Showing papers in "Separation and Purification Methods in 1976"

The Solution-Diffusion Model for Swollen Membranes

Abstract: It has been widely recognized for many years that gases, vapors, liquids, and solutes permeate through non-porous polymer membranes by a solution-diffusion mechanism1–5. However, it was only ten years ago that it was first proposed6 that reverse osmosis might be quantitively described by this mechanistic model. The solution-diffusion model first published by Lonsdale, Merten and Riley6 has been applied with considerable success to describe a variety of systems but the cellulose acetate-water-inorganic salt system has received most attention due to its importance in desalination. It is widely accepted that this model not only describes the process of reverse osmosis but also represents an accurate mechanism in those cases where the membrane structure is truly dense, i. e. non-porous, with no imperfections - this condition refers only to the “active layer” in Loeb-type6 membranes.

Progress in Parametric Pumping

Abstract: Parametric pumping is the name given to a novel separation device developed by Richard Wilhelm and co-workers(1,2,3). The principle of operation depends on an immobile phase (e.g. adsorbent) to alternately retard and release selected species. This action coupled with a synchronous periodic fluid flow causes the selectively adsorbed species to be literally pumped from one region to another. In the successful experiments(2,3) a single packed column was used with reservoirs attached to each end. A water jacket surrounding the bed was heated or cooled synchronously with periodic fluid motion. Figure 1 outlines the principle of operation. Essentially, the process operates in a “bucket-brigade” fashion. If one follows the travels of a single solute (see Figure 1) in a non-adsorbable solvent we see that during downflow the column is cooled thus retarding (adsorption step) the solute, allowing the solvent to move unimpeded. When the flow direction changes to an upward motion, the column is heated, releas...

Sorption and Diffusion in Molecular Sieve Zeolites

Abstract: Recent information concerning the kinetics and equilibria of sorption of various classes of molecule in four representative types of molecular sieve (4A/5A, 13X, natural erionite and H-chabazite) is reviewed. The general relationships between the crystal structure of the sieve, the molecular properties of the adsorbate (particularly the critical diameter and polar nature of the molecule) and the sorption/diffusion behaviour are emphasized.

Molecular Separation Barriers and Their Application to Catalytic Reactor Design

Abstract: The use of semipermeable membranes for multicomponent separations based on molecular size has long been recognized. In certain applications, however, it is often desirable not to effect a separation of chemical constituents, but to sustain a separation which already exists. As an example, the efficient and economical design of a. chemical reactor using an enzyme as a catalyst depends on the accessibility of the reactant to the catalyst as well as on the degree to which a physical separation between the enzyme and the reactor product stream is maintained. A particularly simple and attractive means of achieving this is through the use of semipermeable asymmetric hollow fiber membranes. For example, by sequestering an enzyme solution within the annular macroporous support regions of an asymmetric hollow fiber, a physical separation between enzyme and a reactant solution flowing through the fiber lumen is achieved. In this way, small reactant molecules are free to diffuse across the ultrathin membran...

Separation of Lanthanides and Trivalent Actinides with Pressurized Ion Exchange

Abstract: Certainly, one of the first triumphs of ion exchange chromatography was the separation and identification of fission product rare earths in the Manhattan Project in the early 1940s. Publications de...

The Gas Chromatography of β-Diketonates

Abstract: Since the initial studies of James and Martin1,2 gas chromatography has revolutionized separations in organic and biochemistry. The development of the gas chromatography of metallic species has been relatively slow in coming; however, the inherent advantages of extraordinary sensitivity, speed and ease of separating mixtures of closely related compounds, has promoted a recent surge of interest in the technique. In general, gas chromatographs are not conveniently operated at temperatures in excess of 350° C. This temperature requirement places severe limitations on the types of inorganic compounds that can be chromatographed. In most, but not all cases, the metal complex must exhibit avapor pressure of 0.1 to 1 mm of mercury in order to have a reasonable rate of gas-phase migration through the column3. To meet the requirement, the complexes must be unusually volatile and thermally stable in the chromatographic column. Metal compounds of suitable volatility are limited in number and include metal a...

Analysis of the Apollo 16 Free-Fluid Electrophoresis Experiment

Abstract: The Apollo 16 free-fluid electrophoresis experiment attempted the separation in microgravity of two different-size monodisperse polystyrene latexes under conditions that would give a completely roiled sample on earth because of the thermal convection. The instrument comprised three parallel 0. 63-cm inside diameter 10. 2-cm long Lexan polycarbonate electrophoresis channels, with ted from the channel by semipermeable membranes. The latex samples were contained in cylindrical chambers separated from the electrode by a fixed semipermeable membrane and from the Lexan tube by a movable Kapton polyimide film. Two channels contained 0. 80μm- and 0. 23μ-diameter monodisperse polystyrene latexes and the third, a mixture of the two sizes. The experiment was initiated in microgravity by removing the Kapton films which separated the latex samples from the electrophoresis channels and applying a potential of 300 volts across the electrodes. The results were recorded by photographs taken every 20 seconds.

Separation and Identification of Glycosaminoglycans

Abstract: The term “mucopolysaccharides” was originally introduced by Meyer to describe “hexosamine-containing heteropolysaccharides of animal origin occurring in a pure state or as protein salts”. Many of the names originally assigned to the mucopolysaccharides have since been revised in an effort to systematize the nomenclature (Table 1). Jeanloz2 in 1960 proposed the term “glycosaminoglycuronoglycans” in place of mucopolysaccharides as in most cases they are composed of amino sugars (glycosamino-) and uronic acids (glycurono-) joined in long chains(-glycans). For the sake of simplicity, the term “glycosaminoglycans” is getting acceptance in place of the rather lengthy term “glycosaminoglycuronoglycans” as well as the old and perhaps more familiar term “mucopolysaccharides”. As a matter of convenience, the term “polysaccharides” will be frequently used here, instead of glycosaminoglycans.