Air separation by a high temperature molten salt process

A high temperature molten salt process (the MOLTOX™ system) is being developed for gaseous oxygen production. The system has the potential to serve 90% of future large tonnage oxygen markets, especially combined cycle power plants, and oxygen based metallurgical and chemical technologies. The ability of this chemical separation process to be effectively heat integrated provides oxygen energy savings of up to 40%. This sytem produces very high purity oxygen by heating and depressurizing a molten nitrate salt in a closed loop system. Pilot plant operation has confirmed the process design model used for the economic evaluation. Corrosion results indicate that the materials of construction used in the pilot tests are generally adequate, except at high temperature (650°C) two phase flow locations, namely the oxygen desorption heat exchanger. Research is now focused on the development of a corrosion resistant material of construction to be used in this key equipment item.     

Using Circular Conduits in Ozone Injection

Dissolved oxygen is the amount of oxygen dissolved in water corresponding to an important water quality parameter in rivers, streams, and lakes. Hydraulic structures can increase dissolved oxygen levels by creating turbulent conditions where small air bubbles are carried into the bulk of the flow. A gated conduit is a hydraulic structure that can be used efficiently in aeration and oxygen transfer. The subatmospheric pressure between the upstream and downstream of the gate is the reason for the air injection. Ozone is an unstable gas comprised of three oxygen atoms, and it can be used for water treatment. Ozone is thermodynamically unstable and spontaneously reverts back into oxygen. Ozone has been widely accepted as an effective disinfectant and a chemical oxidant. In this study a series of experiments was conducted to determine the ozone injection performance of circular conduits. Results showed that circular conduits are very effective for ozone injection.     

DIFFUSION COEFFICIENT OF OXYGEN IN LIQUIDS

The laminar dispersion of a solute in a capillary tube is used to measure diffusion coefficient of oxygen in liquids. A Polarographic type oxygen microelectrode is used to detect the pulse. Such a procedure overcomes the problems of measuring dissolved gases and makes it possible to apply this well known technique to oxygen-liquid systems. The results are in agreement with literature values     

Barrier coats versus inert atmospheres. The elimination of oxygen inhibition in free-radical polymerizations

The polymerization of UV-curable coatings that react by a free-radical mechanism is subject to oxygen inhibition which can be avoided by utilizing an inert atmosphere. We demonstrate that wax barrier coats used to prevent evaporation of volatile reactive monomers are equally effective in preventing oxygen inhibition. No quantitative difference is found between the degree and rate of polymerization in an inert atmosphere or with a wax barrier coating. However, when used above a given ceiling temperature, the wax barrier allows oxygen diffusion which inhibits cure.     

Investigation of oxygen diffusion into contact lenses using electron spin resonance spectroscopy

Oxygen permeability is the most important parameter of contact lenses, as lack of oxygen causes corneal edema and threatens the vision of the patient. This study was unique in that it used an electron spin resonance (ESR) technique to determine the oxygen diffusion coefficient (D) of contact lenses. Although there are many methods and techniques for investigating oxygen diffusion into contact lenses, ESR was used for the first time in this study. The ESR technique is based on the scavenging of radicals produced in lenses by oxygen. As a contact lens is not a paramagnetic substance, it cannot give an ESR spectrum. But it does produce an ESR spectrum after γ irradiation. When a vacuum‐irradiated contact lens is exposed to air, the radicals trapped in the lens are transformed into peroxide radicals by the addition of molecular oxygen to the free radicals, and the ESR spectrum begins to change with time. This effect can be used as a tool to measure oxygen uptake in irradiated contact lenses. The oxygen diffusion coefficient of a contact lens was determined from changes in ESR signal intensity varying with time. The diffusion coefficients of oxygen for a contact lens were determined for rapid decay [(1.5 + 0.4) × 10^?8 cm²/s] and slow decay [(1.3 + 0.3) × 10^?9 cm²/s] in this study. These values are in agreement with the D values given in the literature for polymeric materials used for contact lenses. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2937–2941, 2006     

Control and selectivity of photosensitized singlet oxygen production: challenges in complex biological systems

Singlet molecular oxygen is a reactive oxygen species that plays an important role in a number of biological processes, both as a signalling agent and as an intermediate involved in oxidative degradation reactions. Singlet oxygen is commonly generated by the so-called photosensitization process wherein a light-absorbing molecule, the sensitizer, transfers its energy of excitation to ground-state oxygen to make singlet oxygen. This process forms the basis of photodynamic therapy, for example, where light, a sensitizer, and oxygen are used to initiate cell death and ultimately destroy undesired tissue. Although the photosensitized production of singlet oxygen has been studied and used in biologically pertinent systems for years, the photoinitiated behaviour is often indiscriminate and difficult to control. In this Concept, we discuss new ideas and results in which spatial and temporal control of photosensitized singlet oxygen production can be implemented through the incorporation of the sensitizer into a conjugate system that selectively responds to certain triggers or stimuli.     

焦炉废气含氧分析技术改进

炼焦行业当前普遍使用煤气燃烧废气中的含氧量,来衡量煤气燃烧是否充分。较为普遍的做法是实时检测机、焦两侧分烟道中的废气含氧量。这种废气含氧量不能真实地反映出各燃烧室燃烧废气的含氧量,因此不能有效提供所需最佳空气输入量数据。通过技术改进,利用一台氧化锆氧含量分析仪分时扫描多个蓄热室小烟道的燃烧废气含氧量,进而实现了最佳控制全炉所有燃烧室的燃烧状况。该技术的推广应用将有助于焦化企业节能降耗以及自动化操作程度的提高。     

合成氨生产中氧含量控制系统的改进

介绍了合成氨生产中氧含量控制的一种控制方案。氧含量控制系统是一个大时滞系统,大时滞系统的控制问题是过程控制中的难题,本方案采取转移取样点位置的方法来解决这一难题,把合成氨生产中氧含量的取样点移至洗气塔气体出口。改进后时滞在5 s以内,有效地解决了氧含量监测控制的时滞过长的问题。     

密闭容器中残余氧含量测定的思考

在密闭容器中用过量的磷燃烧空气后,利用亚甲基蓝对燃烧剩余气体中的氧气进行定性测量并用控氧仪及气相色谱进行定量测量。结果表明,体系内仍剩余有氧气,根据反应的静置程度,氧含量分别为4.6%和1.27%。     

Influence of oxygen content on structure and properties of pressurelessly sintered aluminum-nitride- and zirconium-boride-doped silicon-carbide ceramics

SiC is a widely used material. Understanding how oxygen content affects the SiC structure and properties is crucial. In this paper, heat treatment was used to prepare SiC powder samples with different oxygen contents, which were doped with AlN and ZrB₂ and were densified by pressureless sintering at 2050 °C. The effect of oxygen content on the sintered SiC structure was determined by X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The results indicated that the oxygen content influenced the SiC phase composition, grain boundaries, and densification. Additionally, the interaction between oxygen defects and AlN played an important role in sintering. The nanoindentation, alternating-current impedance, and thermal conductivity of the densified SiC specimens were also evaluated to elucidate the influence of the oxygen content on the densified-SiC functional properties. The results revealed that the oxygen content affected all the measured mechanical, electrical, and thermal properties. Furthermore, surface oxygen impurities suggested that oxygen content had similar critical effects on both the densified SiC structure and properties.     

Singlet-Oxygen Generation by Peroxidases and Peroxygenases for Chemoenzymatic Synthesis

Singlet oxygen is a reactive oxygen species undesired in living cells but a rare and valuable reagent in chemical synthesis. We present a fluorescence spectroscopic analysis of the singlet-oxygen formation activity of commercial peroxidases and novel peroxygenases. Singlet-oxygen sensor green (SOSG) is used as fluorogenic singlet oxygen trap. Establishing a kinetic model for the reaction cascade to the fluorescent SOSG endoperoxide permits a kinetic analysis of enzymatic singlet-oxygen formation. All peroxidases and peroxygenases show singlet-oxygen formation. No singlet oxygen activity could be found for any catalase under investigation. Substrate inhibition is observed for all reactive enzymes. The commercial dye-decolorizing peroxidase industrially used for dairy bleaching shows the highest singlet-oxygen activity and the lowest inhibition. This enzyme was immobilized on a textile carrier and successfully applied for a chemical synthesis. Here, ascaridole was synthesized via enzymatically produced singlet oxygen.     

Molecular Simulation of Oxygen Sorption and Diffusion in the Poly (lactic acid)

Grand canonical Monte Carlo and molecular dynamics simulation methods are used to simulate oxygen sorption and diffusion in amorphous poly(lactic acid) (PLA). The simulated solubility coefficient of oxygen is close to experimental data obtained from the quartz crystal microbalance but much higher than those from the time-lag method. This discrepancy is explained by using the dual-mode sorption model. It is found that oxygen sorption in PLA is predominantly Langmuir type controlled, em.e., through the process of filling holes. The time-lag method only takes into account oxygen molecules that participate the diffusion process whereas a large proportion of oxygen molecules trapped in the void have little chance to execute hopping due to the glassy nature of PLA at room temperature. The simulated diffusion coefficient of oxygen is reasonably close to the data obtained from the time-lag method. The solubility coefficient of oxygen decreases linearly with increasing relative humidity while its diffusion coefficient firstly decreases and then increases as a function of relative humidity.     

两段式滴管内烟煤富氧空气分级燃烧NOx排放特性研究

随着我国对大气污染物排放监管力度的日益严格,NOx控制技术已广泛应用于工业生产的各个领域。作为一种直接、简便的NOx排放控制技术,富氧空气燃烧技术已经出现在燃气锅炉和内燃发动机等行业,然而在燃煤锅炉行业中却鲜有应用。为了验证富氧空气燃烧技术在煤粉工业锅炉中的NOx减排效果,笔者以神府烟煤作为燃料,利用两段式滴管炉试验系统模拟煤粉在锅炉内燃烧的实际情况,采用热态试验方法,研究了烟煤富氧空气分级燃烧的NOx排放特性,并与单级供风、空气分级燃烧2种燃烧方式下的NOx排放情况进行对比。考察了主燃区温度、二次风配比(以主燃区过量氧气系数表示)、二次风氧浓度等关键因素对NOx排放的影响。结果表明:富氧空气分级燃烧的NOx排放显著低于单级供风燃烧,同时也低于空气分级燃烧的NOx排放。主燃区温度为1 300~1 500℃时,富氧空气分级燃烧的NOx排放减少比例比分级配风燃烧提高了6~12个百分点;富氧空气分级燃烧条件下,随主燃区温度升高,煤粉燃烧更加充分,燃料中N元素分解成NHi、HCN等大量中间产物,使主燃区气氛的还原性增强,被还原的NOx比例增加。因此,NOx排放降低且NOx排放减少比例呈现上升趋势;富氧空气分级燃烧的二次风配比对NOx排放具有显著影响,随着主燃区过量氧气系数的升高,NOx排放均呈现先降低后升高的趋势。因此存在最佳二次风配比,使NOx排放浓度最低。主燃区温度为1 300℃时,最佳主燃区过量氧气系数约为0.58;主燃区温度为1 500℃时,最佳主燃区过量氧气系数约为0.55;在主燃区过量空气系数给定的条件下,提高二次风氧浓度可以延长煤粉颗粒在主燃区的停留时间,并在煤粉颗粒表面形成局部富氧环境,促进煤粉充分燃烧,从而增强主燃区气氛的还原性,降低NOx的生成。因此,当二次风氧浓度为21%~31%时,NOx排放随二次风氧含量的升高而降低。随着二次风氧浓度的逐渐升高,NOx排放的降低趋势逐渐放缓。     

Oxygen mobility in LaCoO3 perovskites

This work reports a study of oxygen mobility in a variety of LaCo_1−xFe_xO₃ perovskites. The methods used to evaluate oxygen reactivity were temperature programmed oxygen desorption and oxygen isotopic exchange. Three kinds of oxygen are distinguished, depending on their reactivities. First, surface oxygens were found to be the most active forms of oxygen. In oxygen desorption experiments, they are responsible for two desorption peaks, designated as ₁- and ₂-oxygens in this work. Grain boundary oxygen is distinguished from bulk oxygen, and is proposed to be responsible for β-oxygen desorption observed at high temperature (>750 °C). These two kinds of oxygen, surface and grain boundary oxygen, are however quickly exchanged with the gaseous oxygen during the isotopic exchange reaction. The third kind, and less reactive, oxygen species is proposed to be the bulk oxygen. The mobility of this oxygen in the bulk of LaCoO₃ is measured by the initial rate of isotopic exchange. Its mobility is related to the activation of the bulk Co³⁺, and migration of some anionic vacancies.     

Optimization of Oxygen Transfer through Membrane Diffusers for Biological Sweetening of Biogas

Biological techniques for the removal of gaseous pollutants such as hydrogen sulfide (H₂S) have proved to be effective, environmentally friendly, and economically viable. However, when high concentrations of H₂S are treated, the process is severely restricted by the oxygen deficit in the liquid phase. The oxygen transfer efficiency provided by a membrane diffuser is evaluated under typical pressure and salinity conditions used for the biological treatment of H₂S in biogas. The optimal operating parameters for enhanced oxygen transfer were determined. The addition of pure oxygen with a membrane diffuser to increase the oxygen transfer rate and the use of a nonaqueous phase to improve oxygen transfer in a bioscrubber system are also evaluated.     

Oxidation of methane on a Au + SrFeO3−δ//YSZ electrode characterised by mass spectroscopy and 18O2 pulses

A solid state electrochemical reactor is described in which reactants can be oxidised at high temperatures over an anode/catalyst using co-fed oxygen gas as well as electrochemically supplied oxygen. The setup permits injection of isotopic pulses in the reactant streams. The composition and isotopic distribution in the products are recorded with a quadrupole mass spectrometer. The use of the system is exemplified by oxidation of methane over a Au + SrFeO_3?δ//YSZ anode at 800–850°C. Pulses of ¹⁸O₂ in the stream of co-fed O₂ were used to study the reactivity and products of gaseous oxygen as distinguished from the electrochemically supplied oxygen. The results indicate that the anode used supports oxygen pumping, but is only moderately active for methane oxidation. The products are mainly CO and CO₂. The content of ¹⁸O in the products is low, indicating that methane oxidation takes place by ¹⁶O-rich lattice oxygen. In comparison, a reference Au//YSZ electrode was found to be a slower anode for oxygen pumping, but a better catalyst for the reaction between CH₄ and gaseous O₂, seemingly involving adsorbed oxygen.     

Consumption of oxygen by mycelial cultures of microorganisms in a fermenter

The hypothesis that highly viscous liquid fermentation media can be segregated into agglomerates, groups of stagnant liquid volumes functioning as separate bioreactors, is proposed. The steady-state distribution of oxygen over the agglomerate depth is theoretically studied. It is shown that the value of the oxygen concentration at the agglomerate surface cannot be used to correctly evaluate the total amount of oxygen in the whole agglomerate volume and that the average rate of oxygen consumption is much lower than the maximum possible value. The dynamics of periodic variation of the oxygen profile in a fermenter with allowance for the coexistence of two radically different zones of mixing, vigorous stirring of liquid near the impeller and its circulatory flow in the remaining volume, is theoretically studied and the total rate of oxygen consumption for a fermenter with liquid circulation is estimated.     

好氧发酵过程微界面传质耦合模拟分析

微生物好氧发酵过程是一个多相生化反应体系,空气中的氧在气液两相间的传质速率对生化发酵过程有重要影响。而气泡中氧的传递特性是气泡的形态、运动及体系温度、压力和物性综合影响的结果。通过建立两组分空气气泡上升及其氧传质耦合模型,进而采用数值模拟描述好氧发酵体系中微界面体系的强化效果。利用能量耗散理论评价制造微气泡体系的能耗,以获得高性价比的气泡形态和较高的氧利用率。计算结果表明,在预设的工况下,液面高度一定的反应器内,初始半径大于500μm的气泡会在短时间内逸出体系,造成物料浪费;而气泡初始半径小于100μm时,其停留时间、传质效率和氧利用率会显著提升。小气泡的生成需要较大的能耗,需要综合生产成本考虑。在不考虑其他因素影响的情况下,体系中的DO值如果维持在20%～30%,可以获得最大的氧气传质速率。     

Comparison of oxygen bomb method to other methods for measuring oxidative stability of peanuts and peanut products

The active oxygen method of the American Oil Chemists' Society has been used extensively to evaluate the oxidative stability of fats and oils. The AOM lacks versatility, however, in that it can be used for only a few products such as lard and vegetable oils. Experience in our laboratory has shown that results also can differ widely, even on the same sample. Recent work with the oxygen bomb at the National Peanut Research Laboratory has shown that it is both reliable and accurate when compared to other methods for measuring the oxidative stability of peanuts and peanut products. Results with the oxygen bomb were compared to the active oxygen method and iodine value of the peants.     

Determination of permeability and diffusivity of oxygen in polymers by polarographic method with inert gas

A modified polarographic method with inert gas for determination of the oxygen permeability in polymers immersed in liquids is described. Owing to the stream of an inert gas towards polymer from the cathode side, lateral oxygen diffusion (edge effects) is minimized. Unlike the standard Fatt method, the method with inert gas is suitable also for thick samples and, therefore, for high-permeable materials. The method was tested for prediction of oxygen permeability in poly(1-vinyl 2-pyrrolidone) (PVP) and poly(2-hydroxyethyl methacrylate) (PHEMA). As an electrolyte, solution of potassium chloride was used. The effect of additional resistances and small lateral diffusion was taken into account. Unexpectedly, oxygen permeability in both polymers was greater for 0.1 M KCl than for 0.5 M KCl. The experimental setup was also used for diffusivity estimation in thick samples of PHEMA and PVP. Here, the oxygen flux response at one sample surface to the stepwise change in oxygen concentration at the other surface is measured and evaluated. The effect of the additional boundary layer on the oxygen transport is taken into account. A simple procedure for the diffusivity determination from the characteristic time of response as a function of the sample thickness is given. Solubility of oxygen in polymer is calculated from the obtained permeability and diffusivity.