Perry s chemical engineers handbook 8e section 16 adsorption and ion exchange

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DESIGN CONCEPTS

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-4

Example 1: Surface Area and Pore Volume of Adsorbent . . . . . . . . . 16-5

Design Strategy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-5

Characterization of Equilibria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-5

Example 2: Calculation of Variance . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-5

Adsorbent/Ion Exchanger Selection . . . . . . . . . . . . . . . . . . . . . . . . . . 16-5

Fixed-Bed Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-6

Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7

Practical Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-7

ADSORBENTS AND ION EXCHANGERS

Classifications and Characterizations . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8

Adsorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8

Ion Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-8

Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-9

SORPTION EQUILIBRIUM

General Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-11

Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-11

Surface Excess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-12

Classification of Isotherms by Shape . . . . . . . . . . . . . . . . . . . . . . . . . . 16-12

Categorization of Equilibrium Models . . . . . . . . . . . . . . . . . . . . . . . . 16-12

Heterogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-12

Isosteric Heat of Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-12

Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-13

Dimensionless Concentration Variables . . . . . . . . . . . . . . . . . . . . . . . 16-13

Single Component or Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-13

Flat-Surface Isotherm Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-13

Pore-Filling Isotherm Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-14

Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-14

Example 3: Calculation of Useful Ion-Exchange Capacity . . . . . . . . . 16-14

Donnan Uptake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-14

Separation Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-14

Example 4: Application of Isotherms . . . . . . . . . . . . . . . . . . . . . . . . . 16-15

Multiple Components or Exchanges . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-16

Adsorbed-Solution Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-16

Example 5: Application of Ideal Adsorbed-Solution Theory . . . . . . . 16-16

Langmuir-Type Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-16

Example 6: Comparison of Binary Langmuir Isotherms . . . . . . . . . . 16-16

Freundlich-Type Relations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-16

Equations of State . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-16

Ion Exchange—Stoichiometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-16

Mass Action. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-17

Constant Separation-Factor Treatment . . . . . . . . . . . . . . . . . . . . . . . . 16-17

CONSERVATION EQUATIONS

Material Balances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-17

Energy Balance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-18

RATE AND DISPERSION FACTORS

Transport and Dispersion Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . 16-18

Intraparticle Transport Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . 16-18

Extraparticle Transport and Dispersion Mechanisms. . . . . . . . . . . . . 16-19

Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19

Intraparticle Mass Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19

Pore Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-19

Solid Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-20

Combined Pore and Solid Diffusion . . . . . . . . . . . . . . . . . . . . . . . . . . 16-21

External Mass Transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-21

Axial Dispersion in Packed Beds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-21

Rate Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-22

General Component Balance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-22

Linear Driving Force Approximation . . . . . . . . . . . . . . . . . . . . . . . . . 16-22

Combined Intraparticle Resistances . . . . . . . . . . . . . . . . . . . . . . . . . . 16-23

Overall Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-24

Axial Dispersion Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-25

Rapid Adsorption-Desorption Cycles . . . . . . . . . . . . . . . . . . . . . . . . . 16-25

Determination of Controlling Rate Factor . . . . . . . . . . . . . . . . . . . . . 16-25

16-1

Section 16

Adsorption and Ion Exchange*

M. Douglas LeVan, Ph.D. J. Lawrence Wilson Professor of Engineering, Department of

Chemical Engineering, Vanderbilt University; Member, American Institute of Chemical Engi￾neers, American Chemical Society, International Adsorption Society (Section Coeditor)

Giorgio Carta, Ph.D. Professor, Department of Chemical Engineering, University of

Virginia; Member, American Institute of Chemical Engineers, American Chemical Society,

International Adsorption Society (Section Coeditor)

*The contributions of Carmen M. Yon (retired), UOP, to material retained from the seventh edition in the “Process Cycles” and “Equipment” subsections are

gratefully acknowledged.

Copyright © 2008, 1997, 1984, 1973, 1963, 1950, 1941, 1934 by The McGraw-Hill Companies, Inc. Click here for terms of use.

Example 7: Estimation of Rate Coefficient for Gas Adsorption . . . . 16-26

Example 8: Estimation of Rate Coefficient for Ion Exchange . . . . . . 16-26

Example 9: Estimation of Rate Coefficient for Protein Adsorption. . 16-26

BATCH ADSORPTION

External Mass-Transfer Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-27

Solid Diffusion Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-27

Pore Diffusion Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-29

Combined Resistances . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-30

Parallel Pore and Solid Diffusion Control . . . . . . . . . . . . . . . . . . . . . . 16-30

External Mass Transfer and Intraparticle Diffusion Control . . . . . . . 16-30

Bidispersed Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-30

FIXED-BED TRANSITIONS

Dimensionless System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-31

Local Equilibrium Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-31

Single Transition System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-32

Example 10: Transition Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-32

Multiple Transition System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-32

Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-33

Example 11: Two-Component Isothermol Adsorption . . . . . . . . . . . . 16-33

Example 12: Adiabatic Adsorption and Thermal Regeneration . . . . . 16-33

Constant Pattern Behavior for Favorable Isotherms . . . . . . . . . . . . . . . 16-34

Asymptotic Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-35

Example 13: Estimation of Breakthrough Time . . . . . . . . . . . . . . . . . 16-36

Breakthrough Behavior for Axial Dispersion. . . . . . . . . . . . . . . . . . . . 16-36

Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-36

Square Root Spreading for Linear Isotherms . . . . . . . . . . . . . . . . . . . . . 16-37

Complete Solution for Reaction Kinetics . . . . . . . . . . . . . . . . . . . . . . . . 16-38

Numerical Methods and Characterization of Wave Shape. . . . . . . . . . . 16-38

CHROMATOGRAPHY

Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-38

Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-38

Elution Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-38

Frontal Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-39

Displacement Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-39

Characterization of Experimental Chromatograms . . . . . . . . . . . . . . . . 16-40

Method of Moments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-40

Approximate Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-40

Tailing Peaks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-41

Resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-41

Prediction of Chromatographic Behavior . . . . . . . . . . . . . . . . . . . . . . . . 16-42

Isocratic Elution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-42

Concentration Profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-44

Linear Gradient Elution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-44

Displacement Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-45

Example 14: Calculation of Band Profiles in

Displacement Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-46

Design for Trace Solute Separations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-48

PROCESS CYCLES

General Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-49

Temperature Swing Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-49

Other Cycle Steps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-50

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-50

Pressure-Swing Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-50

Other Cycle Steps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-51

Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-51

Purge/Concentration Swing Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . 16-52

Inert Purge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-52

Displacement Purge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-53

Chromatography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-53

Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-54

Parametric Pumping. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-55

Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-55

Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-55

Simulated Moving Bed Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-56

Complete Design and Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-57

Other Adsorption Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-58

Hybrid Recycle Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-58

Steam Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-58

Energy Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-58

Energy Conservation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-60

Process Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-60

EQUIPMENT

Adsorption. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-61

General Design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-61

Adsorber Vessel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-61

Regeneration Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-63

Cycle Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-64

Continuous Countercurrent Systems. . . . . . . . . . . . . . . . . . . . . . . . . . 16-64

Cross-Flow Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-64

Ion Exchange . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16-67

16-2 ADSORPTION AND ION EXCHANGE

a Specific external surface area per unit bed volume, m2

/m3

av Surface area per unit particle volume, m2

/m3 particle

A Surface area of solid, m2

/kg

As Chromatography peak asymmetry factor (Fig. 16-32)

b Correction factor for resistances in series (Fig. 16-12)

c Fluid-phase concentration, mol/m3 fluid

cp Pore fluid-phase concentration, mol/m3

cs Fluid-phase concentration at particle surface, mol/m3

Cpf ° Ideal gas heat capacity, J/(molK)

Cs Heat capacity of sorbent solid, J/(kgK)

dp Particle diameter, m

D Fluid-phase diffusion coefficient, m2

/s

De Effective pore diffusion coefficient, m2

/s [Eq. (16-77)]

DL Axial dispersion coefficient, m2

/s [Eq. (16-79)]

Dp Pore diffusion coefficient, m2

/s [Eqs. (16-66), (16-67), (16-69)]

Ds Adsorbed-phase (solid, surface, particle, or micropore) diffusion

coefficient, m2

/s [Eqs. (16-70), (16-71)]

D0 Diffusion coefficient corrected for thermodynamic driving force,

m2

/s [Eq. (16-71)]

D Ionic self-diffusion coefficient, m2

/s [Eqs. (16-73), (16-74)]

F Fractional approach to equilibrium

Fv Volumetric flow rate, m3

/s

h Enthalpy, J/mol;

reduced height equivalent to theoretical plate [Eq. (16-183)]

htu Reduced height equivalent to a transfer unit [Fig. (16-13)]

HETP Height equivalent to theoretical plate, m [Eq. (16-158)]

HTU Height equivalent to a transfer unit, m [Eq. (16-92)]

J Mass-transfer flux relative to molar average velocity, mol/(m2

s);

J function [Eq. (16-148)]

k Rate coefficient, s−1 [Eq. (16-83)]

ka Forward rate constant for reaction kinetics, m3

/(mols)

kc Rate coefficient based on fluid-phase concentration driving force,

m3

/(kg·s) (Table 16-12)

kf External mass-transfer coefficient, m/s [Eq. (16-78)]

kn Rate coefficient based on adsorbed-phase concentration driving

force, s−1 (Table 16-12)

k′ Retention factor [Eq. (16-156)]

K Isotherm parameter

Kc Molar selectivity coefficient

K′ Rational selectivity coefficient

L Bed length, m

m Isotherm exponent; flow ratio in TMB or SMB systems [Eq. (16-207)]

Mr Molecular mass, kg/kmol

Ms Mass of adsorbent, kg

n Adsorbed-phase concentration, mol/kg adsorbent

ns Ion-exchange capacity, g-equiv/kg

N Number of transfer or reaction units; kfaL/(εvref) for external mass

transfer; 15(1 − ε)εpDpL/(εvrefrp

2

) for pore diffusion;

15ΛDsL/(εvrefrp

2

) for solid diffusion; knΛL/(εvref) for linear driving￾force approximation; kacrefΛL/[(1 − R)εvref] for reaction kinetics

(Table 16-13)

Np Number of theoretical plates [Eq. (16-157)]

NPe vrefL/DL, bed Peclet number (number of dispersion units)

p Partial pressure, Pa; cycle time, s

P Pressure, Pa

Pe Particle-based Peclet number, dpv/DL

Qi Amount of component i injected with feed, mol

r, R Separation factor [Eqs. (16-30), (16-32)];

particle radial coordinate, m

rc Column internal radius, m

rm Stokes-Einstein radius of molecule, m [Eq. (16-68)]

rp Particle radius, m

rpore Pore radius, m

rs Radius of subparticles, m

ℜ Gas constant, Pa⋅m3

/(molK)

Re Reynolds number based on particle diameter, dpεv/ν

Sc Schmidt number, ν/D

Sh Sherwood number, kf dp /D

t Time, s

tc Cycle time, s

tf Feed time, s

tR Chromatographic retention time, s

T Absolute temperature, K

u Superficial velocity, m/s

us Adsorbent velocity in TMB or SMB systems, kg/(m2

s)

uf Fluid-phase internal energy, J/mol

us, usol Stationary-phase and sorbent solid internal energy, J/kg

v Interstitial velocity, m/s

Vf Extraparticle fluid volume, m3

W Volume adsorbed as liquid, m3

;

baseline width of chromatographic peak, s (Fig. 16-31)

x Adsorbed-phase mole fraction;

particle coordinate, m

y Fluid-phase mole fraction

z Bed axial coordinate, m; ionic valence

Greek Letters

α Separation factor

β Scaling factor in Polanyi-based models;

slope in gradient elution chromatography [Eq. (16-190)]

∆ Peak width at half height, s (Fig. 16-31)

ε Void fraction of packing (extraparticle);

adsorption potential in Polanyi model, J/mol

εp Particle porosity (intraparticle void fraction)

εb Total bed voidage (inside and outside particles) [(Eq. 16-4)]

γ Activity coefficient

Γ Surface excess, mol/m2 (Fig. 16-4)

κ Boltzmann constant

 Isosteric heat of adsorption, J/mol [Eq. (16-7)]

Λ Partition ratio [Eq. (16-125)]

Λ∞ Ultimate fraction of solute adsorbed in batch

µ Fluid viscosity, kg/(ms)

µ0 Zero moment, mols/m3 [Eq. (16-153)]

µ1 First moment, s [Eq. (16-154)]

ν Kinematic viscosity, m2

/s

Ω Cycle-time dependent LDF coefficient [Eq. (16-91)]

ω Parameter defined by Eq. (16-185b)

ϕ Volume fraction or mobile-phase modulator concentration, mol/m3

π Spreading pressure, N/m [(Eq. (16-20)]

ψ LDF correction factor (Table 16-12)

Ψ Mechanism parameter for combined resistances (Fig. 16-12)

ρ Subparticle radial coordinate, m

ρb Bulk density of packed bed, kg/m3

ρp Particle density, kg/m3 [Eq. (16-1)]

ρs Skeletal particle density, kg/m3 [Eq. (16-2)]

σ2 Second central moment, s2 [Eq. (16-155)]

τ Dimensionless time [Eq. (16-120)]

τ1 Dimensionless time [Eq. (16-127) or (16-129)]

τp Tortuosity factor [Eq. (16-65)]

ξ Particle dimensionless radial coordinate (r/rp)

ζ Dimensionless bed axial coordinate (z/L)

Subscripts

a Adsorbed phase

f Fluid phase

i, j Component index

tot Total

Superscripts

− An averaged concentration

^ A combination of averaged concentrations

* Dimensionless concentration variable

e Equilibrium

ref Reference (indicates feed or initial values)

s Saturation

SM Service mark

TM Trademark

0 Initial fluid concentration in batch

0′ Initial adsorbed-phase concentration in batch

∞ Final state approached in batch

Nomenclature and Units

16-3

GENERAL REFERENCES

1. Adamson, Physical Chemistry of Surfaces, Wiley, New York, 1990.

2. Barrer, Zeolites and Clay Minerals as Adsorbents and Molecular Sieves,

Academic Press, New York, 1978.

3. Breck, D. W., Zeolite Molecular Sieves, Wiley, New York, 1974.

4. Cheremisinoff and Ellerbusch, Carbon Adsorption Handbook, Ann Arbor

Science, Ann Arbor, 1978.

5. Cooney, Adsorption Design for Wastewater Treatment, CRC Press, Boca

Raton, Fla., 1998.

6. Do, Adsorption Analysis: Equilibria and Kinetics, Imperial College,

London, 1998.

7. Dorfner (ed.), Ion Exchangers, W. deGruyter, Berlin, 1991.

8. Dyer, An Introduction to Zeolite Molecular Sieves, Wiley, New York,

1988.

9. EPA, Process Design Manual for Carbon Adsorption, U.S. Envir. Protect.

Agency., Cincinnati, 1973.

10. Gembicki, Oroskar, and Johnson, “Adsorption, Liquid Separation” in Kirk￾Othmer Encyclopedia of Chemical Technology, 4th ed., Wiley, 1991.

11. Guiochon, Felinger-Shirazi, and Katti, Fundamentals of Preparative and

Nonlinear Chromatography, Elsevier, 2006.

12. Gregg and Sing, Adsorption, Surface Area and Porosity, Academic Press,

New York, 1982.

13. Helfferich, Ion Exchange, McGraw-Hill, New York, 1962; reprinted by

University Microfilms International, Ann Arbor, Michigan.

14. Helfferich and Klein, Multicomponent Chromatography, Marcel Dekker,

New York, 1970.

15. Jaroniec and Madey, Physical Adsorption on Heterogeneous Solids, Else￾vier, New York, 1988.

16. Kärger and Ruthven, Diffusion in Zeolites and Other Microporous Solids,

Wiley, New York, 1992.

17. Keller, Anderson, and Yon, “Adsorption” in Rousseau (ed.), Handbook of

Separation Process Technology, Wiley-Interscience, New York, 1987.

18. Keller and Staudt, Gas Adsorption Equilibria: Experimental Methods and

Adsorption Isotherms, Springer, New York, 2005.

19. Ladisch, Bioseparations Engineering: Principles, Practice, and Economics,

Wiley, New York, 2001.

20. Rhee, Aris, and Amundson, First-Order Partial Differential Equations:

Volume 1. Theory and Application of Single Equations; Volume 2. Theory

and Application of Hyperbolic Systems of Quasi-Linear Equations, Pren￾tice Hall, Englewood Cliffs, New Jersey, 1986, 1989.

21. Rodrigues, LeVan, and Tondeur (eds.), Adsorption: Science and Technol￾ogy, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1989.

22. Rudzinski and Everett, Adsorption of Gases on Heterogeneous Surfaces,

Academic Press, San Diego, 1992.

23. Ruthven, Principles of Adsorption and Adsorption Processes, Wiley, New

York, 1984.

24. Ruthven, Farooq, and Knaebel, Pressure Swing Adsorption, VCH Pub￾lishers, New York, 1994.

25. Seader and Henley, Separation Process Principles, 2d ed., Wiley, New

York, 2006.

26. Sherman and Yon, “Adsorption, Gas Separation” in Kirk-Othmer Encyclo￾pedia of Chemical Technology, 4th ed., Wiley, 1991.

27. Streat and Cloete, “Ion Exchange,” in Rousseau (ed.), Handbook of Sepa￾ration Process Technology, Wiley, New York, 1987.

28. Suzuki, Adsorption Engineering, Elsevier, Amsterdam, 1990.

29. Thomas and Crittenden, Adsorption Technology and Design, Butterworth￾Heinemann, Oxford, U.K., 1998.

30. Tien, Adsorption Calculations and Modeling, Butterworth-Heinemann,

Newton, Massachusetts, 1994.

31. Valenzuela and Myers, Adsorption Equilibrium Data Handbook, Prentice

Hall, Englewood Cliffs, New Jersey, 1989.

32. Vermeulen, LeVan, Hiester, and Klein, “Adsorption and Ion Exchange” in

Perry, R. H. and Green, D. W. (eds.), Perry’s Chemical Engineers’ Hand￾book (6th ed.), McGraw-Hill, New York, 1984.

33. Wankat, Large-Scale Adsorption and Chromatography, CRC Press, Boca

Raton, Florida, 1986.

34. Yang, Adsorbents: Fundamentals and Applications, Wiley, Hoboken, N.J.,

2003.

35. Yang, Gas Separation by Adsorption Processes, Butterworth, Stoneham,

Mass., 1987.

36. Young and Crowell, Physical Adsorption of Gases, Butterworths, London,

1962.

16-4

DESIGN CONCEPTS

INTRODUCTION

Adsorption and ion exchange share so many common features in

regard to application in batch and fixed-bed processes that they can be

grouped together as sorption for a unified treatment. These processes

involve the transfer and resulting distribution of one or more solutes

between a fluid phase and particles. The partitioning of a single solute

between fluid and sorbed phases or the selectivity of a sorbent toward

multiple solutes makes it possible to separate solutes from a bulk fluid

phase or from one another.

This section treats batch and fixed-bed operations and reviews

process cycles and equipment. As the processes indicate, fixed-bed

operation with the sorbent in granule, bead, or pellet form is the pre￾dominant way of conducting sorption separations and purifications.

Although the fixed-bed mode is highly useful, its analysis is complex.

Therefore, fixed beds including chromatographic separations are

given primary attention here with respect to both interpretation and

prediction.

Adsorption involves, in general, the accumulation (or depletion) of

solute molecules at an interface (including gas-liquid interfaces, as in

foam fractionation, and liquid-liquid interfaces, as in detergency).

Here we consider only gas-solid and liquid-solid interfaces, with

solute distributed selectively between the fluid and solid phases. The

accumulation per unit surface area is small; thus, highly porous solids

with very large internal area per unit volume are preferred. Adsorbent

surfaces are often physically and/or chemically heterogeneous, and

bonding energies may vary widely from one site to another. We seek to

promote physical adsorption or physisorption, which involves van der

Waals forces (as in vapor condensation), and retard chemical adsorp￾tion or chemisorption, which involves chemical bonding (and often

dissociation, as in catalysis). The former is well suited for a regenera￾ble process, while the latter generally destroys the capacity of the

adsorbent.

Adsorbents are natural or synthetic materials of amorphous or

microcrystalline structure. Those used on a large scale, in order of

sales volume, are activated carbon, molecular sieves, silica gel, and

activated alumina [Keller et al., gen. refs.].

Ion exchange usually occurs throughout a polymeric solid, the solid

being of gel-type, which dissolves some fluid-phase solvent, or truly

porous. In ion exchange, ions of positive charge in some cases (cations)

and negative charge in others (anions) from the fluid (usually an aqueous

solution) replace dissimilar ions of the same charge initially in the solid.

The ion exchanger contains permanently bound functional groups of

opposite charge-type (or, in special cases, notably weak-base exchangers

act as if they do). Cation-exchange resins generally contain bound sul￾fonic acid groups; less commonly, these groups are carboxylic, phospho￾nic, phosphinic, and so on. Anionic resins involve quaternary ammonium

groups (strongly basic) or other amino groups (weakly basic).

Most ion exchangers in large-scale use are based on synthetic

resins—either preformed and then chemically reacted, as for poly￾styrene, or formed from active monomers (olefinic acids, amines, or

phenols). Natural zeolites were the first ion exchangers, and both nat￾ural and synthetic zeolites are in use today.

Ion exchange may be thought of as a reversible reaction involving

chemically equivalent quantities. A common example for cation

exchange is the familiar water-softening reaction

Ca++ + 2NaR A CaR2 + 2Na+

where R represents a stationary univalent anionic site in the polyelec￾trolyte network of the exchanger phase.

Table 16-1 classifies sorption operations by the type of interaction

and the basis for the separation. In addition to the normal sorption

operations of adsorption and ion exchange, some other similar separa￾tions are included. Applications are discussed in this section in

“Process Cycles.”