Application of Chromium and Cobalt Terephthalate Metal Organic Frameworks as Catalysts for the Production of Biodiesel from Calophyllum inophyllum Oil in High Yield Under Mild Conditions

Abstract

This paper describes the application of chromium(III) terephthalate (Cr-Tp) and cobalt(II) terephthalate (Co-Tp) metal organic frameworks, as heterogeneous acid catalysts to avoid the yield reduction caused by saponification during the process of biodiesel production using Calophyllum inophyllum oil. The catalysts were mainly characterized using spectroscopic (FTIR), microscopic (SEM, energy-dispersive X-ray spectroscopy) and X-ray diffractive techniques. The surface acidity and the thermal stability of the catalysts were determined using Hammett indicator and thermo-gravimetric methods, respectively. The catalysts were employed for the pre-esterification of free fatty acid content of the oil before subjecting the oil for the transesterification of its triglyceraldehyde content. The pre-esterification was performed through a couple of successive catalytic cycles under milder conditions [25°, 1 atm, and 2/1 MeOH/oil (w/w) ratio] than the conditions reported so far. The study revealed that the successful pre-esterification required these catalysts in very small amount (< 2.5% by oil weight) and occurred within very short time (2 h for the 1st cycle and 2–4 h for the 2nd cycle), reducing the acid value of C. inophyllum oil significantly (88%) from 56.91 to ~ 6.5 mg KOH g−1. The catalytic activity of these catalysts remained unchanged even after the 10th cycle of catalyst reuse. More importantly, the yield of biodiesel obtained from C. inophyllum oil in this way was significantly high (~ 93%) and free from saponification.