Separation and Purification Technology 161 (2016) 53–60
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Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur
Copoly(alkyl ether imide) membranes as promising candidates for CO2 capture applications Mohamed Krea a,⇑, Denis Roizard b, Eric Favre b a b
Laboratoire Matériaux et Environnement, Université de MEDEA, 26000, Algeria LRGP, CNRS, Université de Lorraine, ENSIC, 1 rue Grandville, 54001 Nancy, France
a r t i c l e
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Article history: Received 7 November 2015 Received in revised form 28 January 2016 Accepted 29 January 2016 Available online 29 January 2016 Keywords: Rubbery polyetherimide Permeability High CO2 selective membranes Gas separation
a b s t r a c t To improve gas separation properties of membranes, the current research trend is to design mixed matrix membranes using various types of nanoparticles. But to be efficient, such particles must be used with already highly selective (a > 40), highly permeable polymeric matrixes (P > 100 Barrer). In that context, we report the results obtained with a series of copolyetherimide polymers (PEI). This polyimide series has two main advantages: it exhibits a high CO2 selectivity associated to a rubbery copolymer. Thus it has the basic requirements to be a good polymer matrix for the preparation of mixed matrix membrane. This new series was prepared with different types of polyoxyether blocks (PEO) using several aromatic monomers and diamines containing polyethyloxide and polypropyloxide moieties. Permeability measurements showed that the membranes with an ether content of 80% exhibited permeabilities of 622 and 14 Barrer for CO2 and N2, respectively, giving rise to a high ideal selectivity of CO2 over N2 (a = 44). The introduction of the propyl side groups in PEI led to linear increases in the permeability when the PEO content was increased. This trend was observed because the presence of propyl groups prevents the crystallization of PEO chains, as often reported in the literature for PEO-based membranes. Ó 2016 Elsevier B.V. All rights reserved.
1. Introduction Membrane-based gaseous separation is a green technology with the potential to improve the economics of natural gas upgrading [1], syngas processing, flue gas rectification, and biomedical practices as well as the separation of greenhouse gases from flue gases [2,3]. The preparation of membranes with superior performance requires overcoming numerous challenges, such as simultaneously achieving the high selectivity and high permeability required for competitive gas separation processes in many applications involving gas separations, such as in natural gas treatment [4–6]. Ideally, the membranes should also exhibit chemical and physical resistance, excellent damage tolerance and durability under various operating conditions, and an absence of defects, and the potential to form flexible membranes is desirable. Thus, developing new membranes with selectivity and useful physical properties is a very active research topic. Various routes are under investigation, from the design of new polymers, such as polymers with intrinsic microporosity (PIMs) [7], to the selection of enhanced selective particles, such as metal organic frameworks (MOFs) [8,9], to the use of mixed ⇑ Corresponding author. E-mail address:
[email protected] (M. Krea). http://dx.doi.org/10.1016/j.seppur.2016.01.045 1383-5866/Ó 2016 Elsevier B.V. All rights reserved.
matrix membranes (MMMs) for the preparation of inorganic membranes, such as carbon membranes or ceramic membranes [10]. Over the past ten years, the possibility of using membranes to capture CO2 from pre-combustion and post-combustion has been examined by numerous teams. In the latter case, the application of membrane technology to capture CO2 from flue gas emitted by power plants is a promising and economical technical answer to reducing anthropogenic CO2 emissions and thus their greenhouse gas effect [11]. Indeed, most CO2 release is produced in postcombustion industrial plants, where the largest contributor to the overall cost is the cost of CO2 capture [12,1]. Although amine absorption methods are [13] currently used at the industrial scale to upgrade natural gas, many studies have shown that this method cannot be viably used to capture CO2 in post-combustion. This is due to the high energetic penalty, i.e., 3 to 3.5 MJ/ton CO2, for large power plants, where CO2 is just a waste with no added value [12]. Compared to membrane technology, these absorption methods also feature several disadvantages, such as the need for solvent regeneration; high solvent volatility, which induces some solvent loss; partial oxidation of the solvent; and the huge space requirements of the absorption columns. For the reasons presented above, gas permeation can be considered a real potential alternative in CO2 capture processes, and CO2 capture is a promising target for the future membrane market [14–
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16]. In fact, the membrane separation process has the advantage of being a continuous, flexible process with a fairly high separation energy efficiency (20 < aideal < 120). In addition, the use of hollow fiber modules can give rise to a significant decrease in the absorber size because hollow fiber modules are known to provide a much higher specific area than conventional absorbers. Indeed, size intensification is very important for CO2 capture given the high flow rates involved in post-combustion (e.g., 500 m/s) [17]. Published works [18] have shown that, for post-combustion flue gas where flue streams are composed of at least 20% CO2, singlestage membrane technology will be a promising technique for carbon dioxide capture from an energetic perspective if the membrane selectivity is at least 40 [19,20]. Furthermore, Merkel et al. have recently reported that two stages of the membrane system can also be cost effective for flue gas with a lower concentration of CO2 (13%) and when using membranes with CO2 permeances greater than 1000 GPU and a CO2/N2 selectivity of 50 at 30 °C [11]. These results reinforce the need to develop new materials for CO2 capture and separation. Table 1 reports the CO2/N2 permselectivities of some polymers and copolymers published between 2002 and 2015 [21–38]. Therefore, to obtain novel tailored materials with tuned superior properties and characteristics for CO2/N2 separations, two promising approaches based on nanostructure modeling have been followed: – The first approach involves the incorporation of highly selective particles, such as molecular sieves or, more recently, metal organic frameworks, within a polymeric matrix, resulting in a hybrid membrane material with superior selectivity over that of the pristine polymer matrix [39–41]. Although some of these materials have shown good permselectivity properties, due to increasing diffusion properties, their defect-free preparation generally remains difficult. The small size difference between CO2 and N2 molecules poses a challenge in this approach. – The second approach for obtaining enhanced CO2 selective polymer involves the synthesis of a new polymer backbone composed of hard and soft building blocks, where the soft block is chosen to induce a high affinity toward CO2. The structural choice of the CO2 selective blocks is made by analogy with the higher solubility of CO2 in some solvents, especially polar solvents, which exhibit high CO2 affinity due to dipole–quadrupole interactions [42,43]. Therefore, this approach utilizes specific monomers to introduce polar moieties into polymer backbones
Table 1 Literature overview of CO2 permeability and CO2/N2 membrane material separation. Membranes
Permeability of CO2 (Barrer)
Selectivity CO2/N2
Refs.
Cellulose Polyimide Polyimide cardo Polyimide silicate Matrimide mixed Matrimide carbonized Polyimide 6FDA Copolyimide 6FDA PDMS-PEO-UU Modified polyethylene oxide PEO–polyamide Nanohybride organic inorganic Functionalized polyaniline PEO–PBT PEGBEM-g-POEM/MgTiO3 PEGBEM-g-POEM (PVC-g-POEM) Polyetheramine/gelatin blend
127–213 23 7–130 20–100 10–44 43–1250 0.6–18 5–456 1000–3000 95.6 132 300–1950
25–50 21 24–40 15–20 20–30 23–25 120–48 12–22 7–11 6–62.9 61 –
[21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32]
3400 750 138.7 43.8 687.7
