Adsorption air separation

Adsorption technology, 13 794-795 Adsorptive air separation, 17 753 Adsorptive bubble separation effluent treatment, 9 432... 

Experience in air separation plant operations and other ciyogenic processing plants has shown that local freeze-out of impurities such as carbon dioxide can occur at concentrations well below the solubihty limit. For this reason, the carbon dioxide content of the feed gas sub-jec t to the minimum operating temperature is usually kept below 50 ppm. The amine process and the molecular sieve adsorption process are the most widely used methods for carbon dioxide removal. The amine process involves adsorption of the impurity by a lean aqueous organic amine solution. With sufficient amine recirculation rate, the carbon dioxide in the treated gas can be reduced to less than 25 ppm. Oxygen is removed by a catalytic reaction with hydrogen to form water. 

Other plant-scale applications to pollution control include the flotation of suspended sewage particles by depressurizing so as to release dissolved air [Jenkins, Scherfig, and Eckhoff, Applications of Adsorptive Bubble Separation Techniques to Wastewater Treatment, in Lemlich (ed.). Adsorptive Bubble Separation Techniques, Academic, New York, 1972, chap. 14 and Richter, Internat. Chem. Eng, 16,614 (1976)]. Dissolved-air flotation is also employed in treating waste-water from pulp and paper mills [Coertze, Prog. Water TechnoL, 10, 449(1978) and Severeid, TAPPl 62(2), 61, 1979]. In addition, there is the flotation, with electrolytically released bubbles [Chambers and Cottrell, Chem. Eng, 83(16), 95 (1976)], of oily iron dust [Ellwood, Chem. Eng, 75(16), 82 (1968)] and of a variety of wastes from surface-treatment processes at the maintenance and overhaul base of an airline [Roth and Ferguson, Desalination, 23, 49 (1977)]. 

Wang, L.K., Adsorptive bubble separation and dispersed air flotation, in Advanced Physicochemical Treatment Processes, L.K. Wang, Y.T. Hung, and N.K. Shammas, Eds, Humana Press, Totowa, NJ,... 

The resulting water is removed by adsorption and the final product is dry hydrogen with the purity of about 98.6 vol% (the balance CH4, N2, and Ar) at 5.0 MPa. The thermal efficiency of the process is 69.5% [4]. Major disadvantages of the POx process are the need for large quantities of pure oxygen (thus, requiring an expensive air separation plant), and the production of large volumes of C02 emissions (0.53-0.63 Nm3 C02 per Nm3 H2 product). 

Cryogen-free electromagnets, 23 856 Cryogenic adsorption processes, 73 461 Cryogenic air separation, 77 275-278, 752-753... 

The age of pressure swing adsorption (PSA) began so far as air separation is concerned in the late 1950s. The first process patent was that of Skarstrom [12]. The scientists and engineers of the Linde Laboratories were very active in this field. It is worth mentioning that the discovery of synthetic zeolite molecular sieves was... 

Air separation by PSA on a large scale is today dominated by machines in which the pressure swing may be from near atmospheric to substantially sub-atmospheric pressure. The industry typically calls these machines vacuum swing adsorption (VSA) separators. A second sub-class in air separation is the machines that use a pressure swing the ranges from somewhat super-atmospheric to sub-atmospheric and these may be called trans-atmospheric PSA. The distinctions made here have implications as to equipment specifications and performance limitations in both bed size factor and O2 recovery. 

ADSORPTION GAS SEPARATION. Gas-phase adsorption is widely employed for die large-scale purification or bulk separation of air, natural gas. chemicals, and petrochemicals (Table 1), In these Lises it is often a preferred alternative to the older unit operations of distillation and absorption. 

Low-temperature adsorption systems continue to find an increasing number of applications. For example, systems are used to remove the last traces of carbon dioxide and hydrocarbons in many air-separation plants. Adsorbents are also used in hydrogen liquefaction to remove oxygen, nitrogen, methane, and other trace impurities. They are also used in the purification of helium suitable for liquefaction (grade A) and for ultrapure helium (grade AAA, 99.999% purity). Adsorption at 35 K will, in fact, yield a helium with less than 2 ppb of neon, which is the only detectible impurity in helium after this treatment. 

Depending on volume and purity requirements, nitrogen can be supplied by several different production systems or delivery systems. Figure 1.1 illustrates some of these systems159. Liquid refers to delivery by trucks or in cylinders Permeation refers to a membrane system Adsorption refers to a PSA system and Distillation refers to a cryogenic air separation plant. 

In the fall of 1948, I was measuring the adsorption characteristics of numerous commercial adsorbents and of the natural zeolite, chabazite. Several uses for silica gel in air separation plants were identified. But the more we learned about chabazite, the more intrigued I became by its potential as a commercial adsorbent as well as its possible use in air purification and separation. I envisioned, as others had before me [1-5], major new separation processes based on a series of different pore size zeolites. The stumbling blocks were that (1) chabazite was the only known zeolite with seemingly practical adsorption... 

Dr LI. Dana, Linde Vice President, hired me and put me to work on air separation. He and Dr. J.M. Gaines, Director of Research, asked me to work on physical adsorption and strongly supported the molecular sieve project at all times. Dr. Dana made the decision to test market and set the initial prices. 

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