Catalytic destruction vs. adsorption in controlling dioxin emission

Promoting effect of FeOx addition on the mechanochemically prepared vanadium-based catalyst for real PCDD/Fs removal and mechanism insight

Industrial-use VOx-based catalysts usually have a higher active temperature window (> 250-300°C), which becomes a "bottleneck" for the practical application of PCDD/Fs catalytic degradation technology. In this work, VOx-FeOx/TiO2 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 flue 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 VOx-FeOx/TiO2 were higher than that of VOx/TiO2 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 V5+ 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) flue 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 VOx-FeOx/TiO2 catalysts and could provide guidelines for the rational design of reliable catalysts for industrial applications.

Review of thermal treatments for the degradation of dioxins in municipal solid waste incineration fly ash: Proposing a suitable method for large-scale processing

Dioxin degradation is considered essential for the environmentally sound management of municipal solid waste incineration fly ash (MSWIFA). Among the many degradation techniques, thermal treatment has shown good prospects owing to its high efficiency and wide range of applications. Thermal treatment is divided into high-temperature thermal, microwave thermal, hydrothermal, and low-temperature thermal treatments. High-temperature sintering and melting not only have dioxin degradation rates higher than 95 % but also remove volatile heavy metals, although energy consumption is high. High-temperature industrial co-processing effectively solves the problem of energy consumption, but with a low fly ash (FA) mixture, and the process is limited by location. Microwave thermal treatment and hydrothermal treatment are still in the experimental stage and cannot be used for large-scale processing. The dioxin degradation rate of low-temperature thermal treatment can also be stabilized at higher than 95 %. Compared to other methods, low-temperature thermal treatment is less costly and energy consumption with no restriction on location. This review comprehensively compares the current status of the above-mentioned thermal treatment methods and their ability to dispose of MSWIFA, especially the potential for large-scale processing. Then, the respective characteristics, challenges, and application prospects of different thermal treatment methods were discussed. Finally, based on the goal of low carbon and emission reduction, three possible approaches for improvement were proposed to address the challenges of large-scale processing of low-temperature thermal treatment, namely, adding a catalyst, changing the FA fraction, or supplementing with blockers, providing a reasonable development direction for the degradation of dioxins in MSWIFA.