Abstract
The thermal behavior of humic acids of fusain (F-HA) and humic acids of demineralized fusain (DF-HA) were investigated at heating rates of 5,20,and 50℃·min-1 using an open system thermogravimetric analyzer coupled to a quadrupole thermogravimetry mass spectrometer (TG-MS).The pyrolytic and hydrogen generation kinetics were analyzed using the distributed activation energy model (DAEM) and the distribution functions of the activation energy were obtained.The results indicated:(1) the distribution function of the activation energy for F-HA has an asymptotic approximation to a Gaussian distribution during pyrolysis.Moreover,it has some symmetry properties and the same peak value as a standard Gaussian distribution.The distribution function of the activation energy for DF-HA has an asymptotic approximation to a Gaussian distribution during pyrolysis and its peak value is less than that of a standard Gaussian distribution.According to the conversion ratio vs temperature,activation energy relationships and the thermal mass loss features of humic acids,four and five stages of a general pyrolytic process were found for F-HA and DF-HA,respectively.The chemical reactions for each stage of the pyrolytic process are discussed in detail.(2) The distribution functions of the activation energy of hydrogen generation for F-HA and DF-HA have an asymptotic approximation to a Gaussian distribution during pyrolysis.The activation energy of hydrogen generation increased with an increase in the conversion yields but it also showed staged features.Based on the kinetic characteristics of their generation during pyrolysis their hydrogen generation processes can be divided into five stages,which reflect the different chemical reaction mechanisms.(3) The demineralization of Yimin fusain influences the thermal behavior,kinetics of the pyrolytic processes and the hydrogen generation of humic acid.
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