Non hazardous reusable
Carbon dioxide is soluble in water. Water scrubbing uses the higher
solubility of CO2 in water to separate the CO2
from biogas. This process is done under high pressure and removes H2S
as well as CO2. The main disadvantage of this process is
that it requires a large volume of water that must be purified and
Polyethylene glycol scrubbing
This process is similar to water scrubbing; however, it is more
efficient. It also requires the regeneration of a large volume of
Carbon molecular sieves
The carbon molecular sieve method uses differential adsorption
characteristics to separate CH4 and CO2. This
adsorption is carried out at high pressure and is also known as
pressure swing adsorption. For this process to be successful, H2S
should be removed before the adsorption process.
There are two membrane separation techniques:
High pressure gas separation
The high pressure separation process selectively separates H2S and
from CH4. Usually, this separation is performed in three stages and
produces 96 per cent pure CH4.
Gas liquid adsorption is a new development and uses micro porous
hydrophobic membranes as an interface between gas and liquids. The
dissolve while the methane (in the gas) is collected for use.
Activated carbon impregnated with potassium iodide can catalytically
react with oxygen and H2S to form water and sulfur. The reaction is
best achieved at 7 to 8 bar (unit of pressure) and 50 to 70 C.
Activated carbon beds also need regeneration or replacement when
Scrubbing and membrane separation
As discussed in the section on
and H2S can be scrubbed by water, polyethylene glycol solutions or
separated using the membrane technique.