以直接轉酯化反應轉化濕藻至被生質柴油及其動力學

Abstract

微藻是一種能行光合作用之單細胞植物，能快速生長同時累積大量油脂於細胞中，因此被認為是極具潛力的生質燃料來源。但由於微藻的收集、乾燥與油脂萃取不易，導致能量成本高，以至於目前微藻轉化之生質柴油仍難有商業價值。為使生產生質柴油更符合經濟與能源效益，設計適當微藻轉化為生質能源的程序乃是重要之課題。 本研究所使用小球藻(Chlorella sp. ESP-6)為原料，並以直接轉酯化反應將濕潤微藻中油脂轉化為生質柴油主要成分─脂肪酸甲酯，本研究將傳統製程上油脂萃取、純化與轉酯化三個單元合併成為二階段反應，先藉由鹼性甲醇溶液破碎微藻細胞、使細胞內油脂釋放到溶液中及加速轉酯化和皂化反應進行，再由酸性甲醇溶液將皂化反應產物轉化為脂肪酸甲酯。實驗結果顯示，二階段直接轉酯化反應所需反應程序時間為傳統製程的二十分之一，且容許進料含有相當的水量，使用濃縮藻液做為原料時的產率約為其他直接轉酯化的2 ~ 6倍。本研究分析反應中催化劑、溫度及甲醇與水的比例對系統的影響，並以二級不可逆反應良好地描述第一階段鹼性反應、以二級可逆反應描述第二階段酸性反應。

Microalgae, a photosynthetic organism, has the ability of fast-growing and lipid accumulating, which makes it a highly potential source of biofuel. However, there are some current technical barriers, such as high energy and organic solvent consumption for harvest, drying and lipid extraction. To make the process of producing biofuel production from microalgae economically feasible, an innovative process was designed to convert lipid inside microalgae into biodiesel.

In this study, Chlorella sp. ESP-6 was used as the source of triglyceride. Direct transesterification (DT) is a method directly converting lipids within algae into biodiesel, fatty acid methyl esters (FAME). In this study, our DT first disrupted the cell wall of microalgae, extracted lipids and converted them by saponification and transesterification with alkali-methanol solution, then converted the product of saponification into FAME by esterification with acid methanol. Result showed that the reaction time of DT is about 1/20 of the traditional drying-extraction- transesterification process with comparable yield. More importantly, this 2 stage DT was insensitive to the water content of the raw material (up to 90%), and the yield was 2 ~ 6 times of other DT methods when using wet microalgae. Meanwhile, the effects of parameters including catalyst concentration, temperature and ratio of methanol and water were evaluated. A second order irreversible and a second order reversible reaction kinetic model were proposed to describe DT satisfactorily.