Some Liquid Thermal Diffusion Separations in a Continuous Thermogravitational Column

Abstract

The separation of three binary mixtures on n-heptane-1,1,2,2-tetrachloroethylene, n-propanol-1,1,2,2-tetrachloroethylene, and n-heptane-methylcyclohexane was studied in a continuously operated thermogravitational column. The effects of feed rate, the ratio of top and bottom product rates, and temperature difference on separation were determined. The separations were found to be dependent on the feed rate with the maximum separation occurring at flow rates approaching zero. Over the range studied, the effect of top to bottom product flow rate ratio was found to be negligible. Temperature difference appeared to influence separation when finite flow rates were used.     

Separation by Thermal Diffusion in a Rotary Column

Abstract

A rotary thermal diffusion column with the inner cylinder rotating and the outer cylinder static was used to separate n-heptane-benzene mixtures at different speeds of rotation. The results show that the column efficiency depends on the speed of rotation. For the optimum speed the increase in efficiency relative to the static column was of the order of 8%. The role of the geometric irregularities in the annulus width on performance of the rotary column is also discussed.     

The Improvement of Separation Theory in a Continuous Thermal Diffusion Column

Abstract

A more precise equation of separation applicable to the whole concentration range in a continuous thermal diffusion column with the feed introduced from any position has been derived. The results are also represented graphically and compared with those obtained by Powers in which he, as well as almost all previous investigators, considered the concentration at the feed position of the column to be approximately the feed concentration.     

Comparison of Various Methods of Calculating a Separation Factor in Thermal Diffusion

Abstract

An improved equation of separation applicable to the whole range of concentration in flat-plate thermal diffusion columns has been derived by the least squares method. Separations calculated from this equation are more accurate than those from the generalized equation obtained by Yeh and Chu, particularly for low flow-rate operations and equifraction solution.     

The Simplified Equation of Separation for the Enrichment of Heavy Water in a Batch-Type Thermal Diffusion Column

Abstract

A simple but precise equation of separation for the enrichment of heavy water in a batch-type thermal diffusion column has been derived with the consideration of a pseudobinary mixture. The experiment has also been conducted for various initial concentrations of D₂O and the results are in agreement with the prediction of the theory.     

Experimental Studies on the Separation of Deuterium Oxide in Continuous Thermal Diffusion Column for Low Concentration Range

Abstract

Separation equations for the enrichment of heavy water in a continuous-flow thermal diffusion column have been derived for low-concentration operations. Experimentals on two feed concentrations of the H₂O-HDO-D₂O system have also been conducted, and the results quantitatively confirm the predictions of theory.     

Optimization and Calculation of Gas Thermal Diffusion Column

Abstract

Analytical dependencies, permitting the optimization of a gas thermal diffusion column (TDC), are obtained. A method for calculation of the geometry and gas flows in TDC or a cascade of TDC (TD-cascade) has been proposed.     

Thermal Separation of Soot Carbon

We present here a simple and versatile variant of the thermal analysis of soot carbon, and a discussion on the encountered analytical artifacts. The method is based on a two-step combustion procedure; the removal of the organic material that does not absorb visible light is optimized during a precombustion step at 340°C during 2 hours under a pure oxygen flow, and the remaining carbon is then determined by coulometric titration of the CO₂ evolved from the combustion of the samples. These analytical conditions minimize the crossover between the different components of the aerosol, but better to a clear-cut division between organics and soot carbon, the quantitative evaluation of their thermal evolution is obtained. Artifacts have been tested thoroughly with various standards and replicates of ambient air samples collected. The method gives reliable soot carbon determination at the microgram level in samples from a wide variety of environments. Combined H / C atomic ratio measurements and investigations of the problems associated with the thermal determination of soot carbon permit gaining some insight on the nature of carbonaceous aerosols. They reinforce the indication that soot carbon is not composed primarily of elemental carbon. Also, it is suggested that highly polymerized natural organic aerosols though different in nature could behave thermally and optically like soot.     

Column Dynamics for Adsorption of Bulk Binary Gas Mixtures on Activated Carbon

Abstract

Dynamics of adsorption from bulk N₂-He, CH₄-He, CO₂-He, CO₂-N₂, and CO₂-CH₄ binary mixtures were measured in a column packed with the BPL activated carbon. The data were analyzed using an adiabatic, isobaric, constant pattern model of column adsorption in conjunction with a linear driving force model for the adsorbate mass transfer. It was found that the mass transfer coefficients for adsorption of CO₂, CH₄, and N₂ were significantly lower during binary co-adsorption in the presence of each other than the corresponding pure component mass transfer coefficients in the presence of nonadsorbing helium. The reduction was more pronounced for the less strongly adsorbed species of the binary mixture. This kinetic interaction between the adsorbates could not be predicted a priori. Equilibrium isotherms for adsorption of pure N₂, CH₄, and CO₂ and for adsorption of CO₂-N₂ and CO₂-CH₄ binaries were also measured on the carbon. The isotherms obeyed the Langmuir equation.     

Separation of Biological Solutes by Liquid Thermal Diffusion

Abstract

A number of phenolic components of urine reactive to phosphomolybic acid were separated by the use of liquid thermal diffusion.     

Gaseous Mixtures Separation via Chemically-Activated Nano Silica-Modified Carbon Molecular Sieves

Silicon - The goal of this research was to study the efficiency of the silica-modified, highly selective synthesized carbon molecular sieves for nitrogen separation in the methane purification...     

Solution of the Diffusion Equations in a Gas Centrifuge for Separation of Multi component Mixtures

Abstract

The demand for stable isotopes in physical and chemical research and in medical diagnostics is growing, and the gas centrifuge process is able to provide large quantities of stable isotopes. A set of diffusion equations describing separation in a gas centrifuge for a multi component mixture is established. These equations involve general diffusion coefficients. Using the radial averaging method and the simplified diffusion transport vector for a multi component isotopic mixture, nonlinear partial differential equations are transformed to a set of nonlinear ordinary differential equations. An iteration method for the solution is presented. The relationship between the separation factor and the mass difference, γ _ij = γ ^Mj _o ^?Mi , is shown to be in agreement with both the computational and the experimental results with very high precision.     

Separation of Methane and Carbon Dioxide Gas Mixtures by Pressure Swing Adsorption

Abstract

Two pressure swing adsorption processes for separation of methane and carbon dioxide gas mixtures are described. One process simultaneously produces a high purity CH₄ and a high purity CO₂ product with high recoveries of both components from the feed gas. The other process only produces a high purity CH₄ product with high recovery. Test data for these processes are reported and their relative advantages are discussed.     

A Separation Factor Method for the Analysis of Ideal Binary Mixtures in Gas-Solid Adsorption

Abstract

A correlation formula based on the separation factor is proposed for the mixture concentration in the adsorbed phase of an ideal binary solution in gas-solid adsorption. This formula is shown to apply to two binary systems (viz., 1,3-butadiene and n-butane on cross-linked polystyrene at 25°C, and acetylene and ethane on activated carbon at 25°C) with similar molecular and thermodynamic properties in the two components for each system. Comparison between the calculated and experimental values of the separation factor showed that the assumption of an ideal mixture is justified for each of these two binary systems. Mixture isotherms for the two ideal binary systems are calculated by the proposed correlation formula from the corresponding single-component isotherms. Good agreement between the calculated and experimental mixture isotherm data confirms that a binary system of two components with similar molecular properties (viz., molecular weight, normal boiling point, vapor pressure, number of carbon atoms in molecules, etc.) tends to form an ideal mixture (i.e., one with a constant separation factor).     

The Separation of n-Paraffins from Paraffin Mixtures

Abstract

The choice of the preferred operative phase for a separation system is determined by many factors, which ultimately affect process practicality as well as the capital and operating costs. Practical considerations, such as the temperature and pressure required to operate in a specific phase or the reactivity and stability of feed and desorbent components at elevated temperature, may dictate the preferred processing strategy. When no such controlling factors exist, the decision becomes less obvious and is, in simplest terms, governed by which phase requires the least adsorbent and desorbent.     

Separation of Tetrahydrofuran from Aqueous Mixtures by Pervaporation

Abstract

Studies on the separation of tetrahydrofuran (THF) and water by pervaporation were conducted. A silicalite-filled silicone composite membrane was used for organic permeation and a polyvinyl alcohol composite membrane for dehydration. Effects of feed concentration, feed temperature, permeate-side pressure, and type of membrane were studied. The silicone composite membrane yielded a selectivity of 205 and a THF flux of 1.1 kg/m²·h at benchmark conditions of 50°C feed temperature, 2 torr permeate-side pressure, and a feed concentration of 4.4% w/w THF. An increase in temperature increased the flux exponentially in an Arrhenius-type manner, but had little effect on selectivity. These data show that the trend agrees with an Arrhenius-type relationship. An increase in feed concentration increased the flux, but the selectivity for THF decreased. As the permeate-side pressure increased, the flux decreased in a sigmoidal fashion, but the selectivity for THF increased. Some initial studies on dehydration were also performed. Use of pervaporation in a solvent recovery/reuse system in industry has also been examined.     

The Enrichment of Heavy Water in a Continuous-Type Inclined Thermal Diffusion Column

Abstract

Equations of the best angle of inclination and the maximum separation for the enrichment of heavy water in a continuous-type inclined thermal diffusion column have been derived. Considerable improvement in separation was obtained by employing the inclined column instead of using the Clusius-Dickel column.     

Influence of the Thermodynamic Parameters and Geometry on the Degree of Separation and Energy Consumption in a Gas Thermal Diffusion Column under Static Conditions

Abstract

The influence of the thermodynamic parameters of a binary gas mixture and the geometry of the column on the degree of separation and energy consumption in a gas thermal diffusion column (TDC) was investigated under static conditions (no gas production). The theoretical results are illustrated with experimental data for a nitrogen-helium mixture in a cylindrical TDC, in the temperature interval 300 to 800 K, and pressures ranging from 24 kPa to 1.1 MPa.