Towards robust cellulose-based nanofiltration membranes

Abstract

The sustainability of cellulose as a material is unquestionable, with it being the most abundant biopolymer on earth. The chemical recalcitrance of cellulose makes its processing challenging but it can also be used as a benefit. This PhD project investigates the recently discovered organic electrolyte solutions (OESs), to dissolve underivatised cellulose and reports the development of cellulose membranes for use in membrane separation applications. Membrane separation processes are well established with many industrial applications. Two examples of membrane separation processes, Nanofiltration (NF) and Ultrafiltration (UF), separate solutes from aqueous feed over a membrane. A challenge for NF and UF is to extend their application range from aqueous to non-aqueous feeds. Meeting this challenge requires solvent stable membrane that preserve their separation characteristics in a wide range of solvents. This emerging technology is termed organic solvent solvent nanofiltration (OSN). Few comercial OSN membranes are stable in dipolar aprotic group of solvents in particular, so cellulose membranes are poised to fill this gap.

This thesis reports investigations on several OESs, with emphasis on cellulose dissolution performance and discovery of efficient co-solvents. These findings were then employed to develop cellulose membranes via Non-solvent Induced Phase Separation (NIPS) methodology and the membranes produced were tested for their permeation, rejection, as well as physical and mechanical properties.

The cellulose membranes developed were shown to be stable and have reasonable flux in wide ranging organic solvents, including dipolar aprotic solvents; can be categorised as UF membranes in terms of their rejection characteristics of non-polar solutes; but are found to be performing at NF range (MW < 1000 Da) for their rejection of polar compounds. Membrane properties can be tuned, to some extent, by using different OESs as the cellulose casting solutions, by changing certain variables such as the non-solvent for the regeneration stage, and by performing chemical crosslinking to the membranes as a post-treatment step.

Date of Award	29 Mar 2023
Original language	English
Awarding Institution	University of Bath
Supervisor	Andrew Johnson (Supervisor), Adam Squires (Supervisor), Janet Scott (Supervisor) & Darrell Patterson (Supervisor)