The Effect of Co-solvent on Esterification of Oleic Acid Using Amberlyst 15 as Solid Acid Catalyst in Biodiesel ProductionIwan Ridwan, Mukhtar Ghazali, Adi Kusmayadi, Resza Diwansyah Putra, Nina Marlina and Eko AndrijantoMATEC Web Conf., 156 (2018) 03002DOI: https://doi.org/10.1051/matecconf/201815603002