An examination of hydrothermal carbonization reaction conditions on hydrochar filterability

Abstract Hydrothermal carbonization (HTC) is often favored over other biomass conversion methods due to its ability to process wet waste. However, the primary HTC product, hydrochar, is generated as part of a solid–liquid slurry and is only useful once the liquid fraction is largely removed. Filtration is typically the first step in the dewatering process, and it is important to understand how hydrochars produced under different HTC reaction conditions affect filtration performance. Here, the filterability of cow manure hydrochar slurries was investigated. Filterability in the form of the specific resistance to filtration was examined for hydrochar slurries produced at 200°C and 260°C, for 10 min and 4 h, with and without the addition of sulfuric acid. By measuring the specific resistance to filtration at three different pressure drops (100, 200, and 300 kPa), it is shown that the hydrochar slurries are extremely compressible. It was observed that hydrochar slurries exhibit reduced filtration resistance when produced at elevated reaction times and temperatures in acid but are less sensitive to changes in pressure drop in the absence of sulfuric acid. The filtration data presented here should provide insight into how to effectively optimize the downstream filtration and dewatering processes for prospective commercial HTC projects and aid in efficient hydrochar separation for various uses.