Thermogravimetric and kinetic studies on pyrolysis of empty fruit bunch over metal-impregnated rice husk ash catalysts

Abstract

Empty fruit bunch (EFB) is a biomass residue from palm oil plantations, abundant in tropical countries like Malaysia. EFB is a valuable resource when utilized for energy recovery. Rice husk ash (RHA), retrieved after pyrolyzing and calcining rice husks, has high silica content and is a low-cost alternative to conventional silica precursors. This study utilizes RHA as a silica precursor for catalyst synthesis, labelled CRHA. CRHA is metal-modified using nickel and iron, forming NiCRHA, FeCRHA and NiFeCRHA catalysts. The synthesized catalysts were applied to the pyrolysis of EFB and compared with HZSM-5 via thermogravimetric analyser (TGA). From TGA, CRHA produced similar amount of volatilized matter (75.1 wt%) to HZSM-5 catalyst (73.3 wt%) while using NiCRHA resulted in the highest amount of volatilized matter (83.9 wt%) among the catalytic runs. Kinetic analysis from the application of Coats-Redfern method showed that the non-catalytic run followed a one-dimensional diffusion while the catalytic runs followed the anti-Jander diffusion. The activation energy, Ea, was overall reduced from 74.15 kJ·mol-1 with the presence of the catalysts in the order of: 69.64 kJ·mol-1 (EFB-NiCRHA) > 64.28 kJ·mol-1 (EFB-CRHA) > 63.57 kJ·mol-1 (EFB-NiFeCRHA) > 58.77 kJ·mol-1 (EFB-FeCRHA) > 53.81 kJ·mol-1 (EFB-HZSM-5). Despite NiCRHA having the highest Ea among the catalytic runs, it also had the highest pre-exponential factor (1.48 × 104 min-1) allowing the reaction to overcome the energy barrier and volatilized the most matter. This study showed that low-cost alternative sources can be used for catalysts synthesis and applied to thermochemical processes like pyrolysis.