Jonathan G. Huddleston

Characterization and comparison of hydrophilic and hydrophobic room temperature ionic liquids incorporating the imidazolium cation

A series of hydrophilic and hydrophobic 1-alkyl-3-methylimidazolium room temperature ionic liquids (RTILs) have been prepared and characterized to determine how water content, density, viscosity, surface tension, melting point, and thermal stability are affected by changes in alkyl chain length and anion. In the series of RTILs studied here, the choice of anion determines water miscibility and has the most dramatic effect on the properties. Hydrophilic anions (e.g., chloride and iodide) produce ionic liquids that are miscible in any proportion with water but, upon the removal of some water from the solution, illustrate how sensitive the physical properties are to a change in water content. In comparison, for ionic liquids containing more hydrophobic anions (e.g., PF6− and N(SO2CF3)2−), the removal of water has a smaller affect on the resulting properties. For a series of 1-alkyl-3-methylimidazolium cations, increasing the alkyl chain length from butyl to hexyl to octyl increases the hydrophobicity and the viscosities of the ionic liquids increase, whereas densities and surface tension values decrease. Thermal analyses indicate high temperatures are attainable prior to decomposition and DSC studies reveal a glass transition for several samples. ILs incorporating PF6− have been used in liquid/liquid partitioning of organic molecules from water and the results for two of these are also discussed here. On a cautionary note, the chemistry of the individual cations and anions of the ILs should not be overlooked as, in the case of certain conditions for PF6− ILs, contact with an aqueous phase may result in slow hydrolysis of the PF6− with the concomitant release of HF and other species.

Room temperature ionic liquids as novel media for ‘clean’ liquid–liquid extraction

The partitioning of simple, substituted-benzene derivatives between water and the room temperature ionic liquid, butylmethylimidazolium hexafluorophosphate, is based on the solutes’ charged state or relative hydrophobicity; room temperature ionic liquids thus may be suitable candidates for replacement of volatile organic solvents in liquid–liquid extraction processes.

Polyethylene glycol and solutions of polyethylene glycol as green reaction media

In this review, we examine the concept that aqueous biphasic reactive extraction (ABRE) can successfully integrate the solvent properties of polyethylene glycol (PEG) and its phase-transfer characteristics into a single efficient system which can additionally be manipulated to facilitate the separation of reactants and/or catalysts from products. We also suggest that the properties of these systems may recommend them as being relatively environmentally benign in comparison to the current use of organic solvents in extraction and in reactive extraction. In developing this concept, we review a number of the physical and chemical properties of PEG and aqueous solutions of PEG in the context of recent applications to chemical reaction engineering. Thus, we cover the interesting physical properties of PEG solutions in water, their unique solvent properties, and finally the metal cation coordination ability of PEG solutions. These properties are important in the application of low molecular weight liquid PEG as a solvent in chemical reactions; in the use of PEG as an alternative phase-transfer catalyst (PTC); and in the application of ABRE in the development of alternative pulping processes, catalytic chemistry, and enzymatic catalysis.

Ionic liquid salt-induced inactivation and unfolding of cellulase from Trichoderma reesei

The potential for performing cellulase-catalyzed reactions on cellulose dissolved in 1-butyl-3-methylimidazolium chloride ([bmim]Cl) has been investigated. We have carried out a systematic study on the irreversible solvent and ionic strength-induced inactivation and unfolding of cellulase from Trichoderma reesei (E.C. #3.2.1.4). Experiments, varying both cellulase and IL solvent concentrations, have indicated that [bmim]Cl, and several other ILs, as well as dimethylacetamide–LiCl (a well-known solvent system for cellulose), inactivate cellulase under these conditions. Despite cellulase inactivity, results obtained from this study led to valuable insights into the requirements necessary for enzyme activity in IL systems. Enzyme stability was determined during urea, NaCl, and [bmim]Cl-induced denaturation observed through fluorescence spectroscopy. Protein stability of a PEG-supported cellulase in [bmim]Cl solution was investigated and increased stability/activity of the PEG-supported cellulase in both the [bmim]Cl and citrate buffer solutions were detected.

Partitioning of small organic molecules in aqueous biphasic systems

Aqueous biphasic systems (ABS) are suitable for the separation of small organic molecules in industrial and environmental applications and thus, it is important to correlate partitioning behavior of model organic solutes with their structure in order to develop predictive models. The partitioning behavior of five, uncharged, substituted benzenes (benzene, toluene. chlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene) were studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts (K3PO4, K2CO3, (NH4)2SO4 and NaOH). For a given solute and a defined concentration of salt, the partition coefficients increase as the deltaGhyd value of the salt anion becomes more negative (e.g., Dbenzene increases in the order OH- <SO42- <CO32- <PO43-). In a given salt, the distribution ratios increase in the order benzene<toluene<chlorobenzene< 1,4-dichlorobenzene< 1,2,4-trichlorobenzene. The partitioning behavior of the solutes in PEG-salt ABS was found to be strongly correlated with their partitioning coefficients in 1-octanol-water biphasic systems.

Investigation of aqueous biphasic systems for the separation of lignins from cellulose in the paper pulping process.

In efforts to apply a polymer-based aqueous biphasic system (ABS) extraction to the paper pulping process, the study of the distribution of various lignin and cellulosic fractions in ABS and the effects of temperature on system composition and solute partitioning have been investigated. The partitioning of three lignin species (Indulin AT, Indulin C, and Reax 85A) have been studied in ABS prepared from stock solutions of 40% (w/w) poly(ethylene glycol) (PEG)-2000 and increasing concentrations of K2CO3, (NH4)2SO4, and NaOH. The partitioning of these lignins is affected by the free energy of hydration of the salt forming the ABS, the tie line length, and the dissociation of the sulfonic acid and hydroxyl groups of the distributed solutes. The partitioning of fibrous cellulose and diethylaminoethyl cellulose have been studied in 40% (w/w) PEG-2000-(NH4)2SO4 ABS. The hydrophilic nature of these species is important in terms of their phase preference when designing a polymer-based aqueous biphasic extraction process for use in a paper pulping process. Both cellulosic samples do not dissolve, but rather report to the salt-rich phase of an ABS. In both chemical pulping and Organosolv pulping, temperatures in excess of 120 degrees C are needed to solubilize the lignin from the cellulose fraction of wood. To study the effects of temperature on the phase diagram and solute partitioning, phthalic acid and NH499TcO4 (as system probes) have been partitioned in 40% (w/w) PEG-2000-(NH4)2SO4 ABS at known tie line lengths as a function of temperature. Temperature does not appear to affect the partitioning results beyond the expected increase in phase divergence as temperature is increased. The PEG-2000 polymer itself appears to be stable to chemical pulping conditions.

Separation and recovery of food coloring dyes using aqueous biphasic extraction chromatographic resins

Aqueous biphasic systems (ABS) and aqueous biphasic extraction chromatographic (ABEC) resins are currently under investigation for their utility in the removal of color from textile plant wastes. The structures of several widely used food colorings, suggest that these dyes would also be retained on the resins. In work currently in progress, we have begun to investigate the retention and resolution of several common food colorings including indigo carmine, amaranth, carminic acid. erythrosin B, tartrazine and quinoline yellow. The relationship between the uptake of these dyes on ABEC resins in terms of the binding strengths and capacities of the resins and their partitioning behavior in ABS is illustrated. Some possible theoretical and practical approaches to the prediction of the partitioning and retention behavior is discussed.

PARTITIONING OF AROMATIC MOLECULES IN AQUEOUS BIPHASIC SYSTEMS

ABSTRACT Aqueous biphasic systems (ABS) may be suitable for the separation of aromatic molecules in industrial and environmental settings; hence it is invaluable to have predictive models of partitioning behavior in these systems for design and evaluation purposes. In a continuing study of the partition of small aromatic organic molecules, the distribution of several relatively hydrophilic substituted benzene species is reported. The partitioning behavior of five charged substituted benzene species (phthalic acid, 4-hydroxybenzoic acid, benzoic acid, salicylic acid, and p-toluic acid) and one uncharged species (1,3-dinitrobenzene) has been studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts [K3PO4, K2CO3, (NH4)2SO4, and NaOH]. Comparison has been made with published data on the partitioning of these solutes in 1-octanol/water biphasic systems. In general, the partition of these species may be understood in terms of the free energ...

Renewable plant-based soybean oil methyl esters as alternatives to organic solvents

The physico-chemical properties of soybean oil methyl ester (SBME), better known as biodiesel, of importance to its use as a solvent in liquid–liquid separations have been examined. Partition coefficients of several organic species between SBME–water have been determined and compared to log P (1-octanol–water). The free energy of transfer of a methylene group has been obtained and the solvent properties of the SBME–water system determined from distribution data of a small solute set using Abrahams generalized solvation equation. Solute distribution behavior is similar to that found for conventional organic solvent–water systems, but is most similar to other vegetable oils such as olive oil. When ionizable solutes are partitioned in the SBME–water system at differing pH, the neutral species show the highest distribution. Partitioning is dependent on the solutes ability to form hydrogen bonds between water and its charged state. Metal ions (e.g., Fe3+, Co2+, and Ni2+) exhibit moderate partitioning to the SBME phase from water only in the presence of extractants. Actinides (UO22+, Am3+) exhibit significant partitioning to the SBME from aqueous solutions with the use of octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO). Soybean oil methyl ester may be a suitable “green” alternative for the replacement of volatile organic solvents in liquid–liquid extractions in selected applications.

Aqueous biphasic systems. Partitioning of organic molecules: A QSPR treatment

The partitioning of 29 small organic probes in a PEG-2000/(NH4)2SO4 biphasic system was investigated using a quantitative structure-property relationship (QSPR) approach. A three-descriptor equation with the squared correlation coefficient (R2) of 0.97 for the partition coefficient (log D) was obtained. All descriptors were derived solely from the chemical structure of the compounds. Using the same descriptors, a three-parameter model was also obtained for log P (octanol/water, R2=0.89); predicted log P values were used as an external descriptor for modeling log D.