(SILMs) for CO2 Separation

Please Cite as: Alkhouzaam, A., Khraisheh, M., Atilhan, M., Al-Muhtaseb, S. A., & Zaidi, S. J. (2016). Membranes for CO2 Separation. Nanostructured Polymer Membranes, Volume 1: Processing and Characterization, 1, 237.

Chapter 7 Membranes for CO2 Separation Abedalkhader Alkhouzaam1, Majeda Khraisheh1, Mert Atilhan1, Shaheen A. AlMuhtaseb1 and Syed Javaid Zaidi2* 1 Chemical Engineering Department, Qatar University, Qatar 2 Center for Advanced Materials, Qatar University, Qatar * Corresponding author: [email protected]

Copyright © 2016. John Wiley & Sons, Incorporated. All rights reserved.

Abstract Membranes are becoming popular for CO2 separation as an environmentally friendly, efficient technology. A comprehensive review of recent studies conducted on CO2 separation from different sources is essential for tracking the progress of membrane development. This chapter reviews the recent studies conducted concerning CO2 permeation properties, breakthroughs and challenges in developing efficient CO2 separation membranes. Three main membrane categories have been reviewed in this chapter: polymeric membranes, mixed matrix membranes (MMMs), and supported ionic liquid membranes (SILMs). Studies conducted on polymeric materials and polymer blending resulted in some efficient CO2 separation membranes such as Matrimid-, 6FDA-, and Pebax-based blend membranes. Some of the MMMs that have been widely investigated have shown promising CO2 separation efficiency. For example, the combination of poly(ionic liquid)s, ionic liquids, and zeolite particles resulted in highly efficient CO2/CH4 separation. Additionally, MMMs containing Pebax and zeolites showed high CO2/N2 separation. Several SILMs were investigated using different ionic liquids. Some of these SILMs achieved high CO2 permeability; however, only a few SILMs have achieved simultaneous high permeability and selectivity, including [bmim][BF4]-, Ammoeng™ 100-, [emim][BF4]-, and [emim][CF3SO3]-based SILMs. The main constraint of the reported membranes is the trade-off relationship between the permeability and selectivity, and both cannot be achieved simultaneously. Keywords: CO2 separation membranes, mixed matrix membranes, polymeric membranes, polymer blends, supported ionic liquid membranes, permeability, selectivity

7.1 Introduction The separation of carbon dioxide (CO2) from various emission sources, such as flue gas from power plants and chemical industries, has been getting more attention due to environmental concerns as result of global warming. It has been predicted that by the year 2100 the CO2 composition may increase up to 570 ppmv in the atmosphere. This increase may cause a rise in

P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.


global temperature of about 1.9 °C and a rise in sea level of 38 m [1]. Numerous methods have been used for the separation of CO2. These methods include adsorption with porous solids (e.g., activated carbon and zeolites), amine absorption cryogenic separation and membranebased separations [2, 3]. The most widely used technology for CO2 separation at industrial scale is amine-based absorption, due to the high capture level of CO2 (up to 90%) [4]. Adsorption technology is also being used for CO2 separation using different types of adsorbents. However, its use in industrial applications is very limited due to the low adsorption capacity. Cryogenic CO2 separation has also been used for CO2 separation from N2 streams. In this process, CO2 is condensed and collected in a multistage process while N2 remains in the gas phase and is released through the top of the chamber [3]. Recently membrane-based processes have also been used for CO2 separation. Their low energy consumption and environmentally friendly nature were the main reasons for the focus of a large number of research studies on membrane technology [5]. Conversely, their low selectivity was the main drawback which requires more development if such technology is to be used in largescale industrial applications [6]. Recently, interest in using ionic liquids (ILs) as an alternative medium for CO2 capture has become the focus of several studies due to their potential advantages compared to other conventional solvents (e.g., monoethanolamine (MEA)) [7]. Their unique properties have made these liquids a promising technology that may overcome several problems associated with the conventional technologies of CO2 separation such as energy consumption [8]. Membranes (which generally consist of a semipermeable, thin, polymeric film) allow selective and specific permeation of some molecules while retaining others [9, 10]. Permeability and selectivity are the two main criteria that must be achieved in a good membrane [5]. A membrane unit is usually small in volume and does not occupy a large area. This technology is less energy intensive, operationally simple and therefore provides low maintenance operation [6, 11]. However, the low flux and separation selectivity of the existing commercial polymeric membranes for some gases limits the possibility to use them in large-scale applications. Hence, a large number of studies have been conducted to develop highly efficient gas separation membranes. The main aim of these studies has been to significantly improve CO2 permeation through the membrane and to maximize the CO2 separation selectivity from other gases (e.g., N2, CH4, H2, etc.). The focus of this chapter is on three categories of membranes for CO2 separation: polymeric membranes, mixed matrix membranes (MMMs), and supported ionic liquid membranes (SILMs). Polymeric membranes have been the interest of several studies due to their ease of manufacture and commercial availability. Mixed matrix membranes, which consist of inorganic material incorporated within the polymeric matrix, have been investigated in several CO2 separation studies using different fillers, supports and fabrication conditions, etc. In MMMs, gas molecules transport through the polymer matrix and the inorganic phase (filler) that act as molecular sieve that increase the separation. Supported ionic liquid membranes (SILMs) is one of the promising techniques that combines the advantages of both membranes and Ils, hence it has become a topic of interest in many recent


studies. In this technology, only a very small amount of ionic liquids need to be immobilized onto a membrane. Therefore, the operating cost using this technology in large-scale CO2 separation will be greatly reduced. This chapter gives a comprehensive assessment of the latest CO2 separation technologies developed in the literature for the three categories mentioned above.

7.2 Fundamentals of Membrane Gas Separation Membranes have been used in several gas separation applications; following are some of these applications [12]: Natural gas treatment (CO2 separation from natural gas streams) Recovery of hydrogen Air separation (such as oxygen enrichment for some medical devices)


Nitrogen enrichment from air that is used as atmosphere protecting process for oxygensensitive compounds. The most commonly used membrane materials for CO2 separation are polymers, which can be processed into high surface area hollow fiber membrane [13]. Inorganic porous membranes are widely used for operation inside combustion chambers due to their ability to withstand high temperatures [14]. The overall use of membranes in CO2 removal applications is more economical due to having a small footprint, good mechanical stability and a larger contact area per unit volume [13]. Membrane systems give reductions of over 70% in size and about 66% in weight compared to conventional separation columns [15]. The highpurity CO2 separation may require numerous membranes with different characteristics, due to their limited ability to achieve high degrees of gas separation [16]. This then increases the complexity, energy consumption and most of all total cost of the operation [9]. Therefore, further improvement is needed before using membranes at a large scale for CO2 capture [17]. Functionalized membranes may contribute to the separation by retaining some components more than others in the diffusion stage (Figure 7.1).


Figure 7.1 Gas separation through pure polymeric and functionalized membranes.

7.2.1 Membrane Gas Permeation Mechanisms


Membrane is the permselective barrier between two phases [18, 19]; hence, the material of the membrane itself is the most essential element of the gas separation process. Three main mechanisms govern the gas permeation through polymeric membranes: molecular sieving, Knudsen diffusion, and solution-diffusion (Figure 7.2).

Figure 7.2 Membrane gas permeation mechanisms through porous and nonporous membranes. In dense membranes, the solution-diffusion mechanism controls the gas permeation through the membrane matrix [20]. Therefore, separation is not only dependent upon molecular size, but also on the chemical interaction between the gas molecules and the membrane during the


diffusion stage. Gas molecules are adsorbed by the membrane surface at the feed side; these molecules then diffuse inside the membrane, and finally desorbed from the membrane to the other side (permeate). In the porous membrane, two other mechanisms control the gas permeation through the membranes: Knudsen diffusion and molecular sieving. In such mechanisms, gas permeation is significantly dependent on the morphology of the membrane (i.e., pore size) as well as the molecular sizes of the permeating gases [21]. In Knudsen diffusion, the separation depends mainly on the mean free path of gas molecules and the pore size. The lower the ratio of mean free path to the pore size (λ/r) the more collisions with the pore wall that result in high separation. Finally, in molecular-sieving membranes, the size of the pore allows small molecules to pass through to the permeate side while preventing larger molecules from passing. Hence, to prepare an efficient molecular sieving membrane, pore size should be adjusted between the sizes of the small and large molecules. Gas separation membranes use the differences in partial pressure as their driving force for separation [22]. One component dissolves into the membrane, diffusing through the membrane before passing to the other side in the final stage [23]. The permeability calculation is carried out starting with the mole balance around the membrane. Then flux and permeability can be calculated using Equations 7.1 and 7.2 respectively. (7.1)


(7.2)

where A is the cross-sectional area of the membrane (cm2), t is the time of the experiment (s), n is the molar volume at standard temperature and pressure (cm3 STP), l is the membrane thickness, and ΔPi is the partial pressure difference of each gas. The permeability Pi and the flux Ji are given in

respectively. The

permeability is usually given by the unit (barrer), where (1 Barrer = 10–10 cm3 (STP) cm cm–2 s–1 cmHg–1). Permeance (Pi/l) instead of permeability is usually used for asymmetric membranes and is given in unit of (GPU), where (1GPU = 10–6 cm3 (STP) cm–2 s–1 cmHg–1). The selectivity or the separation factor αA/B for binary gas separation is calculated using Equation 7.3.


(7.3)

where YA and YB are the mole fractions of the permeate, whereas XA and XB are their corresponding mole fractions in the feed [24]. The selectivity can also be expressed in terms of partial pressures of the two diffusing gases as given by [25–27]: (7.4)

7.2.2 Robeson’s Upper Bound An essential constraint in the development of a membrane for gas separation processes is the trade-off between selectivity and permeability. This trade-off was established by Robeson’s upper bound relationship, which was shown to be valid for several gas pairs including H2/N2, O2/N2, He/N2, CO2/CH4, CO2/N2, H2/CH4, He/H2, H2/CO2, He/CO2, and He/CH4. Robeson’s upper bound is expressed by Equation 7.4. (7.5)


where Pi is the permeability of the high permeable gas, a is the selectivity or the separation factor, k is called the “front factor,” and n is the slope of the log–log limit [28]. The front factor k and the slope values of Robeson’s upper bound relationship are tabulated in Table 7.1.


Table 7.1 Values of the front factor k and the slope n of Robeson’s upper bound correlation [28]. Gas pair k (barrers) n O2/N2 1,396,000 –5.666 CO2/CH4 5,369,140 –2.636 H2/N2

97,650

–1.4841

H2/CH4

27,200

–1.107

He/N2

19,890

–1.017

He/CH4

19,800

–0.809

He/H4

59,910

–4.864

CO2/N2

30,967,000 –2.888

N2/CH4

2,570

–4.507

H2/CO2

4,515

–2.302

He/CO2

3,760

–1.192

NA

NA

He/O2


Figures 7.3, 7.4, 7.5 and 7.6 are plots prepared by Robeson representing CO2/N2, CO2/CH4, H2/CO2 and He/CO2 separation correlations, respectively, of a large number of membranes reported in the literature [28]. The plots show the upper bound, which is a line that links the most permeable membranes at a particular selectivity, for these gas pairs.



Figure 7.3 Robeson’s upper bound correlation for CO2/N2 separation [28].

Figure 7.4 Robeson’s upper bound correlation for CO2/CH4 separation [28].



Figure 7.5 Robeson’s upper bound correlation for H2/CO2 separation [28].

Figure 7.6 Robeson’s upper bound correlation for He/CO2 separation [28]. In Figures 7.4, 7.5, and 7.6, two upper bounds are presented for CO2 separation. “Prior upper bound” refers to the upper bound that was demonstrated in 1991 by Robeson [29], which was then updated in 2008 with the latest results from the literature to the “present upper bound.”


However for CO2/N2, only one upper bound was presented in Figure 7.3 since there was no clear correlation [28]. Figure 7.4 also shows a group of polymers (TR [thermally rearranged]) that shows exceptional CO2/CH4 separation efficiency. However these polymers are unique and considered in the molecular sieving materials class, hence they were not included in the 2008 upper bound. Robeson’s upper bounds are being used in most membrane research studies to compare the separation efficiency of their work with the reported literature.

7.3 Polymeric Membranes for CO2 Separation


Most of the research studies in membrane gas separation have been carried out on nonporous (dense) polymeric membranes. These membranes play an important role in gas separation. Gas permeation through dense membranes is controlled mainly by the solution-diffusion mechanisms. They consist of dense film that allows gas molecules to diffuse through; hence, the separation efficiency is dependent on the diffusivity of gas molecules through the membrane material. Dense membranes are being used in various applications, including gas separation, reverse osmosis, and pervaporation [30]. Dense polymeric membranes are normally synthesized by dissolving the polymer in appropriate solvent, then casting the polymeric solution onto a flat surface, and finally evaporating the solvent (Figure 7.7).

Figure 7.7 Synthesis process of dense polymeric membranes. Nonporous membrane tends to be thicker than the selective layer of an asymmetric membrane. This results in considerably lower gas fluxes than alternative membrane structures. Different types of polymers have been used to develop dense polymeric membranes for CO2 separation from different gases, including polyimides, polysulfones, cellulose, polycarbonates, etc. Tables 7.2 and 7.3 list some of the commonly used polymers for membrane preparation for CO2 separation, their abbreviations, chemical structure and CO2 permeation properties.


Table 7.2 Chemical structure of some polymers used in CO2 membrane separation [25, 31]. Polymer

Abbreviation Structure

Poly(carbonate)

PC


Poly(phenylene oxide) PPO

Poly(ether sulfone)

PES

Polyetherimide

PEI

Poly(ethylene oxide)

PEO

Cellulose

–

Poly (dimethylsiloxane) PDMS


Table 7.3 CO2 permeation properties for some polymers. Polymer

PCO2 (barrer)

Ideal selectivity T (°C) Ref. CO2/N2 CO2/CH4 H2/CO2

17 6.3 4.3 76

79 30.0 23.9 19.9

25 30.0 33.1 6.9

9.9 0.4 – 1.5

Poly(methyl pentene) Poly(dimethyl siloxane) Ethyl cellulose Polyetherimide

84.6 2700 26.5 1.32

12.6 10.8 8.3 28.1

5.7 3.4 1.4 37.7

1.5 0.2 3.3 5.9

Poly(4-methyl-1-pentene)a

77.7

13

6

Poly (4-methyl-1-pentene)b Poly(urethane) Poly(4-methyl-1-pentyne) Poly(4-methyl-1-pentene)

93.8 22.98 10700 84.6

12.7 38.31 8.05 12.63

5.6 35.91 3.9 5.68

Poly(ethylene oxide) Cellulose acetate Polycarbonate (brominated) Poly(phenylene oxide)

35 30

[32] [31]

1.46

35

[33]

1.2 – – –

– – –

[34] [35]

aCasted using carbon tetrachloride bCasted using cyclopentane


Although hundreds of polymers have been studied for CO2 separation, only a few of them have found their way to be used in industry. The following describes the permeation properties of some commercial polymers used for CO2 separation.

7.3.1 Polyimides Polyamides are one of the most extensively investigated polymeric materials for membrane gas separation since they possess very high CO2 permeability, mainly those incorporating the group 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane (6FDA). The most commonly used method in polyimide synthesis is the reaction between a diamine with a dianhydride. Figure 7.8 shows examples of some commonly used dianhydrides in the synthesis of polyimides.


Figure 7.8 Commonly used dianhydrides in polyimide synthesis [25, 36].


Polyimides have become widely used membrane materials for gas and vapor separation due to their excellent thermal, chemical and mechanical stability in addition to their high gas separation. Tables 7.4 and 7.5 compare CO2 permeation and separation properties for several polyimide membranes used in the literature.


Table 7.4 Single gas CO2 permeation properties of some polyimides. Polymer

Gas pair PCO2(barrer) Ideal selectivity ΔP (bar) T (°C) Ref.

Matrimid® 5218 CO2/CH4

6.5

34

10

35

[37]

CO2/CH4

8.34

36.3

2

35

[38]

CO2/N2

6.5

25.6

10

35

[37]

6FDA-mPDA

CO2/CH4

14

70

2

35

[39]

CO2/N2

14

22.58

2

35

H2/CO2

14

3.29

2

35

He/CO2

14

4.21

2

35

6FDA-DAP

CO2/CH4

11

92

2

35

CO2/N2

11

29.73

2

35

H2/CO2

11

3.45

2

35

He/CO2

11

4.09

2

35

CO2/CH4

8

94

2

35

CO2/N2

8

28.57

2

35

H2/CO2

8

4.25

2

35

He/CO2

8

5.38

2

35

31

51

3

–

CO2/N2

31

26

3

–

He/CO2

31

2.8

3

–

CO2/CH4

14

41

3

–

CO2/N2

14

23

3

–

He/CO2

14

2.9

3

–

6FDA-ODA

CO2/CH4

18.6

53.1

10.3

35

[41]

6FDA-DAM

CO2/CH4

842.41

18

6.9

35

[42]

CO2/N2

842.41

15.3

6.9

35

6FDA-DAR


6FDA-SADAF CO2/CH4

6F-SADAF


[40]

Table 7.5 Mixed gas CO2 permeation properties of some polyimides. Polymer Matrimid® 5218

6FDA-ODA

Gas pair Separation factor

PCO2 (barrer)

CO2 % in Feed

ΔP (bar)

T Ref. (°C)

CO2/CH4

31.6

7.26

40

10

35

[37]

CO2/CH4

30

6.66

10

2

35

[38]

CO2/N2

30.5

6.72

40

15

35

[37]

CO2/CH4

48.9

18.6

50

10.34

35

[41]

One of the most investigated polymers in CO2 separation is the commercial polyimide Matrimid® 5218 (Figure 7.9). Matrimid tends to increase the permeability of both CO2 and N2 that causes a small reduction in the CO2/N2 selectivity [43].


Figure 7.9 Chemical structure of Matrimid® 5218 [44]. Tin and coworkers studied the Matrimid permeation properties for gas mixture and pure gas at conditions of 10 bars and 35 °C [37]. A small reduction in CO2/CH4 permeability and selectivity was observed for mixed gas compared to single gas conditions (Figure 7.10). Similar behavior was observed for CO2/CH4 separation by Ebadi et al. at different conditions (2 bars and 35 °C), as shown in Figure 7.11. However, mixed gas CO2 permeability and CO2/N2 selectivity were slightly higher than those at single gas conditions as reported by Tin et al.



Figure 7.10 Comparison of permeation properties of Matrimid® 5218 at single gas and mixed gas conditions [37].

Figure 7.11 Comparison of permeation properties of Matrimid® 5218 at single gas and mixed gas conditions [38]. Most of the synthesized polyimides incorporate the group 6FDA due to their high CO2 permeation properties as presented in Table 7.4 above. The high permeation properties of 6FDA-based polyimides are due to three main reasons [25, 45]: 1. The CF3 groups increase the stiffness of the chain, hence increasing the membrane efficiency in separating molecules on the basis of the steric bulk. 2. CF3 groups also reduce the effective chain packing which increases the gas permeability. 3. The formation of charge-transfer complexes is reduced, hence reducing the probability of


effective chain packing.

7.3.2 Polysulfones


Polysulfone (PSF) is considered to be one of the most widely studied polymeric membrane materials for CO2 separation for several gas streams [25, 46]. Gas permeation properties of PSF blends have been extensively investigated because of their low cost, chemical stability and mechanical strength [47]. These studies include mixed gas and pure gas permeation properties for several gas mixtures, including CO2/N2 and CO2/CH4. Several types of PSF blends have been developed over the years for CO2 separation (Figure 7.12). However, obtaining high selectivity and maintaining membrane efficiency in the presence of complex feed were the two main challenges of PSF development [12]. Many studies have been conducted to overcome these challenges by developing the synthesis process, formulation, and conducting material modification [46].



Figure 7.12 PSF and some PSF-based polymer structures [25]. Several studies have explored the permeation properties of polymeric membranes incorporating polysulfones for CO2/N2 and CO2/CH4 separation. Table 7.6 lists CO2 permeability and ideal selectivities for CO2/CH4 and CO/N2 separation of several PSF-based polymer membranes reported in the literature. All permeation measurements in Table 7.6 were conducted on pure gas measurements at different conditions. Results of mixed gas measurements would differ in values. However, mixed gas data would be more relevant to industrial applications. Table 7.7 compares CO2 permeation properties of PSF at single and mixed gas conditions.


Table 7.6 Single gas CO2 permeation properties of PSF-based membranes for CO2/CH4 and CO2/N2 separation.


Name

PCO2 (barrer)

Selectivity Ref. CO2/CH4 CO2/N2

PSF DMPSF DMPSF-Z TMPSF

5.6 2.1 1.4 21

22 30 34 22

22.4 23.1 24.6 19.8

[48]

HFPSF PSF-F PSF-O TMHFPSF TMPSF-F 3,4PSF PSF-P PSF-M TMPSF-M TMPSF-P BIPSF TMBIPSF 1,3-ADM PSF 2,2-ADM PSF 1,5-NPSF 2,6-NPSF 2,7-NPSF BPSF

12 4.5 4.3 72 15 1.5 6.8 2.8 7 13.2 5.6 31.8 7.2 9.5 1.6 1.5 1.8 3.2

22 24 24 24 26 29 20 25 25 22 22 25 22 24 44 41 36 27

17.9 22.5 21.5 18 9 22.7 21.3 25.5 25 23.2 23.3 26.3 21.8 20.6 28.1 29.4 24.3 32

[49]

[50] [51]

[52] [53] [54]

[55]


Table 7.7 Single gas and mixed gas CO2 permeation properties of PSF. Gas pair Test type CO2/CH4 Single Single Mixed (50% CO2) CO2/N2

Single Mixed (10% CO2)

Selectivity/separation factor

PCO2 (barrer)

ΔP (bar)

T Ref. (°C)

22 21.9 27

5.6 4.6 7.3

10 10 10

35 35 30

[48] [56] [57]

21

5.2

6

35

[58]

N/A

5.2

6–10

35


7.3.3 Polymer Blends Polymer blends have become of interest in many research studies as an easy and low-cost way of developing polymeric materials for membrane gas separation. A polymer blend consist of two or more polymers that have been blended together to develop a new material with different physical properties. Polymer blends offer the potential to tune permeation properties by the correct selection of the component polymers. Additionally, the synthesis cost of an effective polymer can be significantly reduced by the formation of a polymer blend that incorporates cheaper component polymers [59]. Generally, there are two main categories of polymer blends: miscible (heterogeneous) and immiscible (homogeneous) polymer blends. Miscible polymer blend is single phase structure where only one glass transition temperature can be observed. Examples of common miscible polymer blends are poly(styrene)(PS)– poly(phenylene oxide) (PPO) and poly(styrene-acrylonitrile) (SAN)–poly(methyl methacrylate) (PMMA). In contrast, with immiscible polymer blends, two glass transition temperatures can be observed if the blend consists of two polymers. For example, poly(propylene) (PP)–PS and poly(propylene)–poly(ethylene) (PE) are immiscible blends. Different blends have been investigated for CO2 separation, including polysulfones, polycarbonates, poly(ethylene oxide)s, and polyimides (e.g., Matrimid- and 6FDA-based membranes). Table 7.8 lists CO2 permeation properties of some polymer blend membranes in the literature.


Table 7.8 CO2 permeation properties of some polymer blend membranes in the literature. All measurements are for single gas except ‘b’ for mixed gas. Polymer blend

PCO2 (barrer) Ideal selectivity ΔP3 (bar) T (°C) Ref. CO2/N2 CO2/CH4

PANI/PBI (20/80)

1.07

86

104

1.5

30

[60]

PIM-1/PEG (0.5 wt%) PIM-1/PEG (1.5 wt%) PIM-1/PEG (2.5 wt%)

3125 2564 2278

16.1 15.3 16.6

17.8 22.9 33.5

4

30

[61]

PIM-1/PEG (3.5 wt%) PIM-1/PEG (5.0 wt%)

1952 2551

17.0 12.9

39.0 26.0

CS/Pebax (50/50)b PIM-1/Matrimid (50/50) PSF/Matrimid (80/20) PU/PVAc (80/20) 6FDA–TAB/DAM (50/50) 6FDA–TAB/DAM (75/25)

2884 155 – 26.87 155 73.7

65.3 27 – 50.69 23.5 23.8

23.2 28 29.7 41.33 34 44

1–12 3.5 10 10 2

85 35 35 – 35

[62] [63] [64] [34] [65]

PVAm/PEG

5.88a

–

63

1.26

25

[66]

a Permeance in GPU


b Mixed gas (CO /CH 30/70 vol%, CO /N 20/80 vol%) 2 4 2 2

Rabiee and coworkers incorporated poly(tetramethylene ether) glycol (PTMEG) into Pebax 1657 to develop Pebax/PTMEG blend membrane for CO2 separation from N2, H2, and CH4 [67]. The prepared blends were tested on single gas measurement at different temperatures and pressures (25–55 °C and 4–16 bars). The authors reported a slight improvement in CO2/H2 selectivity. However, CO2/N2 and CO2/CH4 selectivities were decreased slightly with the incorporation of PTMEG. The effect of PTMEG incorporation on Pebax permeation properties are illustrated in Figure 7.13.


Figure 7.13 Effect of PTMEG incorporation on CO2 permeation properties of Pebax 1657 (4 bars and 25 °C) [67].


Yong et al. explored CO2 permeation properties of Matrimid blends incorporating PIM-1 (polymers of intrinsic microporosity) with different compositions [63]. The results showed that blending PIM-1 with the Matrimid matrix increased CO2 permeability, however decreased CO2/N2 and CO2/CH4 selectivities from the pure Matrimid (Figures 7.14 and 7.15).

Figure 7.14 CO2/CH4 and CO2/N2 selectivities of PIM-1/Matrimid dense films (35 °C and 3.5 atm) [63].


Figure 7.15 CO2 permeability as a function of PIM-1 composition in Matrimid (35 °C and 3.5 atm) [63]. Rafiq and coworkers explored the CO2/CH4 pure and mixed gas permeation properties for PSF blended with 20 wt% PI (Matrimid® 5218) [64]. Permeation measurements were conducted using different CO2 compositions in the feed at 10 bars and 25 °C. Table 7.9 lists the selectivity data obtained by Rafiq et al. Table 7.9 Pure and mixed gas CO2/CH4 selectivity results for PSF incorporating 20% Matrimid [64]. Ideal selectivity


29.7 ± 0.6

Mixed gas selectivity (25/75) (50/50) (75/25) 29.5 ± 0.4 29.9 ± 0.6 29.8 ± 0.4

A novel polymer blend was prepared by Ghalei et al. consisting of poly(urethane)/poly(vinyl acetate) (PU/PVAc) (80/20) [34]. Pure gas permeation measurements were conducted at room temperature and different pressures (2–10 bars). The reported results showed that incorporating PVAc into PU matrix resulted in higher CO2 permeability as well as higher CO2/N2 and CO2/CH4 selectivity, as shown in Figure 7.16.


Figure 7.16 Comparison between the permeation properties of pure PU and PU/PVAc (80/20) blend membrane (10 bars) [34].


Giel and coworkers prepared a novel polymer blend by casting solutions of polyaniline (PANI) and polybenzimidazole (PBI) at various ratios [60]. Pure gas permeation measurements were conducted on the synthesized membranes at 30 °C and 1.5 bar. The results showed a slight decrease in CO2 permeability with PANI content in PBI (Figure 7.17); while CO2/CH4 and CO2/N2 selectivities were slightly increased (Figure 7.18).

Figure 7.17 CO2 permeability as a function of PANI composition in PBI (30 °C and 1.5 bar).


Figure 7.18 CO2 permeation properties of PANI/PBI blend membrane (30 °C and 1.5 bar) [60].


7.4 Mixed Matrix Membranes Mixed matrix membranes (MMMs), or composite membranes, are well known in polymeric membranes development for gas separation. These membranes incorporate an inorganic material in the form of micro- or nanoparticles, hence combining the ease of polymer processing with the efficient gas permeation of molecular sieve (Figure 7.19) [68, 69]. The use of materials with different permeation properties offers the possibility to synthesize an efficient gas separation membrane. Incorporating an inorganic material into a polymeric membrane can serve as a molecular sieve that enhances the gas permeance through the membrane or as a barrier that reduces the gas permeability [70]. Composite membranes possess an economic advantage over inorganic membranes as they offer the possibility to fabricate large-surface-area polymer membranes. Furthermore, incorporating inorganic materials may enhance the physical, thermal, and mechanical properties of polymer membranes and can be a way to stabilize them against change in selectivity with temperature [71, 72]. The synthesis of efficient MMMs is governed by the following factors:


Figure 7.19 Schematic illustration of MMM incorporating different components of the inorganic filler [68]. 1. The proper selection of the inorganic filler and the polymeric material. 2. The elimination of interfacial defects between the two phases. 3. The proper control of filler dimensions, concentration, and shape. The addition of inorganic filler to the polymer matrix enhances the separation efficiency of the polymeric membrane since these inorganics have superior separation efficiencies compared to the neat polymers. The effective membrane permeability of a gas in MMMs can be predicted by the Maxwell model equation [68]:


(7.6)

where Peff is the effective membrane permeability, Φ is the volume fraction, Pd and Pc are the single component permeability of the dispersed and the continuous phase respectively. Li and coworkers reported the first MMMs made of commercially available poly(amide-bethylene oxide) (Pebax® 1657, Arkema) mixed with the nanosized zeolitic imidazole framework ZIF-7 [73]. The study was conducted using single gas permeation measurements. With low ZIF- loading, CO2 permeability, CO2/N2 and CO2/CH4 separation selectivities were increased; while high ZIF- loadings resulted in a drop in CO2 permeability compared to pure Pebax® 1657 (Figure 7.20).


Figure 7.20 Effect of ZIF-7 loading on CO2 permeability and CO2/CH4 and CO2/N2 selectvities of Pebax® 1657 [73].


Pebax was also used in fabricating MMMs, incorporating carboxylic acid nanogels (CANs) for mixed gas CO2/N2 and CO2/CH4 separation [74]. The authors reported a clear increase in CO2 transport sites through the membrane with the incorporation of CANs into Pedax. Figure 7.21(a) and (b) shows the increase of CO2 permeability and separation factor for CO2/ CH4 and CO2/N2 respectively.



Figure 7.21 Effect of CANs content on gas separation performance of pristine Pebax and Pebax-CANs MMMs for: (a) CO2/CH4 separation and (b) CO2/N2 separation (2 bars and 25 °C) [74]. Novel MMMs were prepared by Sanaeepur et al. by incorporating Co2+ exchanged NaY zeolite, Co(II)–NaY, into the cellulose acetate (CA) using different Co(II)–NaY concentrations [75]. The new CA/Co(II)–NaY MMMs were tested on CO2/N2 separation and showed a clear increase in CO2/N2 selectivity and CO2 permeability compared to the pure CA and CA/NaY membranes (Figure 7.22).


Figure 7.22 Effect of Co(II)–NaY particle loadings on (a) CO2 permeability, and (b) CO2/N2 selectivity of CA membranes (25 °C) [75].


Jomekian et al. prepared Pebax-based MMMs incorporating ZIF-8 particles synthesized at different temperatures [76]. The synthesized MMMs achieved significant improvement in CO2 permeability and CO2/CH4 selectivity in both single and mixed gas permeation tests compared with pure Pebax membrane. Figures 7.23 and 7.24 illustrate the CO2/CH4 permeation properties (at 8 bars) of ZP-60–1 (ZIF-8 was synthesized at 60 °C, Pebax content in solvent is 1 wt%) and ZP-60–4 (ZIF-8 was synthesized at 60 °C, Pebax content in solvent is 1 wt%). The overall results of the study showed competitive CO2/CH4 separation efficiency compared to Pebax-based membranes reported in other studies.

Figure 7.23 Single gas versus mixed gas CO2 permeability obtained with MMMs by Jomekian et al. [76].


Figure 7.24 Single gas versus mixed gas CO2/CH4 selectivity results obtained with MMMs by Jomekian et al. [76].


Novel MMMs were recently prepared by Singh et al. consisting of crosslinked poly(roomtemperature ionic liquid)s (poly(RTIL)s), Zeolite particles, and room-temperature ionic liquids (RTILs) [77]. The prepared MMMs were examined on pure gas CO2/CH4 measurement at 25 °C and 2 bars feed pressure and showed competitive CO2 permeability (260 ± 20 barrers) and CO2/CH4 selectivity compared to other membranes in the literature. Mesoporous and microporous polyimides were used as fillers incorporated into Matrimid-based and 6FDA-IMM-based MMMs in a study conducted on CO2 separation by Rangel et al. [78]. Matrimid-based MMMs exhibited higher gas permeability when compared to pure Matrimid, while the selectivity was maintained. However, 6FDA-IMM-based MMMs showed only small changes in permeation compared to pure 6FDA-IMM. The effect of incorporating inorganic silica nanoparticles into PSF/PI (Matrimid) blends was investigated by Rafiq and coworkers on CO2/CH4 pure and mixed gas permeation [64]. At 2 bar feed pressure, CO2 permeance increased from 73.7 ± 0.2 GPU (87%) to 95.7 ± 0.4 GPU (143%) with the addition of silica contents (5.2 to 20.1 wt%) respectively, compared to PSF/PI blend membrane. The effect of incorporating 15.2 wt% silica nanoparticles on PSF/PI permeation properties is shown in Figure 7.25.



Figure 7.25 Pure and mixed gas CO2/CH4 selectivity results for PSF/PI blend incorporating 15.2 wt% silica nanoparticles (10 bars and 25 °C) [64]. Zornoza and coworkers conducted two studies exploring the effect of dispersed mesoporous silica spheres (MSSs) and hollow silicalite-1 spheres (HZSs) on polysulfone efficiency in CO2/N2 separation [79, 80]. The two studies were conducted for mixed gas feed with 50/50 mol% CO2/N2 at 35 °C and different pressure difference (1.75 and 2.75 bars respectively). Authors found that the optimum MSSs loadings is 8 wt% in PSF, which increased the permeability of CO2 from 5.9 barrer to 12.6 barrer, and the selectivity from 24 to 36. However, loadings of 8 wt% HZSs increased CO2 permeability to 7.2 barrer and the selectivity to 41.7. Another study was conducted by Zornoza et al. on the effect of the flexible metal organic framework, NH2-MIL-53(Al), on PSF efficiency in CO2/CH4 separation [81]. The study used a feed of equimolar CO2/CH4 mixture and was conducted at 3 bars and 35 °C. The highest performance was achieved with 25 wt% NH2-MIL-53(Al), which recorded CO2 permeability of 6 barrer and CO2/CH4 selectivity of 46.2. Guo and coworkers prepared polysulfone-based mixed matrix membranes (MMMs) incorporated with amine-functionalized titanium-based metal organic framework (MOFs), NH2-MIL-125(Ti). The prepared membranes were tested on equimolar CO2/CH4 mixture separation at 10 bars and 30 °C. At these conditions, PSF loaded with 20 wt% NH2-MIL125(Ti) achieved the highest selectivity of 29.5 and CO2 permeability of 22.8 barrer [57]. Rodenas and Dalen et al. investigated the effect of different loadings of NH2-MIL-101(Al) on PSF and polyimide (Matrimid® 5218) [82]. Mixed separation measurements used an equimolar CO2/CH4 mixture at steady operation (3 bars and 35 °C). Matrimid 9725-based MMMs incorporating MIL-125(Ti) and the amine-functionalized counterpart were recently investigated by Anjum et al. [83]. The incorporation of the fillers into Matrimid matrix significantly increased mixed gas CO2 separation efficiency from N2 and CH4. Table 7.10


summarizes the performance of mixed matrix membranes in the studies discussed above and other literature.


Table 7.10 CO2/N2 and CO2/CH4 separation performance of mixed matrix membranes. Mixed matrix membrane

PCO2 Selectivity ΔΡ T Ref. CO2/N2 CO2/CH4 (bar) (°C)

Pebax® 1657 + ZIF-7 (8 wt%)

145a

68

23

Pebax® 1657 + ZIF-7 (22 wt%)

111a

97

30

Pebax® 1657 + ZIF-7 (30 wt%)

41a

105

44

Pebax® 1657 + ZIF-8 (8 wt%)c

613 ± 34a

–

9.3 ± 0.6

Pebax® 1657 + ZIF-8 (8 wt%)d

542 ± 37a 50 ± 4a

–

10.4 ± 0.2

–

30 ± 1

240 ± 10a

–

35 ± 1

170 ± 9a

–

63 ± 5

200 ± 10a

–

70 ± 2

213 ± 9a

–

25 ± 2

240 ± 10a

–

35 ± 1

300 ± 20a

–

31 ± 5

170 ± 10a

–

60 ± 4

200 ± 10a

–

70 ± 2

Matrimid® + PPI-1 (20 wt%)

10.3

22.9

44.8


16.8a

26.7

48.0


20.9a

22

43.5

poly([SMIM][Tf2N]) + [EMIM][Tf2N] +SAPO-34(64–16-20 wt%) poly([SMIM][Tf2N]) +[EMIM][Tf2N] + SAPO-34 (64–16-40 wt%) poly([SMIM][Tf2N]) + [EMIM][Tf2N] + SSZ-13 (64–16-20 wt%) poly([SMIM][Tf2N]) + [EMIM][Tf2N] + SSZ-13 (64–16-25 wt%) poly([VHIM][Tf2N]) + [EMIM][Tf2N] + SAPO-34 (30–30-40 wt%) poly([SMIM][Tf2N]) + [EMIM][Tf2N] +SAPO-34(30–30-40 wt%) poly([VHIM][Tf2N]) + [EMIM][Tf2N] +SSZ-13(50–25-25 wt%) poly([VMIM][Tf2N]) + [EMIM][Tf2N] + SSZ-13(50–25-25 wt%) poly([SMIM][Tf2N]) + [EMIM][Tf2N] + SSZ-13(50–25-25 wt%)

3.75 25 [73]

8

–

[76]

– 2

25 [77]

3

30 [78]



6FDA-IMM + PPI-1 (20 wt%)

202a

17.4

18.5


270a

16.8

16.9


289a

17.7

17.9

PSF + PI + Silica (15.2 wt%)

90b

–

60

2

25 [64]

Matrimid® + MIL-125 (15 wt%)

18a

–

44

9

–

Matrimid® + MIL-125 (30 wt%)

27a

–

37

Matrimid® + NH2-MIL-125 (15 wt%)

17a

–

50

Matrimid® + NH2-MIL-125 (30 wt%)

50a

–

37

PSF + NH2-MIL-53(Al) (25 wt%)

6a

–

27

3

35 [82]

Matrimid®+NH2-MIL-53(Al) (25 wt%)

9a

–

35

1–3

PSF + NH2-MIL-125(Ti) (10 wt%)

18.5a

–

28.3

3

30 [57]


29.3a

–

29.5


40a

–

29.2

PSF + Silica (10 wt%)

9.3a

–

24.5

4.4

35 [84]

PSF + Silica (20 wt%)

19.7a

–

17.9

Matrimid® + Fe(BTC) (10 wt%)

9.5a

–

27.0

5

35 [85]


11a

–

28.0


13.5a

–

30.0

6FDA-Durene + ZIF-71 (10 wt%)

1606a

14.9

20


3435a

12.9

16


5642a

11.5

9.2

Matrimid® + ZIF-8 (20 wt%)

22b

25

22

Matrimid® + ZIF-8 (30 wt%)

23b

27

23

Ultem® + ZIF-8

18b

44

–

6.89 25 [88]

Ultem® + ZIF-8

21b

39

–

30

Ultem® + ZIF-8

26b

36

–

35

PI+Cu3(BTC)2 (3 wt%)

65b

6

8

PI+Cu3(BTC)2 (6 wt%)

37b

6

9

Ultem®(PEI) + HSSZ-13

6.2b

30

44

[83]

3.5 308 [86]

10

25 [89]

1.6

35 [90]

aPermeability (barrer). P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

bPermeance (GPU). cZIF-8 was synthesized at 60 °C, Pebax content in solvent is 1 wt%, mixed gas (10 vol% CO ). 2 dZIF-8 was synthesized at 60 °C, Pebax content in solvent is 4 wt%, mixed gas (10 vol% CO ). 2

7.5 Supported Ionic Liquid Membranes (SILMs) for CO2 Separation


One of the growing processes in the development of membrane science is supported ionic liquid membranes technology (SILMs). Due to their special properties, e.g., high thermal and chemical stability and low vapor pressure, ILs have become an ideal alternative to conventional organic solvents in a wide range of chemical applications at lab scale, such as separation and purification and chemical catalysis [91–96]. The high thermal stability of ionic liquids provides considerable potential to utilize ionic liquids for CO2 capture applications. Most ionic liquids are stable to over 300 °C and therefore less likely to degrade via oxidation, to react with impurities or to be corrosive [97]. In addition, because ILs have negligible vapor pressure, this creates a possibility of ILs regeneration over a wide range of temperatures and pressures. Thus, this offers a new chance for process optimization that is not achievable using traditional liquid media. Additionally, ionic liquids are considered as green solvents compared to other volatile organic solvents. One of the biggest drawbacks to the large-scale use of ILs in CO2 capture is their higher cost compared to the conventional solvents they are proposed to replace [98]. However, by eliminating or reducing process losses through thermal degradation, chemical or oxidative destruction and vapor loss, the solvent amount needed for the process may be greatly reduced [99]. Ionic liquids are being investigated for several membrane applications such as membrane absorption, membrane extraction, membrane extractive distillation, membrane pervaporation, membrane vapor separation, and membrane gas separation [100]. Cserjési and Bélafi-Bakó conducted an extensive review on the current applications of ionic liquids in membrane separation processes [100].

7.5.1 SILM Permeation Properties for CO2/N2 and CO2/CH4 Separation The advantages of both ionic liquids and membranes can be combined by the synthesis of effective supported ionic liquid membranes (SILMs). Many recent studies have discussed the effect of ILs on CO2/N2 and CO2/ CH4 separation through polymeric membranes. These studies were conducted using different membrane support types, conditions and ILs. Some of these studies were performed on the behavior of pure gas through the membrane [101, 102], while others concentrated on mixed gas separation [103–105]. Cserjési et al. investigated SILMs using two common and ten novel types of ionic liquids supported by hydrophobic PVDF having porosity of 75% and pore size of 0.22 µm [101]. Only


eight of these ILs were used in SILMs preparation because others have destroyed the supporting membrane material. Pure gas permeation measurements were conducted at a pressure difference of 2 bars and 30 °C. The obtained CO2/N2 selectivity ranges between 10.9 and 52.6 with Ecoeng™ 1111P and Ammoeng™ 100 respectively. In contrast, the highest CO2/CH4 selectivity was only 13.1 with [emim][CF3SO3]. Another study on SILMs for pure gas permeation was conducted by Bara et al. [102]. Three ionic liquids were used in the study supported by polyethersulfone (PES) with porosity of 80% and 0.2 µm pore size. Permeation measurements were conducted at 0.85 bar and 23 °C. The obtained CO2/N2 selectivities were 27, 21, and 16 with [MpFHim][NTf2], [MnFHim][NTf2], and [MtdFHim][NTf2] respectively. However, CO2/CH4 selectivities were 19, 17, and 13 with [MpFHim][NTf2], [MnFHim] [NTf2], and [MtdFHim][NTf2] respectively.


Neves and coworkers studied the effect of different ILs on the pure gas permeation properties of porous polyvinylidene fluoride (PVDF) [103]. The PVD fused in the study has 75% porosity and 0.22 µm pore size. The prepared SILMs achieved high CO2/CH4 selectivities compared to the literature. CO2/CH4 selectivities were 228 ± 1.5, 113 ± 1.6, 187 ± 1.7, and 105 ± 0.5 with [C4mim][PF6], [C4mim][BF4], [C4mim][Tf2N], and [C8mim][PF6] respectively. In contrast, the obtained CO2/N2 selectivities lie within the reported results in other literature and are 23 ± 0.5, 35 ± 0.2, 39 ± 0.1, and 23 ± 0.5 with [C4mim][PF6], [C4mim][BF4], [C4mim][Tf2N], and [C8mim][PF6]. Scovazzo et al. studied the pure gas permeation properties of several ionic liquids supported by porous glass fiber support to limit the mass transport to molecular diffusion through ILs only. Pure gas permeability measurements were performed at a very low pressure (7 Pa) to prevent the ILs from penetrating the support. The highest CO2/N2 and CO2/CH4 selectivities were 57 ± 4.4 and 23 ± 5.1 respectively and obtained with [emim][dca]; while the lowest selectivities were obtained with [C6mim][Tf2N] and found to be 15 ± 1.8 and 8.5 ± 0.3 for CO2/N2 and CO2/CH4 respectively. Table 7.11 summarizes some of the pure gas permeation results reported in the literature. Table 7.11 Ideal (pure gas) CO2/N2 and CO2/CH4 selectivity values of commonly used ILs. Ionic liquid

PCO2

Ideal selectivity Support membrane CO2/N2 CO2/CH4

[bmim][BF4]

93.9

52.3

8.18

AMMOENG™ 100 ECOENG™ 1111P Cyphos 102 Cyphos 103

93.9 127 637 487

52.6 10.9 41.5 43.1

7.93 6.38 6.87 5.62

Ref.

Polyvinylidene fluoride (PVDF) [101]



Cyphos 104 [emim][CF3SO3]

642 486

31.6 34.0

5.17 13.1

[SEt3][NTf2]

747

26.2

6.67

[MpFHim][NTf2]

320 ± 10

27

19

[MnFHim][NTf2]

280 ± 10

21

17

[MtdFHim][NTf2]

210 ± 10

16

13

Polyethersulfone (PES)

[102]

[C4mim][PF6]

–

23 ± 0.5 228 ± 1.5 Polyvinylidene fluoride (PVDF) [103]

[C4mim][BF4]

–

35 ± 0.2 113 ± 1.6

[C4mim][Tf2N]

–

39 ± 0.1 187 ± 1.7

[C8mim][PF6]

–

23 ± 0.5 105 ± 0.5

[emim][BF4]

968 ± 10 44 ± 1.7 22 ± 1.1 Glass fiber support

[emim][CF3SO3]

1171 ± 16

[emim][Tf2N]

1702 ± 13 23 ± 1.7 12.2 ± 0.9

[C6mim][Tf2N]

1136 ± 20 15 ± 1.8 8.5 ± 0.3

[bmim][BETI] [emim][dca] [thtdp][Cl] [C4mim][BF4]

991 ± 18 16.7 9.9 ± 0.3 1237 ± 30 57 ± 4.4 23 ± 5.1 350 ± 20 15 4 Polyethersulfone (PES) 460 ± 12 12.4 8.2 Polyethersulfone (PES)

[C4mim][PF6]

360 ± 15

13.8

7.3

[C6mim][BF4]

520 ± 11

11.6

7.6

[C4mim][SCN]

42,795

5.3

–

ZIF-71

[C4mim][SCN]

27,584

74.6

–

ZMOF

[C4mim][SCN]

40,188

13.0

–

IRMOF-1

[109]

[C2mim][B(CN)4]

2040 ± 60

53.7

–

Polyethersulfone (PES)

[110]

[C4mim][B(CN)4]

1755 ± 50

39.9

–

[emmim][B(CN)4]

1721 ± 80

45.3

–

[C2mim][B(CN)4]

742

49.1

–

Hydrophilic PTFE

[111]

[C2mim][B(CN)4]

2040

53.7

–

Anodic alumina

[112]

2640 ± 190

21.5

–

Anodized alumina

[113]

[C2mim][Tf2N]

40.5

[104]

18.5


[106] [107]

[108]

Since supported ionic liquid membranes have potential for large-scale use in the industrial applications, several studies have investigated the use of SILMs for mixed gas separation applications (Table 7.13) [103–105]. Neves et al. investigated SILMs based on the 1-n-alkyl3-methylimidazolium cation supported by polymeric membranes for mixed gas separation [103]. CO2/N2 and CO2/CH4 equimolar binary mixtures were used in the permeation measurements at 30 °C and a pressure up to 0.7 bar. Four ionic liquids were used in mixed gas permeation measurements: [C4mim][PF6], [C4mim][BF4], [C4mim][Tf2N], and [C8mim][PF6] supported by polyvinylidene fluoride (PVDF). The results showed that the synthesized SILMs exhibited CO2/N2 selectivity ranging between 20 and 32, which is considered to be normal behavior compared to the reported literature. However in the case of CO2/CH4 separation, the prepared SILMs exhibited high selectivity values up to 200 with [C4mim][PF6]. The lowest CO2/CH4 selectivity was 98, which was obtained with [C8mim][PF6]. Scovazzo et al. [104] studied separation of the binary gas mixtures CO2/CH4 and CO2/N2 using continuous feed of the mixed gas. Six ionic liquids were used in this study, [emim][BF4], [emim][CF3SO3], [emim][Tf2N], [C6mim][Tf2N], [bmim][BETI] supported bypolyethersulfone (PES) membrane and [emim][dca] supported bypolyvinylidene fluoride (PVDF) membrane. The highest CO2/CH4 and CO2/N2 selectivity results were 27 and 21.2, using [emim][BF4] and [emim][Tf2N] respectively. Both supports, PES and PVDF, used in the study have high porosity of 80%. Permeation measurements were conducted at 30 °C and a pressure difference of 2.07 to 3.07 bars. Another study on SILMs for mixed gas separation was conducted by Hojniak et al. [105]. The authors prepared SILMs using porous γ-alumina discs as membrane support with different ionic liquids, monocationic and dicationic ionic liquids. The synthesized ionic liquids are shown in Table 7.12. Copyright © 2016. John Wiley & Sons, Incorporated. All rights reserved.

Table 7.12 List of the synthesized ionic liquids by Hojniak et al. [105]. IL Type ILs Ionic liquid name Monocationic 1a 1-(2-(2-(2-Methoxyethoxy)ethoxy)ethyl)-1-methylpyrrolidinium ptoluenesulfonate 1b 1-(2-(2-(2-Methoxyethoxy)ethoxy)ethyl)-1-methylpiperidinium ptoluenesulfonate 1c 1-(2-(2-(2-Methoxyethoxy)ethoxy)ethyl)-1-methylmorpholinium ptoluenesulfonate 1d 1-(2-(2-(2-Methoxyethoxy)ethoxy)ethyl)-1-methylimidazolium ptoluenesulfonate Dicationic 2a 1,8-Bis[1-methylpyrrolidinium)]-3,6-dioxaoctane di(p-toluenesulfonate) 2b 1,8-Bis[1-methylpiperidinium)]-3,6-dioxaoctane di(p-toluenesulfonate) 2c 1,8-Bis[1-methylmorpholinium)]-3,6-dioxaoctane di(p-toluenesulfonate)


The obtained results showed that the prepared SILMs exhibited comparable behavior to the literature as they lie in the same ranges. CO2/N2 selectivity results obtained with these SILMs ranged between 15.2 and 34.7, while CO2/CH4 selectivity values were between 12.6 and 31.8. Table 7.13 summarizes some of the mixed gas permeation results reported in the literature. Table 7.13 Mixed gas CO2/N2 and CO2/CH4 selectivity values of commonly used ILs. Ionic liquid

Separation factor Support membrane CO2/N2 CO2/CH4

Ref. [103]

[C4mim][PF6]

–

[C4mim][BF4]

–

20 ± 1.6 200 ± 1.5 polyvinylidene fluoride (PVDF) 32 ± 0.1 102 ± 0.6

[C4mim][Tf2N]

–

30 ± 0.5 161 ± 0.5

[C8mim][PF6]

–

21 ± 1.6 98 ± 0.5

[emim][BF4]

3.50a

–

27 ± 0.8 polyethersulfone (PES)

[emim][CF3SO3]

4.88a

–

22 ± 1.2

[emim][Tf2N]

5.58a

21.2

17 ± 0.9

[C6mim][Tf2N]

4.85a

N/A

9.9 ± 0.9

[bmim][BETI]

–

12.2

–

2.36a

–

1aa

–

15.2

12.6

1bb

–

17.2

15.4

1cc

–

17.6

14.2

1dd

–

16.3

16.1

2ae

–

27.9

22.4

2bf

–

24.1

20.2

– 6200

34.7 21

31.8 –

[emim][dca]


PCO2 (barrer)

2cg [C4mim][Tf2N][C4mim] [PF6]

[104]

24 ± 1.4 polyvinylidene fluoride (PVDF) Porous γ-alumina discs

[105]

polyvinylidene fluoride (PVDF)

[114]

aPermeance (GPU)

The use of single gas permeation measurements to model real mixed gas systems can result in significant error as a result of the competition sorption inside the membrane [58]. Several studies showed that the selectivity decreases with mixed gas systems compared to pure gas


systems. Scholes et al. found that the loss percentage in CO2 permeability is about 3.7% for polysulfone. Similar results were observed by Neves et al. with respect to CO2/N2 and CO2/CH4 separation [103]. Separation selectivities with pure gas systems were found to be higher than those with mixed gas measurements. Figures 7.26 and 7.27 compare the CO2/N2 and CO2/CH4 single gas selectivities (ideal selectivities) with mixed gas selectivities. They show that for all tested SILMs, CO2/N2 and CO2/CH4 mixed gas selectivities are lower than those obtained with single gas system. However, the difference between the results obtained with the two systems is not significant due to the low pressure applied across the membrane [12, 103].


Figure 7.26 Single gas versus mixed gas CO2/N2 selectivities for different SILMs reported by Neves et al. [103].


Figure 7.27 Single gas versus mixed gas CO2/CH4 selectivities for different SILMs reported by Neves et al. [103].


Scovazzo et al. [104] also observed a slight reduction in the CO2/N2 mixed gas selectivities when compared with pure gas selectivities (Figure 7.28) using [emim][Tf2N] and [bmim] [BETI] supported by polyethersulfone (PES). In contrast, an opposite observation was reported by authors with respect to CO2/CH4 measurements. CO2/CH4 selectivities obtained with mixed gas system were found to be higher than those obtained with single gas system (Figure 7.29). However, in both CO2/N2 and CO2/CH4 measurements, the variation between selectivities obtained with pure and mixed gas systems is not significant and this can be due to the low pressure applied across the membrane as discussed above.



Figure 7.28 Single gas versus mixed gas CO2/N2 selectivities for different SILMs reported by Scovazzo et al. [104].

Figure 7.29 Single gas versus mixed gas CO2/CH4 selectivities for different SILMs reported by Scovazzo et al. [104].

7.5.2 SILMs Stability in Gas Separation One of the most essential parameters of SILMs in gas separation is their stability under different pressures and temperatures. The high porosity of the support membrane, which is a common issue in most of the reported studies in the literature, can lead to membrane failure


with high pressure due the loss of ILs. Hence, the pressure difference across the membrane is limited to a very low pressure in most of those studies. Hernández-Fernándeza et al. studied the influence of the immobilization method on SILMs stability with respect to ionic liquids loss [115]. SILMs based on [bmim+][BF4–], [bmim+] [PF6–],[bmim+][Cl–] and [bmim+][NTf2–] were synthesized using Hydrophilic Nylon® (polyamide) with 0.45 µm pore size as the support membrane. These SILMs were synthesized by two immobilization methods including pressure or vacuum. In the first method, a small amount of the ionic liquids was added on the membrane surface and placed in an ultrafiltration unit. Then, N2 gas was applied with a pressure of 2 bar to force ILs to flow through the membrane pores. The second method involves submerging the support membrane in a small amount of the ionic liquid and then applying a vacuum to remove the air from the support pores. Stability measurements were conducted using glass diffusion cell for 7 days where TBME and n-Hexane were used as the receiving and feed solutions respectively. Ionic liquid losses were determined by weight difference of the fresh and used membranes. The results of the study are presented in Figure 7.30 and show that SILMs prepared with both methods exhibited large ionic liquid losses.


Figure 7.30 shows that SILMs prepared with vacuum exhibited a loss of 22.5, 32.7, 58.4, and 50.7% with SILMs based on [bmim+][BF4–][bmim+] [PF6–], [bmim+][NTf2–], and [bmim+] [Cl–] respectively. In contrast, SILMs prepared using immobilization with pressure were more stable and exhibited lower IL losses. The losses were 12.6, 15.7, 49.8, and 12.1% with SILMs based on [bmim+][BF4–][bmim+][PF6–], [bmim+][NTf2–], and [bmim+][Cl–] respectively.

Figure 7.30 Ionic liquid loss of SILMs prepared with pressure and vacuum immobilization reported by Hernández-Fernándeza et al. [115]. Neves et al. [103] studied the effect of the applied pressure and the support type on SILMs stability with respect to ILs losses. Two distinct polymeric supports were used, hydrophilic PVDF and hydrophobic PVDF. SILMs weight as a function of time is represented in Figure 7.31(a) and (b) for SILMs based on hydrophilic and hydrophobic supports respectively. The


results showed that SILMs supported by hydrophilic PVDF exhibited lower stability since membrane weight declined by 11 to 13% after 10 h with all SILMs. However, the weight of SILMs supported by hydrophobic PVDF declined by about 1, 3, and 7% with SILMs based on [C4mim][Tf2N], [C4mim][PF6], and [C8mim][PF6] respectively after 1 h and then stabilized. Hence, SILMs with hydrophobic support were considered to be more stable.

Figure 7.31 Weight of SILMs based on (a) hydrophilic, and (b) hydrophobic membranes immobilized with different ILs as a function of time (pressure difference: 1 bar) [103].


The effect of the applied pressure on the ionic liquid loss was also reported in the study for hydrophilic and hydrophobic supports respectively. The results showed that membrane weight of both SILMs declined at 1 bar and continued decreasing with higher pressure until the decrease became significant at a pressure of 2 bar, which indicates the possibility of membrane failure over time. Another study on ionic liquid loss was conducted by Zhao and coworkers [116]. They synthesized SLIMs based on [bmirn][BF4] supported by polyethersulfone (PES), nylon 6 (N6), and polyvinylidene fluoride (PVDF). Ionic liquid loss measurements were conducted with respect to gas separation performance and the SILMs weight loss. Ionic liquid losses were determined after a run of 420 min for PES-based SILMs. However, losses of SILMs based on N6 and PVDF were tested only at 150 min because of membrane failure after this time. Hence, SILMs prepared with PES showed the highest stability compared to the other two support membranes. Stability results of the study are summarized in Table 7.14.


Table 7.14 Ionic liquid losses as a function of pressure and pore size [116]. Membrane Pore size (µm) Cross membrane pressure difference (bar) 0.8 1 2 2.5 3 3.5 PES 0.1 1.8 8.7 45.7 50.3 54.9 68.8 PES 0.2 13.6 18.6 53.1 58 62.9 – PES N6 PVDF

0.45 0.2 0.22

14.7 15.8 25.2

19.7 22.6 32.8

59.1 – –

– – –

– – –

– – –

It is shown that all prepared SILMs exhibited a loss of ILs and this loss is proportional to the pressure difference and the pore size as well. Although SILMs with PES support were more stable than other SILMs, the reported results show about 18.6 and 19.7% loss of ILs with supports having 0.2 μm and 0.45 μm respectively at 1 bar; then ILs loss became more significant (> 50%) at higher pressures. On the other hand, SILMs with N6 and PVDF supports exhibited more ILs losses, hence caused a membrane failure at low pressure after only 150 min.


7.6 Conclusion 1. Membrane-based CO2 separation is well considered today in chemical industries and competes with the conventional CO2 separation technologies such as adsorption, absorption, and cryogenic distillation. Industrial membrane separation of CO2 can overcome safety, environmental, technical and economic aspects. Due to these aspects, thousands of studies were conducted to develop highly efficient CO2 separation membranes. Permeability and separation selectivity are the most important two parameters in a CO2 separation membrane. 2. State-of-the-art membranes for CO2 separation have been reported in this chapter, mainly polymeric, polymer blends, mixed matrix membranes, and supported ionic liquid membranes. A great deal of research has been conducted on developing membrane materials for better CO2 separation from different gas streams (mainly natural gas and flue gas streams). Most of these studies focused on the separation of CO2 from N2 and CH4 as a promising technology in industrial applications. Different types of polymers and their blends have been investigated for CO2 separation. Research on polymeric and polymer blend membranes have resulted in the development of some high CO2 permeable membranes such as poly(4-methyl-1-pentyne), 6FDA-DAM and PIM-1/ PEG. A number of studies are being conducted on mixed matrix membranes development. The MMMs reviewed in this chapter showed a slight improvement in CO2 permeation with moderate separation selectivity. Recently developed MMMs prepared by Singh et al. could clearly


break Robeson’s upper bound for CO2/CH4 separation. However, with respect to CO2/N2 separation, only a few MMMs, such as the Pebax-zeolite MMMs reported by Li et al., could pass the upper bound. Different types of ionic liquids with various supports have been used in the fabrication of supported ionic liquid membranes and showed high CO2 permeance and selectivity. Some of these membranes break Robeson’s upper bound for CO2/N2 such as Cyphos 104-, [SEt3][NTf2]-, [emim][BF4]-, [emim][dca]-, [C2mim][TCB], [C4mim][TCB]-, [C2mim][TCB]-based SILMs. However, SILMs performance with respect to CO2/CH4 separation is still lower than MMMs and polymeric blends. Most SILMs reported in the literature exhibited low stability with respect to ionic liquids loss at high pressures. Overall, all membranes reported in the literature suffer from a trade-off relationship which is that permeability and selectivity cannot be elevated at the same time.

7.7 Overall Comparison and Future Outlook


The overall permeation properties of polymeric membranes, MMMs, and SILMs reported in this chapter are compared in Figures 7.32 and 7.33 with respect to CO2/N2 and CO2/CH4 separation, along with the Robeson’s upper bound. Figures 7.32 and 7.33 provide an approximation of the overall CO2 permeation performance of the discussed membrane categories. The figures indicate that these membranes suffer from a permeability and selectivity trade-off where high permeability and separation selectivity cannot be achieved simultaneously. This trade-off relationship is represented by Robeson’s upper bound, shown in Figures 7.32 and 7.33, that acts as a benchmark for membrane development in the future. Membranes for CO2 separation, mainly from CH4 and N2 streams, offer great potential for cost savings and sustainable energy. The overall results reported in the literature clarify the weaknesses and challenges faced with each membrane category. Dense polymeric membranes and mixed matrix membranes usually require the application of highpressure difference due to the high mass transfer resistance of their structures. Mixed matrix membranes also suffer from poor distribution of nanoparticles in the polymeric matrix and phase separation caused by incompatibility between the inorganic and organic phases. Supported ionic liquid membranes suffer mainly from the penetration of ionic liquids through the membrane support pore at high pressures. Hence, further development needs to be done for such types of membranes to become efficient in large-scale CO2 separation applications. Based on the mentioned challenges and limitations, outlook directions are set as follow:



Figure 7.32 Comparison of CO2/N2 separation properties of membranes in the literature.

Figure 7.33 Comparison of CO2/CH4 separation properties of membranes in the literature. 1. Most of the reported studies were not conducted under industrial conditions. For example, most of these studies were conducted using pure gas feed at low pressures and temperatures. Therefore, these membranes should be fabricated and tested under rigorous environment and conditions (e.g., mixed gas, high pressures and temperatures) to evaluate their stability and ability in industrial applications (e.g., flue gas and natural gas treatment).


2. Highly selective membranes with high CO2 permeability are required so that they can process large volumes of feed streams. 3. In parallel with the experimental search for high efficient membrane materials, additives and fillers, studies on molecular dynamics would lead to better insight into CO2 separation processes and could help in developing engineered molecular structures with high CO2 permeability and separation selectivity. 4. Studies on the effects of filler geometry, size, pore structure, and the polymer-particle interface would result in highly efficient MMMs. This might also help in eliminating the inorganic-organic phase separation problem, hence developing highly CO2 permeable MMMs. 5. The porosity of support membranes in SILMs technology is considered the main reason of SILMs failure at high pressures due to ionic liquids loss through the pores. It is essential to give attention to support these ionic liquids inside a dense polymeric matrix by direct mixing method. This would eliminate or reduce the loss of ionic liquids and combine the separation efficiency of both dense membranes and ionic liquids. 6. Intensive studies on membrane aging, plasticization, and conditioning are recommended.

Abbreviations


[bmim] 1-butyl-3-methylimidazolium bis(perfluoroethyl(suflonyl))imide [BETI] [bmim][PF6] 1-butyl-3-methylimidazolium hexafluorophosphate [bmim] [Tf2N]

1-butyl-3-methyimidazolium bis(trifluoromethanesulfonyl)imide

[C2mim] [B(CN)4]

1-ethyl-3-methylimidazolium tetracyanoborate

[C4mim] [B(CN)4]

1-butyl-3-methylimidazolium tetracyanoborate

[C4mim] [BF4]

1-butyl-3-methylimidazolium tetrafluoroborate

[C4mim] [SCN] [C6mim] [Tf2N]

1-n-butyl-3-methylimidazolium thiocyanate

[C6mim]

1-hexyl-3-methylimidazolium tetrafluoroborate

1-hexyl-3-methyimidazolium bis((trifluoromethyl) sulfonyl)imide


[BF4] [C8mim] [PF6]

1-octyl-3-methylimidazolium hexafluorophosphate

[emim][BF4] 1-ethyl-3-methylimidazolium tetrafluoroborate [emim][dca] 1-ethyl-3-methyimidazolium dicyanamide [emim] [Tf2N]

1-ethyl-3-methyimidazolium bis(trifluoromethanesulfonyl)imide

[emim] [CF3SO3]

1-Ethyl-3-methylimidazolium triflate

[emim] [CF3SO3]

1-Ethyl-3-methylimidazolium trifluoromethanesulfone

[EMIM] [Tf2N]

1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

[emmim] [B(CN)4]

1-ethyl-2,3-dimethylimidazolium tetracyanoborate

[MnFHim] [NTf2]

1-methyl-3-(3,3,4,4,5,5,6,6,6-nonafluorohexyl)-imidazolium bis(trifluoromethane)sulfonimide

[MpFHim] [NTf2]

1-methyl-3-(3,3,4,4,4-pentafluorohexyl)-imidazolium bis(trifluoromethane)sulfonimide

[MtdFHim] [NTf2]

1-methyl-3-(3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorohexyl)-imidazolium bis(trifluoromethane)sulfonimide


[SEt3][NTf2] triethylsulfonium bis(trifluoromethylsulfonyl) imide [SMIM] [Tf2N]

1-styrenemethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

[thtdp][Cl] [VHIM] [Tf2N]

trihexyltetradecylphosphonium chloride 1-vinyl-3-hexylimidazolium bis(trifluoromethylsulfonyl)imide

[VMIM] [Tf2N]

1-vinyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide

1,3-ADM PSF 1,5-NPSF 2,2-ADM PSF

1,3-(4-hydroxyphenyl) adamantine-polysulfone 1,5-dihydroxynaphtalene 2,2-(4-hydroxyphenyl) adamantane-polysulfone



2,6-NPSF 2,7-NPSF

2,6-dihydroxynaphtalene 2,7-dihydroxynaphtalene

6F 6FDA BIPSF BPSF

2,2-bis(4-carboxyphenyl) hexafluoropropane 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane 4,4’-biphenol-polysulfone bromobisphenol A polysultbne

BTDA CA CANs CS Cyphos 102 Cyphos 103 Cyphos 104 DAM DAP DAR DMPSF DMPSF-Z DSDA Ecoeng™ 1111P Fe(BTC) HFPSF HZSs ILs IMM IRMOF-1 MMMs MOFs mPDA MSSs N6

3,3 ‘,4,4’-benzophenone tetracarboxylic dianhydride cellulose acetate carboxylic acid nanogels chitosan trihexyltetradecylphosphonium bromide trihexyltetradecylphosphonium decanoate trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate 2,4,6-trimethyl-1,3-diaminobenzene diaminophenol diamino resorcinol dimethyl bisphenol A polysulphone dimethyl bisphenol Z polysulphone 3,3 ‘,4,4’-diphenylsulfone tetracarboxylic dianhydride 1,3-dimethylimidazolium dimethylphosphate

ODA

4,4’-oxydianiline

iron benzene-1,3,5-tricarboxylate hexafluorobisphenol A polysulphone hollow silicalite-1 spheres ionic liquids bis(4-amino-3-isopropyl-5-methylphenyl)methane metal–organic frameworks mixed matrix membranes metal organic frameworks m-phenylene diamine mesoporous silica spheres Nylon 6



ODPA

4,4’-oxydiphthalic anhydride

PANI PBI PC PDMS PE

polyaniline polybenzimidazole poly(carbonate) poly(dimethyl siloxane) poly(ethylene)

Pebax PEG PEI

poly ether-block-amide polyethylene glycol polyetherimide

PEO PES PI PIM-1 PMDA PMMA PP PPI PPO PS PSF-F PSF-O PTFE PTMEG PU PVAc PVAm PVDF RTILs SADAF SAN SAPO-34 SILMs SSZ-13

poly(ethylene oxide) polyethersulfone polyimide polymer of intrinsic microporosity pyromellitic dianhydride poly(methyl methacrylate) poly(propylene) porous polyimide filler poly(phenylene oxide) poly(styrene) bisphenol F polysulphone bisphenol O polysulphone polytetrafluoroethylene poly(tetramethylene ether) glycol poly(urethane) poly(vinyl acetate) poly(vinylamine) polyvinylidene fluoride room temperature ionic liquids spiro-(adamantane-2,9’(2’,7’-diamino)-fluorene) poly(styrene-acrylonitrile) commercial zeolite particles supported ionic liquid membranes commercial zeolite particles


TAB TMBIPSF

1,2,4,5-tetraaminobenzene tetrahydrochloride tetramethylbiphenol-polysulphone

TMHFPSF TMPSF TMPSF-F

tetramethylhexafluorobisphenol A polysulphone tetramethyl bisphenol A polysulphone tetramethylbisphenol F polysulphone

Ultem® (PEI) polyetherimide ZIFZMOF

commercial imidazole framework zeolitic metal–organic frameworks

References 1. C. Stewart, M.A. Hessami, A study of methods of carbon dioxide capture and sequestration —the sustainability of a photosynthetic bioreactor approach. Energ. Convers. Manage., 46(3), 403–420, 2005. 2. E. Drioli, M. Romano, Progress and new perspectives on integrated membrane operations for sustainable industrial growth. Ind. Eng. Chem. Res., 40(5), 1277–1300, 2001. 3. S. Wong, R. Bioletti, Carbon dioxide separation technologies. Alberta Research Council, 2002. 4. E. Favre, Carbon dioxide recovery from post-combustion processes: Can gas permeation membranes compete with absorption?. J. Membr. Sci., 294(1–2), 50–59, 2007.


5. R.W. Baker, Reviews—Future directions of membrane gas separation technology. Ind. Eng. Chem. Res., 41(6), 1393–1411, 2002. 6. K.A. Berchtold, et al., Novel polymeric-metallic composite membranes for CO2 separations at elevated temperatures. Presented at Fifth Annual Conference on Carbon Capture & Sequestration, Alexandria, Virginia, 2006. 7. M. Hasib-ur-Rahman, M. Siaj, F. Larachi, Review: Ionic liquids for CO2 capture— Development and progress. Chem. Eng. Process., 49(4), 313–322, 2010. 8. D. Wappel, G. Gronald, R. Kalb, J. Draxler, Ionic liquids for post-combustion CO2 absorption. Int. J. Greenhouse Gas Control, 4(3), 486–494, 2010. 9. P. Bernardo, E. Drioli, G. Golemme, Membrane gas separation: A review: State of the art. Ind. Eng. Chem. Res., 48, 4638–4663, 2009. 10. S. Kentish, Investigating viable CO2 capture and separation options. Presented at Towards Zero Emissions, National Conference, Brisbane, Queensland/Australia, 2003. 11. J. Zou, W.S.W. Ho, CO2-selective polymeric membranes containing amines in crosslinked polyvinyl alcohol. J. Membr. Sci., 286(1–2), 310–321, 2006. P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

12. W.J. Koros, R. Mahajan, Pushing the limits on possibilities for large scale gas separation: Which strategies?. J. Membr. Sci., 175(2), 181–196, 2000. 13. M. Freemantle, Membranes for gas separation. C&EN, 83(40), 49–57, 2005. 14. R. Bredesen, K. Jordal, O. Bolland, High-temperature membranes in power generation with CO2 capture. Chem. Eng. Process., 43(9), 1129–1158, 2004. 15. O. Falk-Pedersen, H. Dannström, Separation of CO2 from offshore gas turbine exhaust. Energy Convers. Manage., 38, 81–86, 1997. 16. J. Davison, P. Freund, A. Smith, Putting carbon back into the ground. Report by IEA Greenhouse Gas R&D Programme: Cheltenham, Gloucestershire, pp. 1–28, 2001. 17. M. Gupta, I. Coyle, K. Thambimuthu, CO2 capture technologies and opportunities in Canada, in: 1st Canadian CC&S Technology Roadmap Workshop. Calgary, Alberta, 2003. 18. G.H. Koops, Nomenclature and Symbols in Membrane Science and Technology. Enschede, The Netherlands: European Society of Membrane Science and Technology (EMS), 1995. 19. A.F. Ismail, K.C. Khulbe, T. Matsuura, Gas Separation Membranes: Polymeric and Inorganic, Springer International Publishing, 2015. 20. D.R. Paul, Fundamentals of transport phenomena in polymer membranes, in: Comprehensive Membrane Science and Engineering, E. Drioli, L. Giorno (Eds.), book 1, pp. 75–90, Elsevier: Oxford. 2010.


21. K. Nagai, Fundamentals and perspectives for pervaporation, in: Comprehensive Membrane Science and Engineering, E. Drioli, L. Giorno (Eds), book 2, pp. 243–271, Elsevier: Oxford, 2010. 22. J.G. Wijmans, R.W. Baker, The solution-diffusion model: A review. J. Membr. Sci., 107(1–2), 1–21, 1995. 23. M.D. Jensen, et al., Carbon separation and capture. Report prepared for Plains CO2 Reduction (PCOR) Partnership: North Dakota, pp. 1–27, 2005. 24. A.L. Khan, S. Basu, A. Cano-Odena, I.F.J. Vankelecom, Novel high throughput equipment for membrane-based gas separations. J. Membr. Sci., 354(1–2), 32–39, 2010. 25. C.E. Powell, G.G. Qiao, Polymeric CO2/N2 gas separation membranes for the capture of carbon dioxide from power plant flue gases. J. Membr. Sci., 279(1–2), 1–49, 2006. 26. H. Lin, M. Yavari, Upper bound of polymeric membranes for mixed-gas CO2/CH4 separations. J. Membr. Sci., 475, 101–109, 2015. 27. Y. Zhang, J. Sunarso, S. Liu, R. Wang, Current status and development of membranes for CO2/CH4 separation: A review. Int. J. Greenhouse Gas Control, 12, 84–107, 2013. 28. L.M. Robeson, The upper bound revisited. J. Membr. Sci., 320, 390–400, 2008. P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

29. L.M. Robeson, Correlation of separation factor versus permeability for polymeric membranes. J. Membr. Sci., 62(2), 165–185, 1991. 30. R.W. Baker, Membrane Technology and Applications, 2nd ed., Wiley, 2004. 31. S.P. Nunes, K.V. Peinemann (Eds.), Membrane Technology in the Chemical Industry, 354 pp., Weinheim; New York: Wiley-VCH, 2006. 32. H. Lin, B.D. Freeman, Gas solubility, diffusivity and permeability in poly(ethylene oxide). J. Membr. Sci., 239(1), 105–117, 2004. 33. J.M. Mohr, D.R. Paul, Effect of casting solvent on the permeability of poly(4-methyl-1pentene). Polymer, 32(7), 1236–1243, 1991. 34. B. Ghalei, M.A. Semsarzadeh, A novel nano structured blend membrane for gas separation. Macromol. Symp., 249–250(1), 330–335, 2007. 35. L.M. Robeson, Polymer membranes for gas separation. Curr. Opin. Solid St. M., 4(6), 549–552, 1999. 36. B.J. Koops, C.H. Lüthy, A. Nelis, C. Sieburgh, J.P.M. Jansen, M.S. Schmid (Eds.), Engineering the Human: Human Enhancement between Fiction and Fascination. p. 1 online resource (198 pp.), Springer-Verlag: Berlin; New York, 2013. 37. P.S. Tin, T.S. Chung, Y. Liu, R. Wang, S.L. Liu, K.P. Pramoda, Effects of crosslinking modification on gas separation performance of Matrimid membranes. J. Membr. Sci., 225(1– 2), 77–90, 2003.


38. A.E. Amooghin, M. Omidkhah, H. Sanaeepur, A. Kargari, Preparation and characterization of Ag+ ion-exchanged zeolite-Matrimid®5218 mixed matrix membrane for CO2/CH4 separation. J. Energy Chem., 2016. 39. N. Alaslai, B. Ghanem, F. Alghunaimi, E. Litwiller, I. Pinnau, Pure- and mixed-gas permeation properties of highly selective and plasticization resistant hydroxyl-diamine-based 6FDA polyimides for CO2/CH4 separation. J. Membr. Sci., 505, 100–107, 2016. 40. D. Plaza-Lozano, et al., New aromatic polyamides and polyimides having an adamantane bulky group. Mater. Today Commun., 5, 23–31, 2015. 41. X. Chen, D. Rodrigue, S. Kaliaguine, Diamino-organosilicone APTMDS: A new crosslinking agent for polyimides membranes. Sep. Purif. Technol., 86, 221–233, 2012. 42. W. Qiu, L. Xu, C.C. Chen, D.R. Paul, W.J. Koros, Gas separation performance of 6FDAbased polyimides with different chemical structures. Polymer, 54(22), 6226–6235, 2013. 43. M.D. Guiver, et al., Structural characterization and gas-transport properties of brominated matrimid polyimide. J. Polym. Sci. A: Polym. Chem., 40(23), 4193–4204, 2002. 44. M. Loloei, M. Omidkhah, A. Moghadassi, A.E. Amooghin, Preparation and characterization of Matrimid® 5218 based binary and ternary mixed matrix membranes for CO2 separation. Int. J. Greenhouse Gas Control, 39, 225–235, 2015.


45. Y. Mi, T. Hirose, Molecular design of high-performance polyimide membranes for gas separations. J. Polym. Res., 3(1), 11–19, 1996. 46. H. Julian, I.G. Wenten, Polysulfone membranes for CO2/CH4 separation: State of the art. IOSR J. Eng., 2(3), 484–495, 2012. 47. M. Mulder, Basic Principles of Membrane Technology, 2nd ed., 564 pp., Dordrecht; Boston: Kluwer Academic, 1996. 48. J.S. McHattie, W.J. Koros, D.R. Paul, Gas-Transport properties of polysulfones: 1. Role of symmetry of methyl-group placement on bisphenol rings. Polymer, 32(5), 840–850, 1991. 49. J.S. McHattie, W.J. Koros, D.R. Paul, Gas transport properties of polysulphones: 2. Effect of bisphenol connector groups. Polymer, 32(14), 2618–2625, 1991. 50. J.S. McHattie, W.J. Koros, D.R. Paul, Gas transport properties of polysulphones: 3. Comparison of tetramethyl-substituted bisphenols. Polymer, 33(8), 1701–1711, 1992. 51. C.L. Aitken, W.J. Koros, D.R. Paul, Effect of structural symmetry on gas transport properties of polysulfones. Macromolecules, 25(13), 3424–3434, 1992. 52. C.L. Aitken, W.J. Koros, D.R. Paul, Gas transport properties of biphenol polysulfones. Macromolecules, 25(14), 3651–3658, 1992. 53. M.R. Pixton, D.R. Paul, Gas transport properties of adamantane-based polysulfones. Polymer, 36(16), 3165–3172, 1995. 54. C.L. Aitkin, D.R. Paul, Gas transport properties of polysulfones based on dihydroxynaphthalene isomers. J. Polym. Sci. B: Polym. Phys., 31(8), 1061–1065, 1993.


55. H.J. Kim, S.I. Hong, The transport properties of CO2 and CH4 for brominated polysulfone membrane. Korean J.Chem. Eng., 16(3), 343–350, 1999. 56. H.J. Kim, S.I. Hong, The sorption and permeation of CO2 and CH4 for dimethylated polysulfone membrane. Korean J. Chem. Eng., 14(3), 168–174, 1997. 57. X.Y. Guo, et al., Mixed matrix membranes incorporated with amine-functionalized titanium-based metal-organic framework for CO2/CH4 separation. J. Membr. Sci., 478, 130– 139, 2015. 58. C.A. Scholes, G.Q. Chen, G.W. Stevens, S.E. Kentish, Nitric oxide and carbon monoxide permeation through glassy polymeric membranes for carbon dioxide separation. Chem. Eng. Res. Des., 89(9), 1730–1736, 2011. 59. D.R. Paul, Control of phase structure in polymer blends, in: Functional Polymers, D.E. Bergbreiter, C.R. Martin (Eds.), pp. 1–18, Springer US: Boston, MA, 1989. 60. V. Giel, et al., Polyaniline/polybenzimidazole blends: Characterisation of its physicochemical properties and gas separation behaviour. Eur. Polym. J., 77, 98–113, 2016. 61. X. Mei Wu, et al., Towards enhanced CO2 selectivity of the PIM-1 membrane by blending P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

with polyethylene glycol. J. Membr. Sci., 493, 147–155, 2015. 62. Y. Liu, et al., High permeability hydrogel membranes of chitosan/poly ether-block-amide blends for CO2 separation. J. Membr. Sci., 469, 198–208, 2014. 63. W.F. Yong, et al., Molecular engineering of PIM-1/Matrimid blend membranes for gas separation. J. Membr. Sci., 407–408, 47–57, 2012. 64. S. Rafiq, Z. Man, A. Maulud, N. Muhammad, S. Maitra, Separation of CO2 from CH4 using polysulfone/polyimide silica nanocomposite membranes. Sep. Purif. Technol., 90, 162–172, 2012. 65. R.L. Burns, W.J. Koros, Structure-property relationships for poly(pyrroloneimide) gas separation membranes. Macromolecules, 36(7), 2374–2381, 2003. 66. C. Yi, Z. Wang, M. Li, J. Wang, S. Wang, Facilitated transport of CO2 through polyvinylamine/polyethlene glycol blend membranes. Desalination, 193(1–3), 90–96, 2006. 67. H. Rabiee, A. Ghadimi, S. Abbasi, T. Mohammadi, CO2 separation performance of poly(ether-b-amide6)/PTMEG blended membranes: Permeation and sorption properties. Chem. Eng. Res. Des., 98, 96–106, 2015. 68. H.B. Tanh Jeazet, C. Staudt, C. Janiak, Metal-organic frameworks in mixed-matrix membranes for gas separation. Dalton Trans., 41(46), 14003–14027, 2012. 69. D. Shekhawat, D.R. Luebke, H.W. Pennline, A review of carbon dioxide selective membranes: A topical report. National Energy Technology Laboratory, United States Department of Energy, 2003.


70. C.A. Scholes, S.E. Kentish, G.W. Stevens, Carbon dioxide separation through polymeric membrane systems for flue gas applications. Recent Patents on Chemical Engineering, 1(2), 52, 2008. 71. Q. Hu, et al., Poly(amide-imide)/TiO2 nano-composite gas separation membranes: Fabrication and characterization. J. Membr. Sci., 135(1), 65–79, 1997. 72. P. Bernardo, E. Drioli, G. Golemme, Membrane gas separation: A review/state of the art. Ind. Eng. Chem. Res., 48(10), 4638–4663, 2009. 73. T. Li, Y. Pan, K.V. Peinemann, Z. Lai, Carbon dioxide selective mixed matrix composite membrane containing ZIF-7 nano-fillers. J. Membr. Sci., 425–426, 235–242, 2013. 74. X. Li, et al., High-performance composite membranes incorporated with carboxylic acid nanogels for CO2 separation. J. Membr. Sci., 495, 72–80, 2015. 75. H. Sanaeepur, A. Kargari, B. Nasernejad, A. Ebadi Amooghin, M. Omidkhahd, A novel Co2+ exchanged zeolite Y/cellulose acetate mixed matrix membrane for CO2/N2 separation. J. Taiwan Inst. Chem. E., 60, 403–413, 2016. 76. A. Jomekian, R.M. Behbahani, T. Mohammadi, A. Kargari, CO2/CH4 separation by high P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

performance co-casted ZIF-8/Pebax 1657/PES mixed matrix membrane. J. Nat. Gas Sci. Eng., 31, 562–574, 2016. 77. Z.V. Singh, et al., Determination and optimization of factors affecting CO2/ CH4 separation performance in poly(ionic liquid)-ionic liquid-zeolite mixed-matrix membranes. J. Membr. Sci., 509, 149–155, 2016. 78. E.R. Rangel, E.M. Maya, F. Sanchez, J. de Abajo, J.G. de la Campa, Gas separation properties of mixed-matrix membranes containing porous polyimides fillers. J. Membr. Sci., 447, 403–412, 2013. 79. B. Zornoza, C. Tellez, J. Coronas, Mixed matrix membranes comprising glassy polymers and dispersed mesoporous silica spheres for gas separation. J. Membr. Sci., 368(1–2), 100– 109, 2011. 80. B. Zornoza, O. Esekhile, W.J. Koros, C. Téllez, J. Coronas, Hollow silicalite-1 spherepolymer mixed matrix membranes for gas separation. Sep. Purif. Technol., 77(1), 137–145, 2011. 81. B. Zornoza, et al., Functionalized flexible MOFs as fillers in mixed matrix membranes for highly selective separation of CO2 from CH4 at elevated pressures. Chem. Commun., 47(33), 9522–9524, 2011. 82. T. Rodenas, M. van Dalen, P. Serra-Crespo, F. Kapteijn, J. Gascon, Mixed matrix membranes based on NH2-functionalized MIL-type MOFs: Influence of structural and operational parameters on the CO2/CH4 separation performance. Micropor. Mesopor. Mater., 192, 35–42, 2014.


83. M. Waqas Anjum, B. Bueken, D. De Vos, I.F.J. Vankelecom., MIL-125(Ti) based mixed matrix membranes for CO2 separation from CH4 and N2. J. Membr. Sci., 502, 21–28, 2016. 84. J. Ahn, W.J. Chung, I. Pinnau, M.D. Guiver, Polysulfone/silica nanoparticle mixed-matrix membranes for gas separation. J. Membr. Sci., 314(1–2), 123–133, 2008. 85. S. Shahid, K. Nijmeijer, High pressure gas separation performance of mixed-matrix polymer membranes containing mesoporous Fe(BTC). J. Membr. Sci., 459, 33–44, 2014. 86. S. Japip, H. Wang, Y. Xiao, T.-S. Chung, Highly permeable zeolitic imidazolate framework (ZIF)-71 nano-particles enhanced polyimide membranes for gas separation. J. Membr. Sci., 467, 162–174, 2014. 87. S. Basu, A. Cano-Odena, I.F.J. Vankelecom, MOF-containing mixed-matrix membranes for CO2/CH4 and CO2/N2 binary gas mixture separations. Sep. Purif. Technol., 81(1), 31–40, 2011. 88. Y. Dai, J.R. Johnson, O. Karvan, D.S. Sholl, W.J. Koros, Ultem®/ZIF-8 mixed matrix hollow fiber membranes for CO2/N2 separations. J. Membr. Sci., 401–402, 76–82, 2012. 89. J. Hu, et al., Mixed-matrix membrane hollow fibers of Cu3(BTC)2 MOF and polyimide P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

for gas separation and adsorption. Ind. Eng. Chem. Res., 49(24), 12605–12612, 2010. 90. S. Husain, W.J. Koros, Mixed matrix hollow fiber membranes made with modified HSSZ13 zeolite in polyetherimide polymer matrix for gas separation. J. Membr. Sci., 288(1–2), 195–207, 2007. 91. F. Endres, D. MacFarlane, A. Abbott (Eds.), Electrodeposition from Ionic Liquids, p. 1, Wiley-VCH: Weinheim., 2008. 92. M.N. Koel (Ed.), Ionic Liquids in Chemical Analysis, 414 pp., Analytical chemistry series, Boca Raton: CRC Press, 2009. 93. L.C. Branco, J.G. Crespo, C.A. Afonso, Highly selective transport of organic compounds by using supported liquid membranes based on ionic liquids. Angew. Chem. Int. Ed. Engl., 41(15), 2771–2773, 2002. 94. F.J. Hernández-Fernández, et al., A novel application of supported liquid membranes based on ionic liquids to the selective simultaneous separation of the substrates and products of a transesterification reaction. J. Membr. Sci., 293(1–2), 73–80, 2007. 95. M. Matsumoto, Y. Inomoto, K. Kondo, Selective separation of aromatic hydrocarbons through supported liquid membranes based on ionic liquids. J. Membr. Sci., 246(1), 77–81, 2005. 96. R. Sheldon, Catalytic reactions in ionic liquids. Chem. Commun. (Camb.), 2001(23), 2399–2407, 2001. 97. S.A. Forsyth, J.M. Pringle, D.R. MacFarlane, Ionic liquids—An overview. Aust. J. Chem., 57(2), 113–119, 2004.


98. J. Huang, T. Rüther, Why are ionic liquids attractive for CO2 absorption? An overview. Aust. J. Chem., 62, 298–308, 2009. 99. N. MacDowell, et al., An overview of CO2 capture technologies. Energ. Environ. Sci., 3, 1645–1669, 2010. 100. P. Cserjési, K. Bélafi-Bakó, Application of ionic liquids in membrane separation processes, in: Ionic Liquids: Applications and Perspectives, A. Kokorin (Ed.), InTech, 2011. 101. P. Cserjési, N. Nemestóthy, K. Bélafi-Bakó, Gas separation properties of supported liquid membranes prepared with unconventional ionic liquids. J. Membr. Sci., 349(1–2), 6–11, 2010. 102. J.E. Bara, et al., Gas separations in fluoroalkyl-functionalized room-temperature ionic liquids using supported liquid membranes. Chem. Eng. J., 147(1), 43–50, 2009. 103. L.A. Neves, J.G. Crespo, I.M. Coelhoso, Gas permeation studies in supported ionic liquid membranes. J. Membr. Sci., 357(1–2), 160–170, 2010. 104. P. Scovazzo, D. Havard, M. McShea, S. Mixon, D. Morgan, Long-term, continuous mixedgas dry fed CO2/CH4 and CO2/N2 separation performance and selectivities for room P.M., V. Y. L. N. O. (2016). Nanostructured Polymer Membranes, Processing and Characterization. Somerset: John Wiley & Sons, Incorporated. Retrieved from http://www.ebrary.com Created from qataru-ebooks on 2017-02-13 02:51:26.

temperature ionic liquid membranes. J. Membr. Sci., 327(1–2), 41–48, 2009. 105. S.D. Hojniak, et al., Separation of carbon dioxide from nitrogen or methane by supported ionic liquid membranes (SILMs): Influence of the cation charge of the ionic liquid. J. Phys. Chem. B, 117(48), 15131–15140, 2013. 106. P. Scovazzo, et al., Gas separations using non-hexafluorophosphate [PF6]– anion supported ionic liquid membranes. J. Membr. Sci., 238(1–2), 57–63, 2004. 107. Y.Y. Jiang, et al., SO2 gas separation using supported ionic liquid membranes. J. Phys. Chem. B, 111(19), 5058–5061, 2007. 108. K.M. Gupta, Y. Chen, J. Jiang, Ionic liquid membranes supported by hydrophobic and hydrophilic metal-organic frameworks for CO2 capture. J. Phys. Chem. C, 117(11), 5792– 5799, 2013. 109. K.M. Gupta, Y. Chen, Z. Hu, J. Jiang, Metal-organic framework supported ionic liquid membranes for CO2 capture: Anion effects. Phys. Chem. Chem. Phys., 14(16), 5785–5794, 2012. 110. S.M. Mahurin, P.C. Hillesheim, J.S. Yeary, D.E. Jiang, S. Dai, High CO2 solubility, permeability and selectivity in ionic liquids with the tetracyanoborate anion. RSC Adv., 2(31), 11813–11819, 2012. 111. L.C. Tomé, C. Florindo, C.S. Freire, L.P. Rebelo, I.M. Marrucho, Playing with ionic liquid mixtures to design engineered CO2 separation membranes. Phys. Chem. Chem. Phys., 16(32), 17172–17182, 2014.


112. S.M. Mahurin, J. Lee, G.A. Baker, H. Luo, S. Dai, Performance of nitrilecontaining anions in task-specific ionic liquids for improved CO2/N2 separation. J. Membr. Sci., 353(1–2), 177– 183, 2010. 113. J.J. Close, K. Farmer, S.S. Moganty, R.E. Baltus, CO2/N2 separations using nanoporous alumina-supported ionic liquid membranes: Effect of the support on separation performance. J. Membr. Sci., 390–391, 201–210, 2012. 114. P. Jindaratsamee, A. Ito, S. Komuro, Y. Shimoyama, Separation of CO2 from the CO2/N2 mixed gas through ionic liquid membranes at the high feed concentration. J. Membr. Sci., 423– 424, 27–32, 2012. 115. F.J. Hernández-Fernández, A.P. De los Ríos, F. Tomás-Alonso, J.M. Palacios, G. Víllora, Preparation of supported ionic liquid membranes: Influence of the ionic liquid immobilization method on their operational stability. J. Membr. Sci., 341(1–2), 172–177, 2009. 116. W. Zhao, et al., Membrane liquid loss mechanism of supported ionic liquid membrane for gas separation. J. Membr. Sci., 411–412, 73–80, 2012.
