CaO-Catalyzed Biodiesel Preparation With a Novel Deep Eutectic Ionic Liquid

CaO-Catalyzed Biodiesel Preparation with a Novel Deep Eutectic Ionic Liquid

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

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

^bChemistry Program, Savannah State University, Savannah, GA 31404, USA

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

As a promising replacement of fossil diesel, biodiesel has gained proliferating attention in recent years because of its renewable and environmentally benign characters. Biodiesel is commonly produced by homogeneous catalysts such as sodium or potassium hydroxide in industry which is usually accompanied with side reactions and laborious purification steps. Solid base catalysts such as CaO have been used in the transesterification reaction, leading to several advantages such as low byproducts, easy separation, no corrosion and low waste. However, CaO can be easily poisoned by carbon dioxide and water to form a layer of calcium carbonate and calcium hydroxide on the surface of bulk CaO within a few minutes exposure to air. In many cases commercial CaO needs to be calcined at high temperatures to remove the inactive layer before use.

In our work, we identified a straightforward and energy-efficient method to activate commercial CaO for biodiesel production without any pretreatment. A deep eutectic ionic liquid (DEIL) consisting of choline chloride and glycerol (1:2 molar ratio) was prepared and used to activate commercial CaO to be a catalyst during the transesterification of rapeseed oil to produce biodiesel. The yield of fatty acid methyl ester (FAME) with the addition of DES reached 91.90%, while the FAME yield with no DEIL was only 4.03%. The commercial CaO samples before and after reaction were characterized by Powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Scanning Electronic Microscopy (SEM). These characterizations and analyses indicate that the surface of commercial CaO is typically covered by a layer of CaCO₃ and Ca(OH)₂ which inhibits the activity of CaO, while the addition of DEIL can eliminate the inactive layer to activate CaO bulk due to its strong solvation ability. Moreover, the use of DEIL as co-solvent can also simplify the production separation and purification steps.

Acknowledgment

This project was financially supported by the National Natural Science Foundation of China (21176186).