Ruthenium Catalyzed Permanganate Oxidation Of Aniline: A Kinetic And Mechanism Study

Aniline is a commonly used industrial chemical, which has been widely appliedin the production of plastic, rubber, dyes, medicine, pesticide and so on. Along withhuge amount of consumption is the increasing of aniline pollution in environment.Aniline is a kind of liquid in natural conditions, and has a relatively high solubilityin water, which help it to enter natural water and cause threats to both biotope andhuman health through variety ways. Thus to find a safe, economical method of highefficiency is necessary. Permanganate is a green oxidant which has been used inwater treatment for about fifty to sixty years, and has many applications. Based onthe researches done before, permanganate couldn’t remove trace organic pollutantsfrom water efficiently, and catalytic oxidation was found to be a promising way tosolve this problem. Ruthenium is a kind of noble metal which has been used ascatalyst in the production of synthetic ammonia, also in recent studies, it had beenapplied as catalyst during wet air oxidation process, and showed impressive effects.However few studies had focused on its application on permanganate oxidationsystem, especially at neutral pH. Therefore this study will use ruthenium as catalystin aniline oxidation by permanganate system at neutral pH, try to figure out itsimpaction on this process and predict the mechanism during reaction.It’s proved that the addition of Ru（III） could significantly increase the reactionrate of aniline oxidation by permanganate; it is believed to have parallel paths ofreaction in catalyzed system, and the kinetic equation could be written as:dC/dt=K_n[KMnO₄][Aniline]+K_c[KMnO₄]^0.5[Aniline][Ru（III）]。Results of thermo-dynamic study revealed that aniline oxidation by permanganate was an endothermicreaction. It was analyzed that thermodynamic constant under bothconditions, which indicated that aniline molecules tended to combine together, andthis hypothesis was proved in mechanism analysis. TOC results illustrated thataniline couldn’t be minimized after reaction, and azobenzene was found to be theonly reaction product after GC-MS detection. Apart from these, influence of pH toboth conditions was also learned during research. Reaction velocity could decreaseby200times with pH changing from4to9and catalytic effect increased duringexperiment region（pH=4⁹）. To explain this phenomenon, we believed that pHcould change the existing form of aniline species, which leads to the reduction ofreaction rate.Usually homogeneous catalysis system would add new materials into waterbody, and it’s difficult to separate catalysts from reaction system, thus causedsecondary pollution and increasing of operation cost. In case of this problem, an loading method using AA（activated alumina） as supporter had been studied, andcreated a bead catalyst with ruthenium being the activated component, and itsimpaction, stability, morphology and mechanism to catalyzed oxidaiton system werelearned. Optimum dosage under experiment system was50μmol/L, and this beadcatalyst（Ru-AA） showed best catalytic ability at pH=7, which helped its practicalapplication. After morphology analysis, it’s found that during loading processruthenium had been oxidized to Ru（IV）, which distributed evenly on the surface ofsupporter. Reaction process could hardly cause alteration to the surface feature andmolecule configuration of bead catalysts. After being used for ten times, beadcatalysts still could steadily improve aniline removal rate for about20%, in additionto this, leakage of ruthenium hadn’t been detected. Thus bead catalysts made in thisstudy were of high practicability, and were capable to be an promising catalysts topermanganate oxidation system.