Catalytic Hydropyrolysis of Beetle Killed Trees for the Production of Transportation Biofuels

Abstract

We conducted catalytic hydropyrolysis of beetle-killed trees: Pine, Ash tree, and Redbay in a micro-pyrolyzer (Py/GC–MS) and investigated the performance of heterogeneous catalysts like HZSM-5, NiMo-HZSM-5, and NiRe-HZSM-5. We also investigated the effects of temperature, catalyst-to-biomass ratio, and hydrogen pressure on product yield. Our findings reveal that aromatic yields increase with temperature and catalyst-to-biomass ratio but decline at higher hydrogen pressures; additionally, higher catalyst acidity enhances both total hydrocarbon production and selectivity toward C7–C8 aromatics, with each feedstock exhibiting distinct optimal conditions. The type of metal doped on the HZSM-5 zeolite plays an important role in the process. Under the tested conditions (500°C, 21 bar, and catalyst-to-biomass ratio 10:1), Molybdenum (Mo) outperformed Rhenium (Re) for promoting alkane formation. The NiRe-HZSM-5 catalyst produced only a modest yield of alkanes (0.7 wt.%) compared to the higher yield (10.0 wt.%) observed with NiMo-HZSM-5. Overall, NiMo-HZSM-5 was the optimum catalyst for the production of alkanes. HZSM-5 is the optimum catalyst for the production of aromatic hydrocarbons. To optimize the operating parameters and enhance aromatic yield, we employed a response surface methodology (RSM). The analysis revealed that the maximum product yield of 35.0% is obtained at 570°C, 14 bar, and catalyst-to-biomass ratio of 14:1. The highest aromatic yield of 28.3% is obtained at 562°C, 14 bar, and catalyst-to-biomass ratio of 13:1. The highest alkane yield is 5.7%, obtained at 400°C, 14 bar, and catalyst-to-biomass ratio of 8.6:1.