Optimization of Deacetylation Process for Regenerated Cellulose Hollow Fiber Membranes

Xuezhong He

doi:10.1155/2017/3125413

Abstract

Cellulose acetate (CA) hollow fibers were spun from a CA+ Polyvinylpyrrolidone (PVP)/N-methyl-2-pyrrolidone (NMP)/H2O 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.

Highlights

Carbon membranes have been studied in the last decade as a promising candidate for energy-efficient separation processes such as H2/CH4, H2/CO2, CO2/CH4, and Olefin/Paraffin [1]
There are some literatures reported on the spinning of cellulose acetate (CA) fibers [10,11,12,13,14,15], but those membranes were all used in the dialysis, reverse osmosis (RO), and ultrafiltration (UF) applications
The characteristic adsorption peaks 1030 cm−1, 1230 cm−1, and 1740 cm−1 are attributed to the ether group (]C-O-C), acetyl ester group (]CH3-C=O), and carbonyl group (]C=O) of CA, respectively [15]

Summary

Introduction

Carbon membranes have been studied in the last decade as a promising candidate for energy-efficient separation processes such as H2/CH4, H2/CO2, CO2/CH4, and Olefin/Paraffin [1]. How to prepare cheaper, defect-free, hollow fiber precursor membranes becomes a key issue on the fabrication of carbon membranes. The regenerated cellulose precursors (replace acetyl group with hydroxyl group) from CA hollow fibers can be well used to fabricate the carbon membranes. Son et al reported the deacetylation of CA membranes in KOH ethanol solution (0.5 M) after swelling in 25 mL of an acetone-water mixture (V/V 1/1) for 24 h [15]. They found that deacetylation was very rapid and completed within 20 min, and the deacetylated CA membranes showed the crystal structure of cellulose. No systematic investigation on the influences of deacetylation condition was reported, which is crucial to regenerate cellulose hollow

Methods

Results

Conclusion