Thushari, Indika, and Sandhya Babel. 2018. “Activity of Carbon-Based Solid Acid Catalyst Derived from Palm Empty Fruit Bunch for Esterification of Palmitic Acid”. Environment and Natural Resources Journal 17 (1). Nakhon Pathom, Thailand:Page 54-62; DOI: 10.32526/ennrj.17.1.2019.06. https://ph02.tci-thaijo.org/index.php/ennrj/article/view/162156.