An efficient and reusable Li/NiO heterogeneous catalyst for ethanolysis of waste cottonseed oil

Abstract

In order to use ethanol in place of methanol for biodiesel production a series of Li+ impregnated NiO (Li/NiO) was prepared in nano particle form in aqueous medium without adding any organic solvent or templates. The structure of the catalyst was established by powder XRD, surface morphology, and particle size by field emission scanning and high‐resolution transmission electron microscopy studies. Basic strengths of the catalysts were measured by Hammett indicators and found to be maximum in case of catalyst prepared with 5 wt% Li+ in NiO followed by calcination at 600°C (5‐Li/NiO‐600). Catalyst characterization supported the oxidation of Ni2+ into Ni3+ upon lithium impregnation, which impart the enhanced ethanolysis activity to the Li/NiO catalyst. Under optimized reaction condition of 5 wt% catalyst, ethanol‐to‐oil molar ratio of 12:1 and at 65°C reaction temperature, >98% fatty acid ethyl ester yield was obtained in 3 h. The catalyst was found to be effective for the ethanolysis of vegetable oils (VO) having up to 8.3 wt% free fatty acids. During reusability experiments, Li/NiO catalyst was able to catalyze seven reaction cycles without major loss in activity. The ethanolysis of VO was found to follow pseudo first order kinetics and activation energy for the same reaction was found to be 74.2 kJ/mol. Thus, the present work has demonstrated the development of a “greener” and completely renewable biofuel, fatty acid ethyl esters, using waste cottonseed oil as feedstock.Practical applications: Due to high free fatty acid and water contents, homogenous catalysts could not be employed for the transesterification of waste cooking oils. The present study demonstrates the preparation of Li/NiO and its application as reusable solid catalyst for the ethanolysis of waste cottonseed oil to produce fatty acid ethyl esters.The prepared catalyst 5‐Li/NiO‐600 was able to show the ethanolysis of waste cottonseed oil during seven successive catalytic runs. Thus, catalyst was found to be effective for the preparation of renewable diesel fuel substitute, fatty acid ethyl esters.