Active carbon monoliths from soft brown coal: A systematic study of their preparation, pore structure modification and characterization

Abstract

High surface area active carbons in a ‘honeycomb monolith’ (HM) configuration can be prepared directly from soft brown coal by a novel approach. Kneading the coal into a plasticine consistency enables it to be extruded in HM form, then dried, carbonized and activated, retaining its structural integrity throughout these steps. Unlike higher rank coals, soft brown coal, which inherently contains relatively high oxygen functional group concentrations and high moisture contents, develops a strong H-bonding network during kneading. This opens the way to a novel and simpler method of preparing activated carbons in a monolith configuration. A systematic study was therefore conducted to evaluate the potential of these monoliths for being converted into higher value activated carbons by a low-cost process. Carbon honeycomb monoliths HMs from brown coal were modified by carbon dioxide (CO2) activation with a uniform domain size over a wider range of activation conditions (1–3 h, 750–950 °C) and the products were characterized by N2 adsorption (surface area and porosity), SEM, TEM, Raman spectroscopy, XPS and elemental analysis. The optimum conditions for development of porosity, aromaticity and a graphitizing structure were activation at 900 °C for 3 h. Interestingly, higher temperatures did not yield additional benefits. These materials should be useful in applications requiring highly ordered carbon.