Pyrolysis of Woody Biomass and Waste from Additive Manufacturing for the Synthesis of Chemicals and Transportation Fuels

Abstract

Generating fuels and chemicals using renewable sources is paramount to mitigate the depletion of energy sources and global warming. Pyrolysis produces bio-oil from the thermochemical conversion of biomass, which can be used for resin and bio-fuel synthesis. This study investigated the effects of the different woody biomass (Douglas fir, eucalyptus, and hybrid poplar) on the properties of pyrolysis products. Poplar bio-oil was found to be the best candidate for resin synthesis applications because of its higher hydroxyl concentration and carbon content. Furthermore, the optimization of the pyrolysis reactor was done using the Box-Behnken response surface methodology to determine the effects of operating parameters. The feed rate and square of temperature significantly affected the bio-oil yield whereas, temperature and the interaction between feed rate and bed height-to-diameter ratio were significant for hydroxyl concentration. Additionally, ex-situ catalytic pyrolysis was carried out to study the effect of catalyst (Cu/Al2O3) on bio-oil. Catalytic pyrolysis increased the amount of carbon, alkyl phenol (from 7.72 to 22.52 area %), and hydrocarbons (from 1.59 to 11.28%) in the bio-oil, which were attributed to deoxygenation and alkylation reactions. Pyrolysis bio-oil needs further catalytic hydrodeoxygenation for its suitability in fuel applications. However, catalysts screened so far suffer from coke formation. Thus, the effects of Cu-based catalysts on the severe hydrogen treatment of pyrolysis bio-oil were investigated. Cu/Al2O3 catalyst yielded maximum treated oil (50.5%) with higher carbon conversion (67.64%) than conventional catalysts. Additionally, the coke formation was less than 3% for Cu-based catalysts which could be attributed to the lower acidity of Cu-based catalysts. In addition to fuel, pyrolysis bio-oil could be used to prepare the resin for additive manufacturing. Investigating the circularity of any process is necessary to determine its sustainability. This study further investigated the application of pyrolysis in maintaining the circularity of additive manufacturing. It was observed that sodium silicate in the composite waste of additive manufacturing acts as a catalyst during the pyrolysis, increasing the selectivity towards the generation of hydrocarbons and alkyl phenols. Additionally, sodium silicate increased the phenolic hydroxyl concentration by assisting the degradation of lignin. This proved the applicability of pyrolysis in upcycling additive manufacturing waste to bio-fuel and resin.