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Activated Carbons Produced from Hydrothermally Carbonized Prickly Pear Seed Waste
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0001-8225-9670
Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).ORCID iD: 0000-0002-8143-8279
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Number of Authors: 72022 (English)In: Sustainability, E-ISSN 2071-1050, Vol. 14, no 21, article id 14559Article in journal (Refereed) Published
Abstract [en]

The agro-sector generates organic waste of various kinds, which potentially could be used to prepare functional materials, lessen environmental problems, and enhance circularity. In this context, the hypothesis that was put forward in this work is that prickly pear seed waste from the Tunisian agro-food industry could be used to prepare activated carbons. The prickly pear seed waste was first hydrothermally carbonized and the resulting hydrochar was activated in CO2 at 800 °C. The yield of the hydrothermal carbonization process is of importance, and it was the highest at intermediate dwell times and temperatures, which was ascribed to the re-precipitation of hydrochar particles on the heat-treated biomass. The hydrochars and activated carbons were characterized with scanning electron microscopy, thermogravimetry, Raman spectroscopy, and N2 and CO2 adsorption/desorption analyses. The activated carbons had micro- (<2 nm) and mesopores (2–50 nm), and specific surface areas and total pore volumes of about 400 m2 −1 and 0.21 cm3 g−1. The study showed that the prickly pear seed waste could be effectively transformed into both hydrochars and activated carbons and that is advisable to optimize the hydrothermal process for the mass yield. A life cycle analysis was performed to assess the environmental impact of the production of typical activated carbons using the approach of this study. Further studies could be focused on enhancing the properties of the activated carbons by further optimization of the activation process.

Place, publisher, year, edition, pages
2022. Vol. 14, no 21, article id 14559
Keywords [en]
bio-waste, prickly pear seeds, hydrothermal carbonization, activated carbons, CO2 activation, life cycle assessment, Green & Sustainable Science & Technology
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:su:diva-212591DOI: 10.3390/su142114559ISI: 000885860700001OAI: oai:DiVA.org:su-212591DiVA, id: diva2:1718601
Available from: 2022-12-13 Created: 2022-12-13 Last updated: 2024-04-22Bibliographically approved
In thesis
1.
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2. From blue hydrochars to activated carbons: Hydrothermal carbonization, chemical activation and gas adsorption
Open this publication in new window or tab >>From blue hydrochars to activated carbons: Hydrothermal carbonization, chemical activation and gas adsorption
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hydrothermal carbonization (HTC) of carbohydrates and biomass is a straightforward method for preparing hydrochars at low temperatures of 180-250 °C. Hydrochars are more carbonized than their precursors. Increasing the carbonization degree of hydrochars at hydrothermal temperatures is a scientific quest that is addressed in this thesis. Hydrochars are known to have a spherical or irregular morphology. Here we address thin film hydrochars for the first time.  Hydrochars themselves are carbon precursors for preparing activated carbons. Activated carbons are porous materials that can be used for gas adsorption applications. In this thesis, enhanced adsorption of VOCs at low pressures is addressed by using iron phosphate impregnated activated carbons. Finaly, any chemical process or product including those in this thesis such as HTC, activation, hydrochar and activated carbons may contribute to the issue of environmental degradation positively or negatively. Such environmental impacts are addressed by life cycle assessment of processes of HTC and activation and their related products in the last paper of this thesis. Briefly mentioned, in my first study (Paper I), I focused on the HTC of glucose in the presence of iron (II) sulfate. By changing the concentration of iron (II) sulfate, with a catalytic amount, blue hydrochars were formed at the bottom of the autoclave. The blueness was related to thin film interference. The thin film hydrochars were more carbonized than spherical hydrochars and the yield of HTC has increased in the presence of iron (II) sulfate. The second study (Paper II) is focused on the activation of hydrochars with H3PO4 and H3PO4+FeCl3. We showed that ultramicroporosity and impregnated iron phosphate species enhance the adsorption of VOCs at low pressure. The ACs were impregnated with Fe (PO3)2 and it was shown that Fe (PO3)2 acts as an activation agent which opens up for future studies. In the third study (Paper III), H3PO4-activated carbons were prepared and modified with FeS and FeSe and it was shown that the ACs were also impregnated with Fe2P, in the case of AC-FeS/Fe2P. FeSe and FeS were not detected by XRD. Only large crystals of Fe2P were detected in the sample AC-FeS/Fe2P. In the last study (Paper IV), prickly pear seed biomass from the agro sector in Tunisia was hydrothermally carbonized. The hydrochars were then activated into ACs by CO2 activation. The life cycle assessment of the HTC and activation process was investigated.  

Place, publisher, year, edition, pages
Department of Materials and Environmental Chemistry, Stockholm University, 2024. p. 51
Keywords
hydrochars, activated carbons, hydrothermal carbonization, chemical activation, gas adsorption
National Category
Materials Chemistry
Research subject
Materials Chemistry
Identifiers
urn:nbn:se:su:diva-228549 (URN)978-91-8014-797-2 (ISBN)978-91-8014-798-9 (ISBN)
Public defence
2024-06-14, online via Zoom, public link is available at the department website, Stockholm, 13:00 (English)
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Available from: 2024-05-22 Created: 2024-04-22 Last updated: 2024-05-13Bibliographically approved

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Saadattalab, VahidWang, XiaHedin, Niklas

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