Enhancing coking resistance of ZSM-5 in the conversion of pine sawdust into oxygen-free bio-aromatic hydrocarbons through tandem catalytic hydropyrolysis/vapor-phase hydrotreatment

The conversion of biomass into bio-aromatic hydrocarbons is a crucial aspect of achieving sustainable development. However, inadequate deoxygenation not only reduces the yield of aromatics but also causes instability in the produced biofuels. In this study, a tandem hydropyrolysis/vapor phase hydrotreatment process was conducted in a two-stage pressurized fixed-bed reactor to produce oxygen-free bio-aromatic hydrocarbons from pine sawdust under 0.15 MPa H2 with ZSM-5. The experimental results indicated that oxygen-containing compounds generated during the hydropyrolysis of pine sawdust in the first-stage reactor, were completely hydrodeoxygenated in the second-stage reactor over ZSM-5. This resulted in a total bio-aromatic hydrocarbons yield of 109.6 mg/g, with 81.5% selectivity to monoaromatic hydrocarbons, including benzene, toluene, ethylbenzene, and xylenes (BTEXs). The optimization study revealed that the hydropyrolysis temperature, hydrodeoxygenation temperature, and catalyst-to-biomass mass ratio could be controlled at 550 °C, 450 °C, and 8:1, respectively. The tandem process, conducted under pressurized H2, showed the capability to inhibit the deactivation of ZSM-5, as the low deactivation rate (35.1%) was observed in 15 sequential experiments of pine sawdust with an accumulated catalyst-to-biomass mass ratio of 0.5. The catalytic tandem vapor-phase hydrotreatment strategy offers a promising approach to effectively produce bio-aromatic hydrocarbons from biomass.