Development of two-step noncatalytic esterification of waste cooking oil for biodiesel preparation
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Development of two‑step noncatalytic esterification of waste cooking oil for biodiesel preparation Zahraa A. Alkhafaje1 · Alaa K. Mohammed1 · Israa M. Rashid1 Received: 15 August 2020 / Accepted: 16 September 2020 © Akadémiai Kiadó, Budapest, Hungary 2020
Abstract An innovative two-step noncatalytic esterification technique was proposed to synthesize alkyl esters from free fatty acids simulated in waste cooking oil, as a pretreatment process for biodiesel production, without adding any catalyst under normal conditions of pressure and temperature. The effect of methanol:oil molar ratio, reaction time, mixing rate, and reaction temperature were investigated. The results confirmed that the conversion of the reaction was increased when increasing the methanol molar ratio and decreased in prolonged reaction temperature. High conversion (94.545%) was successfully achieved at optimized conditions of 115:1, 65:1 methanol:oil molar ratio in the first step and second step, respectively, other conditions in both steps were found to be 9 s reaction time, 450 rpm mixing rate, and 62 °C reaction temperature by response surface methodology central composite design. Noncatalytic esterification, which eliminates the complications corresponding with catalyst utilization such as additional cost, time-wasting, and separation requirements, could be considered as a promising pretreatment technique to reduce the high acidity of waste cooking oil to the acceptable limit of 1 mg KOH/g oil or less in two steps, for biodiesel synthesize. Keywords Biodiesel production · Esterification reaction · Waste cooking oil · Pretreatment process · Central composite design
Introduction Nowadays, various researchers have increased the attention to produce biodiesel as an alternative to fossil fuel and sustainable energy source for diesel engines [1, 2]. The main driving forces for biodiesel widespread are biodegradability, renewability, non-toxicity, and limited greenhouse gas emissions (mainly C O2 emissions) [3–5]. * Zahraa A. Alkhafaje [email protected] 1
Biochemical Engineering Department, Al‑Khwarizmi College of Engineering, University of Baghdad, Baghdad, Iraq
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Reaction Kinetics, Mechanisms and Catalysis
The synthesis of biodiesel is generally carried out through transesterification of triglycerides obtained from vegetable oils or animal fats with ethanol or methanol in the existence of a catalyst [6, 7]. Biodiesel feedstocks comprised of refined vegetable oils are of high cost, and represent around 70% of total production cost [8]. Therefore, low-quality or waste oils were used to reduce the price of biodiesel [9]. Waste cooking oil (WCO) can be used as a biodiesel source and partially improve global problems [10]. Besides, the utilization of WCO diminishes the problems of environmental contamination. However, these oils contain impurities such as free fatty acid (FFA) and water. Feedstocks that contain high levels of FFA should be pretreated before the transesterification reaction of triglyceride
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