Regenerable carbon honeycomb monoliths directly prepared from brown coal: A novel carbon product

A novel, straightforward and efficient method for preparing electrically regenerable carbon honeycomb monoliths (CHMs) directly from brown coal is described. Soft brown coal, which inherently contains relatively high oxygen functional group concentrations and high moisture contents, was kneaded with NaOH or KOH to achieve homogenised and smooth dough with plasticine consistency. This method of alkali salt addition leads to a high level of ion-exchange. The exchanged cations form a strong electrostatic network, strengthening the coal structure such that the dough can be directly extruded into high cell density CHMs (e.g., 227 cells/in²) which maintain their structural integrity throughout drying¸ carbonisation and activation processes. It was found that a modest temperature increase (to above 50 °C) enabled by the kneading, played an important role in developing the dough quality via an apparent irreversible, exothermic cross-linking reaction. The fabricated CHMs are structurally robust with high compressive strength (e.g., 40 MPa). They exhibit good electrical conductivity (e.g. 150 S/m) and high surface areas (e.g., 1175 m²/g), which can both be tailored for specific applications. The used CHM was fully regenerated by in-situ resistive heating after liquid adsorption in a short time (30 min) under atmospheric air, thanks to its optimal electrical conductivity and stable structure. These characteristics along with its low material and production cost make this CHM a promising material for a variety of applications, such as methane storage and phenol adsorption.