Influence of mineral matter on pyrolysis of palm oil wastes

The influence of mineral matter on pyrolysis of biomass (including pure biomass components, synthesized biomass, and natural biomass) was investigated using a thermogravimetric analyzer (TGA). First, the mineral matter, KCl, K2CO3, Na2CO3, CaMg(CO3)2, Fe2O3, and Al2O3, was mixed respectively with the three main biomass components (hemicellulose, cellulose, and lignin) at a weight ratio (C/W) of 0.1 and its pyrolysis characteristics were investigated. Most of these mineral additives, except for K2CO3, demonstrated negligible influence. Adding K2CO3 inhibited the pyrolysis of hemicellulose by lowering its mass loss rate by 0.3 wt%/°C, while it enhanced the pyrolysis of cellulose by shifting the pyrolysis to a lower temperature. With increased K2CO3 added, the weight loss of cellulose in the lower temperature zone (200–315 °C) increased greatly and the activation energies of hemicellulose and cellulose pyrolysis decreased notably from 204 to 42 kJ/mol. Second, studies on the synthetic biomass of hemicellulose, cellulose, lignin, and K2CO3 (as a representative of minerals) indicated that peaks of cellulose and hemicellulose pyrolysis became overlapped with addition of K2CO3 (at C/W = 0.05–0.1), due to the catalytic effect of K2CO3 lowering cellulose pyrolysis to a lower temperature. Finally, a local representative biomass—palm oil waste (in the forms of original material and material pretreated through water washing or K2CO3 addition)—was studied. Water washing shifted pyrolysis of palm oil waste to a higher temperature by 20 °C, while K2CO3 addition lowered the peak temperature of pyrolysis by ∼50°C. It was therefore concluded that the obvious catalytic effect of adding K2CO3 might be attributed to certain fundamental changes in terms of chemical structure of hemicellulose or decomposition steps of cellulose in the course of pyrolysis.