Sulphonic-acid functionalized novel Limonia acidissima carbonaceous catalyst for biodiesel synthesis from Millettia pinnata oil: Optimization, kinetics, thermodynamics and cost analysis

Abstract

In order to overcome the current fuel crisis affecting transportation, expanding environmental pollution challenges, and depletion of natural oil resources, a sustainable alternative to petroleum fuels must be developed. Biodiesel has been accepted as a promising substitute for petro-fuels in many countries because it can fulfill the requirements of the transportation industry. The present research introduces biodiesel production from Millettia pinnata (Karanja) oil utilizing waste wood apple (Limonia acidissima) shell in deriving carbonaceous catalysts in view of waste valorization for green energy generation towards alleviation of its ever-growing demand. The feedstock had a high free fatty acid (FFA) concentration based on proximate analysis, which indicated that an acid catalyst was required for fuel production. Analysis of the prepared catalyst was done by SEM, EDAX, FTIR, XRD, and BET. The optimization of esterification was performed with the RSM central composite design (CCD) experimental matrix, while the reaction time was 1.5 h at 55°C with 4 wt. % catalyst under 650 rpm and 50% w/w alcohol concentration. The actual yield was reported to be 98.95% under ideal conditions. The fuel characterization revealed that KOME (Karanja oil methyl ester) possesses physico-chemical characteristics suitable for biodiesel as per ASTM standards. Kinetic studies showed that the esterification follows pseudo-first-order kinetics with an activation energy of 62.61 kJ mol −1. The thermodynamic study confirmed that the acid-catalyzed esterification reaction is endothermic and non-spontaneous. The production cost of catalyst per kg of biodiesel was estimated to be $0.1649.