Low Carbon Economy, 2013, 4, 125-128
http://dx.doi.org/10.4236/lce.2013.43013 Published Online September 2013 (http://www.scirp.org/journal/lce) 125
Improved Carbon Dioxide Capture Using Nanostructured
Ceramic Membranes
Ngozi Claribelle Nwogu, Edward Gobina, Mohammed Nasir Kajama
Centre for Process Integration and Membrane Technology, School of Engineering, Robert Gordon University, Aberdeen, UK.
Email: n.c.nwogu@rgu.ac.uk, e.gobina@rgu.ac.uk, m.n.kajama@rgu.ac.uk
Received August 8th, 2013; revised September 5th, 2013; accepted September 13th, 2013
Copyright © 2013 Ngozi Claribelle Nwogu et al. This is an open access article distributed under the Creative Commons Attribution
License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
A nanoporous-structured tubular hybrid inorganic membrane capable of stripping carbon dioxide from flue gas stream
was designed and tested at laboratory scale to improve compliance with various environmental regulations to cushion
the effect of global warming. Single gas separation experiments using silica modified ceramic membrane were carried
out to investigate individual gas permeation behaviors at different pressures and membrane efficiency after a dip coat-
ing method. Four gases: Nitrogen (N2), Carbon dioxide (CO2), Oxygen (O2) and Methane (CH4) were used. Plots of
flow rate versus pressure were generated. Results show that the gas flow rate increases with pressu re drop. However at
above a pressure of 4 bars, the flow rate of CO2 was much higher than the other gases, indicating dominance of a more
selective absorptiv e type transport mechanism.
Keywords: Ceramic Membrane; Carbon Dioxide Capture; Permeability; Selectivity; Gas Transport Mechanisms
1. Introduction
About one third of the overall CO2 emission globally
comes from energy creation. Its decrease and manage-
ment are vitally critical and they are important factors to
ease global warming [1]. The position of CO2 in global
warming is a present-day ecological concern and needs
urgent attention in the provision of techno logies that will
curtail the emission of CO2 [2]. CO2 removal from flue
gas stream recorded the success with conventional tech-
nology like absorption using glycol, amine and methanol
under low temperature, the process with hot potassium
carbonate, the reaction with calcium oxide and the use of
polymer membrane. These processes employ low tem-
perature resulting in energy losses due to high tempera-
ture recuperation as well as cooling of the gas stream [3].
Owing to the burning desire to abate global warming
especially at the rate of CO2 emission and its concentra-
tion in the atmosphere through flue gases today, inor-
ganic ceramic membrane with distinct characteristics
should be a key issue. Cost effective, energy-saving, high
chemical resistance, cheap materials are needed in the
development of membrane module for manufacturing
purposes. Porous inorganic membrane conquers some
rather than all of the in-built limitations. They can toler-
ate higher temperature and basically limit the connection
between selectivity and permeability. If properly design-
ing the pore size and its distribution decides its selectiv-
ity while the volume fraction porosity regulates and es-
tablishes permeability [3]. Porous inorganic membrane
also shows exceptional evidence of physical and chemi-
cal properties, including unresponsiveness to sarcastic
environment, stability under high temperature, homoge-
neous pore structure and reasonable fluxes [4]. Some
membranes today have been used for decades in CO2
capture, but, because the membrane is used for natural
gas at very high pressure, they are unsuitable for CO2
capture from flue gases. D esign and fabr ication of por ous
ceramic membrane consist of several layers of different
materials namely: Aluminium oxide (Al2O3), Titanium
Oxide (TiO2), Zirconium Oxide (ZrO2), Silicon dioxide
(SiO2), Silicon carbide, Zeolite or a mixture of two mate-
rials applied on an underlying porous stainless steel, α-
alumina, γ-alumina, zirconium, zeolite supports [5]. The
manner in which gas molecules flow across the mem-
brane referred to permeation mechanism is a significant
fact in membrane technology. This flow is generally in-
fluenced by three factors: the gas properties, morphology
of the membrane and the material used for membrane
design. Consequently a hybrid material made from ce-
ramics membrane has been well thought out by means of
Nanotechnology. The technology is eco-friendly, eco-
Copyright © 2013 SciRes. LCE
Improved Carbon Dioxide Capture Using Nanostructured Ceramic Membranes
nomical and very efficient. It’s applicable in all forms of
CO2 elimination from other gases and its effectiveness
increases comparatively to the CO2 concentration in the
flue gas stream feed. Nanotechnology is among the ranges
of technolog ies paying attention to exploring the carbon-
capturing technology [6]. Membrane separation of gases
is a highly complex process and therefore the material
used for its preparation should exhibit a long-lasting
characteristic, stability and modify in an advanced man-
ner to be adapted to separate specific gases.
However, the innovation is that a so called agent is
immobilized in the membrane porous network, thus as-
sisting to attract the CO2, and enhancing its transport
across the membrane. This is in complete contrast to the
more common and older method of using a filter that
separates directly between CO2 and other gases.
2. Experimental
The gas separation experiment was performed using a
membrane support and a nano-structured membrane de-
posited on a macro porous tubular filter employing a re-
peat dip-coating technique [6]. The gases used for the gas
transport tests included Nitrogen (N2), Carbon dioxide
(CO2), Oxygen (O2) and Methane (CH4) respectively.
The experim ent was carried out to i nvestigate the single
gas permeation behaviors of the gases listed above with
the permeation done separately and individually.
In Figure 1, the picture at the top is a tubular ceramic
support before modification while the one at the bottom
is the nano-structured composite which was modified
after a dip coating technique.
Figure 2 shows the permeation cell set up. The com-
ponents of the cell includes: 1) Gas cylinder, 2) pressure
valve, 3) pressure guage, 4) membrane reactor, 5) re-
tentate, 6) permeate and 7) flow meter respectively.
Morphology of Support
The scanning electron microscopy was used to verify the
morphology of the support. The image is shown in Fig-
ures 3 and 4 respectively.
3. Applicable Theory
The manner in which gas molecules flow across compos-
ite membrane comprising of the membrane and the sup-
port with respect to the pressure will be determined. In
addition, a distinction between viscous and Knudsen
flow mechanisms in porous membrane to determine
flaws in the membrane before and after coating will be
illustrated. A schematic illustration of the transport po-
rous is shown in Figure 5 involving interactions be-
tween gas molecules and pore surface to determine flows
in the membrane before and after coating will be illus-
trated. A schematic illustration of the transport process is
Figure 1. Tubular ceramic support (top) and nano-struc-
tured composite (bottom).
Figure 2. Permeation cell.
Figure 3. SEM membrane cross-section.
Copyright © 2013 SciRes. LCE
Improved Carbon Dioxide Capture Using Nanostructured Ceramic Membranes 127
Figure 4. SEM membrane inner surface.
Top layer
Feed gas
Figure 5. Schematic diagram of gas transport through a
coated support membrane.
shown in Figure 5.
Values of gas permeation rate of the top layer from
Figure 5 were calculated using the formula [7]
where F (l/min) is the flow rate through the membrane
and S (m2) is the membrane surface area of the flow
pathway Pf (bar) and Pb (bar) are absolute feed pressure
and borderline pressure between the support and the to-
player. Pb can be calculated from Equation (2) below
supsupsup supsup
 
where C and D are constants relative to membrane sup-
port characteristics and Z given below for gas permeation
through the composite membrane.
4. Results and Discussion
Accordingly, Figure 6 presents a plot of flow rate
against pressure and the trend explains the proportional-
ity for both parameters.
Figure 7 shows the plots of the ratio of flow rate of
CO2 to that of N2 in relationship to the ratio of the mo-
lecular weight of CO2 to that of N2. The trend confirms
that at pressure of 2 bar and above more CO2 was ob-
tained from the separation.
Figure 8 also demonstrated that at pressure of 3 bars
and above more of CO2 was separated from O2 while
Figure 9 illustrates that from 2.4 bars and above more
CO2 will be removed from CH4.
Figure 10 shows that gas flow through the support
(sup) increased as the pressure was increased. For the
Figure 6. Graph of flow rate of N2, CO2, O2 & CH4 versus
Figure 7. Ratio of flow rates and molecular weights of CO2
and N2 at different pressures.
Copyright © 2013 SciRes. LCE
Improved Carbon Dioxide Capture Using Nanostructured Ceramic Membranes
Copyright © 2013 SciRes. LCE
top layer, the effect of pressure on the gas permeation
was negligible even after a pressure build up.
As expected, the layer showed only minor depend ence
of permeance with average pressure suggesting the ab-
sence of defects.
5. Conclusion
Using the combination of Knudsen flow and viscous
flow, it has been possible to extract the transport of the
thin membrane layer in a composite hybrid system. For
the support overall results have shown that both viscous
and Knudsen flow can have a significant effect on the
single gas transport. The dip coating technique had a
significant effect toward achieving a zero level mem-
brane deficiency. However, real flue gas will consist of
mixtures and work is currently ongoing to obtain mixed
gas transport and selectivity.
Figure 8. Ratio of flow rates and molecular weights of CO2
and N2 at different pressures.
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Figure 9. Ratio of flow rates and molecular weights of CO2
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Figure 10. Membrane defect determination.