Binary Composite Membranes

The synthesis of 5 lan thick Ti02 Si02 layers on a porous support can be performed using the procedure given below. First a mixed Ti[(OMe)3]4 alkoxide is synthesized by reacting partially hydrolyzed Si(OMe)4 with Ti-isopropoxide. This inorganic polymer is hydrolyzed at pH 11.0 and treated with 2-methyl-2-4-pentanediol and a binder. This solution is then slip-cast onto a porous support, dried and calcined at 700°C. The membrane can be useful in reverse osmosis applications. 

PHASE SEPARATION/LEACHING METHODS AND CLASS MEMBRANES 

Porous glass membranes are produced by leaching a two-phase glass body in the system Na20-B203-Si02 (Schnabel and Vaulont 1978, Schnabel 1976). 

Under certain time and temperature conditions, the homogeneous glass separates into two phases. One of the phases consists substantially of silicon dioxide which is insoluble in mineral acid. The other phase represents a soluble coherent boric acid phase rich in alkali borate. If the boric acid phase is dissolved out of this heterogeneous glass structure with a mineral acid, a porous skeleton of substantially insoluble silicon dioxide is left. The phase separation region occurs between 500°C and 800 C. 

The homogeneous glass, in which a few percent of alumina is added for better processing, is prepared from a melt at 1300-1500°C (Schnabel 1976) or 1000-1200°C/1450 C (McMillan 1980). It is important for the properties that the melt is as homogeneous as possible. Schnabel (1976,1978) produced glass capillaries or hollow fibers directly from the glass melt at a viscosity of 10 P. The phase separation was carried out by heat treatment between 500-800°C. 

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Table 2.6. Microstructural Characteristics of Some (Nonsupported) Binary Composite Membrane Systems (Uhlhom et al. 1988, Bui raaf, Keizer and van Hassel 1989a, b)...

Binary composite membranes constitute the chief example of membranes classified under (b) in the introductory section. They include binary polymer blends or block or graft copolymers exhibiting a distinct domain structure, filled or semicrystalline polymers and the like. 

B. Will, R.N. Lichtenthaler, Comparison of the separation of mixtures by vapor permeation and pervaporation using PVA composite membranes. Part I. Binary alcohol—water systems, J. Membr. Sci. 68 (1992) 119-125. 

The acid-base Nafion composite membranes include blends of Nafion with polypyrrole (PPy) [98-104], polybenzimidazole (PBI) [105-107], poly (propyleneoxide) (PPO) [108, 109], polyfurfuryl alcohol (PFA) [110], poly(vinyl alcohol) (PVA) [111-115], sulfonated phenol-formaldehyde (sPF) [116], polyvinylidene fluoride (PVdF) [117-122], poly(p-phenylene vinylene) (PPV) [123], poly(vinyl pyrrolidone) (PVP) [124] polyanifine (PANI) [125-128], polyethylene (PE) [129], poly(ethylene-terephtalate) [130], sulfated p-cyclodextrin (sCD) [131], sulfonated poly(ether ether ketone) (sPEEK) [132-135], sulfonated poly(aryl ether ketone) (sPAEK) [136], poly(arylene ether sulfone) (PAES) [137], poly(vinylimidazole) (PVl) [138], poly(vinyl pyridine) (PVPy) [139], poly (tetrafluoroethylene) (PTFE) [140-142], poly(fluorinated ethylene-propylene) [143], sulfonated polyhedral oligomeric silsesquioxane (sPOSS) [144], poly (3,4-ethylenedioxythiophene) (PEDT) [145, 146], polyrotaxanes (PR) [147], purple membrane [148], sulfonated polystyrene (PSSA) [149, 150], polystyrene-b-poly(ethylene-ran-butylene)-bpolystyrene (SEES) [151], poly(2-acrylamido-2-methyl-l-propanesulphonic acid-co-l,6-hexanediol propoxylate diacrylate-co-ethyl methacrylate) (AMPS) [152], and chitosan [31]. A binary PVA/chitosan [153] and a ternary Nafion composite with PVA, polyimide (PI) and 8-trimethoxy silylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS) has also been reported [154]. 

Briefly, the authors of this paper claim that they have presented a method to facilitate the orientation of CNTs on the porous support (PTFE) and the method can easily be adopted to the large-scale membrane production. The PS/CNT/PTFE composite membrane showed the same fast gas transport observed by Holt et al. Then-work also showed for the first time the transport of the binary gas mixtures through the CNTs based membrane. 

The membrane consists of a binary compound AVaBVb of constant composition. Ion activities in the solid state are 1. At the membrane surface the activities of A and B in the aqueous phase are given by the solubility product ... 

Typically, a binary system was selected as the base component of the recipe and the addition of polyelectrolytes to either side (core or receiving bath) was tested to evaluate the change in the capsule properties. The 33 successful multicomponent membrane systems are presented in Table 1. The components of the core material side (21 different chemical compositions) are listed in the first column, while the receiving bath components (20 different chemical compositions) are listed in the second column. With the exception of xanthan and CMC, the first polymer listed on the core side are gelling polymers which form beads with the appropriate ionotropic cation (salt). CMC can also be gelled by ions (alum), although they are considered to be non-compatible for cellular applications. The cations were tested both sequentially, usually with ionotropic cation first, and simultaneously. Walled capsules with adequate mechanical properties were often obtained through the simultaneous application of two polycations. Such a... 

The separation efficiency for a given membrane with a particular binary gas mixture will be dependent mainly upon three factors gas composition, the pressure ratio between feed and permeate gas, and the sepration factor for the two components. A higher separation factor gives a more selective membrane, resulting in a greater separation efficiency. This parameter is a function of the membrane material and is determined by the individual gas permeation rates. 

Figure 9.19 Fraction of benzene in permeate as a function of feed mixture composition for pervaporation at the reflux temperature of a binary benzene/cyclohexane mixture. A 20-qm-thick crosslinked blend membrane of cellulose acetate and polystyrene phosphate) was used [54]. Reprinted with permission from I. Cabasso, Organic Liquid Mixtures Separation by Selective Polymer Membranes, Ind. Eng. Chem. Prod. Res. Dev. 22, 313. Copyright 1983 American Chemical Society...

A binary system consisting of two parts separated by a diathermic, rigid membrane has three degrees of freedom. The particular system under discussion can be made univariant by fixing the temperature and pressure of the pure solvent the equilibrium pressure on the solution is then a function of the composition of the solution. The condition of equilibrium is... 

TVurin, V.A., Berman, A.L., Ryzhova, M.P., Chelomin, V.P. and Korchagin, V.P. (1982). Fatty acid composition of phospholipids of the binary layer of photoreceptor membranes and aminophospholipids of rhodopsin microenvironment in cold and warm blooded vertebrates (In Russian). Zhumal Evolutsionnoy Biochimii i Physiologii 18,101-105. 

The SECM capacity for rapid screening of an array of catalyst spots makes it a valuable tool for studies of electrocatalysts. This technique was used to screen the arrays of bimetallic or trimetallic catalyst spots with different compositions on a GC support in search of inexpensive and efficient electrocatalytic materials for polymer electrolyte membrane fuel cells (PEMFC) [126]. Each spot contained some binary or ternary combination of Pd, Au, Ag, and Co deposited on a glassy carbon substrate. The electrocatalytic activity of these materials for the ORR in acidic media (0.5 M H2S04) was examined using SECM in a rapidimaging mode. The SECM tip was scanned in the x—y plane over the substrate surface while electrogenerating 02 from H20 at constant current. By scanning... 

In general, all elements of the mass transfer matrix depend on the process variables, and in particular on the vapor phase composition. The mass transfer mechanisms in membranes can be rather complicated. However, for the conceptual analysis of the considered membrane process, it is not advantageous to go into the details of mass transport. Therefore, in the following the effective binary mass transfer coefficients k,j are assumed to be constants. 

From Eqs. (7-1) and (7-2), it follows that the separation factor is purely based on the compositions of the entering and exit streams regardless of their flows. Another measure of the separation efficiency of a membrane process is the extent of separation proposed by Rony [1968]. In the context of applying this index of separation efficiency between two comfionents, it is assumed that there is no difficulty in separating the third component Thus the segregation fractions, fiy, are obtained from the molar flow rates of the permeate and retentate streams on the basis of only two components. The extent of separation is defined as the absolute value of a determinant of a binary separation matrix consisting of the segregation fractions as follows ... 

In this paragraph shortly the permeation measurement method is introduced, followed by various examples of permeation through a silicalite-1 membrane on a sintered stainless steel support. This includes unary and binary mixtures as a function of partial pressure, composition and temperature. Finally the present state of modelling permeation through silicalite-1 membranes is reviewed. 

For simplicity of presentation, we assume here membranes containing binary mixtures of acidic and neutral (zwitterionic) lipids. The temporal evolution of the spatially varying charged-lipid compositions on the membrane upper (u) and lower (1) leaflets are linked to the Laplace-Beltrami (LB) operators acting on the corresponding electrochemical potentials through two CH equations (one for each leaflet) each of the form [28] ... 

Figure 4 Adsorption of lysine-13 polypeptide onto ternary phosphatidylcholine (PC)/ phosphatidylserine (PS)/PIP2 lipid membrane with 74 25 1 composition (panels A and B), and onto binary PC/PS lipid membrane with 71 29 composition (panel C). (a) Normalized local fraction of PIP2 lipids in the ternary system, (b) Local PS lipid fractions in the ternary system, (c) Local PS lipid fraction in the binary mixture. All plots shown for f=0.5 ts after beginning of propagation. For these calculations lysine-13 was placed near the membrane, such that the minimum distance between van der Waals radii of lysine-13 and membrane atoms was 3 A, and the peptide was oriented with its major (long) axis parallel to the bilayer plane.

Thus far, only binary mixtures have been separated in the total membrane column. Results of this work have been discussed elsewhere (28,29). A sample shell-side composition profile from a total column experiment with a CO2-O2 mixture is shown in Figure 2. Table I summarizes the total column data obtained to date. 

All procedures for executing the numerical simulation of a multicomponent separation are similar to those described for a binary system, except for evaluating the Initial permeate composition at the residue end of the stripper. Again, the Initial permeate composition will be that of the mixture which permeates through the endmost Increment of the membrane. The appropriate relations are ... 

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