(740f) Amino Acid Ionic Liquids-Based Ion Gel Membranes with Superior Pressure Resistance for CO2 Capture Application

Amino Acid Ionic Liquids-based
Ion Gel Membranes with Superior Pressure Resistance for CO₂ Capture Application

Farhad Moghadam^õ, Eiji
Kamio^õ, Ayumi Yoshizumi^õ and Hideto Matsuyama^õ,*

^õCenter for Membrane and Film Technology,
Department of Chemical Science and Engineering, Kobe University

^* e-mail address: matuyama@kobe-u.ac.jp,
tel.: +81-78-803-6180, fax: +81-78-803-6180

Abstract

Amino acid ionic liquids (AAILs)-based
membranes have been recognized as an attractive alternative to conventional facilitated
transport membranes (FTMs) due to unique properties of AAILs, such as the high
CO₂ absorption capacity, selective reactivity with CO₂,
negligible vapor pressure, high thermal stability, and tunable chemical
structure. The AAILs-based gel membranes as well as supported ionic liquid
membranes previously developed in our group exhibited good CO₂
permeability and CO₂/N₂ selectivity, but the poor
stability under pressurized conditions is a major obstacle to their practical application
[1,2].

Here we present a new class of
AAILs-based ion gel membranes with not only superior CO₂
permeability and CO₂/N₂ selectivity but also excellent
stability under pressurized conditions. The developed AAIL-based gel membranes consisted
of two specific independent interpenetrating polymer networks, so-called
doubel-network (DN) [3]. The DN was composed of two asymmetric polymer
networks of which the first network was a rigid, brittle, and tightly
cross-linked polyelectrolyte and the second network was a soft, ductile and
loosely cross-linked polymer with good compatibility with AAILs. As the solvent
of the DN gels, AAILs composed of phosphonium type cation and prolinate anion
were used because of their excellent CO₂ transport properties [4]. The
mechanical strength of the fabricated AAILs-based DN gel membranes were tested
by compressive and tensile stress-strain measurements, and the DN gels composed
of more than 80wt% AAILs showed more than 25 MPa of compressive and about 0.7
MPa of tensile fracture stresses.

According
to the CO₂ permeation performances of the AAIL-based DN gel
membranes, the DN gels membrane with 85 wt% of AAILs showed remarkable CO₂
permeability of more than 5000 barrer and high CO₂/N₂
selectivity of more than 170 (at 373 K and CO₂ partial pressure 10
kPa). From the trend of the CO₂ and N₂ permeabilities of the
DN gel membranes at different CO₂ partial pressures, we confirmed that
the permeation mechanism of CO₂ and N₂ were facilitated
transport and solution–diffusion mechanisms, respectively. In addition, the pressure
resistance of the DN ion gel membranes containing 85 wt% of AAILs was investigated
by increasing the feed side pressure up to 500 kPa and the stable performance
of membrane were confirmed (Fig.1). Moreover, the DN ion gel membranes exhibited
good durability; the CO₂ permeation performance remained stable more
than 5 days at 500 kPa.

Regarding
the good mechanical strength of AAIL-based DN gels, it was possible to prepare
thin membranes. We fabricated AAIL-based DN gel membranes with different
thicknesses and evaluated the gas permeation mechanisms. From the obtained results,
it was found that CO₂ and N₂ permeances showed reverse
proportional relationship to the DN gel membrane thickness, which clearly demonstrated
that the rate-controlling step of CO₂ and N₂ permeations across
the DN gel membranes were intra-membrane diffusion. In the present stage, the
AAIL-based DN gel membrane with the thinnest thickness (58 mm) showed the CO₂
permeance of ca. 120 GPU and CO₂/N₂ selectivity of ca.
100 under the conditions of T= 373 K
and 10 kPa of the CO₂ partial pressure. However, as the
rate-controlling step of the CO₂ permeation is intra-membrane
diffusion, we could increase the CO₂ permeance by fabricating much
thinner AAIL-based DN gel membranes.

Fig.1. Pressure resistance behavior of
AAILs-based PAMPS/PDMAAm DN ion gel membranes (Experimental conditions: T = 373
K, P_sweep = atmospheric pressure, P_CO2,feed = 10 kPa)

References:

[1] S.
Kasahara, E. Kamio, T. Ishigami and H. Matsuyama,
Chem. Commun., 2012, 48,
6903-6905

[2] S. Kasahara, E. Kamio, A. Yoshizumi
and H. Matsuyama, Chem. Commun., 2014, 50, 2996-2999

[3] J. P. Gong, Y. Katsuyama, T.
Kurokawa and Y. Osada, Adv. Mater.,
2003, 15, 1155-1158

[4] S. Kasahara, E. Kamio, T. Ishigami and H. Matsuyama,
J. Membr. Sci., 2012, 415-416, 168-175