Theoretical Studies on the Taking off of Oxygen-containing Functional Groups in Lignite Model Compounds

The removal reaction mechanism of different kinds of oxygen-containing functional groups in lignite was investigated, benzoic and phenol were chosen as model compounds. Density function theory (DFT) and DFT-based B3LYP method along with mixed basis sets 6-311+G(d,p) were applied in all calculations. The results suggest that removal approaches are different from different kinds of oxygen-containing functional groups and the taking off energy is also different. According to the reaction activation energy of different kinds of reactions, autocatalysis reaction of structure unit containing carboxyl is the easiest. Taking account of the influence of water molecular to the reaction, formic acid and glycerin were studied as model compounds. The results show that water molecular can reduce the reaction activation energy and accelerate the reaction process, the best catalytic effect is achieved with one or two water molecular. The effects of Na+, K+ and their carboxylates to the reaction were studied on glycerin as well. The results suggest that Na+ and K+ can reduce the reaction activation energy by forming complexes with glycerin, which stabilizes the transition state structure. Na+ has a better catalytic effect to the reaction. Comparing with sheer ions, the catalytic effects of carboxylate can' t reach that good. However, potassium carboxylate' s catalytic effect doesn ' t change a lot, while the catalytic effect of sodium carvoxylate has a significant decrease.