Composite membranes pressure

If the system forms azeotropes, then the azeotropic mixtures can be separated by exploiting the change in azeotropic composition with pressure, or the introduction of an entrainer or membrane to change the relative volatility in a favorable way. If an entrainer is used, then efficient recycle of the entrainer material is necessary for an acceptable design. In some cases, the formation of two liquid phases can be exploited in heterogeneous azeotropic distillation. 

Table 6 lists several of the salient properties of this new composite membrane. When salt rejection was evaluated at different pressures in simulated seawater trials, potable water (containing less than 500 ppm dissolved salts) was generated at as low as 600 psi, with very good flux (12 gfd) at that pressure. In spiral-wound membrane element trials on actual 33,000 ppm seawater, potable water was obtained even at 500 psi, albeit at low flux. These results surpass by far the capabilities of any of the "NS" series of membranes. 

In summary, the FT-30 membrane is a significant improvement in the art of thin-film-composite membranes, offering major improvements in flux, pH resistance, and chlorine resistance. Salt rejections consistent with single-pass production of potable water from seawater can be obtained and held under a wide variety of operating conditions (ph, temperature, pressure, and brine concentration). This membrane comes close to being the ideal membrane for seawater desalination in terms of productivity, chemical stability, and nonbiodegradability. 

Over 30 commercial formulations have been surveyed in depth. Compressive strength measurements permit the exclusion of materials obviously prone to fail under pressure. FTIR (MX-1, Nicolet Instrument Corp.) analysis has identified formulations with volatile diluents capable of chemically modifying the composite membrane. Through the use of FTIR it was possible with an otherwise successful formulation to identify the presence of butyl glycidyl ether (BGE) as a diluent. Subsequently experimentation showed that vapor of BGE is capable of plasticizing porous polysulfone with a drop in both flux and rejection of the membrane. Collaboration with the supplier resulted in substitution of a nonvolatile glycidyl ether diluent to avoid the problem. 

Research effort at Albany International Research Co. has developed unit processes necessary for pilot scale production of several species of reverse osmosis hollow fiber composite membranes. These processes include spin-dope preparation, a proprietary apparatus for dry-jet wet-spinning of microporous polysul-fone hollow fibers, coating of these fibers with a variety of permselective materials, bundle winding using multifilament yarns and module assembly. Modules of the membrane identified as Quantro II are in field trial against brackish and seawater feeds. Brackish water rejections of 94+% at a flux of 5-7 gfd at 400 psi have been measured. Seawater rejections of 99+% at 1-2 gfd at 1000 psi have been measured. Membrane use requires sealing of some portion of the fiber bundle for installation in a pressure shell. Much effort has been devoted to identification of potting materials which exhibit satisfactory adhesion to the fiber while... 

Fig. 23. Swelling ratios of NIPA gel and volume fluxes across the composite membrane at various temperatures. Pressure difference between permeate and feed solutions in the permeation experiments is 10 [kg cm-2]...

The poly(ether/amide) thin film composite membrane (PA-100) was developed by Riley et al., and is similar to the NS-101 membranes in structure and fabrication method 101 102). The membrane was prepared by depositing a thin layer of an aqueous solution of the adduct of polyepichlorohydrin with ethylenediamine, in place of an aqueous polyethyleneimine solution on the finely porous surface of a polysulfone support membrane and subsequently contacting the poly(ether/amide) layer with a water immiscible solution of isophthaloyl chloride. Water fluxes of 1400 16001/m2 xday and salt rejection greater than 98% have been attained with a 0.5% sodium chloride feed at an applied pressure of 28 kg/cm2. Limitations of this membrane include its poor chemical stability, temperature limitations, and associated flux decline due to compaction. 

Kawaguchi et al.105) in Teijin Ltd. prepared a similar polyamide composite membrane from piperazine, trimesoyl chloride, and isophthaloyl chloride on a polysulfone support. The membrane exhibited high chlorine-resistance and excellent pressure-resistance. When used for reverse osmosis of an aqueous solution of 0.5% NaCl and NaOCl (available Cl 4 5 ppm) at pH 6.5 7.0, 25 °C, and 42,5 kg/cm2, the water permeation was 1400 and 13301/m2 - day and desalination was 93.4% and 95.7% after 2 and 100 hr, respectively. 

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. 

In the present study we have aimed to separate acetic acid-water mixtures using AN grafted PVA membranes and studied the permeation characteristics of PVA-g-AN membranes as a function of membrane thickness, temperature, feed composition and pressure. 

Since the discovery by Cadotte and his co-workers that high-flux, high-rejection reverse osmosis membranes can be made by interfacial polymerization [7,9,10], this method has become the new industry standard. Interfacial composite membranes have significantly higher salt rejections and fluxes than cellulose acetate membranes. The first membranes made by Cadotte had salt rejections in tests with 3.5 % sodium chloride solutions (synthetic seawater) of greater than 99 % and fluxes of 18 gal/ft2 day at a pressure of 1500 psi. The membranes could also be operated at temperatures above 35 °C, the temperature ceiling for Loeb-Sourirajan cellulose acetate membranes. Today s interfacial composite membranes are significantly better. Typical membranes, tested with 3.5 % sodium chloride solutions,... 

Figure 8.6 The difference between selectivities calculated from pure gas measurements and selectivities measured with gas mixtures can be large. Data of Lee et al. [13] for carbon dioxide/methane with cellulose acetate films. Reprinted from S.Y. Lee, B.S. Minhas and M.D. Donohue, Effect of Gas Composition and Pressure on Permeation through Cellulose Acetate Membranes, in New Membrane Materials and Processes for Separation, K.K. Sirkar and D.R. Lloyd (eds), AIChE Symposium Series Number 261, Vol. 84, p. 93 (1988). Reproduced with permission of the American Institute of Chemical Engineers. Copyright 1988 AIChE. All rights reserved...

Reverse osmosis membranes can be divided into subclasses according to their solute/water selectivity and operating pressure regimes. Figure 30 shows a number of commercial membranes developed for seawater and brackish desalination, and for nanofiltration. These include cellulose ester and polyamide asymmetric membranes available since the 1960s, and high-performance composite membranes developed in the 1970s. Collectively, they make it possible to produce potable water from virtually all saline water sources. 

The biotechnologists have also clarified the regulation mechanism of glutamic acid excretion in bacterial cell membranes and discovered the effect of medium composition, osmotic pressure, biotin, antibiotic, detergent, saturated fatty acid and oleic acid addition on the excretion of amino acids 49). 

Cellulose acetate and linear aromatic polyamide membranes were the industry standard until 1972, when John Cadotte, then at North Star Research, prepared the first interfacial composite polyamide membrane.8 This new membrane exhibited both higher throughput and rejection of solutes at lower operating pressure than the here-to-date cellulose acetate and linear aromatic polyamide membranes. Later, Cadotte developed a fully aromatic interfacial composite membrane based on the reaction of phenylene diamine and trimesoyl chloride. This membrane became the new industry standard and is known today as FT30, and it is the basis for the majority... 

A brackish water having a TDS concentration of 3000 g/m3 is to be desalinized using a thin-fllm composite membrane having a flux rate coefficient, kw, of 1.5 x 10 6 s/m and a mass transfer rate coefficient, kj, of 1.8 x 10 6 m/s. The product water is to have a TDS of no more than 200 g/m3. The flowrate, Qp, is to be 0.010 m3/s. The net operating pressure (APa — AIT) will be 2500 kPa. Assume the recovery rate, r, will be 90 percent. Estimate the rejection rate and the concentration of the concentrate stream. 

Network thermodynamics has also been applied to nonstationary diffusion through heterogeneous membranes concentration profiles in the composite membrane and change of the osmotic pressure have been calculated with the modified boundary and experimental conditions. 

This abstract definition will be explained with the actual example of gaseous permeation through a zeolite/alumina composite membrane. Here, we must investigate the effect of the five following factors on the rate of permeation the temperature (T) when the domain is between 200 and 400 °C, the trans-membrane pressure (Ap) when the domain is between 40 and 80 bar, the membrane porosity (s) ranging from 0.08 to 0.18 m /m, the zeolite concentration within the porous structure (c ) from 0.01 to 0.08 kg/kg and the molecular weight of the permeated gas (M) which is between 16 and 48 kg/kmol. With respect to the first... 

The aspect of hole filling by plasma deposition can be demonstrated by the transport characteristics of LCVD-prepared membranes. First, the porosity as porous media calculated from the gas permeability dependence on the applied pressure can be correlated to the salt rejection of the composite membrane as shown in Figure 34.13. The effective porosity s/, where s is the porosity and q is the tortuosity factor, is measured in dry state and may not directly correlate to the porosity of the membranes in wet state. The effective porosity of LCVD-prepared membranes was measured before the reverse osmosis experiment. The decrease of porosity (as porous media) is clearly reflected in the increase in salt rejection in reverse osmosis. 

Figure 34.15 Reverse osmosis characteristics of composite membranes prepared by plasma polymerization of 4-picoline with and without N2 at two vapor pressures porous polysulfone film as the substrate 1.2% NaCl at 1200 psi.

Fig. 3. (a) permeate flux and separation factor in H2/CO2 mixture/MTES silica composite membrane system at 293K, (b) permeate rate of N2 in MTES silica composite membrane at 293K (c) predicted pressure profile of CO2 on TPABr silica membrane at 4atm... 

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