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Carbon hollow fibers (CHF) were fabricated by carbonization of deacetylated cellulose acetate precursor. To enhance membrane permeation properties, pore structure was tailored by means of an oxidation and reduction process followed by chemical vapor deposition with propene. Permeation properties using shell-side feed configuration of 70 modules (0.2-2 m 2) for both CHF and modified carbon hollow fibers (MCHF) were investigated for single gases, N2 and CO2 at high pressure (2-70 bar feed vs 0.05-1bar permeate pressure) and temperature from 25-120 °C. Maximum CO2 permeance value for a MCHF module was recorded 50,000 times higher as compared to prior modification, and CO2/N2 selectivity was improved 41 times in comparison with CHF for the same module. Results indicated that carbon membranes are hardly effected by high pressure, but significant drop in CO2 permeability was observed at elevated temperature. Simulations of CO2/CH4 separation by MCHF and polymeric membranes were conducted based on Aspen Hysys ® integrated with ChemBrane, and the process was optimized for cost calculation based on membrane area and compression energy. Simulation results indicated that the required separation can be achieved by a single stage process for MCHF, while a two-stage process is needed for the polymeric membranes.

Regenerated cellulose precursor was carbonized to make carbon membranes• O2 permeability increased exponentially with increase in operating temperature • O2/N2 selectivity was between 17-20 for all operating temperatures (23-68 °C)• Thermal, chemical, and online-electrical regeneration methods were investigated

Industrial scale production of carbon membrane is very challenging due to expensive precursor materials and a multi-step process with several variables to deal with. The optimization of these variables is essential to gain a competent carbon membrane (CM) with high performance and good mechanical properties. In this paper, a pilot scale system is reported that was developed to produce CM from regenerated cellulose precursor with the annual production capacity 700 m2 of CM. The process was optimized to achieve maximum yield (>95%) of high quality precursor fibers and carbonized fibers. A dope solution of cellulose acetate (CA)/Polyvinylpyrrolidone (PVP)/N-methyl-2-pyrrolidone (NMP) and bore fluid of NMP/H2O were used in 460 spinning-sessions of the fibers using a well-known dry/wet spinning process. Optimized deacetylation of spun-CA hollow fibers (CAHF) was achieved by using 90 vol% 0.075 M NaOH aqueous solution diluted with 10 vol% isopropanol for 2.5 h at ambient temperature. Cellulose hollow fibers (CHF) dried at room temperature and under RH (80% → ambient) overnight gave maximum yield for both dried CHF, as well as carbon fibers. The gas permeation properties of carbon fibers were also high (CO2 permeability: 50–450 Barrer (1 Barrer = 2.736 × 10−9 m3 (STP) m/m2 bar h), and CO2/CH4 selectivity acceptable (50–500).

Predictive models regarding the aging effect on membrane separation properties are required to estimate the membrane life time with acceptable permeability and selectivity for the respective application. The current article is reporting an insight into this topic regarding the aging of regenerated cellulose-based carbon hollow fibres (CHF) mounted in a membrane module when they were exposed to real biogas in three different fields. CHF were exposed to biogas for almost one year with H2S content extending from 0-2400 ppm, and gas permeation tests for single gases, N2, CO2, CH4, and O2 were analysed periodically at the membrane production facility. CHF storage methods under miscellaneous dry environments like air, vacuum, CO2, etc. were studied. The air flow through bore side of the CHF under controlled conditions had a regenerative effect on the membrane permeability, and the membrane performance was quite steady until after 150 days under laboratory environment.