Research Of Oxidation Characteristics And Mechanism On Lignite Under Mild Conditions

Low-rank coals such as brown coal and lignite are abundantresource, but its low calorific value and high moisture have hindered us from utilizinglow-rank coals effectively. Oxidative depolymerization of coal under mild conditionsis an important method to gain oxygen-containing organic species from coal. Theresearch will focus on the selective decomposition of large molecules of coal intosmall ones, study of oxidative reaction mechanisms, development of an effectiveseparation technique and optimizing oxidation conditions. In this study, Solventsextraction and oxidation of coal under mild conditions can assist the understanding ofcoal chemical structure. It can also offer a potential for conversion of coal into usefulchemicals, allowing for more value-added use of coal resources.The Effects of ratio of coal to H2O2, reaction temperature and residence time onthe oxidation of Hulunbeier lignite coal. The results showed that Hulunbeier lignitewas readily oxidized in H2O2aqueous solution at temperatures above40°C, and theoxidation behavior (oxidation rate, products distribution and yields) were stronglytemperature dependent.Hulunbeier and Shenhua lignite were extracted using different solvents includingCS2, ethanol, and acetone. The compositions of the extractables were analyzed byGC/MS. It was found that the CS2extractables contained the most kinds ofcompounds and a large amount of aliphatic hydrocarbons. The ethanol and acetoneextractables contained mainly oxygen-containing compounds. Shenhua ligniteextractables have more complex structure than Hulunbeier lignite, and contains morearomatic, their derivatives and heterocyclic compounds. Halogen element exists incoal that was further validated.When oxidation of the Hulunbeier solvent-extracted residues in H2O2solutionwas carried out at40°C under different reactor, water-soluble products detected withGC/MS under ultrasonic condition were less than under thermostat water bath. Watersolubles were mainly water-soluble macromolecules with rich-COOH,-OH and C-Ostructure. Oxidation under thermostat water bath got more water-soluble smallmolecules.Oxidation of the solvent-extracted residues in H2O2solution was carried out atdifferent temperatures. Water soluble products during oxidation were analyzed usingthe GC/MS. Aliphatic hydrocarbons were present in products during all oxidationsteps. The relative content of esters in all oxidation steps was high. The existence ofnitrogen in the water soluble contained amino, nitrocellulose, pyrimidine, isoxazole,and thiazole. The chemical changes of raw coal, the solvent-extracted residues, andthe oxidation residues were studied using FT-IR combined curve-fitting technique.Mechanism for H2O2oxidation was also discussed.