The two oxidation reaction processes, which were performed by using 12.7% HNO
3 or moderate pressure oxygen as oxidation reagents, were investigated by chemical and infra-red spectroscopic examinations of each product. The most noticiable differences in these two oxidation reactions were seen in reaction rate as well as selectivity of humic acid formation, namely, by means of HNO
3 oxidation the humic acid was obtained rapidly and selectively.
And also it was found that there were some differences in the properties of the humic acids obtained by each oxidation method; the humic acid from O
2 oxidative coal has larger cation capture capacity than the HNO
3 humic acid, and the former is precipitated more easily from the alkali solution by adding dilute H
2SO
4 than the later.
These natures indicate that there exist some different processes in these two oxidation reactions.
The infra-red spectroscopic and elemental analyses of the oxidized coals suggest as follows;
1) In HNO
3 oxidation, the fission of C-C bond in coal proceeds selectively through the addition of oxide of nitrogen to weak C-C bond, so that the humic acid is obtained in high yield.
2) In O
2 oxidation, oxidative decompostion via surface oxidation proceeds partialy and can not distinguish from the fission of C-C bond in coal, so that the yield of oxidized coal decreases.
3) The difference of reaction rate between O
2 and HNO
3 oxidations might be reduced to the rate of fission of C-C and oxidation of alcoholic OH to carboxylic group.
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