Extraction of butyric acid by a solvent impregnated resin containing ionic liquid

https://doi.org/10.1016/j.reactfunctpolym.2011.04.002Get rights and content

Abstract

Equilibrium and kinetics of extraction of butyric acid (BA) into solvent impregnated resins (SIRs) have been studied. Microporous Amberlite XAD-1180N was impregnated with a new ammonium ionic liquid (IL) trialkylmethylammonium-bis(2,4,4-trimethylpentyl)phosphinate or with its solution in dodecane. No difference in BA extraction equilibrium between the free organic phases and the same phase impregnated in SIRs has been observed. This shows that the polymer matrix of the resin has no significant impact on extraction properties of impregnated IL. SIR impregnated with IL solution in dodecane exhibit faster extraction kinetics with lower saturation times compared to SIR with pure IL, what can be attributed to lower viscosity of the solvent with diluent. The kinetics of extraction into used SIRs with a mean particle diameter of about 660 μm was fast and 95% of their equilibrium saturation was achieved in less than 350 s which is one order of magnitude faster than achieved in adsorption into resins. The value of the effective diffusion coefficient in extraction is larger than in stripping, suggesting that kinetics of the stripping is influenced by the slower decomposition of the complex of BA with IL.

Introduction

Butyric acid (BA) has numerous applications in food, cosmetic and pharmaceutical industries. BA is also a potential building block for organic synthesis in biorefineries [1]. Fermentation of butyric acid has a problem of strong inhibition by the product. Possible solution of this problem is online separation of the BA from the fermentation solution by extraction. Hydrophobic ionic liquids (ILs) show great potential as an extractant of carboxylic acids [2], [3], [4]. However, formation of stable emulsions prevents the application of IL in contactors with phase dispergation. Possible solution of this problem offer pertraction through supported liquid membrane or membrane based solvent extraction [1], [5], [6], [7]. Papers discussing separation of BA by pertraction with trioctylamine (TOA) [8] or IL [9] as carriers and membrane based solvent extraction with TOA [5], [10] have been published.

Another possibility to avoid dispergation of the solvent is the use of solvent impregnated resins (SIRs) [11], which combines the solvent extraction with the advantages of immobilized L/L interface in microporous solid particles. Several SIRs have already been tested for extraction of phenol from its low concentration aqueous solutions [12], [13], [14], methyl-terc-butylether [15], amino acids [16], [17], [18] and carboxylic acids [19], [20]. Overview of systems studied with SIRs is presented in paper [11]. There are also studies concerning the SIRs impregnated with ILs as an extractant for separation of metals [21], [22], [23], [24], [25].

In preparation of the SIR, the extractant and diluent are immobilized inside the pores of the support. There are two basic methods of SIR preparation with possible modifications [26]. In the “dry” impregnation method is the extractant immobilized into the polymeric support after contacting a solution of the extractant in volatile diluent (methanol, ethanol, etc.) with the polymer. Subsequently the diluent is evaporated and pure extractant remains inside the pores of the support. In this method, not all of the void volume inside the particle is filled. In the “wet” impregnation method, in which a solution of the extractant in water insoluble diluent is impregnated, a final three-component SIR (microporous support – extractant – diluent) is obtained.

Mentioned extractive processes utilizing ILs can be used for separation of products in hybrid production – separation processes, e.g. in removal of organic acids from fermentation broth to avoid inhibition by product and prolongation of biomass utilization in fermentation [5], [6], [27], [28].

The aim of this work was experimental study of equilibrium and kinetics of extraction into SIR impregnated with new ammonium IL trialkylmethylammonium-bis(2,4,4-trimethylpentyl)phosphinate (TAMA-BTMPP) which is an ammonium IL with the same anion as in phosphonium IL Cyphos IL-104 studied earlier in papers [2], [3], [4].

Section snippets

Mathematical model of extraction kinetics into SIR

Kinetics of extraction into SIR particles is influenced by the resistance of the boundary layer at particle surface, extraction or stripping kinetics and diffusion in the particle. Analysis of the individual mass-transfer resistances, presented in article for pertraction of lactic acid through supported liquid membrane containing ionic liquid has been presented in paper [9]. In the analysis of SIR extraction and stripping kinetics, it was supposed, that diffusion in the particle has major

Materials

In preparation of aqueous solutions of butyric acid (BA) a 99.5% BA (Fluka, CH) was used as received.

Dodecane (Fluka, CH, M = 170.3 kg kmol−3) was used as a diluent without further conditioning. Its purity was >98%. Basic properties of dodecane are shown in Table 1.

Trialkylmethylammonium chloride (TAMA-Cl, trade name Aliquat 336, Cognis, DE) is used as the extractant or carrier of heavy metals and acids. Product contains besides the predominant trioctylmethylammonium cation also cations with C9 and

L/L and SIR/L extraction equilibrium

Experimental results of L/L and SIR/L equilibrium measurements are shown in Fig. 2, Fig. 3, Fig. 4, Fig. 5. The stripping of BA from free IL and its dodecane solution [29] as well as from prepared SIRs was quantitative.

In the L/L extraction equilibrium experiments it has been observed, that the changes of density of organic phase are low (up to 1.5% for pure IL and up to 1% for IL solution in dodecane). On the other hand, the changes of volume of the organic phase are much more significant

Conclusions

Ionic liquid TAMA-BTMPP is an effective extractant of BA with extractive properties comparable to phosphonium IL Cyphos IL-104 with the same anion. Solvent impregnated resins containing pure TAMA-BTMPP or its dodecane solution have been prepared by immobilization of organic phases in pores of macroporous sorbent Amberlite XAD-1180N. A strong decrease of distribution coefficient has been observed with increasing equilibrium concentration of BA in aqueous phase. It was found, that the presence of

Acknowledgements

Support of the Slovak Grant Agency VEGA No. 1/0876/08 is acknowledged. We thank Cognis (DE) and Cytec (Canada) for kind providing samples of Aliquat 336 and Cyanex 272, respectively.

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