KOH Activation Mechanism in the Preparation of Brewer’s Spent Grain-Based Activated Carbons

Abstract

Understanding the mechanism of KOH activation in the preparation of activated carbon (AC) enables more efficient utilization of biomass. In this study, brewer’s spent grains (BSGs) were carbonized at 500 °C to produce biochar (BC), followed by KOH activation under different activation conditions. The gas and solid products generated during the activation process were analyzed by gas chromatography (GC), X-ray diffraction (XRD), Raman analysis, a surface area and pore size analyzer, and X-ray photoelectron spectroscopy (XPS). The results show that increasing the KOH/BC ratio or the activation temperature could both promote gas production. XPS results indicated that the activator reacted first with -COOH and then with -OH of ACs, with AC5-700 having the highest C-OH content (50.04%). As the KOH/BC ratio increased, more aromatic structures were destroyed, and the porosity of ACs was significantly enhanced, with AC7-700 having the highest Brunauer–Emmett–Teller (BET) specific surface area (SBET) (2997.69 m2/g). At low temperatures, KOH reacted with the active groups of BC and carbon at the edge of the aromatic structure. At high temperatures, the activator (KOH, K2O, and K2CO3) reacted with carbon in the aromatic structure to generate a large number of pores on ACs and expand them. ACs exhibited more pores with higher KOH addition, and a higher activation temperature did not generate more new pores, but expanded the pores more significantly than high KOH addition.