亚硫酸盐强制氧化传递与化学反应动力学

在湿法烟气脱硫的过程中,吸收塔底部发生的反应主要是亚硫酸钙和空气或氧气之间的气液传递与化学反应过程,根据双膜理论模型,分析了该反应的吸收机理,用一种图像边界识别的方法分析亚硫酸盐强制氧化气液反应.在没有催化剂或固定钴离子催化剂浓度时,SO^2-₃存在临界浓度0.328 mol•L^-1.当SO^2-₃的浓度低于0.328 mol•L^-1时,过程为双膜控制,SO^2-₃的反应级数为1;当SO^2-₃的浓度大于0.328 mol•L^-1时,过程逐渐变为气膜控制,SO^2-₃反应级数为0.当固定SO^2-₃浓度时,催化剂钴离子的反应级数则受到气液传质的影响,分为几个阶段,且反应级数不同.     

Mass transfer and kinetics of the three-phase hydrogenation of a dinitrile over a Raney-type nickel catalyst

The hydrogenation kinetics of a dinitrile over a Raney-type nickel catalyst was evaluated from experiments performed in a fed-batch operating autoclave at 320- and 2- hydrogen pressure. This complex catalytic reaction consists of two main parts: almost 100% selective hydrogenation of the dinitrile to the corresponding aminonitrile and consecutive hydrogenation to either the desired primary diamine or to pyrrolidine via ring formation. An extensive study has been made on the effects of mass transfer in the applied slurry-type reactor for this reaction. The gas-liquid mass transfer is enhanced by the presence of catalyst particles, and at typical hydrogenation conditions, k_La values up to can be reached. A Sherwood correlation for the three-phase reactor showed that important parameters in the gas-liquid mass transfer are stirrer speed and the density and viscosity of the solvent. The kinetic experiments were performed in absence of mass and heat transfer limitations. The kinetic data were modeled using two rate models based on Langmuir-Hinshelwood kinetics, assuming the reaction of dissociatively adsorbed hydrogen and nitrile compound as rate-limiting step. The first model involved competitive adsorption between hydrogen and organic compound and the second model was based on non-competitive adsorption. Both models successfully described both reaction parts. The reaction of dinitrile to aminonitrile is nearly 100% selective due to the relatively strong adsorption of the dinitriles as compared to the aminonitriles. By increasing the hydrogen partial pressure, higher yields of primary amine can be obtained. The models predict that operating in the mass-transfer regime at relatively high temperatures reduces the formation of the primary diamine.     

A spillover approach to oxidation catalysis over copper and manganese mixed oxides

The activity of a hopcalite-type catalyst for H₂ and CO oxidation is compared with that of single-phase oxides CuO, Mn₂O₃ and CuMn₂O₄ (spinel) and a mixture of 1:1 CuO and Mn₂O₃ in order to elucidate the effects that are responsible for the high catalytic activity of the former. The reaction rates over the hopcalite catalyst calcined at 550°C (a mixture of CuO, Mn₂O₃ and CuMn₂O₄) are very close to those of the physical mixture of CuO and Mn₂O₃, being much greater than the rates over the single-phase oxides. CuO, Mn₂O₃ and CuMn₂O₄ show a kinetic compensation behavior both in H₂ and CO oxidation. By taking into account the activation energies and the reducibility measured by TPR it was concluded that the oxidation reactions over CuO follow a redox mechanism using lattice oxygen, while over Mn₂O₃ the mechanism is associative involving adsorbed oxygen species. Based on the TPR and kinetic results, the synergy between copper and manganese oxides in hopcalite and in the CuO–Mn₂O₃ mixture is assigned to a spillover effect.     

Multi-component ion exchange kinetics with PAN-KCoFC composite ion exchanger

An ion exchange kinetic study was performed using PAN-KCoFC for removal of cesium ion from mixed solution of Cs, Sr, Ni and Ba ions. Uptake curves were obtained for a multi-component ion exchange system as well as binary system. A PAN-KCoFC composite ion exchanger showed higher selectivity for Cs ion over the Sr, Ba, Ni ions. A homogeneous model could predict accurately the uptake curve for both the binary and multi-component systems. Solid phase effective pore diffusivities obtained by modeling ranged between 10⁻⁵ cm₂/min and 10⁻⁶ cm₂/min.     

Mn对Al2O3-ZrO2-C耐火材料抗氧化性的影响

固定主要原料烧结板状刚玉、锆莫来石、石墨,添加剂Al粉、Si粉以及结合剂热固性酚醛树脂等的加入量,加入不同量的Mn配制成Mn、C质量比不同的Al2O3-ZrO2-C试样,埋炭烧成后检测各试样的抗氧化性.结果表明试样的氧化层厚度先随Mn加入量的增加(即Mn与C质量比的增大)而减小,即抗氧化性提高;至Mn与C质量比为14时,氧化层厚度最小,即抗氧化性最佳;当Mn含量继续增加时,氧化层厚度又开始增加,即抗氧化性降低.     

The reduction and oxidation behaviour of manganese oxides

The reduction of manganese oxides with methane was studied to investigate the suitability of manganese as an oxygen storage compound. Manganese oxides are reduced by CH₄ to a lower-valent manganese oxide, producing CO₂ and water. Once the manganese oxide is reduced, it can be regenerated, i.e. reoxidised. By integrating this exothermic oxidation cycle with endothermic methane reforming, a new setup for exothermic, small scale syngas production is obtained. Manganese oxides can be reduced to manganese(II) oxide with methane at temperatures higher than 723 K. Reoxidation of MnO at 823 K leads to the formation of Mn₂O₃ at 823 K. At 1073 K reoxidation of MnO gives Mn₃O₄ , which corresponds to a lower Mn-valency than expected thermodynamically. Subsequent oxidation–reduction cycles lead to an increase in reduction temperature, probably due to a higher crystallinity.     

Adsorption equilibrium and kinetics studies of divalent manganese from phosphoric acid solution by using cationic exchange resin

There are numerous impurities in wet-process phosphoric acid, among which manganese is one of detrimental metallic impurities, and it causes striking negative effects on the industrial phosphoric acid production and downstream commodity. This article investigated the adsorption behavior of manganese from phosphoric acid employing Sinco-430 cationic ion-exchange resin. Resorting FT-IR and XPS characterizations, the adsorption mechanism was proved to be that manganese was combined with sulfonic acid group. Several crucial parameters such as temperature, phosphoric acid content and resin dose were studied to optimize adsorption efficiency. Through optimization, removal percentage and sorption capacity of manganese reached 53.12 wt%, 28.34 mg·g⁻¹, respectively. Pseudo-2nd-order kinetic model simulated kinetics data best and the activation energy was evaluated as 6.34 kJ·mol⁻¹ for the sorption reaction of manganese. In addition, the global adsorption rate was first controlled by film diffusion process and second determined by pore diffusion process. It was found that the resin could adsorb up to 50.24 mg·g⁻¹ for manganese. Equilibrium studies showed that Toth adsorption isotherm model fitted best, followed by Temkin and Langmuir adsorption isotherm models. Thermodynamic analysis showed that manganese adsorption was an endothermic process with enhanced randomness and spontaneity.     

Study on the reaction rate of sulfite oxidation with cobalt ion catalyst

Wet limestone scrubbing is the most common flue gas desulfurization process for control of sulfur dioxide emissions from the combustion of fossil fuels, and forced oxidation is a key past of the reaction. In the present work the oxidation rate was experimentally studied by contacting pure oxygen with a sodium sulfite solution. The sulfite oxidation reaction rate was then measured photographically for various sodium sulfite and Co²⁺ concentrations. The sulfite oxidation reaction rate was affected by the mass transfer characteristics of the gas-liquid absorbers with the cobalt ion catalyst as well as the reaction kinetics. The sulfite oxidation reaction rate controlled by the reaction kinetics was first order with respect to the sulfite. When the sulfite oxidation reaction rate was controlled by the gas-liquid rate of mass transfer characteristics, the reaction was zeroth order with respect to the sulfite.     

多孔固体催化剂颗粒的几何形状对外扩散传热、传质的影响

以普兰特推出的边界层理论为依据，讨论了多孔固体催化剂颗粒的几何形状（颗粒度和几何外形）对其周围传热、传质过程的影响，分析结果较满意地解释了以往的实验结果。     

The Role of Mass Transfer in the Kinetics of Chemical Oxidation of Anthracine Slurry to Anthraquinone in a Batch Stirred Tank Reactor

The kinetics of chemical oxidation of anthracine powder by acidified dichromate in a batch agitated vessel stirred by a 45° four pitched blade turbine impeller was studied under different conditions. Variables studied were impeller rotation speed, solution physical properties and temperature. The rate of anthracine oxidation was found to increase with temperature according to the Arrhenius equation with an activation energy of 3.98 cal/mole. The rate of anthracine oxidation was found to increase with 0.56 power of impeller rotation speed. The value of the activation energy and the sensitivity of the rate of oxidation to stirring lend support to the diffusion‐controlled nature of the reaction. The data were correlated by the equation: Sh = 0.5 · 10^–3 Sc^0.33 · Fr^0.33 Implication of the above equation for the operation of industrial reactors was noted.     

Experimental and modeling study of the kinetics of oxidation of ethanol-n-heptane mixtures in a jet-stirred reactor

The kinetics of oxidation of ethanol-n-heptane mixtures (20-80 and 50-50 mol.%) was studied experimentally using a fused-silica jet-stirred reactor. The experiments were performed in the temperature range 530-1070 K, at 10 atm, at two equivalence ratios (0.5 and 1), and with an initial fuel concentration of 750 ppm. A kinetic modeling was performed using schemes resulting from the merging of validated kinetic schemes for the oxidation of the components of the present mixtures (n-heptane and ethanol). Good agreement between the experimental results and the computations was observed under the present conditions when using detailed chemistry whereas the used of semi-detailed chemistry yielded acceptable but less accurate prediction of the fuel oxidation kinetics.     

Kinetic and reaction mechanisms of calcium bisulfite catalytic oxidation

In this paper, the oxidation of calcium bisulfite in the presence of ferrous ions as a catalyst is studied in a laboratory scale apparatus at a fixed oxygen partial pressure (21.3 kPa) and at a temperature of 45 °C. The analysis of the experimental results, carried out by using the theory of mass transfer with chemical reaction, indicates that the slow reaction regime has been explored, and the transition from the kinetic to the diffusional subregime identified. A kinetic analysis allows to develop a reaction rate equation, assuming that the bisulfite oxidation in the presence of ferrous ions follows a parallel reaction mechanism; the resulting overall reaction rate has been found to be of first order with respect to ferrous ion concentration and of three halves with respect to bisulfite concentration. Moreover, the catalytic effect of ferrous ions has been compared with that of manganese ions previously studied, showing that ferrous is a catalyst more active than manganese.     

Immobilization of manganese tetraphenylporphyrin on Au/SiO2 as new catalyst for cyclohexane oxidation with air

Manganese tetraphenylporphyrin was successfully immobilized on Au/SiO₂, by using mercaptopyridine with sulfhydryl and pyridyl groups as bridging agent. The synthesized catalyst with novel structure was characterized by FTIR spectroscopic technique, XPS measurement, TG–DTA analysis and so on. During aerobic oxidation of cyclohexane in the presence of this material, the conversion of cyclohexane and total selectivity to cyclohexanone and cyclohexanol were up to 5.39% and 88.74%, respectively.     

Light-off curve of catalytic reaction and kinetics

The light-off curve is the conversion-temperature plot of a catalytic reaction; it is usually used in catalyst development. The possibility to deduce kinetic information such as the apparent reaction order or mass transfer limitation from the shape of the curve is examined here. The light-off plots obtained by numerical simulation with several different rate equations are compared between themselves and with experimental curves. This is illustrated with the oxidation of carbon monoxide and methane on noble metal catalysts with different degree of mass transfer resistance. The comparison is complemented with the Arrhenius plots, i.e. the logarithm of the apparent rate constant versus the reverse of temperature.From the shape of the curves, the three following situations can be discriminated: first-order kinetics, negative first-order kinetics in the absence or in the presence of external mass transfer limitation. The range of diffusional limitation is well defined for negative-order reaction. However, the mass transfer resistance is difficult to evidence for first-order reaction. It is observed that the Langmuir-Hinshelwood reaction kinetic model is not convenient to represent the effect of strong external transport limitation on a reaction in the regime of reactant inhibition (negative apparent reaction order).     

邻二甲苯氧化法制苯酐用催化剂的进展

介绍了邻二甲苯氧化法制苯酐用催化剂的研究情况、发展概况和开发过程中的技术关键。认为国内应加强该领域的研究开发。     

Removal of iron and manganese from groundwater by oxidation and microfiltration

Iron and manganese can be removed from groundwater by a process which combines oxidation and microfiltration (MF), especially when the concentrations of these metals are high and variable. The present experimental work focused on the MF of iron and manganese oxide suspensions in order to study the effects of the operating variables (tangential flow rate, pressure, metal feed concentrations) on permeate quality and permeation flux decline, i.e., membrane fouling. Artificial and natural groundwaters in which iron and manganese were previously oxidized were used to perform laboratory-scale MF experiments. The results show that the oxide particles, with sizes ranging from 1.5 to 50μm, were efficiently microfiltered even at high concentrations. Within the experimental limits, the effect of operating pressure appeared to be much more significant than the those of tangential flow rate and feed concentration. A relatively high and constant permeation rate of 0.5 m/h was obtained at a pressure below 10 kPa, whereas rapid permeation flux declines were observed at higher pressure. Both artificial and natural groundwaters always exhibited very similar behavior.     

Kinetics of catalyzed and non-catalyzed oxidation of soot from a diesel engine

To comply with the new regulations on particulate matter, car manufacturers more and more commonly use diesel particulate filters (DPF). The working of these systems needs to periodically burn soot that has been accumulated during the loading of the DPF. This paper describes the kinetics of the non-catalytic and catalytic oxidation of real diesel soot with oxygen. From these experiments, mechanisms for catalyzed and non-catalyzed soot oxidation have been proposed.     

Equilibrium and kinetics of heavy metal ion exchange

Ion exchange has a great potential to remove heavy metals from industrial wastewaters or heavy metal-containing sludge. In order to design and operate heavy metal removal processes, the equilibrium relationship between ions and resin must be known a prior. A series of ion-exchange equilibrium tests of Cu²⁺/H⁺, Zn²⁺/H⁺, and Cd²⁺/H⁺ systems using Amberlite IR-120 were performed. The equilibrium data were analyzed by the Langmuir isotherm, Freundlich isotherm, and selectivity coefficient approaches. The thermodynamic parameters such as Gibbs free energy change, enthalpy change, and entropy change were calculated. By comparison of the selectivity coefficients, the affinity sequence to IR-120 is Cu²⁺ > Zn²⁺ > Cd²⁺ > H⁺. Moreover, in order to understand the heavy metal extraction kinetics in the presence of Amberlite IR-120, the ion-exchange kinetics was also studied. The ion-exchange kinetic data were regressed by the pseudo first-order, second-order models, and a reversible reaction model. The activation energies calculated from the rate coefficients at different temperatures are 15.41, 7.04, and 17.01 kJ/mol for copper, zinc, and cadmium, respectively. Although the pseudo first- and second-order models are easier to use for data analysis, the resultant model parameters depend on operating conditions. The reversible reaction model is capable to predict the effects of resin to solution ratio, initial heavy metal concentration, and temperature on the ion-exchange kinetic curves.     

乙烯在银催化剂上氧化本征动力学的研究

采用固定床恒温积分反应器，对YS-6型银催化剂进行乙烯氧化本征动力学研究。选择与工业应用接近的条件进行动力学实验，根据建立的动力学模型。用动力学试验数据采用双响应Marquardt法，以转化率，选择性为目标函数进行待定参数估值。确定待定参数，得到本征动力学方程，根据数学统计检验，文中所建立的模型残差分布合理。参数回归显著，能够反映YS-6型催化剂的反应特性。