Enhanced Light Aromatic Yield from Lignite Pyrolysis by Remedying the Acid Sites of Different Hierarchical HZSM-5

Abstract

A series of HZSM-5 treated by NaOH followed by supporting sulfated zirconia (ATₓSZ/H5) was prepared and used for catalytic reforming of lignite pyrolysis volatiles. ATₓSZ/H5 was found to be a potentially promising catalyst for removing oxygen from vapors to produce aromatics and olefin. The highest yields of benzene, toluene, ethylbenzene, xylene, and naphthalene (BTEXN) were obtained over 3% SZ supported on HZSM-5 treated by 0.2 mol/L NaOH (AT₀.₂SZ/H5) as a result of the abundant hierarchical pores and suitable acidic density. Moreover, raising the NaOH concentration for zeolites caused the enhancement of olefin yields. The polycyclic aromatic hydrocarbons chemisorbed over zeolite can be activated by the hydrogen transfer reaction to increase the selectivity of C₂₊. Comprehensive catalyst characterization using temperature-programmed desorption with ammonia, N₂ physisorption, X-ray diffraction, and inductively coupled plasma optical emission spectrometry enabled establishing structure–performance relationships with a major role of the zeolite structure, density of strong acid sites, and mesoporosity. ATₓSZ/H5 exhibited a suitable physicochemical property, including the addition of strong acid species and acidity, suitable pore structure, and specific surface area. Additionally, in comparison to H5, the yields of BTEXN over AT₀.₂SZ/H5 increased from 12.8 to 18.9 mg/g, but excessive alkali over H5 had a negative effect on the BTEXN yield because of the structure collapse.