ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Insight into the effect of alkali treatment on enhancing adsorptivity of activated carbon for HCl removal in H₂ feedstock

Anis Usmani, Panuwat Watthaisong, Nurak Grisdanurak, and Suwit Suthirakun

Department of Chemical Engineering, Faculty of Engineering, Thammasat School of Engineering, Thammasat University, Pathumthani, Thailand

E-mail: gnurak@engr.tu.ac.th

Received: 13 September 2021  Accepted: 29 January 2022

Abstract:

The removal of contaminated HCl gas in the petrochemical plants is essential to prevent corrosion problems, catalysts poisoning, and downstream contamination. Alkali-treated activated carbon (AC) was proposed as an effective adsorbent for HCl removal. Understanding the underlying mechanism of HCl adsorption on modified AC is key to design promising strategies for removal of HCl and other chlorinated hydrocarbon gases in the H₂ feedstock. Here, a combined experimental and computational approach was used to study the role of alkali treatment on the adsorption behavior of HCl on the AC surfaces. We find that an interplay between alkali ions and oxygen-containing functional groups on the AC surface plays a crucial role in stabilizing the adsorbed HCl. The origin of such stable adsorbed configurations can be attributed to the dissociative adsorption of HCl leading to a formation of low energy species such as water, OH^– and Cl^– anions. These anions are electrostatically stabilized by the alkali ions resulting in a strong adsorption of −3.61 eV and −3.69 eV for Na⁺ and K⁺, respectively. Close investigation on charge analysis reveals that the epoxy functional group facilitates adsorbent-surface charge transfer where O and Cl atoms gain more charges of 0.37 e and 0.58 e which is in good correlation with the improved adsorption strength. The calculated results are consistence with the experimental observations that the Langmuir adsorptivity has been enhanced upon alkali modification. The maximum adsorption capacity of AC has been improved approximately by 4 times from 78.9 to 188.9 mg/g upon treatment.

Keywords: DFT; HCl removal; Graphene; Alkali treatment

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-022-02111-5

Chemical Papers 76 (7) 4203–4216 (2022)