Biodiesel from transesterification at low temperature by AlCl3 catalysis in ethanol and carbon dioxide as cosolvent: Process, mechanism and application

Qingqing Guan, Hua Shang, Jing Liu, Junjie Gu, Bin Li, Rongrong Miao, Qiuling Chen and Ping Ning

Applied Energy, 2016, vol. 164, issue C, 380-386

Abstract: Finding a more efficient method for the transesterification of triglycerides to biodiesel fuel (BD) is important in today’s world. In this study, transesterification of trilaurin was carried out in a solution containing 4wt% of the Lewis acid AlCl3 dissolved in a cosolvent of ethanol and 5MPa CO2. A conversion rate of over 90% was achieved within 1h at the low temperature of 180°C. The process indicates a co-catalytic effect of the Lewis acid and CO2. We postulate several key steps for the mechanism. First, the CO2–ethanol mixture enhances the hydrogen bonding, increasing the concentration of C2H5O. Second AlCl3 attacks the oxygen of COC to weaken the bonds to form carbonyl carbon OR1, which is then easily attacked by C2H5O to give the transesterified product (C2H4COOR1). Third, AlCl3 is finally replaced by H to form glycerin (GL) and intermediates, such as unmethyl esterified compounds (uME). AlCl3 was used as a flocculant and catalyst for converting waste cooking oil (WCO) to BD. The process achieved 97% free fatty acid (FFA) conversion at 120°C in 90min, making it one of the most efficient systems available for WCO recovery. AlCl3 was also successfully applied to microalgae, signaling the potential for a process that combines harvesting, lipid extraction, and transterification, leading to fully integrated, microalgae-based BD production.

Keywords: Transesterification; Lewis acid; Triglycerides; CO2; Ethanol (search for similar items in EconPapers)
Date: 2016
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (3)

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DOI: 10.1016/j.apenergy.2015.11.029

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