Study On The Distribution Of O-containing Functional Groups In Low Rank Coals And Its Removal Methods

The high oxygen content and water content in low rank coals have importantinfluence on clean utilization process. This paper empolyed the back-titration andinstrument methods to analyse the distribution of O-containing functional groups inlignite. Using the low-temperature heat treatment, solvent extraction and swellingpyrolysis, the removal behaviour of O-containing functional groups were examinedunder these processes. And the gas evolution was examined in the low-temperatureheat treatment process. The results showed that the oxygen groups in low rank coal ismainly consists of the acidic O-containing functional groups, and the chemicalmethod can effectively quantify out around78%of the O-containing functionalgroups. Combined with the instrument method for the determination of inactive etherbond, the distribution of O-containing functional groups in low rank coal wasobtained with the combination of methods. The significant relation between thesurface properties of lignite and the content of O-containing functional groups wasfound, and the relation between the high moisture holding capacity and O-containingfunctional groups in accord with a multiple linear equation:MHC=2.655[-COOH]+2.912[-OH]+0.209[-OCH₃]-3.321S_non-O+1.341. Solvent extractionprocess mainly formed hydrogen bond between solvent and the O-containingfunctional groups which take the place of the hydrogen bonding between oxygencontaining functional groups, especially decline the content of phenolic hydroxylgroups. The O-containing functional groups can be easyly removed in the process ofswelling-pyrolysis as the result of swelling stretched the coal macromolecularnetwork. Dynamics show that activation energy of carboxyl group is lower thancarbonyl during de-oxygenation.