Abstract
Olive trimmings (OT) were used as feedstock for an in-depth experimental study on the reaction kinetics controlling hydrothermal carbonization (HTC). OT were hydrothermally carbonized for a residence time τ of up to 8 h at temperatures between 180 and 250 °C to systematically investigate the chemical and energy properties changes of hydrochars during HTC. Additional experiments at 120 and 150 °C at τ = 0 h were carried out to analyze the heat-up transient phase required to reach the HTC set-point temperature. Furthermore, an original HTC reaction kinetics model was developed. The HTC reaction pathway was described through a lumped model, in which biomass is converted into solid (distinguished between primary and secondary char), liquid, and gaseous products. The kinetics model, written in MATLABTM, was used in best fitting routines with HTC experimental data obtained using OT and two other agro-wastes previously tested: grape marc and Opuntia Ficus Indica. The HTC kinetics model effectively predicts carbon distribution among HTC products versus time with the thermal transient phase included; it represents an effective tool for R&D in the HTC field. Importantly, both modeling and experimental data suggest that already during the heat-up phase, biomass greatly carbonizes, in particular at the highest temperature tested of 250 °C.
Highlights
In the last few decades, the need to find new environmentally friendly and sustainable technologies to produce clean energy from waste biomass has inspired scientific research to study and develop more efficient and reliable tools for waste biomass exploitation
Hydrochar yields decreased with temperature and residence time except for residence times higher than 3 h
Tests performed at 180 and 250 ◦ C and 6–8 h of residence time showed an increase in hydrochar yield compared to 3 h residence time, which could be explained by an increased contribution of back-polymerization at longer residence times [17]
Summary
In the last few decades, the need to find new environmentally friendly and sustainable technologies to produce clean energy from waste biomass has inspired scientific research to study and develop more efficient and reliable tools for waste biomass exploitation Among these technologies, pyrolysis of agricultural and agro-industrial waste has received particular attention from the points of view of process dependent bio-char properties [1,2,3], pyrolysis kinetics [4,5], and innovative technology development [6]. The main product of HTC is a carbon-rich solid material referred to as hydrochar, which finds application as high energy bio-fuel [12,13,14,15,16,17,18,19,20,21], as a pre-treated material for anaerobic digestion enhancement [15,22], as a soil amendment [14,23,24], Energies 2019, 12, 516; doi:10.3390/en12030516 www.mdpi.com/journal/energies
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
