Energy Conservation Using Membrane Separation Technology
M. M. Khan1, M. D. Eqbal*1, M. Danish1 & M Yusuf Ansari2
1
Department of Chemical Engineering, 2Department of Petroleum Studies
Z.H. College of Engineering & Technology
Aligarh Muslim University, Aligarh-202002
driving force which is generated through the lowering
the partial pressure .However it is very selective.
Abstract – Energy is most vital aspect of any chemical
industry. Many chemical processes are highly energy
intensive such as distillation processes. Saving even small
amount of energy consumption of any process may leads to
large profit. A lot of attempts are being made to save
energy by different technologies; however, membrane
separation technology offers the possibility in large scale
reduction of energy. The membrane technology is not only
eco-friendly but also reduces the energy and expenses. One
of the major reasons behind the great popularity of this
membrane technology is that it saves energy in chemical
separation processes and petroleum refining applications.
New approach in separation technology such as the hybrid
of distillation column with membrane separation is very
promising with respect to energy conservation point of
view. Demerits of distillation column can be eliminated
using this hybrid technology. In this paper attempts has
been made to discuss the promising option for
conservation of energy using membrane separation
technology.
I.
II. ENERGY CONSUMPTION IN SEPARATION
PROCESSES
As we know that the separation process is very
energy intensive process. Since more than 40% of the
total energy consumption is used in separation process
and 90% of this energy is used in distillation process.
An attempt to reduce this energy consumption has a
great impact on the industry economy and sustainability.
III. ENERGY CONSERVATION IN SEPARATION
PROCESSES
Due to the fast depletion of resources and scarcity
of energy there is a great need to conserve it. In this
paper, the methods are being discussed to conserve the
energy in separation process especially distillation
processes is under the target due to its unavoidable
popularity. For example in petrochemical industry the
membrane separation saves the purpose of reducing the
energy consumption to 70% in the production of various
chemicals such as ethanol, ethylene glycol, acetic acid
and ethyl acetate. Thus installing a membrane separation
unit, with the distillation column is called hybrid
distillation column reduces the reflux ratio thus enabling
the large reduction in energy utilization.
INTRODUCTION
Separation processes are very common in chemical
and petrochemical industry. It is one of the most energy
intensive as well as capital intensive industrial
processes. About 40-70% of the capital is invested in the
separation process. Distillation is the most common
separation process used in almost all the chemical and
petroleum industry. It has been reported that more than
half of the total energy consumption is accounted under
distillation. Membrane separation technology is the
emerging technology which offers an alternative path
for the various separation processes which can reduce
energy consumption significantly. The membrane
separation process along with the distillation process is
called hybrid separation process, are found to be more
sustainable and economical. One of the main advantages
of the membrane separation is that it is not based on the
vapor liquid equilibrium. In addition to it the separation
which takes place trough the membrane is due the
IV. DESCRIPTION OF MEMBRANE SEPARATION
PROCESS
Membrane separation process is very simple
process to understand. In this process membrane acts as
semi permeable barrier between two liquid phases, or a
liquid and a gas phase or two gas phases and separation
occurs due to different sorption and diffusion behavior.
When feed is passed through the membrane the
permeate passes through the membrane and retentate is
blocked.
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International Journal on Mechanical Engineering and Robotics (IJMER)
an important role in the energy profile of the whole
process. For example, multiple choices are available for
placing the membrane unit in hybrid membrane
distillation column such as (i) before the feed fed in to
distillation column, (ii) at the top of the column, (iii) at
the bottom of the column, and (iv)at the intermediate
point of column.
The process of hybrid distillation column is quite
simple, feed is fed in distillation column and the process
is same as conventional, however when the membrane
separation unit get combined with distillation column, it
affects the entire separation process. The reflux ratio is
reduced causing the reduction in number of stages
distillation column. As a result the total heat duty of the
entire process become lesser and it leads to the reduction
in energy consumption. In short membrane separation
unit reduces the load on distillation column.
V. HYBRID DISTILLATION COLUMN (HDC)
Membrane technology had appeared in the late
1960s till then its application is growing day by day.
Membrane distillation is one of the emerging
technologies of membrane engineering which is used as
the separation process .Hybrid distillation column is
basically a distillation column along with the membrane
separation plant attached to it. In this process the vapor
molecule are transported through the membrane due to
difference in vapor pressure.
VIII. SEQUENCING OF HYBRID DISTILLATION
MEMBRANE SEPARATION UNIT
In the first sequence, Error! Reference source
not found., the membrane separation unit is connected
with the distillation column through the distillate stream.
As the distillate stream enter to the membrane with less
purity the permeates gives the maximum pure distillate
while the retentate is sent back to the column below the
reflux stage since it does not matches with the reflux
composition purity. This sequence ultimately decreases
the reflux ratio which decreases the load on the column
and hence the energy consumption is decreased.
VI. ADVANTAGES OF HYBRID MEMBRANE
DISTILLATION COLUMN

Low operating temperature

Low hydrostatic pressure

Capable to utilize low grade waste

Use the alternative energy sources such as
geothermal, solar energy can be used

Can be used with the working distillation unit
by the addition of membrane separate unit

Can be used in different configuration to
separate closed boiling mixture, azeotropic
mixture and ternary mixture.

Achieved a better, cheaper, easier, enhance
separation.
VII. PROCESS DESCRIPTION OF HYBRID
SEPARATION
Hybrid separation system is a concept in which two
different separation processes get combined to give a
better separation with the objective of efficient energy
reduction. In particular, the combination of the
distillation column with the membrane separation unit
can be a good example of hybrid separation system. In
this type of system, sequencing of separation units plays
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International Journal on Mechanical Engineering and Robotics (IJMER)
so it is joined with the distillate while the retentate is
pushed back into the column below that intermediate
point. In this case also the load on the distillation
column is minimized, causing the reduction in the reflux
ratio which leads to the decrease in the energy
consumption.
configuration, Error!
Reference source not found., is basically the type of
third configuration in which membrane is connected in
between the distillation column and feed is taken from
intermediate point. If the purity of permeate does not
matches with the distillate then it is send back to the
column between reflux and intermediate point and the
retentate is given below the intermediate point.
The
fourth
possible
IX. ENERGY CONSERVATION IN HYBRID
DISTILLATION COLUMN
The energy demand in distillation column is depend
upon the reflux ratio and given by the following
equation
Energy demand=(R+1)*Heat of vaporization (Eq 1)
If we replace this conventional distillation column
completely by the membrane separation unit we need
only to supply the heat of vaporization which is the only
energy required for the separation. Thus it saves huge
amount of energy however, it cannot be possible due to
need for high performance of membrane and large
investment cost. So there is needed to connect the
membrane separation unit with the distillation tower
which is also effective enough to reduce the large
amount of energy required in conventional distillation
process.
In the second sequence, Error! Reference source
not found., the membrane is put in the feed stream
both output streams that are permeate and retentate from
the membrane enter the distillation column. Since the
permeate is much pure than the retentate so it lies on the
top of column while retentate is given at the bottom of
the column and feed enters in the middle.
In the third configuration, Error! Reference
source not found., the membrane is placed anywhere
in the intermediate points of the column. From that inter
mediate point a stream is fed to the membrane, the
composition of the permeate matches with the distillate
It has been observed that in order to separate the
mixture of water and acetic acid in equal mass fraction
to get 99% distillate and 99% at bottom with reflux ratio
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International Journal on Mechanical Engineering and Robotics (IJMER)
as 5 is about 162000 kcal/hr, Error! Reference source
not found.. If this conventional distillation is
completely replaced by the pervaporation for the same
feed and distillate the energy is required is only 27000
Kcal/hr for the membrane of selectivity 400, Error!
Reference source not found.. This energy is about 6
times lesser than the energy supplying in conventional
distillation. But when we have hybrid system that is
distillation membrane system the energy required for the
same operation is about 35000 Kcal/hr, Error!
Reference source not found.. This case study is
performed by Masahiko Matsukata et al (2011).
the reboiler. Hybrid technology gives better separation
result when distillation is carried out at cryogenic
temperature such as in case of ethylene and propylene,
energy requirement is very high thus creating a high
load on the condenser. Hence hybridization of the
membrane with distillation column is quite satisfactory
in reducing the energy consumption especially when the
key component of the distillation goes to extreme end.
XI. REFERENCES
[1]
Ellen S. Lenz, Jose A. Caballero, Ignacio E.
Grossmann, Majid Keyvani, Design of hybrid
distillation-vapor membrane separation system.
[2]
I-Lung Chien. (2012),Opportunities for energy
saving in azeotropioc separation processes.
Process system
[3]
Masahiko Matsukata , Eiichi Kikuchi, Ken-ichi
Sawamura.(2011), Review on prospects for
energy saving in distillation process with micro
porous membranes. Membrane separation and
technology,Vol.14
[4]
M. S.EI-Bourawi, Z. Ding, R.Ma, M. Khayet.
(2006). A framework for better understanding
membrane distillation separation process.
Membrane Science 285., 4-29
[5]
P. Kresis , A. Gorak. (2006).Process analysis of
hybrid separation process, Combination of
distillation
and
pervaporation.
Chemical
engineering research and design,87(A7), 595-600
[6]
TorbjcrnPettersen, Kristian M. Lien. (1995).
Design of hybrid distillation and vapor
permeation processes. Membrane Science 99.,
21-30
[7]
Wolfgang Stephan a, Richard D. Noble a, Carl
A. Koval.(1995). Design methodology for a
membrane/distillation column hybrid process.
Membrane Science 99.,259-272
[8]
Yellaiah Naidu, Ranjan K. Malik. (2011). A
generalized
methodology
for
optimal
configurations
of
hybrid
distillation–
pervaporation processes. chemical engineering
research and design 8 9.,1348–1361.
X. CONCLUSION
The hybrid membrane distillation is very useful, as
conventional distillation become very expensive, when
the relative volatility is closed to one due to the load on
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