Decomposition kinetics of hydrogen bonds in coal by a new method of in-situ diffuse reflectance FT-IR

The kinetics of decomposition of hydrogen bonds in a Chinese lignite was studied using a new method of in-situ diffuse reflectance FT-IR (DRIFT) with pulverized coal samples directly. In addition, a new experimental technique in DRIFT measurement to avoid the condensation of volatile matter at high temperatures was introduced and used in this work. Based on two hypotheses, the single reaction model is used to calculate kinetic parameters for decomposition of hydrogen bonds (except OH-π) in coal heated up to 560°C. The results show that the decomposition of carboxylic acid dimers, OH-N and SH-N follows the second order reaction, while the decomposition of OH-OR2, tightly bound hydroxyl tetramers and self-associated hydroxyls follows the first order reaction. The calculated activation energies of some hydrogen bonds agree well with those obtained with other methods in references. Among the six types of hydrogen bonds studied, the decomposition of carboxylic acid dimers, OH-N, SH-N and tightly bound hydroxyl tetramers can be divided into two stages (230-380°C and 380-500°C), while that of OH-OR2 and self-associated hydroxyl groups can be treated as only one stage. Moreover, the mechanism of decomposition of tightly bound hydrogen bond was suggested based on the comparison of decomposition activation energy of self-associated OH with its bond strength in references.