Clay-catalyzed in situ pyrolysis of cherry pits for upgraded biofuels and heterogeneous adsorbents as recoverable by-products

Despite the promise of waste-to-energy conversions, bio-oils produced via thermochemical techniques such as pyrolysis suffer from high viscosity and acidity, which render the oils unstable and corrosive. While pyrolysis biocrude can be upgraded downstream, the use of precious metal catalysts limits the economic feasibility of biomass to biofuel conversions. To address these economic limitations, the present work explores the use of clay minerals as inexpensive catalysts to upgrade bio-oils in situ. Cherry pits, a representative carbonaceous agro-industrial waste, were pyrolyzed at 600 °C for 1 h in the presence of a series of clay minerals. For some clays, the bio-oils produced from catalyzed pyrolysis exhibited lower oxygen and fatty acid content than bio-oil from non-catalyzed pyrolysis. The heterogeneous clay-cherry pit biochar mixtures had higher surface areas and surface chemistries with increased free and intermolecularly bonded hydroxyl groups relative to those of pure cherry pit biochar. However, adsorption studies using methylene blue as a model organic contaminant showed that these heterogenous chars had a decreased adsorption capacity, likely due to a loss of surface functional groups. The addition of clay materials to the pyrolysis stream yields a biocrude more amendable to downstream upgrading and a heterogeneous biochar-clay mixture capable of (though certainly not optimized for) adsorbing a model organic compound. Graphical abstract