Mixed matrix membranes comprising PMP polymer with dispersed alumina nanoparticles fillers to Separate CO2/ N2

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Mixed matrix membranes comprising PMP polymer
with dispersed alumina nanoparticles fillers to
Separate CO2/ N2
Amir Hossein Saeedi Dehaghani a*
, Vahid Pirouzfar b
, Ebrahim Akhondi c
a
Petroleum Engineering Group, Faculty of Chemical Engineering, Tarbiat Modares University, P.O.
Box: 14115-114, Tehran, Iran
b
Young Researchers and Elite Club, Central Tehran Branch, Islamic Azad University, Tehran, Iran
c
Department of Chemical Engineering, Central Tehran Branch, Islamic Azad University, Tehran, Iran
Abstract
Regards to evolution of the desirable properties and chemical structure in high performance of gas
separation by membrane, mixed matrix membranes (MMMs) as one of types, need to carefully design
and control to realize high efficiency. This research investigates the role of main parameters in the
fabrication and performance analysis of MMMs prepared through blending of alumina nano particles
(Al2O3) and poly (4-methyl-1-pentyne) known as PMP with various weight percentages of alumina
nano-particles in PMP precursor. Precursor and resultant MMMs were characterized using TGA and
SEM techniques. SEM images demonstrated the proper dispersion of Al2O3 particles in precursor
matrix. Results indicated that the microstructure of the precursor, blend composition and the content
of nano particles play an important role in gas transport properties of the resulting MMMs. The
influence of the percentage of alumina nano particles used in the precursor matrix on the CO2 and N2
permeability and CO2/N2 ideal selectivity of the MMMs illustrated in a trend. Using higher alumina
content resulted in membranes with higher permeability and ideal selectivity. The highest rate of CO2
and N2 permeability could be obtained from PMP-alumina with loading of 30 wt.% alumina (PMP30)
at 10 bar. Furthermore, these results suggest that PMP30 MMMs (at operating pressure of 8 bar) are
exceptional candidates for the CO2/N2 separation, offering enhanced gas pair selectivity in the range
*
Corresponding author: A. H. Saeedi Dehaghani; Tel: +98 912 2892230.
E-mail address: asaeedi@modares.ac.ir
Manuscript Click here to download Manuscript Manuscript-R2.doc

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of 4.5-5 depending on the operating pressure. The results of this research revealed that high-
performance gas separation by MMMs can be realized through adopting a judicious combination of
blending and dispersing technique.
Key Words:
Mixed matrix membranes, CO2/N2 separation performance, PMP, Al2O3 nano particles, Selectivity
and permeability, Operating pressure
1. Introduction
The exceeding trend of global warming has been directed into various problems and proper solutions
should be taken. One of the problems is the excessive emission of greenhouse gases in the
environment [1-4]. Figure 1.a represents other factors associated with human activities and their
contribution in the production of greenhouse gases [5,6]. According to this figure, energy supply (due
to burning natural gas, coal, and oil to generate electricity, heat, and transport) is the largest source of
greenhouse gases. In the case of fossil fuels, oil and refining industries, natural gas, petrochemicals,
power plants and coal resources can be also noted as major producers of destructive greenhouse gases
in the atmosphere. It should be considered that carbon dioxide scores the highest rate of greenhouse
gases emissions due to human activities (Figure 1.b) [5-8].
Within recent years, membrane separation processes have had acceptable performance to prevent
greenhouse gas emissions due to lower power consumption [9-17]. These processes have been
introduced as an alternative to the gas and petrochemical refinery conventional processes and have
constituted a significant share of the industry market. Therefore, the development and improvement of
membrane separation systems is of utmost importance [18]. One importance area is the separation of
CO2 (as greenhouses gas) from N2. In comparison to other commercial method for this separation,
new developed membranes must offer considerable improvements in CO2 and N2 permeance and
CO2/CH4 selectivity. Development of polymeric materials is one of the widest growing topics of
membrane science and technology. However, these membranes are somewhat imperfect in meeting
the requirements of current membrane application [19,20]. Mixed matrix membranes (MMMs)

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presents an appealing approach for improving the CO2/N2 separation properties. They synthesizes
from impermeable or rigid permeable particles as filler dispersed in a continuous polymeric matrix.
The potential fillers such as zeolites [21-23], carbon nanotubes (CNT) [24-26], carbon molecular
sieve (CMS) [27] metal organic framework (MOF) [28,29], graphene [30-32], silica and metal oxide
nanoparticles [33,34] are used in MMMs preparation.
Recent researches showed that metal oxide nanoparticles among the various types of fillers could be
used as a potential filler substitute for MMMs synthesis owing to their ease of processing, excellent
thermal and electrical properties as well as appropriate interaction with the polymeric phase. The
presence of these nanoparticles in the polymer structure is followed by increased permeability of
gases and more stability in thermal, mechanical, and chemical features of the membranes are followed
by the presence of nanoparticles in the polymer structure. As a result, increasing of different particles
has been considered in the structure of polymer chains and the preparation of suitable membrane in
gas separation processes [19,20,33].
Ebadi et al. [36] evaluated properties of CO2 / N2 separation using ABS/PEG composite membranes.
Membranes made in pressure of 1 to 8 bar were tested. Their outcomes demonstrated that the
membrane PEG 20000 / ABS (% 10 weight PEG) had the best performance in terms of permeability
and ABS / PEG400 and ABS / PEG20000 had the best performance in terms of selectivity. According
to their report, ABS / PEG20000 membrane compared to similar membranes in CO2 separation. They
attributed the high selectivity of the membrane to the high solubility of carbon dioxide molecules and
strong interactions with polar groups of PEG 20000.
Jindaratsamee et al. [37] studied the effects of temperature and types of ions on CO2 permeability and
the separation factor of CO2 / N2 through ionic liquid membranes. As the temperature for all types of
ionic liquids got an increase, CO2 permeability was grown, too. According to experimental data, the
maximum and minimum permeability values were obtained with TF2N and PF6 membranes,
respectively. However, the separation factor of CO2 / N2 declined unlike CO2 permeability. TF2N
membrane with the highest permeability had the lowest selectivity.
Zhao et al. [38] studied CO2 and N2 gas separation properties for both pure and mixed gas states by
polyaniline (PANI) nanoparticles within the polyvinyl amine network (PAVm) and alloy membrane

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of PSF / PVAm. Their results clearly presented better CO2 permeability and higher CO2 / N2
selectivity for PSI / PVA-PANI in membranes compared to PSF / PVAm membrane. The interaction
between CO2 and PANI nanoparticles increased the CO2 / N2 selectivity. The increased amorphous
areas and the free volume at the intersection adjacent to PVAm and PANI raised the CO2 / N2
permeability and selectivity due to PVAm polymer chain disruptions at presence of PANI
nanoparticles. This specified a significant enhancing in CO2 permeability of GPU1200 and CO2 per
N2 selectivity of 120 so that 852% and 137% got increased in CO2 and CO2 / N2 were obtained in
comparison to PDF / PVAm membranes, respectively.
In another study, Dai et al [39] examined the effects of adding ZIF-8 on polyetherimide hollow fiber
membranes in CO2/N2 separation. For both types of hollow fibers (pure polymer and hollow fibers of
composite network), gas permeability was reduced as the temperature that dwindled although an ideal
selectivity showed an increase. For the mixture of gases with hollow fibers of composite network, the
permeability and selectivity values were obtained as the functions of feed pressure and temperature so
that CO2 / N2 selectivity got up to 32 and it scored 20% increase in selectivity in comparison to pure
polymer hollow fiber.
Recently, Ahmad et al. [40] assessed CO2 / N2 separation using carbon nanotubes (MWCNTs)
cellulose acetate polymer network. Membranes made as pure membrane and composite membranes
with carbon nanotubes of P and F (P- MWCNTs, F -MWCNTs) types were tested by adding 0.05, 0.1,
and 0.2% by weight of the particles. Through increasing pressure from 1 to 3 Kpa for pure membrane
and 0.1 P, the permeability of CO2 and N2 and CO2 / N2 selectivity was almost constant, but with the
adding of MWCNTs-F up to 0.1% wt, N2 permeability was unchanged. Increasing the permeability of
CO2 directs into increasing CO2 / N2 selectivity. Moreover, membrane performance improved and
CO2 permeability and CO2 / N2 selectivity increased by adding 0.05 and 0.1% wt of MWCNTs-F at the
pressure of 3 Kpa , In contrast, the amounts of permeability and selectivity decreased sharply by
adding 0.2% wt. According to their collected data, 0.1% wt was the best sample in order to accelerate
the selectivity by 40. They considered this behavior as the result of increasing the ability of
MWCNTs-F particles within polymer chains. Consequently, this issue related to an increase in the
space between the layers of the membrane and permeability.

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Regarding the remarkable developments within the past few years, industrial application as well as
gas separation processes with membranes have tendency towards the use of high permeable glass
polymeric materials with high free volume. Among these polymers, poly (1-trimethylsilyl-1-propyne)
has the highest rate of permeability. Remarkably, the permeability behavior of Poly (4-methyl-1-
pentene) is similar to poly (1-trimethylsilyl-1-propyne), but it has better chemical resistance than poly
(1-trimethylsilyl-1-propyne) [41].
Yu et al. [42] studied the use of highly permeable glass polymers. They used 5 species of
polyphenylene oxide glass-polymer (PPO) and silica nanoparticles to investigate CO2 / N2 separation
properties. In the meantime, BSPPOdp 9010/Silica with 9 and 23% by weight of nano particles has the
best performance among the constructed membranes. This membrane has high permeability over 130,
317 Bar, and selectivity of 36.1 and 35.2 at room temperature and pressure of 0.71 bar, respectively.
They described solubility of gases prevailing penetration and controlling permeability rate.
He et al. [43] investigated MMMs comprised of PMP and silica metal nano particles in n-C4H10/CH4
separation. Their experimental results presented that PMP membrane exposes different gas separation
performance compared to silica/PMP MMMs. The enhancing in the dispersed nano particles weight
percentage in the polymer network resulted in selectivity increasing of n-C4H10/CH4. The ideal
selectivity of resultant MMM from PMP filled with 45 wt% of nano particles increased by two- to
three-fold compared to the virgin PMP membrane and reached 26. In addition, the n-C4H10
permeability increased by two- to three-fold compared to the virgin PMP.
Therefore, this study attempted to make it possible to achieve permeability values from poly (4-
methyl-1-pentene) with desirable properties such as high free volume, good thermal stability, high
initial decomposition temperature, and low density with the addition of aluminum oxide nanoparticles
in the polymer network. Totally, this study aimed at better gas permeability by making nanocomposite
membranes of high free volume by mineral additives for polymeric structure. Accordingly, PMP was
used as membrane matrix (the dominant phase) and alumina nanoparticles were practiced as additives.
Better structure of membranes made by differential scanning calorimetry (DSC) and scanning electron
microscopy (SEM) were studied. The permeability of CO2 and N2 pure gases and the selectivity with

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pure and nanocomposite membranes were measured in constant pressure system. Finally, the
performance of membranes made and membranes with Robeson's upper limit were compared.
2. Materials and methods
2.1. Materials
Poly (PMP) (4methyl-1-pentene) with low molecular weight (Sigma-Aldrich) was used as polymer
matrix membranes. Carbon tetrachloride (CCl4) (purity of 99.8%, Merck) was also used as organic
solvent polymer in casting process of solution. The nanoparticle of alumina (Al2O3) was purchased
from US Research Company as additives in polymer matrix. Alumina nano particles have size smaller
than 100 nm.
2.2. Preparation of Precursors Membranes
Polymeric precursors were fabricated using PMP polymer due to the following technique. Initially, a
certain amount of PMP powders was located in a vacuum oven at 60 °C for 6h to remove any
moisture. In the next step, the powders were gradually dispersed and dissolved in hot CCl4 at 3wt%
for a few hours while mixing using a magnetic stirrer.
2.3. Preparation of Mixes Matrix Membranes
At first, Al2O3 nanoparticles were dispersed in solvent under stirring for 8 h to prepare the mixed
matrix membranes. Next, a suspension comprised of a specific amount of alumina and solvent was
sonicated for 15 min to obtain a uniform distribution in the solvent. Then, PMP powders were
gradually added and mixing was continued and stirred for another day to allow for completing
homogenization of the blended components. The resultant solution was passed through a 0.2µm filter
to eliminate possible dust particles and undissolved materials. After degassing, the polymer solutions
were cast on a flat Teflon plate to evaporate the solvent of the cast film using a film applicator. The
wet films were located inside a vacuum oven (20 mmHg) to slow evaporation of CCl4 and prevent any
defect during the membrane formation process. The temperature protocol for the oven was set
according to the following steps: 24hr at 55 °C and 6 hr at 60 °C to allow slow evaporation of the
solvent.

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2.4. Characterization Methods
2.4.1. SEM morphology
Scanning electron microscopy (KYKY-EM3200) was applied In order to study the distribution of
nanoparticles in the polymer matrix and distribution of nanoparticles. For this purpose, the
membranes first immersed in liquid nitrogen and then were broken from cross-sectional area. Due to
images of greater clarity, membranes were coated with a thin layer of gold.
2.4.2. Thermal properties
The Glass transition temperature (Tg) and the degree of crystallinity were appraised using differential
scanning calorimetry analysis (DSC). It was possible to access to this material using Perkin Elmer
Pyris 1 with heat rate of 5°C/min temperature range from 0 to 100 ° C.
2.5. Calculation of gas permeability
The permeability of pure gas for developed membranes was evaluated for N2 and CO2 at 25 °
C. The
gas permeability was calculated using the following equation:
10
0
273.15 10
( )
760 (( 76) /14.7)
vl dp
P
AT p dt



(1)
Where P is the gas permeability in Barrer (1 Barrer = 1×10−10
cm3
(STP) cm/cm2
sec cmHg), A refers
to effective area of the membrane (cm2
), T is the operating temperature (K), v is the volume of the
down-stream chamber (cm3
), l is the membrane thickness (cm). Fig. 2 illustrates a schematic diagram
and lab-scale of experimental setup for selectivity and permeability measurement. The amount of
permeability of pure gas feed with various feed pressure and temperature were determined by
applying of Gas Chromatography (GC) and other facilities. The ideal selectivity was determined by
dividing the permeability of gases as equation (2).
2
2
2/2
N
CO
NCO
P
P
 (2)

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In this equation, PCO2 and PN2 are permeability of CO2 and N2 gases, respectively.
3. Results and Discussion
3.1. Morphology and Characterization results
Figures 3 and 4 illustrate top views and cross section images of pure and mixed matrix network
membranes. The images show the distribution of alumina nanoparticles as mineral additives into the
polymer matrix membranes. Figure 4.a~f displays cross section images of pure membrane to be
5~30% by weight of alumina nanoparticles. According to figure 4, the smooth cross section of pure
membrane lost its integration due to the addition of alumina nanoparticles to the polymer matrix.
Figure 3 shows that all of these membranes are quite dense. Moreover, the images taken feature out a
uniform structure with a good distribution of alumina nanoparticles in the polymer network. On the
other hand, little accumulation of nanoparticles in high weight percentages is observed as the result of
increasing the percentage of pure alumina nanoparticles in the pure polymer matrix membrane. In
contrast, non-specific pores are seen in these images. Furthermore, better distribution has been
conducted in low weight percentages and especially in 10 and 15% by weight of nanoparticles,
Holistically, the images reveal appropriate adaptations of polymer and alumina nanoparticles so that
the interface between the polymer / particle is virtually devoid of non-selective pores leading to better
selectivity in 5, 10 and 15 wt% alumina. High permeability and good selectivity of membranes
confirm this regard. Fig. 5 shows the TGA results for a pure and mixed matrix membranes composed
of PMP- nano particle using the constant temperature increment rate (10 °C/min). According to TGA
graph, pure PMP demonstrated an appropriate thermal stability. This figure represents that pure PMP
illustrated the thermal degradation temperature of 320 C, which is related to the polymer degradation.
For MMMs, the Td increased significantly to 400 °C. The enhancement of degradation temperature in
these membranes prompted by presence of nanoparticles can be attributed to the high thermal stability
of nano-particles.
3.2. Study of membrane performance and gas separation

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Permeability properties of pure carbon dioxide and nitrogen in the pure polymeric membrane and
mixed matrix network were measured and evaluated by designed separation system. Table 1 presents
the physical properties of CO2 and N2. Data for membrane permeability and selectivity for membranes
made through increasing nanoparticle composition and feed pressure variations was calculated based
on constant temperature of 25°C and different pressures of 2, 4, 6, 8 and 10 bar.
3.2.1. The effect of alumina nanoparticles on the permeability of membranes
For all mixed matrix membranes made in different pressures of the input feed, the permeability of
carbon dioxide and nitrogen gas was measured. Table 2 carries out the results of permeability and
ideal selectivity in the pressure of 4 bar and the temperature of 25°C. The results specify that CO2
permeability scores greater amounts in all membranes in comparison to nitrogen. For adding
nanoparticles, higher growth rate has been remarked. Comparing to nitrogen, large amounts of CO2
permeability could be related to smaller kinetic of CO2, high condensability, polarity, and having
higher interactions of this polar gas with polar groups in polymer matrix.
According to data reported in Table 2, the increase in the permeability of each gas has enhanced the
weight percentage of nanoparticles in the polymer matrix. The CO2 permeability increased intensify.
In addition to permeability, increasing of the nanoparticles percentage in a polymer matrix improved
CO2 / N2 selectivity. For example, the amounts of permeability for CO2 in the pressure of 4 bar for
pure membrane and mixed matrix network containing 30% by weight of nanoparticles are 129.14 and
329.62 bar, respectively (a growth rate of 252%). However, increase in permeability for N2 is much
less and increased from 5.46 Bar to 8.73 bar (growth rate of 160%). Finally, CO2 / N2 selectivity
increased from 23.56 to 37.3.
Due to interactions between nanoparticles and the polymer network at the intersection as well as the
presence of alumina nanoparticles within the polymer chain segments, voids at the intersection of
polymer / particle have increased following an increase in the permeability of gases. The presence of
nanoparticles in the polymer matrix moves up the free volume of the resulting membrane which
subsequently increases the gas permeability values. This increase in free volume can be attributed to
polymer chain rupture due to exposure to alumina nanoparticles among polymer chains within the

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polymer matrix. Regarding Table 1, CO2 has smaller molecular size than other passing gases. Thus, it
has higher permeation in comparison to N2. Consequently, high CO2 polarity causes interaction with
polar groups of the polymer chain and it is directed to higher solvability and solubility of CO2 than
N2. Therefore, the penetration of CO2 is facilitated through increasing wt% of nanoparticles of
alumina and CO2 has greater permeability comparing to N2.
Regarding the increase in gas selectivity, it can be stated the increase of nanoparticles accelerates free
volume in the polymer network. Eventually, it causes more condensable penetrating gas leakage.
Since the condensability of CO2 is very high and N2 scores are low solubility, the selectivity of
CO2/N2 is enhanced. The enhancement of nano scale particles percentage provide more
particle/polymer interfacial area and increase filler–polymer interface contact. The nano particles may
be act as a pores and capillaries modifier or even as a thin selective layer during the preparation of
MMMs.
3.2.2. Feed pressure effect on the properties of nanocomposite membrane separation
Figure 6 turns out the effect of feed pressure from 2 to 10 bar on permeability of each gas within PMP
polymer membrane and mixed matrix membranes containing 10, 20 and 30% by weight of alumina
nanoparticles. Rising feed pressure improves the permeability of gases followed by an increase in
ideal CO2/N2 selectivity. According to Figure 6, in the pressure of 2 bar, the gas permeability in 30
wt% nanoparticles was 166.5 Bar and 6.19 Bar, respectively. These values have been increased in the
same mixed matrix membrane and in the pressure of 10 bar up to 532 Bar and 10.18 Bar. Therefore,
the permeability of gases is much affected by feed pressure passing through the membrane. It is also
possible that CO2 in comparison with N2 has higher permeability and pressure has much more
influential on CO2 passing.
As shown in figure 6, the increased feed pressure accelerates the permeability of both gases passing
through the membrane. This increase was high for pressure changes of 2 to 8 bar, but the intensity of
the permeability growth had been slightly reduced in the pressure of 10 bar. The highest increase in
permeability had been observed at pressure of 2 to 4 bar. It can be concluded that membrane-softening

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phenomenon (even with low intensity) has occurred. According to data from Figure 7, N2
permeability had no significant change by increasing pressure. In contrast, CO2 scored a significant
increase, substantially increasing CO2/N2 ideal selectivity.
The effect of pressure on the permeability of gases can be justified based on dissolution-penetration
mechanism. As shown in equation (3), the permeability of each gas is equal to penetration rate
multiplied by solubility rate:
exp i
i
FV
D
V


 
  
 
(2)
Where D represents the diffusion coefficient and the kinetic phenomenon of transmission and has
transmission rate, whereas S is a thermodynamic parameter reflecting solubility of adsorbed gas. As
mentioned above, the increase in the input feed pressure increases the permeability of gases. This
means that the pressure was under the influenced of diffusion co-efficiency, solubility or both of
them. Based on non-polar N2 gas (Table 1), it has greater kinetic size and lower condensability in
comparison to CO2. In addition, N2 with linear, compacts the chemical structure and without polar
torque had little interaction with the polymer network and lower solubility. According to above, the
free volume of the polymer and low permeability values obtained for N2. It can be concluded that
pressure changes only affected on the diffusion co-efficiency of N2. The effect was small and N2
permeability increased slightly.
In addition to penetration, other factors affect CO2 transmittance. Data obtained from tests
demonstrate a substantial increase in CO2 permeability. Increased feed pressure is followed by an
increase in CO2 penetration and gas permeability is grown as well. Carbon dioxide has better
penetration than nitrogen owing to smaller kinetic size and further increasing effect on gas diffusion
co-efficiency for the pressure changes. It determines high levels of permeability. It should be
considered in polymers with high free volume (here, poly (4-methyl-1-pentene) membrane),
penetration is involved not only in the mechanism for gas leakage but also in the condensability and
solubility. Therefore, CO2 with high polarity and high condensability can have many interactions with
polar groups of polymer and greater permeability in membrane. In addition, membrane-softening

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phenomenon occurred (even with low intensity) and concentration of CO2 increased in the polymer
network by increasing the inlet gas pressure. Increased concentrations can be led to increase the
solubility of gas in the polymer network and more on permeability. The effects of CO2 softening on
polymer matrix had changed by increasing the input feed pressure. Consequently, this caused more
solubility resulting in high permeability of CO2 compared with N2.
Figure 8 shows ideal selectivity of CO2/N2 for polymeric membranes (pure and mixed matrix) in
weight percentages of 10, 20, and 30 of alumina nanoparticles. According to the Figure 8, the all
membranes selectivity values improved by the pressure increase. The increase in selectivity occurred
in pressure up to 8 bar. A slight decrease had been observed in the amounts in order to change
pressure from 8 bar to 10 bar. It should be remarked that both the increase in pressure and gas
diffusion co-efficiency could have opposite effect. Extremely high pressures are directed into
lowering permeability in the membrane and diffusion co-efficiency of gases is also reduced. This
means that dense polymer chain caused a slight decline in gas permeability by increasing the pressure.
For this reason, the permeability had a slight increase at high-pressures such as 10 bar in comparison
to 8 bar. Compared to N2, the permeability for CO2 with smaller kinetic size reflected higher
transmittance and the permeability decreases. It is followed by a decline in CO2/N2 selectivity at the
pressure of 10 bar.
CO2/N2 increased selectivity can be considered due to high condensability of CO2 and it has more
interactions with polymer chain compared to N2. In addition, condensable gas permeability increases
more than non-condensable gas through increasing the alumina nanoparticles in a polymer matrix and
an increase in the free volume. In fact, improved diffusion co-efficiency with increased feed pressure
could be added, all of which increased selectivity. Accordingly, dissolution selectivity plays more
effective role in comparison to penetration in increasing CO2/N2 selectivity.
The increasing of nano particles content significantly increases the CO2 and N2 permeability. This
properties result from an enhancement in free volume because of the presence of extra void volume at
the interface between nano particles and polymer as well as the inefficient network chain packing.
Moreover, the large gases permeability (N2) is more improved by the increasing of nano particles
resulting from the enhancement in free volume, which strongly rises the permeability and coefficient

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of diffusion, and consequences in a reduction in gas pair selectivity. Consequently, the incorporation
of Al2O3 nano particles did not result in an overall improvement in gas transport properties of
permeability versus performance of selectivity in relation to the upper bound. However, it is notable
that impermeable and rigid nano sized Al2O3 can be disrupted polymer chain network packing.
Therefore, as shown in the Figs 6-8, the higher loading of the Al2O3 in PMP matrix (up to 30 wt.%) at
low feed pressures cannot be useful. This is only slightly can be effective with respect to molecular
sieving properties at higher pressures. Furthermore, it was detected that dispersion of Al2O3
nanoparticles at higher loading (more than 40 wt.%) leads to aggregate formation on the surface of the
membrane.
3.3. Membrane performance
Due to advances in separation industry as well as the use of polymeric membranes for gas separation
processes, the use of these membranes still faces limitations because of the interfering relationship
between permeability and selectivity of membranes measured by Robeson's upper limit (Figure 9).
This figure verifies that embedded nano particle in PMP and higher pressure improves the CO2/N2
selectivity. The high free volume of PMP and higher pressure are the main factors affecting the
performance of MMMs derived from PMP to overcome the Robeson upper bound. In general, MMMs
with high selectivity and permeability are certainly more remarkable for industrial application.
Table 3 indicates the permeability behavior of several mixed matrix membranes and PMP30
membrane. As summarized in this table, the MMMs have been generally produced by incorporating
potential fillers such as Metal oxide nano particles, Zeolite, CNT, silica, CMS and MOF in the
polymer matrix. From data, it could be found that the performance of MMM depends appreciably on
the filler and polymer matrix as well as the interaction of inorganic and organic phases. The
employing of zeolite in the mixed matrix membrane preparation has received ample interests due to
their gas transport properties and separation performance. Inorganic zeolites dispersed in the organic
polymer network improve the separation performance of the polymeric membranes. This perception
mixes the benefits of both inorganic and organic materials: economical process ability and mechanical
reliability of the polymeric materials with high gas separation performance of zeolite molecular sieve.

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Also, in comparison of molecular sieving fillers, the nanoparticles such as MgO, SiO2 and Al2O3 with
high specific area award proper distribution of metal oxide nano particles in polymeric matrix. This
contribution of particles in the mixed matrix would consequence in increasing of gas permeability and
selectivity. On the other hand, these can be moderated the overall diffusivity selectivity due to the
incapability of the improved structure through higher porosity of nano particles to selectively classify
and distinct the molecules with unlike size. Data from this table can be confirmed that the MMM
made of PMP and Al2O3 has acceptable permeability value. Besides, it have high gas pair selectivity
which is several times more than the selectivity of common polymeric membrane. Also, as implied
from the results, the gas permeability of poly PMP30 was considerable than other gas separating
mixed matrix membranes. This relates to outstanding properties of poly (4-methyl-1-pentene) with
high free volume, low density, and appropriate thermal stability in high thermal operations as well as
the good specification of Al2O3 as dispersed phase. The results of this research (high permeability and
high selectivity) could be counted as an ideal choice for industrial applications of separating
greenhouse gases and waste gases of chimneys.
4. Conclusion
Advanced mixed matrix membranes were developed from the blend of PMP and alumina nano
particles. The effect of different Al2O3 nano particles content was investigated on the performance of
these membranes for CO2/N2 separation applications. The percentage of nano particles was important
to control the CO2 and N2 permeability and gas pair selectivity of the precursors and also derived
mixed matrix membranes filled with alumina nanoparticles. Results of thermo-gravimetric analysis
illustrated that thermal stability of MMMs gets the increases for the sake of high thermal stability of
Al2O3 in comparison to pure PMP. Furthermore, SEM images verified a uniform dispersion of Al2O3
nano particles in the precursor matrix network without considerable agglomeration.
Mixed matrix membranes derived from PMP with 30%wt alumina nano particles (PMP30) exhibited
more remarkable CO2/N2 separation performance than other mixed matrix membranes. It should be
considered that a higher percentage of nano particles can raise permeability and selectivity for CO2/N2
separation. If the operating pressure is changed from 2 to 8 bar, the ideal CO2/N2 selectivity increases

15
approximately 2 times accompanied by an enhancement in the permeability. High CO2/N2 ideal
selectivity of 120 is obtained in a membrane prepared by PMP30 at 8 bar, whose value is the highest
among all the resultant mixed matrix membranes. The MMMs developed in this research can be
applied as a CO2/N2 separation appropriate membranes with effective performance for various
applications.
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Carbon
Dioxide (fossil
fuel use)
57%
Carbon Dioxide
(deforestation,
decay of
biomass, etc.)
17%
Methane
14%
Nitrous
Oxide
8%
Carbon
Dioxide
(other)
3%
Fluorinated
gases
1%
Energy supply
26%
Industry
19%
Forestry
17%
Agriculture
14%
Transport
13%
Residential &
Commercial
buildings
8%
Waste &
Wastewater
3%
Fig 1. (a) human activities factors and their contribution in the production of greenhouse gases (b) rate of
greenhouse gas emissions due to human activities [7,8]
(a) (b)
Figures Click here to download line figure Figures-R.pptx

Fig 2. Designed and created setup for gas separation properties: a) Schematic diagram b) lab-scale
(a) (b)

Fig 3. SEM images of top view of (a) Pure PMP, and MMMs of (b) PMP-Al2O3 (5%),
(c) PMP-Al2O3 (10%) (d) PMP-Al2O3 (15%) (e) PMP-Al2O3 (20%) (f) PMP-Al2O3 (30%)
(a) (b) (c)
(d) (e) (f)

Fig 4. SEM images of cross-sectional view of (a) Pure PMP, and MMMs of (b) PMP-Al2O3 (5%),
(c) PMP-Al2O3 (10%) (d) PMP-Al2O3 (15%) (e) PMP-Al2O3 (20%) (f) PMP-Al2O3 (30%)
(a) (b) (c)
(d) (e) (f)

Fig 5. The results of the TGA carried out on membranes applying constant temperature protocols (10
oC/min). Weight Loss [%] versus Temperature
WeightLoss[%]
Temperature [°C]

Fig. 6. Performance of MMMs with various compositions for CO2 permeability at different
operating pressure
0
100
200
300
400
500
600
1 2 3 4 5 6 7 8 9 10 11
PermeabilityOfCO2(barrer)
Pressure (bar)
PMP
PMP10
PMP20
PMP30
PMP40

Fig. 7. Performance of MMMs with various compositions for N2 permeability at different
operating pressure
0
100
200
300
400
500
600
1 3 5 7 9 11
PermeabilityOfN2(barrer)
Pressure (bar)
PMP
PMP10
PMP20
PMP30
PMP40

Fig. 8. Ideal gas pair selectivity of MMMs with various compositions for CO2/N2 at different
operating pressure
1.5
21.5
41.5
61.5
81.5
101.5
121.5
141.5
1 3 5 7 9 11
Selectivity(CO2/N2)
Pressure (bar)
PMP
PMP10
PMP20
PMP30
PMP40

1
10
100
1000
0.0001 0.01 1 100 10000
Revised Upper Bound (Robeson 2009)
PMP (Pure)
PMP-Al2O3 (5%),
PMP-Al2O3 (10%),
PMP-Al2O3 (15%),
PMP-Al2O3 (20%),
PMP-Al2O3 (30%),
CO2/N2idealselectivity
CO2 Permeability (Barrers)
Fig. 9. Performance of mixed matrix membranes prepared for CO2/N2 separation with respect
to revised Robeson trade-off line.

Table 1. Physical properties of CO2
and N2
CO2
N2
Molecular weight 44.01 28.01
Kinetic diameter, A 3.3 3.64
Specific volume at 70 °F, 1 atm, ml/g 547 861.5
Sublimation point at 1 atm, °C -78.5 -195.8
Triple point pressure, atm 5.11 0.121
Triple point temperature, °C -56.6 -210
Density, gas at 0 °C, 1 atm, g/l 1.977 1.25
Specific gravity, gas at 0 °C, 1 atm (Air = 1) 1.521
Critical temperature, °C 31 -147.1
Critical pressure, atm 72.9 33.5
Critical density, g/ml 0.468 0.311
Viscosity, gas at 70 °F, 1 atm, cp 0.0148 0.017
Solubility in water at 25 °C, 1 atm, ml/l water 759 23
Tables Click here to download table Tables.doc

Table 2. Permeability and ideal gas selectivity of the pure
PMP and MMM for various compositions at operating
pressure of 4 bar and 25
°
C.
Permeability
(Barrer)
Selectivity
run
Percentage of Al2O3
(wt. %)
PCO2 PN2 α CO2/N2
1
PMP-Al2O3
0 129.1 3.40 38.18
2 5 151.1 2.65 57.25
3 10 185.8 2.71 68.58
4 15 237.9 2.92 81.47
5 20 280.7 3.12 89.96
6 30 325.6 3.54 92.12

Table 3. Separation performance of PMP30 membrane in comparison of other investigated
MMMs
Conventional
fillers
Typeof
polymer
Typeoffiller
Percentageof
filler(wt.%)
Operating
Temperature
(°C)
Operating
Pressure(bar)
Permeability
(Barrer)
αCO2/N2
Ref.
PCO2 PN2
Metaloxide
nano
particles
Matrimid MgO 20 35 10 11.64 0.52 22.4 [45]
BSPPOdp 8020 SiO2 9 25 7.1 48 1.2 40 [46]
PMP Al2O3 30 25 8 527.8 9.26 57.0 This
work
Zeolite
6FDA-durene ZIF-8 33.3 35 3.5 1553 140 11.1 [47]
PDMC SSZ-13 20 35 4.5 88.6 2.11 41.9 [48]
poly(RTIL) and RTIL SAPO 10 35 4 70 2.30 30.4 [25]
Carbon
nanotubes
polyethersulfone MWCNTs 10 25 2 3.5 0.18 19.4 [49]
Pebax-1657 CNTs 5 21 2.4 102 1.4 72.9 [50]
poly(ether sulfone) CNTs 10 25 2 3.4 0.15 22.7 [51]
Silica
poly(amide-6-b-
ethylene oxide)
silica 10 21 2.2 205 2.85 72 [52]

Graphical abstract Click here to download attachment to manuscript Graphical abstract.pptx

Mixed matrix membranes comprising PMP polymer with dispersed alumina nanoparticles fillers to Separate CO2/ N2

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