At room temperature and atmospheric pressure,
carbon dioxide is a gas. However, small amounts of
gas can dissolve in water.
There are many ways to separate dissolved
CO2 from water. One way is to raise
the temperature of the water, or lower the
pressure. Either of these methods will
encourage any dissolved gases in the water,
including CO2, to bubble out of the
water and enter the surrounding atmosphere.
Another method involves pumping
the water through a device called a membrane
contactor. A membrane is a barrier that allows
some things to pass through it, but not others.
For example, air filters often use membranes that
trap particles in the air, and allow clean air to
pass through. In the case of a membrane
contactor for CO2 removal, the membrane
allows CO2 and other gases to pass
through it, but not water. So, when water and
dissolved CO2 flows past the membrane,
the CO2 leaves the water and passes
through the membrane, leaving water with much less
An example flow rate for a membrane
contactor, meaning how quickly you can remove gas,
is around 100 gallons of water per minute.
And, the volume of the ocean has been estimated to
be about 0.3 billion cubic miles, or about
330,000,000,000,000,000,000 gallons. So, to filter
the CO2 from the ocean using a single
membrane contactor would take approximately
6,000,000,000,000 years, or 6,000 times longer
than the lifetime of the universe!
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