Abstract
In this study, valorisation of high acid value waste cooking oil into biodiesel has been investigated. Non-catalytic transesterification using supercritical methanol has been used for biodiesel production. Four controllable independent process variables have been considered for analysis including methanol to oil (M:O) molar ratio, temperature, pressure and time. Uncommon effects of process variables on the reaction responses, e.g. biodiesel and glycerol yields, have been observed and extensively discussed. Response surface methodology (RSM) via Central Composite Design (CCD) has been used to analyse the effect of the process variables and their interactions on the reaction responses. A quadratic model for each response has been developed representing the interrelationships between process variables and responses. Analysis of Variance (ANOVA) has been used to verify the significance effect of each process variable and their interactions on reaction responses. Optimal reaction conditions have been predicted using RSM for 98% and 2.05% of biodiesel and glycerol yields, respectively at 25:1 M:O molar ratio, 265 °C temperature, 110 bar pressure and 20 min reaction time. The predicted optimal conditions have been validated experimentally resulting in 98.82% biodiesel yield, representing 0.83% relative error. The quality of the produced biodiesel showed excellent agreement with the European biodiesel standard (EN14214).
Highlights
The increasing demand of energy from the domestic and industrial sectors combined with possible scarcity of petroleum based fuels in the near future have boosted the research for alternative sustainable fuels [1]
The main aim of this study is to investigate the feasibility of supercritical methanolysis for biodiesel synthesis from very low quality waste cooking oil (WCO)
Response surface methodology (RSM) was applied for the design of experiments (DOE) in order to optimise reaction parameters for higher biodiesel yield
Summary
The increasing demand of energy from the domestic and industrial sectors combined with possible scarcity of petroleum based fuels in the near future have boosted the research for alternative sustainable fuels [1]. Acid catalysed esterification of FFA to FAAE occur as a pre-treatment step This is followed by an alkaline catalysed transesterification of triglycerides to FAAEs. the long reaction time and low recovery of catalyst were considered as main disadvantages of two-steps proposed technique [12]. El-Gendy et al [20] have studied the optimisation of biodiesel production from waste cooking oil using CaO obtained from calcination of eggshells They have obtained 96% yield of biodiesel at 6:1, 3 wt%, 60 min and 200 rpm for M:O molar ratio, catalyst weight percentage reaction time and stirring rate, respectively. Milano et al [28] have studied conversion of mixture of WCO and Calophyllum inophyllum oil using microwave irradiation-assisted alkaline catalysed method They have reported 97.65% yield of biodiesel within 7.15 minutes at M:O volumetric ratio, catalyst concentration and stirring rate of 59.60% (v/v), 0.774 wt% and 600 rpm, respectively.
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