Cobalt-doped CaO catalyst synthesized and applied for algal biodiesel production Velentina Das a, c, * , Abhishek Mani Tripathi b , Manash Jyoti Borah a , Nurhan Turgut Dunford c , Dhanapati Deka a a Biomass Conversion Laboratory, Department of Energy, Tezpur University, 784028, Assam, India b Forest Research Institute, University of Quebec in Abitibi-Temiscamingue, Amos, J9T 2L8, Quebec, Canada c Department of Biosystems and Agricultural Engineering, Oklahoma State University, 74078, Oklahoma, USA article info Article history: Received 11 September 2018 Received in revised form 5 June 2020 Accepted 9 July 2020 Available online 4 August 2020 Keywords: Scenedesmus quadricauda CoeCaO catalyst Co-precipitation method Biodiesel Catalyst reusability abstract Microalgal biomass is a potential feedstock for biofuel production because of its oleaginous nature and fast growth rate. Furthermore, its cultivation does not compete with crop producing land and thereby eliminating food vs. fuel dilemma. This study describes a low-cost nutrient mediated cultivation method for growing lipid enriched algal biomass from Scenedesmus quadricauda in BG11 media in a raceway pond. A renewable heterogeneous catalyst is synthesized using calcium oxide obtained from calcination of waste egg shells and modified using cobalt nitrate hexahydrate by co-precipitation method. The synthesized catalyst is characterized by XRD, SEM, EDX, FTIR, TEM techniques. Lipid extracted from the biomass is converted to biodiesel using the synthesized catalyst. The formation of biodiesel is confirmed using 1 H NMR, 13C NMR and GC-MS techniques. The result demonstrated that the CaOeCo catalyst has very high catalytic activity for biodiesel production. The integrated process described in this study has potential for producing environmentally benign fuels and a heterogeneous catalyst from renewable sources. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction To meet the energy requirements of human beings, sustainable development is the key for protection of both environment and energy security of a nation. With the depletion of fossil fuels, alternative renewable fuels harnessed from biomass are being developed. In general, it can be said that biofuel burn cleaner fuel compared to fossil fuels because of their lower sulfur and nitrogen contents. These biofuel also helps in mitigating the atmospheric carbon dioxide emissions [1]. There is lot of feedstocks for biodesel from non-edible seed oil, waste cooking, but present work focuses on using microalgae from environment point of view [1]. Some microalgae strains drawing attention as a source of feedstock for biodiesel production because of its high cellular lipid content and higher photosynthesis rates than higher plants [2]. Microalgae can utilize 3e5% of the solar energy compared to the other crops which utilize 0.5% [3e5]. Several microalgae strains have lipid content over 60% by weight of dry biomass, while average biomass lipid content ranges between 20 and 50 wt%. Microalgae can grow 12 times faster and yield 30 times more triacylglycerides (TAG) per hectare as compared to other oil producing land crops. Besides, microalgae do not require arable land for its cultivation, so, it does not compete with food production. Algal biomass can be grown in wastewater using industrial CO 2 (flue gases). Hence microalgae cultivation can be cleaned and environmental benign approach for biomass production [5]. TAG obtained from algal biomass can be directly utilized for diesel engines, but due to its high viscosity and low volatility, direct TAG combustion causes engine problems such as stickiness and injector plugging [6,7]. Problems like these need TAG to be upgraded before utilizing it as biofuel. In general, TAG is converted to fatty acid alkyl esters (FAAE) via transesterification with an alcohol. FAAE are usually referred to as first generation biofuels [8e10]. The transesterification process takes place in the presence of an acid or a base in the form of ho- mogeneous or heterogeneous catalyst, or lipase enzyme [11e 14]. The catalytic transformation of lipids by transesterification using an * Corresponding author. Biomass Conversion Laboratory, Department of Energy, Tezpur University, 784028, Assam, India, Department of Energy, Tezpur University, Napam, Tezpur- 784028, Assam, India, Phone: +918402847602 E-mail addresses: velen.mani09@gmail.com, velentina.d@icloud.com (V. Das). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene https://doi.org/10.1016/j.renene.2020.07.040 0960-1481/© 2020 Elsevier Ltd. All rights reserved. Renewable Energy 161 (2020) 1110e1119