Gas Separation & Purification最新文献

A silica membrane was formed by chemical vapor deposition using tetraethylorthosilicate in macropores of an α-alumina tube or a γ-alumina film coated on the α-alumina tube. The reactant was evacuated through the porous wall, and silica was deposited in the macropores at 600–700 °C. When the silica membrane was formed in a γ-alumina film coated on the α-alumina tube, hydrogen permeance at a permeation temperature of 600 °C was 3 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹, which was one order of magnitude higher than that of a membrane formed directly on the α-alumina tube. H₂/N₂ selectivity determined from the permeance of each component was 100–1000. To separate hydrogen selectively from abundant steam, however, a higher permselectivity was required. The membrane formed in the γ-alumina film at 650 °C showed a hydrogen permeance of 3 × 10⁻⁸ mol m⁻² s⁻¹ Pa⁻¹ and an H₂/H₂O selectivity of 7.6 at 400 °C.

Dynamic liquid hold-up was measured with an air/aqueous sodium citrate buffer solution at 20–40 °C, and an air/water system at 23 °C, in a 0.1 m diameter/1 m high glass column covered by a heat-isolating vacuum jacket and packed with 0.012 m nominal size ceramic Raschig rings. The superficial gas velocity range was extended to 1.2 m s⁻¹. Experimental results of this work were compared with literature data, with different correlations and with a general equation. All expressions were found to be unacceptable for the air/buffer system and useable for the air/water system. In the case of the air/buffer solution a new correlation is recommended on the basis of our measured data and literature values.

Fundamentals and computer-aided methods of practice for the calculation and checking of azeotropes, and for the qualitative and rigorous determination of separating spaces for closed distillation are presented, which are valid for non-ideal multicomponent systems. Separating spaces can occur in azeotropic systems only and are decisive for the separability of a system, if distillation is the separation technique. As a prerequisite, a rigorous mathematical model of the vapour-liquid equilibrium is required. The eigenvalues and eigenvectors of the Jacobian matrix of the equilibrium concentrations are the key ingredients of several methods: the eigenvalues describe the asymptotic behaviour of closed distillation profiles, which indicates the order according to which components can be separated; the eigenvalues enter a topological equation for checking the thermodynamic consistency of the azeotropes of a system; the eigenvectors initiate paths connecting azeotropes and pure substances, from the network of which separating spaces can be deduced qualitatively; and eigenvectors are essential to initiate the rigorous profiles of separating spaces.

High-temperature measurements of the adsorption properties of strongly adsorbed hydrocarbon vapours on a wide range of commercially available adsorbents are presented. These adsorbents include various cationic forms of the type A, X and Y zeolites, activated alumina and carbon, and some clays. The studies are based upon pulse chromatography experiments using low concentrations of hydrocarbon vapours (toluene and methylcyclohexane) in nitrogen carrier gas. The temperature range of investigation was chosen as 400–700 K, which is typical for the catalytic dehydrogenation of methylcyclohexane to toluene. Even at these temperatures, the relatively strong adsorption properties of the hydrocarbons necessitated the use of high carrier gas flow rates. As a consequence, significant deviation from isobaric operation existed. In this work, non-isobaric pulse chromatography theory was applied to the first moment data, and found to describe accurately the adsorption trends. Furthermore, the temperature dependence of the adsorption equilibria parameters could be determined. The data provide a useful reference in the design and assessment of processes in which the simultaneous operations of high-temperature chemical reaction and adsorptive separation take place, as in chromatographic and pressure swing based reactors.

Conventionally, high purity O₂ has been separated and recovered from air by cryogenic air separation plants. Recently, PSA (pressure swing adsorption) technology has improved and a new process is proposed to produce high purity O₂ by PSA. In this technology, the removal of Ar (argon) by CMS (carbon molecular sieves) and the removal of N₂ from O₂ and N₂ mixtures by zeolite is the key technology for the production of high purity O₂. Concerning this technology, several patents for the production of high purity O₂ have been issued. We have conducted a series of experiments to optimize the high purity O₂ PSA process and have found an interesting result. In this paper, various factors that affect the economics of the high purity O₂ generator are discussed.

The zero length column (ZLC) technique has been successfully used to measure diffusivities in zeolite crystals. However, in industrial applications pellets with bidisperse structure, containing macropores and micropores (crystals), are commonly used as zeolites. In this paper, a model of ZLC desorption curves for bidisperse porous materials is developed. Model equations are analytically solved for linear systems. A numerical solution of model equations using orthogonal collocation is also used. The various regions of control (macropore diffusion, micropore diffusion) are identified. Simulations allow the choice of operating conditions for the ZLC technique. Procedures for the analysis of ZLC experiments are reported.

Results of an experimental and theoretical study of a parallel passage adsorbent contactor are reported. Theoretical considerations suggest that such an adsorber should be preferable to the traditional packed bed for applications in which pressure drop is important. An expression for the HETP (height equivalent to a theoretical plate) for a parallel passage contactor, analogous to the van Deemter equation for the packed bed, is derived and verified experimentally for the adsorption of several light gases from a helium carrier in an adsorber consisting of parallel sheets of activated carbon fibre adsorbent. The extension to a multiple passage system and the effect of moisture in the feed gas were also investigated. A high selectivity ratio ($\text{αCO}{}_2\text{N}{}_2$) and a diffusion time constant of about 10 ms for adsorption of CO₂ and N₂ on activated carbon fibre (ACF) adsorbent confirm that such a parallelsided duct coated with ACF sheets would be well suited to a dual piston rapid pressure swing adsorption system for large throughput and low value added applications such as CO₂ removal from stack gas.

The degradation of aqueous diethanolamine (DEA) solutions by carbon disulfide (CS₂) was investigated using a batch reactor at temperatures ranging from 120 to 190 °C, DEA concentrations of 2 to 6 M and $\text{CS}{}_2\text{DEA}$ mole ratios of 0.05 to 0.23. Reaction products identified by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS), melting point determination, elemental analysis and infrared analysis include monoethanolamine, bis(hydroxyethyl)-ethylenediamine, bis(hydroxyethyl)-piperazine, hydroxyethyl-oxazolidone, hydroxyethyl-imidazolidone, tris(hydroxyethyl)-ethylenediamine, bis(hydroxyethyl)-imidazolidone and an insoluble, sulfur-rich, linear, polymeric solid. The formation of the products increased with temperature, DEA concentration and $\text{CS}{}_2\text{DEA}$ mole ratio. A mechanism for the formation of the products is presented, and the experimental data are consistent with a first-order overall reaction with respect to DEA.

In this experimental study the water gas shift (WGS) reaction is considered as a particular application of a catalytic membrane reactor (CMR). Experiments on the WGS reaction were carried out using a composite palladium membrane obtained by coating an ultrathin double-layer palladium film on the inner surface of the support of a commercial tubular ceramic membrane by a so-called co-condensation technique. The best operating conditions were determined at various $\text{H}{}_2\text{O}\text{CO}$ molar ratios, temperature, P_Iumen, gas feed flow, and with and without nitrogen sweep gas. For a non-porous stainless steel tube and for the commercial ceramic membrane having the same geometrical dimensions, the conversion results are always lower than the equilibrium value. For the composite palladium membrane, the conversion also depends on the flow of the sweep gas utilized. For example, using a nitrogen sweep gas flow of 28.2 cm³/min, the maximum conversion value reaches 99.89%. The study of the effect of temperature on conversion of carbon monoxide in the WGS reaction shows that at higher reaction temperature, the thermodynamic equilibrium conversion of CO decreases. In contrast for the CMR considered in this work, there is a maximum conversion value around 600 K. This value is a compromise between the kinetic rate of the reaction (which increases with increasing temperature) and thermodynamic considerations for the WGS reaction. The effect of the time factor ($\text{W}\text{F}$) on conversion of CO, with and without sweep gas at three different temperatures (595, 615 and 633 K) shows that at greater $\text{W}\text{F}$ there are correspondingly higher values of the CO conversion for each temperature considered. For each temperature there is a slight effect of the sweep gas, and this is higher at 595 K. The good performance of the composite ceramic-palladium membrane is confirmed by a comparison with experimental results recently presented in the literature for the same reaction. Reaction tests have been carried out for a feed mixture also. In this case, however, the resulting values are always below the equilibrium ones.