Plasticized membranes, separation

A thin plastic membrane separates hydrogen from air. The molar concentrations of hydrogen in Ihe membrane at the inner and outer surfaces are determined to be 0.045 and 0.002 kmol/m respectively. The binary diffusion coefficient of hydrogen in plastic at the operation temperature is 5.3 X lO mVs. Determine the mass flow rate of hydrogen by diffusion through the membrane under steady conditions if the thickness of the membrane is (a) 2 ram and (b) 0.5 mni,... 

Kozlowski, C. A., Girek, T., Walkowiak, W., Koziol, J. J. (2005). Apphcation of hydrophobic [beta]-cycladextrin polymer in separation of metal ions by plasticized membranes. Separation and Purification Technology 46 136-144. 

Lithium batteries using solid cathodes typically use a thin lithium-metal foil or disk as the anode a transition metal oxide, metal sulfide, or a fluoride as the cathode and an organic electrolyte. The cathode material is either coated onto a foil substrate (often aluminum) or embedded into an expanded metal or perforated metal substrate. The anode and cathode are separated by a microporous plastic membrane separator, usually polyethylene and/or polypropylene. 

Based upon the above concept, three different types of membrane separation, i.e., (1) liquid membrane separation which utilizes lipophilic anion-exchangers as mobile carriers, (2) polymeric membrane separation in which the anion-exchange sites function as fixed carriers, and (3) polymeric plasticizer membrane separation in which the membrane is composed of polymeric support, membrane plasticizer, and lipophilic anion-exchangers as a novel membrane material are discussed in relation to their transport efficiency and selectivity for separation of heavy metal chloride complexes. 

The membrane transport experiments were first conducted in a cylindrical dialysis cell (membrane area, 0.8 cm ) shown in Figure 10. The source phase solution was a 250 mL of 0.25 M MgCl2 solution which contained 0.10 mM Pb(II) and Cd(II). The receiving phase was 5.0 mL of pure water. Plots of the EF value versus time for competitive transport of Pb(II) and Cd(II) are presented in Figure 12a. Selective permeation of Cd(II) over Pb(II) was observed, which is consistent with the selectivity obtained for the polymeric membrane separation. The EF for both heavy metals increased with time and reached values of 13.3 and 0.7 for Cd(II) and Pb(II), respectively after 6 h. As shown in Figure 11, the polymeric membrane separation required the permeation time of 40 h to achieve the EF value of 5.8 for Cd(II), whereas such EF value was recorded only after 2 h for the polymeric plasticizer membrane separation. Thus it is evident that the polymeric plasticizer membrane revealed a superior transport efficiency and selectivity to the conventional polymeric anion-exchange membrane. 

Liquid membrane electrodes are shown in Figure 3(a). Typically an organophilic porous plastic membrane separates the internal reference from the sample solution. Another reservoir contains a liquid ion-exchanger, which saturates the pores in the membrane. The calcium electrode uses calcium dodecyl phosphate [(ROlj POjJj Ca where R is the dodecyl radical, dissolved in dioctyl phenylphosphonate. 

While it would be difficult to enumerate all of the efforts in the area of implants where plastics are involved, some of the significant ones are (1) the implanted pacemaker, (2) the surgical prosthesis devices to replace lost limbs, (3) the use of plastic tubing to support damaged blood vessels, and (4) the work with the portable artificial kidney. The kidney application illustrates an area where more than the mechanical characteristics of the plastics are used. The kidney machine consists of large areas of a semi-permeable membrane, a cellulosic material in some machines, where the kidney toxins are removed from the body fluids by dialysis based on the semi-permeable characteristics of the plastic membrane. A number of other plastics are continually under study for use in this area, but the basic unit is a device to circulate the body fluid through the dialysis device to separate toxic substances from the blood. The mechanical aspects of the problem are minor but do involve supports for the large amount of membrane required. 

A novel capillary electrophoresis method using solutions of non-crosslinked PDADMAC is reported to be effective in the separation of biomolecules [211]. Soil studies conducted with PDADMAC report the minimization of run-off and erosion of selected types of soils [212]. In similar studies, PDADMAC has found to be a good soil conditioner [213]. The use of PDADMAC for the simultaneous determination of inorganic ions and chelates in the kinetic differentiation-mode capillary electrophoresis is reported by Krokhin [214]. Protein multilayer assemblies have been reported with the alternate adsorption of oppositely charged polyions including PDADMAC. Temperature-sensitive flocculants have been prepared based on n-isopropylacrylamide and DADMAC copolymers [215]. A potentiometric titration method for the determination of anionic polyelectrolytes has been developed with the use of PDADMAC, a marker ion and a plastic membrane. The end-point is detected as a sharp potential change due to the rapid decrease in the concentration of the marker due to its association with PDADMAC [216]. 

Regenesys uses DuPont s Nafion (Section 6.1.7) as the perm-selective sodium ion transfer membrane, separating the two half cells. Figure 2.1. Diffusion of sodium ions in the concentration difference across the Nafion membrane is one of the irreversibilities of the system. The low-cost plastic (e.g. polyethylene) tanks and pipework are treated with fluorine to provide bromine resistance, and are able to operate with, and contain, both electrolytes at ambient temperature. 

Cellulosic Membranes. The first asymmetric membrane for gas separation appeared in 1970 (Table II), and It was not surprising that this membrane was a modified CA membrane of the Loeb-Sourirajan type (17). Gelled CA membranes for water desalination must be stored wet In order to maintain their permeation performance. However, In gas permeation, wet, plasticized membranes tend to lose their properties with time due to plastic creep of the soft material under pressure and due to slow drying during which the microporous sublayer may collapse and thus increase the thickness of the dense skin-layer. Gantzel and Merten (17) dried CA membranes with an acetyl-content of 39.4% by quick-freezing and vacuum sublimation at... 

Diaphragm—(1) A flexible ring covered with rubber or other plastic material, fitted over the cervix of the uterus to prevent pregnancy. (2) Muscular membrane separating the abdominal and thoracic cavities, used for respiration. 

Thus, each side of the anode is divided into three compartments separated by the ion-selective membranes. Tie bolts keep the stack tightly sealed. The membrane separating the catholyte from the electrolyte is an Ionics CR-6170 alkali-resistant membrane. The membrane separating the anolyte from the electrolyte is an Ionics CR-61-CZL-183 acid-resistant membrane (Ionics, Inc., Water-town, Mass). The two membranes are separated by a I in. thick plastic spacer. Effective area of the membranes is one square foot. 

Following the initial feasibility studies of Lubbers and Opitz, Cardiovascular Devices (GDI, USA) developed a GasStat extracorporeal system suitable for continuous online monitoring of blood gases ex vivo during cardiopulmonary bypass operations. The system consists of a disposable plastic sensor connected inline with a blood loop through a fiber optic cable. Permeable membranes separate the flowing blood from the system chemistry. The C02-sensitive indicator consists of a fine emulsion of a bicarbonate buffer in a two-component silicone. The pH-sensitive indicator is a cellulose material to which hydroxypyrene trisulfonate (HPTS) is bonded covalently. The 02-sensitive chemistry is... 

Polymer-based LMs have been known for over 40 years and have been used as the sensing membranes of ion-selective electrodes (ISEs) and optodes where they have been usually referred to as plasticized membranes. However, separation... 

Tayeb, R., Fontas, C., Dhahbi, M., Tingry, S., and Seta, P. 2005. Cd(II) transport across supported liquid membranes (SLM) and polymeric plasticized membranes (PPM) mediated by Lasalocid A. Separation and Purification Technology 42 189-193. 

Fig. 39.1a shows a schematic representation of the HUP/C supercapacitor a pure solid electrolyte membrane separates two composite electrodes composed of a mixture of highly polarizable electrode particles and electrolyte crystallites. Current collectors and plastic encapsulation complete the component. The manufacturing process involves (i) synthesis of electrolyte powder for the pure electrolyte membrane (ii) synthesis of the intimate mixture of composite electrode parts (iii) pressure performing of the membrane (iv) assembly of the two composite electrodes and the... 

The construction of ISEs used in clinical measurements is of the membrane electrode type, i.e., the ion-sensitive membrane separates the sample from an internal reference electrolyte, which is the site of the internal reference element, usually a silver wire covered by silver chloride. The membrane can be shaped to different forms such as flat, convex, tubular, etc. Sodium sensitive membranes are made from special composition glass, the other ion-sensitive membranes from a polymer matrix such as plasticized polyvinylchloride (PVC) or silicon rubber. The particular selectivity of polymer membranes is first of all due to a small percentage of active material, e.g., valinomycin, dissolved in the polymer. Important secondary effects have been attributed to the type and permittivity of the polymer. The useful lifetime of the sensors also depends on the polymer. The time response [13] may again depend on membrane composition. 

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