초임계 메탄올을 이용한 유채유 바이오디젤 제조

Abstract

본 연구에서는 초임계 메탄올을 이용하여 유채유(Rapeseed oil)를 FAMEs(fatty acid methyl esters)로 전환시킨 후 반응변수에 따른 영향과 속도론에 관하여 기초연구를 하였다. 실험은 반응온도 240℃~320℃, 압력 100bar~350bar, 반응시간 0min~50min, 몰 비 30:1~75:1(Methanol : oil)까지 변화시켜 비활성 분위기인 닫힌계에서 수행하였다. 반응 후의 액상을 회전식 증발기를 통하여 잔류메탄올을 증발시키고 층 분리 후 상층을 GC(gas chromatogram)로 정성 및 정량분석 하였다. 반응압력과 몰 비를 고정하기위한 실험에서 가장 좋은 수율을 보이는 200bar, 60:1 로 고정하였으나, 압력에 따른 차이는 10% 이내로 많은 영향은 없는 것으로 보였고 메탄올과 oil의 몰 비에 대한 영향은 메탄올이 많을수록 좋았으나 60:1과 75:1은 거의 비슷한 수율을 보였다. 초임계 메탄올 하에서 생성된 FAMEs는 주로 methyl palmitate (C16:0), methyl stearate(C18:0), methyl oleate (C18:1), methyl linoleate (C18:2), methyl linolenate(C18:3) 이였으며, 280℃ 이상에서는 이중결합구조를 가지고 있는 methyl oleate, methyl linoleate, methyl linolenate는 반응시간에 따라 수율이 증가했다가 감소하는 것을 볼 수 있었다. 한편 Triglycerides, Diglycerides, Monoglycerides, Free fatty acids를 포함하는 uME(unmerhyl esterified compounds)가 FAMEs로 전환된 양을 Conversion [wt%]으로 계산하여 초임계를 이용한 유채유 바이오디젤 제조의 속도론적 접근을 하였다. 초임계 메탄올에 의한 유채유 바이오디젤의 합성반응을 비가역 1차 속도식을 따르는 구간에서 속도상수 및 Arrehenius plot에 의한 활성화 에너지를 구하였다.; Biodiesel is an alternative fuel for diesel engines whish is commonly prepared from vegetable oils via transesterification with alcohols. the product is called as fatty acid methyl esters or biodiesel. In this study, biodiesel production from rapeseed oil using supercritical methanol was carried out by varying the operating parameters such as temperature(240℃~320℃), pressure(100bar~350bar), the molar ratio of methanol to oil(30~75) and reaction time (0~50min ). In order to evaluate of reaction parameters on the content of FAMEs, batch-type reactor was used to prepare biodiesel. we set the time as the starting point of reaction when the temperature and pressure reach the prescribed values above supercritical point. The recovered liquid products were analyzed by GC(FID) and EN14103 was used for the analysis of product sample. The highest FAMEs content was shown at the reaction pressure of 200bar. The content of FAMEs increased with increasing the molar ratio of methanol to oil but the content of FAMEs was slightly affected by molar ratio of methanol to oil above 60. As the reaction proceeded, the content of FAMEs increased slowly and was in equilibrium, below 280℃, whereas that of FAMEs increased rapidly and then decreased, above 280℃. Result showed that the content of FAMEs was affected by thermal stability of biodiesel throughout the reaction. The kinetic behavior of transesterification of rapeseed oil in supercritical methanol had been investigated. This reaction was assumed to proceed in the irreversible first order reaction as a function of the concentration of uME (unmethyl esterfied compounds) and reaction temperature. From the Arrhenius plots, the activation energy was evaluated to be 50.18kJ/mol for biodisel production from rapeseed oil in supercritical methanol.