Influence of inorganic content on hydrochar quality from high-ash agar extraction waste via hydrothermal carbonization
Abstract
Agar solid waste (ASW) has potential as a feedstock for hydrochar production because of its organic content; however, its high inorganic fraction, predominantly silica, limits its application. Furthermore, studies specifically investigating the hydrothermal carbonization (HTC) of ASW remain limited, given its high ash content and low energy value. This study investigated the HTC of ASW at varying temperatures (180–220 °C) and reaction times (30–90 minutes), with particular emphasis on how two inorganic components (celite versus perlite) affect hydrochar yield, composition, and energy properties. The resulting hydrochars were characterized using CHNSO, proximate, SEM, and FTIR analysis. The results revealed high ash contents reaching 77.7–92.08%, corresponding to HHV of 2.3–3.4 MJ kg⁻¹, while FTIR spectra confirmed strong silica presence through prominent Si–O–Si absorption bands. Therefore, the study provides valuable insights into silica-rich biomass behavior during HTC. The study also evaluated the relationship between HHV and ash content and analyzed the kinetic model. The results demonstrate the significant influence of inorganic components on carbonization pathways, highlighting opportunities to enhance hydrochar quality through pretreatment strategies such as acid/alkaline leaching or mineral separation.