Sorption of CO2 on low-rank coal: Study of influence of various drying methods on microporous characteristics

• CO2 adsorption experiments were carried out on coal dried in different ways.
• The influences of drying conditions on micropore characteristics were confirmed.
• The effect of low temperature on a freeze-dried sample is explained.

Various drying procedures were applied to North Bohemian low-rank coal. Dried samples were subjected to CO2 sorption analysis. Adsorption data were evaluated according to the Dubinin–Radushkevich and Medek equation to describe the micropore parameters. It was proven that drying conditions may have an impact on the monitored characteristics of the studied coal, particularly on the surface area of the micropores and the abundance of the most frequent pores. The observed textural parameters do not depend on the drying period but are a function of the drying temperature and may also be influenced by the presence of an oxidising atmosphere. Temperatures higher than 60 °C can cause alterations in the structure of the coal. Both the surface area of the micropores and the abundance of the most frequent pores of the studied coal increase in the following range of techniques: convection oven drying < inert-gas purging, microwave irradiation < hot-oven vacuum pumping < freeze-drying (lyophilisation). Due to the specific drying conditions, the freeze-dried sample showed the highest surface area of micropores.