Permeability of dilute ionic liquid solutions through a nanofiltration membrane – Effect of ionic liquid concentration, filtration pressure and temperature Olli Nakari, Arto Pihlajamäki ⇑ , Mika Mänttäri School of Engineering Science, Lappeenranta University of Technology, P.O. Box 20, FI-53851 Lappeenranta, Finland article info Article history: Received 25 November 2015 Received in revised form 26 February 2016 Accepted 29 February 2016 Available online 2 March 2016 Keywords: Ionic liquid [emim][OAc] Membrane separation Nanofiltration Recycling abstract Nanofiltration is studied to separate glucose from dilute ionic liquid [emim][OAc]–water solutions. The aim of the research is to evaluate the effect of filtration pressure, temperature and ionic liquid (IL) con- centration on the separation of ionic liquid and glucose. This kind of separation challenge can be formed in the regeneration of cellulose fibres in a wet spinning bath. The separation tests are done with an NF270 nanofiltration membrane. The tolerance of the NF membrane in ionic liquid is also estimated. Effective osmotic pressures and viscosity were found to have a major role in the permeability of the membrane when filtration was done at dilute IL solutions. Temperature was found to have a significant effect on the flux due to reduced viscosity at higher temperatures. The flux was increased by about 50% when the temperature increased from 20 °C to 40 °C. The best possible separation factor values were achieved when the feed solution contained 1 wt% [emim][OAc] at 20 °C temperature and the filtration pressure was 6 bars. On the basis of the IL concentration and temperature test series, a good separation window for this kind of solution would be at permeate flux values from 50 L m 2 h 1 to 100 L m 2 h 1 . After a test series in concentrations of IL from 0.5 wt% to 10 wt%, the pure water permeability (PWP) was reduced by 23% from the original. The decline of PWP during the temperature tests series was 33%. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Since the beginning of this century, ionic liquids (ILs) have been studied intensively as dissolving agents for wood or cellulose. The research has focused lately especially on room temperature ionic liquids (RTILs), which are composed entirely of ions and are fluids below 100 °C. RTILs have advantageous properties, such as a low vapour pressure and low melting point. They are non-flammable and have high thermal stability as well as high ionic conductivity. Modern ILs contain an organic cation, which are often quarternised aromatic or aliphatic ammonium ions. Anions are organic or inor- ganic. Typical anions in ILs are hexafluorophosphate [PF 6 ]  , tetrafluoroborate [BF 4 ]  , alkyl sulphates [RSO 4 ]  , alkyl sulfonates [RSO 3 ]  , halides as chloride Cl  , bromide Br  , iodide I  or nitrate [NO 3 ]  [1–4]. Chemical treatment of wood has been traditionally done by pulping processes in a large scale. Due to the well-known pulping processes and ready infrastructures, a new economically valuable process concept has to introduce some special properties [5]. Tailor-made ILs need to have some advantages in processing wood in a new way. Some of these benefits could be a high dissolution capacity for cellulose, specific dissolution (i.e. dissolves only one component of the whole wood), low melting point, good thermal stability, non-volatility, non-toxicity, chemical stability, or no cel- lulose structure degradation during processing, and easy cellulose regeneration from IL-solutions [6]. The recycling of ILs from process solutions is one of the key issues for the development of an economical process, because IL is usually the most expensive chemical in process solutions. When wood is dissolved in IL, cellulose can be recovered by precipitating it with the addition of an anti-solvent and then filtering it out from the solution [2]. After the separation of cellulose for value added products, the ILs need to be extracted, purified and recycled back to dissolve cellulose again in order to maintain an economical and sustainable process. Although recent academic focus in this field has been on the dissolution of wood or cellulose in ILs, some studies have aimed at the purification of ILs and separation of the dissolved com- pounds from IL–water solutions. The recovery and purification of different ILs have been done at least by membrane filtrations http://dx.doi.org/10.1016/j.seppur.2016.02.052 1383-5866/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail addresses: olli.nakari@lut.fi (O. Nakari), arto.pihlajamaki@lut.fi (A. Pihlajamäki), mika.manttari@lut.fi (M. Mänttäri). Separation and Purification Technology 163 (2016) 267–274 Contents lists available at ScienceDirect Separation and Purification Technology journal homepage: www.elsevier.com/locate/seppur