A semi-empirical model for the air oxidation kinetics of UO<Subscript>2</Subscript>

UO₂ is readily oxidized to U₃O₈ at a high temperature, and this reaction has received considerable attention in the field of nuclear fuel cycles. A voloxidation process which makes use of the characteristics of a UO₂ oxidation has been developed to treat the spent fuels produced by irradiation of UO₂. In this work, semi-empirical kinetic models to describe the sigmoidal behavior of a UO₂ oxidation were selected and compared in order to obtain a kinetic expression with different temperatures. Two basic approaches of a nucleation-and-growth model and an autocatalytic reaction model were adequate enough to describe the S-shaped oxidation behavior, and an equation to correlate the model parameters with the temperature was introduced. The calculation results of the two models satisfy the experimental data for UO₂ spheres and the activation energy of a reaction rate constant was evaluated. The models were also adopted as a surface reaction time term for a UO₂ pellet.     

Oxidation of cellulose in pressurized carbon dioxide

This work presents first results upon oxidation of type II cellulose by nitrogen dioxide dissolved in carbon dioxide at high pressure. This reaction leads to oxidized cellulose, a natural-based bioresorbable fabric used for biomedical applications. The oxidation reaction takes place in a heterogeneous fluid-solid system. Kinetics of oxidation is presented here and effects of operating conditions such as pressure, temperature and initial moisture content of cellulose are investigated. Results are presented in terms of degree of oxidation of cellulose and quality of the final oxidized cellulose, which has been characterized using liquid-state and solid-state ¹³C NMR. The experimental results show the existence of possible secondary reactions which may lead to oxidized cellulose with insufficient mechanical strength. An attempt is made to evidence and understand the role of CO₂ as a solvent in this system. Indeed, although supercritical CO₂ appears to be a suitable candidate as a solvent for oxidation reactions, some inhibiting effect on nitrogen dioxide activity are observed in this case.     

On the behaviour of nitrate esters in acid solution. III. Oxidation of ethanol by nitric acid in sulphuric acid

The oxidation of ethanol as a model of the alcohols produced in the hydrolysis of nitrate esters, by nitric acid in aqueous sulphuric acid solutions has been studied with the aim to obtain information on the decomposition reaction of “spent acids”. The results show, in agreement with previous suggestions from this laboratory, that ethanol is firstly oxidized to acetaldehyde via a reaction initiated by nitric acid but carried on by NO₂ radical. The latter is formed by the interaction of nitric and nitrous acids. The acetaldehyde is then oxidized by two independent paths leading one to acetic acid and the other to oxalic acid and eventually to CO₂. The relevance of these findings on the understanding and on the control of „spent acids”︁ is briefly discussed.     

轻质燃料油的氧化脱硫研究

研究了H2O2以及促氧剂AC和TFAC对汽油中硫醇的氧化脱除效果。实验结果表明，H2O2可能有效的将汽油中硫醇氧化并且添加促氧剂能明显改善H2O2的作用效果。同时，工艺条件结果表明，较低反应温度，较短反应时间以及高剂油比对硫醇的氧化脱除反应有利。     

加压流化床中褐煤空气氧化制取腐殖酸的研究

为了加速空气氧化生成腐殖酸的反应速度,以及为采用连续过程的可能性提供科学和工艺的依据,在加压流化床中进行了札賚诺尔褐煤空气氧化制取腐殖酸的研究。在本试验装置中考察了压力（0～20大气压）、温度（150～190℃）等条件对腐殖酸生成速度的影响。试验结果指出:压力对于腐殖酸的生成速度有显著影响,达到腐殖酸含量为80％左右所需要的时间与压力成反比关系;温度也是影响腐殖酸生成速度的重要因素,但在该种反应器中,由于结构的限制,散出在氧化早期所产生的大量反应热是很困难的,因此反应温度难以进一步提高,而存在一个“高限温度”。 在本文试验条件下最佳的工艺条件为:20大气压,170℃,反应1.5小时;或为5大气压,190℃,反应2.5～3小时。在这两种情况下,氧化煤中腐殖酸含量为85～87％左右,羧基含量为2.1～2.4毫克当量数/克无灰无水氧化煤左右。     

Oxidation Behavior of SiC-Whisker-Reinforced Alumina-Zirconia Composites

During high-temperature oxidation in air, SiC-whisker-reinforced Al₂O₃—ZrO₂ composites degrade by the formation of a whisker-depleted mullite-zirconia scale. The reaction kinetics have been studied as a function of time and temperature for composites with whiskers preoxidized for different times. The evolution of the microstructure has been investigated by optical, scanning and transmission electron microscopy. Possible reaction mechanisms have been discussed. A model compatible with our observations on Al₂O₃—ZrO₂—SiC and the results reported in the literature for Al₂O₃—SiC whisker composites is proposed: The oxidation occurs at an internal reaction front. Oxygen diffuses along dislocations and grain boundaries through the mullite scale to react at this front with silicon carbide, thereby forming amorphous silica and graphite. Silica penetrates grain boundaries and further reacts with alumina and zirconia to form mullite and zircon, while the second reaction product, graphite, is oxidized into carbon monoxide when the reaction front moves deeper into the sample.     

A kinetic model for partial oxidation of ethane to acetic acid on promoted VPO catalyst

The partial oxidation of ethane to acetic acid on promoted VPO with Mo, using an Mo/V ratio of 0.2, has been investigated experimentally and theoretically. The reaction was carried out in a differential reactor at 1360 kPa, in the temperature range 548–623 K, with space times of 1.2–3.6 s and oxygen concentrations of 5–20%. The rate of oxidation of ethane was found to be approximately first order in ethane and zero order in oxygen at 548 K. At 623 K, the order of reaction with respect to ethane decreased to about 0.5, while that for oxygen increased to about 0.27. A kinetic model has been developed, which assumes that adsorbed oxygen reacts with ethane to form ethene, acetic acid, CO and CO₂. Ethene is further oxidized to acetic acid, CO and CO₂ through a redox mechanism. The model exhibits good agreement with the experimental data. © 2000 Society of Chemical Industry     

Highly efficient and organic nitrogen‐containing cation‐promoted aerobic oxidation of alkylaromatics in the presence of N‐hydroxyphthalimide

BACKGROUD: Direct oxidation of alkylaromatics to the corresponding aromatic ketone is an important process in the manufacture of perfumes, pharmaceuticals, flavors, dyes and agrochemicals. For example, tetralin is oxidized to produce 1‐tetralinone, which is a key intermediate in the commercial production of 1‐naphthol, 2‐hydroxy‐1‐tetralone, aureolic acid antibiotics and other pharmaceuticals. RESULTS: In this investigation, it was found that alkylaromatics could be efficiently and selectively oxidized to the corresponding aromatic ketones when methyl violet was employed as a promotor in the presence of N‐hydroxyphthalimide (NHPI); tetralin was oxidized with 89% conversion and 76% selectivity to 1‐tetralinone under 0.3 MPa of O₂ at 75 °C for 2.5 h. The effects of temperature, oxygen pressure, reaction time and additive inclusion were studied in detail. A possible reaction mechanism for tetralin oxidation has been proposed. CONCLUSION: It was demonstrated that methyl violet could efficiently promote the aerobic oxidation of alkylaromatics in the presence of NHPI under mild conditions. Further investigations indicated that the nitrogen cation had a crucial promotion effect in the oxidation process. Copyright © 2009 Society of Chemical Industry     

瞬变应答法研究苯催化氧化的反应机理

采用瞬变应答法研究了苯在钒催化剂上催化氧化的反应机理。通过对应答曲线的分析,证明氧首先被催化剂表面吸附,然后以较慢的速率转化为晶格氧,这一步是苯催化氧反应速率的控制步骤。吸附氧是生成 CO 和 CO_2的氧源;晶格氧是生成顺酐的氧源。气相苯不直接参与反应,但以较快的速率可逆吸附于催化剂上,吸附的苯与晶格氧反应生成中间物 IN,IN 进一步氧化生成顺酐。顺酐可逆吸附于催化剂上,其介吸速率较慢。中间物和吸附的顺酐对反应起阻滞作用。     

反应条件对石蜡深度氧化制取二元酸的影响

研究了石蜡液相深度氧化过程中氧吸收量与氧化蜡组成变化的关系。结果说明,深度氧化蜡绝大部分是由多官能团酸组成,其官能团除羧基为主外,次为酯基,其量为羧基的一半,羰基较少,而羟基几无。C_4～C_（10）二元酸在氧化醋酸价为250毫克KOH/克左右时开始有明显的含量,并且随着氧化深度的增加而含量迅速增加。在适宜的催化剂和较好的气液接触情况下,石蜡能否快速定向深度氧化的关键在于恰当的选择温度和氧分压;使整个反应过程中氧化尽可能在化学动力学控制范围内进行,减少扩散因素的影响。试验结果表明,氧化蜡的酯价/酸价比值可作为反映氧扩散速度是否满足氧化动力学速度的需要,也可以估计氧化所能达到的最高酸价。氧化过程中物料收率变化的规律说明,在反应后期氧化蜡收率的显著降低,与此时CO_2和冷凝水相的生成速度迅速增加有关。氧化至酸价400以上后,C_4～C_（10）二元酸的收率最高可达40％（对原料石蜡）。从色谱分析结果得知,在C_4～C_（10）的单体二元酸分布中,一般皆以丁二酸为最多,次为戊二酸,并且C_4～C_5和C_6～C_（10）二元酸的收率相近。     

Oscillatory CO Oxidation Over Pt/Al2O3 Catalysts Studied by In situ XAS and DRIFTS

Fresh and mildly aged Pt/Al₂O₃ model diesel oxidation catalysts with small and large noble metal particle size have been studied during CO oxidation under lean burn reaction conditions to gain more insight into the structure and oscillatory reaction behaviour. The catalytic performance, CO adsorption characteristics using in situ DRIFTS and oxidation state using in situ XAS were correlated. Stable and pronounced oscillations only occurred over the catalyst with smaller particle sizes. Characteristic for this catalyst are low-coordinated surface Pt sites (more corner and edge atoms) which seem to become oxidized at elevated temperature as evidenced by in situ DRIFTS and in situ XAS. In situ XAS further uncovered that the oxidation of the Pt surface starts from the end of the catalyst bed and the oxidation state oscillates like the catalytic activity.     

Anodic oxidation of triphenylphosphinephenylimine

Anodic oxidation of triphenylphosphinephenylimine in acetonitrile has been examined by voltammetry, controlled potential coulometry, and electron spin resonance spectroscopy. Product analyses showed that triphenylphosphine oxide and mixtures of polymeric oxidized salts of aniline are major products along with unreacted starting material. A reaction sequence is proposed in which the primary electrode reaction is a one-electron oxidation followed by rapid cleavage of the radical cation at the PN bond and reaction of the fragments with solvent. Aniline is oxidized anodically to form various polymeric species and liberate protons. Protonation of the starting material renders it electrochemically inert with the result that a large proportion of it is recovered.     

微波辅助复合氧化法合成氧化玉米淀粉

以玉米淀粉为原料、以过氧化氢和过硫酸钾为复合氧化剂、以Fe2＋为催化剂,在酸性条件下采用微波辅助复合氧化法合成氧化玉米淀粉。以反应温度、微波催化合成/萃取仪功率、催化剂质量分数（占干淀粉总量,下同）、复合氧化剂质量分数（占干淀粉总量,下同）、淀粉乳浓度、体系pH值、反应时间等因素为变量,以氧化度为衡量指标,采用单因素实验和正交实验确定微波辅助复合氧化法合成氧化玉米淀粉的最佳工艺条件为：反应温度55℃、微波催化合成/萃取仪功率400 W、催化剂质量分数0.3%、复合氧化剂质量分数8%、淀粉乳浓度45%、体系pH值4.00、反应时间21min,在此条件下,可以制得氧化度为0.140%的氧化玉米淀粉。     

Electrochemical oxidation of 2-naphthol with in situ electrogenerated active chlorine

The electrochemical oxidation of 2-naphthol mediated by active chlorine electrogenerated in situ on a Ti-Ru-Sn ternary oxide has been studied by galvanostatic electrolysis under different experimental conditions. Measurements of chemical oxygen demand (COD), HPLC and GC analyses have been used to follow the oxidation. In the absence of NaCl, only a small fraction of 2-naphthol was oxidized by direct electrolysis, while its complete mineralization was obtained in the case of chlorine-mediated electrolysis. In particular, the rate of naphthol oxidation was found to increase with chloride concentration, pH and to be independent of current density. Analysis of oxidation product has shown that initially organochlorinated compounds have been formed which have been further completely oxidized.     

超声条件下柴油氧化脱硫的研究

采用H2O2-甲酸作为氧化剂将催化裂化柴油中的硫化物（主要为苯并噻吩类）氧化成相应的砜,同时引入超声波为反应提供能量,考察（油/剂）比、氧化温度、反应时间、萃取静置时间、（萃取剂/油）比和萃取次数等因素对脱硫效果的影响。在适宜条件下,脱硫率可达94.2%,收率可达90%以上。     

The reaction network of the selective oxidation of n-butane on (VO)2P2O7 catalysts: Nature of oxygen containing intermediates

The reaction network of the partial oxidation of n-butane to maleic anhydride on (VO)₂P₂O₇ has been investigated using steady-state and transient experiments in a Temporal-Analysis-of-Products (TAP) reactor under vacuum conditions to identify by mass spectrometry possible intermediate products and in a tubular fixed bed reactor at atmospheric pressure to derive information on the role of the detected and other potential intermediates in the reaction network. The oxidation of butane, butadiene, tetrahydrofuran, dihydrofuran, and furan has been studied in the TAP reactor and, additionally to these compounds, crotonaldehyde, crotonlactone, and malealdehydic acid were oxidized in the tubular flow reactor. From the results obtained it can be concluded that the main reaction pathway from butane to maleic anhydride proceeds via the intermediate products n-butenes, butadiene, crotonaldehyde, dihydrofuran, furan, and crotonlactone.     

玉米H_2O_2氧化淀粉的制备及其性能研究

采用双氧水为氧化剂,CuSO4等为催化剂,玉米原淀粉为原料,制备了玉米H2O2氧化淀粉,并分析比较了双氧水在有催化剂和无催化剂条件下的氧化程度,对所制备氧化淀粉的性能进行测定和分析。结果显示,以CuSO4为催化剂、中性条件下H2O2的催化作用最强,其制得的玉米氧化淀粉羧基含量为0.45%,透光率高为82%,产品两周内不凝沉。     

Ozonation of Sulfur-Containing Aliphatic Compounds in Aqueous Solution. I

In view of the possible reaction of ozone with sulfur containing natural and anthropogenic compounds, the oxidation products of sulfur-containing aliphatic model compounds in pure water in dependence on pH value were investigated.

In the first part, as a model compound for thioether, thiodiglycolic acid was investigated. The rate of elimination is independent of pH-value. At pH 3 as primary product thionyldiglycolic acid is formed, which undergoes further oxidation, but very slowly, to sulfonediacetic acid, which is very stable against ozone attack at pH 3. At pH 7 and higher, however, thionyldiglycolic acid is oxidized faster to sulfonediacetic acid, and this compound is oxidized to sulfoacetic acid, oxalic acid, glyoxylic acid, sulfateion, and CO₂ after longer reaction times. In all cases, sulfite as an inorganic intermediate product could not be identified. Also the intermediate products in pure solutions are ozonized. The mass balances show that 90 to 95% of the oxidation products could be identified. Based on these results, reaction schemes are discussed.     

Direct partial oxidation of methane into synthesis gas over Rh|YSZ|Ag

An electrochemical membrane reactor, RhIYSZIAg, has been tested for the partial oxidation of CH₄ to CO/H₂ under oxygen pumping through YSZ. An ionically transported oxygen species over the Rh anode was highly active for the partial oxidation. The reaction mode of the CH₄ oxidation strongly depends on the surface state of Rh particles; a highly oxidized Rh surface accelerates complete oxidation of CH₄ to CO₂/H₂O, while a reduced Rh surface catalyzes the partial oxidation to CO/H₂. Oxygen concentration over the Rh predominantly determines the selectivity; a high oxygen concentration leads to the complete oxidation, while an adsorbed oxygen species gives the partial oxidation.     

Modelling microbial fuel cells with suspended cells and added electron transfer mediator

Derivation of a mathematical model for microbial fuel cells (MFC) with suspended biomass and added electron-transfer mediator is described. The model is based on mass balances for several dissolved chemical species such as substrate, oxidized mediator and reduced mediator. Biological, chemical and electrochemical reactions can occur in the bulk liquid and at the electrode surface, respectively. Model outputs include time-dependent production of current and electrical charge, current–voltage and current–power curves, and the evolution of concentrations of chemical species. The model behaviour is illustrated using a test case based on detailed experimental observations reported in the literature for a microbial fuel cell operated in batch mode and repeatedly fed with a single substrate. A detailed model parameter estimation procedure is presented. The model simulates the current–time evolution and voltage–current curves in the MFC with glucose as anode substrate and the ferrocyanide/ferricyanide redox couple as the oxidation reaction at the cathode. Simulations show the effect of different parameters (electrical resistance, mass transfer resistance, exchange current, coulombic yields and biomass, substrate and mediator concentrations) on the MFC characteristics. The model explains how the endogenous metabolism or intracellular substrate storage could lead to a non-zero background current even when the added substrate has been depleted. Different trends (increasing or decreasing) in the initial current are explained by the initial oxidation state of the mediator (oxidized or reduced, respectively). The model has potential applications for other bioelectrochemical systems.