Carbon Membranes with Extremely High Separation Factors and Stability

Abstract

For some time, carbon molecular sieve membranes (CMSMs) have been promoted as energy‐efficient candidates for gas separation due to their high selectivity, permeability, and stability in chemically aggressive environments. Nevertheless, these membranes have not yet been made into commercial products due to a significant decrease in performance when exposed to humidity and/or oxygen. Herein, disruptive CMSMs with extremely high separation performance and stability, even in the presence of humidity, are reported. The carbon membranes are prepared from a renewable, low‐cost precursor with a single carbonization step. Water vapor adsorption/desorption studies demonstrate that these membranes have a linear water vapor adsorption isotherm, characteristic of a homogeneous distribution of hydrophilic sites on the pore surfaces, allowing for water molecules to hop continuously between sites and avoiding the formation of pore‐blocking water clusters. These results are a breakthrough toward bringing this new type of membrane to a commercial level.

Cellulose-Based Carbon Molecular Sieve Membranes for Gas Separation: A Review

“…Recently, in 2019, the same group reported a new work on CMSM based on cellophane paper precursor [75]. Rodrigues et al [75] presented a CMSM with extremely high separation performance: the CMSM carbonized at 600 • C is situated far above Robeson's upper bound, showing a O 2 /N 2 selectivity greater than 800, a CO 2 /CH 4 selectivity greater than 2600 and a H 2 /CH 4 selectivity greater than 25,000, but with low permeability. These cellulose-based CMSM shows the highest Robeson Index values for the O 2 /N 2 and CO 2/ CH 4 separations, 63 and 100, respectively.…”

“…These cellulose-based CMSM shows the highest Robeson Index values for the O 2 /N 2 and CO 2/ CH 4 separations, 63 and 100, respectively. X-ray photoelectron spectroscopy (XPS) and Inductively coupled plasma (ICP) analyses proved the presence of metallic and semi-metallic groups (ionic sodium and silica nanoparticles) homogeneously distributed on the membrane surface, providing polar sites that allow the water molecules to jump between them avoiding the formation of water clusters [75]. This confers a very high humidity stability to these membranes (absence of pore blockage) and a very high water vapor permeability.…”

“…Despite the great expectation of the cellophane-based paper carbon membranes [75], such as its very high selectivity, >800 for O 2 /N 2 , the permeability of O 2 is low (1 barrer). To overcome this limitation, Rodrigues et al developed a high-performance cellulose-based CMSM prepared from an optimized ionic liquid-regenerated cellulose precursor [30].…”

“…Therefore, typically, lower permeability and higher selectivity is achieved increasing the end carbonization temperature. However, the mechanical stability is also influenced by the carbonization end temperature [30,75], and CMSMs carbonized at higher temperatures are usually more brittle. Therefore, a compromise between membrane performance and mechanical stability should be attained.…”

“…Campo et al [58], in 2010, and Rodrigues et al [75], in 2019, both presented a study of the influence of the end carbonization temperature (in a range of 400 to 600 • C) on the performance of cellophane paper based CMSM. The permeability of all gases increased with the carbonization end temperature up to 550 • C, decreasing thereafter.…”