Nitrogen, separated from carbon dioxide

In gas separation with membranes, a gas mixture at an elevated pressure is passed across the surface of a membrane that is selectively permeable to one component of the mixture. The basic process is illustrated in Figure 16.4. Major current applications of gas separation membranes include the separation of hydrogen from nitrogen, argon and methane in ammonia plants the production of nitrogen from ah and the separation of carbon dioxide from methane in natural gas operations. Membrane gas separation is an area of considerable research interest and the number of applications is expanding rapidly. 

Kusakabe K, Kuroda T, and Morooka S. Separation of carbon dioxide from nitrogen using ion-exchanged faujasite-type zeolite membranes formed on porous support tubes. J Membr Sci 1998 148(l) 13-23. 

Fig. 2.1 Photosynthesis and respiration. Left side is Fig. 1.6. Right side shows photosynthesis in which sunlight and water in the atmosphere are absorbed by plants and algae to generate ATP and NADPH, which make carbohydrates and other organic carbon products from carbon dioxide, which is absorbed from the atmosphere separately. All of the carbon in plants and algae is ultimately derived from a single source, carbon dioxide, and they are called autotrophs. Nitrogen is obtained mostly as ammonia from bacterial metabolism of proteins from dead organism in the soil...

Separation selectivity in IMS can be affected in a number of ways. The most direct approach is to modify or change the buffer gas (see also Chapter 11). For example, carbon dioxide as a bnffer gas, due to its higher polarizability, can separate ions that cannot be separated with nitrogen alone. Four common buffer gases used in IMS are helium, argon, nitrogen (air), and carbon dioxide, with respective polarizabilities of 0.205, 1.641, 1.740, and 2.911 debye. One separation that has danonstrated the effects of buffer gases on resolution is that of chloroaniline from iodoaniline. In helium, for which the size of the ion is dominant, chloroaniline, the... 

Other membrane-based gas-separation applications that developed in the late 1980s and the 1990s include the separation of carbon dioxide from natural gas, separation of organic vapors from air and nitrogen, and dehydration of air. Table 7.3 lists the major companies involved in the industry and their principal markets. Currently, total industry sales are estimated to be about US 200 million. Of all the industrial membrane-separation processes, gas separation is... 

Post-combustion capture involves separating the carbon dioxide from other exhaust gases after combustion of the fossil fuel. Post-combustion capture systems are similar to those that already remove pollutants such as particulates, sulfur oxides, and nitrogen oxides from many power plants. 

L. Liu, A. Chakma, X. Feng, Preparation of hollow fiber poly(ether block amide)/polysulfone composite membranes for separation of carbon dioxide from nitrogen, Chem. Eng. J., 105,... 

Figure 2.7 Robeson plot illustrating the tradeoff between selectivity (a, ALPHA) and permeability (P) for the separation of carbon dioxide from nitrogen with polymer membranes [47]. The circles indicate all literature data considered relevant. The upper bound line is an empirical judgment of the outermost range of reliable data. Reprinted from Robeson IM. The upper bound revisited. J Membr Sci 2008 320(1—2) 390—400. Copyright (2008), with permission from Elsevier.

Gas mixture separation processes are based on the specific pore size distribution of CMS, which permits diffusion of different gasses at different rates. These processes aim to either recover and recycle valuable constituents from industrial waste gases, or to separate small gas molecules by preferential adsorption. The latter is at present the most important large scale application of CMS. Separations that have been accomplished include oxygen from nitrogen in air, carbon dioxide from methane in natural gas, ethylene from ethane, linear from branched hydrocarbons (such as n-butane from isobutane), and hydrogen from flue gases [6]. 

Recently, Ekiner and Simmons reported on membranes for the production of oxygen-enriched air, nitrogen-enriched air, for the separation of carbon dioxide from hydrocarbons, and the separation of hydrogen from various petrochemical and oil refining streams [82]. The membranes are made with blends of PAs, Pis and PI-PAs. They show high strength, chemical resistance, and are suitable for high pressure and temperature applications. 

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