脱硝催化剂的失活机理及其再生技术

采用SEM、XRD和XRF对电厂失活脱硝催化剂进行表征,探讨其失活原因和机理。结果表明:电厂脱硝催化剂失活的主要原因是活性组分V的流失及碱金属K、碱土金属Ca和As元素造成的催化剂中毒,烟气中飞灰的沉积也有一定的影响。经吹扫、水洗、酸洗和V负载再生,催化剂的各项物化性质基本恢复,NOx转化率基本达到新鲜催化剂的水平。水洗主要去除催化剂中的碱金属,酸洗主要去除As2O3,负载V补充催化剂活性组分。V再生催化剂在较高温度下的抗硫性能更好。     

SCR脱硝催化剂失活机理研究综述

在烟气脱硝系统中,选择性催化还原催化剂的中毒和再生是广泛关注的问题。从催化剂的烧结、As、Ca、碱金属中毒等方面阐述了SCR脱硝催化剂的失活机理。通过总结催化剂的各种失活机理,可以有针对性地根据锅炉特性、燃料特性以及飞灰的成分进行SCR脱硝系统的优化设计,制定防止选择性催化还原催化剂失活的措施,这对延长催化剂寿命,降低SCR脱硝系统的运行维护费用具有重要意义。     

烟气脱硝低温选择性催化还原金属氧化物催化剂的研究进展

低温选择性催化还原(SCR)技术具有很高的脱硝效率。概述了低温SCR金属氧化物催化剂的制备方法和性能,分析了催化剂的失活原因和再生方法,探讨了催化反应的机理,并介绍了低温SCR技术在工业烟气脱硝中的应用案例。SCR催化剂未来的发展不仅要以低温下的高活性和高选择性为主要目的,还要考虑到催化剂的抗失活性能(如抗硫性和抗水稳定性)和操作温度范围,使其可广泛应用于不同的工况中,以满足我国日益提高的环保要求。     

含Cu-Zn废催化剂的综合利用

含 Cu- Zn催化剂 ,如 Cu/Zn/Al催化剂 ,主要用于合成氨工业、制氢工业的低温变换反应 ,合成甲醇和催化加氢反应。用于合成甲醇时 ,催化剂中 Cu O的质量分数为 45 %～ 65 % ,Zn O的质量分数为 2 5 %～ 45 % ;用于低温变换反应时 ,Cu O的质量分数为30 %～ 40 % ,Zn O的质量分数为 40 %～ 5 0 %。由于在使用过程中都是使用还原状态的铜 ,因此造成催化剂失活的原因具有一些共同的特点 ,如硫中毒、卤素中毒、热老化等。这使得此类催化剂寿命短 ,再生困难 ,因而产生大量的失活催化剂。如果能较好地处理和利用这些废催化剂 ,可充分利用资源 ,…     

脱除SO2活性炭的再生方法

分别用溶剂和气体对脱除SO2后失活的活性炭进行了再生。在固定床反应器上考察了再生后活性炭的脱硫性能。实验结果表明：用溶剂再生时,质量分数为60％的HNO3溶液的再生效果最好,活性炭的再生率达到80％以上。用气体再生时,400℃左右时的再生效果最好,活性炭的再生率达到70％以上。再生后活性炭的比表面积和pH是衡量活性炭再生效果的重要参数。在实际脱硫生产中,用H2O对失活活性炭进行反复洗涤再生,是一种经济、实用的方法,活性炭的再生率达60％以上。     

SCR烟气脱硝钛载催化剂的研究进展

综述了SCR烟气脱硝钛载催化剂的研究进行,重点介绍了国内外TiO2载体原料、钒基活性组分、非钒基活性组分以及催化剂失活原因等方面的研究进展。采用低成本工业级TiO2或偏钛酸作为载体,可开发出催化活性温度低、高抗硫中毒和稳定性高的SCR脱硝催化剂,这对我国NOx污染的治理具有重要意义。     

燃煤锅炉脱硝催化剂再生技术研究进展

简述了脱硝催化剂再生的市场背景,介绍了脱硝催化剂再生的方法以及催化剂活性的评价方法。综合分析了目前脱硝催化剂再生技术的原理及有效性,以中毒原因为线索介绍了目前主流的脱硝催化剂再生方案。     

低温NH_3-SCR脱硝催化剂的研究现状与进展

高效催化剂的研制与开发是低温氨气选择性催化还原(NH_3-SCR)脱硝技术的核心。从活性组分(单一氧化物型、复合氧化物型)和载体(金属氧化物、碳基材料、分子筛)两方面详细介绍了低温NH_3-SCR催化剂,总结了其研究现状,并讨论了其抗水、抗硫性能及失活原因。指出在保证催化剂具有较高活性的同时提高其抗水、抗硫性能,是低温NH_3-SCR催化剂未来研究的重点。     

粉状废活性炭再生利用

本文以酸碱化学处理为基础,采用浮选法再生净化葡萄糖母液失活的粉状废活性炭。试验结果表明,此法工艺过程简单,操作简便,再生炭质量较好,成本低,适于中小型葡萄糖厂就地再生。     

TiO2光催化法降解空气中的苯

以紫外灯为光源,采用P25型TiO₂光催化降解空气中的苯。为保证TiO₂的高分散性、增加其在铝板上的附着牢固性,加入了聚乙烯醇和硅溶胶,这在一定程度上增加了催化剂对光能的利用率,但也造成了催化剂活性的降低。实验结果表明：苯的光催化降解反应属一级动力学反应;苯降解率随初始苯质量浓度的增加而减小,随反应面积的增大而增大,在253.7 nm波长光源下的降解效果优于365.0 nm;苯降解所得的气相产物主要为CO₂和CO;随使用次数的增加,催化剂失活现象逐步显现;双氧水对催化剂的再生效果优于去离子水。     

Distribution of Cd,Ck, Pb and Zn in Soil and Vegetation Compartments in Stands of Five Boreal Tree Species in N.E. Sweden

Concentrations and total quantity of cadmium (Cd), cupper (Cu),lead (Pb) and zink (Zn) were determined in biomass and soil compartments in a replicated tree species experiment with 27-yr-old stands growing on former farmland in N.E. Sweden. Sequentialextractions of soil samples were performed in order to estimate the exchangeable and an organically bound fraction of each element. The tree species included were Picea abies (L.)H. Karst., Pinus sylvestris L., Pinus contorta Dougl., Larix sibirica Ledeb., and Betula pendula Roth.Tree species influenced the rate of removal of Cu, Pb and Zn incase of stemwood harvesting, and of Cd, Cu and Zn in the case ofwhole-tree harvesting. B. pendula and P. abies had higher quantities and average concentrations of Zn in the biomass. For all species, >50% of the Zn in the stems was found in the bark. P. abies and L. sibirica had higher quantities of Cu in the biomass than the other species.P. abies and P. contorta had high quantities of Cd inthe biomass in relation to the other species. Branches and stembark contained high concentrations of Cd and Pb in relation to foliage and stemwood. Dead branches had especially high concentrations of Pb. The high accumulation rate of Zn in thebiomass of B. pendula was related to a low exchangeable amount of Zn in the A horizon. In the superficial centimeters ofthe A horizon, a depletion similar to that found for Zn was detected for Cu, whereas for Cd and Pb, no correlations were found between quantities of elements in the trees and element pools in the soil.     

Starch-plastic materials—Preparation,physical properties,and biodegradability (a review of recent USDA research)

Recent starch-plastic research at the National Center for Agricultural Utilization Research is reviewed and related worldwide efforts are noted. Properties of starch that influence its formulation and performance in plastics are discussed. Methods are given for preparation of starch-poly(methyl acrylate) graft copolymer, starch-poly(ethylene-co-acrylic acid), and starch-poly(ethylene-co-acrylic acid)-polyethylene plastics. Their physical properties are discussed, as is degradability by enzymes or amylolytic organisms from soil, ponds, and streams.The mention of firm names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over other firms or similar products not mentioned.     

四氮唑废水处理工艺设计

高浓度、高盐分的四氮唑生产废水通过三效蒸发浓缩,馏出液经铁炭氧微电解和混凝预处理,再采用水解酸化一接触氧化一反应二沉主体组合工艺进行处理。研究了该工艺所需构筑物和设备的设计与选型。该工艺在正常运行条件下,处理后出水pH6～9,COD 302mg／L,BOD5 108mg／L,SS30mg／L,色度36倍,水质达到GB8978--1996（污水综合排放标准》三级标准。     

Application of Cellulose Microfibrils in Polymer Nanocomposites

Cellulose microfibrils obtained by the acid hydrolysis of cellulose fibers were added at low concentrations (2–10% w/w) to polymer gels and films as reinforcing agents. Significant changes in mechanical properties, especially maximum load and tensile strength, were obtained for fibrils derived from several cellulosic sources, including cotton, softwood, and bacterial cellulose. For extruded starch plastics, the addition of cotton-derived microfibrils at 10.3% (w/w) concentration increased Young’s modulus by 5-fold relative to a control sample with no cellulose reinforcement. Preliminary data suggests that shear alignment significantly improves tensile strength. Addition of microfibrils does not always change mechanical properties in a predictable direction. Whereas tensile strength and modulus were shown to increase during addition of microfibrils to an extruded starch thermoplastic and a cast latex film, these parameters decreased when microfibrils were added to a starch–pectin blend, implying that complex interactions are involved in the application of these reinforcing agents.     

Bioassessment of silvicultural impacts in streams and wetlands of the Eastern United States

Bioassessment is a useful tool to determine the impact of logging practices on the biological integrity of streams and wetlands. Measuring biota directly has an intuitive appeal for impact assessment, and biota can be superior indicators to physical or chemical characteristics because they can reflect cumulative impacts over time. Logging can affect stream and wetland biota by increasing sedimentation rates, altering hydrologic, thermal, and chemical regimes, and changing the base of food webs. Biotic impacts of logging on streams compared to wetlands probably differ, and in this paper we review some of those differences. In streams, invertebrates, fishes, amphibians, algae, and macrophytes have been used as indicators of logging impacts. In wetlands, bioassessment is just beginning to be used, and plants and birds are the most promising indicator taxa. Various best management practices (BMPs) have been developed to reduce the impacts of logging on stream and wetland biota, and we review quantitative studies that have evaluated the efficacy of some of these techniques in streams and wetlands in the eastern United States. Remarkably few studies that address the overall efficacy of BMPs in limiting biotic changes in streams and wetlands after BMP implementation have been published in scientific journals, although some work exists in reports or is unpublished. We review these works, and compile conclusions about BMP efficacy for biota from this body of research.     

Characterization of air emissions and residual ash from open burning of electronic wastes during simulated rudimentary recycling operations

Air emissions and residual ash samples were collected and analyzed during experiments of open, uncontrolled combustion of electronic waste (e-waste), simulating practices associated with rudimentary e-waste recycling operations. Circuit boards and insulated wires were handled separately to simulate processes associated with metal recovery. The average emissions of polychlorinated dibenzodioxins and dibenzofurans (PCDD/PCDFs) were 92 ng toxic equivalency (TEQ)/kg [n = 2, relative standard deviation (RSD) = 98%] and 11 900 ng TEQ/kg (n = 3, RSD = 50%) of the initial mass of the circuit boards and insulated wire, respectively. The value for the insulated wire is about 100 times higher than that for backyard barrel burning of domestic waste. The emission concentrations of polybrominated dibenzodioxins and dibenzofurans (PBDD/PBDFs) from the combustion of circuit boards were 100 times higher than for their polychlorinated counterparts. Particulate matter (PM) sampling of the fly ash emissions indicated PM emission factors of approximately 15 and 17 g/kg of the initial mass for the circuit boards and insulated wire, respectively. Fly ash samples from both types of e-waste contained considerable amounts of several metallic elements and halogens; lead concentrations were more than 200 times the United States regulatory limits for municipal waste combustors and 20 times those for secondary lead smelters. Leaching tests of the residual bottom ash showed that lead concentrations exceeded U.S. Environmental Protection Agency landfill limits, designating this ash as a hazardous waste.     

Does Soil Acidification Affect Spruce Needle Chemical Composition and Tree Growth?

In 1994, a large survey of soil chemistry was undertaken in thecounty of Värmland in central Sweden (Lundström et al., 1998).The southern part of the county was affected by soilacidification whereas there were no such indications in thenorthern part. To investigate the influence of soil chemistryon the trees at the specific sites, the survey was continued byan analysis of needle chemistry (Norway spruce) which wasundertaken at 150 of the 180 sites, and of tree growth at 65 ofthe 180 sites. Growth was expressed as a ratio between expectedgrowth, estimated with a national, empirical growth model, andthe growth observed in the field. In statistical analyses,using rank correlation, PCA and PLS, there were only weakindications of an influence of soil chemistry on needlechemistry and on tree growth. A moderate correlation betweennitrogen and sulphur in needles was found, which wasinterpreted as an effect of deposition and of processes in thetree canopy. No obvious regional pattern of the growth ratiowas found, in contrast to the clear pattern of soilacidification. The statistical analysis could not with anycertainty point out any of the soil chemistry variables asespecially important for the tree growth ratio.     

Solubility and Potential Mobility of Heavy Metals in Two Contaminated Urban Soils from Stockholm,Sweden

The solubility and potential mobility of heavy metals (Cd, Cu,Hg, Pb and Zn) in two urban soils were studied by sequential andleaching extractions (rainwater). Compared to rural (arable) soils on similar parent material, the urban soils were highlycontaminated with Hg and Pb and to a lesser extent also with Cd,Cu and Zn. Metal concentrations in rainwater leachates were related to sequential extractions and metal levels reported fromStockholm groundwater. Cadmium and Zn in the soils were mainly recovered in easily extractable fractions, whereas Cu and Pb were complex bound. Concentrations of Pb in the residual fractionwere between two- and eightfold those in arable soils, indicatingthat the sequential extraction scheme did not reflect the solidphases affected by anthropogenic inputs. Cadmium and Zn conc. inthe rainwater leachates were within the range detected in Stockholm groundwater, while Cu and Pb conc. were higher, whichsuggests that Cu and Pb released from the surface soil were immobilised in deeper soil layers. In a soil highly contaminatedwith Hg, the Hg conc. in the leachate was above the median concentration, but still 50 times lower than the max concentration found in groundwater, indicating the possibilityof other sources. In conclusion, it proved difficult to quantitatively predict the mobility of metals in soils by sequential extractions.     

High Immobilization of NH4+ in Danish Heath Soil Related to Succession,Soil and Nutrients: Implications for Critical Loads of N

During recent decades heathlands havechanged into grasslands in regions with high atmosphericnitrogen deposition. In regions with intermediatedeposition level (e.g., Denmark) changes have been lesspronounced which may be due to delay or decrease inresponse of the ecosystem. The mor layer (O horizon) mayplay an important role for this delay due to high sinkstrength for N. In this study, the capacity for netNH₄ ⁺ immobilization and mineralization wasstudied during short- and long-term incubations (2–36 days)of mor samples from Danish dry inland heaths. High short-term capacity for net NH₄ ⁺ immobilization wasfound to be a general characteristic of Danish heath morlayers both under heather (Calluna vulgaris) andcrowberry (Empetrum nigrum ssp nigrum), the latterdominating late stages in heathland succession. The netNH₄ ⁺ immobilization was higher under youngcompared to old or dead vegetation, and higher on lessnutrient poor soils than on extremely nutrient poor soils.The addition of N, P and C stimulated CO₂ productionand net NH₄ ⁺ immobilization, but not net Nmineralization. The immobilization of ¹⁵NH₄ ⁺caused release of dissolved organic N, increased N anddecreased C/N ratio in the microbial biomass, and indicatedgrowth of microorganisms with other metabolic abilitiesthan the indigenous population. No evidence was obtained ofstabilization of immobilized ¹⁵NH₄ ⁺ intosoil organic matter during the experiment. On background ofthe results and current knowledge it was concluded that therecognition of the high capacity for net NH₄ ⁺immobilization in mor layers does not allow for a raiseof critical loads for N for northern dry inland heaths.     

Biodegradation of Injection Molded Starch-Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) Blends in a Natural Compost Environment

Injection molded specimens were prepared by blending poly (hydroxybutyrate-co-valerate) (PHBV) with cornstarch. Blended formulations incorporated 30% or 50% starch in the presence or absence of poly-(ethylene oxide) (PEO), which enhances the adherence of starch granules to PHBV. These formulations were evaluated for their biodegradability in natural compost by measuring changes in physical and chemical properties over a period of 125 days. The degradation of plastic material, as evidenced by weight loss and deterioration in tensile properties, correlated with the amount of starch present in the blends (neat PHBV < 30% starch < 50% starch). Incorporation of PEO into starch-PHBV blends had little or no effect on the rate of weight loss. Starch in blends degraded faster than PHBV and it accelerated PHBV degradation. Also, PHBV did not retard starch degradation. After 125 days of exposure to compost, neat PHBV lost 7% of its weight (0.056% weight loss/day), while the PHBV component of a 50% starch blend lost 41% of its weight (0.328% weight loss/day). PHB and PHV moieties within the copolymer degraded at similar rates, regardless of the presence of starch, as determined by ¹H-NMR spectroscopy. GPC analyses revealed that, while the number average molecular weight (Mn) of PHBV in all exposed samples decreased, there was no significant difference in this decrease between neat PHBV as opposed to PHBV blended with starch. SEM showed homogeneously distributed starch granules embedded in a PHBV matrix, typical of a filler material. Starch granules were rapidly depleted during exposure to compost, increasing the surface area of the PHBV matrix.