Chemically bound water in brown coal and impact of ambient oxidation on its characteristics

This study adopted a molecular dynamics simulation technique to investigate characteristics of chemically bound water in brown coal and effects of ambient oxidation and temperature at varying total system water contents (TSWC). The Hatcher’s brown coal model structure was utilized to simulate a non-altered lignite-water system. An oxidized system was created by modifying the Hatcher’s model structure with an application of oxidation reaction pathways that have been reported to be spontaneous at ambient condition. Elemental analysis indicated that the oxidized system was equivalent to about 103-day aerial oxidation of the Victorian brown coal at 35 °C. Three types of chemically bound water, namely WH, WLH and WNF were defined from the molecular dynamics perspective considering hydrogen(H)-bonding and distance from lignite surface. Effects of ambient oxidation and temperature on contents of each type of chemically bound water, defined as percentage of corresponding water molecules with respect to TSWC (e.g., PH and PNF), were analyzed separately. Shear viscosity and diffusion of water in brown coal were investigated and linked to chemically bound water contents. Results indicate that characteristics of chemically bound water are influenced by ambient oxidation, temperature and TSWC. The property of WH governs the viscous characteristics of water in brown coal.