Valorisation of red beet waste: one-step extraction and separation of betalains and chlorophylls using thermoreversible aqueous biphasic systems

Globally, up to 50% of root crops, fruits and vegetables produced is wasted. Beetroot stems and leaves fit into this scenario, with only a small fraction being used in cattle food. One way of approaching this problem is through their valorisation, by extracting and recovering valuable compounds present in this type of waste that could be used in other applications, while contributing towards a circular economy. In this work, a new integrated process using thermoreversible aqueous biphasic systems (ABS) composed of quaternary ammonium-based ionic liquids (ILs) and polypropyleneglycol 400 g mol−1 (PPG) is shown to allow the one-step extraction and separation of two pigment classes—betalains and chlorophylls—from red beet stems and leaves. The pigment extraction was carried out with a monophasic aqueous solution of the IL and PPG, whose phase separation was then achieved by a temperature switch, resulting in the simultaneous separation of chlorophylls and betalains into opposite phases. A central composite design was used to optimise the extraction parameters (time, temperature, and solid : liquid (S/L) ratio) of both pigment extraction yields, reaching at 20 °C, 70 min and a S/L ratio of 0.12 a maximum extraction yield of 6.67 wt% for betalains and 1.82 wt% for chlorophylls (per weight of biomass). Moreover, it is shown that aqueous solutions of ILs better stabilise betalains than the gold standard solvent used for the extraction method. Among the studied systems, the ABS comprising the IL N-ethyl-N-methyl-N,N-bis(2-hydroxyethyl) bromide ([N21(2OH)(2OH)]Br) presented the best separation performance, with an extraction efficiency of 92% and 95% for chlorophylls and betalains, respectively, for opposite phases. The pigments were removed from the respective phases using affinity resins, with high recoveries: 96% for betalains and 98% for chlorophylls, further allowing the IL reuse. Finally, the cyto- and ecotoxicities of the quaternary ammonium-based ILs were determined. The obtained results disclosed low to negligible toxicity in the thousands of mg L−1 range, with [N21(2OH)(2OH)]Br being harmless from an ecotoxicological point of view. Overall, it is shown here that the developed process is an innovative approach for the one-step extraction and selective separation of pigments contributing to the valorisation of waste biomass

Multiphase equilibrium in mixtures of [C(4)mim][PF6] with supercritical carbon dioxide, water, and ethanol: Applications in catalysis

The ionic liquid [C(4)mim][PF6] and supercritical carbon dioxide produce multiphase systems when mixed with ethanol and water. Mixtures of these four solvents can be made to go, by small changes in composition, through a succession of phase changes, involving one, two and three-phase situations. Increasing carbon dioxide pressure induces first the appearance of an intermediate liquid phase and later the merging of this phase with the gas, leaving all the ionic liquid in a separate, denser liquid. This succession is suitable to carry out reaction cycles in ionic liquid-based solvents, with complete recovery of the reaction product by CO2 decompression

Phase behaviour of room temperature ionic liquid solutions: an unusually large co-solvent effect in (water plus ethanol)

A surprising mixed solvent effect, both in its magnitude and direction, has been found in the phase diagram of the ternary mixture of ([C4mim][PF6]+(water+ethanol)). For a molar ratio of 1∶1 of water to ethanol, the co-solvent effect in the near-critical demixing temperature can be as large as 80 K

Design of task-specific fluorinated ionic liquids: nanosegregation versus hydrogen-bonding ability in aqueous solutions

We demonstrate that fluorinated ionic liquids reduce the impact of the addition of water upon the ionic liquid's H-bond acceptance ability. This is a key factor to obtain functionalized materials to be used e.g. in the dissolution of biomolecules, extraction processes or material engineering

Thermophysical and thermodynamic properties of 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium hexafluorophosphate over an extended pressure range

The current study focuses on 1-butyl-3-methylimidazolium tetrafluoroborate, [bmim] [BF4], and 1-butyl3-methylimidazolium hexafluorophosphate, [bmim] [PF6]. The objective is to study the influence of pressure as well as that of the anion on several properties of this type of ionic liquid. The speed of sound and densities in pure ionic liquids (ILs) as a function of temperature and pressure have been determined. Several other thermodynamic properties such as compressibilities, expansivities, and heat capacities have been obtained. To the best of our knowledge, this research comprises both the first speed of sound data and the first evaluation of heat capacities at high pressures for ILs. Speed of sound measurements have been carried out in broad ranges of temperature (283 < T/K < 323) and pressure (0.1 < p/MPa < 150), sometimes inside the metastable liquid region using a nonintrusive microcell. The T-P melting line of [bmim] [PF6] has also been determined by an acoustic method. Density measurements have been performed for broad ranges of temperature (298 < T/K < 333) and pressure (0.1 < p/MPa < 60) using a vibrating tube densimeter. The pressure dependence of the heat capacities, which is generally mild, is found to be highly dependent on the curvature of the temperature dependence of the density

Two ways of looking at Prigogine and Defay's equation

In the search for understanding of several types of abnormal thermodynamic behaviour in the vicinity of critical lines of binary liquid mixtures, we have revisited an apparently forgotten relationship between the pressure dependence of the critical temperature and the second derivatives with respect to the composition of the volumetric and enthalpic properties of the mixture. We refer to an equation originally developed in the fifties by Prigogine and Defay and soon afterwards analysed by others. Under some restrictive assumptions, the T-p slope of the critical locus can simply be inferred from the ratio between v(E) and h(E). The interest and usefulness of this approximate relation is self-evident. Values for any one of the three properties involved, (dT/dp)(c), v(E) or h(E), can be assessed based on the availability of the other two. Moreover, the amplitude of the divergence of thermodynamic response functions to criticality are intimately associated with the slope of the critical locus. A link between critical behaviour and solution excess properties is thus established. For instance, double critical points tend to occur if one of the excess properties changes its sign as the temperature or pressure is varied. In this work, we have started a detailed study of the practical limits of validity of the approximate relation. Five binary liquid mixtures were tested, all of them sharing a UCST/LCSP-type of phase transition. Although, from a theoretical perspective, the original second-derivatives approach should perform better, in practice, the direct ratio of the excess properties constitutes a superior strategy for obtaining (dT/dp)(c) values. The underlying reasons for this are discussed in detail. The T-p critical slope is normally found to play a secondary role in assessing the critical amplitudes of diverging thermodynamic functions

Pressure, isotope, and water co-solvent effects in liquid-liquid equilibria of (ionic liquid plus alcohol) systems

Liquid-liquid phase splitting in ternary mixtures that contain a room-temperature ionic liquid and an alcohol aqueous solution-namely, [bmim] [PF6] + ethanol + water and [bmim] [NTf2] + 2-methylpropanol + water-is studied. Experimental cloud-point temperatures were obtained up to pressures of 400 bar, using a He-Ne laser light-scattering technique. Although pressurization favors mutual miscibility in the presence of high concentrations of alcohols, the contrary occurs in water-rich solutions. Both ternary mixtures exhibit a very pronounced water-alcohol co-solvent effect. Solvent isotope effects are also investigated. Phase diagrams are discussed using a phenomenological approach based on a "polymer-like" G(E) model coupled with the statistical-mechanical theory of isotope effects. The combined effect of a red shift of -15 cm(-1) for the O-H deformation mode of ethanol with a blue shift of +35 cm(-1) for the O-H stretching mode, both of which occurring after liquid infinite dilution in the ionic liquid, rationalizes the observed isotope effect in the phase diagram. Predicted excess enthalpy (H-E) values are inferred from the model parameters. Furthermore, using the Prigogine-Defay equation, an estimation of the excess volumes (V-E) is obtained

Criticality of the [C(4)mim] [BF4] plus water system

A study of the behavior of the response functions of the [C(4)mim][BF4] + water ionic binary solution near its liquid-liquid critical point at atmospheric pressure is presented. Phase equililibrium temperatures, which allow to obtain the critical coordinates of this system, are determined. Measurements of the isobaric heat capacity per unit volume in the critical region indicate Ising-like behavior. The slope of the critical line, (dT/dp)(c), is estimated by means of Prigogine and Defay's equation using experimentally determined excess volumes and excess enthalpies as a function of temperature. (dT/dp)(c) is found to be near zero. The consequences of this fact for the global critical behavior of second-order volumetric derivatives are discussed

Double critical phenomena in (water plus polyacrylamides) solutions

Aqueous solutions of a copolymer derivative of a polyacrylamide showed very interesting behavior, that in which the system evolves from one kind of double criticality (pressure-hypercritical point) to another (temperature-hypercritical point) as polymer molecular weight decreases. While in the neighboring region of the former point one expects a change from contraction to expansion upon mixing with increasing pressure; in the latter, mixing should be accompanied by a change in the sign of the excess enthalpy as temperature increases. L-L equilibria studies were performed in a wide range of (T, p) experimental conditions (300 <T/K <460, 0 <p/bar <700). Poly(N-isopropylacrylamide), usually called PNIPAAM, and its copolymer derivative poly(N-isopropylacrylamide/1-deoxy-1-methacrylamido-D-glucitol), herein referred to as CP, were investigated for several chain lengths and compositions. An He/Ne laser light scattering technique was used for the determination of cloud-point (T, p, x) conditions. The experimental results were used to assist in the determination of computed values at temperatures beyond experimental accessibility, which are obtained by the application of a modified Flory-Huggins model. The model also estimates the excess properties of these solutions. Because of the intrinsic self-associating nature of these systems, all studied solutions show a lower critical solution temperature (LCST). Both modeling results and H/D isotope substitution effects suggest also the existence of upper critical solution temperatures (UCST) and therefore closed-loop-type phase diagrams. However, these upper-temperature branches are experimentally inaccessible. Pressure effects are particularly interesting. For a low-MW CP, experimental data display a tendency toward a reentrant T-p locus, which supports the conjecture that these systems are inherently of the closed-loop type. In the cases of PNIPAAMs and high-MW CPs, the T-p isopleths show extrema. The copolymer aqueous solutions under study in this work model a single chemical system where pressure-hypercritical behavior evolves to a temperature-hypercritical one as the chain length decreases

A detailed thermodynamic analysis of [C(4)mim][BF4] plus water as a case study to model ionic liquid aqueous solutions

Since determining experimentally a wide variety of thermophysical properties - even for a very small portion of the already known room temperature ionic liquids ( and their mixtures and solutions) - is an impossible goal, it is imperative that reliable predictive methods be developed. In turn, these methods might offer us clues to understanding the underlying ion - ion and ion - molecule interactions. 1-Butyl-3-methylimidazolium tetrafluoroborate, one of the most thoroughly investigated ionic liquids, together with water, the greenest of the solvents, have been chosen in this work in order to use their mixtures as a case study to model other, greener, ionic liquid aqueous solutions. We focus our attention both on very simple methodologies that permit one to calculate accurately the mixture's molar volumes and heat capacities as well as more sophisticated theories to predict excess properties, pressure and isotope effects in the phase diagrams, and anomalies in some response functions to criticality, with a minimum of information. In regard to experimental work, we have determined: ( a) densities as a function of temperature (278.15 <T/ K <333.15), pressure ( 1 <p/bar <600), and composition (0 <x(IL) <1), thus also excess molar volumes; (b) heat capacities and excess molar enthalpies as a function of temperature ( 278.15 <T/ K <333.15) and composition ( 0 <xIL <1); and ( c) liquid - liquid phase diagrams and their pressure ( 1 <p/ bar <700) and isotopic (H2O/D2O) dependences. The evolution of some of the aforementioned properties in their approach to the critical region has deserved particular attention