反應蒸餾系統之熱整合側流蒸餾塔序列

Abstract

反應蒸餾可在單一設備中同步進行化學反應與初步分離，但後續產品純化及未反應物回收仍可能消耗大量能源。本研究探討塔間熱整合與液相側流配置對反應蒸餾製程能耗及經濟效益的影響，並以乙酸甲酯水解及碳酸二乙酯合成作為案例。針對每一反應系統，分別建立傳統反應蒸餾序列、反應分壁式蒸餾塔、堆疊式蒸餾序列及堆疊式側流蒸餾序列。所有流程均使用 Aspen Plus 建模，並透過模擬退火演算法調整塔板數、進料位置、側流條件及操作參數，在維持相同產品規格的條件下最小化年度總成本。 乙酸甲酯水解系統的結果顯示，最佳化後的堆疊式蒸餾序列表現最佳。相較於最佳化傳統序列，其外部能源需求與年度總成本分別降低 16.0% 與 10.7%。在此系統中，液相側流雖然降低第二塔的分離負荷，卻同時提高第一塔的再沸器負荷，且削弱兩塔之間的熱負荷匹配。因此，加入側流後未能進一步改善整體經濟效益。 在碳酸二乙酯合成系統中，堆疊式側流蒸餾序列獲得最低的能源需求與年度總成本。相較於最佳化傳統序列，其能源需求與年度總成本分別降低 46.8% 與 30.0%；相較於未設置側流的堆疊式蒸餾序列，則進一步降低 1.6% 與 1.4%。此結果顯示，側流配置可改善第一塔與第二塔之間的物料分配，但其效益取決於側流組成、分離負荷轉移及塔間熱負荷匹配，而非在所有反應系統中皆能產生相同程度的節能效果。 綜合兩個案例可知，塔間熱整合是降低外部公用設施需求的主要因素；側流配置則提供額外的物料分配自由度，其經濟效益具有明顯的系統相依性。本研究建立的比較與最佳化方法可作為評估熱整合及側流反應蒸餾流程的設計基礎。

Although reactive distillation can reduce the equipment required for reaction and primary separation, considerable energy may still be consumed in downstream product purification and reactant recovery. This study evaluates the effects of intercolumn heat integration and liquid side streams on the energy and economic performance of two reactive systems: methyl acetate hydrolysis and diethyl carbonate synthesis. Four configurations were developed for each system, namely a conventional reactive-distillation sequence, a reactive dividing-wall column, a stacked distillation sequence, and a stacked side-stream distillation sequence. The processes were modeled in Aspen Plus and optimized using simulated annealing. Column stage numbers, feed locations, side-stream conditions, and operating variables were adjusted to minimize the total annual cost while satisfying identical product-purity specifications. For methyl acetate hydrolysis, the optimized stacked distillation sequence achieved the lowest total annual cost. Relative to the optimized conventional sequence, it reduced the external energy requirement by 16.0% and the total annual cost by 10.7%. Introducing a liquid side stream reduced the separation duty of the second column but increased the reboiler duty of the first column and weakened the heat-duty matching between the two columns. Consequently, the side-stream configuration did not provide an additional economic benefit for this reaction system. For diethyl carbonate synthesis, the stacked side-stream distillation sequence exhibited the best overall performance. Its energy requirement and total annual cost were 46.8% and 30.0% lower, respectively, than those of the optimized conventional sequence. Compared with the corresponding stacked sequence without a side stream, additional reductions of 1.6% in energy requirement and 1.4% in total annual cost were obtained. The comparison demonstrates that intercolumn heat recovery is the principal contributor to the improvements achieved by the stacked configurations. The benefit of introducing a side stream is system-dependent and is governed by the side-stream composition, the redistribution of separation duty, and the resulting heat-duty match between the integrated columns. These findings provide a quantitative basis for applying stacked and stacked side-stream configurations to reactive distillation processes.