Theoretical Study On The Mechanism And Kinetics Of Phenol Oxidation Degradation Reaction In The Atmosphere

Using the density functional theory(DFT) and the transition state theory(TST), the mechanism and kinetics of the oxidation degradation of phenol in the atmosphere are investigated. The research includes as follows:1. Theoretical study on the mechanism and kinetics for the reaction of phenol with OH radical.Using DFT method, and CBS-APNO methods, the mechanism and kinetics for the addition and hydrogen abstraction reaction of phenol with OH radical are inverstigated. All state point structures (including reactant, reactant complex, transition state and product radical) , energies, and vibrational frequencies are calculated. The addition reaction for phenol with OH radical are the favored reacton pathway. Otherwise, the direct and indirect hydrogen abstraction reaction are more difficult. Ortho-position addition reaction has the lowest reaction energy(-17.45kcal/mol) and activity energy(-4.64kcal/mol). The product radical at ortho position is the most stable. Using transition state theory, the rate constants of addition reactions are calculated in the temperature range of 200 to 360K, fitting in the following expressions: ko-add =1.92×10-19×T2.04exp(1847/T) kipso-add=4.08×10-20×T2.36exp(497/T) kp-add =1.38×10-19×T2.17exp(389/T) km-add=1.01×10-19×T1.20exp(-219/T)The overall reaction rate constants are the agreement with the available experimental values The branching ratio of ortho-position addition reaction is 93.3-99.5% in the temperature range of 200 to 360K. 2. Theoretical study on the reaction mechanism and kinetics of phenol-OH with O2 .The addition reaction and hydrogen abstraction of phenol-OH with O2 are investigated useing DFT method: the addition reaction forms peroxy radicals, and the hydrogen abstraction reaction can foem catechol,resorcinol,hydroquinone and HO2 radical. The rate constants of each reaction channel are also calculated by using transition state theory with Eckart tunneling correction over 200-360K.It's found the addition reactions of phenol-OH at ortho or meta position with O2 have three reaction channels. However, a minimum activatiy energy of the reaction pathways has the maximum reaction energy, so the three reaction channels are the competitive channels, the addition reaction of phenol-OH at para position with O2 has two competitive reaction pathways, and the addition reactions of phenol-OH at ipso position with O2 has only one main reaction pathway.In the reaction of phenol-OH at ortho position with O2, the rate constant of hydrogen abstraction (1.17×10-16 cm3 molecule-1 s-1) is significantly higher than of the addition reaction; The rate constant of addition reaction of phenol-OH at ortho position or para with O2 is the same of the abstraction reaction. The calcluated rate constants are good agreement with the experimental values.3. Theoretical study on the reaction mechanisms of phenol-OH-O2 peroxy radicals.There are 16 bicyclic radicals from peroxy radical cyclization and there are 24 different reaction pathways. The study shows that four bicyclic radicals are relatively stable, and six reaction pathways are the main reaction pathway. They are the spontaneous exothermic reaction, and have a faster reaction rate.Bicyclic radicals will futher react to form more stable epoxide radicals, 24 epoxide radicals are calculated and are more sable than bicyclic radicals. It includes 34 reaction pathways to epoxide radical, and it's found they are spontaneous exothermic reaction.Because four bicyclic radicals are stable, the reaction pathways (OB2-OC2, OB2-OB3, PB2-PC4, IB2-IC2, MB3-MC3, MB3-MC4) are the main reaction channel.Our theoretical study on the mechanism and kinetic of phenol oxidative degradation determine the major degradation pathways to make up for deficiencies in the experiment. For further study of ring-opening reaction products of phenol and its impact on the environment provides the necessary, reliable theoretical data.