Adsorption Dynamics of Air on Zeolite 13X and CMS Beds for Separation and Purification
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Adsorption Dynamics of Air on Zeolite 13X and CMS Beds for Separation and Purification JEONG-GEUN JEE AND SANG-JIN LEE Department of Chemical Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749, Korea HEUNG-MAN MOON Cryogenic Research Center, Dae-Sung Industrial Gases Co., 781-1 Wonsi-dong, Ansan-si, Gyeonggi-do, 425-090, Korea CHANG-HA LEE∗ Department of Chemical Engineering, Yonsei University,134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749, Korea [email protected]
Abstract. The adsorption dynamics of N2 , O2 , and Ar in kinetic separation bed with CMS and equilibrium separation bed with zeolite 13X were investigated by using dried air as a feed. In the CMS bed initially saturated with He, Ar was the first breakthrough component showing a small roll-up and N2 followed at a very close interval. Then, the breakthrough of O2 occurred with a broad roll-up due to its fast diffusion rate and the relatively slow diffusion rate of N2 . In the zeolite 13X bed initially saturated with O2 , the breakthrough of Ar first occurred with roll-up owing to the strong adsorption of N2 , then the breakthrough of N2 followed after a very short interval. Based upon these results, the cyclic adsorption dynamics of the zeolite 13X VSA for air bulk separation and CMS PSA for oxygen purification were studied. The five-step two-bed O2 VSA with zeolite 13X produced O2 of over 90% purity with high recovery. The MTZ variation of N2 during the adsorption and vacuum steps was described in detail. In the case of the six-step two-bed PSA process for O2 purification, O2 of 99.8+% purity could be produced from the binary mixture (O2 /Ar—95:5 vol.%). The dynamic adsorption behaviors were investigated by using a concentration-dependent rate model incorporated with mass, energy, and momentum balances. The model reasonably predicted the adsorption dynamics at the equilibrium and kinetic separation beds. Keywords: separation and purification, adsorption dynamics, zeolite 13X, CMS, air
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Introduction
The commercial applications for the adsorptive generation of oxygen from ambient air using several zeolites have been grossed during the last 30 years. Especially, the vacuum swing adsorption (VSA) process for ∗ To
whom correspondence should be addressed.
air separation is competitive with the pressure swing adsorption (PSA) process for the production of over 15 TPDc oxygen (Yang, 1987). Lots of VSA processes for air separation have generally been operated in the range of 1.1 to 1.8 atm for adsorption pressure and 0.05 to 0.3 atm for desorption pressure. Commercial VSA processes can produce O2 of 90–94% purity from air.
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Recently, the demand for the high purity oxygen of over 99% has increased tremendously in many industries (Hayashi et al., 1996). In addition, the demand for high purity O2 of over 99.8% is increasing greatly because the semi-conductor industries have been expanded. This high purity oxygen can be produced by removing N2 and Ar impurities contained in the product of the VSA process. Carbon mo
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