Influence of sequential HTC pre-treatment and pyrolysis on wet food-industry wastes: Optimisation toward nitrogen-rich hierarchical carbonaceous materials intended for use in energy storage solutions

Due to elevated protein content, the food-industry bio-wastes are promising feedstock to produce hierarchical (micromesoporous) carbonaceous materials with the intended use as electrodes in the energy storage solutions. However, the high initial water content, makes their direct activation through high-temperature processes costineffective due to significant heat requirements. In this study, the influence of pretreatment with hydrothermal carbonization (HTC) on wet food-industry bio-wastes, further pyrolysed, was investigated. Selected wastes (brewer's spent grains, spent coffee grains and spent sugar beets) were pre-treated by HTC at 180 degrees C or 240 degrees C, and then pyrolysed at 500 degrees C or 700 degrees C. Obtained materials were examined using elemental analysis, gas adsorption (N-2 and CO2) and FT-IR. Besides minor differences caused by the bio-composition of wastes, the general trends were similar for feedstock. The pretreatment had a beneficial influence on the properties of all wastes. The HTC at 180 degrees C and pyrolysis at 700 degrees C for all wastes show the most promising total specific surface area 560 +/- 10 m(2)/g and accessible specific surface area 96 m(2)/g. Those conditions simultaneously did not reduce the total solid yield in comparison to the one-step process. The pre-treatment at 240 degrees C led to elevated nitrogen incorporation in the carbonaceous structure compared to HTC at 180 degrees C. However, it formed a hierarchical structure that was not stable for the thermal treatment. Study proves the HTC pre-treatment at 180 degrees C is beneficial for the conversion of food-industry bio-wastes into hierarchical carbonaceous material for their use in the energy storage systems application.

Automated summary

This study investigates the impact of hydrothermal carbonization (HTC) pretreatment on wet food-industry bio-wastes before pyrolysis, and finds that HTC pretreatment at 180 degrees Celsius is beneficial for converting waste into efficient carbonaceous materials for energy storage system applications.