NiB2O4 (B = Mn or Co) catalysts for NH3-SCR of NOx at low-temperature in microwave field

● Microwave-assisted catalytic NH₃-SCR reaction over spinel oxides is carried out. ● SCR reaction temperature is tremendously lowered in microwave field. ● NO conversion of NiMn₂O₄ is highly up to 90.6% at 70°C under microwave heating. Microwave-assisted selective catalytic reduction of nitrogen oxides (NO_x) was investigated over Ni-based metal oxides. The NiMn₂O₄ and NiCo₂O₄ catalysts were synthesized by the co-precipitation method and their activities were evaluated as potential candidate catalysts for low-temperature NH₃-SCR in a microwave field. The physicochemical properties and structures of the catalysts were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), N₂-physisorption, NO adsorption-desorption in the microwave field, H₂-temperature programmed reduction (H₂-TPR) and NH₃-temperature programmed desorption (NH₃-TPD). The results verified that microwave radiation reduced the reaction temperature required for NH₃-SCR compared to conventional heating, which needed less energy. For the NiMn₂O₄ catalyst, the catalytic efficiency exceeded 90% at 70 °C and reached 96.8% at 110 °C in the microwave field. Meanwhile, the NiMn₂O₄ also exhibited excellent low-temperature NH₃-SCR reaction performance under conventional heating conditions, which is due to the high BET specific surface area, more suitable redox property, good NO adsorption-desorption in the microwave field and rich acidic sites.     

700 MW燃煤机组SCR运行适应性改造分析

目前大型燃煤电厂普遍采用选择性催化还原法脱硝工艺,其应用过程中存在由于机组调峰导致投运率不高的普遍问题。从脱硝反应过程和催化剂特性两方面出发,分析造成上述问题的原因,并根据省煤器结构及其换热特性,提出了两种不同的改进方案。通过对比择优,选择增设省煤器烟气旁路的改进措施,并提出相应的控制策略、安全性评估及其注意事项,可为同类型机组提供借鉴。     

Assessment of the emission of PCDD/Fs and dioxin-like PCBs from an industrial area over a nearby town using a selective wind direction sampling device

The development of new sampling devices or strategies to assess the concentration of persistent organic pollutants (POPs) in the environment has increased in the last two decades. In this study, a selective sampling device was used to evaluate the impact of potential local sources of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) and dioxin-like polychlorinated biphenyl (dl-PCBs) emissions on the ambient air levels of such compounds in a town near an important industrial estate. Average concentrations of target compounds of up to 2.5 times for PCDD/Fs and 2 times for dl-PCBs were found to come from the industrial state confirming this area as the main responsible for the majority of such compounds reaching the town.This finding was supported by a PCDD/F and dl-PCB sample profile analysis and a principal component analysis (PCA), which established a direct link between the dioxin-like compounds found in the samples collected in the town and their source.     

Selective removal of diclofenac from contaminated water using molecularly imprinted polymer microspheres

A molecularly imprinted polymer (MIP) was synthesized by precipitation polymerization using diclofenac (DFC) as a template. Binding characteristics of the MIP were evaluated using equilibrium binding experiments. Compared to the non-imprinted polymer (NIP), the MIP showed an outstanding affinity towards DFC in an aqueous solution with a binding site capacity (Q_max) of 324.8 mg/g and a dissociation constant (K_d) of 3.99 mg/L. The feasibility of removing DFC from natural water by the MIP was demonstrated by using river water spiked with DFC. Effects of pH and humic acid on the selectivity and adsorption capacity of MIP were evaluated in detail. MIP had better selectivity and higher adsorption efficiency for DFC as compared to that of powdered activated carbon (PAC). In addition, MIP reusability was demonstrated for at least 12 repeated cycles without significant loss in performance, which is a definite advantage over single-use activated carbon.     

Kinetic and 2D reactor modeling for simulation of the catalytic reduction of NOx in the monolith honeycomb reactor

Emission of NO_x is of primary environmental concern in the oil sands industry. Selective catalytic reduction (SCR) is one of the best NO_x reduction technologies. The present study discusses the testing of a mechanistic kinetic model for the SCR of NO_x to describe the kinetics of V₂O₅/TiO₂ catalysis at atmospheric pressure and a temperature of 623 K in a monolith honeycomb reactor. The modeling results impart insight into the significance of the diffusion with reaction steps and guidance for optimal monolith design for SCR. The validated expression would predict the conversion performance of the catalysts for different values of temperature inlet and ammonia concentration. A good agreement between experimental and model results has been obtained. A heterogeneous numerical model consisting of coupled mass and momentum balance equations was solved using the finite elements method without neglecting the axial dispersion term. The operating range for the catalyst relies on the NO conversion and emission. The optimum operating range for the best performance of the reactor is discussed.     

Bio-economic evaluation of implementing trawl fishing gear with different selectivity

The paper develops a biological-economic evaluation tool to analyse the consequences for trawl fishers of implementing more selective fishing technologies. This is done by merging a dynamic biological population model and an economic cost–benefit evaluation framework to describe the consequences for the fish stocks, fishermen and society. The bio-economic evaluation is applied to the case of the Danish trawl fishery in Kattegat and Skagerrak, which experiences a high level of discards and bycatches of several species. Four different kinds of selectivity scenarios are evaluated in comparison with a baseline. The results from the evaluation are indicators for the consequences on ecological and economic levels. The results show that implementation of different selective fishing gear in the Kattegat and Skagerrak mixed trawl fisheries generally implies a trade off over time between rebuilding the stocks and economic loss. Moreover, the analysis shows that implementation of more selective gear is not always beneficial.     

国内外炼厂气脱硫技术现状与建议

为降低能耗、操作费用和投资，传统的胺法已有巨大的改进，８０年代中期以来，ＭＤＥＡ工艺在国内外推广应用的成绩显著，已从发挥其选吸优势向利用其节能降耗优势扩展。目前，ＭＤＥＡ工艺已成为气体尤其是炼厂气脱硫脱碳的主体工艺之一。阐述国内外炼厂气脱硫技术的现状与建议     

Chorionic villus sampling and selective termination of a chromosomally abnormal fetus in a triplet pregnancy

Transabdominal chorionic villus sampling (CVS) was performed on a patient with a triplet pregnancy. The karyotypes were as follows: 46,XX; 46,XY; and 46,XY/47,XXY. Selective termination was done on the affected fetus successfully by intrathoracic potassium chloride (KCI) injection. Amniocentesis which was performed at the same time confirmed the CVS results, showing the same mosaic findings. Following the procedure, the pregnancy proceeded uneventfully and two normal newborns were delivered at term.     

Effect of silica additive on the thermal stability of catalysts for NOx abatement

The aim of the plesent investigation was to study the effect of SiO₂ addition on the thermal deactivation of V₂O₅/WO₃/TiO₂ catalysts used for NOx pollution abatement. The results suggest that the degradation of the catalytic properties is strongly correlated to the structural ageing which is, in turn, mainly related to the anatase–rutile phase transformation and to the WO₃ phase segregation. The addition of SiO₂ strongly influences the temperature at which these phenomena occur. In fact, it was found that the introduction of this oxide stabilizes the material, retarding the collapse of surface area, and increases the temperature of the anatase to rutile phase transition.     

Role of NO in Hg oxidation over a commercial selective catalytic reduction catalyst V2O5–WO3/TiO2

Experiments were conducted in a fixed-bed reactor that contained a commercial catalyst, V₂O₅–WO₃/TiO₂, to investigate mercury oxidation in the presence of NO and O₂. Mercury oxidation was improved by NO, and the efficiency was increased by simultaneously adding NO and O₂. With NO and O₂ pretreatment at 350°C, the catalyst exhibited higher catalytic activity for Hg⁰ oxidation, whereas NO pretreatment did not exert a noticeable effect. Decreasing the reaction temperature boosted the performance of the catalyst treated with NO and O₂. Although NO promoted Hg⁰ oxidation at the very beginning, excessive NO counteracted this effect. The results show that NO plays different roles in Hg⁰ oxidation; NO in the gaseous phase may directly react with the adsorbed Hg⁰, but excessive NO hinders Hg⁰ adsorption. The adsorbed NO was converted into active nitrogen species (e.g., NO₂) with oxygen, which facilitated the adsorption and oxidation of Hg⁰. Hg⁰ was oxidized by NO mainly by the Eley–Rideal mechanism. The Hg⁰ temperature-programmed desorption experiment showed that weakly adsorbed mercury species were converted to strongly bound ones in the presence of NO and O₂.