Physicochemical structure and gasification reactivity of co-pyrolysis char from two kinds of coal blended with lignocellulosic biomass: Effects of the carboxymethylcellulose sodium

To investigate the influencing mechanism of alkalis on char structure evolution and gasification reactivity during co-pyrolysis of coal and lignocellulosic biomass, carboxymethylcellulose sodium (CMC) was selected as a typical organic sodium salt and introduced to the pyrolysis of bituminous coal (BC) and anthracite coal (AC) respectively. Physicochemical characteristics of the char samples were examined by N₂ adsorption/desorption measurement, scanning electron microscopy (SEM) and Raman spectra under different CMC mass ratio. Fractal theory and deconvolution method were applied to quantitatively analyze the surface morphology, pore property and microcrystalline structure of the char. Thermogravimetric analyzer and non-isothermal kinetics method were used to determine the gasification reactivity and kinetic parameters of the char. The results indicated that the addition of CMC promoted the development of pore structure from both BC and AC char samples. The fractal dimension can quantitatively describe the complexity and heterogeneity of pore structure and surface morphology of char sample. The fractal dimension obtained from SEM images of co-pyrolysis char was in range 1.41–1.68 and higher than that of the coal char, which meant CMC promoted the heterogeneity of co-pyrolysis char. Peak fitting analysis on the Raman spectra illustrated that the value of A_D/A_All and A_D/A_G increased with the mass ratio of CMC, indicating that addition of CMC reduced the ordering of co-pyrolysis char structure. Synergistic effect was observed during the gasification process of co-pyrolysis char. The evolution of physicochemical structure and organic sodium lead to higher reactivity and lower activation energy during gasification of co-pyrolysis char than the raw coal char. This paper provides insight on the effects of organic sodium salt on products evolution during co-pyrolysis of coal and biomass.