重氧水分离级联中氘和氧18浓度分布及其影响

在水精馏法分离同位素的系统中,氘和氧18同时得到富集,情况比较复杂。为使该系统的模拟更加贴近实际情况,提出了一种可同时计算氘和氧18浓度分布及氧16/氧18分离系数的新方法。此方法将不同的水分子划分为四个集总,简化了复杂的同位素交换反应网络。然后利用ASPEN PLUS的反应精馏模块进行计算。对一个五塔级联的水精馏制氧18水系统的模拟计算表明,产品中氘浓度达到了70.7%,氧18浓度达到了98.0%。在最后一个精馏塔内,随着氘含量的增加,氧16/氧18分离系数α_cal从接近α_H216O/H218O变得更接近α_D216O/D218O。     

Process design considerations and steady-state operational data for the separations of isotopes of oxygen

Operational data for the separation of oxygen isotopes are given on flow rates, concentrations and concentration profiles of the isotope separation plant of the Weizmann Institute of Science which has reached steady-state operational conditions with regard to the rare and more difficult to separate oxygen-17 isotope. This plant consists of two sections, namely packed distillation columns and thermal diffusion columns. Data on the columns and packing characteristics are given. The concentrations reached in the distillation section are up to 98% of oxygen-18 and up to 20% of oxygen-17. In the thermal diffusion section, concentrations of oxygen-18 up to 99.9% and of oxygen-17 up to 96% have been attained.     

Exchange and oxidation of CO on O-predosed Rh---Al2O3 and Rh---CeO2 catalysts

Exchange and oxidation of C¹⁶O were investigated at 450°C on ¹⁸O-predosed Rh and Pt catalysts supported on A1₂O₃, CeO₂ and CeO₂-Al₂O₃. In all cases, a rapid exchange of C¹⁶O with the surface can be observed. CO oxidation leads to C¹⁶O₂, C¹⁶O¹⁸O and C¹⁸O₂. Significant formation of C¹⁶O₂ is due to the relatively high ¹⁶O coverage in reaction resulting from the C¹⁶O exchange and from an exchange between O surface species and ¹⁶O internal atoms. Hydrogen is also formed via a water-gas shift reaction (CO + surface OH) in higher proportion on CeO₂-containing catalysts than on A1₂O₃. Chlorine inhibits all the reactions (exchange, oxidation and WGS) and particularly the internal exchange.     

Multistage Process of Deuterium and Heavy Oxygen Enrichment by Membrane Distillation

Abstract

Deuterium and oxygen-18 isotope enrichment in water by membrane distillation were studied in a 4-stage cascade. Two configurations of membrane distillation (MD) employing PTFE-flat-sheet membranes were investigated, including direct contact MD and air gap MD. The first, direct contact MD is more efficient. It is characterized by high distillate flow rate. The temperature polarization coefficients were higher for direct contact MD. H/D and ¹⁶O/¹⁸O separation factors were determined in the 4-stage cascade.     

Mechanism of N2O decomposition over a Rh black catalyst studied by a tracer method: The reaction of N2O with O(a)

N₂O decomposition on an unsupported Rh catalyst has been studied using tracer technique in order to reveal the reaction mechanism. N₂¹⁶O was pulsed onto ¹⁸O/oxidized Rh catalyst at 220°C and desorbed O₂ molecules (m/e=32,34,36) were monitored by means of mass spectrometer. The ¹⁸O fraction in the desorbed dioxygen was the same value as that on the surface oxygen. The result shows that the O₂ molecules desorb via Langmuir–Hinshelwood mechanism, i.e., the desorption of dioxygen through the recombination of adsorbed oxygen. On the other hand, TPD measurements in He showed that desorption of oxygen from the Rh black catalyst occurred at the higher temperatures. Therefore, reaction-assisted desorption of oxygen during N₂O decomposition reaction at the low temperature was proposed.     

同位素水精馏非稳态过程制备低氘水的研究与应用

根据水精馏过程中氢、氧稳定同位素的分离特性,以及同位素精馏的稳态和非稳态级联过程的理论分析和研究,应用于水精馏法生产重氧(18O)水的分离过程,在连续生产重氧(18O)水的同时,间歇副产低氘水,使一套同位素分离装置能同时制备二种同位素产品,开发了同位素水的综合制备的技术,提高了分离装置的有效利用率.     

Characterization of the dynamic oxygen migration over Pt/CeO2-ZrO2 catalysts by O/O isotopic exchange reaction

To characterize the oxygen mobility over metal supported catalysts on a dynamic and in situ base, ¹⁸O/¹⁶O isotopic exchange reaction combined with CO oxidation was designed and exemplified on three kinds of three way catalysts of Pt/CeO₂-ZrO₂ (CZ-O, CZ-D and CZ-R). The obtained oxygen diffusion coefficients, oxygen release rate, and oxygen storage capacity were discussed and correlated with XRD spectra and other physical parameters. It was found that the oxygen mobility and oxygen storage capacity were parallel to the structural homogeneity of Zr introduction into the CeO₂ frame work, and decreased as: CZ-R > CZ-D > CZ-O. These results indicated that this combined isotopic exchange technique could be used to quantify the surface and bulk oxygen mobility, the oxygen storage capacity and oxygen release rate over the metal supported catalysts, and could be employed as a meaningful probe into the nature of CeO₂-ZrO₂ oxygen storage material. The oxygen mobility is also another important indicator for the development of oxygen storage materials.     

Heterogenous azeotropic distillaion-homotopy-continuation methods

An algorithm for the simulation of three-phase distillation towers and associated phase separators is presented. The algorithm utilizes the homotopy-continuation method of Allgower and Georg[1] to accurately track the homotopy path, with extensions to avoid limit points when multiple solutions are encountered and when liquid phases are introduced on the trays. The Allgower and Georg algorithm is also extended to track solution paths in parametric studies. Emphasis is placed on the calculation of liquid—liquid equilibria, with a reliable, yet efficient, homotopy-continuation algorithm introduced. An effective method for incorporating the LLE algorithm in the homotopy-continuation algorithm for heterogenous distillation is also introduced.

The combined algorithms have located two steady-state solutions for an industrial azeotropic distillation tower a very narrow range of the reflux ratios, one with a single liquid phase on the trays, the other with two liquid phases on 70% of the trays. In addition, for the dehydration of ethanol with benzene, it has detected a region in which five steady-state solutions exist for the same specifications. Three of these solutions were reported by Magnussen .[2] and observed in dynamic simulations by Prokopakis and Seider[3].     

Quantitative comparison of dynamic controllability between a reactive distillation column and a conventional multi-unit process

A comparison of the steady-state economic optimum designs of two alternative chemical processes was presented in a previous paper [Kaymak, D. B., & Luyben, W. L. (2004). A quantitative comparison of reactive distillation with conventional multi-unit reactor/column/recycle systems for different chemical equilibrium constants. Industrial & Engineering Chemistry Research, 43, 2493–2507]. A generic exothermic reversible reaction A + B ↔ C + D occurs in both flowsheets, which consist of a conventional multi-unit reactor/separator/recycle structure and a reactive distillation column. Results showed that the reactive distillation process is significantly less expensive than the conventional process for a wide range of the chemical equilibrium constant when there is no mismatch between the temperature favorable for reaction and the temperature favorable for vapor–liquid separation.

A reactive distillation column has fewer control degrees of freedom than a conventional multi-unit system. Therefore a reactive distillation column may have worse dynamic response than a conventional process. The purpose of this paper is to compare the dynamic controllability of these two alternative processes.

Three different chemical equilibrium constants are considered. Several control structures are developed for each flowsheet, and their effectiveness is evaluated. Disturbances in production rate and fresh feed compositions are considered.

The conventional multi-unit process provides significantly better control. The operability region is much larger, there is less variability in product quality and the dynamic responses are faster than those of the reactive column. Thus, these results demonstrate that there is a significant trade-off in this system between optimum economic steady-state design and dynamic controllability.     

Study of surface reaction mechanisms by O/O and H/D isotopic exchange

Surface diffusion of active species is a general phenomenon in catalysis: rates of migration often being much higher than turnover frequencies of reaction, surface species can migrate and visit a great number of active sites in between two successive catalytic cycles. ¹⁶O/¹⁸O and H/D isotopic exchange is a very useful technique to elucidate reaction mechanisms involving mobility steps of O- and H-containing reactive species. The method is based on the measurement of the rates of exchange between gaseous ¹⁸O₂ (or D₂) and ¹⁶O species (or OH) species of the support via metal particles, small metallic clusters acting as porthole of O or H on the support. Simple kinetic models allow to calculate surface and bulk diffusivities on the oxide used as support. As a rule, a significant O mobility can only be observed above 200 °C for most oxides. Furthermore, very great differences of diffusivity (five orders of magnitude) are recorded between silica (on which OH groups are virtually immobile) and oxides like ceria exhibiting a very high oxygen mobility. Differences of diffusivity (two orders of magnitude) are much less for hydrogen than for oxygen. This method can give useful information about reactions catalyzed by metal/oxide systems in which surface diffusion can play a decisive role in the mechanism: steam reforming, water gas shift, hydrocarbon oxidation, aromatic hydrogenation, methanol synthesis, coke formation). For oxides such as Ce_xZr_1−xO₂ mixed oxides, O mobility is so high that surface and bulk mobility can no longer be distinguished. More complex kinetic models requiring computer simulation of all the steps of adsorption, desorption, diffusion and exchange simultaneously have been developed.     

变压精馏分离乙酸甲酯-甲醇-乙酸乙酯体系的设计与控制

聚丙烯醇的生产过程会产生乙酸甲酯-甲醇-乙酸乙酯共沸混合物,如果不及时处理,必然会造成环境污染和资源浪费。本文采用变压精馏的方式,针对乙酸甲酯-甲醇-乙酸乙酯体系设计了两种产品顺序不同的变压精馏分离序列,并采用遗传算法以年度总费用最小为目标,对两种分离序列进行优化设计以获得最优的设计参数。优化结果表明,两种变压精馏分离方案的设备投资费用分别为5.6×10⁵ USD/a和5.7×10⁵ USD/a,能耗费用分别为8.8×10⁵USD/a和1.0×10⁶USD/a。此外,对具有经济优势的变压精馏分离方案进行了控制结构的构建,使该过程在面对进料流量扰动和进料组分扰动时仍能维持稳定,稳定之后的三种产品纯度仍能维持在设定值附近。     

Defective structure, oxygen mobility, oxygen storage capacity, and redox properties of RE-based (RE = Ce, Pr) solid solutions

Defective structures, surface textures, oxygen mobility, oxygen storage capacity (OSC), and redox properties of RE_0.6Zr_0.4O₂ and of RE_0.6Zr_0.4−xY_xO₂ (RE=Ce, Pr; x=0, 0.05) solid solutions have been investigated using X-ray diffraction (XRD), temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), O₂−H₂ and O₂−CO titration, ¹⁸O/¹⁶O isotope exchange, CO pulsing reaction, and X-ray photoelectron spectroscopy (XPS) techniques. The effects of doping noble metal onto RE_0.6Zr_0.4−xY_xO₂ on oxygen mobility and surface oxygen activities have also been studied. Based on the experimental outcomes, we conclude that: (i) a Pr-based solid solution has better redox behavior than a Ce-based one; (ii) incorporation of yttrium ions in the lattices of CZ and PZ solid solutions could result in an enhancement in oxygen vacancy concentration, Ce⁴⁺/Ce³⁺ and Pr⁴⁺/Pr³⁺ redox properties, lattice oxygen mobility, and oxygen storage capacity; and (iii) doping the noble metal (Rh, Pt, and Pd) onto RE-based solid solution has positive effect on the properties concerned in this work.     

The Use of Isotopic Tracers in Studying Catalysts and Catalytic Reactions

Nonradioactive tracers such as deuterium, ¹⁸O, ¹⁵N, and ¹³C and radioactive tracers such as tritium and ^l4C have been used extensively for studying the properties of catalysts and the details of catalytic reactions. In the present paper an attempt will be made to show how the uses that have been made of isotopes in catalysis can be divided into one of three categories accordingly as they are concerned with (1) the study of the chemisorption of molecules on a catalyst surface and the nature of the catalyst surface; (2) the measurement of the extent to which the atoms from the structure of the solid catalyst take part in a catalytic reaction and become a part of the product; and (3) the details of the mechanism by which the catalytic reactions take place on the catalyst surface. These three categories will now be discussed and illustrated.     

T型分子筛膜的制备及其对含酸乙腈-水的分离性能

石化医药行业会产生大量乙腈废液,通过无机分子筛膜分离技术进行回收可以创造可观的经济价值。然而,乙腈废液水含量较高,并且具有一定的酸性,目前应用比较广泛的NaA型分子筛膜不能在该体系下长期使用。使用自制的平均粒径为600 nm的T型分子筛作为晶种,采用真空涂敷法将晶种负载在α-Al₂O₃载体管表面,在150 ℃下水热晶化16 h制备出T型分子筛膜,并对其做膜性能评价实验。结果表明,自制的T型分子筛膜在进料流量为3.5 L/h、温度为100 ℃条件下对含有1%（质量分数）乙酸和10%水（质量分数）的乙腈混合溶液进行膜分离脱水实验,渗透通量为2.51 kg/（m ²·h）;在120 h长时间运行过程中,分离系数保持在2 250以上,T型分子筛膜性能基本保持不变。     

KBaB5O9的两步法制备及其过程动力学研究

本文利用溶液法制备了K₂Ba[B₄O₅(OH)₄]₂·8H₂O,并将其进行热处理制备得到了KBaB₅O₉,利用XRD、FT-IR、TG-DTA-DTG对样品进行了表征。分析研究了由K₂Ba[B₄O₅(OH)₄]₂·8H₂O热处理制备KBaB₅O₉过程中的物相变化过程,其物相变化经历脱结晶水、脱羟基、重结晶、再分解、熔融再结晶5个阶段,其中结晶水的脱失分两步进行。运用Kissinger法、Flynn-Wall-Ozawa法、Šatava-Šesták法对K₂Ba[B₄O₅(OH)₄]₂·8H₂O结晶水第二步脱失过程的动力学参数进行了计算,可知K₂Ba[B₄O₅(OH)₄]₂·8H₂O结晶水第二步脱失过程的活化能E_s为151.94 kJ/mol,指前因子的对数值lg A_s为21.25 min^-1,机理函数G(α)=(1-2α/3)-(1-α)^2/3(其中α为转化率)。     

Transferts ioniques durant l'oxydation anodique d'un hydroxyde de nickel

On cherche à déterminer la nature et l'intensité des transferts anioniques responsables de l'oxydation de l'hydroxyde de nickel bivalent, formé en couches minces par dépôt cathodique. L'échange isotopique ¹⁶O–¹⁸O, combiné avec le dosage de l'oxygène par activation nucléaire, constitute l'instrument puissant de cette étude. Il s'y adjoint diverses techiques de caractérisation physicochimique ou isotopique (¹H–³H) plus classiques Les résultats mettent en évidence l'importance des échanges d'anions OH⁻ et permettent de calculer le courant d'échange et le coefficient d'autodiffusion anionique. On montre que ces phénomènes sont étroitement déterminés par l'irréversibilité des transports ioniques et qu'on ne saurant envisager une stoechiométrie prècise et immuable.

Abstract

The aim is to determine the nature and the intensity of the anion transfer that is the basis of the oxidation of bivalent nickel hydroxide obtained in thin layers by cathodic electrodeposition. Isotopic exchange ¹⁶O–¹⁸O, associated with estimation of oxygen by means of a nuclear reaction, has been used. Other more classical physico-chemical or isotopic (¹H–³H) techniques have also been used. The results show the importance of OH⁻ ion exchange and permit the calculation of the exchange current and anion self-diffusion coefficient. It is shown that these phenomena are closely related to the irreversibility of ionic transport so that one cannot think of a precise and fixed stoichiometry.

Abstract

Die Arbeit behandelt die Bestimmung der Art und der Intensität der ionischen Übertragungen die die Oxydation des bivalenten Nickelhydroxyds in dünnen, durch kathodische Ablagerung erzeugten, Schichten bedingen. Zu dieser Untersuchung benutzte man das sehr wirksame Hilfsmittel des Isotopenumtausches ¹⁶O–¹⁸O verbunden mit der Dosierung des Sauerstoffs durch nukleare Aktivierung. Ausserdem wurden auch weitere klassischere Verfahren zur physico-chemischen oder isotopischen (¹H–³H) Charakterisierung angewendet. Die Ergebnisse zeigen die Wichtigkeit des OH⁻ Anionenaustausches und ermöglichen die Berechnung des Austauchstromes und des Selbstdiffusionskoeffizienten. Weiterhin wird gezeigt dass die Erscheinungen durch die Irreversibilität der Ionenübertragung streng bestimmt werden und dass eine genaue und feste Stöchiometrie nicht in Betracht kommt.     

Recycling and Reuse of Ionic Liquid in Homogeneous Cellulose Acetylation

Molecular distillation was used to recover ionic liquid (IL) 1-allyl-3-methylimidazolium chloride (AmimCl) in homogeneous cellulose acetylation. The five factors that affect the separation efficiency of molecular distillation, namely, feed flow rate, distillation temperature, feed temperature, wiper rotating speed, and distillation pressure, are discussed. The optimal recovery condition was determined via orthogonal experiments using an OA₉(3⁴) design. The IL was recycled and reused 5 times in the homogeneous cellulose acetylation system under optimal conditions. The purity of recycled IL the 5th time reached 99.56%. FT-IR (Fourier transform infrared spectroscopy) and ¹H NMR (nuclear magnetic resonance) spectroscopy showed that the structure of the recovered IL is not changed. This work proves that AmimCl has excellent reusability, and that molecular distillation is an effective method for recovering IL in homogeneous cellulose acetylation.     

低温吸附法分离氢同位素

液氮温度下用分子筛Y在自行设计的单塔变压吸附装置上进行氢氘气体分离的研究,考察了流量与压力对分离效果的影响,在气体总压力0.40 MPa、总流量129.79 cm3/min与吸附床长度1.0 m时氢氘气体之间的分离因子可达到1.52。然而压力为0.013 9 MPa与0.017 5 MPa时D2与H2在分子筛Y上的平衡吸附量比值仅分别为1.18和1.17。结合平衡吸附和动态分离之间的差异,表明吸附法能够有效分离氢同位素气体的机理是基于动力学效应。     

H2/HD/HT电解-精馏级联分离过程理论分析

为研究电解精馏级联氢同位素分离过程的规律性,建立了理论模型,并以H2/HD/HT为对象计算研究了系统分离行为。获得了电解和精馏过程系统的浓集行为： 电解池中HDO浓度从2.88×10-4 增长到 8.35×10-4, HTO浓度从1.0×10-6 增长到6.34×10-6;精馏柱再沸器中HD浓度达到0.033,HT浓度达到6.06×10-5。由于H/D和H/T电解池分离因子的差异,63.4%的HTO仍然留在电解池中,造成精馏柱再沸器中HT浓缩倍数不如HD。随时间的增长,脱氘（氚）率下降。     

Recoveries of deuterium from the separation of water–isotope mixture in batch-type thermal diffusion columns under unsteady-state operation

Heavy water (D₂O) is the most feasible moderator and coolant in nuclear-fission reactors while deuterium (D) will be the nuclear fuel for thermonuclear fusion in the distant future. The recoveries of deuterium in D₂O and HDO from the separation of water–isotope mixture (H₂O–HDO–D₂O) by thermal diffusion has been estimated. First, the degrees of separation for each component of water–isotope mixture in thermal diffusion columns were predicted, then the recoveries of deuterium in each component were estimated from the molecule weights. It was found that the maximum recovery of deuterium might be obtained when the feed concentration of D₂O is 0.22 mass fraction.