固體酸觸媒合成生質柴油及其反應動力參數探討

Abstract

本研究利用一種親油性固體酸觸媒，來合成生質柴油。合成生質柴油主要的反應，為三酸甘油酯與甲醇在觸媒的催化下，進行轉酯化而生成甲基酯。和傳統的液體鹼在均相中反應比較，固體觸媒具有易和產物分離，可重覆使用，無廢酸鹼液的優點。本研究中，利用葡萄糖為原料的固體酸觸媒，來催化轉酯化反應。葡萄糖在氮氣中經過673K的焦碳化後，再將其置入濃硫酸中，進行423K的熱處理，生成一種以碳為主體，且具有濃硫酸酸強度的固體酸觸媒。批式轉酯化反應在高壓反應器中，反應條件為423K，250psi，加入3wt%固體酸觸媒，大豆油與甲醇的莫耳數比為30比1的情況下，甲基酯(Fatty acid methyl esters, FAMEs)的產率，可以在兩小時後，達到最高約90%。以棕櫚酸加入大豆油模擬自由脂肪酸(Free fatty acid,FFA)對轉酯化的影響，發現固體酸可進行酯化，不影響大豆油轉酯化速率。綜合反應結果，推導出Langmuir-Hinshelwood反應速率式，顯示親油性的固體酸碳觸媒，有利於大豆油吸附，促進反應速率。

A hydrophobic solid acid catalyst for the synthesis of biodiesel was investigated in this research. Biodiesel is synthesized from the catalytic reaction of glyceride with methanol. Methyl esters are produced from this transesterification reaction. In comparison to traditional liquid base catalysts, solid catalysts have the advantage of easy catalyst and product separation, and can be used repeatedly. Glucose was the raw material for the solid acid catalyst prepared for transesterification reaction in this work. Glucose at 673K under nitrogen gas will undergo carbonization, thereafter the catalyst is treated with concentrated sulfuric acid for sulfonation at 423K. The solid acid catalyst is a carbon support with concentrated sulfuric acid groups. The transesterification reaction was carried out in a high pressure reactor, the reaction conditions are 423K, 250psi, 3wt% solid acid catalyst and a soybean oil to methanol molar ratio of 30:1. Under the given reaction conditions, the yield of fatty acid methyl esters (FAMEs) can reach 90% within 2 hours. Palmitic acid was added to soybean oil to simulate the effect of free fatty acids(FFA), on the transesterification reaction. Results showed that it had no effect on the transesterification of soybean oil. A rate equation was proposed based on the Langmuir-Hinshelwood approach, results indicate that the solid acid catalyst improves the adsorption of soybean oil therefore increase the reaction rate.