Effects Of Alkali/Alkaline Earth Metal On The Pyrolysis Characteristics And Dynamics Of Biomass

Biomass absorbs various nutrients in the soil in the growth process, so it contains alkali metal salts and alkaline earth metal salts. Although the contents of metal salts are not high, they still play an important role on the pyrolysis process. Due to the various kinds of salts in biomass, the effect of each single metal salt on the pyrolysis process was investigated after the biomass was acid demineralized. In this thesis, two plants (Pinus sylvestris and lauan) and their three main components (cellulose, hemicellulose and lignin) were selected as the objective biomass.Firstly, the alkali metals and alkaline earth metals of the biomass were removed by acid demineralization, and then metal salts were added to the samples quantitatively. The content of K+, Ca2+, Mg2+analysised by atomic absorption experiment showed that pickling desalination efficiency was over 90%, higher than that of water desalination. The scanning electron microscopy analysis revealed that demineralizing biomass by 5wt% hydrochloric acid for two hours slightly undermined the surface structure of the biomass. Due to the particle sizes of cellulose, hemicellulose and lignin were of 100μm, adding salts by the mechanical dry mixing method are able to contribute to the desired mixing results; The scanning electron microscope analysis showed that the salts added by impregnation method could be evenly distributed on the graded and pickled Pinus sylvestris and lauan samples.Then, different original and synthetic samples were analyzed by thermo gravimetric analyzer(TGA). The influences of metallic salts of KCl, CaCl2 and MgCl2 on pyrolysis characteristics of biomass were investigated. Regarding with the thermal gravimetric analysis, it was found that the pyrolysis catalyst of CaCl2 could inhibit the condensation reaction during the thermal decomposition of biomass, resulting in the shoulder-like peak of the mass loss curve of hemicellulose and pickling sylvestris, and producing more low molecular weight compounds to promote the thermal decomposition process. MgCl2 had a good catalytic effect on the prolysis of cellulose, gradually decreasing the maximum rate of pyrolysis and the pyrolysis temperatures. But MgCl2 had a little effect on the prolysis of hemicellulose with the negligable variation. Despite the little impact of KCl on the pyrolysis of three major components, KCl was a better pyrolysis catalytic for the prolysis of pickling sylvestris biomass.Finally, all the experimental results were simulated by two mathematical models of Kissinger differential method and Flynn-Wall-Ozawa (FWO) method. It is found that Kissinger differential method was suitable for simulating the TGA graphs. While the activation energy value of the decomposition of biomass calculated by FWO method was higher and more accurate than that of Kissinger differential method. The FWO method also avoided the separate calculation of activation energy in case of two peaks of DTG figure. When the two kinds of dynamics analysis was used on the same sample, although there are some differences in the activation process and the final value, the trend demonstrated by was the same.