A J C SIAN OURNAL OF HEMISTRY A J C SIAN OURNAL OF HEMISTRY https://doi.org/10.14233/ajchem.2023.24009 INTRODUCTION Dependence on imported crude oil, along with concerns about global climate change produced by greenhouse gas emissions from fossil fuels, is having an increasingly negative influence on several countries’ national security, economic and environmental policies. As the world’s population increases, the demand for transportation increases, resulting in a rise in fossil fuel consumption [1-3]. Due to the limited supply and negative environmental impact of conventional fossil fuels, the critical need for better and longer-lasting alternative fuels derived from renewable sources has increased. The majority of renewable fuels offer a variety of environmental benefits over conventional fuels, including reduced greenhouse gas emis- sions and pollution [4]. Biofuel has recently gained substantial interest in many countries globally due to its renewable nature, low carbon impact and biodegradability [4,5]. Among biomass sources, vegetable oils and animal fats have garnered consider- able attention as a potential source for producing a petroleum based diesel fuel substitute [6]. Vegetable oils have played a significant role in developing alternative fuels, despite the num- erous issues connected with utilizing them directly in diesel engines, especially direct injection engines. These issues linked REVIEW Production of Biodiesel in the Presence of Co-Solvents in Transesterification: A Review K.A. VIRAJ MIYURANGA , UDARA S.P.R. ARACHCHIGE *, , B.M.C.M. BALASURIYA , R.A. JAYASINGHE and N.A. WEERASEKARA Department of Civil and Environmental Technology, Faculty of Technology, University of Sri Jayewardenepura, Homagama, Sri Lanka *Corresponding author: Tel: +94 76 8675825; E-mail: udara@sjp.ac.lk Received: 6 August 2022; Accepted: 19 November 2022; Published online: 30 January 2023; AJC-21106 Consumption of fossil fuels has resulted in several economic and environmental consequences, prompting a quest for renewable energy sources rather than a reliance on fossil fuels. Biodiesel is a renewable source of energy that can be substituted for fossil fuel-based diesel fuel. Transesterification is the most economically viable way of producing biodiesel. However, the biodiesel manufacturing method based on transesterification has a disadvantage due to the immiscibility of the two key reactants, alcohol and oil, which results in a mass transfer resistance and reduces biodiesel yield. Several researchers have investigated using another solvent called a co-solvent to overcome the mass transfer barrier in the reaction medium. The purpose of this review was to examine the influence of several co-solvents on biodiesel synthesis that had been previously investigated the research. Keywords: Biodiesel, Co-solvent, Fossil fuels, Renewable energy, Transesterification. This is an open access journal, and articles are distributed under the terms of the Attribution 4.0 International (CC BY 4.0) License. This license lets others distribute, remix, tweak, and build upon your work, even commercially, as long as they credit the author for the original creation. You must give appropriate credit, provide a link to the license, and indicate if changes were made. with the large triglyceride molecule and its larger molecular mass can be resolved by chemically modifying vegetable oils to produce biodiesel, comparable to diesel [6]. As a result of this growing attention, the quest for alternative renewable fuels such as biodiesel has intensified. According to estimations, biodiesel/bioethanol may replace 10% of diesel fuel consump- tion in Europe and 5% of total fuel demand in Southeast Asia [2]. Biodiesel is a type of fuel that is clean and ecologically friendly. It may be manufactured from vegetable oils or animal fats [3]. Microemulsion, pyrolysis (thermal cracking) and trans- esterification are among the alterations that have been employed. Transesterification is feasible in manufacturing a more environ- mental friendly and cleaner fuel from vegetable oil due to the flexibility, simplicity and high yield of readily available raw materials [6,7]. Transesterification is a reversible reaction that occurs when the reactants triglycerides and methanol are mixed with the help of catalyst (Fig. 1). The forward transesterification reaction is in the first order, whereas the reverse transesteri- fication reaction is in the second-order [8]. The reaction of triglycerides with methanol proceeds stepwise to generate the intermediates diglyceride and monoglyceride, with succee- ding reactions yielding glycerol and biodiesel [9]. Asian Journal of Chemistry; Vol. 35, No. 2 (2023), 254-276