Transport Mechanism of Carbon Membranes

Yamaguchi T, Koval CA, Noble RD, and Bowman CN. Transport mechanism of carbon dioxide through perfluorosulfonic ionomer membranes containing an amine carrier. Chem. Eng. Sci. 1996 51 4781 789. 

Separation of the polar gases such as carbon dioxide, hydrogen sulfide and sulfur dioxide behaves in many respects differently from other nonpolar gases. Their transport mechanisms through porous membranes are often different and therefore their separation performances can also be markedly different. This has been observed for separating carbon dioxide from other nonpolar, non-hydrocarbon gases. 

The membranes used in the present study contained 50.0 wt% PVA (60 mol % cross-linked by formaldehyde), 20.7wt% AIBA-K, 18.3wt% KOH, and 11.0wt% poly(allylamine), unless otherwise stated. Figure 9.3 presents a schematic of the C02 transport mechanism in the membranes. The membranes synthesized contained both AIBA-K and KHCO3-K2CO3 (converted from KOH) as the mobile carriers, and poly(allylamine) as the fixed carrier for C02 transport. AIB A is a sterically hindered amine, and its reaction with C02 is depicted in Equation 9.12.49 Poly(allylamine) is a nonhindered amine, and its reaction is shown in Equation 9.13. The reaction mechanism of the C02 with KHC03-K2C03 is presumably similar to that of hindered amine-promoted potassium carbonate described in Equation 9.14 50... 

Mass transfer of gas through a porous membrane can involve several processes depending on the pore stmcture and the solid [1]. There are four different mechanisms for the transport Poiseuille flow Knndsendiflusion partial condensation/capillaiy diffusion/selective adsorption and molecular sieving [2, 3]. The transport mechanism exhibited by most of carbon membranes is the molecular sieving mechanism as shown in Fig. 2.1. The carbon membranes contain constrictions in the carbon matrix, which approach the molecular dimensions of the absorbing species [4],... 

Certain enzymes shown to be present in myelin could be involved in ion transport. Carbonic anhydrase has generally been considered a soluble enzyme and a glial marker but myelin accounts for a large part of the membrane-bound form in brain. This enzyme may play a role in removal of carbonic acid from metabolically active axons. The enzymes 5 -nucleotidase and Na+, K+-ATPase have long been considered specific markers for plasma membranes and are found in myelin at low levels. The 5 -nucleotidase activity may be related to a transport mechanism for adenosine, and Na+, K+-ATPase could well be involved in transport of monovalent cations. The presence of these enzymes suggests that myelin may have an active role in ion transport in and out of the axon. In connection with this hypothesis, it is of interest that the PLP gene family may have evolved from a pore-forming polypeptide [9],... 

The mechanism of transport of GPG using SLM has been studied at the authors laboratory [56]. GPG could be permeated from alkaUne feed of carbonate buffer into an acidic stripping solution of acetate buffer across the membrane comprising Aliquat-336 in -butyl acetate immobiUzed in a polypropylene (Gelgard 2400) support. The transport mechanism is a case of counter transport exhibiting overall rate dependence on solute diffusion in the membrane phase as well as the mass transfer across the aqueous boundary films. 

Almost all diuretics exert their action at the luminal surface of the renal tubule cells. Their mechanism of action includes interaction with specific membrane transport proteins like thiazides, furosemide etc., osmotic effects which prevent the water permeable segments of the nephron from absorbing water like mannitol, and specific interaction with enzyme like carbonic anhydrase inhibitors i.e. acetazolamide, and hormone receptors in renal epithelial cells like spironolactone. 

In bacteria, Na+ is often replaced by H+ as the carrier of nutrients. The best known mechanisms of this sort are the various galactoside (e.g., lactose) transporters, because lactose is an important carbon source for many bacteria. The work that can be performed (e.g., in transporting a nutrient) by generating a proton gradient across membranes may be expressed by the following, which encompasses both the chemical component (concentration gradient) and the electrical component in the form of the membrane potential AW ... 

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