The document compares and contrasts the processes of absorption and adsorption. It defines absorption as the taking in of substances across tissues by diffusion or osmosis, which occurs throughout the bulk of an absorbent. Adsorption is defined as the adhesion of molecules to the surface of a solid particle. Some key differences highlighted are that absorption is a bulk phenomenon while adsorption occurs only on surfaces, absorption does not depend on temperature while adsorption does, and absorbed materials do not form chemical bonds with the absorbent while adsorbed materials bond via Van der Waals forces or covalent bonds. The document provides a table comparing the two processes across several criteria.

1. Asst. Prof. Krishna Parmar
Environmental Enginnering
Diwaliba Polytechnic
Air pollution control
Chapter 4
Air pollution control Methods and Equipments

2. Basis for comparison Absorption Adsorption
Definition
Absorption is the process
of taking or assimilating
substances into a surface
like a cell or across the
tissues by the process of
diffusion or osmosis.
Adsorption is the process
of adhesion of molecules
of liquid or gases onto the
surface of a solid particle.
Phenomenon
Absorption is a bulk
phenomenon where
molecules of absorbate
enter into the absorbent.
Adsorption is a surface
phenomenon where the
molecules simply attach to
the surface of the
adsorbent.
Principle
Substances get absorbed
into an absorbent due to
the availability of space
and the nature of the
particle.
Substances get adsorbed
onto the surface of an
adsorbent because the
adsorbent has vacant
spaces that stimulate the
adhesion of particles onto
the spaces.

3. Absoprtion Vs Adsorption

5. Basis for comparison Absorption Adsorption
Heat exchange
Absorption is an
endothermic process as
the energy is given from
the outside of the surface,
and the overall energy of
the absorbent increases
after absorption.
Adsorption is an
exothermic process as the
energy of the surface
decreases as it leads to a
reduction in residual forces
of the surface.
Rate
Absorption takes place at a
uniform rate.
The rate of adsorption
increases steadily until it
reaches equilibrium.
Bonding
The absorbed materials
remain in the absorbent
without having any
chemical interactions with
the absorbent.
The adsorbed materials
remain attached to the
adsorbent with either Van
der Wall’s forces or
covalent bonds.

6. Basis for comparison Absorption Adsorption
Temperature
Absorption doesn’t depend
on the temperature of the
system.
Adsorption is a
temperature-dependent
phenomenon.
Concentration
The concentration of the
absorbate in the absorbent
is uniform after absorption.
The adsorbate is more
concentrated on the
surface than the other
parts of the adsorbent.
Separation
Absorbed materials can be
separated into different
phases based on their
chemical interaction with
the phases.
Adsorbed materials can be
separated by passing new
substance through the
surface of the adsorbent,
which replaces the
previously adsorbed
material.

7. Basis for comparison Absorption Adsorption
Application
Various living and non-
living systems utilize
absorption. Living systems
like unicellular organisms
use the absorption
phenomenon for the intake
of nutrients and water.
Non-living systems like
refrigerators utilize
absorption for cold
storage.
Various living and non-
living systems also utilize
adsorption. Living systems
like viruses use the
phenomenon of
adsorption for attachment
to the bacteria or other
organisms. Separation
processes like adsorption
chromatography use the
principle of adsorption for
the separation of mixtures.

9. Activated Carbon