ReaxFF MD and detailed reaction kinetic study on the thermal cracking and partial combustion of anisole: a biomass model tar compound.

Methods of partial oxidation for biomass tar conversion were studied based on their detailed reaction mechanism. The good accuracy of the modeling results compared with the experimental data indicate that the model was reasonable. Anisole was chosen as the tar model component for partial combustion with equivalence ratios (ER) from 0 to 0.8. The results show that oxygen promotes the pyrolysis of anisole and thereby the tar conversion rate. An appropriate amount of oxygen could crack tar into flammable small-molecule gases (H2, CO) and inhibit the generation of polycyclic aromatic hydrocarbon (PAH) compounds. In addition to the introduction of active free radicals, partial oxidation could also improve tar cracking by exothermic oxidation to produce amounts of heat. Typical PAH production was studied based on the rate of product formation (ROP). The results show that active radicals, such as H and OH, promote tar cracking. A detailed reaction pathway for tar conversion was built. Staged oxygen supply benefited the cracking of tar into small-molecule gases and inhibited the formation of PAHs.

Quantum Chemical and Kinetic Studies of N2O Formation during Interaction between Char(N) and NO: Influence of Oxygen, Active Sites, and Nitrogen Status.

In order to obtain a deep insight into the N2O formation mechanism in a fluidized bed, density functional theory was used to investigate the interaction between char(N) and NO at a molecular level. Three key influencing factors for the formation of N2O, namely, active sites, nitrogen status, and oxygen molecules, were taken into study. The geometric structures, electron distribution characteristics, and reaction paths were optimized and calculated. The outer orbital electron properties of char(N) and NO indicate that NO acts as an oxidizer, which tends to abstract electrons from char(N) during the char(N)-NO interaction. A stable N2O molecule has a singlet state and presents as a linear molecular structure. The chemisorption on the char surface will weaken the bond energy of NO from 620 to 94.1 kJ/mole, which promotes the catalytic reduction of NO. Active sites on the char surface benefit the reduction of NO to N2, rather than N2O, which indicates that excessive high temperatures will inhibit the production of N2O. The combination of pyridine nitrogen and NO to form N2O needs to overcome a much higher energy barrier of 357.4 kJ/mole. The initial chemisorption of oxygen molecules on the char surface will promote the formation of N2O by lowering the dissociation energy of N2O from the char surface as well as exposing nitrogen to the char surface.