A study of torrefied cardboard characterization and applications: Composition, oxidation kinetics and methane adsorption

Abstract

Torrefaction is proposed as a valorization process for non recycled cardboard. Torrefied cardboard was physically and chemically characterized and it was proposed for energy production and methane adsorption. The surface area and pore volume obtained were among 3.0-6.0m²/g and 5.7·10^-3-2.3·10^-2cm³/g, respectively. The carbon content increased with temperature and residence time of torrefaction. Oxidation kinetics of torrefied cardboard at different temperatures (250-300°C) and at different plateaus (60-120min) were tested. Torrefied cardboard was chemically treated with KOH in order to study the effect of K on thermal oxidation kinetics. It was observed that high torrefaction temperatures and residence times lead to a more stable char. Furthermore, kinetic parameters were obtained by iso-conversional methods and Coats and Redfern method. Attending to iso-conversional method, a decrease of E_a was observed with both, temperature and residence time of torrefaction. Whereas chemically treated presented highest E_a values than torrefied cardboard. In addition, regarding Coats and Redfern method, the oxidation model was not highly modified by torrefaction temperature and residence time. However, for chemically treated samples the oxidation model was modified by K presence. Finally, CH₄ adsorption capacity of torrefied cardboard was studied at 30°C and atmospheric pressure. CH₄ partial pressures tested were lower than 0.45kPa. It was observed that CH₄ adsorption capacity increased with torrefaction time and decreased with chemical treatment. Thus, for the tested samples, the highest adsorption capacity observed was 5.70mgCH₄/g of sample.

Keywords: Agriculture greenhouse gases; Biochar; CH(4) adsorption; Modeling; Torrefaction; Waste valorization.