Novel cellulose ultrafiltration membranes

Novel cellulose ultrafiltration membranes


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Due to its energy-efficient and environmentally friendly operation, membrane technology has established itself as a versatile separation process in the industry in the recent decades.
A very important membrane process is ultrafiltration (UF), which is used for water treatment or critical separation steps in bioprocess engineering. Commercial membranes are usually produced from synthetic polymers derived from non-renewable fossil resources and which are non-biodegradable. Therefore, the membrane preparation from inexhaustible and cheap natural resources like cellulose is emphasized. Because of their chemical properties, cellulose cannot be dissolved in most common organic solvents, which complicates the direct processing into membrane by phase inversion. Ionic liquids, a relatively new class of solvents, can be used to dissolve cellulose under very mild and, thus, also environmentally friendly conditions [1]. However, the use of ionic liquids as solvent for large scale manufacturing is hindered by their high costs and their high viscosity. Previous work from our group has shown that the addition of an aprotic polar co-solvent decreases the viscosity of solution and is beneficial for the dissolution and processing of cellulose to porous materials [2]. Cellulose membranes are very hydrophilic and not prone to most kinds of fouling, which is potentially a very big advantage. However, cellulose membranes have generally a shorter lifetime compared to other polymer-based membrane materials due to their lower mechanical, chemical and thermal stability.

To obtain the highest possible separation efficiency, membranes with a small thickness of the separating active layer are desired. Since the stability decreases with decreasing layer thickness, the thin membranes must be deposited to a porous support layer. Usually the support is based on a different material such as, for example, poly(ethylene terephthalate). The vision of this work is the production of fully cellulose-based-composite membranes, which are expected to have some advantages, in particular with respect to the adhesion at the interface of the two layers. These UF membranes are prepared from solutions of cellulose in various ionic liquids and co‑solvent on a macroporous cellulose support via non-solvent induced phase separation (NIPS). The effect of ionic liquid type, co-solvent and polymer concentration on membrane performances will be studied in detail. One aim of this work is to obtain membranes with the highest possible and thus competitive UF separation performance by selecting suitable processing conditions.

References

  1. R. P. Swatloski, S. K. Spear, J. D. Holbrey, R. D. Rogers, J. Am. Chem. Soc. 2002, 124, 4974
  2. A. Wittmar, M. Ulbricht, Ind. Eng. Chem. Res. 2017, 56, 2967

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