| Recently,significant progress on the control of NOx and SO2 has been made in China,while the regional complex air pollution characterized by high O3 and PM2.5 concentrations has become a vital environmental problem.Volatile organic compounds(VOCs),as an important precursor of O3 and PM2.5,play a key role in the formation of complex air pollution.The source emission profiles of VOCs have become the base for screening out priority control pollutants due to the varieties of VOCs species and atmospheric reaction activity.For the treatment of VOCs,catalytic combustion has been considered as a promising technique owing to its high efficiency,low energy consumption,and superior applicability.It’s of great significance to evaluate the effect of catalytic combustion technology.Taken color steel industry as an example,this paper systematically investigated the generation and treatment of VOCs of the industry from aspects of VOCs source emission profiles and the application performance of several industrial catalysts in the market.Sorbent adsorption and thermal desorption gas chromatography mass spectrometry method was employed to detect the components of VOCs source samples.The results revealed that more than 22 VOCs species were detected in tail gas,including ketones,alcohols,esters,ethers,aromatics and nitrogen-containing substances.Maximum incremental reactivity(MIR)and fractional aerosol coefficients(FAC)potential calculation results showed that,aromatics offered the biggest contribution to the formation of ozone with the oxygenated hydrocarbons offering the rest.And the contributions to the formation of secondary organic aerosols were all generated from aromatics.Isobutanol,isopropyl alcohol,butyl acetate,toluene and dimethylformamide(DMF)were selected to evaluate the catalytic activity of the industrial transition metal catalysts and noble metal catalysts based on the source profiles analysis.The results showed that the T90 of the transition metal catalyst to different VOCs ranged from 196℃ to 270 ℃,and the T90 of noble metal catalysts ranged from 176 ℃ to 420 0C.The degradation efficiency of noble metal catalysts showed a significant difference due to different noble metal contents.The mineralization rate of the two types of catalysts for most VOCs is above 80%,except for DMF,whose mineralization is 60%-70%.In terms of the conversion rate of NO,generated during the decomposition of DMF,the conversion capacity of the transition metal catalyst is stronger than noble metal catalysts,and the conversion rate of NO is 91%at 390.The changes of both the activity of the noble metal catalysts under operation and the by-products were also tracked to evaluate the service life of noble metal catalysts.The degradation activity of industrial noble metal catalysts decreased slowly with the increase of service duration,and the maximal by-products increased accordingly.The T90 of the catalyst decreased from 194 ℃～-298 ℃ to 213 ℃～337℃ after 360 days’service,and the conversion rate of NO is reduced from 61.7%to 55.1%.The decrease of the activities of the noble metal catalysts is attributed to the sintering and sequentially dropping of coating,which could miinish the specific surface area,pore volume and noble metal content.This study develops a research system which uses source emission profiles to understand the characteristics of the exhaust gas followed by screening out suitable catalysts for catalytic combustion treatment.Moreover,this paper can provide an example for source emission profiles analysis and treatment of VOCs of other industries. |
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