4-methylquinoline Ozonation Catalyzed By Ceramic Honeycomb

The coal gasification technique has developed rapidly in China to deal with the energy and environment crisis over the last decade.However,a large amount of wastewater containing refractory and persistent organic pollutants is produced during coal gasification process.Quinoline compounds,as typical pollutants in coal gasification wastewater,are harmful to aquatic creature and human health.Herein,we use 4-Methylquinoline?4-Meq?as a targeted pollutant to investigate the heterogeneous catalytic ozonation process in order to exploit a prospective advanced treatment technique for coal gasification wastewater.Ceramic honeycomb?CH?catalytic ozonation can efficiently degrade 4-Meq and improve the mineralization efficiency with increased utilization efficiency of ozone.The removal efficiency of CH catalytic ozonation is 1.2 times as that of ozonation under the same reaction conditions?initial pH=7,catalyst dosage 116.9 g/L?after reaction for 60 min,and a 4%increase of COD removal is obtained in catalytic ozonation process compared to ozonation.Alkaline condition can significantly promote catalytic efficiency.H₂O₂ is introduced to the CH catalytic ozonation,inducing a synergistic effect to produce more free hydroxyl radicals.The removal efficiency of CH catalytic ozonation with H₂O₂ is 1.5 times as that of ozonation under the same reaction conditions.Metal modification is employed to improve the surface properties of CH and promote the removal efficiency of 4-Meq.The specific surface areas of Mg/CH and Cu/CH are 2.2 times and 3 times as that of CH,respectively,and the pore volumes of Mg/CH and Cu/CH also are increased apparently compared with CH.CO2-TPD experiments indicate that more basic sites are generated on the surface of Mg/CH than that of CH,promoting the generation of free hydroxyl radicals and adsorption of acidic intermediates.The mineralization efficiency is therefore increased to 2.5 times as that of CH catalytic ozonation.Fluorine modification is another effective approach to improve the catalytic activity of CH.TA-PL and TBA experiments reveal that F/CH catalytic ozonation follows hydroxyl radical mechanism.Acid sites increased on F/CH surface are proved with NH3-TPD experiments.More rough surface and higher expose of active acid sites of F/CH are responsible for the increased removal efficiency.The mineralization of 4-Meq by F/CH catalytic ozonation is 2.3 times as that of CH catalytic ozonation.The nitrogen element in 4-Meq are converted to ammonia nitrogen,nitrate nitrogen,and organic nitrogen during catalytic ozonation.The presence of active sites and unsaturated bonds on the surface of catalyst contribute to the formation of CH-OH structure,which is beneficial to the decomposition of ozone and generation of free radicals.Seven main intermediates are determined by LC-MS and GC-MS.Combined with DFT calculation it is clear that 4-Meq degrades gradually under the attack of ozone or free radicals by the process of demethylation,benzene ring opening and pyridine opening.Compared with ozonation,the addition of catalysts can significantly enhance the removal efficiency of 4-Meq.The CH catalytic ozonation in the presence of H₂O₂ or with modified catalysts like Cu/CH,Mg/CH and F/CH can further improve the removal and mineralization efficiency.Catalytic ozonation with modified CH is proved to be an effective approach for quinoline degradation,which is a new technical route for coal gasification wastewater treatment.