Renewable aromatic hydrocarbons production from catalytic pyrolysis of lignin with Al-SBA-15 and HZSM-5: Synergistic effect and coke behaviour

Abstract

With a focus on converting waste to energy, this study integrated the macromolecular reaction ability of Al-SBA-15 and the shape selectivity of HZSM-5 for the production of renewable aromatic hydrocarbons. Results demonstrated that the catalytic pyrolysis of lignin with both Al-SBA-15 and HZSM-5 was able to improve the mono-aromatic hydrocarbons (MAHs) production while inhibiting the formation of undesirable poly-aromatic hydrocarbons (PAHs), thus controlling the MAHs and PAHs content in the bio-oil. At optimal operation conditions (pyrolysis temperature: 550 °C, Al-SBA-15/HZSM-5 ratio: 1:3), the MAHs content was 42.57% higher than that catalyzed by HZSM-5 only (28.30%). The PAHs content was only 27.13%. Typical MAHs (benzene, toluene and xylene, denoted as BTX) and PAHs selectivities were determined as 55.91% and 38.92%, respectively. Thermogravimetry-differential thermogravimetric (TG-DTG) analysis indicated that the used HZSM-5 was principally composed of graphite-like coke and a negligible content of fibrous-like coke. The coke content was observed as 5.65% compared to 10.52% in the HZSM-5 only. Furthermore, the efficient synergistic effect of Al-SBA-15 and HZSM-5 resulted in the deep conversion and directional reforming of the lignin pyrolysis vapors. This study can promote the high-grade utilization of lignin through the application of feasible fixed-bed catalytic pyrolysis technology.