Abstract
Nanofiltration is considered to be an appropriate separation technique in the production of bio-based materials. For the utilization of process streams from the viscose-fiber production, understanding the separation behavior of organic compounds in highly alkaline solutions is necessary. Experiments with succinic acid in sodium hydroxide (NaOH) solutions with varying concentrations up to 5 mol L−1 were performed with the NP030 membrane from Microdyn Nadir. Furthermore, experiments with aqueous disodium succinate and solutions of sodium sulfate in sodium hydroxide were carried out. The influence of concentration ratios and temperature was studied. The Spiegler and Kedem model as well as the Pusch model were applied to fit the experimental data. Additionally, scanning electron microscopy (SEM) and infrared (ATR–IR) measurements were performed to validate the chemical and thermomechanical stability of the membrane. The succinic acid retention varies with its degree of dissociation. In a fully dissociated form, the NaOH concentration shows no impact on the retention. In contrast, the retention of sulfate decreases with increasing NaOH concentration.
Highlights
Nanofiltration has the potential to be a highly effective separation method for the utilization of viscose-fiber production side streams
Succinic acid and disodium succinate were quantified by high performance liquid chromatography (HPLC) analysis
8 the slope retention of sodium ions is related to the retention of succinate ions by the law of electroneutrality, the data points for 1 M NaOH is five times steeper than for 5 M NaOH
Summary
Nanofiltration has the potential to be a highly effective separation method for the utilization of viscose-fiber production side streams. It can be used as a downstream process for the purification of process chemicals. In addition to the viscose-fiber production, membrane processes in strong alkaline solutions are under investigation for streams of the cotton industry as studied by Son [6]. The influence of sodium hydroxide concentrations in the range of 1 up to 5 mol L−1 on the retention performance of nanofiltration membranes has not been studied so far. The comparison of disodium succinate and sodium sulfate should help to improve the knowledge of membrane retention mechanisms and could indicate the possibility of separation between organic and inorganic divalent ions
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