Morphology and microstructure of co-pyrolysis char from bituminous coal blended with lignocellulosic biomass: Effects of cellulose, hemicellulose and lignin

Highlights: • Influence of biomass model compounds on co-pyrolysis char structure was investigated. • Transformation of carbon structure was explored by Raman and spectral deconvolution. • Evolution of surface morphology was quantitatively described by the fractal analysis. • Three biomass model compounds showed different influence on the structure evolution. - Abstract: Co-pyrolysis of coal and lignocellulose biomass and coal is the key step of other co-thermochemical conversion, and conversion of co-pyrolysis char is the rate-determining step of co-gasification and co-combustion. In this paper, the influence of biomass model compounds (cellulose, hemicellulose, and lignin, abbreviated as CE, HCE and LIG) on the co-pyrolysis char structure transformation was investigated. Carbon structure and surface morphology of co-pyrolysis char were examined by Raman spectroscopy and scanning electron microscope (SEM). A comprehensive comparison of Raman spectral deconvolution methods based on various fitting functions and peak numbers was explored, and Gaussian-Lorentzian-function with no less than nine peaks showed the best performance. Three biomass model show different effects on the transformation of microstructure structure. The addition of CE increased the ordering of char structure. HCE promoted the disordering degree of microstructure structure and reached the maximum at 50% HCE mass ratio. The microstructure structure changes of co-pyrolysis char for 25% and 50% LIG mass ratios were not evident, while 75% LIG increased the disordering degree of the co-pyrolysis char. Fractal analysis was applied for describing the char surface morphology quantitatively with two and three-dimensional fractal dimensions. CE decreased the fractal dimensions of co-pyrolysis, and the influence of HCE and LIG depended on the mass ratio.