Effect Of Small Molecular Compound In Coal On Quick Coal Liquefaction Reactivity At High Temperature

The small molecule compound is a constituent with abundant hydrogen element in coal organic matter. It would have effect on the reaction of quick coal liquefaction at high temperature. However, the mechanism is not clear. The related research was carried out in this paper and the corresponding results are described as follows:Yanzhou coal and Shenfu coal were extracted separately using tetrahydrofuran in the soxhlet extractor in order to divided into the small molecule compound and remaining coal. During this experiment it was found that the extraction ratio of two samples reached to peak after12hours, and it is14.0%for Yanzhou coal and10.7%for Shenfu coal.Secondly, According to the infrared spectra, the small molecule compound encompasses several functional group such as aliphatic hydrocarbon, aromatic hydrocarbon, phenol, alcohol and ethers etc., and the content of aliphatic hydrocarbon reduced in the remaining coal where the network structure of macromolecule changed hardly. Moreover, the weight-average molecular weight of small molecule compound of Yanzhou coal is400by the gel chromatography analysis and its density is1.1924g/cm3by the pycnometer method.Next, it was noticed that there were some changes in the surface structure of extracted coal, e.g. it became spongy and the pore structure increased from microporous to mesoporous. In addition, the ratio of hydrogen to carbon dropped after small molecule compound was extracted, indicating the small molecule compound is rich-hydrogen component. Based on the thermogravimetric experiments of raw and extracted coals, the mass loss of extracted coal and the loss rate lessenned and the maximum temperature of weight loss was up slightly. These results mean small molecule compound influences the pyrolysis behavior of coal to some extent. As can be seen of the thermal decomposition kinetics before and after extracting coals, although the chemical bond of extracted coal was impaired partly, the major structure of coal has no changes and the pyrolytic reaction is still first-order for three stages in the coal pyrolysis process, which is same as the raw coal. And the activation energy of pyrolysis reaction within each stage decreases compared with the raw coal, revealing more readily pyrolysis after removing small molecule compound from coal.After the experiments of high temperature rapid liquefaction for Yanzhou coal, it is clear that the liquefaction conversion rate of extracted coal is higher that the raw coal and the products of its liquefaction tend to lighter constituents. Through a series of data analysis for extracted coal, some useful informations are obtained.①The major structure of coal has no destruction and the reaction of high temperature rapid liquefaction of extracted coal is still through breaking firstly the bridged bond of coal macromolecule by pyrolysis reaction, then hydrogenation liquefaction.②Coal structure becomes looser than raw coal and some cross-bond energy decreases, leading to easier pyrolytic and liquefaction reaction under the appropriate liquefaction conditions and adequate activated hydrogen source.③The pore structure of coal changes from micropore before extraction to mesopore after extraction, decreasing the transfer resistance of hydrogen-donor solvent. All these effects can increase the conversion rate of remaining coal.Furthermore, it is shown from the liquefaction experiments that the small molecule compound is a kind of hydrogen-rich component offering activated hydrogen in the process of liquefaction and the hydrogen-donating effect is inferior to the stonger hydrogen-donor solvent like tetralinFinally, compared with the results of high temperature rapid liquefaction of remaining coals under different operation conditions, the optimal reaction time is around5min as same as unextracted coal, which means it is reasonable to choose5min as the reaction of liquefaction. Moreover, the liquefaction conversion rate will enhance as the cold initial pressure of hydrogen rise. In the liquefaction process, the rational amount ratio between solvent and coal is2.5. And the iron catalyst with high dispersion has remarkable effect on the high temperature rapid liquefaction of remaining coal. The conversion rate of liquefaction will be highest when the extraction time is equal to7hours, meanwhile, the yield of oil and asphaltene is maximum.