結合滲透蒸發的氧化石墨烯/甲殼素複合膜反應器以提升酯化反應效率

Abstract

文獻指出分離程序的操作成本占化工產業的一半以上，而整合滲透蒸發技術將大幅減少能源消耗。我們設計滲透蒸發反應器，使用氧化石墨烯/幾丁聚醣複合膜，將乙酸、乙醇酯化反應程序與滲透蒸發結合，實驗顯示此膜能維持一定的對水選擇率將生成的水移除，根據勒沙特列原理反應向右而突破平衡轉化率。並探討反應溫度、固體酸觸媒用量、初始反應物莫爾比的影響，結果顯示提高反應溫度、觸媒用量對轉化率提升有正面助益，初始反應物莫爾比則有一最適比例，在初始乙醇/乙酸比=2:1、反應溫度70oC、2.25wt%觸媒量情況下，相比平衡的情況可提升8%轉化率。 並嘗試結合滲透蒸發與預酯化，由於生質柴油的原料油為廢食用油，其中含有2~7%的自由脂肪酸(Free Fatty Acid)，會與鹼觸媒發生皂化，降低觸媒效率，所以進行轉酯化前會先用酸觸媒進行預酯化降低FFA至0.5wt%以下。我們嘗試結合滲透蒸發提升預酯化去除自由脂肪酸效果，選擇棕櫚酸與過量甲醇進行反應，尋找適當動力參數，當甲醇:棕櫚酸=20:1、10wt%Amberlyst 15觸媒、4wt%氧化石墨烯複合膜、反應溫度50oC，在8小時內可以提升20%轉化率。

The separation process accounts for over 50% of the operating cost in chemical engineering industry based on the literature survey. A pervaporation process with existed distillation tower would significantly reduce energy consumption. We designed a system of pervaporation apparatus and used graphene oxide/chitosan membrane. The esterification of ethanol and acetic acid with pervaporation was performed, and the experiment results showed that the conversion is enhanced due to continuous removal of the water from the solution. The overall reaction favors the product side as described by Le Chatelier principle. We investigated various kinetic parameters included reaction temperature, loadings of solid acid catalyst and initial molar ratio of ethanol to acid. The results showed higher temperature and more catalyst loadings had positive influence. The conversion increased 8% under the optimal conditions at 70oC, 2.25wt% catalyst and initial ratio of ethanol to acetic acid =2:1 . In addition, we tried the combination of pervaporation and pre-esterification process of biodiesel production. There existed 2 to 7wt% of free fatty acid (FFA) in the feedstock. FFA would react with base catalyst to produce soap and reduce the yield of biodiesel. Generally, the pre-esterification was applied before transesterification step to reduce the amount of FFA lower than 0.5wt%. We integrated pervaporation with pre-esterification together to study the enhancement of eliminating FFA. We chose palmitic acid as a representative of FFA. The conversion was enhanced by 20% under the conditions, methanol: palmitic acid=20:1 and 10wt% of solid acid catalyst at 50oC.