Reaction condition optimization and degradation pathway in wet oxidation of benzopyrazole revealed by computational and experimental approaches

The nitrogen heterocyclic compounds (NHCs) are very toxic and widely used in many industries, while the treatment of NHCs in wastewater has not attracted enough concern till now. Here we studied the complete degradation of a typical NHCs, benzopyrazole (BP), in wet oxidation. The effects of different operation parameters, such as stirring speed, temperature, reaction time and initial pH, on BP degradation and chemical oxygen demand (COD) removal were studied. BP was totally degraded and the COD removal efficiency achieved 76.7%, after 120 min reaction at 220 degrees C with initial pH 6.5. Meanwhile, 81.7% of the nitrogen from BP was removed from the solution. The toxicity of the BP solution was reduced by 95.2% after wet oxidation at 240 degrees C for 180 min. The influences of coexisted NO3-, CO32-, SO42- and PO43- ions were also investigated. With quantum chemical calculation and intermediates analysis by electrospray ionization mass spectrometry, a very detailed degradation pathway of BP in wet oxidation was proposed.