PGPR 2021 First Asian PGPR Indonesian Chapter International e-Conference 2021 Volume 2022 Research article Green Nano-Composite of CaO/K-Sulfated TiO 2 and Its Potential as a Single-Step Reaction Solid Catalyst for Biofuel Production I Nengah Simpen 1 *, I Nyoman Suprapta Winaya 2 *, I Dewa Gede Ary Subagia 2 , and I Wayan Budiarsa Suyasa 1 1 Department of Chemistry, Faculty of Mathematics and Natural Sciences, Udayana University, Indonesia 2 Department of Mechanical Engineering, Faculty of Engineering, Udayana University, Indonesia ORCID I Nengah Simpen http://orcid.org/0000-0003-1296-1215 Abstract. In the esterification-transesterification method, a catalyst increases the reaction rate to produce biofuel (biodiesel). This study investigated the use of a solid catalyst consisting of green nano-CaO as a support modified by KOH solution and sulfated TiO 2 for converting waste frying oil (WFO) into biodiesel in a single-step esterification-transesterification reaction. With nano-CaO prepared from eggshell, a green nanocomposite of CaO/K-sulfated TiO 2 was synthesized by physical mixing and the hydrothermal method. Crystallite size, surface basicity-acidity, functional groups, and surface morphology were used to characterize the solid catalyst, which was then tested for its ability to convert WFO into biodiesel. The results showed that green-CaO had nanoparticles (93.13 nm) and that its size decreased after being modified with KOH (46.43 nm) and sulfated TiO 2 (62.10 nm), with CaO/K-sulfated TiO 2 being the optimum surface acidity-basicity. The optimum conditions for conversion were found to be 5% catalyst concentration to oil, a molar ratio of methanol/oil of 9:1, and a reaction time of 60 minutes, which resulted in a biodiesel mass yield of 94.17% higher than CaO/K (67.88%). WFO was successfully converted into fatty acid methyl esters, according to the GC-MS analysis of the biodiesel. The synthesized solid catalyst has the potential to be used in single-step esterification-transesterification reactions to produce biodiesel. Keywords: Biofuel, CaO/K-sulfated TiO 2 Green Nano-composite, Eggshell, Single-step Reaction, Waste Frying Oil 1. Introduction Biodiesel is considered for substituting fossil-diesel due to biodegradable, renewable nature, and environmentally non-toxicity. The biodiesel is a liquid fuel which produced from long chain fatty acids of biological sources (animal fats, virgin vegetable oils, and waste oil). It is popular synthesized in transesterification and esterification methods with ethanol or methanol and catalyst [1-3]. When free fatty acids (FFAs) more than 1% in oil, biodiesel production is carried out in double-steps reaction, namely the How to cite this article: I Nengah Simpen*, I Nyoman Suprapta Winaya*, I Dewa Gede Ary Subagia, and I Wayan Budiarsa Suyasa , (2022), “Green Nano-Composite of CaO/K-Sulfated TiO 2 and Its Potential as a Single-Step Reaction Solid Catalyst for Biofuel Production” in First Asian PGPR Indonesian Chapter International e-Conference 2021, KnE Life Sciences, pages 382–392. DOI 10.18502/kls.v7i3.11146 Page 382 Corresponding Authors: I Nengah Simpen and I Nyoman Suprapta Winaya; emails: nengahsimpen@unud.ac.id and ins.winaya@unud.ac.id Published 07 June 2022 Publishing services provided by Knowledge E I Nengah Simpen et al. This article is distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use and redistribution provided that the original author and source are credited. Selection and Peer-review under the responsibility of the PGPR 2021 Conference Committee.