Experimental determination of fluid-film mass transfer coefficient from adsorption uptake curve

To design fixed-bed adsorbers, kinetic parameters such as the fluid-film mass transfer coefficient and intraparticle diffusivity are required. The fluid-film mass transfer coefficient is usually estimated by theoretical and/or empirical equations. Most of the equations were derived from experimental data obtained through techniques other than adsorption. Thus, values estimated from empirical equations are unreliable to use for adsorption systems. The fluid-film mass transfer coefficients (kF) were determined experimentally from adsorption uptake curves measured under conditions of low Reynolds numbers. The experimental kF values were compared with several empirical equations, such as Carberry equation. The experimental values were found to be always 4/3 of the Carberry and Yoshida et al. equation. The experimental kF values were converted into modified kF values (=kFΔav = kFɛp/φs), and compared with these equations. The particle void (ɛp) and shape factor (φs) were introduced into the particle surface area (av) for experimental values to modify the area where mass transfer at the fluid-film boundary surrounding adsorbent particles affects. Those kF values were nearly identical, suggesting that only mass transfer around particle pores contributes to the kF value for adsorbent particles. To represent the mass transfer at fluid film appropriately, kFav should be employed, since the error of av is included in kF value.

► The fluid-film mass transfer coefficient was determined experimentally from adsorption uptake curve. ► The experimentally obtained values were found to be always 4/3 of those estimated by Carberry's empirical equation. ► The particle surface area (av) where mass transfer at the fluid-film boundary surrounding adsorbent particles affects was modified by the particle void (ɛp) and shape factor (φs) for experimental values. ► The modified experimental values and estimated values were nearly identical each other. ► It is suggested that only the pore openings, not the entire particle surface strongly contribute to mass transfer at the fluid-film boundary.