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Comparative study on the effect of ZnCl2, a 60:20:20 mol % eutectic of ZnCl2-NaCl-KCl and CO2 during activation of pinewood

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Abstract

Chemical activation in molten salts is a recent development in the field of tailoring activated carbon, where a combination of activating agents is used rather than a single compound. However, a comprehensive understanding of differences in catalytic activity is lacking. So, the question remains which chemical activation method is more beneficial. This research compares the catalytic effect of ZnCl2 as a single activating agent and its eutectic mixture of ZnCl2-KCl-NaCl (60:20:20 mol %). Pinewood shavings were chemically activated at 400 °C in a mass ratio of 5 to 1 (salt to biomass) and then washed to remove the activating agent. Obtained materials were subsequently physically activated using CO2 at 800 °C in an attempt to further increase their surface area. Properties of obtained carbons were characterized by elemental and proximate analyses, ICP-AES, FTIR, gas adsorption (N2, CO2), and adsorption (iodine, methylene blue, and molasses). Chemical activation with ZnCl2 and the eutectic mixture resulted in a surface area of respectively 910 m2/g and 917 m2/g with significant differences in porosity. The eutectic mixture created a greater proportion of micropores. ZnCl2 was more beneficial for mesoporosity which was formed over a broad range, whereas the eutectic mixture created mesopores in a narrower size range (19–27 nm). Subsequent CO2 gasification widened the pores and lowered the surface area, decreasing the adsorption capacity. This study illustrates that employing mixtures of molten salts has several advantages over a single activating agent and might lead to further development of tailor-made activated carbons.

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The authors declare that any information regarding the presented data in this work will be provided on request.

Change history

Abbreviations

AAEMs:

Alkali and alkaline earth metals

AC:

Activated carbon

EEM:

Experimental eutectic mixture

MB:

Methylene blue

PSD:

Pore size distribution

S:B ratio:

Salt to biomass weight ratio

SSA:

Specific surface area

TT:

Treatment temperature

Vpore :

Pore volume

VPfraction :

Volumetric fraction of specific pores in total pore volume

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Acknowledgements

The authors would like to express their gratitude to the department of Prof. Dr. Andrea Kruse at the University of Hohenheim and to the department of Prof. Dr. ir. Stefaan De Neve at Ghent University for granting access to their facilities. The company Desotec is thanked for their aid in this project. Elien Beyls is thanked for her aid with graphical design, display and overall support.

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Authors and Affiliations

  1. Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000, Ghent, Belgium

    Jonas De Smedt, Przemyslaw Maziarka & Frederik Ronsse

  2. Department of Conversion Technologies of Biobased Resources, Institute of Agricultural Engineering, University of Hohenheim, Grabenstrasse 9, 70599, Stuttgart, Germany

    Przemyslaw Maziarka & Pablo J. Arauzo

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  1. Jonas De Smedt
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  3. Pablo J. Arauzo
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  4. Frederik Ronsse
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Contributions

JDS: Conceptualization, methodology, validation, investigation, visualization, writing original draft. PM: Formal analysis, review and editing. PJA: Resources, review and editing. FR: Review and editing, supervision, funding acquisition.

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Correspondence to Jonas De Smedt.

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Highlights

• Activation in a eutectic mixture generates carbons with an adsorption capacity of industrial grade.

• Use of the eutectic medium yielded 10 wt. % more activated carbon compared to pure ZnCl2.

• Activation with a eutectic mixture leads to higher microporosity than ZnCl2.

• The eutectic mixture creates mesoporosity over a narrower range (18 to 28 nm) than ZnCl2.

• Consecutive physical activation reduces the specific surface area of both carbons.

The original online version of this article was revised: Due to the author’s name Jonas De Smedt was incorrectly written as Jonas Smedt De Smedt.

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De Smedt, J., Maziarka, P., Arauzo, P.J. et al. Comparative study on the effect of ZnCl2, a 60:20:20 mol % eutectic of ZnCl2-NaCl-KCl and CO2 during activation of pinewood. Biomass Conv. Bioref. (2023). https://doi.org/10.1007/s13399-023-05123-7

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