In situ catalytic pyrolysis of Jatropha wastes using ZSM-5 from hydrothermal alkaline fusion of fly ash

Abstract

In this work, ZSM-5 catalysts was successfully synthesized from fly ash via alkali fusion followed by hydrothermal treatment with the initial SiO2/Al2O3 ratios of 24 and 40 (HZSM5-FA). HZSM-5 synthesized with SiO2/Al2O3 ratios of 40 exhibited superior physical and textural properties such as higher crystallinity, larger surface area, and smaller particle size. After synthesis, the catalytic activity of HZSM5-FA with SiO2/Al2O3 ratios of 40 was investigated via fast pyrolysis of Jatropha wastes in order to upgrade the evolved vapor using Py-GC/MS technique. In addition, the ZSM-5 prepared from chemical reagents (HZSM5-CV) were evaluated for comparison. The pyrolysis temperature was set at 500 °C with the Jatropha wastes to catalyst ratio of 1:1–1:10. The major components from non-catalytic fast pyrolysis were acids (51%) and nitrogen containing compounds (20%). Other organic compounds were ketones, alcohols, esters, ethers, phenols and sugars. The presence of HZSM5-FA contributed to the elimination of undesirable oxygenated compounds such as fatty acids which could mitigate problem regarding acidity and instability in bio-oil. In addition, this synthesized material also remarkably improved the hydrocarbon selectivity, especially aromatic hydrocarbons. Higher catalyst contents had positive effect on the formation of aromatic hydrocarbons and tended to promote deoxygenation and denitrogenation. At high catalyst proportion (biomass to catalyst ratio of 1:10), HZSM5-FA produced the highest hydrocarbon selectivity of 97%, mainly benzene, toluene and xylene (BTX), which are valuable products due to their high heating values. Interestingly, the catalytic activity of HZSM5-FA was comparable to that of the HZSM5-CV in terms of reducing oxygenates as well as nitrogenous compounds and consequently increasing hydrocarbon compounds. Overall, HZSM-5 derived from fly ash can be economically used as a potential catalyst for pyrolysis oil upgrading applications.