Precise Hydrogen Sieving by Carbon Molecular Sieve Membranes Derived from Solution-Processable Aromatic Polyamides

Abstract

Aromatic polyamides (aramids) are broadly used to manufacture desalination membranes; however, they are rarely considered for gas separation. Here, we report precise hydrogen sieving in ultramicroporous carbon molecular sieve (CMS) membranes derived from an uncrosslinked aramid synthesized by stirred interfacial polymerization of diamine and mixed diacid chloride monomers. While hydrogen bonds gave the aramid precursor unattractive separation performance, they were leveraged to provide aramid-derived CMS membranes with ultrahigh H2/CO2 selectivity exceeding all known CMS membranes. Adsorption in aramid-derived CMS membranes suggested their ultrahigh H2/CO2 selectivity was attributable to diffusion selectivity above 3000. The excellent solution processability of uncrosslinked aramids allowed the fabrication of scalable CMS hollow fiber membranes. The findings of this work open the door to a new class of highly selective CMS membranes for H2 separation and CO2 capture.

Precise molecular sieving using metal‐doped ultramicroporous carbon membranes for H2 separation

“…CMS membranes carbonized at both 600 C and 700 C demonstrated separation performance which surpassed the upper bound. 45 Compared with other high-performance polymeric, 46 inorganic membranes such as MoS 2 , 47 GO 48 membranes, mixed matrix membranes, [49][50][51][52][53][54] and CMS membranes 9,[16][17][18][19][55][56][57][58][59][60][61][62] reported in the literature, CMS- highlighting its potential applicability in H 2 /CO 2 engineering separation processes.…”

“…Synthesis of ordered microstructure that contains <3.3 Å ultramicropores in the CMS membranes to limit the CO 2 diffusion within the pore channels has been demonstrated as an effective strategy to enhance H 2 /CO 2 separation efficiency. [16][17][18][19] For example, Hu et al 16 reported a polymer precursor cross-linked strategy by introducing pyrophosphoric acid into polybenzimidazole (PBI) precursor membrane, the graphitization of the PBI-derived CMS membranes was increased, leading to a more ordered carbon structure, thereby achieving high H 2 /CO 2 selectivity. Similarly, it has been reported that when elevating the carbonization temperature, such as above 900 C, the graphitic transition of the carbon structure was heightened, and the selectivity of H 2 /CO 2 in CMS membranes is greatly enhanced.…”

“…Similarly, it has been reported that when elevating the carbonization temperature, such as above 900 C, the graphitic transition of the carbon structure was heightened, and the selectivity of H 2 /CO 2 in CMS membranes is greatly enhanced. [17][18][19] When carbonized at an extremely high temperature, the carbon plates tended toward more orderly alignment in a short range, which facilitated the packing of the carbon strands and induced the creation of narrower ultramicropores. For instance, an aramid-derived CMS membrane pyrolyzed at 925 C exhibited an ultrahigh H 2 /CO 2 ideal selectivity of 366.…”

“…For instance, an aramid-derived CMS membrane pyrolyzed at 925 C exhibited an ultrahigh H 2 /CO 2 ideal selectivity of 366. 18 Similarly, CMS membrane derived from an aromatic intrinsically microporous ladder polymer precursor carbonized at 900 C presented a tightly packed dominantly ultramicroporous CMS structure, which severely restricted the gas transport of CO 2 , showed remarkable selectivity for H 2 /CO 2 to 248. 19 Recently, the utilization of transition metal-assisted catalyzed graphitization has also been demonstrated as a facile method to induce a more ordered carbon structure.…”

Advancements in defect engineering of two-dimensional nanomaterial-based membranes for enhanced gas separation

“…A variety of two-dimensional materials are currently being explored for the creation of membranes with sieving capabilities. 86,87 However, precise control over pore size remains a challenge, limiting this approach primarily to laboratory research and posing obstacles to widespread industrial application. In actual membrane fabrication, the pore size and distribution are often random, leading to a variety of gas transport mechanisms, with molecular sieving being just one of many possibilities.…”