Oil palm residue as precursors for low transition temperature mixture extracted lignin

Abstract

Lignin is a complex biopolymer in lignocellulosic biomass. It is a promising feedstock for producing various products, including chemicals and biofuels. Lignin extraction can be achieved via different routes such as organosolv, acid, alkaline, ionic liquids (ILs), and low transition temperature mixtures (LTTMs). LTTM is attractive for its biocompatibility, biodegradability, more straightforward synthesis procedure, lower precursor price, and toxicity than the aforementioned options. In this work, we report the use of an LTTM made from a combination of sucrose-malic acid-water (SMAW) to harvest lignin from four oil palm residues (i.e. empty fruit bunch (EFB), trunk (OPT), mesocarp fibre (MSF), and kernel shell (PKS)). There is still a knowledge gap on the applicability of SMAW to extract lignin from different oil palm residues. Limited studies have examined the properties of the SMAW-extracted lignin, particularly the lignin purity and thermal behaviour. Our results indicated SMAW as a sustainable LTTM solvent for lignin extraction for these four oil palm residues. EFB harvested the highest SMAW LTTM-extracted lignin yield of 27.23% with a lignin purity of 74.93%. TGA curves and DTG curves implied that the extracted lignin was thermally more reactive than alkaline lignin and served as an attractive precursor for thermochemical conversion processes.