Abstract
γ-Valerolactone (GVL) was selected as a renewable green solvent to prepare membranes via the process of phase inversion. Water and ethanol were screened as sustainable non-solvents to prepare membranes for nanofiltration (NF). Scanning electron microscopy was applied to check the membrane morphology, while aqueous rose Bengal (RB) and magnesium sulphate (MgSO4) feed solutions were used to screen performance. Cellulose acetate (CA), polyimide (PI), cellulose triacetate (CTA), polyethersulfone (PES) and polysulfone (PSU) membranes were fine-tuned as materials for preparation of NF-membranes, either by selecting a suitable non-solvent for phase inversion or by increasing the polymer concentration in the casting solution. The best membranes were prepared with CTA in GVL using water as non-solvent: with increasing CTA concentration (10 wt% to 17.5 wt%) in the casting solution, permeance decreased from 15.9 to 5.5 L/m2·h·bar while RB rejection remained higher than 94%. The polymer solubilities in GVL were rationalized using Hansen solubility parameters, while membrane performances and morphologies were linked to viscosity measurements and cloudpoint determination of the casting solutions to better understand the kinetic and thermodynamic aspects of the phase inversion process.
Highlights
Membrane technology offers separations in the chemical industry and water treatment of small molecules from solvent or water streams by using membranes and providing an economically viable alternative for separation and purification [1,2]
The best membranes were prepared with cellulose triacetate (CTA) in GVL using water as non-solvent: with increasing CTA concentration (10 wt% to 17.5 wt%) in the casting solution, permeance decreased from 15.9 to 5.5 L/m2·h·bar while rose Bengal (RB) rejection remained higher than 94%
NF membranes based on Cellulose acetate (CA), PI, CTA, PES and PSU have been successfully prepared using GVL as a bio-based green solvent via NIPS
Summary
Membrane technology offers separations in the chemical industry and water treatment of small molecules (solutes) from solvent or water streams by using membranes and providing an economically viable alternative for separation and purification [1,2]. In nanofiltration (NF), the separation process is run under pressure, rejecting molecules with a molecular weight of 200–1000 Da. Several techniques have been applied to prepare polymeric membranes, including temperature and non-solvent induced phase separation (TIPS and NIPS) [3,4,5]. In the NIPS process, a film cast from a polymer solution is immersed in a coagulation bath. Tetrahydrofuran (THF), N,N-dimethylformamide (DMF), 1-methyl2-pyrrolidone (NMP) and other conventional solvents are usually used in membrane. Tetrahydrofuran (THF), N,N-dimethylformamide (oDf 1M8 F), 1-methyl-2-pyrrolidone (NMP) and other conventional solvents are usually used in membrane preparation due to the good solubility of common polymers [18,24], but have all been classified as highly concerned solvents by ECHA [2,23].
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