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THERMAL PROCESS ENGINEERING ABSORPTION AND ADSORPTION

BASIC KNOWLEDGE

BASIC KNOWLEDGE

ABSORPTION

ADSORPTION

Absorption is used to remove one or more gaseous
components from a gas flowusing a solvent. Absorption can have different aims:

Production of a liquid; one example would be
obtaining hydrochloric acid by absorption of HCl
gas in water.

The gaseous component to beremoved is a product
that is wanted.

At least three substances are involved in the
absorption: the gaseous component to be removed
(absorbate), the carrier gas and the solvent
(absorbent).

Thegaseous component to be removed is
unwanted. This could be the case when removing
contaminantes from an exhaust gas flow.

Absorption
Absorption

(pressure , temperature )

Regeneration(pressure , temperature )

Adsorption is used to remove individual components from a
gas or liquid mixture. The component to be removed is physically or chemically bonded to a solid surface.
Thecomponent removed from a gas or liquid mixture
by adsorption can either be a product that is wanted or
an impurity. In the latter case, the aim could be to clean
exhaust gases.
The solid is referredto as the adsorbent and the adsorbed
component as the adsorbate. Where possible, the adsorbent
should only bond the adsorbate and not the other components in the mixture to be separated. Otherimportant requirements for the adsorbent are a large specific surface (high
porosity) and good regeneration properties. Activated carbon
is a frequently used adsorbent.
As adsorption is enhanced by lowtemperature and high
pressure, high temperature and low pressure are used
to promote regeneration, i.e. desorption. This means that
water vapour or hot inert gas can be used to regenerate theadsorbent.

If a fluid with a constant concentration of a
component to be removed (adsorbate) flows
into a fixed bed adsorber, the adsorbate is
initially completely adsorbed in the lower area
of...