respectively) (Gabriel et al. 2013; Muñoz et al. 2015). Among biological methods,
photosynthetic H 2 S removal is attracting a significant attention based on its
simultaneous occurrence during CO 2 capture in algal–bacterial photobioreactors,
which will drastically reduce the operating cost of biogas upgrading (Table 8).
Finally, the removal of volatile fatty acids and siloxanes is mainly conducted in
conventional adsorption units due to its compact nature and extensive design
Table 7 Physical/chemical technologies for CO 2 removal from biogas (Bauer et al. 2013;
Muñoz et al. 2015)
Technology Fundamentals
Design parameters Operational parameters
Water
scrubbing
Pressurised water is used for the
absorption of CO 2 from biogas
in a packed bed. CO 2 separation
is based on the higher aqueous
solubility of CO 2 compared to
that of CH 4 (24 times more
soluble)
1 absorption
column + 2
stripping columns
Concentrations of
CH 4 > 96% and of
CO 2 < 2%
Operating
pressure = 6–10 bar
Recycling water flow
rates = 0.18–0.23
m
3 water/Nm
3
biogas
Electricity
consumption = 0.24
kWh/Nm
3
Chemical
Scrubber
Absorption + reaction in
solvents based on amines or
basic solutions (NaOH, KOH,
CaOH, K 2 CO 3 , etc.)
1 absorption
column + 1
stripping column
Operating
pressure = 1–2 bar
Electricity
consumed = 0.13 kWh/
Nm
3
Thermal energy for
solvent regeneration
0.55 kWh/Nm
3
Organic
solvent
scrubbing
CO 2 absorption based on
polyethylene glycol solvents
(Selexol® o Genosorb®) with a
5 times higher CO 2 solubility
than water
1 absorption
column + 2
desorption column
Concentrations of
CH 4 = 96–98.5%
Electricity
consumed = 0.22 kWh/
Nm
3
Thermal energy for
solvent regeneration:
0.4–0.51 kWh/Nm
3
Pressure
swing
adsorption
Selective separation of CO 2
over CH 4 based on a selective
adsorption or size exclusion in
the adsorbent bed
Adsorbent
materials:
Activated carbon,
silica gel, Zeolites
4 columns
operated
sequentially
Concentrations of
CH 4 = 96–98%
Electricity
consumed = 0.26 kWh/
Nm
3
Membrane
separation
Selective permeation of CO 2
and H 2 S through
semi-permeable membranes
Gas–gas or liquid–
gas configurations
Single stage or
multiple stage
configurations
Electricity
consumed = 0.26 kWh/
Nm
3
264
F. Passos et al.
photosynthetic H 2 S removal is attracting a significant attention based on its
simultaneous occurrence during CO 2 capture in algal–bacterial photobioreactors,
which will drastically reduce the operating cost of biogas upgrading (Table 8).
Finally, the removal of volatile fatty acids and siloxanes is mainly conducted in
conventional adsorption units due to its compact nature and extensive design
Table 7 Physical/chemical technologies for CO 2 removal from biogas (Bauer et al. 2013;
Muñoz et al. 2015)
Technology Fundamentals
Design parameters Operational parameters
Water
scrubbing
Pressurised water is used for the
absorption of CO 2 from biogas
in a packed bed. CO 2 separation
is based on the higher aqueous
solubility of CO 2 compared to
that of CH 4 (24 times more
soluble)
1 absorption
column + 2
stripping columns
Concentrations of
CH 4 > 96% and of
CO 2 < 2%
Operating
pressure = 6–10 bar
Recycling water flow
rates = 0.18–0.23
m
3 water/Nm
3
biogas
Electricity
consumption = 0.24
kWh/Nm
3
Chemical
Scrubber
Absorption + reaction in
solvents based on amines or
basic solutions (NaOH, KOH,
CaOH, K 2 CO 3 , etc.)
1 absorption
column + 1
stripping column
Operating
pressure = 1–2 bar
Electricity
consumed = 0.13 kWh/
Nm
3
Thermal energy for
solvent regeneration
0.55 kWh/Nm
3
Organic
solvent
scrubbing
CO 2 absorption based on
polyethylene glycol solvents
(Selexol® o Genosorb®) with a
5 times higher CO 2 solubility
than water
1 absorption
column + 2
desorption column
Concentrations of
CH 4 = 96–98.5%
Electricity
consumed = 0.22 kWh/
Nm
3
Thermal energy for
solvent regeneration:
0.4–0.51 kWh/Nm
3
Pressure
swing
adsorption
Selective separation of CO 2
over CH 4 based on a selective
adsorption or size exclusion in
the adsorbent bed
Adsorbent
materials:
Activated carbon,
silica gel, Zeolites
4 columns
operated
sequentially
Concentrations of
CH 4 = 96–98%
Electricity
consumed = 0.26 kWh/
Nm
3
Membrane
separation
Selective permeation of CO 2
and H 2 S through
semi-permeable membranes
Gas–gas or liquid–
gas configurations
Single stage or
multiple stage
configurations
Electricity
consumed = 0.26 kWh/
Nm
3
264
F. Passos et al.