Optimization of Deacetylation Process for Regenerated Cellulose Hollow Fiber Membranes

Abstract

Cellulose acetate (CA) hollow fibers were spun from a CA+ Polyvinylpyrrolidone (PVP)/N-methyl-2-pyrrolidone (NMP)/H 2 O dope solution and regenerated by deacetylation. The complete deacetylation time of 0.5 h was found at a high concentration (0.2 M) NaOH ethanol (96%) solution. The reaction rate of deacetylation with 0.5 M NaOH was faster in a 50% ethanol compared to a 96 vol.% ethanol. The hydrogen bond between CA and tertiary amide group of PVP was confirmed. The deacetylation parameters of NaOH concentration, reaction time, swelling time, and solution were investigated by orthogonal experimental design (OED) method. The degree of cross-linking, the residual acetyl content, and the PVP content in the deacetylated membranes were determined by FTIR analysis. The conjoint analysis in the Statistical Product and Service Solutions (SPSS) software was used to analyze the OED results, and the importance of the deacetylation parameters was sorted as Solution > Swelling time > Reaction time > Concentration. The optimal deacetylation condition of 96 vol.% ethanol solution, swelling time 24 h, the concentration of NaOH (0.075 M), and the reaction time (2 h) were identified. The regenerated cellulose hollow fibers under the optimal deacetylation condition can be further used as precursors for preparation of hollow fiber carbon membranes.

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

“…The release of molecular spacers during carbonization may occur by either of the following two mechanisms: (i) simple evaporation, only possible with small molecules, Figure 6. Scheme of the hollow fiber dry-wet spinning machine (reproduced with permission from [31]).…”

“…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.…”

“…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]. Therefore, there is a need to replace the acetyl group for a hydroxyl group.…”

“…The solution can be aqueous, but it is more efficient when prepared in ethanol. The time of chemical exposure, the hydroxyl concentration, the content of the solution and the reaction time are very important parameters for this pre-treatment [31].…”

“…A complementary study of the optimization of the deacetylation process conditions in sodium hydroxide ethanolic solutions was performed by He in 2017 [31]. The experimental variables considered were the concentrations of NaOH (0.05 M, 0.075 M and 0.1 M) and ethanol (96 vol.% and 50 vol.%) employed on preparing the NaOH solution; the time the fibers were placed in a 10 wt% glycerol bath (swelling time) and the deacetylation reaction time.…”