Production of alternative liquid fuels from catalytic hydrocracking of plastics over Ni/SBA-15 catalyst

Abstract

The extremely increasing amount of plastic waste due to the development of human society, economics and urbanization is an emergency task that must be urgently handled in order to reduce environmental problems. Although the plastic wastes can be converted to alternative liquid fuels through pyrolysis process, the compositions in the pyrolysis oil depended on the chemical structure of raw materials and pyrolysis condition affect its quality. Thus, this research aimed to comparatively investigate the production of alternative liquid fuels obtained from mixed plastics containing polystyrene (PS)/polyethylene terephthalate (PET)/polyethylene (PE)/polypropylene (PP) at 20/5/35/40 (w/w) via non-catalytic cracking (under N2 atmosphere), non-catalytic hydrocracking (under H2 atmosphere), and catalytic hydrocracking over 10 wt% Ni/SBA-15 catalyst conducted at an atmospheric pressure and 650 °C for 1 h. The product yields and chemical compositions (paraffins, olefins, aromatics and PAHs) in the liquid products generated from these processes were investigated and also compared to ones obtained from the non-catalytic processes of each plastic. Herein, the characteristics of 10 wt% Ni/SBA-15 catalyst was analyzed by N2-adsorption/desorption, X-ray diffraction (XRD), and H2-temperature programmed reduction (H2-TPR). The results indicated that the non-catalytic processes of PS provided the highest content of oil and wax product (ca. 92 wt%). Whereas, the non-catalytic hydrocracking of the mixed plastics gave the lowest one (ca. 69 wt%). However, the catalytic hydrocracking over 10 wt% Ni/SBA-15 catalyst (2.5 – 10.0 wt% based on the mixed plastics) could suppress the cracking and yielded the higher amount of oil and wax to ca. 76–80 wt%. To consider the chemical compositions in the liquid phase, the PAHs formation was relied on the aromatic structure in the feedstocks. The liquid product derived from the non-catalytic processes of PS contained the highest amount of PAHs compounds (2622–2926 ppm) followed by the mixed plastics. When the 10 wt% Ni/SBA-15 catalyst was applied to the catalytic hydrocracking of the mixed plastics, the amount of PAHs in the liquid product decreased from 1621 ppm to ca. 1000 ppm (30 – 40% PAHs reduction) without the reduction of heating value when compared to one obtained from the non-catalytic processes.