The measurement of retained fission gas compositions and their isotopic distributions in an irradiated oxide fuel by inert gas fusion-mass spectrometric analysis

In this work, an easy, fast and reliable measurement technique for the quantitative determination of retained fission gases in an irradiated oxide fuel was developed. Many experiments were conducted to determine the optimum conditions for fusion of an oxide fuel, for the quantitative collection and measurements of the released gases. Ion implantation technology was applied to make a krypton or xenon references in a solid matrix. A fragment of oxide fuel, about 0.1 g of an unirradiated SIMFUEL, was completely fused with excess metallic fluxes, 1.0 g of nickel and 1.0 g of tin, in a graphite crucible of a helium atmosphere for 120 s at 850 A as a mixture of metals and alloys. About 96 ± 3 to 98 ± 4% of the krypton and xenon that were injected into the instrument using a standard gas mixture was reproducibly recovered by collecting the releasing gas through the instrument for 120 s. Using the same fusion and collection conditions, it was possible to recover about 97 ± 3% of the injected krypton and xenon by fusing a fragment of SIMFUEL which was wrapped with krypton or xenon implanted aluminum foils. The recovery test results of krypton and xenon using ion planted aluminum foils gave encouraging results suggesting their potential use as a reference specimen. It was confirmed that a fragment of irradiated oxide fuel, 0.051 g, with a code burn-up of 56.9 MWd/MtU, was completely fused as the mixture of metals and alloys through the fusion conditions and more than 99% of the retained fission gases were recovered during the first fusion. Since no cryogenic trap was needed, the collected gas could be measured directly and thus the analysis time could be further reduced. Approximately 7 min was sufficient to finish the measurement of retained fission gases in the irradiated oxide fuel using the developed procedure.     

Hydrate capture CO2 from shifted synthesis gas,flue gas and sour natural gas or biogas

CO₂ capture by hydrate formation is a novel gas separation technology, by which CO₂ is selectively engaged in the cages of hydrate and is separated with other gases, based on the differences of phase equilibrium for CO₂ and other gases. However, rigorous temperature and pressure, high energy cost and industrialized hydration separator dragged the development of the hydrate based CO₂ capture. In this paper, the key problems in CO₂ capture from the different sources such as shifted synthesis gas, flue gas and sour natural gas or biogas were analyzed. For shifted synthesis gas and flue gas, its high energy consumption is the barrier, and for the sour natural gas or biogas (CO₂/CH₄ system), the bottleneck is how to enhance the selectivity of CO₂ hydration. For these gases, scale-up is the main difficulty. Also, this paper explored the possibility of separating different gases by selective hydrate formation and reviewed the progress of CO₂ separation from shifted synthesis gas, flue gas and sour natural gas or biogas.     

Effect of temperature fluctuation on hydrate-based CO_2 separation from fuel gas

A new method of temperature fluctuation is proposed to promote the process of hydrate-based CO2 separation from fuel gas in this work according to the dual nature of CO2 solubility in hydrate forming and non-hydrate forming regions [1].The temperature fluctuation operated in the process of hydrate formation improves the formation of gas hydrate observably.The amount of the gas consumed with temperature fluctuation is approximately 35% more than that without temperature fluctuation.It is found that only the temperature fluctuation operated in the period of forming hydrate leads to a good effect on CO2 separation.Meanwhile,with the proceeding of hydrate formation,the effect of temperature fluctuation on the gas hydrate gradually reduces,and little effect is left in the completion term.The CO2 separation efficiencies in the separation processes with the effective temperature fluctuations are improved remarkably.     

Hydrate-based carbon dioxide capture from simulated integrated gasification combined cycle gas

The equilibrium hydrate formation conditions for CO2/H2 gas mixtures with different CO2 concentrations in 0.29 mol% TBAB aqueous solution are firstly measured.The results illustrate that the equilibrium hydrate formation pressure increases remarkably with the decrease of CO2 concentration in the gas mixture.Based on the phase equilibrium data,a three stages hydrate CO2 separation from integrated gasification combined cycle (IGCC) synthesis gas is investigated.Because the separation efficiency is quite low for the third hydrate separation,a hybrid CO2 separation process of two hydrate stages in conjunction with one chemical absorption process (absorption with MEA) is proposed and studied.The experimental results show H2 concentration in the final residual gas released from the three stages hydrate CO2 separation process was approximately 95.0 mol% while that released from the hybrid CO2 separation process was approximately 99.4 mol%.Thus,the hybrid process is possible to be a promising technology for the industrial application in the future.     

Simulation of thermobaric conditions of the formation,composition, and structure of mixed hydrates containing xenon and nitrous oxide

Structural, dynamic, and thermodynamic features of double hydrates of xenon and nitrous oxide are calculated. Thermodynamic stability regions of these hydrates are found. At the atmospheric pressure the xenon hydrate is in the equilibrium with the gas phase at temperatures up to 263 K, whereas at these pressures the nitrous oxide hydrate decomposes already at 218 K. A strong dependence of the equilibrium temperatures and pressures of the formation/decomposition of double nitrous oxide and xenon hydrates on the composition of their mixture in the gas phase is shown.     

Effect of antiplasticization on selectivity and productivity of gas separation membranes

Addition of certain low molecular diluents cause glassy polymers to become stiffer owing to reduced rates of segmental motions. This antiplasticization response is accompanied by a decrease in permeability to gases and may be accompanied by either an increase or a decrease in the selectivity of transport for any two gases. When compared to the trade-off between selectivity and productivity of gas separation membranes made from a variety of polymer structures, antiplasticization does not offer any advantageous combination of these traits for either polysulfone or poly(phenylene oxide). However, this approach may have value when increased selectivity at the expense of productivity is justified but developing membranes from another polymer is not desirable.     

A new correlation for predicting hydrate formation conditions for various gas mixtures and inhibitors

In the last 50 years, several studies have been performed on the measurement and prediction of hydrate forming conditions for various gas mixtures and inhibitors. Yet, the correlations presented in the literature are not accurate enough and consider most of the time, simple pure gases only and their mixtures. In addition, some of these correlations are presented mainly in graphical form, thus making it difficult to use them within general computer packages for simulation and design. The purpose of this paper is to present a comprehensive neural network model for predicting hydrate formation conditions for various pure gases, gas mixtures, and different inhibitors. The model was trained using 2387 input–output patterns collected from different reliable sources. The predictions are compared to existing correlations and also to real experimental data. The neural network model enables the user to accurately predict hydrate formation conditions for a given gas mixture, without having to do costly experimental measurements. The relative importance of the temperature and the different components in the mixture has also been investigated. Finally, the use of the new model in an integrated control dosing system for preventing hydrate formation is discussed.     

Kinetic theory of gas separation in a nanopore and comparison to molecular dynamics simulation

Kinetic mesoscopic theory derived from an atomistic model is applied to study permeation and separation of gases in a single rectangular pore. The goal is to judge the analytical method against the results of molecular dynamics simulation and to demonstrate the ease and relevance of analytical theories to calculate density profiles, flux, permeance, and separation factors. The permeance is linked to the amount of gas adsorbed in the pore and the effect of the effective gas-wall interaction on adsorption is explored. The effects of pore size, temperature, and the parameters of the pore wall interaction are investigated and reproduce the trends found in the numerical simulation of permeation of a mixture of methane and carbon dioxide in a carbon nanopore.     

Modeling gas separation in metal-organic frameworks

The gas adsorption and CO₂ separation properties of 9 different metal-organic frameworks (MOFs) have been modelled with grand canonical Monte Carlo (GCMC) adsorption simulations. Adsorption of both pure gases and gas mixtures has been studied. MOFs are shown to have high selectivity for polar gases such as CO₂ over non-polar gases such as N₂. Selectivity of one polar gas from another can be altered by changing the polarity of the framework, pore geometry and also temperature. Often features that lead to good selectivity of CO₂ from N₂ also lead to poor selectivity of CO₂ from H₂O.     

Separation of gas mixtures using a range of zeolite membranes: a molecular-dynamics study

Gas separation efficiencies of three zeolite membranes (Faujasite, MFI, and Chabazite) have been examined using the method of molecular dynamics. Our investigation has allowed us to study the effects of pore size and structure, state conditions, and compositions on the permeation of two binary gas mixtures, O(2)N(2) and CO(2)N(2). We have found that for the mixture components with similar sizes and adsorption characteristics, such as O(2)N(2), small-pore zeolites are not suited for separations, and this result is explicable at the molecular level. For mixture components with differing adsorption behavior, such as CO(2)N(2), separation is mainly governed by adsorption and small-pore zeolites separate such gases quite efficiently. When selective adsorption takes place, we have found that, for species with low adsorption, the permeation rate is low, even if the diffusion rate is quite high. Our results further indicate that loading (adsorption) dominates the separation of gas mixtures in small-pore zeolites, such as MFI and Chabazite. For larger-pore zeolites such as Faujasite, diffusion rates do have some effect on gas mixture separation, although adsorption continues to be important. Finally, our simulations using existing intermolecular potential models have replicated all known experimental results for these systems. This shows that molecular simulations could serve as a useful screening tool to determine the suitability of a membrane for potential separation applications.     

Molecular Dynamics Simulation of Structure II Clathrate Hydrates of Xenon and Large Hydrocarbon Guest Molecules

Molecular dynamics (MD) simulations of structure II clathrate hydrates are performed under canonical (NVT) and isobaric–isothermal (NPT) ensembles. The guest molecule as a small help gas is xenon and gases such as cyclopropane, isobutane and propane are used as large hydrocarbon guest molecule (LHGM). The dynamics of structure II clathrate hydrate is considered in two cases: empty small cages and small cages containing xenon. Therefore, the MD results for structure II clathrate hydrates of LHGM and LHGM + Xe are obtained to clarify the effects of guest molecules on host lattice structure. To understand the characteristic configurations of structure II clathrate hydrate the radial distribution functions (RDFs) are calculated for the studied hydrate system. The obtained results indicate the significance of interactions of the guest molecules on stabilizing the hydrate host lattice and these results is consistent with most previous experimental and theoretical investigations.     

Theoretical study on concentration polarization in gas separation membrane processes

A mathematical model was established successfully to analyze the gas separation concentration polarization which becomes an important problem due to the rapid development of membranes, especially the increase of permeation rate. The influences of membrane performance and operation parameters on concentration polarization were studied in terms of permeation fluxes of the more and the less permeable gases and separation factor. Sample calculations were presented for the two typical gas separation applications, hydrogen recovery and air separation, with shell side feed in hollow fiber module. The permeation rate was found to be a dominating factor in affecting concentration polarization, while the influences of separation factor to be significant initially and to level off gradually. Increasing feed gas velocity leads to a decrease in the concentration polarization. Operation pressures' effect is limited and the composition of feed gas shows no effect. The range in which concentration polarization is significant has been identified by studying the combined effects of the permeation rate, separation factor and feed gas velocity. Concentration polarization is important for process analysis and design when the permeation rate of the more permeable gas is larger than 1×10⁻⁴ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ (100 GPU).     

Peak capacity of ion mobility mass spectrometry: the utility of varying drift gas polarizability for the separation of tryptic peptides

Ion mobility mass spectrometry (IM-MS) peptide mass mapping experiments were performed using a variety of drift gases (He, N2, Ar and CH4). The drift gases studied cover a range of polarizabilities ((0.2-2.6) x 10(-24) cm3) and the peak capacities obtained for tryptic peptides in each gas are compared. Although the different gases exhibit similar peak capacities (5430 (Ar) to 7580 (N2)) in some cases separation selectivity presumably based on peptide conformers (or conformer populations), is observed. For example the drift time profiles observed for some tryptic peptide ions from aldolase (rabbit muscle) show a dependence on drift gas. The transmission of high-mass ions (m/z > 2000) is also influenced by increased scattering cross-section of the more massive drift gases. Consequently the practical peak capacity for IM-MS separation cannot be assumed to be solely a function of resolution and the ability of a gas to distribute signals in two-dimensional space; rather, peak capacity estimates must account for the transmission losses experienced for peptide ions as the drift gas mass increases.     

Multicomponent gas separation by selective surface flow (SSF) and poly-trimethylsilylpropyne (PTMSP) membranes

A selective surface flow (SSF) membrane consisting of a thin layer of a nanoporous carbon was produced in a tubular form using a macroporous alumina support. The membrane was tested for hydrogen enrichment applications. Simulated waste gases from a petrochemical refinery and a hydrogen pressure swing adsorption unit were used as the feed gas to the membrane. Very high rejections of C₁C₃ hydrocarbons (saturated and unsaturated) and carbon dioxide over hydrogen were exhibited by the membrane at low feed gas pressures. The hydrogen enriched stream was produced at the feed gas pressure.The separation characteristics of a polymeric poly-trimethylsilylpropyne (PTMSP) membrane in a tubular form was also tested for the same applications using identical conditions of operation. This membrane also selectively rejected heavier components of the feed gas mixture over hydrogen and produced the hydrogen enriched stream at the feed gas pressure. The SSF membrane exhibited much higher hydrogen recovery and hydrocarbon rejections than the PTMSP membrane for these applications under identical conditions of operations using identical support materials.     

Influences of different types of magnetic fields on HCFC-141b gas hydrate formation processes

Gas hydrates are crystalline compounds formedwhen gas molecules or volatile liquid molecules comein contact with water molecules through weak van derWaals force at favourable pressure and temperature.Refrigerant gas hydrates can be effectively formed atappropriate temperature (5—12℃) with a high reac-tion heat (320—380 kJ/kg). Because of their particularthermodynamic properties, refrigerant gas hydrate,especially low pressure refrigerant gas hydrate, hasbeen considered as one of the most pr…     

Evaluation of a mathematical model using experimental data and artificial neural network for prediction of gas separation

In recent times, membranes have found wide applications in gas separation processes. As most of the industrial membrane separation units use hollow fiber modules, having a proper model for simulating this type of membrane module is very useful in achieving guidelines for design and characterization of membrane separation units. In this study, a model based on Coker, Freeman, and Fleming＇s study was used for estimating the required membrane area. This model could simulate a multicomponent gas mixture separation by solving the governing differential mass balance equations with numerical methods. Results of the model were validated using some binary and multicomponent experimental data from the literature. Also, the artificial neural network （ANN） technique was applied to predict membrane gas separation behavior and the results of the ANN simulation were compared with the simulation results of the model and the experimental data. Good consistency between these results shows that ANN method can be successfully used for prediction of the separation behavior after suitable training of the network     

Ordering and Clathrate Hydrate Formation in Co‐deposits of Xenon and Water at Low Temperatures

Local ordering in co‐deposits of water and xenon atoms produced at low temperatures can be followed uniquely by ¹²⁹Xe NMR spectroscopy. In water‐rich samples deposited at 10 K and observed at 77 K, xenon NMR results show that there is a wide distribution of arrangements of water molecules around xenon atoms. This starts to order into the definite coordination for the structure I, large and small cages, when samples are annealed at ～140 K, although the process is not complete until a temperature of 180 K is reached, as shown by powder Xray diffraction. There is evidence that Xe ? 20 H₂O clusters are prominent in the early stages of crystallization. In xenon‐rich deposits at 77 K there is evidence of xenon atoms trapped in Xe ? 20 H₂O clusters, which are similar to the small hydration shells or cages observed in hydrate structures, but not in the larger water clusters consisting of 24 or 28 water molecules. These observations are in agreement with results obtained on the formation of Xe hydrate on the surface of ice surfaces by using hyperpolarized Xe NMR spectroscopy. The results indicate that for the various different modes of hydrate formation, both from Xe reacting with amorphous water and with crystalline ice surfaces, versions of the small cage are important structures in the early stages of crystallization.     

The separation power and thermodynamic work of separation for a three-flow unit during the equilibrium separation of a binary gas mixture

Equations for calculating the separation power and thermodynamic work of a three-flow separation element and cascade for the separation of a binary gas mixture are discussed.     

二维气相色谱法分析天然气水合物区沉积物间隙水中示踪气体的浓度

利用微流路控制技术中心切割装置(Deans Switch)、两根色谱柱(PoraPLOT Q和Molsieve 5A)和3个检测器(脉冲氦离子化检测器、火焰光度检测器、热导检测器),建立了一种二维气相色谱分析系统,实现了海洋中多种示踪气体组分(氢气、甲烷、二氧化碳、硫化氢)的同时分析和精确测定。氢气、甲烷、二氧化碳、硫化氢的含量分别在2～1030、0.6～501、120～10500和0.2～49.1 μmol/mol范围内的校正曲线线性关系良好,检出限分别为0.51、0.17、82和0.08 μmol/mol,10次重复测定含量的相对标准偏差均小于10%。通过对南海天然气水合物区沉积物间隙水顶空气的测定,表明该方法方便、灵敏、可靠,易于实现海上现场测定;与以往采用多种分析方法分别测定示踪气体相比,大大节省了样品量。该方法适用于海洋天然气水合物、海底热液等资源的调查和海洋溶解态气体的研究等。