Separation Process Design – Summary lectures + reader
Lecture 1 - Introduction
Separation process -> always consists of multiple separation steps (unit operations) -> never one
separation step!
Two existing types of separations:
1. Phase/particle separation: 2 or more phases (solid, liquid, gas) are separated from each other.
2. Molecule separation: molecules of different compounds are separated from each other.
Phase separations are harder than molecule separations in general!
Designing process -> use:
1. Experience
2. General scheme for separation processes:
3. Some general rules:
- Remove the most plentiful and/or easiest to remove impurities first
- Make the most difficult and expensive separations last
- Use the greatest differences in the physico-chemical properties between the product and the
impurities
,- Select and sequence processes that exploit different driving forces for separation
- Minimize costs and use of energy and additional materials
- Maximize efficiency, selectivity, concentration factor and purity of the product
- Use mathematical models and experiments
Driving forces for biotechnological separation processes are differences in:
1. Volatility
2. Solubility/polarity
3. Density
4. Size
5. Electrical charge
When modelling a separation unit use:
- Mass balances
- Energy balances
- Force balances
- Equilibrium-based approach (thermodynamic approach) or rate-based approach
Symbols + units used in this course:
Phase/Particle separations Molecule separations
Quantity Symbol Unit Symbol Unit
Stream flow rate φ m3 s-1 F mole s-1
Volumetric or ε m3 m-3 x or y mole mole-1
mole fraction (volumetric (mole fraction)
fraction)
Distribution m mole mole-1
coefficient
(equilibrium
constant)
Density ρ kg m-3
Total cT moles m-3
concentration
Velocity v m s-1
Superficial u m s-1 u m s-1
velocity
Area A m2
Pressure Δp Pa
difference
Flux J mole m-2 s-1
Diffusion D m s-2
coefficient
Boundary layer δ m
thickness
Distance z m
perpendicular to
interface
Transfer k m s-1
coefficient
Specific interface a m2 m-3
area
, Volume V m3 V m3
Heat input NQ W NQ W
Electrical power P W P W
input
Separator Yi Yi
efficiency for
component i
Separator Φij Φij
selectivity for
components i + j
Concentration CFi CFi
factor for
component i
Performance indicators separation process:
1. Efficiency (Y)
2. Concentration factor (CF)
3. Selectivity (Φ)
A good separation process has a:
1. High efficiency -> much product is recovered and not much product is lost (economically good)
2. High concentration factor -> much higher concentration of product in the outgoing stream than in
the ingoing stream of the separator (facilitates further processing)
3. High selectivity -> much higher product-solvent ratio in the outgoing stream than in the ingoing
stream of the separator
A single separator seldom scores well on all goals (high efficiency, high concentration factor, high
selectivity)!
Efficiency whole process = efficiencies single steps of process multiplied
Concentration factor whole process = concentration factors single steps of process multiplied
Lecture 2 – Mass balances, energy balances, thermodynamic equilibrium
General mass balance process:
Accumulation = in – out + production – consumption
No reaction occurs in a separation process so production = 0 and consumption = 0
General mass balance separation process:
Accumulation = in – out
Steady state/continuous process? -> accumulation = 0
, Mass balance for phase/particle separator:
Accumulation = in - out
Include density (ρ) in mass balance!
No accumulation (steady state)? -> divide mass balance by density (ρ) -> result = volumetric balance
Mass balance for molecule separator:
Accumulation = in – out
Sum of mole fractions (x or y) = 1
Sum of volumetric fractions (ε) = 1
For 1 unit operation you have:
- Multiple mass balances -> # = amount of components you have in your unit operation -> total mass
balance is NOT an extra equation, you can use it instead of one of the component balances, but you
cannot use it together with all the component balances
- 1 energy balance
Sorts of energy (all units are J mole-1):
1. Kinetic energy (ek): the energy which leads to motion of objects/particles.
2. Potential energy (ep): the energy an object/particle has due to its position in a force field.
- Electrical energy
- Gravitational energy
3. Internal energy (eI): the energy of a mass which is determined by random motions of the
molecules of that mass so which is determined by the temperature.
General energy balance process:
Accumulation = in – out + production – consumption
Energy can’t be produced or consumed so production = 0 and consumption = 0
General mass balance (separation) process:
Accumulation = in – out
Continuous process/steady state? -> accumulation = 0
Energy balance molecule separator in steady state:
0 = Σ Fi (ek,i + ep,i + eI,i) – Σ Fo (ek,o + ep,o + eI,o) + Σ pi Fi VM,I – Σ po Fo VM,o + P + NQ
Σ Fi (ek,i + ep,i + eI,i) -> input of energy via molecules which enter the separator
Σ Fo (ek,o + ep,o + eI,o) -> output of energy via molecules which leave the separator
Σ pi Fi VM,I -> input of energy by doing work to let the molecules enter the separator
Σ po Fo VM,o -> output of energy by doing work to let the molecules leave the separator
P -> other work done which increases (+P) or decreases (-P) the energy of the separator
NQ -> added (+NQ) of substracted (NQ) heat from the separator
Lecture 1 - Introduction
Separation process -> always consists of multiple separation steps (unit operations) -> never one
separation step!
Two existing types of separations:
1. Phase/particle separation: 2 or more phases (solid, liquid, gas) are separated from each other.
2. Molecule separation: molecules of different compounds are separated from each other.
Phase separations are harder than molecule separations in general!
Designing process -> use:
1. Experience
2. General scheme for separation processes:
3. Some general rules:
- Remove the most plentiful and/or easiest to remove impurities first
- Make the most difficult and expensive separations last
- Use the greatest differences in the physico-chemical properties between the product and the
impurities
,- Select and sequence processes that exploit different driving forces for separation
- Minimize costs and use of energy and additional materials
- Maximize efficiency, selectivity, concentration factor and purity of the product
- Use mathematical models and experiments
Driving forces for biotechnological separation processes are differences in:
1. Volatility
2. Solubility/polarity
3. Density
4. Size
5. Electrical charge
When modelling a separation unit use:
- Mass balances
- Energy balances
- Force balances
- Equilibrium-based approach (thermodynamic approach) or rate-based approach
Symbols + units used in this course:
Phase/Particle separations Molecule separations
Quantity Symbol Unit Symbol Unit
Stream flow rate φ m3 s-1 F mole s-1
Volumetric or ε m3 m-3 x or y mole mole-1
mole fraction (volumetric (mole fraction)
fraction)
Distribution m mole mole-1
coefficient
(equilibrium
constant)
Density ρ kg m-3
Total cT moles m-3
concentration
Velocity v m s-1
Superficial u m s-1 u m s-1
velocity
Area A m2
Pressure Δp Pa
difference
Flux J mole m-2 s-1
Diffusion D m s-2
coefficient
Boundary layer δ m
thickness
Distance z m
perpendicular to
interface
Transfer k m s-1
coefficient
Specific interface a m2 m-3
area
, Volume V m3 V m3
Heat input NQ W NQ W
Electrical power P W P W
input
Separator Yi Yi
efficiency for
component i
Separator Φij Φij
selectivity for
components i + j
Concentration CFi CFi
factor for
component i
Performance indicators separation process:
1. Efficiency (Y)
2. Concentration factor (CF)
3. Selectivity (Φ)
A good separation process has a:
1. High efficiency -> much product is recovered and not much product is lost (economically good)
2. High concentration factor -> much higher concentration of product in the outgoing stream than in
the ingoing stream of the separator (facilitates further processing)
3. High selectivity -> much higher product-solvent ratio in the outgoing stream than in the ingoing
stream of the separator
A single separator seldom scores well on all goals (high efficiency, high concentration factor, high
selectivity)!
Efficiency whole process = efficiencies single steps of process multiplied
Concentration factor whole process = concentration factors single steps of process multiplied
Lecture 2 – Mass balances, energy balances, thermodynamic equilibrium
General mass balance process:
Accumulation = in – out + production – consumption
No reaction occurs in a separation process so production = 0 and consumption = 0
General mass balance separation process:
Accumulation = in – out
Steady state/continuous process? -> accumulation = 0
, Mass balance for phase/particle separator:
Accumulation = in - out
Include density (ρ) in mass balance!
No accumulation (steady state)? -> divide mass balance by density (ρ) -> result = volumetric balance
Mass balance for molecule separator:
Accumulation = in – out
Sum of mole fractions (x or y) = 1
Sum of volumetric fractions (ε) = 1
For 1 unit operation you have:
- Multiple mass balances -> # = amount of components you have in your unit operation -> total mass
balance is NOT an extra equation, you can use it instead of one of the component balances, but you
cannot use it together with all the component balances
- 1 energy balance
Sorts of energy (all units are J mole-1):
1. Kinetic energy (ek): the energy which leads to motion of objects/particles.
2. Potential energy (ep): the energy an object/particle has due to its position in a force field.
- Electrical energy
- Gravitational energy
3. Internal energy (eI): the energy of a mass which is determined by random motions of the
molecules of that mass so which is determined by the temperature.
General energy balance process:
Accumulation = in – out + production – consumption
Energy can’t be produced or consumed so production = 0 and consumption = 0
General mass balance (separation) process:
Accumulation = in – out
Continuous process/steady state? -> accumulation = 0
Energy balance molecule separator in steady state:
0 = Σ Fi (ek,i + ep,i + eI,i) – Σ Fo (ek,o + ep,o + eI,o) + Σ pi Fi VM,I – Σ po Fo VM,o + P + NQ
Σ Fi (ek,i + ep,i + eI,i) -> input of energy via molecules which enter the separator
Σ Fo (ek,o + ep,o + eI,o) -> output of energy via molecules which leave the separator
Σ pi Fi VM,I -> input of energy by doing work to let the molecules enter the separator
Σ po Fo VM,o -> output of energy by doing work to let the molecules leave the separator
P -> other work done which increases (+P) or decreases (-P) the energy of the separator
NQ -> added (+NQ) of substracted (NQ) heat from the separator
