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Authors: XIAO MAN
Keywords: biodiesel, biocatalysis, whole-cell, microalgae, packed-bed reactor,response surface methodology
Issue Date: 10-Jan-2011
Abstract: Biodiesel (i.e. Fatty acid methyl ester, FAME) has gained widespread importance in recent years as an alternative, renewable liquid transportation fuel. The use of fungal cells with an intrinsically high lipase activity, in conjunction with porous biomass support particles (BSPs), represents an attractive and cost-effective technology to produce biodiesel. A strain of Aspergillus niger isolated from atmospherically-exposed bread and Jatropha curcas seed was utilized as a whole-cell biocatalyst for palm oil methanolysis to produce biodiesel. The A.niger strain had a lipase activity of 212.58 mU/ml after 144-h incubation at 25 °C with an initial pH value of 6.5, using 7 % polypeptone (w/w on basal medium) as the nitrogen source and 3% olive oil (w/w on basal medium) as a carbon source. The A niger cells spontaneously immobilized within polyurethane biomass support particles (BSPs) during submerged fermentation. An 8% water content and a temperature of 40 °C in the presence of 30 immobilized-BSPs, resulted in an 87% FAME yield after 72 h. Enzymatic transesterification of waste cooking oil, comprising fats, oil and grease (FOG), to produce biodiesel, was investigated using A. niger immobilized BSPs. Response surface methodology (RSM), with a five-level-three-factor central composite rotatable design (CCRD), was used to optimize the reaction variables. Under optimized conditions, the predicted value of maximum FAME yield (i.e. 91.3%) was in close agreement with the experimental value (i.e. 91.8%). Biodiesel production via transesterification of microalgae lipid-oil from Nannochloropsis sp. in the presence of n-hexane or tert-butanol was also investigated. In an n-hexane system, RSM with a five-level-three-factor CCRD, was used to optimize the reaction variables. A second-order polynomial model was derived for FAME yield using a multiple regression analysis. To examine the effect of different microalgae oil-lipid feedstock on whole cell biocatalyzed transesterification reaction, lipids extracted from both Nannochloropsis sp. and Chlorella were converted to FAME. Nannochloropsis sp. proved to be a more suitable feedstock for biodiesel production than Chlorella, with a FAME yield of 68.2% compared to 50.3%. In tert-butanol system, the reaction variables were optimized using RSM with a five-level-four-factor CCRD. The addition of this benign polar solvent, tert-butanol, avoided methanol inhibition on lipase activity and enhanced the reaction rate. The results of RSM analysis showed that the interaction between solvent and methanol amount on FAME yield was stronger than other variables. A FAME yield of 47.5 ± 0.1 % under optimized conditions was achieved after a 24-h reaction time which agreed well with the predicted value of 49.9 %. Enzymatic transesterification of palm oil to biodiesel with A. niger immobilized BSPs was scaled up in a packed-bed reactor (PBR). FAME yield was enhanced with an increase of PBR flow rate in the range of 0.15 to 30h/l, where inefficient mixing of the reaction mixture at lower flow rates resulted in low conversion rates i.e. 69% after 72-h reaction. Glutaraldehyde (GA) solution (0.5 vol.%) was used to stabilize lipase activity, which led to a high FAME yield (> 90%) in the PBR after 72-h of reaction time at a flow rate of 15 l/h, and a water content of 15%. Moreover, a high conversion rate (> 85%) was maintained after four palm oil batch conversion cycles in the PBR. The research shows that transesterification in a PBR system using BSP-immobilized A niger whole-cell biocatalyst has the potential for larger-scale enzymatic biodiesel production.
Appears in Collections:Ph.D Theses (Open)

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