Preoxidation Enables Enhanced Separation Performance in Cellulose-Derived Carbon Molecular Sieve Membranes for CO ₂ Removal from Natural Gas

Cellulose-based carbon molecular sieve (CMS) hollow fiber membranes show promising potential for natural gas sweetening, owing to their low cost, high CO2/CH4 selectivity, robust mechanical stability, and resistance to plasticization. However, the dense and highly crystalline structure of cellulose usually leads to a relatively low CO2 permeability in cellulose-derived CMS membranes. In this work, we propose a preoxidation strategy for cellulose to construct a cross-linked network. During preoxidation, hydrogen bonds and partial glycosidic linkages in the cellulose chains were cleaved, while hydroxyl groups were oxidized to oxygen-containing functional groups such as carboxyl and aldehyde groups. These subsequently formed an ester-bond cross-linked network. This approach effectively suppressed excessive shrinkage of the membranes during carbonization, thereby preserving a more open porous structure. As a result, the obtained hollow fiber CMS membranes exhibited a significant increase in CO2 permeability, reaching 1026 Barrer (approximately 3 times higher than that of untreated membranes) while maintaining a high CO2/CH4 selectivity of 110. Furthermore, the separation performance was evaluated under high-pressure mixed-gas conditions (10% CO2/90% CH4). The CMS hollow fiber membranes demonstrated stable operation for over 100 h with a CO2/CH4 separation factor of ∼130, highlighting their potential for practical application in natural gas sweetening. This method is facile and provides an effective solution for the performance enhancement and structural design of cellulose-based separation membranes.