Coalification of Expired Oatmeal: Hydrothermal Carbonization for Solid Biofuel Production

Yusuf, O. Ajagbe and Betül, Ercan and Koray, Alper and Ilknur, Durukan and Suat, Ucar and Kubilay, Tekin and Sebestyén, Zoltán and Czégény, Zsuzsanna and Selhan, Karagöz (2026) Coalification of Expired Oatmeal: Hydrothermal Carbonization for Solid Biofuel Production. ACS SUSTAINABLE RESOURCE MANAGEMENT. ISSN 2837-1445

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Abstract

Hydrothermal carbonization (HTC) of food waste is challenging because food-waste feedstocks are heterogeneous and compositionally variable, and their major components—carbohydrates, proteins, and lipids—undergo different transformations during HTC. A well-characterized feedstock can therefore provide a more controlled basis for assessing HTC behavior and product properties. Here, expired oatmeal (EO), containing 68.66 wt % carbohydrates, 12.99 wt % protein, and 7.25 wt % oil, was used as a model food-waste feedstock. HTC experiments were conducted at 200–250 °C, with solid-to-water ratios of 12.5–50 g EO per 150 mL water and residence times of 1.5–12 h. The resulting hydrochars were characterized using thermogravimetry–mass spectrometry (TG-MS), pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), and conventional analytical techniques. Compared with raw EO (HHV: 18.1 MJ kg–1), all hydrochars showed markedly improved fuel properties, with HHVs of 29.3–32.3 MJ kg–1 and ash contents of 0.14–0.48 wt %, compared with 1.62 wt % for the raw feedstock. HTC also increased fixed carbon and decreased volatile matter, while the H/C and O/C atomic ratios decreased to 0.91–1.14 and 0.12–0.21, respectively, placing the hydrochars in or near the bituminous-coal region of the Van Krevelen diagram. The hydrochars exhibited high heating values and low ash contents, supporting their potential as solid biofuel candidates; the use of a well-characterized feedstock provides a reliable basis for evaluating HTC behavior and supports the design of waste-to-energy conversion systems.

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