with case studies of three processes with realistic reaction kinetics and vapor-liquid equilibrium models: hydrolysis of methyl lactate, esterification of formic acid, and production of 1,1-dimethoxyethane. CAP can be improved on average 41.9 percent if the appropriate method is employed.
Off-cut recycling in BREAD processes is then studied. The strategy is to recycle off-cut to the next batch as a part of the initial feed. This transforms the operation problem from single batch problem into a batch-to-batch problem. The pseudo-steady-state concept is applied to BREAD processes to simplify the optimization problem. Optimization based on maximizing CAP for the batch-to-batch problem is demonstrated using three real chemistry processes. The results show that the optimal operating recipe and CAP when off-cut is recycled are similar to the case when off-cut is collected but not recycled, and the CAP is on average almost twice (93.3% more) the maximum that can be achieved when off-cut is not used. Therefore, recycling off-cut may not only save the trouble of processing the off-cut, but also make the process more economical.
Last, simultaneous optimization of equipment design and process operation is investigated for BREAD processes. The minimal total annual cost problem is illustrated with two realistic chemical systems, hydrolysis of methyl lactate and esterification of formic acid. The effect of design and operating variables on TAC is investigated. The optimization results suggest that a reflux policy which maintains constant distillate composition can provide nearly optimal operation. The column should be designed with an adequate number of stages so that the CAP improvement by further increasing the number of stages is insignificant. Vapor boilup rate should be specified to make the best use of the available operating time, and the optimal vapor boilup rate is primarily affected by the catalyst loading. The insight into the effect of process design variables on design performance is used to develop an efficient algorithm for determining simultaneously the optimal column design and operating policy.

並列關鍵字

batch ； reactive distillation ； design ； optimization

參考文獻

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