Gas-liquid separation membranes

Since polymers of substituted PA have good solubility and good air stability, they make good membranes. Even though substituted PA do not possess very high conductivity, some of them exhibit excellent gas and liquid permeability. These two factors combined imply that substituted polyacetylenes could potentially be used for the oxygen enrichment of air and the separation of ethanol-water mixtures [111]. 

Polymer membranes can be used to separate two liquids by per-vaporation. One application of this property is in the distilling industry where alcohol or trace organics need to be separated from 

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Commercially PTFE is available in granular and fine powder resin forms and aqueous dispersions. The granular form of PTFE resin is prepared by suspension polymerization process in an aqueous mediiun with little or no dispersing agent. These forms of PTFE resins are mainly used for compression molding and ram extrusion. The fine PTFE powder is prepared by controlled emulsion polymerization and it is useful for paste extrusion into tapes, tubes, pipe liners, insulation layer of wires, gas-liquid separation membranes and fibers. 

A special type of cross-flow reactor was developed in the laboratories of Vogt [16] to handle continuous gas / liquid reactions. The challenge in the reactor design was to combine efficient gas-liquid mixing, liquid level control in the reactor, turbulent flow across the membrane, and efficient gas-liquid separation to avoid gas contacting the membrane, which would lead to a shunt of gas. The total internal volume should not... 

Creed et al. [68] described a hydride generation inductively coupled plasma mass spectrometric method featuring a tubular membrane gas-liquid separator for the determination of down to 100 pg of arsenic in seawater. 

At high current densities it is also particularly important to ensure that the electrolyser is free from pressure-induced vibrations, which may quickly lead to membrane damage. The vibrations tend to arise if waves form in the gas-bearing liquid in the electrolyser s gas-liquid separation chamber and block the egress of gas through the nozzle of the chamber outlet, as illustrated in Fig. 17.12, leading to sharply fluctuating pressure in the chamber. 

The introduction of hydrides into plasma-based instmmentation has also been achieved. The sensitivity increases markedly when compared with conventional nebulization because of the improved transport efficiency of the analyte to the atom cell (close to 100%). Often, a membrane gas-liquid separator is usee ensure that aerosol droplets of liquid do not reach the plasma. 

Magnuson, M.L., Creed, J.T. and Brockhoffl C.A. (1997) Speciation of arsenic compounds in drinking water by capillary electrophoresis with hydrodynamically modified electro-osmotic flow detected through hydride generation inductively coupled plasma mass spectrometry with a membrane gas-liquid separator./. Anal. At. Spectrom., 12, 689-695. 

Regardless of the chemical vapor transfer mode, CVG uses a gas-liquid separator to separate the chemical vapor from the liquid reagents prior to its introduction into the atomizer. There are several designs of gas-liquid separators, but they can be classified into three basic types hydrostatic separators, forced outlet separators, and membrane separators. A detailed description of gas-liquid separators will be found in specialized monographs.32... 

Segmented polyimide-polydimethylsiloxane copolymers have been successfully synthesized both in laboratory and industrial quantities to produce multiphase siloxane-modified polyimides. The siloxane detracts somewhat from the otherwise excellent thermo oxidative stability of the polyimide, but it does produce a number of important properties. These include multiphase behavior, improved adhesion to many substrates, improvements in fire resistance and enhanced gas and liquid separation membranes, where one wishes not only to maximize the contribution of the siloxane to permeability, but also to utilize the imide to re-... 

Ko, F.H., Chen, S.L., and Yang, M.H. Evaluation of the gas-liquid separation efficiency of a tubular membrane and determination of arsenic species in groundwater by liquid chromatography coupled with hydride generation atomic absorption spectrometry. J. Anal. Atom. Spectrom. 1997, 12, 589-595. 

Arsenic speciation in saline waters can be made using a tubular membrane as a gas-liquid separator for HG-ICP-MS.75 The detection limit achieved using this technique is at the picogram level. The separation step is very important during the sample process because of the presence of the chloride (estuarine and open ocean waters contain high levels of chloride). HC1 is commonly used in the HG processes, which result in a matrix extremely high in chloride. For the separation step to be performed prior to the ICP-MS technique, some studies are carried out using capillary electrophoresis (CE) as a separation technique,76 which includes the interface for CE and ICP-MS.76 77... 

Urtiaga et al. (2001) studied the parallelism and the differences in PV and vacuum membrane distillation (VMD) in the removal of volatile organic compounds (VOCs) from aqueous streams. In their study, two gas-liquid separation processes, PV and VMD, were compared in the application to the separation of chloroform-water mixtures. Both technologies include the transfer of separated compounds initially in liquid phase through a membrane to a low-pressure gas phase. The use of a solid membrane enhances the separation efficiencies. However, PV and VMD are based on different mechanisms and employ membranes of different characteristics. Selective membranes need to be used in PV processes, while the VMD process requires the use of microporous nonselective membranes. 

Purified NaCl solution and water enter the anode compartment and the cathode compartment, respectively, of a conventional bipolar membrane electrolyzer. The anolyte and the catholyte flow to their respective gas-liquid separators. The chlorine gas and the NaOH solution then join in the reactor to form NaOCl solution. Depleted brine from the chlorine separator returns to the brine section for resaturation. Hydrogen from its separator is normally mixed with a large amount of air before discharging to the atmosphere. The operating conditions for the Ionics cell and similar systems are as follows ... 

To prove the technical viability of CO2 liquefaction and separation from the off-gas, a CO2 capture apparatus was designed and assembled. The appearance of the membrane reformer system equipped with CO2 capture apparatus is shown in Fig. 12.11. The experimental apparatus was composed of the water removal equipment, a gas compressor, a chiller, gas-liquid separator and liquefied COj tank. In the preliminary operation test in connection with the 40 Nm%-class membrane reformer, it was demonstrated that over 90% of CO2 in the off-gas can be captured. The total CO2 emission in hydrogen production was decreased by 50% with only 3% energy loss This experimental result suggests that the membrane reformer has the potential to reduce its CO2 emission to half with a minor energy loss by applying the CO2 capture system. 

This part, on applications, covers the following unit operations 8. Evaporation 9. Drying of Process Materials 10. Stage and Continuous Gas-Liquid Separation Processes (humidification, absorption) 11. Vapor-Liquid Separation Processes (distillation) 12. Liquid—Liquid and Fluid-Solid Separation Processes (adsorption, ion exchange, extraction, leaching, crystallization) 13. Membrane Separation Processes (dialysis, gas separation, reverse osmosis, ultrafiltration) 14. Mechanical-Physical Separation Processes (filtration, settling, centrifugal separation, mechanical size reduction). 

H2S can be separated frran the gas by the use of semi-permeable membranes. H2S (and CQ2) can pass the membrane whereas CH4 cannot [18, 37]. In addition, gas-liquid absorption membranes can be used. The membranes are micro pwous and have hydro-phobic pK ierties the molecules in the gas stream, flowing in one direction, difiiise through the membrane and are absorbed on the other side by the liquid, flowing in counter current At a temperature of 25—35 °C the H2S concentration of the raw gas of 2 % could be reduced to less than 250 cm% thus yielding an efficiency of more than 98 %. NaOH is used as the absobent in liquid [ 18,46]. 

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