共查询到20条相似文献,搜索用时 15 毫秒
1.
A Co–B alloy/ethylenediamine (EDA) hybrid electrode system has been developed by adding EDA into electrolyte. Charge–discharge measurements show that the inorganic–organic hybrid electrode system exhibits high discharge capacity and long cycle life at elevated temperature (55 °C). Specifically, in the electrolyte containing 0.09 M EDA additive, the discharge capacity of Co–B alloy electrode after 100 cycles is still up to 601.7 m Ah g−1 at 55 °C. However, for the electrode in EDA-free electrolyte, its discharge capacity is sharply decreased to only 138.5 m Ah g−1 after 100 cycles. ICP-OES and IR measurements are used to clarify the reason of the improvement in the electrochemical properties. These results show that beneficial effect of EDA on electrochemical properties of Co–B alloy electrode can be attributed to in situ electrochemical oxidation of EDA during discharge cycles. First the oxidation of EDA contributes to part of the discharge capacity and secondly the oxidation products absorbed on the electrode may help to suppress the dissolution of Co at elevated temperature. Evidence is presented suggesting that the oxidation of Co can induce co-oxidation of EDA. 相似文献
2.
A.C. Cascalheira 《Electrochimica acta》2004,49(27):5023-5028
Cyclic voltammetry has been used to investigate the behaviour of copper surfaces in sodium salicylate aqueous solutions. The observed copper anodic passivation dependence on the presence of salicylate ion in solution is explained. The analysis of the experimental data supports the formation of a complex passivating film formed by a Cu2O inner layer and a mixed cupric oxide/cupric salicylate outer layer; this film provides a partial passivation of the copper surface and can be completely removed upon excursion to negative potentials values; the composition of the passivating layer depends on the electrolyte nature, i.e. sodium salicylate ion and solution pH, and on the potential programme the copper electrode is subjected to. 相似文献
3.
The electrooxidation of phenol is of interest as a model compound for the treatment of aqueous organic wastes. The effect of voltage, concentration and temperature on the electrochemical oxidation of acidic dilute aqueous solutions of phenol was studied. Electrolysis was carried out by recirculating phenol solutions through a flow-by electrochemical reactor employing a reticulated glassy carbon anode. Concentrations of phenol and some breakdown products were monitored using HPLC analysis. Increased voltage was found to shift the product distribution to favour more oxidized products but also to increase electrode corrosion and decrease current efficiency. Higher phenol concentrations (over the range of 5-20 mmol/L) showed a shift in product distribution to favour less oxidized, mostly insoluble products. Elevated temperatures (about 50°C and higher) showed a marked ability to reduce electrode passivation and increase the phenol oxidation rate. 相似文献
4.
PX氧化反应动力学模型研究 总被引:3,自引:1,他引:2
建立了一套半连续的PX高温催化氧化反应动力学实验装置,并进行了相关的动力学研究。依据实验数据和机理分析,提出了反应组分抑制的动力学模型。 相似文献
5.
The measurement of the kinetics of fast chemical reactions, such as hydrocarbon pyrolysis, is often hampered by limitations of the experimental reactor. To overcome problems in getting to reaction temperature, a micro-reactor system has been developed with temperature rise times (TRT) in the millisecond range. Data is presented for the dynamic response of a Curie Point pyrolyser along with a computer simulation of how the gas-filled micro-reactor would respond. The importance of temperature rise time is clearly demonstrated by the computer simulations of propane and naphtha pyrolysis in the temperature range of 600°C and 1100°C. 相似文献
6.
Electrochemical oxidation of methanol on carbon supported Pt/Ru gas diffusion electrodes was investigated in a cyclone flow cell at room temperature using chronoamperometry, cyclic voltammetry and electrochemical impedance spectroscopy. The influence of the flow rate was checked. It was proved that the cyclone cell is suitable for the investigation of methanol electrooxidation and provides additional information on the mass transfer limitations in the electrode assembly. Chronoamperometric measurements showed slow, but constant current decay at all investigated potentials. Impedance measurements in water and methanol containing solutions were performed and the experimental data were fitted to an appropriate equivalent circuit. 相似文献
7.
Bora Aydin 《Chemical engineering science》2005,60(23):6687-6701
Despite the hydrodynamics of trickle beds experiencing high pressures has become largely documented in the recent literature, trickle bed hydrodynamic behavior at elevated temperatures, on the contrary, largely remains terra incognita. This study's aim was to demonstrate experimentally the temperature shift of trickle-to-pulse flow regime transition, pulse velocity, two-phase pressure drop, liquid holdup and liquid axial dispersion coefficient. These parameters were determined for Newtonian (air-water) and non-Newtonian (air-0.25% Carboxymethylcellulose (CMC)) liquids, and the various experimental results were compared to available literature models and correlations for confrontation and recommendations. The trickle-to-pulse flow transition boundary shifted towards higher gas and liquid superficial velocities with increasingly temperatures, aligning with the findings on pressure effects which likewise were confirmed to broaden the trickle flow domain. The Larachi-Charpentier-Favier diagram [Larachi et al., 1993, The Canadian Journal of Chemical Engineering 71, 319-321] provided good predictions of the transition locus at elevated temperature for Newtonian liquids. Conversely, everything else being kept identical, increasingly temperatures occasioned a decrease in both two-phase pressure drop and liquid holdup; whereas pulse velocity was observed to increase with temperature. The Iliuta and Larachi slit model for non-Newtonian fluids [Iliuta and Larachi, 2002, Chemical Engineering Science 46, 1233-1246] predicted with very good accuracy both the pressure drops and the liquid holdups regardless of pressure and temperature without requiring any adjustable parameter. The Burghardt et al. [2004, Industrial and Engineering Chemistry Research 43, 4511-4521] pulse velocity correlation can be recommended for preliminary engineering calculations of pulse velocity at elevated temperature, pressure, Newtonian and non-Newtonian liquids. The liquid axial dispersion coefficient (Dax) extracted from the axial dispersion RTD model revealed that temperatures did not affect in a substantial manner this parameter. Both Newtonian and power-law non-Newtonian fluids behaved qualitatively similarly regarding the effect of temperature. 相似文献
8.
A novel annular reactor for kinetic studies at high temperature and flow conditions has been designed to keep eccentricity tolerances below 10%. In a previous work, we have shown that it is very important to keep such low eccentricity values in order to collect reliable kinetic data from this type of reactors. As proposed in this study, a modified reactor with the use of a spacer could guarantee an annular duct with low levels of eccentricity. Manufacturing tolerances or deformation effects giving rise to eccentricity can be significantly minimised when using this apparatus. The reactor has been both experimentally and theoretically characterised. Carbon monoxide oxidation was used as a model reaction under mass-transfer limited conditions revealing an eccentricity of ∼5%. With such small eccentricity levels, a concentric annular form can be assumed in the reactor analysis. Simple 1D or 2D models can therefore be inexpensively used in the evaluation of the kinetic data. Also, prior to the design of the annular reactor, a numerical investigation was carried out to clarify the effects of eccentricity, physical properties of the carrier gas and the annular aspect ratio on mass-transfer limitations. Contrary to expectations, a considerable increase in the fuel mass-diffusivity by carrier gas substitution did not change the mass-transfer rates for cases when eccentricity and aspect ratios were high. 相似文献
9.
New time averaged data of two-phase flow in bubbly and slug regimes are presented. A modified dual spherical tipped optical fiber probe is used to measure local void fractions, gas velocity and bubble sizes. Hot film anemometry was used to measure the local mean liquid velocity axially. The void fraction, gas and liquid velocities values were presented as averages over the long and short dimensions respectively. Also core values of these variables are presented along the smaller dimension of 12.7 mm, near the plane of symmetry of the longer dimension, to show the most general trend of the different bubbly and slug flow runs. Bubble sizes obtained experimentally were compared with predictive models applied to circular geometries and were found to have a reasonable agreement. It was also interesting to find that local void fractions measured using hot film anemometers were comparable to those found by optical fiber probes. Frequencies of interfacial passage of bubbles and slugs are presented which show rather flat profiles across the channel. It is hoped that these data can be further used in predictive two-phase two-fluid models in the future. Lastly of interest is the fact that slip values near the boundaries were shown to be less than 1.0 for some cases in bubbly flow similar to those observed in circular geometries. 相似文献
10.
Characterization and activity of Fe-ZSM-5 catalysts for the total oxidation of phenol in aqueous solutions 总被引:2,自引:0,他引:2
Nguyen Huu Phu Tran Thi Kim Hoa Nguyen Van Tan Hoang Vinh Thang Pham Le Ha 《Applied catalysis. B, Environmental》2001,34(4):267-275
Fe-ZSM-5 zeolites with of Si/Fe ratios varying from 40 to 200 were synthesized and characterized by IR, XRD, SEM, ESR and ion-exchange techniques. From the obtained results, it is possible to conclude that, these zeolites have a good crystallinity and that the incorporation of Fe3+ ions into the MFI-structure depends on the Si/Fe ratios in the gel: the higher the Si/Fe ratio, the more the percentage of Fe3+ions is incorporated into the MFI lattice.
Catalytic properties of Fe-ZSM-5 were studied in the oxidation of phenol. The reaction was performed in a static system, at the atmospheric pressure, 343 K, and with H2O2 concentration, which exceeds stoichiometric concentration for complete oxidation of phenol to carbon dioxide and water. From the catalytic results, it can be concluded that framework Fe can catalyze more completely phenol oxidation than the extra-framework Fe does. 相似文献
11.
12.
以水为工质对不同板间距的三角槽道脉动流流动阻力特性进行了研究。基于受力平衡方程,建立了适用于三角槽道脉动流压降的数学模型,用于理论分析流动阻力的影响因素。通过实验测试与数值模拟,校验数学模型的合理性,并且对三角槽道脉动流流动阻力进行分析。结果表明,流动阻力主要受板间距、涡旋拟“能”两方面因素影响,且与板间距呈反比,与涡旋拟“能”呈正比;板间距的缩小,会使流动阻力增加,当缩小到板间距与槽深比值为1.0时,出现流动阻力的阶越式增长,上升1个数量级;造成流动阻力骤升的主要原因在于:随着板间距的缩小,流场结构逐渐变化,三角槽道内涡旋的影响区域由“三角槽内部”逐渐转变为“整个流道”,且主流区壁面出现流动分离,出现涡旋流动与波状流共存现象,使流动阻力大幅提升。 相似文献
13.
D.R. Morris Fang Jiang J.M. McINERNEY D.H. Lister 《Journal of Applied Electrochemistry》1999,29(8):971-977
A nonisothermal, solid state electrochemical sensor for monitoring hydrogen or oxygen dissolved in high temperature (to about 500 K) water is described. Nafion® in the form of tube was used as the electrolyte. The reference electrode at ambient temperature and pressure was a saturated aqueous solution of Fe2+ and Fe3+ sulphates. Sensor voltage measurements with dissolved hydrogen showed good reproducibility and long term stability. A regression equation for the hydrogen concentration related to cell voltage and water temperature was derived. Sensor voltage measurements with dissolved oxygen showed relatively poor reproducibility and long term stability. This is attributed to the greater complexity of electrode reactions involving oxygen and water. 相似文献
14.
In this study, the electrochemical behavior of tiron in aqueous solutions and the influence of pH were investigated. A change of pH mainly produces the following results. In acidic solutions of pH below 4, the electrode reaction of tiron exhibits a simple process at a relatively high potential with a favorable quasi-reversibility. The tiron redox reaction exhibits fast electrode kinetics and a diffusion-controlled process. In solutions of pH above 4, the electrode reaction of tiron tends to be complicated. Thus, acidic aqueous solutions of pH below 4 are favorable for the tiron as active species of a redox flow battery (RFB). Constant-current electrolysis shows that a part of capacity is irreversible and the structure of tiron is changed for the first electrolysis, which may result from an ECE process for the tiron electro-oxidation. Thus, the tiron needs an activation process for the application of a RFB. Average coulombic and energy efficiencies of the tiron/Pb battery are 93 and 82%, respectively, showing that self-discharge is small during the short-term cycling. The preliminary exploration shows that the tiron is electrochemically promising for redox flow battery application. 相似文献
15.
采用欧拉-欧拉双流体模型,基于水-玻璃珠体系,对长×宽×高尺寸为240 mm×12 mm×1800 mm的竖直窄通道充分发展段内液固两相流动特性进行了数值模拟。结果表明,沿窄通道竖直方向0.7 m以上液固两相流动进入充分发展阶段,在充分发展阶段的窄通道截面上,狭长方向与狭窄方向各位置颗粒速度及浓度均呈中心区域高、贴近边壁区域低的分布趋势;随着入口液速提高,截面各位置颗粒速度均提高,而颗粒浓度在流道中心区域降低,在贴近壁面区域升高;随着初始固相体积分数增加,截面各位置颗粒浓度均提高,而颗粒速度在流道中心区域略有降低,在贴近壁面区域略有升高;在窄通道截面狭长方向两端靠近三边壁影响的区域存在颗粒增浓效应,在截面狭窄方向颗粒速度和浓度分布梯度较大的区域无量纲占比随着入口液速的提高而提高,随着初始固相体积分数的提高而减小。 相似文献
16.
Bora Aydin 《Chemical engineering science》2008,63(6):1510-1522
The effects of temperature and pressure on the structure of the trickle-to-pulse flow regime transition in slow-mode cyclic operation in trickle-bed reactors were reported. The relationship between liquid holdup and liquid velocities at the trickle-to-pulse flow transition in cyclic operation, the shock wave behavior as a function of bed depth, as well as the pulsing flow regime properties were investigated for Newtonian (air-water) and non-Newtonian (air-0.25% carboxymethylcellulose (CMC)) liquids. At a given temperature, the breakthrough, plateau and decay times of the shock wave were found to decrease with bed depth. The pulse velocity and pulse frequency for pulsing flow regime both in cyclic operation and in natural pulsing (constant-throughput operation) were observed to increase with temperature. However, increasing the reactor pressure led to increased pulse frequency and decreased pulse velocity. Analysis of the transition liquid holdups for natural pulse flow and cyclic operation revealed that the liquid holdup decreased with temperature and pressure. The transition liquid holdups and superficial liquid pulse velocities in symmetric peak-base cyclic operation surpassed those in constant-throughput operation for given temperature, pressure and gas velocity, giving rise to wider trickle flow regime area in cyclic operation. The behavior of both Newtonian and power-law non-Newtonian fluids was similar regarding the effect of temperature, pressure and gas velocity. 相似文献
17.
Electrochemical studies of sodium borohydride in alkaline aqueous solutions using a gold electrode 总被引:1,自引:0,他引:1
S. Colominas 《Electrochimica acta》2009,54(13):3575-3579
Cyclic voltammetry using a gold disk working electrode has been employed for quantifying sodium borohydride in alkaline aqueous media. A 6 mm diameter disk working electrode is shown to offer higher sensitivity compared to a 1 mm diameter electrode, demonstrated by the slope of the calibration curve being 38 times greater when the 6 mm electrode is used. The dynamic range is also greater with the 6 mm electrode, evidenced by the square of the correlation coefficient for regression over the same concentration range. The influence of the matrix on the calibration curves was evaluated; 2 M NaOH, 2 M NaOH + 10% NaBO2, 2 M NaOH + 20% NaBO2, 2 M NaOH + 25% NaBO2, and 25% NaBO2 in solution at pH 12 were the matrices investigated. The matrix was shown to affect the calibration curves; generally, increasing content of NaBO2 caused the slope to decrease. Cyclic voltammetry was then used to assess the stability of sodium borohydride in aqueous solutions of different compositions. 相似文献
18.
Ali Güner 《应用聚合物科学杂志》1999,72(7):871-876
Intrinsic viscosity measurements were carried out on dextran samples (of different molecular weights) in aqueous solutions at 25, 28, 31, 34, 37, 40, and 43°C. The extrapolation methods were used for the data; they gave unperturbed dimensions, K0, of the chain. The unperturbed root‐mean‐square end‐to‐end distance 〈r2〉[STACK]1/20[ENDSTACK] calculated for the polymer samples in water indicate that the polymer coils are slightly contracted in this solvent as the temperature is increased. The long‐range interaction parameter, B, was also determined. In aqueous dextran solutions, this showed a significant decrease in the long‐range interactions between 25 and 43°C. The values of Θ = 317.82 and 316.57 K were obtained from the temperature dependence of the interaction parameter B in the Kurata–Stockmayer–Fixman and Berry equations. Calculated values were interpreted mainly on the basis of hydrogen‐bond formation between polymer segments and dextran–water molecules in solution. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 871–876, 1999 相似文献
19.
20.
Performance of the proton exchange membrane fuel cell(PEMFC) is appreciably affected by the channel geometry. The branching structure of a plant leaf and human lung is an efficient network to distribute the nutrients in the respective systems. The same nutrient transport system can be mimicked in the flow channel design of a PEMFC, to aid even reactant distribution and better water management. In this work, the effect of bio-inspired flow field designs such as lung and leaf channel design bipolar plates, on the performance of a PEMFC was examined experimentally at various operating conditions. A PEMFC of 49 cm~2 area, with a Nafion 212 membrane with a 40% catalyst loading of 0.4 mg·cm-2 on the anode side and also 0.6 mg·cm~(-2) on the cathode side is assembled by incorporating the bio-inspired channel bipolar plate, and was tested on a programmable fuel-cell test station.The impact of the working parameters like reactants' relative humidity(RH), back pressure and fuel cell temperature on the performance of the fuel cell was examined; the operating pressure remains constant at 0.1 MPa. It was observed that the best performance was attained at a back pressure of 0.3 MPa, 75 °C operating temperature and 100% RH. The three flow channels were also compared at different operating pressures ranging from 0.1 MPa to 0.3 MPa, and the other parameters such as operating temperature, RH and back pressure were set as 75 °C,100% and 0.3 MPa. The experimental outcomes of the PEMFC with bio-inspired channels were compared with the experimental results of a conventional triple serpentine flow field. It was observed that among the different flow channel designs considered, the leaf channel design gives the best output in terms of power density. Further,the experimental results of the leaf channel design were compared with those of the interdigitated leaf channel design. The PEMFC with the interdigitated leaf channel design was found to generate 6.72% more power density than the non-interdigitated leaf channel design. The fuel cell with interdigitated leaf channel design generated5.58% more net power density than the fuel cell with non-interdigitated leaf channel design after considering the parasitic losses. 相似文献