Effect of particle size on the surface oxidation and flotation behavior of galena particles in lime system

ABSTRACT

In this research, the effect of particle size on the surface oxidation and flotation behavior of galena in the lime system was studied. Coarse (?0.074 + 0.038 mm), intermediate (?0.038 + 0.025 mm) and fine (?0.025 mm) galena particles were used in the experiment. The dissolution tests, flotation tests, and sorption tests were accomplished. Through further analysis by XPS, the effect of particle size and lime was observed. The decrease of mineral particle sizes increased the adsorption ratio of collector and the dissolution of galena, while the hydrophilic product OH^?/Ca(OH)⁺ produced by dissolution occupied the dominant position, which led to the minerals hydrophilic.     

甲酸甲酯合成与转化的催化技术

本文评述了甲酸甲酯(MF)合成与转化的催化技术,展示了从MF出发发展C_1化学的可能途径,在MF的合成方面详细地分析了从甲醇出发的羰化法、脱氢法和氧化法催化技术,简介了我们的有关研究工作。     

The effects of bleached and unbleached rosemary oleoresins on light-sensitized oxidation of soybean oil

Bleached and unbleached forms of a rosemary oleoresin (RO) in stripped and nonstripped soybean oil behave both as antioxidant and prooxidant in a light-induced oxidative system. At 0.02 and 0.05% levels, RO had the greatest antioxidant activity, while at 0.01 and 0.5% levels it had the highest prooxidant activity in both stripped and nonstripped soybean oil. Treatment of both soybean oil systems with tertiary butylhydroquinone controlled light-induced oxidation of the oil better than did the oleoresin treatments. The prooxidant activity of the 0.5% RO level was probably due to an excess of prooxidant components being carried into the oil at that level, whereas the reduced antioxidant activity at 0.01% was probably due to the low initial level of active antioxidant components being added to the oil. Published as Journal Series No. 10072, Nebraska Agricultural Research Division, Department of Food Science and Technology, University of Nebraska, Lincoln, NE 68583-0919.     

Exploring single electrode reactions in polymer electrolyte fuel cells

Utilising a pseudo-reference electrode in polymer electrolyte fuel cells allows for the separation of anodic and cathodic contributions to the entire cell impedance. Modelling the impedance responses by using equivalent circuits inhibits the investigation of kinetic parameters of the basic electrochemical reactions, which take place at single electrode-electrolyte interfaces. Therefore, we evaluate single electrode impedance measurements by a kinetic model, which is based on specific reaction pathways, either for the oxygen reduction reaction (ORR) or the hydrogen oxidation reaction (HOR). As a consequence, it is possible to obtain kinetic parameters for the specific reaction of interest. Furthermore, the information gained from the single electrode impedance measurements and the kinetic model can give insight into single reactions steps. In particular, the ORR has to include a chemical step in the reaction pathway.     

THE ROLE OF LATTICE OXYGEN IN THE DYNAMIC BEHAVIOR OF OXIDE CATALYSTS

The lattice of an oxide catalyst used for oxidation reactions can act as a reservoir for oxygen, storing and releasing it for reactions at the catalyst surface under appropriate conditions. The implication of this oxygen storage property of an oxide catalyst on its dynamic response characteristics has been investigated through an experimental study of 2-butene oxidation over vanadium oxide as a model reaction. Isothermal reaction rate measurements in a differential reactor and nonisothermal studies in a single pellet reactor have been carried out. Following a step increase in the feed butene concentration, isothermal reaction rate overshoot and pellet temperature overshoot were observed. These observations could be modelled in a qualitatively correct way by a very simple model accounting for the participation of lattice oxygen in the catalytic reactions under dynamic conditions. It is demonstrated through model simulations that the ignition characteristics of a catalyst pellet are significantly affected by the participation of the lattice oxygen, when steady state multiplicity is present.     

On the nature of the active state of silver during catalytic oxidation of methanol

Under the applied high reaction temperatures (900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (O) apart from O atoms dissolved in the bulk (O). Methanol oxidation to formaldehyde proceeds through this O species as demonstrated by application of a variety of spectroscopic techniques.     

甲缩醛空气氧化制甲醛催化剂的研制和工艺条件探讨

考察了铁钼催化剂对甲缩醛空气氧化制甲醛的催化性能。制备了多种不同钼铁比和第三、第四组分的催化剂,进行了活性评价和筛选,探讨了适宜的工艺条件范围。对于所选定的催化剂(钼铁比为1.82～1.88;铬铁比为0.1～0.38)在适宜的工艺条件(甲缩醛进料浓度4.5～5.5％;甲缩醛和氧气进料比1:2.0±0.2;空速12000～22000h~(-1);热点温度370～390℃)下,甲醛收率可达85％左右。     

环十二烷空气催化氧化制环十二醇及酮

研究了以偏硼酸为催化剂的环十二烷常压空气氧化制环十二醇、酮的反应规律,采用鼓泡搅拌釜作为反应器,在间歇操作方式下,通过改变通氧速率、搅拌转速、反应温度、催化剂用量,测定了反应液中烷、醇、酮的浓度随反应时间的变化关系,得到了醇、酮选择性与烷转化率的关系,确定了适宜的工艺操作条件。在连续操作方式下,通过改变烷的进料速度,测得了反应产物中烷、醇、酮的浓度随空时的变化关系,并与间歇操作获得的实验结果进行了比较。     

十二钨酸络钴酸钾氧化肼、不对称二甲肼和羟胺的动力学和机理

本文研究了十二钨酸络钴酸钾(K_5Co(Ⅲ)W_(12)O_(40),简记为Co(Ⅲ)WO)氧化电位和pH的关系,Co(Ⅲ)WO在最大吸收处(388nm)吸光度和浓度间的关系。用分光光度法研究了Co(Ⅲ)WO在HAc-NaAc缓冲体系中氧化硫酸肼、不对称盐酸二甲肼、硫酸羟胺的动力学,给出了相应的表观活化能、活化熵等动力学参数,讨论了通过氩键传递电子的可能性。     

Effect of the metal oxide loading on the activity of silica supported MoO3 and V2O5 catalysts in the selective partial oxidation of methane

Precipitated silica catalysts loaded with either MoO₃ (0.2–4.0 wt%) or V₂O₅ (0.2–5.3 wt%) have been studied in the selective partial oxidation of methane to formaldehyde with molecular oxygen at 520 °C. The functionality of the SiO₂ surface towards the formation of HCHO is significantly promoted by V₂O₅, while it is depressed by the MoO₃.