Carbon-Dioxide-Selective Membranes

Bai H, Ho WSW (2009) New carbon dioxide-selective membranes based on sulfonated polybenzimidazole (SPBI) copolymer matrix for fuel cell applications. Ind Eng Chem Res 48(5) 2344-2354... 

D. Shekhawat, D. R. Luebke, H. W. Pennline, A review of carbon dioxide selective membranes, A Topical Report, DOE/NETL-2003/1200 December 1, 2003. 

R2. Rechnitz, G. A., Nogle, G. J., Bellinger, M. R., and Lees, H., Determination of total carbon dioxide in serum and plasma using a carbonate ion-selective membrane electrode. Clin. Chim. Acta 76, 295-307 (1977). 

Fonong and Rechnitz (1984a) entrapped the enzyme physically with a dialysis membrane at the sensing tip of a carbon dioxide selective electrode. The sensor was suitable for salicylate concentrations in the range 0.04-2.2 mmol/l. 

Rao et al. studied ethanol oxidation reaction in a real fuel cell using 40% Pt/C as cathode and Pt/C (20% and 40%), PtRu/C, and PtaSn/C as anodes [51]. Their DBMS sensor consisted on a cylindrical detection volume through which anode outlet flow passes. This volume was separated from the vacuum system of the mass spectrometer by a microporous Teflon membrane (pore size 0.02 (im and thickness of 110 (im) supported by a Teflon disk. For Pt/C and 0.1 M ethanol the carbon dioxide selectivity increased with the reaction temperature. The selectivity was highest at 0.5-0.6V and doubled from 60°C (40%) to 90°C (ca. 85%). At higher potentials the CO2 selectivity decreased and increased the acetaldehyde production. CH3CHO formation also increased at lower temperatures (at 90 °C and low, ethanol concentration was almost absent). At high ethanol concentrations the selectivity to carbon dioxide decreased but this effect was less significant than temperature effect at least for ethanol concentrations lower than 1M. 

Li T, Pan Y, Peinemann K-V, Lai Z. Carbon dioxide selective mixed matrix composite membrane containing ZIF-7 nanofiller. J Membr Sci 2013 425 235-12. 

Glassy polymer membranes have been used by gas processors for more than 30 years. Their main current applieation is the removal of carbon dioxide from natural gas. Despite several obvious advantages (compactness, modularity), membrane technology still occupies a minor, though continuously growing, part in the natural gas treatment market, if compared to other conventional solvent solutions. The main limit of commercial carbon dioxide removal membranes resides in their relatively moderate CO2/CH4 selectivity. Consistent R D efforts are presently eonducted to overcome this limitation on a wide... 

Carbon-dioxide-selective separation is becoming an important issue in areas such as petrochemical engineering (e.g., CO2 removal from natural gas), environment (e.g., CO2 removal from flue gas), agriculmre (e.g., control of CO2 concentration), and other related industries. Membranes can selectively separate CO2 from industrial processes. 

This chapter reviews the recent developments of two types of facilitated transport membranes (1) supported liquid membranes (SLMs) with strip dispersion and (2) carbon-dioxide-selective polymeric membranes, for environmental, energy, and biochemical applications. 

This chapter reviews and discusses recent advances in carbon-dioxide-selective polymer membranes for hydrogen purification and carbon dioxide removal. 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

FoUowiag Monsanto s success, several companies produced membrane systems to treat natural gas streams, particularly the separation of carbon dioxide from methane. The goal is to produce a stream containing less than 2% carbon dioxide to be sent to the national pipeline and a permeate enriched ia carbon dioxide to be flared or reinjected into the ground. CeUulose acetate is the most widely used membrane material for this separation, but because its carbon dioxide—methane selectivity is only 15—20, two-stage systems are often required to achieve a sufficient separation. The membrane process is generally best suited to relatively small streams, but the economics have slowly improved over the years and more than 100 natural gas treatment plants have been installed. 

Ion-selective electrodes can also become sensors (qv) for gases such as carbon dioxide (qv), ammonia (qv), and hydrogen sulfide by isolating the gas in buffered solutions protected from the sample atmosphere by gas-permeable membranes. Typically, pH glass electrodes are used, but electrodes selective to carbonate or sulfide may be more selective. 

In gas separation with membranes, a gas mixture at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the mixture. The basic process is illustrated in Figure 16.4. Major current applications of gas separation membranes include the separation of hydrogen from nitrogen, argon and methane in ammonia plants the production of nitrogen from ah and the separation of carbon dioxide from methane in natural gas operations. Membrane gas separation is an area of considerable research interest and the number of applications is expanding rapidly. 

The lipid bilayer arrangement of the plasma membrane renders it selectively permeable. Uncharged or nonpolar molecules, such as oxygen, carbon dioxide, and fatty acids, are lipid soluble and may permeate through the membrane quite readily. Charged or polar molecules, such as glucose, proteins, and ions, are water soluble and impermeable, unable to cross the membrane unassisted. These substances require protein channels or carrier molecules to enter or leave the cell. 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

The only ceramic membranes of which results are published, are tubular microporous silica membranes provided by ECN (Petten, The Netherlands).[10] The membrane consists of several support layers of a- and y-alumina, and the selective top layer at the outer wall of the tube is made of amorphous silica (Figure 4.10).[24] The pore size lies between 0.5 and 0.8 nm. The membranes were used in homogeneous catalysis in supercritical carbon dioxide (see paragraph 4.6.1). No details about solvent and temperature influences are given but it is expected that these are less important than in the case of polymeric membranes. 

Reflectance measurements provided an excellent means for building an ammonium ion sensor involving immobilization of a colorimetric acid-base indicator in the flow-cell depicted schematically in Fig. 3.38.C. The cell was furnished with a microporous PTFE membrane supported on the inner surface of the light window. The detection limit achieved was found to depend on the constant of the immobilized acid-base indicator used it was lO M for /7-Xylenol Blue (pAT, = 2.0). The response time was related to the ammonium ion concentration and ranged from 1 to 60 min. The sensor remained stable for over 6 months and was used to determine the analyte in real samples consisting of purified waste water, which was taken from a tank where the water was collected for release into the mimicipal waste water treatment plant. Since no significant interference fi-om acid compounds such as carbon dioxide or acetic acid was encountered, the sensor proved to be applicable to real samples after pH adjustment. The ammonium concentrations provided by the sensor were consistent with those obtained by ion chromatography, a spectrophotometric assay and an ammonia-selective electrode [269]. 

In higher vertebrates this enzyme is quite abundant in the brain mainly as the cytosolic isoenzymes CA II, CA IV, and the membrane-bound isoform CA XIV (104,175 179). The inhibition of the brain CAs causes a selective increase of the cerebral blood flow with concomitant rise of carbon dioxide partial pressure (104,175-179). As a result CA inhibitors are recognized as potent candidates for treatment of... 

Mixed matrix membranes have been prepared from ABS and activated carbons. The membranes are intended for gas separation. A random agglomeration of the carbon particles was observed. A close interfacial contact between the polymeric and filler phases was observed. This morphology between inorganic and organic phases is believed to arise from the partial compatibility of the styrene/butadi-ene chains of the ABS copolymer and the activated carbon structure. A good permeability and selectivity for mixtures of carbon dioxide and methane has been reported (91,92). 

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