利用半批次反應萃取蒸餾生產不同醇類與乙酸在酯化反應下的產物

Abstract

批次反應蒸餾(Batch reactive distillation)是一種結合了反應蒸餾的優點和批次程序的彈性的整合製程。半批次反應萃取蒸餾(Semi-batch reactive extractive distillation)則是一種批次反應蒸餾的衍生，在批次反應蒸餾中使用其中一反應物當作連續性的側進料。不同醇類與乙酸的酯化反應常被用於研究批次反應蒸餾或半批次反應萃取蒸餾的設計或最適化設計的模組。 在乙酸丁酯與乙酸戊酯的系統當中，最輕成分是一落在兩相區之內的非勻相三成份共沸物，其在分相槽中分相之後可以得到高純度的水相(99.5%水)。藉由將水相從塔頂被移除，油相全回流至蒸餾塔中，批次反應蒸餾可以得到高純度的產物。 在乙酸異丙酯系統中，雖然最輕成分也是一落在兩相區之內的非勻相三成份共沸物，使用批次反應蒸餾製程，其在分相槽中分相之後只能得到95%純度的水相。使用半批次反應萃取蒸餾則可以增進其生產的效率和產品的純度。使用乙酸做為連續性的側進料可以大幅的降低塔頂產物中的異丙醇濃度，使得塔頂產物的濃度更接近酯-水邊緣。此混合物經由在分相槽(decanter)中分相可以得到高純度的水相，而油相則為酯水雙成份混合物。藉由另一逆轉式批次蒸餾塔(Inverted Batch Distillation Column)和一分相槽(decanter)可進一步分離油相中的酯與水而得到高純度的酯產物。 在乙酸乙酯系統中，最輕成分為一勻相三成份共沸物，其並非落在兩相區之中，因此無法使用上述乙酸丁酯與乙酸戊酯的系統當中的批次反應蒸餾的製程來獲得高純度的酯，只能適用於在乙酸異丙酯系統當中所使用的半批次反應萃取蒸餾製程。 在乙酸甲酯系統中，最輕成分為一勻相雙成份共沸物(甲醇與乙酸甲酯)，其並非落在兩相區之中，因甲醇比乙酸易揮發很多，因此比較適合用於半批次反應萃取蒸餾製程。使用乙酸做為連續性的側進料可以大幅的降低塔頂產物中的甲醇濃度，使得塔頂產物為高純度的乙酸甲酯(97.5%)。 在這篇論文中，分別研究半批次反應萃取蒸餾生產不同醇類(甲、乙、丙醇)與乙酸的在酯化反應下的產物。三個系統皆採用乙酸為一連續性的側進料，側進料可大幅降低塔頂產物中的醇濃度。在乙酸乙酯和乙酸異丙酯系統中，油相產物需利用逆轉式批次蒸餾塔(Inverted Batch Distillation Column)和一分相槽(decanter)做進一步的分離與純化。而乙酸甲酯系統則可以直接從塔頂產物中得到高純度的酯產物。在乙酸甲酯系統中，參數之間的交互影響性非常大，我們藉由探討其中不同參數對彼此的影響來研究初步的最適化設計。

Batch reactive distillation (BRD) is an integrated process which combines the advantages of reactive distillation and the flexibility of batch processes. Semi-batch reactive extractive distillation (SBRED) is a design alternative for BRD in which one reactant is continuously fed into the column during the batch. Esterifications of low molecular weight alcohols (methanol-amyl alcohol) with acetic acid have been studied as model systems for the design and optimization of BRD and SBRED processes. For n-butyl acetate and amyl acetate system, the lowest-boiling point (unstable node) is a ternary heterogeneous azeotrope located in a two-liquid region. The phase split naturally provides high purity of water (99.5%) in aqueous phase. A BRD process is feasible in these two systems because water can be removed from the reflux drum (decanter) at the top of the column. For isopropyl acetate system, the lowest-boiling point (unstable node) is also a ternary heterogeneous azeotrope located in a two-liquid region. However, the aqueous phase only provides 95% of water. It showed that SBRED can improve the production efficiency. The concentration of isopropyl alcohol in the distillate can be efficiently reduced by feeding acetic acid as an entrainer into the column continuously so that the distillate composition is closer to the water-acetate edge. High purity of water can be collected in aqueous phase and binary mixture of water and acetate can be collected in organic phase. Then a non reactive inverted batch distillation column with a decanter is used to withdraw high purity of acetate from the organic phase. For ethyl acetate system, the lowest-boiling point (unstable node) is a ternary azeotrope which is not located in a two-liquid region. Therefore, unlike previous systems, BRD with a decanter is not feasible. In our work, we consider the application of SBRED similar to isopropyl acetate system. For methyl acetate system, the lowest-boiling point (unstable node) is a binary azeotrope (of methanol and methyl acetate) which is not located in a two-liquid region. The SBRED system is preferable because methanol is much more volatile than acetic acid. The concentration of methanol in the distillate can be efficiently reduced by using a side feed entrainer. Eventually high purity methanol (97.5%) can be achieved within a single column. In this thesis, the esterifications of acetic acid with three different alcohols (methanol, ethanol, isopropanol) using SBRED are studied. All three systems use acetic acid as a side feed entrainer to drag the alcohol down, thereby preventing the alcohol from going up as a distillate. For ethyl acetate and isopropyl acetate system, the organic phase product needs to be further purified by using a nonreactive inverted batch distillation column. For methyl acetate system, we study the preliminary optimization to show that how we adjust the parameters to improve the dynamic process while the parameters are highly interdependent with each other.