A novel extractive reactor technology for biodiesel production from waste cooking oil

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Embargoed until 2014-01-31
Copyright: Mahmud, Mohd Sabri
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Abstract
Biodiesel is touted as potential alternative energy to reduce the over-dependency upon the depleting and hazardous hydrocarbon fuel. The pursuit of a feasible biodiesel technology however still remains due to the feedstock limitations of the conventional inorganic-catalysed methods. The design of a process that is adaptable to the nature of low-grade and non-edible oils or fats such as those using lipase-catalysed process is thus favourable. Therefore, the main thrust of this thesis is to employ a novel extractive basket impeller column (BIC) reactor for the production of biodiesel. Studies on the inherent reaction kinetics of the production of ethyl oleate (key fatty acid ethyl ester (FAEE) from the biodiesel process using bioethanol) by ethanolic esterification and transesterification reactions of oleic acid and waste cooking oil (WCO) respectively, were conducted under monophasic and biphasic (two-immiscible liquid) conditions using Novozym 435 lipase as biological catalyst. Feed reactant-mole ratios and initial water contents were varied. In microaqueous environments, the Ping-Pong-Bi-Bi kinetic model of the esterification reaction revealed an optimum at a stoichiometric mixture of ethanol-oleic acid and was similarly demonstrated in the reaction rate analysis of waste cooking oil transesterification. In biphasic media, the maximum rate was further increased and a sinusoidal trend that was probably attributed to the dynamic ethanol distribution and the conformational change of lipase active site due to water interaction. Interestingly, in the biphasic esterification reaction with simultaneously-varied feed ratios, the optimum was skewed at a 4-fold molar excess of oleic acid. As the reaction rates were enhanced from the use of water probably associated with the positive allosterism of the lipase, the potential of a solvent extraction system using water was consequently investigated using the BIC. Preliminary tests using a single stage operation revealed that besides having an optimum stirring speed, the reaction yield also improved when the viscosity of the substrate was reduced at the same stirring speed, even though viscosity reduction involved the use of ethanol, a competitive inhibitor. This phenomenon is probably due to flow restrictions imposed by the basket mesh on relatively high viscous oily co-reactant. At a stirring speed of 600 rpm and above, a vortex probably formed creating a saturated low-viscous-liquid zone attributed to the swirling ethanol phase as evidenced by a dilatant characteristic of shearing stress during agitation and the subsequent GC analysis. These rheological issues and the probability of vortex formation are influential factors in the extractive reaction using the basket impeller. Reaction rate studies were conducted at different solvent-feed ratios and stirring speeds in a 9-stage BIC column. The Damköhler number obtained was below unity suggesting that the reaction occurred at an excellent extraction condition. Significantly, the efficiency of the column was more than 200% compared to a single stage operation. This study also showed the negative effect of high WCO flow relative to the ethanol aqueous flow and the deterioration effect of stirring at speeds higher than 500 rpm due to the aforementioned vortex appearance. Using the reaction rate data collected at the optimum BIC condition, a fixed capital cost analysis was performed and consequently revealed feasibility of this extractive reaction concept can achieve a 50% reduction in the production cost of 8000 tonnes per annum production.
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Author(s)
Mahmud, Mohd Sabri
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Adesina, Adesoji
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Publication Year
2011
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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