Effect of protic ionic liquid treatment on the pyrolysis products of lignin extracted from oil palm biomass

The lignin extracted from biomass acts as a renewable energy source with a vast range of value-added applications. Aprotic ionic liquid pyridinium formate [PyFor] has been successfully used for lignin extraction from various morphological parts of oil palm biomass (OPB) plant such as empty fruit bunches (EFB), palm mesocarp fibre (PMF) and palm kernel shell (PKS). In this study, the pyrolysis of [PyFor] extracted lignin samples is studied in the kinetic regime using thermogravimetric analyzer in a non-isothermal manner. Three kinetic models such as; Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Starink were employed to determine activation energies (Ea) of [PyFor] extracted lignin samples. The average Ea for EFB lignin using FWO, KAS and Starink methods were 28.44, 23.74 and 23.94 kJ/mol respectively while for PMF and PKS lignins were 62.97, 55.28, 56.83 kJ/mol and 129.20, 122.93, 119.28 kJ/mol respectively. Starink method was further used to determine the pre-exponential factor and thermodynamic parameters for kraft lignin (KL) and [PyFor] extracted lignins. The thermo-kinetics and thermodynamic parameters indicate that [PyFor] treatment increased the thermal stability of extracted lignins. Calorific and CHNS values of both OPB and [PyFor] extracted lignins showed that [PyFor] treatment affected the lignin and carbon content of EFB, PMF and PKS lignins. The calorific values of the PKS lignin (28.20 kJ/g) were found to be higher than those of EFB (27.05 kJ/g) and PMF (27.40 kJ/g) lignins. Elemental analysis showed that the higher calorific values of PKS lignin are due to higher carbon content. Py-GC/MS analysis indicated that [PyFor] extracted lignins provided more phenolic and aromatic contents with the least acid concentrations making them suitable biofuels. It was concluded that [PyFor] treatment provided a potential way to improve the thermal conversion efficiency of extracted lignins.