The impregnation effect on low and middle rank coals structure reorganization and their behavior during pyrolysis

Main structural parameters of low and middle rank coals and genesis (Cdaf=64.3–87.2%) were determined by method of X-ray diffraction. The interrelation between structural parameters (Lc, La, h/l002) and carbon content (Cdaf) of coal was found. It is determined that impregnating of coals by 1 M of inorganic substance solution (KOH, CaO, HCl) and water leads to a change in the initial coal structure and is determined by a reagent nature. Data of IR-spectroscopy and X-ray diffraction for parent and impregnated coals suggest that the effect of inorganic substances on coal involves substitution of free acid group protons with metal (K, Ca) cations and a rupture of C–O–C and C–C bonds takes place as well as a rupture of organo-mineral bonds (O–Me–O), sulfide bridges and a destruction of cation-forming complexed (HCl). The influence of extraplanar deformational vibrations of CH2– and CH3-bonds of carbon skeleton with a successive redistribution of aromatic and aliphatic fragments in coal structure is increased. The correlation between the degree of interlayer ordering (h/l002) of parent and impregnated coals and the pyrolysis liquid products at a temperature of 500°C was found. It was shown that coals impregnated in the course of pyrolysis increases the liquid products yield, 1.5–2.0 times, in comparison with untreated coals. Thermogravimetric analysis (TGA) data were used to determine the energies of activation (Eef) for some coals. The correlation between TGA and X-ray diffraction data was found.