Industrial-use VOx-based catalysts usually have a higher active temperature window (>250-300℃),which becomes a“bottleneck”for the practical application of PCDD/Fs catalytic degradation technology.In this work,VO...Industrial-use VOx-based catalysts usually have a higher active temperature window (>250-300℃),which becomes a“bottleneck”for the practical application of PCDD/Fs catalytic degradation technology.In this work,VO_(x)-FeO_(x)/TiO_(2) catalyst prepared via mechanochemically method was investigated for the catalytic removal of PCDD/Fs.The removal efficiency of 1,2-DCBz,pure PCDD/Fs gas generated in the lab,PCDD/Fs from actual fue gas,long-term were studied,and the degradation mechanism was explored using FTIR and TOFMS.The degradation efficiency of 1,2-DCBz and PCDD/Fs on VO_(x)-FeO_(x)/TiO_(2) were higher than that of VO_(x)/TiO_(2)catalyst,and the optimal FeOx addition ratio was 3 wt.%.The characterization results show that the addition of FeOx can effectively improve the pore structure,surface acidity,and VOx dispersion of the catalyst,thus contributing to increasing the V^(5+)content and surface-active oxygen,which is conducive to the improvement of adsorption and redox performance of the catalyst.Under the actual MSWI (municipal solid waste incineration)fue gas,the PCDD/Fs removal efficiency over VTi-3Fe-MC maintained long-term stability,higher than 85%for 240 min.This result was not significantly reduced compared with the data obtained in the laboratory.According to the analysis results of intermediate products by FTIR and GC-TOFMS,it can be inferred that the epoxidation fracture of benzene ring is the rate-limiting step of dioxin catalytic degradation reaction.This work gives an in-depth view into the PCDD/Fs removal over VO_(x)-FeO_(x)/TiO_(2) catalysts and could provide guidelines for the rational design of reliable catalysts for industrial applications.展开更多
For the first time in P. R. China, six locations were investigated regarding the impact of poloychlorinated dibenzo-p-dioxins (PCDs) and polychlorinated dibenzofurans (PCDFs) in contaminated sediments and soils in the...For the first time in P. R. China, six locations were investigated regarding the impact of poloychlorinated dibenzo-p-dioxins (PCDs) and polychlorinated dibenzofurans (PCDFs) in contaminated sediments and soils in the Ya-Er Lake area . Total concentrations of PCDDs from 70 to 1.6 ×105 ng/kg dw ,median 7.9×104 ng/kg dw and of PCDFs from 1.8 to 1.8 ×104ng/kg dw ,median 9.2 ×103 ng/kg dw were measured . The internaional toxic equivalents (I-TEQ) varied from 0.14 to 8.1×10 2 ng/kg dw,median 4.1×102 ng/kg dw The PCDDs pattern showed that the concentration of OCDD was significantly higher than that of the low chlorinated congeners . The results indicated that parts of Ya-Er Lake are heavily pollutad by there chiorinated compounds. Comparison of our results with the pattern of sediments showed significant differences . The asults are of special importance bocause the pollution that affected Ya-Er Lake may spread to agricultural land and the Changjiang River.展开更多
The graphite electrode sludge was sampled from a huge chloralkali plant in central China. The total level of PCDD/F was found as high as 378.85 ng/kg sludge (dry weight). The patterns of PCDD/F in each homologue indic...The graphite electrode sludge was sampled from a huge chloralkali plant in central China. The total level of PCDD/F was found as high as 378.85 ng/kg sludge (dry weight). The patterns of PCDD/F in each homologue indicated the predominance of tetra- to octa-chlorinated PCDFs. Furthermore, the toxic 2,3,7,8-substituted PCDFs constituted over 80% of the total PCDFs in the sludge and the corresponding PCDDs were only at 15 |ig/kg level. The calculated value of the international toxic equivalence (I-TEQ) in sludge was 21.65 (ig/kg sludge (dry weight). This typical 'dioxin chloralkali pattern' was apparently identified in the sediments near the effluent outlet of the chloralkali plant.展开更多
In this study,the formation mechanism and removal efficiency of polychlorinated dibenzo-p-dioxins, dibenzofurans（PCDD/Fs） achieved with bag filter（BF） in an electric arc furnace（EAF） in Taiwan is evaluated via i...In this study,the formation mechanism and removal efficiency of polychlorinated dibenzo-p-dioxins, dibenzofurans（PCDD/Fs） achieved with bag filter（BF） in an electric arc furnace（EAF） in Taiwan is evaluated via intensive stack sampling and analysis.The results indicate that the PCDD/F concentration measured in the stack gas of the EAF investigated was 0.16 ng I-TEQ/m1,which was significantly lower than the PCDD/F emission limit（0.5 ng I-TEQ/m;） set for existing EAFs in Taiwan.Due to the low operating temperature（<60℃） of the BF adopted by the EAF investigated,76%of total toxicity PCDD/Fs could be removed from the flue gas stream. In addition,the partitioning of PCDD/Fs between vapor and solid phase at different locations in EAF did not change significantly,while a reduction of solid-phase PCDD/Fs was observed at the outlet of BF.As the chlorination level of PCDD/Fs congener increases,the vapor pressure of PCDD/F congener decreases,resulting in the increase of PCDD/Fs existing in solid phase.Hence,the removal efficiencies of highly chlorinated congeners were significantly higher than that of lowly chlorinated congeners.PCDFs accounted for more than 85%of the TEQ in flue gas of the EAF investigated,among them 2,3,4,7,8-PeCDF（> 43%） was of the highest contribution.Overall,2,3,7,8-TCDD,2,3,7,8-TCDF and 2,3,4,7,8-PeCDF can serve as the unique congeners in the flue gas of the stainless steel EAF process.展开更多
At combustion of hospital waste numerous harmful pollutants were formed inclusive persistent PCDD/F （polychlorinated dibenzodioxines and dibenzofuranes） compounds. To eliminate these substances an existing incinerat...At combustion of hospital waste numerous harmful pollutants were formed inclusive persistent PCDD/F （polychlorinated dibenzodioxines and dibenzofuranes） compounds. To eliminate these substances an existing incinerator consisting of the furnace heat exchanger with flue gas cleaning was used. This incinerator had a capacity of 250 kg of waste per hour. Elimination od acid gases was executed by dosing of solid sorbents （calcium hydrate and bicarbonate） at two points of the waste gases duct. Local temperatures of waste gases at these two points were different. Sorbents were dosed at different distances from the textile filter by which ash and sorbent were separated from the stream of waste gases. By this arrangement it was possible to alter the residence time of sorbents in waste gases. The effect of addition of bicarbonate on dechlorination and desulphurisation was also studied. The executed experiments indicated that at dosing of calcium hydroxide into waste gases at higher temperatures sulphur oxides reacted preferably to hydrogen chloride. The strong effect of HCI in waste gases on formation of PCDD/F was proved. For sufficient elimination of persistent compounds from waste gases it was necessary to add beside calcium hydrate also active carbon. Two types of sorbents based on carbon were tested, namely Norit and Chezacarb B. Both were macroporous. Chezacarb B was carbon black from the process of hydrogen production by partial oxidation. Efficiency of both sorbents for removal of PCDD/F was similar.展开更多
基金supported by the Natural Science Foundation of Zhejiang Province (No. LY21E060007)the National Natural Science Foundation of China (No. 52006191)。
文摘Industrial-use VOx-based catalysts usually have a higher active temperature window (>250-300℃),which becomes a“bottleneck”for the practical application of PCDD/Fs catalytic degradation technology.In this work,VO_(x)-FeO_(x)/TiO_(2) catalyst prepared via mechanochemically method was investigated for the catalytic removal of PCDD/Fs.The removal efficiency of 1,2-DCBz,pure PCDD/Fs gas generated in the lab,PCDD/Fs from actual fue gas,long-term were studied,and the degradation mechanism was explored using FTIR and TOFMS.The degradation efficiency of 1,2-DCBz and PCDD/Fs on VO_(x)-FeO_(x)/TiO_(2) were higher than that of VO_(x)/TiO_(2)catalyst,and the optimal FeOx addition ratio was 3 wt.%.The characterization results show that the addition of FeOx can effectively improve the pore structure,surface acidity,and VOx dispersion of the catalyst,thus contributing to increasing the V^(5+)content and surface-active oxygen,which is conducive to the improvement of adsorption and redox performance of the catalyst.Under the actual MSWI (municipal solid waste incineration)fue gas,the PCDD/Fs removal efficiency over VTi-3Fe-MC maintained long-term stability,higher than 85%for 240 min.This result was not significantly reduced compared with the data obtained in the laboratory.According to the analysis results of intermediate products by FTIR and GC-TOFMS,it can be inferred that the epoxidation fracture of benzene ring is the rate-limiting step of dioxin catalytic degradation reaction.This work gives an in-depth view into the PCDD/Fs removal over VO_(x)-FeO_(x)/TiO_(2) catalysts and could provide guidelines for the rational design of reliable catalysts for industrial applications.
文摘For the first time in P. R. China, six locations were investigated regarding the impact of poloychlorinated dibenzo-p-dioxins (PCDs) and polychlorinated dibenzofurans (PCDFs) in contaminated sediments and soils in the Ya-Er Lake area . Total concentrations of PCDDs from 70 to 1.6 ×105 ng/kg dw ,median 7.9×104 ng/kg dw and of PCDFs from 1.8 to 1.8 ×104ng/kg dw ,median 9.2 ×103 ng/kg dw were measured . The internaional toxic equivalents (I-TEQ) varied from 0.14 to 8.1×10 2 ng/kg dw,median 4.1×102 ng/kg dw The PCDDs pattern showed that the concentration of OCDD was significantly higher than that of the low chlorinated congeners . The results indicated that parts of Ya-Er Lake are heavily pollutad by there chiorinated compounds. Comparison of our results with the pattern of sediments showed significant differences . The asults are of special importance bocause the pollution that affected Ya-Er Lake may spread to agricultural land and the Changjiang River.
文摘The graphite electrode sludge was sampled from a huge chloralkali plant in central China. The total level of PCDD/F was found as high as 378.85 ng/kg sludge (dry weight). The patterns of PCDD/F in each homologue indicated the predominance of tetra- to octa-chlorinated PCDFs. Furthermore, the toxic 2,3,7,8-substituted PCDFs constituted over 80% of the total PCDFs in the sludge and the corresponding PCDDs were only at 15 |ig/kg level. The calculated value of the international toxic equivalence (I-TEQ) in sludge was 21.65 (ig/kg sludge (dry weight). This typical 'dioxin chloralkali pattern' was apparently identified in the sediments near the effluent outlet of the chloralkali plant.
文摘In this study,the formation mechanism and removal efficiency of polychlorinated dibenzo-p-dioxins, dibenzofurans（PCDD/Fs） achieved with bag filter（BF） in an electric arc furnace（EAF） in Taiwan is evaluated via intensive stack sampling and analysis.The results indicate that the PCDD/F concentration measured in the stack gas of the EAF investigated was 0.16 ng I-TEQ/m1,which was significantly lower than the PCDD/F emission limit（0.5 ng I-TEQ/m;） set for existing EAFs in Taiwan.Due to the low operating temperature（<60℃） of the BF adopted by the EAF investigated,76%of total toxicity PCDD/Fs could be removed from the flue gas stream. In addition,the partitioning of PCDD/Fs between vapor and solid phase at different locations in EAF did not change significantly,while a reduction of solid-phase PCDD/Fs was observed at the outlet of BF.As the chlorination level of PCDD/Fs congener increases,the vapor pressure of PCDD/F congener decreases,resulting in the increase of PCDD/Fs existing in solid phase.Hence,the removal efficiencies of highly chlorinated congeners were significantly higher than that of lowly chlorinated congeners.PCDFs accounted for more than 85%of the TEQ in flue gas of the EAF investigated,among them 2,3,4,7,8-PeCDF（> 43%） was of the highest contribution.Overall,2,3,7,8-TCDD,2,3,7,8-TCDF and 2,3,4,7,8-PeCDF can serve as the unique congeners in the flue gas of the stainless steel EAF process.
文摘At combustion of hospital waste numerous harmful pollutants were formed inclusive persistent PCDD/F （polychlorinated dibenzodioxines and dibenzofuranes） compounds. To eliminate these substances an existing incinerator consisting of the furnace heat exchanger with flue gas cleaning was used. This incinerator had a capacity of 250 kg of waste per hour. Elimination od acid gases was executed by dosing of solid sorbents （calcium hydrate and bicarbonate） at two points of the waste gases duct. Local temperatures of waste gases at these two points were different. Sorbents were dosed at different distances from the textile filter by which ash and sorbent were separated from the stream of waste gases. By this arrangement it was possible to alter the residence time of sorbents in waste gases. The effect of addition of bicarbonate on dechlorination and desulphurisation was also studied. The executed experiments indicated that at dosing of calcium hydroxide into waste gases at higher temperatures sulphur oxides reacted preferably to hydrogen chloride. The strong effect of HCI in waste gases on formation of PCDD/F was proved. For sufficient elimination of persistent compounds from waste gases it was necessary to add beside calcium hydrate also active carbon. Two types of sorbents based on carbon were tested, namely Norit and Chezacarb B. Both were macroporous. Chezacarb B was carbon black from the process of hydrogen production by partial oxidation. Efficiency of both sorbents for removal of PCDD/F was similar.
