High Ionic Liquid Concentrations Research Articles

A Thermophilic Ionic Liquid-Tolerant Cellulase Cocktail for the Production of Cellulosic Biofuels

Generation of biofuels from sugars in lignocellulosic biomass is a promising alternative to liquid fossil fuels, but efficient and inexpensive bioprocessing configurations must be developed to make this technology commercially viable. One of the major barriers to commercialization is the recalcitrance of plant cell wall polysaccharides to enzymatic hydrolysis. Biomass pretreatment with ionic liquids (ILs) enables efficient saccharification of biomass, but residual ILs inhibit both saccharification and microbial fuel production, requiring extensive washing after IL pretreatment. Pretreatment itself can also produce biomass-derived inhibitory compounds that reduce microbial fuel production. Therefore, there are multiple points in the process from biomass to biofuel production that must be interrogated and optimized to maximize fuel production. Here, we report the development of an IL-tolerant cellulase cocktail by combining thermophilic bacterial glycoside hydrolases produced by a mixed consortia with recombinant glycoside hydrolases. This enzymatic cocktail saccharifies IL-pretreated biomass at higher temperatures and in the presence of much higher IL concentrations than commercial fungal cocktails. Sugars obtained from saccharification of IL-pretreated switchgrass using this cocktail can be converted into biodiesel (fatty acid ethyl-esters or FAEEs) by a metabolically engineered strain of E. coli. During these studies, we found that this biodiesel-producing E. coli strain was sensitive to ILs and inhibitors released by saccharification. This cocktail will enable the development of novel biomass to biofuel bioprocessing configurations that may overcome some of the barriers to production of inexpensive cellulosic biofuels.

Electrospinning of Ion Jelly fibers

Ion Jelly materials combine the chemical versatility and conductivity of an ionic liquid (IL) with the morphological versatility of a biopolymer (gelatin). They exhibit very interesting properties, such as conductivities up to 10−4Scm−1, and high thermostability up to 180°C, and have been used successfully to design electrochromic windows. In this work we report on the preparation of Ion Jelly fibers through electrospinning in order to obtain high surface area conductive materials. We have used the IL 1-(2-hydroxyethyl)-3-methyl-imidazolium tetrafluoroborate ([C2OHmim]BF4), which exhibits conveniently high ionic conductivity (over 10−3Scm−1) and electrochemical stability (electrochemical window over 6.0V). The morphology of the obtained fibers was quantified using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). We found that on average the effect of the IL on fiber diameter differs for lower and higher IL concentrations and that this effect was correlated with the initial conductivity and viscosity of Ion Jelly electrospinning solution. Moreover we also found that conductivities of Ion Jelly fibers are of the same order of magnitude as the conductivities of Ion Jelly dense films (~10−4Scm−1). To the best of our knowledge, this is the first report on the incorporation of an IL into gelatin fibers using electrospinning. This opens up new opportunities for the application of gelatin fibers in electrochemical and biomedical devices.

Ionic liquid-dependent morphological changes of CdOx and ZnOx deposited on multiwalled carbon nanotubes

We demonstrated the in situ synthesis of CdOx and ZnOx and their direct deposition on the multiwalled carbon nanotubes (MWCNTs) through an ionic liquid-assisted sonochemical method (ILASM). The morphologies of CdOx and ZnOx such as nanoparticles and layers were determined by the types of ionic liquids (ILs). When MWCNTs were functionalized by less polar and more viscous ILs such as BMimPF6 and HMimBF4 compared to BMimBF4, the layered structures or aggregation of CdOx and ZnOx were constructed. For the presence of BMimBF4, the discrete CdOx and ZnOx nanoparticles were formed due to the fast growth into nanocrystals by the high mobility of precursors. Furthermore, nanoparticles were not uniformly coated and aggregated in polar BMimHSO4 and high concentration of IL. Therefore, the morphologies of the decorated nanoparticles could be controlled by the properties of ILs as the mobility of precursors for particle growth was strongly influenced by the surface chemistry of MWCNTs.

Simple purification of ionic liquid solvents by nanofiltration in biorefining of lignocellulosic substrates

Abstract Ionic liquids are excellent but expensive solvents to dissolve lignocellulose for biofuel production. Since it is presumed that ionic liquids cannot be cost-effectively purified in large-scale processes, they are simply avoided as solvents. Thus, this study aims to investigate the feasibility of ionic liquid purification via nanofiltration membranes with regards to permeate flux and rejection performance. Two commercially available polyamide and one polyimide membranes were used to separate saccharide products from various feed concentrations of the ionic liquid 1,3-dimethylimidazolium dimethylphosphate. At high concentrations of ionic liquid, there was a marked decrease in permeate flux for all tested membranes due to low permeability of the ionic liquid and due to osmotic pressure differences. At low feed concentrations of this ionic liquid, the concentration of products in the permeate was significantly lower using the polyamide membranes than with the polyimide membranes. Conversely, at high feed ionic liquid concentrations, the contaminant concentrations significantly decreased using the polyimide membrane. In conclusion it is feasible to recover ionic liquid solvent up to a purity of 80% by using both polyamide and polyimide membranes. Since they are non-volatile and environmentally friendly in general, ionic liquids are very suitable candidates to replace conventional organic solvents in lignocellulose refining.

Metagenomic cellulases highly tolerant towards the presence of ionic liquids—linking thermostability and halotolerance

Cellulose is an important renewable resource for the production of bioethanol and other valuable compounds. Several ionic liquids (ILs) have been described to dissolve water-insoluble cellulose and/or wood. Therefore, ILs would provide a suitable reaction medium for the enzymatic hydrolysis of cellulose if cellulases were active and stable in the presence of high IL concentrations. For the discovery of novel bacterial enzymes with elevated stability in ILs, metagenomic libraries from three different hydrolytic communities (i.e. an enrichment culture inoculated with an extract of the shipworm Teredo navalis, a biogas plant sample and elephant faeces) were constructed and screened. Altogether, 14 cellulolytic clones were identified and subsequently assayed in the presence of six different ILs. The most promising enzymes, CelA2, CelA3 (both derived from the biogas plant) and CelA84 (derived from elephant faeces), showed high activities (up to 6.4 U/mg) in the presence of 30% (v/v) ILs. As these enzymes were moderately thermophilic and halotolerant, they retained 40% to 80% relative activity after 34 days in 4 M NaCl, and they were benchmarked with two thermostable enzymes, CelA from Thermotoga maritima and Cel5K from a metagenome library derived from Avachinsky crater in Kamchatka. These enzymes also exhibited high activity (up to 11.1 U/mg) in aqueous IL solutions (30% (v/v)). Some of the enzymes furthermore exhibited remarkable stability in 60% (v/v) IL. After 4 days, CelA3 and Cel5K retained up to 79% and 100% of their activity, respectively. Altogether, the obtained data suggest that IL tolerance appears to correlate with thermophilicity and halotolerance.

Thermodynamic studies of the ionic liquid 1-hexyl-3-methylimidazolium chloride [C 6mim][Cl] in polyethylene glycol aqueous solutions

Vapour pressure osmometery (VPO) measurements at T = 308.15 K for {[C 6mim][Cl] + water}, {[C 6mim][Cl] + (0.005, 0.0155, and 0.0263) mol · kg −1 PEG2000 + water} and {[C 6mim][Cl] + (0.0017, 0.0052, and 0.0088) mol · kg −1 PEG6000 + water} systems and isopiestic measurements at T = 298.15 K for {[C 6mim][Cl] + PEG2000 + water} and {[C 6mim][Cl] + PEG6000 + water} systems have been carried out. The VPO measurements were carried out at very low concentrations of PEG and from which the values of the water activities, osmotic coefficients, vapour pressure and activity coefficients were obtained. The data obtained from the VPO method show that over the whole concentration range of the ionic liquid (IL), the activity coefficients of [C 6mim][Cl] in the presence of PEG2000 are increased. Although, at high IL concentrations, the values of the activity coefficient of [C 6mim][Cl] in the presence of PEG6000 are also increased, however for low concentrations of IL the values of the activity coefficient of [C 6mim][Cl] in pure water are larger than those in aqueous PEG6000 solutions. For a known IL concentration, the values of water activity coefficient for the binary {[C 6mim][Cl] + water} system are larger than those for the ternary {[C 6mim][Cl] + PEG + water} systems and decrease by increasing the concentration of PEG or decreasing the molar mass of PEG. The constant water activity lines of the all ternary systems obtained from the isopiestic method show positive deviation from the linear isopiestic relation (Zdanovskii–Stokes–Robinson rule) derived using the semi-ideal hydration model. The results have been interpreted in terms of the solute–water and solute–solute interactions.

Water Solubilization Capacity and Volume-Induced Percolation of Sodium Bis(2-ethylhexyl)sulfosuccinate Microemulsions in the Presence of 1-Alkyl-3-Methylimidazolium Chloride Ionic Liquids

The water solubilization capacity of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in isooctane microemulsions in the presence of chloride anion-based ionic liquids (ILs), such as 1-ethyl-3-methylimidazolium chloride (emimCl), 1-butyl-3-methylimidazolium chloride (bmimCl), and 1-octyl-3-methylimidazolium chloride (omimCl), was investigated. The water solubilization capacity is enhanced at low IL concentrations but decreases at high concentrations of IL. Meanwhile, the water solubilization capacity increases with the increase of chain length of ILs at low IL concentrations. The effect of ILs on the volume-induced percolation of AOT microemulsions was also studied. For the microemulsions, with an increasing volume fraction of dispersed phase (Φ), no percolation phenomena can be observed at high concentrations of IL, whereas the percolation conductance occurs at low IL concentrations and the percolation threshold (Φp) increases with the increase of IL concentrations. For the IL-containing microemulsions, the ...

Studies of laccase from Trametes versicolor in aqueous solutions of several methylimidazolium ionic liquids

Stability and kinetic behavior of laccase from Trametes versicolor in the presence of several ionic liquids from the methylimidazolium family have been investigated. In general laccase stability diminished as the size of the alkylic substitute in the methylimidazolium ring increased. Higher concentrations of ionic liquids caused more destabilization than lower ones. Thus, low concentrations of [C 2mim +][ EtSO 4 - ] allowed maintaining enzymatic stability. [C 4mim +][Cl −] appeared to have a stabilizing effect on laccase, as little activity decay was observed within three weeks. Kinetic studies indicated that both [C 2mim +][ EtSO 4 - ] and [C 4mim +][Cl −] inhibited laccase activity, although 10-fold more [C 2mim +][ EtSO 4 - ] than [C 4mim +][Cl −] was required to cause the same degree of inhibition. A kinetic model was developed to represent the experimental data.

Correlation between thermostability and stability of glycosidases in ionic liquid

The activity and stability of a β-glycosidase (Thermus thermophilus) and two α-galactosidases (Thermotoga maritima and Bacillus stearothermophilus) were studied in different hydrophilic ionic liquid (IL)/water ratios. For the ILs used, the glycosidases showed the best stability and activity in 1,3-dimethylimidazolium methyl sulfate [MMIM][MeSO(4)] and 1,2,3-trimethylimidazolium methyl sulfate [TMIM][MeSO(4)]. A close correlation was observed between the thermostability of the enzymes and their stability in IL media. At high IL concentration (80%), a time-dependent irreversible denaturing effect was observed on glycosidases while, at lower concentration (<30%), a reversible inactivation affecting mainly the k (cat) was obtained. The results demonstrate that highly thermostable glycosidases are more suitable for biocatalytic reactions in water-miscible ILs.

Fluorescence and Circular Dichroism Spectroscopy of Cytochrome c in Alkylammonium Formate Ionic Liquids

The structural stability of cytochrome c has been studied in alkylammonium formate (AAF) ionic liquids such as methylammonium formate (MAF) and ethylammonium formate (EAF) by fluorescence and circular dichroism (CD) spectroscopy. At room temperature, the native structure of cytochrome c is maintained in relatively high ionic liquid concentrations (50-70% AAF/water or AAF/phosphate buffer pH 7.0) in contrast with denaturation of cytochrome c in similar solutions of methanol or acetonitrile with water or buffer cosolvents. Fluorescence and CD spectra indicate that the conformation of cytochrome c is maintained in 20% AAF-80% water from 30 to 50 °C. No such temperature stability is found in 80% AAF-20% water. About one-third of the enzyme activity of cytochrome c in 80% AAF-20% water can be maintained as compared with phosphate buffer, and this is greater than the activities measured in corresponding methanol and acetonitrile aqueous solutions. This biophysical study shows that AAFs have potential application as organic solvent replacements at moderate temperature in the mobile phase for the separation of proteins in their native form by reversed phase liquid chromatography.

Experimental Investigation on the Solubility and Initial Rate of Absorption of CO2 in Aqueous Mixtures of Methyldiethanolamine with the Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate

In this paper we present the results of the initial absorption rate and solubility of CO2 in aqueous 4 M methyldiethanolamine (MDEA) mixed with various concentrations of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) at (303, 313, 323, and 333) K. All experiments were carried out at low partial pressures of CO2, below 110 kPa. The results of this research suggested that the presence of a low concentration of [bmim][BF4] in aqueous 4 mol·L−1 MDEA has no significant effect on the mixture loading capacity, but increased the initial absorption rate. The amine CO2 loading capacity showed a significant decrease in the presence of high concentrations of ionic liquid in the mixture.

Determination of Aluminum Ion with Morin in a Medium Comprised by Ionic Liquid–Water Mixtures

In this study we have employed two ionic liquids (ILs) as a new media for the analysis of aluminum in aqueous solutions by spectrofluorimetric method. ILs are liquid salts and they have no measurable vapor pressure up to their thermal decomposition point, >300 °C. This lack of vapor pressure makes these materials highly attractive for many studies as they can be used as clean solvents. Besides they are promising environments for analysis purposes and optical sensor designs. The results revealed that absorption, excitation and emission spectra of the morin-Al complex exhibited considerable changes in moieties. The morin-Al complex was stable at aluminum concentrations below 9.1 mg L(-1) in 25% 1-butyl-3-methylimidazolium bromide (IL-I)-water binary mixtures. The higher concentrations of IL (>25% by volume) was not suitable for the complex formation thus in pure IL media the complex formation even at high aluminum concentrations was not observed. The complex stoichiometry ratio of aluminum:morin was 2:1 in IL-I-water binary mixtures. The linear concentration range was 0.045-7.2 mg L(-1) with a correlation coefficient of r = 0.9909. The detection limit was found to be 0.036 mg L(-1). Cu(2+), Mn(2+) and PO (4) (3-) ions exhibited less interfering effect in presence of IL-I and the tolerance limit of Cu enhanced 10 times when compared with ethanol.

Novel biocompatible cholinium-based ionic liquids—toxicity and biodegradability

The synthesis, characterisation and toxicological assessment of a new group of environmentally friendly ionic liquids are presented. Focussing on the toxic effect of the anion, the ionic liquids were designed by combining the benign cholinium cation, [NMe3(CH2CH2OH)]+, with a range of linear alkanoate anions ([CnH2n+1CO2]−, n = 1-9), as well as two structural isomers (n = 3 or 4). The toxicity of these ionic liquids was evaluated using filamentous fungi as model eukaryotic organisms. Surprisingly, most of the tested species showed active growth in media containing extremely high ionic liquid concentrations, up to molar ranges in some cases. The biodegradability of these ionic liquids was assessed, and new biotechnological applications for them are proposed, e.g. as solvents for biopolymers. This study leads to the better understanding of the anion influence on the ionic liquid toxicity, but its core is the recognition that conscious design of ionic liquids can be used to deliver truly biocompatible salts without adversely affecting one of the most striking of their properties—their outstanding solvent ability.

Selection of Ionic Liquids as Entrainers for the Separation of Ethyl Acetate and Ethanol

This work tries to explore the relation between molecular structures of ionic liquids (ILs) as entrainers and separation performance on ethyl acetate (1) and ethanol (2). The vapor−liquid equilibrium (VLE) data have been measured for ethyl acetate (1) + ethanol (2) containing ILs at 101.32 kPa. The ionic liquids investigated were 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]+[BF4]−) and 1-methyl-3-octylimidazolium tetrafluoroborate ([OMIM]+[BF4]−), as well as 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM]+[BF4]−) that has been studied in our previous work. All the ILs could give rise to the salting-out effect. It was found that, at low IL concentration, the separation ability of ILs is in the order [EMIM]+[BF4]− > [BMIM]+[BF4]− > [OMIM]+[BF4]−, while at high IL concentration (x3 = 0.10−0.30) the separation ability of ILs is in the order [OMIM]+[BF4]− > [EMIM]+[BF4]− > [BMIM]+[BF4]− due to the difference of polarity of the three ILs and demixing effect. [EMIM]+[triflate]− was included as entrainer and compared with the tetrafluoroborate-based ILs. The measured ternary data were correlated using the NRTL model.

Determination of the adsorption mechanism of imidazolium-type ionic liquids onto kaolinite: implications for their fate and transport in the soil environment

Environmental context. The present paper looks at the possible spreading of a new class of chemicals, namely, ionic liquids in soils. These ionic liquids have gained increasing attention, and their environmental impact and fate needs to be determined before accidental release. The paper specifically focusses on the adhesion mechanisms of these chemicals onto a type of clay, kaolinite. It was found that a multilayer adhesion mechanism occurs. Sorption of ionic liquids on kaolinite indicates that these chemicals can modify the clay surfaces, which may lead to changes in its natural geochemical cycles. Abstract. In the present study, the mechanism of sorption of ionic liquids onto kaolinite clay mineral has been investigated in detail. Results obtained indicate a multilayer type of adsorption. At final saturations, the highest distribution coefficients were found for the long alkyl chain molecules. The mean free energy values obtained are below values of a typical ion-exchange process, which thus suggests that the adsorption mechanism is a combination of electrostatic interaction and physical sorption. At the beginning of the binding process (formation of a monolayer), ion-exchange and van der Waals interactions are predominantly responsible for the process, whereas at higher concentrations of ionic liquids, dispersive interactions become dominant. Thermodynamic parameters were also calculated from graphical interpretation of experimental data. Negative values of ΔG indicate a spontaneous sorption process for ionic liquids. Standard heats of adsorption were found to be exothermic and entropy contributions were negative in all cases studied.

Trichoderma reesei derived cellulase activity in three N,N-dimethylethanolammonium akylcarboxylate ionic liquids

AbstractThe activity and denaturation extent of cellulase from Trichoderma reesei (E.C. 3.2.1.4) was investigated in three representative N,N-dimethylethanolammonium akylcarboxylate ionic liquids. Significant cellulase activity and absence of enzyme unfolding was found in all concentrations of N,N-dimethylethanolammonium acetate (DMEAA), including the pure liquid. Activities in 20% and 40% (v/v) solutions of DMEAA were equal to citrate buffer controls. Lower enzymatic activities and denaturation were observed in solutions of the corresponding formate and octanoate ionic liquids, although cellulose hydrolysis still proceeded at a substantial rate. The results provide the first proof-of-principle that cellulose can be enzymatically hydrolyzed in the presence of high ionic liquid concentrations.

Using ionic liquid [EMIM][CH 3COO] as an enzyme-‘friendly’ co-solvent for resolution of amino acids

An ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate [EMIM][CH 3COO], was used in 0–4.0 M (∼60% IL, v/v), as a nonvolatile organic medium for the enzymatic resolution of amino acids. When dl-phenylalanine methyl ester was studied as a model substrate, high enantiomeric excesses (ee) of l-amino acid were obtained in all ionic concentrations; however, lower yields were observed at high IL concentrations. This IL is more enzyme-‘friendly’ than the hydrophilic organic solvent acetonitrile and those ILs containing chaotropic anions (such as [EMIM][OTs]). Among three proteases and two lipases investigated, lyophilized Bacillus licheniformis protease exhibited the best enantioselectivity and activity. Highly enantioselective resolutions were also produced for several other amino acids in 2.0 M IL. Interestingly, high ee were also found in deuterium oxide (D 2O) rather than in ordinary water, and a further enhancement was achieved with the co-existence of [EMIM][CH 3COO]. The heavy water effect was explained in terms of protein stabilization by D 2O. The secondary structural changes of enzyme in various media were interpreted by the second derivatives of FT-IR spectra.

Influence of Water on the Surface of the Water-Miscible Ionic Liquid 1-Butyl-3-methylimidazolium Tetrafluoroborate: A Sum Frequency Generation Analysis

Sum frequency generation spectroscopy (SFG) was used to study the influence of water on the surface of the water-miscible ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The orientation of the cation at the gas-liquid interface was analyzed as a function of ionic liquid concentration in water for concentrations from 0 to 1 mole fraction of the ionic liquid. The cation was found to be oriented with the imidazolium ring nearly parallel to the surface plane with a tilt angle > or = 70 degrees when the ionic liquid was dry. Furthermore, no noticeable change in the orientation was observed when high concentrations of water were mixed with the ionic liquid. The cation butyl chain is projecting into the gas phase with a CH(3) tilt angle of 54 +/- 2 degrees when the ionic liquid is dry and 46 +/- 4 degrees when mixed with water. Water is oriented at the surface only for concentration < or = 0.02 mole fraction of the ionic liquid. At higher ionic liquid concentrations (mole fractions > or = 0.05) the gas-liquid interface resembles that of the pure ionic liquid.

Effects of ionic liquids on the survival, movement, and feeding behavior of the freshwater snail, Physa acuta

Room-temperature ionic liquids (ILs) are being promoted as environmentally friendly alternatives to volatile organic solvents currently used by industry. Because ILs are novel and not yet in widespread use, their potential impact on aquatic organisms is unclear. We studied the effects of several ILs on the survivorship and behavior (movement and feeding rates) of the freshwater pulmonate snail, Physa acuta. Median lethal concentrations (LC50s) of ILs with imidazolium- and pyridinium-based cations and Br- and PF6- as anions ranged from 1 to 325 mg/L. Toxicity was greatest for ILs with eight-carbon alkyl chains attached to both imidazolium and pyridinium rings and declined with shorter alkyl chains, indicating a positive relationship between alkyl chain length and toxicity. Compared to controls, snails moved more slowly when exposed to butyl- and hexyl-cation ILs at 1 to 3% of LC50 concentrations but were not affected at higher IL concentrations (4-10% of LC50), which is characteristic of U-shaped dose-response curves. Snail movement was not affected by ILs with octyl alkyl groups. Grazing patterns, however, indicated that snails grazed less at higher IL concentrations. Physa acuta egestion rates were reduced in the presence of ILs at 3 to 10% of LC50 concentrations. Thus, nonlethal IL concentrations affected P. acuta behaviors, potentially impacting individual fitness and food web interactions. These results provide initial information needed to assess the potential hazards of ILs should they reach freshwater ecosystems.

Digital image holography for diffusion measurements in molten salts and ionic liquids - method and first results

Mutual diffusion coefficients of alkali-silver-nitrate molten salts and of mixtures between [BMIm]PF 6 and methanol have been measured using Digital Image Holography. The diffusion coefficients of the alkali-silver nitrate molten salt systems show an exponential temperature and a parabolic concentration dependence. Compared to the hot molten salt systems very low values of the diffusion coefficient of methanol/[BMIm]PF 6 especially at high ionic liquid concentrations are obtained and therefore long measuring times (up to 4 days) must be accepted. Even under these conditions, the method of Digital Image Holography is able to produce reliable diffusion data. The differential diffusion coefficient of methanol/[BMIm]PF 6 plotted against the concentration shows an inverse exponential dependence on the concentration.