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Breakthrough analysis of a structured adsorbent bed Netprasat, Vorapoj

Abstract

The objectives of the present study were to compare the adsorption isotherms of various gases on various adsorbents using gravimetric, volumetric, and chromatographic methods: to determine whether the Langmuir isotherm model is appropriate for the N₂ adsorption isotherms up to 300 kPa on zeolite NaX and zeolite LiX; to identify the dominant dynamic behaviour through a laminate bed of these and other adsorbents and to determine the effect of flowrate on the magnitude of the axial dispersion or mass transfer resistance within the laminated bed of adsorbent. The gas adsorption isotherms of CO, and CO₂ on zeolite 13X were obtained using the volumetric, gravimetric, and chromatographic methods. The isotherms obtained from the volumetric and gravimetric methods showed good agreement. The gravimetric method was used to measure adsorption isotherms of N₂ up to 300 kPa for N₂ on zeolite LiX relevant in the air separation industry. The N₂ adsorption capacity of zeolite LiX, obtained in the present study, was higher than the N2 adsorption capacity of NaX or 13X used traditionally for air seperation. The chromatographic method was used to determine the dispersion and mass transfer coefficients in a laminated bed of adsorbent. The results suggested that at low interstitial velocities, υ < 1.7 cm/sec, dispersion dominated, while at high interstitial velocities, υ » 1.7 cm/sec, macropore and micropore mass transfer resistance dominated. Estimated dispersion and external fluid film mass transfer resistances were consistent with literature values. However, the micropore diffusivity obtained was lower than that reported in available literature data. The difference was most likely due to the inaccuracy in the results obtained using only two particle sizes. Furthermore, from the mass transfer resistances obtained for PSA with short cycle times using laminate beds, fast PSA with cycle time of 0.6 to 3 seconds is possible.

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