Synthesizing a transesterification catalyst via a condensation reaction and assessment of the mechanism using density functional theory

Abstract

BACKGROUNDA solid acid (SPEI–EN–OHCMs) having dendritic –NH2 groups was prepared via oxidation of hydrothermal carbon microspheres (OHCMs) followed by a condensation reaction with the –NH2 groups of polyethyleneimine and sulfonation. The mechanism by which –COOH groups on the surfaces of oxidized hydrothermal carbon microspheres reacted with these –NH2 groups was assessed using density functional theory (DFT).RESULTActivation using a combination of 1–(3–dimethylaminopropyl)–3–ethyl carbodiimide hydrochloride (EDC) and hydroxysuccinimide (NHS) was found to promote the formation of amide bonds such that –NH2 groups were bonded to the microsphere surfaces. This effect provided more bonding sites for –SO3H groups. The DFT results indicated that the energy barrier on the potential energy surface in the presence of EDC and NHS was lowered by 18.1 kcal/mol. X–ray photoelectron spectroscopy (XPS) analyses also confirmed the introduction of –NH2 groups followed by –SO3H groups onto the surfaces of the OHCMs. The concentration of surface acid sites on the SPEI–EN–OHCMs was found to be as high as 11.8 mmol·g−1. Thermogravimetric (TG) data and elemental analysis results showed that the –SO3H groups on the SPEI–EN–OHCM surfaces were thermally stable below 180 °C.CONCLUSIONThis SPEI–EN–OHCMs were used to promote the transesterification reaction of waste frying oil (WFO) with methanol. A trial with a methanol/oil molar ratio of 10:1 at 110 °C for 4 h gave a fatty acid methyl esters (FAMEs) yield of 92.3%. After four reuses, an SPEI–EN–OHCMs specimen provided a FAMEs yield of 54.3%.This article is protected by copyright. All rights reserved.