Hydrothermal carbonization of soybean hulls for the generation of hydrochar: A promising valorization pathway for low value biomass

A novel approach is applied using Hydrothermal Carbonization (HTC) to produce hydrochar from soybean hulls in which it was found that processing variables significantly affect morphology and physico-chemical characteristics of the resultant hydrochars. The produced hydrochar has high potential for applications in high value carbon applications including catalysts, supercapacitors , absorbents, and nanocomposite agents. • HTC is feasible for valorization of soybean hull. • Carbon spheres with time-dependent sizes formed in the presence of citric acid (CA) • CA increased the yield of hydrochars, carbon content, and higher heating value. • Hydrochar with citric acid catalyst had better thermal stability. • High commercial valorization potential for agricultural soybean waste. A novel approach is proposed for applying Hydrothermal Carbonization (HTC) to produce hydrochar from soybean hulls in which it was found that processing variables significantly affect morphology and physico-chemical characteristics of the resultant hydrochars. All HTC experiments were done at 250 °C at varying pH environments (acidic and neutral) and three processing times. It was found that carbon spheres formed in the presence of citric acid whose sizes were time dependent. Citric acid increased the yield of hydrochars and carbon content, and also lead to higher heating value (HHV). Nevertheless, the effect of processing time (0.5 h vs. 6 h) on a number of the hydrochar materials characteristics was found to be surprisingly small; however, the 0.5 h hydrochar surface area was twice that of the treatment for 6 h.