Studies in gas separation by pressure swing adsorption and ultrasonic regeneration of adsorbents.

Separation and purification of gas mixtures using pressure swing adsorption (PSA) has increasingly become an economic alternative to energy-intensive methods such as cryogenic distillation. One of the leading applications of PSA technology is air separation. The initial part of the dissertation discusses various issues concerning the different stages of an air separation plant: namely, the air-prepurification unit (APU), air separation unit (ASU) and oxygen/argon separation unit. The APU in an air separation plant is designed to remove impurities such as CO2, water-vapor, and hydrocarbons which can severely hamper the later stages. Different materials such as gamma-alumina and natural and modified zeolites have been surveyed for their utility as sorbents for air prepurification by PSA. Low concentration pure component and mixed adsorption isotherms of air-impurities on these sorbents have been measured using sensitive static volumetric/gravimetric instruments and infrared spectroscopy. The performance of the sorbents for a PSA air prepurification operation has been studied using computer simulation. Moreover, theoretical studies have also been conducted to compare LiX and NaX zeolite sorbents for producing O2 from air, and to study the feasibility of using a carbon molecular sieve for the kinetic separation of oxygen from argon by PSA. The determination of pore size distribution (PSD) of microporous materials is an important aspect of catalyst and sorbent development. The Horvath-Kawazoe equation has long been a popular model for obtaining the PSD by the measurement of a single adsorption isotherm. However it suffers from certain conceptual flaws. New improved models based on the Horvath-Kawazoe principle have been proposed which overcome the flaws of the original model and provide better PSD predictions over a broader range of micropore size. Finally, the feasibility of using ultrasound for the difficult regeneration of spent sorbents such as activated carbon and polymeric resin is discussed. Application of an ultrasonic field in an aqueous environment causes phenomena such as cavitation and acoustic microstreaming which can help in the desorption of strongly adsorbed species from the sorbent surface. A significant enhancement in the desorption rate of a model compound (phenol) was observed in the presence of ultrasound and its mechanism was investigated.Ph.D.Applied SciencesChemical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123924/2/3001039.pd