Pilot–Scale Production of Carbon Hollow Fiber Membranes from Regenerated Cellulose Precursor-Part I: Optimal Conditions for Precursor Preparation

Abstract

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).

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

“…A H 2 permeability of 980 barrer with a H 2 /CH 4 permselectivity of 490 [76] displays a Robeson Index of 24.3. In a series of works, May-Britt Hägg et al produced hollow fiber CMSM by a dry-wet spinning method using as polymer precursor cellulose acetate (CA), from ACROS, with a molecular mass (MM) of 100,000 g•mol -1 and an average acetyl content of 39.8% [31,[76][77][78][79][80][81]. This acetyl content was later removed by a deacetylation process.…”

“…A pilot-scale production of carbon hollow fiber membranes from regenerated cellulose acetate precursor and with an annual production capacity 700 m 2 of carbon membrane was reported by Haider [80,81]. A dope solution of cellulose acetate (CA) mixed with PVP and NMP and bore fluid of NMP and water was used in the dry-wet spinning process.…”

“…The cellulose acetate precursor used by some authors has an average acetyl content of 40% [31,[76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92]. The direct carbonization of cellulose acetate membranes can form defects on the carbon matrix or even turn it into dust [31].…”

“…The deacetylation process of cellulose acetate was also optimized in a pilot industrial scale production facility to produce hollow fibers [80]. Hollow fibers with the best mechanical properties and separation performances were obtained with 2.5 h of deacetylation at room temperature.…”

“…Hollow fibers with the best mechanical properties and separation performances were obtained with 2.5 h of deacetylation at room temperature. The effect of other pre-treatments was also assessed, namely: (i) water washing; (ii) glycerol treatment concentration (5, 8, 10 and 15 vol% in water) to remove residual NMP; (iii) glucose washing with glucose playing the role of molecular spacer and (iv) fiber drying parameters (humidity, extra-load and temperature) [80]. The best permeation results after carbonization were obtained when the precursor fibers were washed from NMP using water at 30 • C for 3 h, followed by the immersion in a circulating glycerol solution with 5 vol% of glycerol.…”