Separation of CO2 using biochar and KOH and ZnCl2 activated carbons derived from pine sawdust

• Published in: Journal of environmental chemical engineering 2023-12, Vol.11 (6), p.111378, Article 111378
• Main Authors: Pimentel, Catarina Helena, Díaz-Fernández, Lidia, Gómez-Díaz, Diego, Freire, María Sonia, González-Álvarez, Julia
• Format: Article
• Language: English
• Subjects: Activated carbon; CO2 adsorption; CO2/N2 selectivity; Heat of adsorption; Isotherm models; Pine sawdust
• ISSN: 2213-3437
• DOI: 10.1016/j.jece.2023.111378

Due to the CO2 emissions and greenhouse effect, reducing its harmful impacts on climatic conditions is necessary. CO2 adsorption in a microporous carbon structure is one of the more effective separation techniques to avoid this type of emissions. In this work, one biochar (BC) and five activated carbons (ACs) were produced from Pinus radiata sawdust by chemical activation with potassium hydroxide (KOH) or zinc chloride (ZnCl2). Characterization was performed by scanning and transmission electron microscopy (SEM and TEM), surface area and pore size distribution by volumetric N2 and CO2 adsorption experiments using the Brunauer-Emmet-Teller (BET) and Barret-Joyner-Halenda (BJH) methods, respectively, X-ray diffraction (XRD), elemental analysis and X-ray photoelectron spectroscopy (XPS). The performance efficiency of the carbons was analyzed in terms of CO2 adsorption capacity at an absolute pressure range of 0–760 mmHg and at different temperatures (0, 25 and 50 ºC). The apparent and IAST selectivity of CO2 over N2 were determined and all carbons showed preferential sorption for CO2. Langmuir, Freundlich and Toth isotherms were employed to analyze pure CO2 and N2 adsorption data and the Toth isotherm gave the best fit. The carbon activated at 600ºC with KOH at a ratio of 1:4 w/w achieved the largest CO2 uptake (5.79 mmol/g at 0 °C and 750 mmHg) due to a combination between high microporosity (89 %) and surface area (2437 m2/g). This carbon also reached a relatively high selectivity. [Display omitted] •Carbons derived from pine sawdust with high CO2 uptake are effectively prepared.•At lower temperatures and higher pressure, carbons showed high adsorption capacity.•The highest CO2 capture capacity of 5.79 mmol/g at 0 ºC and 750 mmHg is achieved.•High microporosity and surface area shown crucial for high CO2 adsorption capacity.•Heats of adsorption found were low which indicates a physical adsorption.