Quality improvement of syngas from gasification process of palm kernel using NiO/CaO catalysts on ceramic supporter in coupled with biochar absorbent from agricultural residues

Abstract

In this study, palm kernel shells were utilized in the gasification process to produce syngas. In addition, biochar prepared from pyrolysis of the left-over mangosteen and durian peels were used in the gasification process to enhance the tar removal efficiency. The expected outcomes of this study could result in not only the generation of renewable energy from but also the waste utilization of agricultural residues. The effect of catalysts and biochar on the syngas quality improvement were particularly studied. Palm kernel shell was used as raw material. The compositions and heating values of the biomass were characterized by the proximate, ultimate, and bomb analyses, respectively. Syngas was produced from a downdraft gasifier connected with catalytic and adsorption units in sequence. The gasification process was operated with 1 kg of palm shell per batch at a fixed air flow rate of 25 L/min. The NiO/CaO (10 %wt) catalysts on ceramic supporter with various NiO contents of 2%, 4%, and 8% were synthesized by co-impregnation. Biochars were synthesized by pyrolysis process of durian and mangosteen peels at around 300 - 500 °C for 2 hrs. Morphology and compositions of the synthesized catalysts and biochar were analyzed. The results of SEM analysis showed that the NiO and CaO were deposited and well dispersed on the porous ceramic ring supporters. The presence of active NiO on the catalyst was also confirmed in FTIR result with (wavelength of 692 cm−1). Biochar from durian and mangosteen peels, with BET surface area of 0.9219 - 0.9989 m2/g and adsorption pore size of 11.193 - 11.912 nm, were obtained from a pyrolysis process at 400 - 700 °C. The syngas samples were collected from the gasification unit every 15 min to 60 min. The gas chromatography was used to analyze the syngas compositions. The GC results indicated that increasing NiO contents in the catalysts tended to result in increasing CH4 composition of the syngas for both systems with and without biochar. With tar filtration unit containing biochar, the ability of tar removal was significantly increased by 2 to 9 times comparing to the system without biochar.