Abstract
The liquid phase dehydration of ethanol solutions with type 3A molecular sieves in fixed-bed adsorption columns has been studied under ambient conditions. The breakthrough curves for this system are well predicted by the model of Weber and Chakravorti, which considers both the effects of external film and internal pore diffusional resistances. The concept of mass transfer zone (MTZ) provides a simple design procedure for the system. The fraction ability of the adsorbent within the mass transfer zone to adsorb solute was found to have a constant value of 0.43. The MTZ length was observed to be independent of bed height. Variations of MTZ length with feed concentration and fluid velocity were evaluated.
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Abbreviations
- C:
-
concentration of sorbate in bulk liquid phase
- Co :
-
initial value of C
- Dm :
-
molecular diffusivity
- Dp :
-
pore diffusion coefficient (defined on a pore sectional area basis)
- De :
-
effective diffusivity = ∈pDpCo/qs
- f:
-
fractional ability of adsorbent in MTZ to adsorb solute at the breakthrough point, dimensionless
- kf :
-
external fluid film mass transfer coefficient, cm/s
- Lo :
-
length of fixed bed
- LMTZ :
-
length of mass transfer zone
- MTZ:
-
mass transfer zone or adsorption zone
- Np :
-
dimensionless parameter defined in Eq. (2)
- Nf :
-
dimensionless film resistance parameter defined in Eq. (3)
- qs :
-
saturation adsorbed phase concentrations (particle volume basis)
- q:
-
adsorbed phase concentration averaged over a particle
- Q:
-
fractional approach to equilibrium = q/qs = C/Co
- Qe :
-
fractional adsorbate concentration at bed exhaustion, arbitrarily defined at 0.95
- Qb :
-
fractional adsorbate concentration at breakthrough, arbitrarily defined at 0.075
- Rp :
-
particle radius
- t:
-
time
- tE :
-
exhaustion time of the bed
- tB :
-
breakthrough time
- V:
-
fluid velocity in the bed
- We :
-
quantity of anhydrous ethanol from a fixed-bed adsorber at bed exhaustion
- Wb :
-
quantity of anhydrous ethanol from fixed-bed adsorber at the breakthrough point
- θ:
-
dimensionless time variable defined in Eq. (4)
- ∈p :
-
porosity of particle
- ∈:
-
voidage of adsorbent bed
Referfece
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Ruthven, D.M. (1984), Principles of adsorption and adsorption processes Wiley, New York.
Weber, T. W. and Chakravorti, R. K. (1974),AIChE J. 20, 228.
Cooper, R. S. and Liberman, D. A. (1970),Ind. Eng. Chem. Fund. 9, 620.
Lukchis, G. M. (1973),Chem. Eng. 6, 111.
Michaels, A. S. (1952),Ind. Eng. Chem. 35, 1296.
Treybal, R. E. (1980),Mass Transfer Operations, McGraw-Hill, New York.
Wakao, N. and Funazkri, T. (1978),Chem. Eng. Sci. 33, 1375.
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Teo, W.K., Ti, H.C. Liquid phase dehydration of ethanol solutions in a fixed bed of molecular sieves. Appl Biochem Biotechnol 24, 521–532 (1990). https://doi.org/10.1007/BF02920275
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DOI: https://doi.org/10.1007/BF02920275