CO2 adsorption of lignite chars after one-step KOH activation

Abstract

The design and development of low-cost sorbents is vital for CO₂ capture from flue gases. In this study, the lignite char from Ordos coal (SE) was treated by a one-step KOH activation method to prepare microporous activated carbons for CO₂ adsorption. The textural pore properties, surface functional groups and element contents of SE before and after activation were characterized and discussed; the effects of the mass ratio of KOH to SE, activation temperature and time, as well as the adsorption temperature on CO₂ adsorption for prepared porous sorbents were investigated and optimized; the isosteric heat of adsorption and adsorption kinetics for the optimized sorbent were further calculated and fitted. When the mass ratio of KOH to SE was 1 : 1, the activation temperature and time were 700 °C and 120 min respectively, and the sorbent of K/SE700(120) showed an adsorption capacity of 1.35 mmol g⁻¹ at 20 °C, which dropped by 2.96% after ten regenerations. The Langmuir adsorption isotherms fitted the adsorption data of K/SE700(120) well, and the isosteric heats of adsorption were 11–13 kJ mol⁻¹, showing the physisorption characteristic. In addition, the good fit of the adsorption data to the Avrami model suggested that there are multiple adsorption routes for K/SE700(120).