Recovery of carbon from HTL-derived liquid waste through hydrothermal carbonization

The carbon-rich aqueous phase derived from hydrothermal liquefaction of biomass poses a potential problem for the environment. This post-hydrothermal liquefaction wastewater (PHWW) can contain a significant fraction of the feedstock, impacting the overall process economy of HTL. The scaling up of the HTL largely depends on using PHWW, ensuring a reduction of material loss through the aqueous phase. The present work aims to use the PHWW as a precursor through another low-temperature thermochemical process, hydrothermal carbonization (HTC), to recover the organic carbon from the aqueous products for further utilization. The hydrochar recovered from PHWW can contain up to 70% carbon, with zero ash content. The absence of ash also resulted in materials with high HHV, between 24.2 MJ/kg and 28.35 MJ/kg. The FTIR analysis confirmed the presence of certain functional groups in the carbon and indicated that the recovered carbon has adaptable qualities that make it appropriate for various industrial applications, including gas purification, water treatment, pollutant removal, etc. The results signify the suitability of HTC as a carbon recovery process from HTL-derived wastewater. The recovery of carbon and converting it to valuable materials will reduce the waste generation from HTL and make the process more sustainable. • PHWW from HTL was valorized via HTC to recover carbon-rich hydrochar. • Hydrochar showed up to 70% carbon and high HHV (24.2–28.35 MJ/kg) with no ash. • HTC enables carbon recovery from HTL wastewater for value-added applications.