Use of Deep Eutectic Ionic Liquid for Biodiesel Preparation From Base-Catalyzed Transesterification of Rapeseed Oil

Use of Deep Eutectic Ionic Liquid for Biodiesel Preparation from Base-Catalyzed Transesterification of Rapeseed Oil

Wei Huang ^a, Shaokun Tang,*^a Hua Zhao ^b

^a Key Laboratory for Green Chemical Technology of Ministry of Education, School of Chemical Engineering & Technology, Tianjin University, Tianjin 300072, China

^b Chemistry Program, Savannah State University, Savannah, GA 31404, USA

*Corresponding author. Tel: +86-22-27408578; E-mail address: shktang@tju.edu.cn

As a renewable and biodegradable fuel, biodiesel has been attracting research attention for the last decade in the face of diminishing oil supplies. To overcome hurdles of the conventional reaction and purification processes for biodiesel preparation, a number of new approaches have been actively pursued including new solid catalysts, novel reaction process, and co-solvents in recent years. However, these new methods are associated with new problems such as lower product yield, higher energy consumption, higher costs and so on.

In our work, a deep eutectic ionic liquid (DEIL), choline chloride and glycerol (1:2, molar ratio), was prepared and used in the transesterification reaction of rapeseed oil to biodiesel catalyzed by NaOH. Response surface methodology (RSM) and Box-Behnken Design (BBD) were employed to examine different reaction parameters such as methanol/oil molar ratio, catalyst concentration and DEIL concentration, and optimize the reaction conditions for achieving the maximum yield of fatty acid methyl ester (FAME).

Our data have suggested that the FAME yield of up to 88% could be obtained at the optimum conditions; this yield was higher than that of the reaction under the same condition parameters without the addition of DEIL (74%). A statistical analysis of variance (ANOVA) indicates that a second-order polynomial model appears to represent the actual relationship between the response and the significant variables, with a very low probability value (0.0001) and a high satisfying determination coefficient (R²=0.9724).

The addition of DEIL to the transesterification reaction improved the FAME yield and enabled an easy and thorough separation of glycerol from the reaction mixture during and after reaction. This study exemplifies a cost-effective and environmental benign approach to biodiesel production by using the DEIL as a co-solvent for the transesterification reaction.

Keywords: deep eutectic ionic liquid, biodiesel, transesterification, base catalyst, response surface methodology