Ionic Liquid-based Aqueous Two-phase Systems Research Articles

Extraction of low-concentration bio-based diols and dicarboxylic acids using ionic liquid-based aqueous two-phase systems: Experimental and theoretical studies

Biochemical pathways to generate renewable and high value-added diols and dicarboxylic acids have attracted increasing interest. However, the diols/dicarboxylic acids usually exist in the form of low-concentration aqueous solution after the bioprocesses, causing the issues of low efficiency and high energy consumption in the separation and recovery of these highly hydrophilic bioproducts. Here, we developed an aqueous two-phase system (ATPS) consisting of ionic liquid (IL) and inorganic salt for efficient extraction of the bio-based diols and dicarboxylic acids. The optimal salt, IL, and extractant to feed volume ratio were K4P2O7, [Bmim][C12H23O2], and 1:4, respectively. The selected IL showed large capacity and good reusability, with the highest dehydration rate reaching up to 97.6%. More importantly, the IL-based ATPS exhibited effectiveness and high efficiency in the separation of various low-concentration diols and dicarboxylic acids, with the recovery exceeding 91.9%. To explore the extraction mechanism, the structural and interactions analyses were conducted by DFT calculations. The strength of hydrogen bond interactions formed between diols/dicarboxylic acids and ILs and those between salts and water largely determines the extraction performance. Moreover, three descriptors that can well represent the H-bond basicity and polarizability/dipolarity of ILs were established to facilitate the IL evaluation and screening.

Efficient Fractionation of Lipids in a Multiproduct Microalgal Biorefinery by Polymers and Ionic Liquid-Based Aqueous Two-Phase Systems

For a multiproduct microalgal biorefinery, most of the cell components should be extracted and fractionated. This work investigates the fractionation of lipids from other microalgal components (pigments, proteins, carbohydrates) using polymers and IL solutions in aqueous two-phase systems (ATPS). The microalgal lipids poorly migrated to the aqueous phases of ATPS and were recovered (97% of the total fatty acids) in a third phase (interphase) formed between the top and bottom phases. Studies with canola oil and purified phospholipids suggest that the high amount of oil, phospholipids, and other natural emulsifiers present in the microalgae mixed with the high amount of water in the ATPS form an emulsion which is difficult to fractionate. However, a solution of polypropylene glycol 400 (25% w/w) displaced 73% of lipids in an immiscible layer which was easy to recover. When combining this approach with a subsequent ATPS, most of the microalgae biomolecules (lipids, proteins, pigments, carbohydrates) could be fractionated in a three-step mild separation concept.

Environmentally Benign and Recyclable Aqueous Two-Phase System Composed of Distillable CO2-Based Alkyl Carbamate Ionic Liquids

Ionic liquid-based aqueous two-phase systems (IL-ATPSs) have been studied comprehensively as a potential alternative method for protein purification. One of the distinct features of IL-ATPS is that the polarity of the IL can be adjusted by different combinations of cation and anion, providing flexibility in governing the partition of proteins between phases. However, the conventional IL-ATPS usually has poor environmental footprint and low recyclability, thereby hampering the systems for practical use in protein separation. To address these shortcomings, here we explored the distillable CO2-based alkyl carbamate ILs as phase-forming components. N,N-dimethylammonium N′,N′-dimethylcarbamate (DIMCARB) was able to form ATPS with polypropylene glycol (PPG). The liquid–liquid equilibrium data of ATPSs composed of PPG with different molecular mass and DIMCARB were determined. As both phase-forming components are thermosensitive, the effect of temperature on the phase diagram of the PPG 400 + DIMCARB system was also evaluated. The partition behavior of model proteins (i.e., bovine serum albumin and lysozyme) in the PPG + DIMCARB systems were assessed. Both model proteins tend to migrate to the more hydrophilic IL-rich phase, when a higher temperature or a higher molecular mass of PPG was used. The DIMCARB was recovered via rotary evaporation, while the PPG 400 was recovered from a secondary two-phase system thermally induced from the primary ATPS. The recovered components were subsequently used to prepare a new batch of ATPS. The phase composition of the new system as well as the partition coefficients of both model proteins in the recycled system were maintained, thereby proving the feasibility of reusing both phase-forming components. Overall, the recyclable and biodegradable phase-forming components used in the newly developed PPG + DIMCARB system make the ATPS a sustainable and eco-friendly system for protein purification.

Extraction in cholinium-based magnetic ionic liquid aqueous two-phase system for the determination of berberine hydrochloride in Rhizoma coptidis.

A magnetic ionic liquids (MILs)-based aqueous two-phase system (MIL-ATPs) obtained by mixing with a series of inorganic salts, which involves five cholinium MILs with the piperidinyloxy radical anion is reported for the first time. Phase diagrams for the new ATPs were experimentally determined at different temperatures (298.15–318.15 K) and the liquid–liquid equilibrium data for two-phase systems were correlated according to the empirical nonlinear expression. The effects of the types of MILs, temperature and inorganic salts on the binodal curve are discussed in detail. The MIL-ATPs coupled with HPLC-UV analysis was developed in the quantitation of berberine hydrochloride in Rhizoma coptidis. Under optimal conditions, the partition coefficient of berberine hydrochloride was 127.68 with the precision values (RSD%) of 1.40% and 2.83% for intra-day (n = 6) and inter-day (n = 3), respectively. The limit of detection (LOD) and limit of quantification (LOQ) for berberine hydrochloride were 0.023 mg L−1 and 0.077 mg L−1, respectively. The recoveries were obtained in the acceptable range of 97.4–101.2%. Moreover, the content of berberine hydrochloride in the raw material of Rhizoma coptidis was measured as 123.95 mg g−1 with this method. Finally, 99.8% MIL was recovered for cycle application after the removal of berberine hydrochloride by using D101 resin. This study provides a meaningful reference for the application of MIL-ATPs with great prospects.

Mathematical Model of the Phase Diagrams of Ionic Liquids-Based Aqueous Two-Phase Systems Using the Group Method of Data Handling and Artificial Neural Networks

Development of ionic liquid-based aqueous two-phase systems as a new viewpoint in the expansion of research in the field of biological materials separation depends on accurate determination of phase diagram. In this work, the efficiency of artificial neural network was studied aiming to forecast the formation possibility of phase diagrams of aqueous two-phases systems for the ability of range of ionic liquids composed of different anions with a selected salt. In order to investigate effects of the anion of ionic liquids on phase diagram, this study was performed on 472 of experimental data. On the basis of the accurate set of statistical measurements obtained, a good agreement between the experimental data points and the predicted values was gained. Furthermore, the group method of data handling was applied to model the molality of ionic liquids and a reasonable agreement was obtained between experimental data and the predicted values of this model.

Effects of DC electric field on phase equilibrium and partitioning of ionic liquid-based aqueous two-phase systems

The liquid–liquid equilibrium and partitioning of ionic liquid-based aqueous two phase systems (ILATPS) including [Bmim]Cl-K2HPO4 ATPS, [Bmim]BF4-NaH2PO4 ATPS and [Bmim]BF4-Na3C6H5O7 ATPS in a DC electric field were extensively studied. The demixing rates of three ILATPSs with different tie-line lengths (TLL) were measured at different DC voltage levels with normal polarity (NP) or reverse polarity (RP), respectively, and the partitioning of ILs and model proteins (including lysozyme and bovine serum albumin) were investigated simultaneously. [Bmim]Cl-K2HPO4 ATPS had higher overall salt concentrations (>15wt%) and lower overall IL concentrations (<20wt%) compared with [Bmin]BF4-based ATPSs, which led to faster two phase separation rates and higher efficiency of electrokinetic demixing mainly due to the salting-out effect. The effects of TLL and DC voltage on the dispersing and gathering of IL molecules in the three ILATPS collectively gave the electrokinetic promotion (accelerate ILATPS demixing rate) and electrokinetic inhibition (decelerate ILATPS demixing rate) for the ILATPS demixing. In [Bmim]BF4-NaH2PO4 ATPS, the highest promotion demixing were at TLL=55, 90V (RP), while the highest inhibition demixing were at TLL=64, 150V (RP). The movement and type of organic cations or inorganic anions of IL molecules played an important role in IL partitioning in the three ILATPSs, which generally caused the partition coefficient of IL to decrease in NP and increase in RP to different degrees. There were two different protein partitioning characteristics in the three ILATPS that most model proteins distributed in the IL-rich phase in [Bmim]Cl-K2HPO4 ATPS due to the salting-out effect and distributed in the salt-rich phase in [Bmim]BF4-based ATPS due to hydrophobic repulsion. For the model protein partitioning in the electric field, the DC voltage and electric polarity had no significant effect on the protein partitioning trend.

Modeling of the binodal curve of ionic liquid/salt aqueous systems

Ionic Liquid-based Aqueous Two Phase Systems (ILATPS) are an innovative technique to separate biomolecules that combines the advantages of liquid–liquid extraction and hydrophilic ionic liquids. Most ILATPS are based on ionic liquids and conventional inorganic salts, and the phase envelope, described by the binodal curve, is usually modeled by empirical equations that are used to determine the phase compositions and assess the ionic liquid recyclability. However, these empirical equations may provide a poor extrapolation ability or low accuracy at the extreme regions of the binodal curve or suffer from problems of convergence. Therefore, the aim of this work is the analysis of the binodal curve equations, comparing the models reported in the literature to describe ILATPS and proposing alternative equations to improve accuracy or to reduce the mathematical complexity. For this purpose, a database compiling binodal experimental data of 100 ILATPS has been built, so that the analysis could make it possible to obtain representative conclusions for all these systems. Several models were developed, and different statistical criteria were used to assess the advantages and disadvantages of each one of these models for the binodal curve. The results show that, when accuracy is critical, a proposed model with just an additional parameter reduced more than 25% the residual mean squared error (RMSE) with respect to the commonly used equation, without losing the statistical significance of the parameters. For complex problems where an explicit equation in both the concentration of ionic liquid and of salt is needed, the use of an explicit model developed with 3 adjusted parameters that kept high accuracy (R2 > 0.996 and RMSE < 0.66) is proposed. Finally, the analysis also revealed that a fitting method based on the minimization of relative errors is recommended to increase the accuracy of the binodal curve at high salt concentrations, which is the crucial region for assessing the recyclability of the ionic liquid.

Partitioning behavior of recombinant lipase in Escherichia coli by ionic liquid-based aqueous two-phase systems

Evaluations of ILATPSs were performed with a variety of ionic liquids and salts as phase components to figure out their competencies in the recovery of lipase from a fermentation broth of E. coli using banana waste as a substrate.

Partitioning of Vanillin in Aqueous Two-Phase Systems Formed by Cholinium Chloride and K3PO4

Abstract In recent years, the partitioning of food and pharmaceutical materials in ionic liquid-based aqueous two-phase systems (ATPSs) has attracted the attention of researchers to itself as a new approach. A new type of these aqueous two-phase systems is based on cholinium chloride. Cholinium chloride is a type of vitamin B, which is an appropriate and biocompatible ionic liquid (IL) for the processes of the extraction and separation in the food and pharmaceutical industries. In this study, with respect to the effective development of aqueous two-phase systems in vanillin separation, an aqueous two-phase system containing cholinium chloride and potassium phosphate salt has been used. The effect of the variables such as the temperature, salt weight fractions, ionic liquid weight fractions, and vanillin concentration on the partitioning coefficient of vanillin was evaluated. The results indicated that by increasing the salt weight fraction and decreasing the cholinium chloride weight fraction, the partition coefficient of vanillin increased. Nevertheless, in all stages the vanillin showed a tendency to migrate toward the ionic liquid-rich phase. The recovery percentage of vanillin showed that the cholinium chloride-based systems have the ability to improve the vanillin recovery in the ionic liquid-rich phase.

Determination of sunset yellow and tartrazine in food samples by combining ionic liquid-based aqueous two-phase system with high performance liquid chromatography.

We proposed a simple and effective method, by coupling ionic liquid-based aqueous two-phase systems (IL-ATPSs) with high performance liquid chromatography (HPLC), for the analysis of determining tartrazine and sunset yellow in food samples. Under the optimized conditions, IL-ATPSs generated an extraction efficiency of 99% for both analytes, which could then be directly analyzed by HPLC without further treatment. Calibration plots were linear in the range of 0.01–50.0 μg/mL for both Ta and SY. The limits of detection were 5.2 ng/mL for Ta and 6.9 ng/mL for SY. This method proves successful for the separation/analysis of tartrazine and sunset yellow in soft drink sample, candy sample, and instant powder drink and leads to consistent results as obtained from the Chinese national standard method.

Isolation of natural red colorants from fermented broth using ionic liquid-based aqueous two-phase systems

There is a growing demand for natural colorants. This is prompting the search for new alternative and "benign" separation systems allowing higher recoveries, extraction yields, and selectivities. This work investigates the use of aqueous two-phase systems (ATPS) based on ionic liquids as extraction processes for the recovery of red colorants from the fermented broth of Penicillium purpurogenum DPUA 1275. Several ATPS based on quaternary ammonium and imidazolium were studied in this work aiming at separating the red colorants produced from the remaining colorants and contaminant proteins present in the fermented broth. The results suggest that the red colorants can be isolated by an appropriate manipulation of some of the process conditions, such as the use of quaternary ammonium with short alkyl chains, alkaline media, and short tie-line lengths (extraction point systems with lower concentrations of ionic liquid). These conditions allow large partition coefficients for the red colorants (K red=24.4±2.3), high protein removal (60.7±2.8%) and selectivity parameters (S red/prot=10.05).

Extraction of trace tilmicosin in real water samples using ionic liquid-based aqueous two-phase systems

The effective method of ionic liquid-based aqueous two-phase extraction, which involves ionic liquid (IL) (1-butyl-3-methyllimidazolium chloride, [C4mim]Cl) and inorganic salt (K2HPO4) coupled with high-performance liquid chromatography (HPLC), has been used to extract trace tilmicosin in real water samples which were passed through a 0.45 μm filter. The effects of the different types of salts, the concentration of K2HPO4 and of ILs, the pH value and temperature of the systems on the extraction efficiencies have all been investigated. Under the optimum conditions, the average extraction efficiency is up to 95.8%. This method was feasible when applied to the analysis of tilmicosin in real water samples within the range 0.5-40 μg mL(-1). The limit of detection was found to be 0.05 μg mL(-1). The recovery rate of tilmicosin was 92.0-99.0% from the real water samples by the proposed method. This process is suggested to have important applications for the extraction of tilmicosin.

Liquid–liquid equilibrium phase behavior of iminazolium-based ionic liquid aqueous two-phase systems composed of 1-alkyl-3-methyl imidazolium tetrafluoroborate and different electrolytes ZnSO4, MgSO4 and Li2SO4 at 298.15 K: Experimental and correlation

Ionic liquid-based aqueous two-phase systems offer an attractive alternative to volatile organic solvents in liquid–liquid extraction. In this work, the phase diagrams of the 1-alkyl-3-methyl imidazolium tetrafluoroborate ([C2mim]BF4/[C4mim]BF4)+ZnSO4/MgSO4/Li2SO4+H2O ATPSs were determined at 298.15K. Three empirical equations were used to correlate the binodal data and the optimum equation was selected. The effective excluded volume (EEV) values obtained from the binodal model for these systems were determined. The EEV and the binodal curves plotted in molality both indicate that the salting-out abilities of the three salts follow the order: ZnSO4>MgSO4>Li2SO4, while the phase-separation abilities of the investigated ILs are in the order of [C4mim]BF4>[C2mim]BF4. Finally, the liquid–liquid equilibrium data were successfully correlated by the Othmer-Tobias and Bancroft equations, meanwhile the slope of tie line increased with an increase in cation alkyl chain length.

Investigation of a phosphate/1-butyl-3-methylimidazolium trifluoromethanesulfonate/water system for the extraction of 1,3-propanediol from fermentation broth

The recovery of 1,3-propanediol from fermentation broth is challenging because of its high polarity and high boiling point. Extraction is an attractive alternative to the commonly used distillation process, which is very energy intensive and thus costly. Due to the low solubility of 1,3-propanediol in organic solvents, extraction has not yet been considered. Ionic liquid-based aqueous two-phase systems could constitute an alternative extraction system for the purification of 1,3-propanediol and are therefore investigated in this study. The distribution coefficient of 1,3-propanediol and the selectivity for it over the by-products of the fermentation, i.e., acetic acid and butyric acid, are determined in different ionic liquid-based aqueous two-phase systems. Based on these results, the ionic liquid-based aqueous two-phase system, phosphate/1-butyl-3-methylimidazolium trifluoromethanesulfonate (Im4,1 CF3SO3), is chosen for further investigation. The effects of the temperature, pH and Im4,1 CF3SO3, phosphate and 1,3-propanediol mass fractions on the phase diagram are examined. Furthermore, the influence of the fermentation by-products on the liquid–liquid equilibrium is determined. All experiments were performed using synthetic media to identify the effects of the process parameters independently from non-ideality incorporated through the use of real fermentation broth. To verify that this approach leads to correct results, results obtained with fermentation broth were compared to those obtained with synthetic media prior to these experiments. The recovery and potential re-use of the ionic liquid, Im4,1 CF3SO3, is finally analysed by repeating some of the experiments with recovered ionic liquid.

Extraction of Puerarin using Ionic Liquid Based Aqueous Two-Phase Systems

Various ionic liquid-based aqueous two-phase systems (IL-ATPS) were evaluated to extract puerarin. The results indicated that the nature of ILs, the salting-out ability of salt, and the acidity and basicity of the salt-rich solution had important influence on the extraction efficiency. Various factors were optimized systematically, that is, the amount of IL, salt, puerarin, and short-chain alcohol. Under the optimal experimental conditions (the amount of K2HPO4 0.30–0.42 g/mL, [Bmim]Br 0.30–0.36 g/mL and 1.0 mL puerarin stock solution), the extraction efficiency of puerarin was over 99% by a single-step extraction, which indicated that the evaluated IL-ATPS was a prospective extraction medium. Finally, the IL-ATPS was successfully used to extract puerarin from Radix Puerariae Lobatae extracts.

Isolation and purification of aloe anthraquinones based on an ionic liquid/salt aqueous two-phase system

Abstract To explore mild and efficient techniques for separation and purification of the active ingredients in natural plants is still ongoing. Ionic liquid (IL) is a new class of molten salts that are liquid at ambient temperature, which has many unique properties is safe and environmentally friendly chemical. Aqueous two-phase systems (ATPSs) based on ILs and salts were applied to isolate and purify anthraquinones (AQs) from aloe leaves. The main affecting parameters on the partitioning behavior and extraction efficiency were investigated through the partitioning process: type and mass of salt, pH, extraction temperature, and equilibrium time of the systems. Aloe AQs preferentially migrated into the IL-rich phase. Under the optimal conditions, the maximal extraction efficiency 92.1% of total AQs was obtained with the [C 4 mim]BF 4 /Na 2 SO 4 system at 25 °C and pH 4.0. The reverse extraction experiments were done by adjusting pH with IL being recycled. Furthermore, the major constituents of aloe-emodin and chrysophanol were analyzed by a HPLC method. Ionic liquid-based ATPSs (ILATPSs) are great candidates for the replacement of volatile organic compounds in typical liquid–liquid extraction. This proposed extraction technique opens up new possibilities in purification of other active ingredients in natural plants or biologic samples.

Extraction of 1,3-propanediol from aqueous solutions using different ionic liquid-based aqueous two-phase systems

The separation of 1,3-propanediol from water is challenging because of its high polarity and high boiling point. Thus far, extraction has not been considered a potential separation method because of the extremely low solubility of 1,3-propanediol in organic solvents. However, aqueous two-phase systems could be used to overcome this limitation. Hence, the aim of the present study was to investigate the ability of water miscible ionic liquids to build aqueous two-phase systems for the separation of 1,3-propanediol. Different ionic liquids were tested using 1-butyl-3-methylimidazolium trifluoromethansulfonate as the initial ionic liquid, and the type of anion (dicyanamide, thiocyanate, methysulfate) and structure of the cation (1-butyl-3-methylmorpholinium, 1-butyl-3-methylpyrrolidinium, 1-ethyl-3-methylimidazolium, 1-methoxyethyl-3-methylimidazolium) were independently varied. All investigated ionic liquids showed the ability to form two phases by adding a mixture of K2HPO4 and KH2PO4; however, the phase forming strength differs. An increase in the polarity of the ionic liquid leads to smaller miscibility gaps of the resulting aqueous two-phase systems. Additionally, the performance of the aqueous two-phase systems in the extraction of 1,3-propanediol was investigated. The results indicated that all of the aqueous two-phase systems are suitable for the extraction of 1,3-propanediol and the distribution coefficient of 1,3-propanediol depends on the polarity or hydrogen-bond accepting strength of the cation and anion.

Ionic liquid-based aqueous two-phase extraction within a microchannel system

Ionic liquid-based aqueous two-phase systems (IL-ATPSs) are great candidates for the replacement of volatile organic solvents in liquid–liquid extractions. Besides, microfluidic separation techniques are a promising alternative to conventional systems since they provide continuous operation, better performance and easier capacity increase by a numbering-up approach. Herein, the advantages of IL-ATPSs and microfluidic continuous separation were combined within a microfluidic device with parallel flow allowing for the separation of the two phases at the exit of the microchannel. An aqueous solution of [C4mim] [BF4] and d-fructose was used as an IL-ATPS and compared with a conventional ATPS consisted of polyethylene glycol/salt solution. Based on the evaluated partitioning coefficient of a model substance, namely bovine serum albumin, the ionic liquid concentration and pH value of the IL-ATPS have been selected for the use within a pressure-driven microchannel system with y-shaped inlet and outlet. Furthermore, a three-dimensional model considering convection in the flow direction and diffusion in all spatial directions at steady-state conditions was developed, validated by experimental results and used to assess the feasibility of micro-scale parallel flow extraction in a wide range of flow rates. The chosen IL-ATPS was shown to be much more efficient media for continuous microfluidic extraction as compared to conventional ATPS, primarily due to much lower dynamic viscosity of IL-rich phase related to PEG-rich phase.

Production and purification of an extracellular lipolytic enzyme using ionic liquid-based aqueous two-phase systems

The ability of ionic liquid-based aqueous two-phase systems (ATPS) to purify lipase produced by fermentation is here evaluated and compared against conventional PEG-based ATPS systems. Four ionic liquids, chosen after screening of a larger number of ionic liquids are evaluated, with the maximum purification and higher recovery being obtained for the systems based on [C8mim]Cl. It is shown that IL-based ATPS have a performance superior to PEG-based ATPS for the purification of this enzyme.

Driving forces of protein partitioning in an ionic liquid-based aqueous two-phase system

Extraction of catalytically active biomolecules using ionic liquid-based aqueous two-phase systems (IL-based ATPS) composed of the IL Ammoeng™ 110 and K 2HPO 4/KH 2PO 4 represents a powerful tool for the integration of several process steps into one unit operation within downstream processing. The technique can be used in order to combine the purification of active enzymes with the performance of enzyme-catalysed reactions. However, a fundamental understanding of the driving forces which are involved in the partitioning of proteins between the two phases is still lacking. By investigating the distribution of four model proteins at varying system characteristics of the IL-based ATPS, we found a combination of different interactions between the proteins and the ionic liquid to be responsible for the enrichment within the IL-containing upper phase. Among these, the proteins’ charge as well as the molecular weight is of major importance. Therefore, we propose the electrostatic interaction between the charged amino acid residues at a protein's surface and the positively charged IL-cation to be the main driving force of the extraction process. Based on these findings, a model for describing protein partitioning in IL-based ATPS was established and employed for predicting the partition coefficient of two further model proteins, pepsin and hemoglobin.