preprints.org > chemistry and materials science > chemical engineering > doi: 10.20944/preprints202406.0070.v1

Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Version 1 : Received: 31 May 2024 / Approved: 3 June 2024 / Online: 6 June 2024 (03:16:18 CEST)

The pyrolysis process has emerged as an attractive option for waste treatment. In this technology, inorganic compounds play catalytic effects in the pyrolytic reaction of organic materials, increa-sing the char's yield, porosity, and physicochemical properties. The present research investigates and compares the slow pyrolysis of spent coffee grounds (SCG) using potassium hydroxide (KOH) (weight ratio of 1:1) and landfill leachate membrane concentrate (LLMC) residue (weight ratio of 1:1) as pyrolitic additives. We hypothesized that the high content of alkali and alkaline earth metals in LLMC could enhance the yield or improve the quality of the carbon-based material produced in pyrolysis. This strategy could be a sustainable alternative for valorizing SCG and landfill wastes, replacing catalyzing agents such as steam, CO2, and chemical additives used on an industrial scale. The char yields in slow pyrolysis ranged from 18 to 24%. The SCG had a low specific surface area (4.5 m2 g-1), contrasting with the notable surface areas observed in both ac-tivated chars. In particular, the KOH-activated char displayed a higher surface area than the LLMC-activated char (1960 vs. 1130 m2 g-1). On the other hand, the combustion enthalpy of the LLMC-activated material was estimated at 22 MJ kg-1. This value was 22% higher than the energy enthalpy of SCG and KOH-activated char used for comparison. Our findings confirm that pyrolysis of SCG with KOH produces a microporous material with a high specific surface area. In contrast, the resulting LLMC-activated char demonstrates a higher calorific value. Our findings could contribute to establishing potential industrial applications for SCG and LLMC residues to produce energy and high-value materials.

landfill leachate; membrane concentrate; spent coffee grounds; thermogravimetric analysis; waste-derived char

Chemistry and Materials Science, Chemical Engineering

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