Oxidation Of XL And Some Coal-related Model Compounds

The mild oxidation of lignite is an important approach to achieve high-efficiency utilize.In the paper,the factors influencing the oxidizing depolymerization of Xilinguole lignite(XL)were studied.The structural characteristics of insoluble macromolecular skeletal in lignite and the depolymerization of covalent cross-linking in macromolecular skeletal structure were also investigated.The mechanisms of oxidizing depolymerization of macromolecular skeletal structure of XL,based on the oxidation of some coal-related model compounds,were finally proposed.Results indicate that(1)The effect of reaction temperature and hydrogen peroxide concentration on the oxidizing depolymerization is very obvious.The excessive increase of the oxidation time could lead to the decarbonxylation reaction of the insoluble molecular structure and the carboxyl functional group in the water-soluble products,so it is not conducive to the high-efficiency utilize for lignite.The oxidation products of XL are mainly composed of small molecule dicarboxylic acids and benzoic acids.(2)Oxidizing depolymerization conversion of XL raw coal is higher than its thermal extraction residue under the same oxidation condition due to the high active cross-linking structure.The oxidizing reaction mainly happens in the aliphatic structures to rupture the bridge bonds between aromatic nucleuses and the side-chain substituents,so malonic acid and succinic acid predominate in the small molecular polycarboxylic acids determined in the water-soluble fractions from the oxidation.(3)The experimental results showed that the released volatile products were dominated by lower-ring(1,2-rings)aromatic clusters in the insoluble macromolecular skeletal structure during the flash pyrolysis of thermal extraction residue and oxidized residue,for example,(alkyl)benzene,indene,indane,(alkyl)naphthalene,etc.There were a little heterocyclic aromatic compounds and phenols detected.(4)Oxidation results of model compounds conducted in H2O2 aqueous solution without catalyst were not ideal.Model compounds with carbon chain bridge such as diphenyl methane,diphenyl ethane were difficult to be oxidized,but the structures of benzene ring on the hydroxyl substitution or the existence of oxygen atom in the bridge bond can promote the oxidation reaction.In the oxidation product of 4-benzyloxyphenol applying Fe2+ as catalyst,the compounds of malonic acid and succinic acid were detected.Malonic acid was also detected in the catalytic oxidation products of other oxygen-containing model compounds,however,the succinic acid was not found.