From glucose-based carbohydrates to phenol-rich bio-oils integrated with syngas production via catalytic pyrolysis over an activated carbon catalyst†
The catalytic pyrolysis of carbohydrates over a phosphoric acid-activated carbon catalyst (ACC) was investigated to obtain phenol-rich bio-oils and syngas production in a facile fixed bed reactor for the first time. The central composite design (CCD) was adopted to optimize the experimental operating conditions of glucose catalytic pyrolysis, where the effects of reaction temperatures and ratios of catalyst to reactant on product distributions were studied. The main chemical components of the obtained catalytic bio-oils from glucose were phenols, ketones, and anhydrosugars, in which the selectivity of phenols ranged from 4.8 to 100% depending on various reaction conditions. The highest selectivity of phenols was achieved at a reaction temperature of 450 °C with a catalyst to reactant ratio of 1. Carbon monoxide, carbon dioxide, methane, and hydrogen were the main gas fractions in the gaseous products, where high concentrations of carbon monoxide (50.2%) and hydrogen (9.2%) could be attained. Additionally, the catalytic pyrolysis of cellulose with different catalyst to reactant ratios at a reaction temperature of 450 °C was also investigated and the results exhibited a similar phenomenon to that of glucose. A high selectivity of phenols (96.7%) could also be achieved integrated with a high concentration of carbon monoxide (42.1%). The mechanism of phenol generation was further discussed and the “phenol pool” was proposed to describe the catalytic function of the ACC in the catalytic conversion of volatiles into phenols. Our findings suggest that the catalytic pyrolysis of renewable and earth-abundant carbohydrates over the ACC might provide a novel and viable route to generate high-purity phenols to ultimately advance the utilization of biomass energy.