Quality improvement of syngas from gasification process of palm kernels using NiO/CaO catalysts on ceramic supporters coupled with biochar absorber from agricultural residues

In this study, palm kernel shells were utilised 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 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 utilisation of agricultural residues. The effect of catalysts and biochars on the syngas quality improvement were particularly studied. Palm kernel shells (PKS) were used as raw materials. The composition and heating values of the biomass were characterised by proximate, ultimate, and bomb analysis. Syngas was produced from a downdraft gasifier connected with catalytic and adsorption units in sequence. The gasification process was operated with 1 kg of PKS per batch at a fixed air flow rate of 25 L/min. The NiO/CaO (10 %wt) catalysts on ceramic supporters with various NiO contents of 2%, 4%, and 8% were synthesised by co-impregnation. Biochars were synthesised by pyrolysis process of durian and mangosteen peels at around 300 - 500°C for 2 hrs. Morphology and compositions of the synthesised catalysts and biochars were analysed. 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 (Fourier transform infrared) results (wavelength of 615 cm⁻¹). Biochars from durian and mangosteen peels, with BET (Brunauer-Emmett-Teller) 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 to 60 minutes. The gas chromatography was used to analyse 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.