Influence of mixed methods on the surface area and gas products of activated carbon
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Carbon Letters https://doi.org/10.1007/s42823-020-00130-4
ORIGINAL ARTICLE
Influence of mixed methods on the surface area and gas products of activated carbon Sang Youp Hwang1 · Gi Bbum Lee1 · Ho Kim1 · Jung Eun Park1 Received: 11 December 2019 / Revised: 30 January 2020 / Accepted: 12 February 2020 © Korean Carbon Society 2020
Abstract Upgraded activated carbons (ACs) are typically synthesized by mixed methods, such as solid–solid mixing and wet impregnation of low-grade ACs with KOH. This study compares the properties of upgraded ACs prepared by different methods using elemental analysis, X-ray photoelectron spectroscopy, N 2 adsorption isotherms, and X-ray diffraction. In ACs produced by the solid–solid mixing, the ratio of potassium activator is proportional to the surface area and amount of gas produced. However, in wet impregnated ACs, the potassium ratio exhibits a zero or negative correlation. It is demonstrated that potassium ions in solution are not transferred to K2O and do not contribute to the surface area and pore size, generating less amount and different composition of gases. As such, impregnated ACs exhibit similar surface areas and large pores, regardless of the potassium ratio. The physical properties, such as specific surface areas and pore size distribution, of ACs using wet impregnation were similar to the ACs generated by the water physical activation. It indicated that the KOH does not efficiently act as a chemical activator in the wet impregnation method. Therefore, a certain amount and suitable mixing method of chemical activator play an important role in the property upgrade of ACs. Keywords Activated carbon · Potassium hydroxide · Chemical activation · Carbon monoxide · Surface area
1 Introduction Activated carbon (AC) is a porous carbonaceous material with a highly developed surface area and rich surface groups. It has numerous applications including the adsorption of both gases and liquids from aqueous solutions, gas separation, solvent recovery, energy conversion, and catalyst support [1–3]. Especially, a large surface area and pore size are beneficial for various AC applications; however, this requires very expensive manufacturing methods [4, 5]. Therefore, activation methods and conditions required to manufacture high-surface area AC (> 2000 m2/g) are of substantial research interest [6, 7]. Generally, ACs are produced by two main methods: physical and chemical activation. Physical activation includes the carbonization of the precursor in an inert atmosphere or activation of the resulting char using an activation agent such as steam or CO2 at high temperature (1000–1200 °C) * Jung Eun Park [email protected] 1
Department of Plant Engineering, Institute for Advanced Engineering, Yongin 17180, Republic of Korea
[8–10]. During chemical activation at relatively low temperatures (600–900 °C), the precursor is mixed with a certain amount of activation agent such as KOH, K2CO3, NaOH, H3PO4, or ZnCl2, which leads to the development of porous structures in the material [11
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