醋酸乙酯為重要工業成品，廣泛應用於各種工業領域。目前商業化醋酸酯化製程大多採行液相酯化反應，然液相酯化反應受熱力學平衡限制，等莫耳醋酸和乙醇進行酯化反應所得之醋酸乙酯產率低於67 mol%，亦即有30 mol%以上的醋酸與乙醇未完全反應，而其中乙醇會和產物中的醋酸乙酯與水形成乙醇-水、乙醇-醋酸乙酯之二成分共沸，及乙醇-水-醋酸乙酯之三成分共沸，所以欲分離產物中之乙醇-水-醋酸乙酯需耗用很多能源，因此傳統之醋酸乙酯製程約有90%的能源是消耗在分離乙醇-水-醋酸乙酯的程序上，而其中最重要的分離關鍵為乙醇的存在，因為乙醇的存在除了導致多重共沸外，其三成分共沸組成為均勻互溶相，無法利用蒸餾直接分離，先需採用加水萃取法降低醋酸乙酯產物中之乙醇含量，才可利用共沸蒸餾純化醋酸乙酯與水。所以開發一高效率的酯化製程以提高乙醇轉化率，將可提升製程的能源使用效率。本研究成功的在不改變傳統酯化製程的流程下，利用製程技術將等莫耳酯化反應的one-pass乙醇轉化率由67 mol%提高至85 mol%以上，使產物流中之乙醇含量由14wt%降低至6.5wt%，產物流中之乙醇含量降低將有助於後端之醋酸乙酯分離純化，此新製程之關鍵技術為所採用之反應溫度，控制反應溫度介於傳統之液相酯化和氣相酯化反應之間，並允許反應組成於反應器中由液相轉換成氣相，因為液相反應所需之反應器較小和反應物與觸媒接觸時間較長，而氣相酯化反應之平衡常數高於液相酯化反應可獲得較高之乙醇轉化率，所以控制反應起始於液相，終於氣相，如此可同時解決液相酯化反應產率低及氣相反應需要較大反應器之缺點，且使用之HZSM-5沸石觸媒已完成570小時之壽命實驗，經過製程評估此製程之可降低一半製程廢水、及節省1/3純化所需之蒸汽耗用量。 Ethyl acetate (EAc) is an important feedstock in chemical industry. Most of the commercial processes for EAc production are via liquid-phase esterification. Owing to the thermodynamics limitation, the overall yields of EAc are confined to 67% with equimolar reactants feed of acetic acid and ethanol. Consequently, there are 30% of unreacted reactants with azeotropic by-products of ethanol-water, ethanol-EAc and ethanol-water-EAc. To separate these impurities is laborious and energy consuming. Over 90% of overall energy supply of EAc production is consumed by the separation of ethanol-water-EAc azeotropes. The key factor is ethanol. Owing to its difficulty in separating by direct distillation, the most plausible way is water extraction to reduce the ethanol content in EAc followed by azeotropic distillation for purification. In order to improve the EAc distillation process, a high-efficiency, low energy-consuming esterification process has been developed. In this study, the one-pass ethanol conversion was successfully improved from 67mol.% to 85mol.% while the ethanol concentration was decreased from 14wt.% to 6.5wt% without changing the flow sheet of traditional esterification process. One of the critical parameters in this novel EAc synthesis process is the reaction (esterification) temperature. By keeping it between the liquid-phase and gas-phase operation regimes during which parts of the reacting composition were vaporized. The major consideration is based on the equilibrium constants in the gas-phase reaction which are higher than those in the liquid-phase. The initial reaction stage in the liquid-phase has the advantage of smaller reactor size and more efficient contacting with the catalysts. As the equilibrium had been achieved in the final gas-phase, a higher conversion of ethanol was obtained due to the equilibrium constant constraints. Consequently, either of the equilibrium conversion constraint for the liquid-phase regime and larger reactor volume requirement for the gas-phase reaction has been overcome. In addition, the solid acid catalysts used in this novel process has low impact to the environment without corrosion to the reactor wall. These catalysts had been passed for performance after 2200 h of duration. Evaluation also shows that half of the process water and one-third of consumption of purification steam can be saved
