Recovery of the N,N-Dibutylimidazolium Chloride Ionic Liquid from Aqueous Solutions by Electrodialysis Method

Abstract

Ionic liquids (ILs), named also as liquid salts, are compounds that have unique properties and molecular architecture. ILs are used in various industries; however, due to their toxicity, the ILs' recovery from the postreaction solutions is also a very important issue. In this paper, the possibility of 1,3-dialkylimidazolium IL, especially the N,N-dibutylimidazolium chloride ([C₄C₄IM]Cl) recovery by using the electrodialysis (ED) method was investigated. The influence of [C₄C₄IM]Cl concentration in diluate solution on the ED efficiency was determined. Moreover, the influence of IL on the ion-exchange membranes' morphology was examined. The recovery of [C₄C₄IM]Cl, the [C₄C₄IM]Cl flux across membranes, the [C₄C₄IM]Cl concentration degree, the energy consumption, and the current efficiency were determined. The results showed that the ED allows for the [C₄C₄IM]Cl recovery and concentration from dilute solutions. It was found that the [C₄C₄IM]Cl content in the concentrates after ED was above three times higher than in the initial diluate solutions. It was noted that the ED of solutions containing 5-20 g/L [C₄C₄IM]Cl allows for ILs recovery in the range of 73.77-92.45% with current efficiency from 68.66% to 92.99%. The [C₄C₄IM]Cl recovery depended upon the initial [C₄C₄IM]Cl concentration in the working solution. The highest [C₄C₄IM]Cl recovery (92.45%) and ED efficiency (92.99%) were obtained when the [C₄C₄IM]Cl content in the diluate solution was equal 20 g/L. Presented results proved that ED can be an interesting and effective method for the [C₄C₄IM]Cl recovery from the dilute aqueous solutions.

Keywords: 1,3-dialkylimidazolium ionic liquids; N,N-dibutylimidazolium chloride; electrodialysis; ionic liquids recovery.

Figure 1

The effect of [C₄C₄IM]Cl concentration in the initial diluate on the LCD.

Figure 3

SEM micrograph of the tested heterogeneous ion-exchange membranes before and after ED: (a) AM(H)PP; (b) CM(H)PP membrane.

Figure 2

The effect of [C₄C₄IM]Cl concentration in the initial diluate on the: (a) recovery ratio, (b) concentration rate, (c) IL molar flux across ion-exchange membranes, (d) electrodialysis current efficiency, (e) stack energy consumption.

Figure 4

Experimental ED set-up for [C₄C₄IM]Cl recovery. D—diluate, C—concentrate, ERS—electrode rinse solution, AEM—anion-exchange membrane, CEM—cation-exchange membrane.