© 2018 Semarang State University  Corresponding author: Chemical Engineering Department, Faculty of Engineering, Universitas Negeri Semarang, Indonesia E-mail: ratnadewi.kusumaningtyasl@mail.unnes.ac.id ISSN 2303-0623 e-ISSN 2407-2370 Jurnal Bahan Alam Terbarukan http://journal .unnes.ac.id/nju/index.php/jbat Synthesis of ZnO/CaO Catalyst from Eggshell Waste for Biodiesel Production Dino Wicaksono, Ratna Dewi Kusumaningtyas  DOI 10.15294/jbat.v8i1.20185 Chemical Engineering Department, Faculty of Engineering, Universitas Negeri Semarang, Indonesia Article Info Abstract Article history: Received November 2018 Accepted April 2019 Published June 2019 The diminishing of fossil fuel reserve has raised a consideration on the renewable energy development. Biodiesel is among the promising renewable energy which is feasible for large- scale production. Biodiesel is generally synthesized through the alkaline-catalyst transesterification of vegetable oil. The common catalyst for biodiesel is homogeneous base catalysts which are active but show several drawbacks related to the environmental aspects. Therefore, development of heterogeneous alkaline catalyst for biodiesel production is critical. CaO catalyst is considered a favourable heterogeneous base catalyst for transesterification reaction and it can be derived from various natural resources. In this work, CaO catalyst from eggshell was synthesized from eggshell waste. To improve the catalyst activity, CaO was combined with ZnO active metal, resulting ZnO/CaO catalyst. In this research, the development, characterization, and application of ZnO/CaO catalyst for waste cooking oil (WCO) transesterification to produce biodiesel has been investigated. Various concentration of ZnO was combined with CaO to determine the best formulation of ZnO/CaO catalyst development. It was demonstrated that the addition of ZnO active metal on CaO catalyst could remarkably improve the biodiesel yield through WCO transesterification reaction. The addition of 6% ZnO active metal on CaO, forming ZnO/CaO 6% catalyst, has exhibited the optimal enhancement of biodiesel yield. Furthermore, it was found that the optimum amount of ZnO/CaO 6% catalyst added in the reaction system was 3% w/w catalyst/WCO. Keywords : Eggshell; ZnO; CaO; Transesterification; Waste cooking oil INTRODUCTION The issue on fossil fuel reserve depletion has significantly increased the attention on the renewable energy development. Among the prospective alternative energy that is feasible to be produced in mass-production scale is biodiesel. Biodiesel can be derived from various vegetable oils and animal fats (Kusumaningtyas et al., 2016). Waste cooking oil (WCO) is including the potential feedstock for biodiesel synthesis. WCO contains carcinogenic compounds, thus, from the health standpoint it is not suitable for human consumption. On the other hand, if WCO is thrown away as waste, it will cause the environmental problem. Therefore, utilization of WCO as biodiesel feedstock will provide an economical value-added (Garrigós, 1999). One important factor to achieve a high yield on biodiesel production is catalyst. The most common catalyst in biodiesel production is homogeneous alkaline catalyst, such as potassium hydroxide or sodium hydroxide (Ehsan & Chowdury, 2014). However, homogeneous catalyst demonstrates several drawbacks such as it has low selectivity, corrosive property to the equipment and difficulty in product separation. Besides, it is not reusable so that it causes catalyst waste. Hence, development of heterogeneous catalyst becomes essential (Fan et al., 2018). Among the heterogeneous alkaline catalyst for biodiesel synthesis, CaO has gained notable interest due to its advantages. CaO catalyst has a high basicity strength. It is also cheap, non- corrosive, and low environmental impact (Kaewdaeng et al., 2017). Kawashima et al. (2009)