Hydrogen gas is a popular type of gas used for water heating, space
heating, cooking, electricity generation, welding and cutting, and also used
in the purification of other chemical materials as well as their mixing. For
all these applications, purified hydrogen is very essential and there are
different measures undertaken in gas plants and laboratories to purify
hydrogen.
Hydrogen Purity Grades
There are various purity grades of hydrogen available used in many purposes
and there is the need to minimize contaminants. One is the "pre-purified
grade". This grade has a minimum purity of 99.95%, containing less than
20 ppm oxygen with a dew point of less than -59°C. This purity of
hydrogen is referred to as "3-nines." Another purity grade is the "ultra-high
purity (Gold Label) grade". This grade provides 99.999% molecular
hydrogen and referred to as "5-nines". There is another grade
known as "Research Grade". This grade has even fewer impurities,
and is available in small lecture bottles.
Purity Methods
Scrubbers
Hydrogen can be purified using scrubbers. In other words the gas containing
water and potassium hydroxide (KOH) can be purified by scrubbing and passing
through a water column.
Catalytic Recombination Purifier
The catalytic recombination purifier works at at room temperature or higher
and removes hydrogen and contaminant oxygen , and results in the formation
of water vapor. However this is easily removed when required. The ratio of
gas is 2:1 hydrogen gas present in two parts and oxygen one part. Complete
removal of the undesirable oxygen impurity is done with the help of a
stoichiometric or greater quantity of hydrogen. The purifier is based on
platinum group metals (PGM) which are supported on the surface of alumina
pellets. These pellets are absorbed by screens in a pipe section. While the
gas is being treated, it flows through the pipe treated.
Polymeric Hollow-fiber Membrane Purifiers
This method uses the principle of selective permeation to separate gases.
There is a characteristic permeation rate for each gas, which is a function
of the gas ability to dissolve and diffuse through a membrane. This process
lets the "fast" gases like hydrogen to be separated from "slow"
gases like oxygen.
Hydrogen Dryers
For removing water contamination and moisture of hydrogen, dryers are used
which are of various types like refrigeration dryers, coalescers, membrane
dryers, desiccant dryers and molecular sieve dryers.
Hydrogen
Purity Test
