Membrane Gas Separation Edited by Yuri Yampolskii and Benny Freeman
© 2010 John Wiley & Sons, Ltd
14
Membrane Engineering: Progress
and Potentialities in Gas Separations
Adele Brunetti
a
, Paola Bernardo
a
, Enrico Drioli
a,b
and Giuseppe Barbieri
a
a
National Research Council – Institute for Membrane Technology (ITM – CNR), The University of
Calabria, Rende, Italy
b
The University of Calabria – Department of Chemical Engineering and Materials, Rende, Italy
14.1
Introduction
In the last few years the potentialities of membrane operations have been widely recog-
nized. The attention to the process intensifi cation (PI) strategy, as the best available
approach for an appropriate sustainable industrial growth [2] , confi rmed that membrane
engineering is a powerful tool to realize best this strategy. Today,
membrane technology
for gas separation (GS) is a well - consolidated technique, in various cases competitive
with traditional operations. Separation of air components, H
2
from refi nery industrial gases,
natural gas dehumidifi cation, separation and recovery of CO
2
from biogas and natural gas
are some examples in which membrane technology is already applied at industrial level
[3,4] . The separation of air components or oxygen enrichment
has advanced substantially
during the past 10 years. The oxygen - enriched air produced by membranes has been used
in several fi elds, including chemical and related industries, the mechanical fi eld, food
packing, etc. In industrial furnaces and burners, for example, injection of oxygen - enriched
air (30 – 35% of oxygen) leads to higher fl ame temperature and reduces the volume of
parasite
nitrogen to be heated; this means lower energy consumption. Mixtures containing
more than 40% oxygen or 95% nitrogen can also be obtained. Today, membranes dominate
the fraction of the nitrogen market for applications less than 50 tons/day and relatively
low purity (95 – 99.5% nitrogen). On the contrary, oxygen separation with membranes is
282
Membrane Gas Separation
still underdeveloped. The main reason is that most of the industrial oxygen applications
require purity higher than 90%, which is easily achieved by adsorption or cryogenic
technologies, whereas it is diffi cult to obtain with a single membrane stage. The
possibility
of utilizing membrane technology in solving problems such as the greenhouse effect
related to CO
2
production is also ongoing. Membranes able to separate CO
2
from fl ue gas
streams emitted by power plant, kilns, steel mills, etc. with a high CO
2
/N
2
selectivity,
might be used at any large - scale industrial CO
2
source. The
separation and recovery of
organic solvents from gas streams is also rapidly growing at industrial level. Polymeric
rubbery membranes that selectively permeate volatile organic compounds (VOC) and
gasoline vapours in particular from air or nitrogen have been used. Such systems typically
achieve greater than 99% removal of VOC from the feed gas and reduce the VOC content
of the stream to 100 ppm or less.
Amorphous perfl uoropolymers might be utilized for casting asymmetric composite
membranes [5] with interesting selectivity and permeability for various low molecular
species. Their cost is, however, a negative aspect. The possibility of also realizing
new mass transport mechanisms as the ones characterizing the perovskite membranes
is becoming of interest. The case of O
2
and H
2
transport
in ion transport membranes
might be extended to other species by realizing new specifi c materials. Molecular
dynamics studies, fast growing in this area, might contribute to the design of these
new inorganic materials or to the appropriate functionalization of existing polymeric
membranes.
The signifi cant positive results achieved in GS membrane systems are, however, still
far from realizing the potentialities of this technology. Problems related to pre - treatment
of the streams,
to the membrane life time, to their selectivity and permeability still exist,
slowing down the growth of large - scale industrial applications. Together with the inves-
tigation of new polymeric, inorganic and hybrid materials, the design and optimization
of new membrane plant solutions, also integrated with the traditional operations, will
lead to signifi cant innovation toward the large - scale diffusion of the membranes for GS.
With the introduction of process intensifi cation strategy and of the methods related to it,
large new areas will be open for GS membrane systems. Some
of the drawbacks of the
membrane operations such as the necessity of pre - treatment, might be solved by com-
bining various membrane operations in the same industrial process, by developing better
membranes (higher chemical stability, permeability and selectivity) and modules. In this
respect, the role of chemical engineering is crucial.
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