Reaction Kinetics of Immobilized-Cell Denitrification. I: Background and Model Development

A simplified, quasi-steady-state model has been formulated for groundwater denitrification using immobilized cells. The model takes into account the diffusion-limited penetration of nitrate and nitrite into the immobilized-cell biocatalyst particle, uniform intraparticle cell density, equivalent slab geometry for the spherical particle, zero-order intrinsic reaction kinetics of the immobilized cells, sequential reduction of nitrate to nitrite and nitrite to dinitrogen within the particle, no inhibition of the sequential reactions by either nitrate or nitrite, and ideal plug flow conditions in the bioreactor. As a result, the reaction in the bulk fluid of the plug-flow bioreactor can be described by a half-order kinetics, and the process is characterized by the half-order reaction rate constants for nitrate and nitrite reduction. These constants incorporate the intrinsic reaction kinetics of the immobilized cells, the size and packing density of biocatalyst particles in the reactor, and the effective diffusion coefficients of nitrate and nitrite in the particle matrix.     

稀土尾矿催化脱硝可行性实验研究

采用X射线荧光光谱分析仪(XRF)、X射线衍射仪(XRD)、扫描电镜(SEM)对稀土尾矿进行表征分析发现,稀土尾矿所含元素较多,矿物与矿物间嵌布关系复杂。针对稀土尾矿的特性,利用立管炉对稀土尾矿催化脱硝性能进行测试。结果表明:NO转化率随着反应温度和气体停留时间的增加而增加,且固定床反应器NO转化率要高于鼓泡床反应器NO转化率。当反应温度为800℃时,NO转化率达98.7%。利用拟薄水铝石和稀土尾矿为原料进行研磨焙烧制备脱硝催化剂。稀土尾矿总量不变,随着拟薄水铝石质量的增加,NO转化率也相应增加。当反应温度为600℃时,拟薄水铝石与稀土尾矿质量比为1∶2的催化剂比纯稀土尾矿的NO转化率提高15%。热力学计算结果表明,含铁量较多的稀土尾矿用于CO还原脱硝是可行的。     

Reaction of the hydrogen-absorbing intermetallic compound TiFe with oxygen. II. Kinetics of oxidation of TiFe in air

We have studied air oxidation (600–950°C) of TiFe alloy by the gravimetric method. We describe the oxidation process by a parabolic time law as well as an exponential temperature law. The weight increase isotherms have breaks, the two parts of the lines corresponding to a periodic increase in the rate constant at temperatures less than 800°C and a decrease at temperatures higher than 800°C. The activation energy also increases above 800°C, and the difference between the oxidizability of TiFe and its analog TiNi decreases. The change in the oxidation mechanism for TiFe is hypothetically determined by the increase in the role of rutile in high-temperature oxidation, and the possibility of diffusion of titanium through interstitial positions of the rutile (TiO₂) lattice, similar to previously studied oxidation.     

Aerobic Methane Oxidation Coupled to Denitrification: Kinetics and Effect of Oxygen Supply

Aerobic methane oxidation coupled to denitrification (AME-D) is a process in which aerobic methanotrophs oxidize methane and release organic compounds that are used by coexisting denitrifiers as electron donors for denitrification. This process is potentially promising for denitrification of wastewater or landfill leachate poor in organic carbon using methane produced onsite as external electron donor. We studied the kinetics of an aerobic methane-oxidizing denitrifying culture and investigated the effect of dissolved oxygen (DO) concentration and air supply rate on AME-D using a batch reactor and a semicontinuous reactor setup. At methane concentrations of 18–33% in air and air flow rates of 15–35?mL?air?L?1?liquid?min?1, the DO concentration was less than 0.01?mg?L?1 and the nitrate removal reached a maximum value of 56.7?mg?NO3–N?g?1?VSS?d?1 with 79% being attributed to denitrification. When the air supply rate was increased to 70?mL?air?L?1?liquid?min?1 resulting in a drop in methane content to 10%, the DO concentration in the bioreactor rose to about 0.8–1.0?mg?L?1 and the total nitrate removal dropped to about 10?mg?NO3–N?g?1?VSS?d?1 with none of it being attributed to denitrification.     

冶金化学动力学研究中应注意的几个问题

根据有关文献资料,对冶金化学动力学研究与应用中容易忽视的几个问题作了分析,指出了问题的症结所在,在此基础上提出了研究冶金化学动力学时应注意的几个问题。     

Sydney Soil Model. II: Experimental Validation

This paper presents simulations of the mechanical behavior of reconstituted and natural soils using a new model presented in a companion paper and referred to as the “Sydney soil model.” It is demonstrated that the performance of the proposed model is essentially the same as that of modified Cam clay model when describing the behavior of clays in laboratory reconstituted states. The model has also been employed to simulate the drained and undrained behavior of structured clays and sands, including calcareous clay and sand. Five sets of conventional triaxial tests and one set of true triaxial tests have been considered. It is demonstrated that the new model provides satisfactory qualitative and quantitative modeling of many important features of the behavior of structured soils, particularly in capturing various patterns of the stress and strain behavior associated with soil type and structure. A general discussion of the model parameters is also included. It is concluded that the Sydney soil model is suitable for representing the behavior of many soils if their ultimate state during shearing can be defined by an intrinsic and constant stress ratio M* and a unique relationship between mean effective stress and voids ratio, i.e., a unique p′-e curve.     

Kinetics of the zinc slag-Fuming Process: part II. mathematical model

A mathematical model of zinc slag fuming has been formulated based on the kinetic conception of the process developed in Part I of this paper. Each of the major reaction zones in the furnace — the slag bath where reduction of zinc oxide and ferric oxide takes place and the tuyere gas column where oxidation of coal and ferrous oxide occurs — have been characterized mathematically. The two zones and the water-jacketed furnace wall have been linked by overall heat and mass balances. Insufficient information is available, however, to characterize quantitatively two of the important kinetic processes occurring in the furnace: the division of coal between entrainment in the slag, combustion in the tuyere gas column and bypass; and oxygen utilization. To overcome this problem the model has been fitted to the data from eleven industrial fuming cycles. Consistent values have been obtained for these kinetic parameters over five different fuming operations indicating that the kinetic conception of the process is sound. The results indicate that about 33 pct of the injected coal is entrained in the slag, 55 pet combusts in the tuyere gas column, and 12 pct bypasses the bath completely. Oxygen utilization has been found to be high and can be correlated to bath depth. Formerly Graduate Student     

Reaction Kinetics of FeO Containing Molten Slags

The kinetic study of FeO‐containing slag is valuable if we consider slag‐gas and slag‐metal reactions in steelmaking process. In the present work, the reduction rate of Fe_tO‐SiO₂–TiO₂–MO_x (MO_x = CaO, MgO, AlO_1.5, PO_2.5) melts in equilibrium with solid iron by CO gas was measured using the thermobalance system at 1673 K. A rate equation was developed based on the results obtained. The mechanisms of the reaction and the effect of P₂0₅ as a surfactant were discussed. Solid CaO was reacted with FeO‐containing slag at 1573 to 1673 K. The CaO–slag interface was analyzed by SEM and EDX, and the reacted layers were identified. The rate of solid CaO dissolution into a stagnant FeO‐containing slag at hot‐metal temperatures was explained by the FeO diffusion in slag phase.     

Kinetics of Oxidation Reaction for Magnetite Pellets

An experiment for the oxidation process of single magnetite pellet and theoretical analysis based on modified unreacted core shrinking (MUCS) model were carried out, and the controlling mechanisms of the initial and developing reactions were examined, respectively. From the study of the initial reaction, it was found that the chemical reaction of surface is the controlling step of the overall reaction when the temperature is up to about 750 K, while the mass transfer through the gaseous boundary layer dominates the reaction rate when the temperature is above 750 K. As the reaction developing within the pellet, the mass transfer through the produced layer becomes the controlling step. In addition, the effects of reaction conditions (such as oxygen concentration, temperature) on the fractional oxidation of magnetite pellet were determined.     

Si、Al还原渣中V2O5反应动力学研究

为采用V2O5直接合金化冶炼高速钢,进行了渣中Si、Al还原渣中v2O5反应动力学试验,考察了温度、熔渣组成等因素对还原反应速度的影响,并对反应机理进行探索,找出还原反应速度的限制环节.试验结果表明,渣中v2O5向反应界面的扩散是速度限制环节.通过动力学试验研究结果最终确定V2O5直接合金化的工艺路线是:Si预还原→A...     

Determining Minor Head Losses in Drip Irrigation Laterals. II: Experimental Study and Validation

Values of friction coefficient K and equivalent length le were determined for various emitter models using analytical and experimental procedures developed in the companion paper by Juana et al. in 2002. Flow contraction coefficient Cc for water jets discharging through orifices with angle α=45° is suggested when the emitters have hydrodynamic geometry at the insertion. Otherwise, α=90° or, as an extreme value, α=180° is preferred. Both criteria K and le showed a reasonable agreement for minor losses evaluation produced at emitter insertions along drip laterals. Accuracy on their determination was analyzed. Larger dispersion of K and le values was observed when lateral head losses were small. Inlet head, Reynolds number, and emitter spacing did not show a clear effect on K and le values, whereas the effect of obstruction ratio r of the pipe cross-sectional area at the emitter location was of practical significance. Parameters of the emitter discharge equation determined with lateral tests were comparable to those obtained on an emitter testing bench using the International Standard procedure.     

Study on Roast Reaction Kinetics and Crystal Behavior of Ceria-Based Rare Earth Polishing Powder

The TG-DTA curve of the thermal decomposition process of hydrous cerium carbonate was tested in the air. The roasting process was investigated by means of DTA thermal analysis technique. The kinetics of thermal decomposition process was calculated by means of Freeman-Carroll was proved. The apparent activation energy of the dehydrating to hydrous cerium carbonate was E = 7.40 kJ · mol⁻¹, the chemical reaction series was n = 2.28 and the apparent activation energy of the thermal decomposition reaction of cerium carbonate was E = 334.4 kJ · mol⁻¹, and the chemical reaction series n = 3.67. Connected with the kinetics calculation, the influence of different temperature on the ceria crystal structure was studied by means of XRD.     

Control of Reaction Kinetics During Friction Stir Processing

Friction stir processing (FSP) was used to successfully embed galfenol particles into aluminum (AA 1100 Al) matrix uniformly. However, intermetallic layer of Al₃Fe was formed around the galfenol particles. Activation energy for Al₃Fe formation during FSP was estimated, and attempts were made to minimize the Al₃Fe layer thickness. By changing the processing conditions, FSP successfully eliminated the intermetallic layer. Hence, FSP, in addition to microstructural control, can successfully fabricate intermetallic-free embedded regions by controlling the reaction kinetics.     

硅还原钨酸钙固相反应实验研究

为研究CaWO₄与Si在直接合金化炼钢过程中的低温固相反应过程,采用差示热分析仪在10℃/min恒速升温条件下对CaWO₄与Si粉末混合物进行热分析实验,通过高温炉恒温实验对CaWO₄与Si球团在1400℃恒温30 min的反应生成物及反应率进行分析,结合熔点测试实验分析了球团在升温过程中的物理变化行为。实验结果表明,CaWO₄与Si在1400℃以下所发生的还原反应为全固相反应,反应生成物为W、WSi₂、W₅ Si₃、Ca3（Si₃O₉）、SiO₂,CaWO₄球团在1400℃30 min的反应率达到93.41%,固相反应过程中CaO不能促进反应的进行;CaWO₄与Si 1400℃以下恒速升温条件下表观反应符合Avarami-Erofeev方程,反应机理为随机形核和随后生长,表观反应动力学表达式为dα/dt=11.68e^{-51.75×103/RT}·4（1-α）[-ln（1-α）]^3/4。     

Thermal Decomposition Reaction Kinetics Model of Powdered Bastnaesite

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Low Temperature Hot Corrosion of Cobalt-Base Alloys: Part II. Reaction Mechanism

This paper presents a mechanism of low-temperature hot corrosion that is based on rapid dissolution of the more noble metal or metal oxide in liquid salts. It is proposed that the rapid degradation of cobalt-base alloys results from dissolution of cobalt or cobalt oxides on the surface, which prevents the formation of a protective Cr₂O₃ or A1₂O₃ film. The reaction occurs in two stages: (a) an initial stage, during which an Na₂SO₄-CoSO₄ liquid forms on the surface, and (b) a propagation stage, during which SO₃ migrates inward and cobalt outward through the molten salt. At longer times, cobalt dissolves at the scale/salt interface and forms Co₃O₄ and/or CoSO₄(s) in different regions of the reaction product. The mechanisms of transport of various reactants and products through the liquid salt and the effects of their relative transport rates on the reaction product morphology have been considered.     

Using the Kinetics of Biological Flocculation and the Limiting Flux Theory for the Preliminary Design of Activated Sludge Systems. II: Experimental Verification

Current activated sludge models consider that the removal of biodegradable organics by suspended growth includes: rapid enmeshment of the organic particles in the microbial floc, hydrolysis of the complex organic molecules into readily biodegradable organic substances, and oxidation of dissolved organic substances. All of the models assume that hydrolysis is the rate-limiting step, but none considers the role that the kinetics of biological flocculation and the sludge-settling characteristics may play in defining the activated sludge operating parameters. Several researchers have studied the kinetics of biological flocculation, and have analyzed its role on the removal of particulate chemical oxygen demand in suspended growth reactors. It has been demonstrated that a large proportion of the organic matter present in sewage can be removed by biological flocculation using short hydraulic retention times and subsequent settling. The first paper demonstrates that the one-dimensional limiting flux theory may be useful for coupling the sludge-settling properties with the aeration tank behavior, and the second paper presents experimental evidence that the proposed model is a reasonable first approximation that can be used for activated sludge system design and operation.     

Experimental benznidazole encephalopathy: II. Electroencephalographic and morphological alterations

Glycated hemoglobin can be degraded by proteolytic enzyme(s) in the erythrocyte. The enzyme(s) co-elutes with glycated hemoglobin when the latter is separated from erythrocyte lysates using the cation-exchanger Bio Rex-70. A further purification of the Bio Rex eluant on DEAE Sephadex A-50 separated the enzyme(s) from glycated hemoglobin. Studies with the Bio Rex eluant showed that degradation of glycated hemoglobin is maximum at 37 degrees C at pH 8.6. Proteolytic degradation is inhibited by 5 mM N-ethylmaleimide (NEM), 5 mM ethylenediamine tetraacetic acid (EDTA) and 0.6 mM n-p-tosyl-L-lysine choromethyl ketone (TLCK) (100-87 and 76% inhibition respectively). This study also examines the possibility that oxidative-damage to glycated hemoglobin increases its susceptibility to proteolytic degradation. When incubated with various anti-oxidants like DTPA, uric acid, mannitol and butylated hydroxy toluene (BHT), proteolytic degradation of glycated hemoglobin decreased by 66.1, 50.7 and 38% respectively.     

Strain Energy During Mechanical Milling: Part II. Experimental

The strain energy stored in mechanically milled 5083?Al powders was investigated using two experimental approaches: thermal and microstructural analysis. The experimental results show that mechanically milled 5083?Al powders store strain energy on the order of a few tens of joules per gram. These experimental results are consistent with the calculated strain energy stored in mechanically milled powders. The experimentally measured strain energy stored in powders increases with an increase in attritor diameter, impeller??s rotational frequency, and ball-to-powder mass ratio; however, it decreases with an increase in ball diameter. These trends were in good agreement with the calculated strain energy stored in powders as a function of the corresponding processing parameters.