Energy & Fuels, Vol.27, No.11, 6419-6429, 2013
Effects of Aromatic Solvents and Temperature on Rearrangement of Hydrogen Bonds in Brown Coals
Aromatic hydrocarbons are usually the main components of the hydrogen-donor solvents in direct coal liquefaction, but little is known about hydrogen bonding between aromatic solvents and brown coals. To simulate the coal- solvent interaction during heating, benzene vapor was introduced into the reaction system of coal pyrolysis. Then we measured infrared spectrograms of brown coals using the in situ diffuse reflectance infrared Fourier transformation (DRIFT) technique to investigate the effects of aromatic solvents and temperature on the rearrangement of hydrogen bonds in brown coals. We found that aromatic solvents show a circulating promotion effect on the rearrangement of hydrogen bonds, that is, free OH groups produced by the gradual decomposition of cyclic OH tetramers bond to adsorbed benzene to form OH-pi hydrogen bonds, which reinforce the decomposition of cyclic OH tetramers due to increasing steric hindrance. In addition, OH ether hydrogen bonds and self-associated OH n-mers show special variation regularity in the presence of benzene during heating due to oxygen-containing small molecules involved in the rearrangement of hydrogen bonds, and OH ether hydrogen bonds are more susceptible to the steric hindrance than self-associated OH n-mers during coal pyrolysis. The effects of adsorbed benzene are not completely identical for some kinds of hydrogen bonds in different brown coals.