乙酰丙酸正丁酯之反應蒸餾製程設計

Abstract

乙酰丙酸正丁酯，英文學名Levulinic Acid Butyl Ester(LABE)或稱為左旋糖酸正丁酯，其高辛烷值、高含氧量且不溶於水造成汙染的特性，目前被視為一種極具應用潛力的汽柴油添加劑。同時，生產LABE的原料「正丁醇(n-Butanol)與乙酰丙酸(LA)」兩者皆能分別從製造生質燃料的程序中獲得，例如：生質正丁醇能夠由製造生質丙酮的ABE(Acetone-butanol-ethanol)發酵製程中獲得，而LA可經由木質纖維素水解製程中獲得，是一種應用相當廣泛的中間產物。如此，LABE能夠成為一個相當具有價值的生質材料。 乙酰丙酸之酯類的傳統製程主要分為兩個部分。首先，將乙酰丙酸(LA)轉化成當歸內酯(Angelica lactone)，再將其與醇類混合反應成LA之酯類。然而，兩步驟的反應將使的流程變得複雜並付出較高的成本。除此之外，另一個製程是直接將LA與醇類混合進行酯化反應，但此反應受限於反應平衡的限制，必須要能分離未反應的物質並回流再混合進行反應，如此可能與傳統製程有類似的高操作成本問題。對於直接的酯化反應而言，利用「反應蒸餾」的方式，能夠大幅簡化因酯化系統中的平衡反應，使得程序中含有較複雜的反應與分離系統之問題。 在反應蒸餾系統中，正丁醇(n-Butanol)與LA將分別在適當的位置進到蒸餾塔中，此反應的硫酸觸媒將預先與LA混合再進到蒸餾塔內。反應蒸餾塔的精餾段為非均相共沸的蒸餾系統，其目的為在塔頂分離酯化的副產物─水，而反應段在精餾段之下，其目的是將LA與正丁醇進行酯化反應生成LABE，並在塔底分離酯化的主產物─LABE。本研究使用ASPEN plus當作程序模擬軟體，得到以當量比之反應物進料時，此強化程序應用於LABE製程的反應與分離系統相當具有可行性。

Butyl Levulinate (LABE) is one of the potential fuel additives due to its good characteristics such as high octane number, high oxygen content, and low water solubility, etc. In the mean time, the raw materials that can produce LABE are n-Butanol (n-butyl alcohol) and Levulinic acid (LA). Both of them can come from biochemical conversions. For example, the biobutanol can be produced by ABE (Acetone-Butanol-Ethanol) fermentation process, and LA is one of the famous intermediate from hydrolysis of lignocellulostic biomass. Therefore, LABE becomes the variable biomass material. The traditional process to manufacture levulinic ester takes two-step reactions. First, converting the Levulinic acid to angelica lactone and then followed by reaction of angelica lactone with alcohol. However, the two-step reactions may result in complicated process flowsheet and high operating cost. Direct esterification is an alternative way to produce levulinic esters, but the equilibrium limitation still have similar problem like the traditional process. This work aims to use the reactive distillation for simplifying the process of direct esterification of Levulinic acid to Butyl Levulinate. In the reactive distillation system, n-Butanol (n-butyl alcohol) and Levulinic acid are added into the column with sulfuric acid as the catalyst. Levulinic acid and n-Butanol are converted to Butyl Levulinate as bottom product in the reaction section. The rectifying section is the heterogeneous azeotropic distillation system that can separate high purity water as the top product. By using ASPEN plus as simulation platform, the economy and applicability of the proposed reactive distillation process with stoichiometric feed of Levulinic acid and n-Butanol is illustrated in this study.