Economical and green biodiesel production process using river snail shells-derived heterogeneous catalyst and co-solvent method Wuttichai Roschat a , Theeranun Siritanon a , Teadkait Kaewpuang a , Boonyawan Yoosuk b , Vinich Promarak c,⇑ a School of Chemistry, Institute of Science, Suranaree University of Technology, Muang District, Nakhon Ratchasima 30000, Thailand b Renewable Energy Laboratory, National Metal and Materials Technology Center (MTEC), National Science and Technology Development Agency, 114 Thailand Science Park, Phahonyothin Road, Klong 1, Klong Luang, Pathumthani 12120, Thailand c Department of Material Science and Engineering, School of Molecular Science & Engineering, Vidyasirimedhi Institute of Science and Technology, Wangchan, Rayong 21210, Thailand highlights  River snail shells-derived CaO catalyst was synthesized for the first time.  98.5% FAME yield was achieved in 90 min under the use 10% v/v of THF in methanol.  The transesterification reaction mechanism is experimentally demonstrated.  The co-solvent method of THF/ methanol successfully decreases activation energy of reaction. graphical abstract Palm oil Methanol Biodiesel + Glycerol River snail shells 800 ° C, 3 h Calcination CaO catalysts 10% v/v THF in methanol, 65 ° C, 90 min article info Article history: Received 2 January 2016 Received in revised form 4 March 2016 Accepted 5 March 2016 Available online 11 March 2016 Keywords: River snail shells CaO catalyst Biodiesel Reaction mechanism and kinetics Co-solvent abstract River snail shells-derived CaO was used as a heterogeneous catalyst to synthesize biodiesel via transes- terification of palm oil with methanol. The shell materials were calcined in air at 600–1000 °C for 3 h. Physicochemical properties of the resulting catalysts were characterized by TGA–DTG, XRD, SEM, BET, XRF, FT-IR and TPD. CaO catalyzed transesterification mechanism of palm oil into biodiesel was verified. The effects of adding a co-solvent on kinetic of the reaction and %FAME yield were investigated. %FAME yield of 98.5% ± 1.5 was achieved under the optimal conditions of catalyst/oil ratio of 5 wt.%; methanol/oil molar ratio of 12:1; reaction temperature of 65 °C; 10% v/v of THF in methanol and reaction time of 90 min. The results ascertained that river snail shells is a novel raw material for preparation of CaO cat- alyst and the co-solvent method successfully decreases the reaction time and biodiesel production cost. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Biodiesel is known to be an alternative to diesel fuel derived from petroleum source. It can be used on its own or mixed with diesel in any diesel–engine vehicles. Advantages of biodiesel are biodegradability, non-toxicity, and lower CO 2 and sulfur emission (Wang et al., 2015). Biodiesel is composed of long chain fatty acid alkyl esters typically produced from a reaction between a triglyc- eride in fats or oils and short chain alcohols, mainly methanol (Leung et al., 2010). Generally, biodiesel production via transesterification reaction requires a catalyst to promote the reaction. Commonly, homoge- neous catalysts such as KOH and NaOH are widely used because they give high biodiesel yield under mild reaction condition and short reaction time (Lee et al., 2015). However, the use of these cat- alysts has drawbacks as large amount of water is required to wash http://dx.doi.org/10.1016/j.biortech.2016.03.038 0960-8524/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +66 33 014150; fax: +66 33 014445. E-mail address: vinich.p@vistec.ac.th (V. Promarak). Bioresource Technology 209 (2016) 343–350 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech