USE OF 2,2-DIMETHOXYPROPANE AND H-1-NMR TO DISTINGUISH AND QUANTIFY THE EXTERNAL AND INTERNAL SORBED WATER IN COALS

Physisorbed and chemisorbed water in coal can be effectively removed b y the use of 2,2-dimethoxypropane (DMP) which reacts with the water to form methanol and acetone. This reaction is rapid and endothermic. An H-1 NMR method, based on this reaction, was developed to measure the amount of water in coals of different rank. Integrations of the methyl resonances from acetone and the methylene resonances of cycloheptane, an internal hydrogen standard, were used to determine the number of m oles of water reacted. The method was also used to determine the diffu sion kinetic parameters and type of diffusion associated with the chem ical dehydration of coals. The initial mechanism for the diffusion of the solvent-reactant into the macromolecular structure of coal can be either Fickian or Case II depending on the coal. From the kinetic stud y, it was found that external and internal sorbed water were removed s equentially. Free or surface sorbed water is nearly instantaneously re moved followed by the water in the internal structure of the coal. It was found that low-rank coals have up to 70% of their total water at o r near the surface and readily accessible to chemical dehydration, whe reas in high-rank coals about 30% of the water is readily accessible. The remaining water is in the internal structure of the coal.