A two-stage processing of cherry pomace via hydrothermal treatment followed by biochar gasification

Poland is the EU’s largest producer of cherry, which largely is further processed. As a consequence, a problematic waste – cherry pomace – is generated as by-product. Among the new sustainable technologies for organic waste valorization particularly perspective are thermochemical methods, which can be divided into conventional one, i.e., dry route (e.g. pyrolysis, gasification) and wet route (i.e. hydrothermal treatment). Herein, we proposed a two-stage thermochemical processing route for the conversion of cherry pomace, i.e., hydrothermal treatment followed by CO2 gasification. Firstly, we transformed the feedstock into biochar via hydrothermal processing. The aim of this stage was to analyze the effect of processing temperature (200–350 °C) on the distribution of the yield of various groups of products. The residual biochar was obtained with the highest yield (33–57 wt%). Among the gas-phase products, the dominant constituent was CO2. The upgrading of the biochars through gasification with CO2 to ensure the sustainability of conversion was the subsequent step. The quality of the biochars was examined by infrared spectroscopy, proximate and ultimate analysis, SEM, and low-temperature nitrogen adsorption. The activation energy ranged between 668 and 732 kJ mol−1 for the gasification of the biochar prepared at 275 and 200 °C, respectively. It was found that biochars produced at different conditions exhibit various properties as a result of gradual degradation of the original components of the raw material and increase in aromaticity occurring with the increase in the processing temperature.