Effect Of Oxygen-containing Functional Groups Content On Moisture Re-adsorption And Pyrolysis Reactivity Of Lignite

Oxygen-containing functional groups are polar and have strong hydrophilicity. The moisture re-adsorption of lignite after common evaporation drying is closely related to oxygen-containing functional groups. Simultaneously, there is a correspongding relationship between oxygen-containing functional groups and part of the pyrolysis products. Thus, the research of effect of oxygen-containing functional groups content on moisture re-adsorption and pyrolysis reactivity of lignite is of great significance for controlling moisture re-adsorption, reducing moisture content and lignite subbesquent pyrolysis processing and conversion.In this paper, Yuanbaoshan lignite was subjected to low temperature pyrolysis under a nitrogen atmosphere and high pressure hydrothermal treatment. The oxygen-containing functional groups content of different samples were measured by chemical titration and their moisture re-adsorption capability were also investigated. The samples after low temperature pyrolysis were oxidized by30%(mass fraction) hydrogen peroxide(H2O2) aqueous solution in order to change the content of oxygen-containing functional groups in the samples. And then the moisture re-adsorption capability of coals after oxidation was studied. The pyrolysis reactivity of different coal samples were investigated by thermo gravimetric (TG) analysis. The main results are as follows:1. With the increase of pyrolysis temperature, oxygen-containing functional groups content of samples after pyrolysis reduces and the equilibrium moisture re-adsorption rates decline with the decrease of the content of oxygen-containing functional groups. For Yuanbaoshan lignite, when the temperature reaches400℃, the equilibrium moisture re-adsorption rate is5.86%which is the smallest, while the value of raw lignite is21.5%.2. Oxygen-containing functional groups content of coal samples after oxidation increase at differently extent, which makes the equilibrium moisture re-adsorption rates increased. The more the content of oxygen-containing functional groups is, the higher the moisture re-adsorption capability becomes. There is a positive correlation relationship between both of them.3. Equilibrium moisture re-adsorption rates of samples after hydrothermal treatment also decline with the decrease of oxygen-containing functional groups content. Equilibrium moisture re-adsorption rates reaches smallest (11.5%) when the temperature is350℃. Compared with the pyrolysis samples at the same treatment temperature, low temperature pyrolysis has more advantages in the removal of oxygen-containing functional groups and weakening moisture re-adsorption capability of lignite. 4. The pyrolysis reactivity of coal samples in low-temperature phase (120℃～600℃) has good responsiveness to the change of oxygen-containing functional groups content. The pyrolysis reactivity in low-temperature phase is enhanced with the increase of the content of oxygen-containing functional groups, and when the content decreases the pyrolysis reactivity is also be weaken.