High-Energy-Density Hydrochar and Bio-Oil from Hydrothermal Processing of Spent Coffee Grounds—Experimental Investigation

Mariusz Wądrzyk (), Jakub Katerla, Rafał Janus, Marek Lewandowski, Marek Plata and Łukasz Korzeniowski
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Mariusz Wądrzyk: Faculty of Energy and Fuels, AGH University of Krakow, 30-059 Kraków, Poland
Jakub Katerla: Faculty of Energy and Fuels, AGH University of Krakow, 30-059 Kraków, Poland
Rafał Janus: Faculty of Energy and Fuels, AGH University of Krakow, 30-059 Kraków, Poland
Marek Lewandowski: Faculty of Energy and Fuels, AGH University of Krakow, 30-059 Kraków, Poland
Marek Plata: Faculty of Energy and Fuels, AGH University of Krakow, 30-059 Kraków, Poland
Łukasz Korzeniowski: Faculty of Energy and Fuels, AGH University of Krakow, 30-059 Kraków, Poland

Energies, 2024, vol. 17, issue 24, 1-18

Abstract: Spent coffee grounds (SCGs), a by-product of coffee brewing, have high application potential. However, their high moisture content complicates conventional conversion without energy-intensive drying. This study explores a new route to convert SCGs to high-carbon bioproducts, such as hydrochar and bio-oil, through hydrothermal processing. The effect of the processing variables, i.e., temperature, residence time, and the application of the binary solvent as a reaction medium, on the distribution of the resultant bioproducts was investigated. The quality of the fabricated bioproducts was analyzed by means of instrumental techniques such as EA, ATR-FTIR, GC-MS, and GC-TCD-FID. Two dominant fractions were liquid bio-oil and solid hydrochar. The highest char yield (39 wt.%) was observed under milder conditions (low T and short residence times), while more severe conditions led to an increase in bio-oil formation, which reached a maximum of 46 wt.%. The resulting bio-oils were of similar quality, presenting high carbon content (71–74 wt.%) and energetic values (approximately 35 MJ/kg). Also, hydrochars showed a noticeable energy densification compared to raw materials, where the C content and HHV reached up to 73.8 wt.% and 30 MJ/kg, respectively. The addition of co-solvent to water improves the bio-oil yield as a result of the enhanced stabilization of reactive intermediates.

Keywords: spent coffee grounds; hydrothermal treatment; solvothermolysis; bio-oil; hydrochar (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2024
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