Pressure Swing
Adsorption
Group 6
Ryan Hummel, Mike DeGuzman,
David Vuong, and Miyoko
Ohashi
What is Pressure Swing
Adsorption?
• Requires a selective adsorbent
• Usually binary separation
• Not a continuous process
Skarstrom Cycle
• Published in
1959
• Two beds, four
steps
• Difference in
purity
• Improvements on
the cycle
General Equations
• Assumptions
-process is considered an adiabatic
system
-gas flow rate is affected by bed
height and time
-pressure drop can be ignored
-negligible mass transfer between
gas phase and solid phase
-Mass balances
Ci
C
u  bulk qi
u i C

0
t
z
z
 t
-Energy balances
( g C pg  bulk Cs )
n
q
T
T
 ( g C pg )u
 bulk  i H j  0
t
z
j 1 t
-Linear driving force model is
adopted as the mass transfer
equation
qi
 ki (qi*  qi )
t
qi* 
qmi bi Pi
n
1  b j Pj
j 1
• Four cycle process
• PSA unit on the
steam reformer
supplied to
Hickson & Welch,
Castleford,
England
• Hydrogen
purification
system
• Linde AG, Linde
Gas Division,
Germany
• Hydrogen
purification
system
• Process
• capacity
Competing Methods to PSA
• Other methods used for gas
separation include:
– Cryogenics
– Noncryogenics
Cryogenics
• Cryogenics:
– Operated under low
temperature.
(T = 100K – 150K)
– This involves
liquid to separate
gas
• Both temperature
and pressure are
controlled.
• Difference
between boiling
points is
utilized.
(Extremely low
temperature is
necessary for
the separation
of gases such
as air.
Cryogenics
• Low temperature achieved by:
– evaporation of highly volatile liquids
or
– expansion of gases under low pressure
Noncryogenics (Swing
Adsorption)
• Vacuum Swing
Adsorption (VSA)
• Recovery of methane
from coal mine
methane gas.
– Lower pressure
– Nitrogen and oxygen
were removed 96-98%
than PSA (to the
from the methane-rich
vacuum level)
gas.
– Vacuum is used to
evacuate after the • High purification
level
product gas is
• Quick
adsorbed.
– Regeneration cycle
takes seconds.
Noncryogenics (Swing
Adsorption)
• Temperature Swing
Adsorption (TSA)
– High temperature
let the gas to
escape.
– One cycle takes
hours
– lots of
adsorbents are
necessary.
– If combined with
PSA  Pressure
Temperature Swing
Adsorption (PTSA)
Other Noncryogenics
Product not very pure
 not good for most industrial uses
• Solvent
Absorption:
– Liquid absorbs the
desired gas
selectively.
– common in soda
manufacturing.
• Membrane
Separation:
– membrane diffusion
 uses different
velocity of gas
molecules.
– inexpensive method
PSA – gas separation
process
• Methods
contribute to:
• air separation
– collection of
potentially
useful gases
(carbon dioxide
and hydrogen).
• Removing harmful
gases (VOCs
(volatile
organic
compounds), CO2,
NOX, or SO2).
The End