abstract
Sponge-like biochar sorbents were prepared from the dissolution of chitosan followed by freeze-drying methodology and pyrolysis at three different temperatures (400, 600, and 800 degrees C) to produce sustainable N-enriched carbon materials with enhanced CO2 uptake from CO2/CH4 and CO2/N-2 gas mixtures. The pyrolysis process was reproduced by operando TGA-IR to study the gas evolved from the pyrolysis process. It was found that the pyrolysis temperature highly influences the textural properties of the chitosan sponge-like biochar materials, impacting mainly the amount and type of the N-species on the sample but also at the microporosity. XPS revealed the transformation of the amino groups from chitosan into pyridinic-N, pyrrolic-N, graphitic center-N, and graphitic valley-N or pyridine-N oxide species during the pyrolysis process. Increasing the pyrolysis temperature enhanced the quantity of the latter two N-type species. All sponge-like biochars adsorbed higher amounts of CO2 compared with CH4 and N-2 gases, with maximum CO2 uptake (similar to 1.6 mmol.g(-1)) at 100 kPa and 25 degrees C for the sample pyrolyzed at 600 degrees C (named CTO_P600). Biochar produced at 800 degrees C showed no longer adsorption capacity for CH4 and N-2, having the highest selectivity value for CO2/N-2 separation under continuous flux conditions among all prepared biochar sorbents. Isobaric CO2 adsorption measurements on the CTO_P600 sorbent revealed that physisorption phenomena predominantly governed the CO2 adsorption process, which was confirmed by its consistent adsorption capacity after 10 consecutive adsorption-desorption cycles. Moreover, the biochar exhibited tolerance to water vapor adsorption, indicating its suitability to work under moisture-rich conditions.
keywords
PORE-SIZE CHARACTERIZATION; CARBONACEOUS MATERIALS; THERMAL-STABILITY; FUNCTIONAL-GROUPS; ACTIVATED CARBON; ADSORPTION; CHITOSAN; BIOGAS; PURIFICATION; TEMPERATURE
subject category
Engineering
authors
Lourenco, MAO; Frade, T; Bordonhos, M; Castellino, M; Bocchini, S; Pinto, ML
our authors
Mirtha A. O. Lourenço
Researcher
Moisés Luzia Pinto
Research AssistantProjects
CICECO - Aveiro Institute of Materials (UIDB/50011/2020)
CICECO - Aveiro Institute of Materials (UIDP/50011/2020)
Associated Laboratory CICECO-Aveiro Institute of Materials (LA/P/0006/2020)
Rationale design of sustainable porous organosilicas for optimal CO2 uptake from biogas (GRACE)
acknowledgements
This work was developed within the scope of the projects UIDB/50011/2020, UIDP/50011/2020 and LA/P/0006/2020 (CICECO), and UIDB/04028/2020 and UIDP/04028/2020 (CERENA), financed by Portuguese national funds through Fundacao para a Ciencia e a Tecnologia (FCT) /MEC (PIDDAC), and when applicable co -financed by the European Regional Development Fund (ERDF) under the PT2020 partnership agreement. M.A.O.L thanks IIT for the research support, FCT for the Junior Researcher Position (2021.01158.CEECIND), and the funding from the European Union's Horizon Europe research and innovation program under the Marie Sklodowska-Curie PF grant agreement No 101090287. M.B. acknowledges FCT for the Ph.D. Grant (SFRH/BD/147239/2019).