564 / 2018-10-10 15:42:00

Lewis acid-catalyzed in situ transesterification/esterification of tigernut in sub/super-critical ethanol: an optimization study

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Abstract
Lewis acid-catalyzed in situ transesterification/esterification of tigernut (cyperus esculentus) was conducted in sub/super-critical ethanol. An L16 (44) orthogonal array design (OAD) with four factors at four levels was employed to investigate the influence of the process variables on the product distribution and the composition of crude biodiesel (CBD). The four factors were temperature (230-290 °C), time (0-90 min), ethanol to feedstock ratio (E/F) (4/3-16/3 mL/g), and catalyst type (ZnCl2, FeCl3, SnCl2, and H3PO4). The results showed that catalyst type and E/F ratio were the two most influential variables affecting the yield and composition of the CBD. Of those Lewis acids tested, SnCl2 showed the highest performance in terms of CBD yield and its esters content. Increasing the E/F ratio basically led to higher yield of CBD and higher esters content of the CBD. Higher temperature and longer reaction time resulted in an obvious increase in gas yield, but had no significant effect on the yield and quality of the CBD. The produced CBD had extremely low N and S content (0.2-0.6 wt.% and less than 0.1 wt.%, respectively), and was abundant in fatty acid esters (~70%), mainly ethyl oleate and ethyl palmitate, making it more suitable for the subsequent biofuel production.
Keywords: Tigernut, Lewis acid, transesterification/esterification, Orthogonal design, crude biodiesel