Kinetic Modeling of Coal Swelling in Solvent

To better understand the coal swelling kinetics in solvent, a kinetic model based on a pseudopolymolecular reaction is proposed to model the swelling data up to the quasi-equilibrium stage. The swelling isotherms of a Chinese sub-bituminous coal, named Coal-1, in carbon disulfide (CS2), N-methyl-2-pyrrolidinone (NMP), and CS2/NMP mixtures with the different volumetric mixing ratios at various temperatures were obtained by a so-called linear variable differential transformer (LVDT) deformation transducer, continually. The corresponding kinetic parameters, including the rate constants, order of the pseudopolymolecular reaction, apparent activation energy, and pre-exponential factor, were obtained with the coefficients of determination, R-2, range between 0.851 and 0.999. The kinetic parameters obtained with obvious meanings which are useful for better understanding the mechanism of the coal swelling in solvent as well as the structure of coal. The apparent activation energy for Coal-1 swelling in CS2 is 8.9 kJ/mol, which corresponds to the dissociation energy barrier of van der Waals forces. It is less than that for Coal-1 swelling in NMP, 40.9 kJ/mol, which corresponds to the dissociation energy barrier of hydrogen bonds. It implies that the dissociation of the noncovalent bonds in coal is crucially important during coal swelling in solvent. The CS2 in the test system appeared as "catalyst", accelerating the swilling rate by lowering the energy barrier.