Photocatalytic Oxidative Depolymerization Of Coals And Dagang Vacuum Residue

Efficient and clean utilization of heavy carbon resources ( HCRs ) is the ultimate goal to solve energy source problems in China, but the understanding of theirs structure is still a principal question must be first considered. Photocatalytic oxidation ( PCO ) depolymerization of coals and Dagang Vacuumn Reside (DVR) can understand the structure properties of HCRs from molecular level, selective, non-destructive, and provide a basis of utilizing HCRs efficient and clean because many organic compounds in HCRs can be converted successfully into oxygen-containing compounds selectively.As important HCRs, Shenfu bituminous coal (SFBC), Geting coal (GTC), Xilinhaote coal (XLC) and Huolinguole coal (HLC) have different photocatalytic oxidation properties. To understand their structure in detail, three systems were used to degrade coals, including solid phase mixture open system (SPMOS), heterogeneous hydration suspension open system (HHSOS), heterogeneous hydration suspension closed system (HHSCS). Separated organic matters (OMs) with acetone or methanol and analyzed with GC/MS and FTIR were finished to understand the experimental effect. The results indicate that coals can be oxidized successfully in these systems, although the different coals exist different oxidation effect. Methyl groups and methylenes in fused ring aromatic hydrocarbons or branched-chain alkyanes can be oxidized preferentially by hydroxyl free radicals substituting and produce a large number of hydroxyl compounds. Then these hydroxyl compounds were oxidized continuously in illuminating with UV light to generate to carbon dioxide and water. The species and number of oxygen-containing compounds (including acids, esters, ketones, epoxides etc.) in the oxidation coals was increasing comparing with in the raw coals. At the same time the relative content of the aromatic compounds reduced in the process and carbon chain in long chain alkyl compounds were also degraded in the photooxidation process. The extract yield of coal is improved obviously in the oxidation process, too.DVR, as heavy oil in China, contains a large number of OMs and possesses the potential application prospect, however understanding its structure is a vital problem to realize its effective conversion and utilization as similar to coals. In order to realize DVR oxidation and deploymerization, the cyclohexane solution of DVR was illuminated with low pressure mercury lamp at the room temperature for 13 hours, and the effect was detected with GC/MS. The results show that DVR has been oxidized effectively, a large number of acids (36.05%), oxalic esters (14.56%), epoxides compounds (19.12%) are converted from alkanes or branched-chain alkanes. So the treatment can improve the effective utilization of DVR. To explain the mechanism of PCO deploymerization coals and DVR, analytic reagents including benzene, toluene, xylene, phenol, naphthalene series compounds and liquid paraffin, as model compounds, were oxidized respectively in the same condition with coals and DVR oxidation. The experimental results indicate that the oxidation of hydroxyl radicals is an important method in PCO. The formation of free radicals in the surface of photocatalyst continuously through illuminating with UV light and the production of electrons-holes pairs (e^-/h⁺) via electron transition between conduction band and valence band are principal source of PCO. The formation of large number of free radicals cause the oxidative dehydrogention of OMs in coals and DVR. Active hydrogens substituted by the free radicals atoms in macromolecular compounds in coals or DVR, hydroxyl compounds including alcohols and phenols can be produced. Then the hydroxyl compounds reacted with each other or the other organic compounds to generate aldehydes, ketones and esters, or lead to the degradation of coals and DVR through removing water. In addition to the part of cyclic-hydrocarbons compounds had ring-opening reaction during the photo-catalytic oxidation process.To improve the PCO' effect, different homemade photocatalysts of doping coal were prepared by Sol-Gel method and characterized by XRD, TEM and BET techniques, and then optimized selection and applied on the coals and DVR deploymerization respectively. The result shows that the SFC (12wt%)-TiO₂ photocatalyst is especially suitable for complex organic compounds deploymerization because of being with the structure of loose and dual aperture. Just the structure causes the photocatalyst with the strong adsorptive property and high activities, when the SFC-TiO₂ as photocatalyst are used in the reaction, even if expand the amount of coals and DVR the similar result can also be obtained and the oxidation effect is more remarkable as using the homemade pure TiO₂.