Membranes carbon dioxide permeation

Carbon dioxide permeates the membranes at least as readily as does chlorine. This fact will produce a significant increase in CO2 concentration in a recycle system. For best results at highest chlorine recovery, it will pay to keep the CO2 concentration in the membrane feed-gas low. This can be accomplished in most plants by acidification of cell-feed brine. Acidification is highly recommended in any case when a very high degree of chlorine recovery is required, whether by... 

Carbon Dioxide Permeation in a Zeolite-Based Ceramic Porous Membrane... 

Carbon Dioxide Permeation, k, and Membrane Average Pore Diameter, t/v... 

The results of gas permeability, hydrogen, helium, methane, nitrogen, oxygen, argon, and carbon dioxide permeation under pressure of 100 mmHg with Membranes A to C. For all samples, the permeation rates were found to be proportional to the molecular weight powered to -0.5. This means that for all membrane samples, the flow in the pores become a Knudsen-type flow and each membrane sample had a linear plot, indicating the absence of pinholes. 

In the treatment of biogas the Joule-Kelvin effect cannot be neglected. A biogas feed contains art equimolar mixture of methane to carbon dioxide. If a pressure of 50 bar is applied at the feed side at 30°C calculate then the recovery S at which the permeate temperature has been decreased below 0°C.(Assume that only carbon dioxide permeates through the membrane and that beat transfer is much faster than mass transfer). The Joule-Kelvin coefficient of carbon dioxide is, = 1.2 K/bar. 

Rui, Z., Anderson, M Lin, Y.S., and Li, Y, (2009) Modeling and analysis of carbon dioxide permeation through ceramic-carbonate dual-phase membranes,... 

Ortiz-Landeros, Norton, T., and Lin, Y.S. (2013) Effects of support pore structure on carbon dioxide permeation of ceramic-carbonate dual-phase membranes. Chem. Eng. Sci, 104,... 

These observed effects of fibres prepared using higher bore liquid flowrate having larger methane and carbon dioxide permeate flux can be explained in two ways. The increased flux could be due to the fact that increased bore liquid flowrate produces fibres with thinner walls. The increased permeate flow could also be due to the formation of a more open structured membrane. It is likely the increased permeate flux is due to a combination of the two reasons. 

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. 

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],... 

After preformation, the substrates and carbon dioxide were supplied continuously. The membrane reactor was pressurized at the feed side up to 20 MPa with the reaction mixture. A trans-membrane pressure was created by opening a needle valve on the permeate side after which the continuous process started. 

Fukushi and Hiiro et al. [24] described a method for determining total carbon dioxide in seawater by capillary isotachoelectrophoresis following isolation of the carbon dioxide by membrane permeation. 

Gogel et al. [118] compared two CFPs, one untreated and one treated (25 wt% PTFE) as the anode DL (both were TGP-H-120). The fuel cell was operated at a cell temperature of 110°C, and it was observed that the DL without any treatment performed better. However, the difference between both materials was very small and the methanol permeation was actually reduced (increased Faradaic efficiency) with the treated DL. A possible explanation for this is that methanol is oxidized more effectively at the anode due to the formation and stabilization of carbon dioxide bubbles in the active area. As a consequence, the methanol concentration gradient across the membrane is reduced. 

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...

Figure 8.31 Flow scheme of one-stage and two-stage membrane separation plants to remove carbon dioxide from natural gas. Because the one-stage design has no moving parts, it is very competitive with other technologies especially if there is a use for the low-pressure permeate gas. Two-stage processes are more expensive because a large compressor is required to compress the permeate gas. However, the loss of methane with the fuel gas is much reduced...

Figure 8.32 A typical membrane/amine plant for the treatment of associated natural gas produced in carbon dioxide/enhanced oil projects. The membrane permeate gas is often used as a fuel for the amine absorption plant...

At the permeate side of the membrane the reaction is reversed, and bicarbonate ions form carbon dioxide, water, and carbonate ions. 

The transport rates of carbon dioxide and hydrogen sulfide through these carbonate membranes can be significantly increased by adding catalysts to increase the rates of the slow reactions of Equations (11.21) and (11.22). A variety of materials can be used, but the anions of the weak acids such as arsenite, selenite and hypochlorite have been found to be the most effective. Small concentrations of these components increase permeation rates three- to five-fold. 

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