Introduction to Mass Transfer Operations (1 of 5)

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1. Introduction
2. Overview of Separation Processes
3. Separation by Phase Creation & Phase Addition
4. Separation by Barrier
5. Solid Agent Addition
6. Separation by External Force/Gradient
7. Separations involving Solids
8. Mechanical-Physical Separations
9. Concepts in Separation Technology
10. Conclusion

▪ Overview of the Separation Technologies & Mass Transfer
Operations
▪ Understand the principles governing Mass Transfer & Separations
▪ Relate how Mass Transfer Phenomena can be exploited in Mass
Transfer Unit Operations
▪ Get to know several Equipment used in each Process
▪ Get to know several Industrial Applications based on these
concepts:
▪ distillation, gas absorption, stripping, scrubbing, etc…
▪ Understand the importance of Method Selection

▪ Explain the role of separation operations in the chemical and other
industries.
▪ Understand the five basic separation techniques works.
▪ Use the concept of key components and separation factor to measure
separation between two key components
▪ Understand the concept of sequencing of separation operations
▪ Explain the major differences between chemical and physical
separation processes.
▪ Make a selection of separation operations based on factors involving
feed and product property differences and characteristics of
separation operations.

▪ Typically, it is the main focus of an Industry.
▪ You will most likely model/design/operate/control/simulate a Unit
Operation that requires a Separation Technology
▪ This will help you with further Mass Transfer Operations.
▪ Absorption, Distillation, Extraction
▪ Humidification, Drying, Evaporation, Leaching, etc…
▪ Understand what are the different types of units and how they
work will give you an advantage in Process Separation
Technology

▪ Understand how Mass Transfer Operations are categorized
▪ Homogeneous vs. Heterogeneous
▪ Phase Addition
▪ Phase Creation
▪ Barriers
▪ Solid Agents
▪ Mechanical / Physical Separations

▪ Mass Transfer Operations I / Process Separations:
▪ Gas Absorption
▪ Simple Distillation / Flash Distillation
▪ Binary Distillation
▪ Liquid-Liquid Extraction
▪ Solid Separations
▪ Membranes
▪ Mass Transfer Operations II
▪ Multicomponent Distillation
▪ Distillation Sequencing
▪ Azeotropic Distillation
▪ Membrane Separations
▪ Drying & Solid Separations
Alternatives:
• Mass Transfer Unit Operations
• Modern Separation Techniques
• Design & Selection of Separation
Processes
• Novel Separation Technologies
• Advanced Separation Processes
• Advanced Engineering Separations
Typically, Solid or Mechanical-Physical
Separations are not studied in this subject.

▪ Separation can be defined as an operation by which a
mixture is resolved in to its components.
▪ There are many types of Separations:
▪ Physical/Mechanical
▪ Chemical
▪ Biochemical

▪ Any type of Unit Operation or Process which involves Mass Transfer Phenomena
▪ Mass Transfer requires:
▪ Driving Force (Change in concentration, partial pressure, gradient, or molar fraction)
▪ Common examples:
▪ Distillation
▪ Mixing & Agitation
▪ Evaporation → Concentration
▪ Gas Absorption
▪ Leaching & Washing
▪ Filtration
▪ Drying & Humidifying

▪ Mass Transfer Operation (MTO) →
▪ An operation/process involving mass transfer phenomena.
▪ Does not limits to separation
▪ Evaporation of a substance such as a spill will be MT
▪ Separation Process (SP) →
▪ Requires a Separation can be defined as an operation by which a mixture is resolved in to
its components
▪ Mixtures can be Homogeneous & Heterogeneous

▪ Case 1 → Mass Transfer Operations takes place – No Separation Process does
▪ YOUR ANSWER
▪ Case 2 → Mass Transfer Operations does not takes place – Separation Process does
▪ YOUR ANSWER
▪ Case 3 → Mass Transfer Operations takes place –Separation Process does
▪ YOUR ANSWER
▪ Case 4 → No Mass Transfer Operations takes place – No Separation Process does
▪ YOUR ANSWER

▪ Case 1 → Mass Transfer Operations takes place – No Separation Process does
▪ Mixing, Agitation
▪ Case 2 → Mass Transfer Operations does not takes place – Separation Process does
▪ Separation of garbage, decanting*, filtration*
▪ Case 3 → Mass Transfer Operations takes place –Separation Process does
▪ Distillation, Evaporation
▪ Case 4 → No Mass Transfer Operations takes place – No Separation Process does
▪ Heating of water from 25°C to 30°C

▪ Mixing → spontaneous
▪ Agitation → non-spontaneous, typically pattern
▪ Separation → non-spontaneous, requires high amount of energy

Separation Process
Engineering
2nd Edition
by Phillip Wankat
Unit Operations of Chemical Engineering
7th edition
by W. McCabe (Author), J. Smith (Author),
Harriott Emeritus (Author)
Principles and Modern Applications
of Mass Transfer Operations
2nd Edition
by Jaime Benitez

Mass-Transfer Operations
3rd Edition
by Robert E. Treybal
Transport Processes and
Separation Process Principles
5th Edition
By Geankoplis, Hersel ,Lepek
Separation Process Principles
2nd Edition
by J. D. Seader, E. J. Henley,
D. K. Roper (Author)

Hanbook of Separation
Process Technology
1st Edition
by Ronal W. Rousseau
Mass Transfer
Principles & Operations
1st Edition
by A.P. Sinha Parameswar

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1. History & Status Quo
2. ESA & MSA
3. Classification of MTO
1. Method
2. Phase
4. Equilibrium vs. Rate Based Processes

▪ FOOD!
▪ Extracting Ores
▪ Perfumes from flowers
▪ Dyes from plants
▪ Evaporation of sea water → sea salt
▪ Distil Liquor!

▪ Prehispanic → Mezcal & Tequila

▪ Middle East & Arabia →
▪ Alambique; al-inbīq ‫األنبيق‬

▪ Europe
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▪ Industrial Revolution:
▪ Modern Processes
▪ Kerosene & Oil

▪ Check out how Sea-Salt is produced:
▪ https://www.youtube.com/watch?v=0vVyw2rVA4Q
▪ https://www.youtube.com/watch?v=C19PIEe5Ti8

▪ Ores
▪ Chemical Processes
▪ Scents
▪ Water Treatment
▪ Pharmaceutics

▪ Typical Yield:
▪ 15 g per 1000kg of “ore”
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▪ Identify probable Separation Units
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▪ Check out:
▪ https://www.youtube.com/watch?v=vUybtRlaLLw
▪ Clearly → Distillation is present:
▪ What other separation process is present?
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▪ Check out this video
▪ Its about Enfleurage:
▪ the extraction of essential oils and perfumes from
flowers using odorless animal or vegetable fats.
▪ https://www.youtube.com/watch?v=ThFHh1kdCFE

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▪ Hi!
▪ This time you need to do something of your own!
▪ We will perform a Leaching (Solid to Liquid Extraction)
▪ Steps:
▪ 1. Go to your kitchen
▪ 2. Get your grounded coffee
▪ 3. Heat water up to 80°C
▪ 4. Mix water and grounded coffee → Let it LEACH for 4 mins
▪ 5. Filter solid particulate
▪ 6. Enjoy a great Cup of Coffee
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▪ Can you name processes that involve:
▪ Evaporation
▪ Drying
▪ Leaching
▪ Filtration
▪ Maceration

▪ Can you name processes that involve:
▪ Evaporation – Of any Stew so food flavors get more concentrated or the so called
“reduction” of creams.
▪ Drying – Many fruits may be dried up
▪ Leaching – Coffee! Or Tea! You want the soluble flavors from the solid particles
▪ Maceration – Adding Oil to Garlic, Onion and Species then macerating the pieces so the
flavors are added to the Oil.
▪ Filtration – On the previous example, you could filter the solids so the oil has now the
flavor but still remains a single phase (liquid)

▪ What are MSA & ESA?
▪ MSA (Mass Separating Agent) & ESA (Energy Separating Agent)
▪ Advantages & Disadvantages

▪ The most common separation operations based on interphase mass transfer
between two phases.
▪ If the feed is a single-phase solution:
▪ A second separable phase must be developed before separation of the species can be
achieved.
▪ The second phase is created by:
▪ an energy separating agent (ESA) and/or
▪ added as a mass-separating agent (MSA)
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▪ An ESA:
▪ Energy Separating Agent
▪ An ESA involves:
▪ heat transfer or
▪ transfer of shaft work to/from the mixture.
▪ An example of shaft work:
▪ Creation of vapor from a liquid phase by reducing the pressure.

▪ MSA: Mass Separating Agent
▪ Example: Addition of a Stream or component to the mixture.
▪ An MSA may be partially immiscible with one or more mixture
components
▪ It is frequently the constituent of highest concentration in the
added phase.
▪ Alternatively, the MSA may be miscible with a liquid feed
mixture
▪ BUT may selectively alter partitioning of species between liquid and
vapor phases.
▪ This facilitates a separation when used in conjunction with an
ESA
▪ E.g. extractive distillation

▪ Disadvantages of using an MSA:
▪ Requires separator recovery → requires additional steps to recover the MSA for recycle
▪ need for MSA makeup
▪ possible MSA product contamination
▪ more difficult design procedures.
▪ When immiscible fluid phases are contacted:
▪ intimate mixing is used to enhance mass-transfer rates so that the maximum degree-of-
partitioning of species can be approached rapidly.
▪ After phase contact:
▪ the phases are separated by employing gravity and/or an enhanced technique such as
centrifugal force.
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▪ Mechanisms of Separation
▪ Classification
▪ Types of Separation

▪ Mixing of chemicals is “natural” → increases ENTROPY
▪ Separation of Chemicals Requires the us of Energy
▪ Separation can be:
▪ Homogeneous → one continuous phases/system
▪ Heterogeneous → different phases
▪ IF 2 or more immiscible phases → mechanical separation will go first (typicall)

Main Classifications via:
▪ Type of Method (Direct/Indirect)
▪ Properties Exploited
▪ Separation Methods
▪ Phase Involved (L-L, S-L, G-L, etc)

▪ Direct method:
▪ Only energy is added or removed
▪ Eg.Distillation , evaporation, crystallization-Product is obtained in a single stage.
▪ Indirect method :
▪ Involves addition of foreign substance
▪ Eg.Extraction , absorption, adsorption-Product is obtained in a second operation
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▪ Molecular Properties
▪ Molecular Weight
▪ Van der Waals Volume/area
▪ Molecular shape (accentric factor)
▪ Dipole moment
▪ Polarizability
▪ Dielectric constant
▪ Electric charge
▪ Radiues of gyration
▪ Thermodynamics & Transport Properties
▪ Vapor Pressure
▪ Solubility
▪ Adsorptivity
▪ Diffusivity

▪ Homogeneous
▪ Phase Addition
▪ Phase Creation
▪ Barriers
▪ Solid Agent
▪ External Field
▪ Heterogeneous
▪ Wet Scrubbing
▪ Leaching/Washing
▪ Solid Drying & Humidification
▪ Evaporation, crystallization, etc.
▪ Decanting
▪ Hydrocycloning
▪ Settling
▪ Sedimentation
▪ Floatation
▪ Centrifugation
▪ Filtration
***This course is based on this classification
Mech.Phys.
MTO involving Solids

▪ Gas-Gas
▪ N/A* Readily missibles
▪ Gas-Liquid
▪ Gas Absorption
▪ Distillation / Evaporation
▪ Humidification/Drying
▪ Gas-Solid
▪ Humidification/Drying
▪ Adsorption & Ion Exchange / Chromatography
▪ Filtration
▪ Liquid-Liquid
▪ Extraction
▪ Liquid-Solid
▪ Crystallization
▪ Leaching & Washing
▪ Solid-Solid
▪ Typically covered in a “Solids Handling” or “Solid Particle Operations” or “Mechanical Physical Separations”
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▪ Separation by Phase Addition
▪ Separation by Phase Creation
▪ Separation by Barrier
▪ Separation by Solid Agent
▪ Separation by Force Field/Gradient
▪ Mechanical Physical Separation

▪ The most common separation technique
▪ Creates a second phase, immiscible with the feed phase, by
energy (heat and/or shaft-work) transfer or by pressure reduction.
▪ Common operations of this type are:
▪ Distillation →which involves the transfer of species between vapor and
liquid phases, exploiting differences in volatility (e.g., vapor pressure
or boiling point) among the species
▪ Crystallization → which exploits differences in melting point

▪ This technique adds another fluid phase, which selectively
absorbs, extracts, or strips certain species from the feed.
▪ The most common operations of this type are:
▪ Liquid–liquid extraction → where the feed is liquid and a second,
immiscible liquid phase is added; and absorption, where the feed is
vapor, and a liquid of low volatility is added.
▪ In both cases, species solubilities are significantly different in the
added phase

▪ Less common, but of growing importance, is the use of a barrier
▪ Usually a polymer/ceramic membrane → which involves a gas or liquid feed and
exploits differences in species permeabilities through the barrier.
▪ Semi-permeable Barriers:
▪ Microporous or nonporous membranes
▪ Polymer / Natural Fiber / Ceramic /metals / etc.
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▪ Also of growing importance are techniques that involve contacting a
vapor or liquid feed with a solid agent
▪ Most commonly, the agent consists of particles that are porous to
achieve a high surface area, and differences in species adsorbability
are exploited.
▪ Process using solid mass separating agents
▪ Activated carbon
▪ Aluminium oxide
▪ Silica gel
▪ Calcium aluminosilicate zeolite

▪ Finally, external fields (centrifugal, thermal, electrical, flow, etc.)
▪ These are applied in specialized cases to liquid or gas feeds, with electrophoresis
being especially useful for separating proteins by exploiting differences in electric
charge and diffusivity.

▪ Filtration of Solid-Liquid
▪ Settling & Sedimentation in Particle-Fluid
▪ Centrifugation
▪ Mechanical Size Reduction
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▪ Equilibrium Based Operations
▪ Rate Based Operations

▪ Equilibrium-Based Methods
▪ In equilibrium model, the vapour and liquid phases are assumed to be in thermal
equilibrium
▪ Murphree vapour phase efficiency is used to describe the departure from the
equilibrium.
▪ The equilibrium model is comparatively simple
▪ The accuracy of the model depends on the prediction of Murphree efficiency
▪ Rate-Based Methods
▪ Eliminates the necessity of using M. efficiencies
▪ It is capable of predicting the actual performance of the process.
▪ The rate-based model is accurate, but more complicated than equilibrium model
▪ It might be difficult to converge.
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▪ Typically, you will:
▪ Write MESH equations for an equilibrium stage in a multicomponent
vapor–liquid cascade.
▪ Explain how equilibrium stages can be combined to form a
countercurrent cascade of N equilibrium stages that can be used to
model:
▪ absorption, stripping, distillation, and extraction.
▪ Discuss different methods to solve the MESH equations and the use of
the tridiagonal-matrix algorithm.
▪ Solve rigorously countercurrent-flow, multi-equilibrium stage,
multicomponent separation problems by the bubble point and sum-
rates methods

▪ Except for simple cases, such as binary distillation, or when physical
properties or stage efficiencies are not well known:
▪ the design methods described in Ponchon Savarit / McCabe Thiele; are suitable
only for preliminary-design studies.

▪ Final design of multistage, multicomponent separation equipment
requires rigorous determination of:
▪ temperatures, pressures, stream flow rates, stream compositions, and heat-
transfer rates at each stage
▪ Solving material-balance, energy-balance, and equilibrium relations for each
stage!
▪ Unfortunately, these relations consist of strongly interacting nonlinear
algebraic equations, where solution procedures are difficult and tedious.

▪ However, once the procedures are
programmed for a high-speed digital
computer
▪ solutions are usually achieved rapidly and
almost routinely.
▪ Therefore, analysis of solution methods used
in process simulators for:
▪ absorption, stripping, distillation, and liquid–
liquid extraction.
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▪ A mathematical model needs to be developed for an equilibrium
stage for vapor– liquid contacting.
▪ The resulting equations, when collected together for a
countercurrent cascade of stages, are called the MESH equations.
▪ Mass Balance
▪ Equilibrium Calculations
▪ Sum of unity (mole fractions)
▪ H - Enthalpy Balance
▪ *All utilize an algorithm for solving a tridiagonal-matrix equation

▪ The Theoretical Model for an Equilibrium
▪ For any stage in a countercurrent cascade, we assume:
▪ phase equilibrium is achieved at each stage
▪ no chemical reactions occur
▪ entrainment of liquid drops in vapor and occlusion of vapor
bubbles in liquid are negligible.

▪ Rate Based Operations will NOT assume Equilibrium between
stages:
▪ Equations are required so they model a non-equilibrium stage
▪ equilibrium is assumed only at the interface between phases.
▪ Explain component-coupling effects in multicomponent mass
transfer.
▪ Main goal is to estimate transport coefficients and interfacial
areas required for rate-based calculations.
▪ Typically, we will use a process simulator or stand-alone
computer program to make a rate-based calculation for a vapor–
liquid separation problem.
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▪ A little bit of History:
▪ 1893:
▪ Equations for equilibrium-based distillation models were first
published by Sorel back in.
▪ They consisted of total and component material balances around top
and bottom sections of equilibrium stages
▪ They included:
▪ total condenser
▪ Reboiler
▪ corresponding energy balances with provision for heat losses
▪ Sorel used graphs of phase-equilibrium data instead of equations.

▪ 1921:
▪ Because of the complexity of Sorel’s model, it was not widely applied
until 1921
▪ It was adapted to graphical-solution techniques for binary systems
▪ First by Ponchon
▪ Then by Savarit who used an enthalpy-concentration diagram.
▪ 1925:
▪ A much simpler, but less-rigorous, graphical technique was developed
by McCabe and Thiele
▪ They eliminated the energy balances by assuming constant vapor and
liquid molar flow rates
▪ except across feed or sidestream withdrawal stages.

▪ 1925
▪ So far, equilibrium models have been “good enough” for our models.
▪ However, for most industrial applications:
▪ assuming equilibrium of exiting-phase compositions is not reasonable.
▪ In general:
▪ exiting vapor-phase mole fractions are not related to exiting liquid-phase
mole fractions by thermodynamic K-values.
▪ To overcome this limitation of equilibrium-based models:
▪ A proposed overall stage efficiency for converting theoretical (equilibrium)
stages to actual stages.

▪ Experimental data show that this efficiency varies:
▪ From 5 to 120%
▪ High Values:
▪ large-diameter, single-liquid-pass trays because of a crossflow effect
▪ Low values:
▪ Absorption columns with high-viscosity, high-molecular-weight absorbents.
▪ An improved procedure to account for non-equilibrium with
respect to mass transfer was introduced by Murphree in 1925.
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▪ This method incorportates the Murphree vapor-phase tray
efficiency:
▪ (EMV)i,j:
▪ directly into Sorel’s model to replace the equilibrium equation based on
the K-value.
▪ These assumes:
▪ (1) uniform concentrations in vapor and liquid streams entering and
exiting a tray
▪ (2) complete mixing in the liquid flowing across the tray
▪ (3) plug flow of the vapor up through the liquid
▪ (4) negligible resistance to mass transfer in the liquid.

▪ 1932
▪ Two iterative, numerical methods were developed for obtaining a
solution to Sorel’s model for multicomponent mixtures.
▪ 1938
▪ Smoker did just that, for the distillation of a binary mixture by
assuming not only constant molar overflow, but also constant
relative volatility.
▪ Smoker’s equation is still useful for super fractionators involving
close-boiling binary mixtures, where that assumption is valid.

▪ 1940-1958:
▪ The Thiele–Geddes method requires specification of the
number of equilibrium stages, feed-stage location, reflux
ratio, and distillate flow rate, for which component product
distribution is calculated.
▪ The Lewis–Matheson method computes the stages required
and the feed-stage location for a specified reflux ratio and
split between two key components.
▪ These two methods were widely used for the simulation and
design of single feed, multicomponent distillation columns
prior to the 1960s.
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▪ 1958
▪ The breakthrough in computerization of stage-wise
calculations occurred when Amundson and co-workers,
starting in, applied techniques of matrix algebra.
▪ This led to successful computer-aided methods, based on
sparse-matrix algebra, for Sorel’s equilibrium based model.
▪ Although the computations sometimes fail to converge
▪ the methods are widely applied and have become flexible and
robust.

▪ Development of a realistic, non-equilibrium transport/rate-
based model has long been a desirable goal.
▪ 1977:
▪ Waggoner and Loud proposed:
▪ Rate-Based Models for Vapor–Liquid Separation Operations
▪ This is based on a rate-based, mass transfer model limited to nearly
ideal, close-boiling systems.
▪ However:
▪ an energy-transfer equation was not included
▪ because thermal equilibrium would be closely approximated for
a close-boiling mixture)
▪ the coupling of component mass-transfer rates was ignored.

▪ 1979
▪ Krishna and Standart:
▪ showed the possibility of applying rigorous, multicomponent mass- and heat transfer
theory to calculations of simultaneous transport.
▪ 1985
▪ The theory was further developed by Taylor and Krishna:
▪ This lead to the first rate-based, computer-aided model for:
▪ trayed columns
▪ packed distillation columns
▪ other continuous separation operations.
▪ Their model applies the two-film theory of mass transfer

▪ 1985
▪ It includes the assumption of phase equilibria at the interface, and
provides options for:
▪ vapor and liquid flow configurations:
▪ trayed columns, including plug flow and perfectly mixed flow, on
each tray.
▪ The model does not require tray efficiencies or values of HETP
▪ The correlations of mass-transfer and heat-transfer coefficients
are needed for the particular type of trays or packing employed.

▪ 1994
▪ The model was extended in by Taylor, Kooijman, and Hung
to include:
▪ Effect of liquid droplet entrainment in the vapor and
occlusion of vapor bubbles in the liquid,
▪ Column-pressure profile,
▪ Interlinking streams, and
▪ Axial dispersion in packed columns.
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▪ The 1985 model:
▪ required the user to specify the column diameter and tray
geometry or packing size,
▪ The 1994 version includes
▪ a design mode that estimates column diameter for a specified
fraction of flooding or pressure drop.

▪ Rate-based models are available in process simulators:
▪ RATEFRAC of ASPEN PLUS, ChemSep and CHEMCAD.
▪ The use of rate-based models is highly recommended for cases of low
tray efficiencies
▪ (e.g. absorbers) and distillation of highly non-ideal multicomponent
systems.

▪ Rate-based models of multicomponent, multistage, vapor–
liquid separation operations became available in the late
1980s.
▪ These models are potentially superior to equilibrium-based
models for all but near-ideal systems.
▪ Rate-based models incorporate rigorous procedures for
component-coupling effects in multicomponent mass
transfer.
▪ The number of equations for a rate-based model is greater
than that for an equilibrium-based model because separate
balances are needed for each of the two phases.
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▪ Rate-based models are influenced by the
geometry of the column internals.
▪ Correlations are used to predict mass-transfer and
heat transfer rates.
▪ Tray or packing hydraulics are also incorporated
into the rate-based model to enable prediction of
column-pressure profile.

▪ Phase equilibrium is assumed only at the phase
interface.
▪ Computing time for a rate-based model is not generally
more than an order of magnitude greater than that for
an equilibrium-based model.
▪ Both the ChemSep and RATEFRAC rate-based computer
programs offer considerable flexibility in user
specifications

Equilibrium Based:
▪ More Simple, less equations
▪ Assume Equilibrium in all stages
▪ Entrainment of liquid drops in
vapor and occlusion of vapor
bubbles in liquid are negligible.
▪ MESH Equations used
▪ Murphree Efficiencies Required
and critical
Equilibrium Stage Rate Stage
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Rate Based:
▪ Much more equations, more
complex, more time of
convergence
▪ Doe not Equilibrium
▪ Correlations for MT used
▪ More realistic approach
Equilibrium Stage Rate Stage

Introduction to Mass Transfer Operations (1 of 5)

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