Gas Separation by Mixed Matrix Membranes with Porous Organic Polymer Inclusions within o-Hydroxypolyamides Containing m-Terphenyl Moieties

Abstract

A hydroxypolyamide (HPA) manufactured from 2,2-bis(3-amino-4-hydroxy phenyl)-hexafluoropropane (APAF) diamine and 5′-terbutyl-m-terphenyl-4,4′′-dicarboxylic acid chloride (tBTpCl), and a copolyimide produced by stochiometric copolymerization of APAF and 4,4′-(hexafluoroisopropylidene) diamine (6FpDA), using the same diacid chloride, were obtained and used as polymeric matrixes in mixed matrix membranes (MMMs) loaded with 20% (w/w) of two porous polymer networks (triptycene-isatin, PPN-1, and triptycene-trifluoroacetophenone, PPN-2). These MMMs, and also the thermally rearranged membranes (TR-MMMs) that underwent a thermal treatment process to convert the o-hydroxypolyamide moieties to polybenzoxazole ones, were characterized, and their gas separation properties evaluated for H2, N2, O2, CH4, and CO2. Both TR process and the addition of PPN increased permeability with minor decreases in selectivity for all gases tested. Excellent results were obtained, in terms of the permeability versus selectivity compromise, for H2/CH4 and H2/N2 separations with membranes approaching the 2008 Robeson’s trade-off line. The best gas separation properties were obtained when PPN-2 was used. Finally, gas permeation was characterized in terms of chain intersegmental distance and fraction of free volume of the membrane along with the kinetic diameters of the permeated gases. The intersegmental distance increased after TR and/or the addition of PPN-2. Permeability followed an exponential dependence with free volume and a quadratic function of the kinetic diameter of the gas.

Gas Permeability, Fractional Free Volume and Molecular Kinetic Diameters: The Effect of Thermal Rearrangement on ortho-hydroxy Polyamide Membranes Loaded with a Porous Polymer Network

“…Here, the kinetic diameters given by Breck [29,37] were used. Some data of gas permeabilities shown in Figures 4 and 5 have been previously reported by Soto et al [14,23,24].…”

“…The fraction of trapped free volume seems to be lower for the tBTpCl-APAF matrix than for the 6FCl-APAF one, possibly because tBTpCl-APAF could approach PPN better. Indeed, the lower trapped free volume for the tBTpCl-APAF matrix could be correlated, for example, with its smaller mean chain length, δ c as detected by WAXS [14,23] as shown in Figure 11, where δ (the gas kinetic diameters of the gases used here) and δc are compared with the pore size distribution of PPN as detected by adsorption-desorption isotherms. This could be explained in terms of the better penetration and compatibility of PPN and the tBTpCl-APAF matrix.…”

“…The polymers and MMM membranes synthetized at the SMAP group and tested elsewhere [14,23,24] were used. Key data on the synthesis and manufacture of these polymers and MMMs are given below to contribute to readability.…”

“…Two HPAs, 6FCl-APAF and tBTpCl-APAF, synthetized by the low-temperature polycondensation process with activation of the diamines by in situ silylation [25], whose schemes are shown in Figure 2, were used as a polymeric matrix or continuous phase. In brief, 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane (APAF, CymitQuimica, Barcelona, Spain, CAS #83558-87-6) was mixed with 2,2 -bis(4-carboxy-phenyl)hexafluoropropane diacid chloride (6FCl, synthetized according to Smith et al 2014 [26]) and 5 -tertbutyl-mterphenyl-4,4 -dichloride acid (tBTpCl) synthetized as described in a previous work [23] with stoichiometric ratios in N,N-Dimethylacetamide (DMAC, CymitQuimica, CAS #127-19-5), before the addition at 0 • C of chlorotrimethylsilane (CTMS, CymitQuimica, CAS #75-77-4), anhydrous pyridine (CymitQuimica, CAS #110-86-1) and 4-(Dimethylamino)pyridine (DMAp, CymitQuimica, CAS #1122-58-3), under nitrogen stream overnight.…”

“…Both polymer matrices, the PPN used as filler and all MMMs therefore obtained were properly characterized in previous works [14,23,24].…”