Tailored Media for Homogeneous Cellulose Chemistry: Ionic Liquid/Co-Solvent Mixtures

Co-solvents can minimize two of the major problems associated with the use of ionic liquids (ILs) as solvents for homogeneous derivatization of cellulose: high viscosity and limited miscibility with non-polar reagents or reaction products. Thus, the effects of 18 solvents and 3 binary solvent mixtures on cellulose solutions in three ILs were systematically studied with respect to the solution phase behavior. The applicable limits of these mixtures were evaluated and general guidelines for the use of co-solvents in cellulose chemistry could be advanced: Appropriate co-solvents should have EN T values (normalized empirical polarity) > 0.3, very low ``acidity`` (alpha < 0.5), and relatively high ""basicity`` (beta >= 0.4). Moreover, novel promising co-solvents and binary co-solvent mixtures were identified.

Hydrogen production by steam reforming of ethanol over Ni-based catalysts promoted with noble metals

The catalytic activity of Ni/La(2)O(3)-Al(2)O(3) Catalysts modified with noble metals(Pt and Pd) was investigated in the steam reforming of ethanol. The catalysts were characterized by ICP, S(BFT), X-ray diffraction, temperature-programmed reduction, UV-vis diffuse reflectance spectroscopy and X-ray absorption fine structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of La(2)O(3) dispersed on the alumina. The promoting effect of noble metals included a marked decrease in the reduction temperatures of NiO species interacting with the support. due to the hydrogen spillover effect, facilitating greatly the reduction of the promoted catalysts. it was seen that the addition of noble metal stabilized the Ni sites in the reduced state throughout the reaction, increasing ethanol conversion and decreasing coke formation, irrespective of the nature or loading of the noble metal. (C) 2009 Elsevier B.V. All rights reserved.

Superoxide Dismutase 1-mediated Production of Ethanol- and DNA-derived Radicals in Yeasts Challenged with Hydrogen Peroxide MOLECULAR INSIGHTS INTO THE GENOME INSTABILITY OF PEROXIREDOXIN-NULL STRAINS

Peroxiredoxins are receiving increasing attention as defenders against oxidative damage and sensors of hydrogen peroxide-mediated signaling events. In the yeast Saccharomyces cerevisiae, deletion of one or more isoforms of the peroxiredoxins is not lethal but compromises genome stability by mechanisms that remain under scrutiny. Here, we show that cytosolic peroxiredoxin-null cells (tsa1 Delta tsa2 Delta) are more resistant to hydrogen peroxide than wildtype (WT) cells and consume it faster under fermentative conditions. Also, tsa1 Delta tsa2 Delta cells produced higher yields of the 1-hydroxyethyl radical from oxidation of the glucose metabolite ethanol, as proved by spin-trapping experiments. A major role for Fenton chemistry in radical formation was excluded by comparing WT and tsa1 Delta tsa2 Delta cells with respect to their levels of total and chelatable metal ions and of radical produced in the presence of chelators. The main route for 1-hydroxyethyl radical formation was ascribed to the peroxidase activity of Cu, Zn-superoxide dismutase (Sod1), whose expression and activity increased similar to 5- and 2-fold, respectively, in tsa1 Delta tsa2 Delta compared with WT cells. Accordingly, overexpression of human Sod1 in WT yeasts led to increased 1-hydroxyethyl radical production. Relevantly, tsa1 Delta tsa2 Delta cells challenged with hydrogen peroxide contained higher levels of DNA-derived radicals and adducts as monitored by immuno-spin trapping and incorporation of (14)C from glucose into DNA, respectively. The results indicate that part of hydrogen peroxide consumption by tsa1 Delta tsa2 Delta cells is mediated by induced Sod1, which oxidizes ethanol to the 1-hydroxyethyl radical, which, in turn, leads to increased DNA damage. Overall, our studies provide a pathway to account for the hypermutability of peroxiredoxin-null strains.

A microscopic view of substitution reactions solvated by ionic liquids

The solvation effect of the ionic liquid 1-N-butyl-3-methylimidazolium hexafluorophosphate on nucleophilic substitution reactions of halides toward the aliphatic carbon of methyl p-nitrobenzenesulfonate (pNBS) was investigated by computer simulations. The calculations were performed by using a hybrid quantum-mechanical/molecular-mechanical (QM/MM) methodology. A semiempirical Hamiltonian was first parametrized on the basis of comparison with ab initio calculations for Cl(-) and Br(-) reaction with pNBS at gas phase. In condensed phase, free energy profiles were obtained for both reactions. The calculated reaction barriers are in agreement with experiment. The structure of species solvated by the ionic liquid was followed along the reaction progress from the reagents, through the transition state, to the final products. The simulations indicate that this substitution reaction in the ionic liquid is slower than in nonpolar molecular solvents proper to significant stabilization of the halide anion by the ionic liquid in comparison with the transition state with delocalized charge. Solute-solvent interactions in the first solvation shell contain several hydrogen bonds that are formed or broken in response to charge density variation along the reaction coordinate. The detailed structural analysis can be used to rationalize the design of new ionic liquids with tailored solvation properties. (c) 2008 American Institute of Physics.

Application of an anaerobic packed-bed bioreactor for the production of hydrogen and organic acids

This study investigates the feasibility of an anaerobic bioreactor for treating low contents of organic matter to generate organic acids and hydrogen. The device employed for this purpose was a horizontal packed-bed bioreactor fed with glucose-based synthetic wastewater and operated with hydraulic retention times from 0.5 to 2 h. A microbial biofilm was developed without previous inoculation, using expanded clay beads (4.8-6.3 mm) as support material. Alkalinity was found to be the main parameter affecting the production of hydrogen and organic acids, and the system produced optimal output when operating without a buffer agent. The average hydrogen production was 2.48, 2.15 and 1.81 molH(2) mol(-1) of glucose for NaHCO3 influent concentrations of 0, 1000 and 2000 mg L-1, respectively. The operational regime of the bioreactor, the support material and the controlled alkalinity were effective in selecting and immobilizing microbial fermenting biofilms, which successfully produced hydrogen and organic acids throughout the operating period. Exploratory assays indicated the feasibility of organic acid extraction using an anionic polymeric resin. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Long-term stability of hydrogen and organic acids production in an anaerobic fluidized-bed reactor using heat treated anaerobic sludge inoculum

This study evaluates the stability of hydrogen and organic acids production in an anaerobic fluidized-bed reactor (AFBR) that contains expanded clay (2.8-3.35 mm in diameter) as a support medium and is operated on a long-term basis. The reactor was inoculated with thermally pre-treated anaerobic sludge and operated with decreasing hydraulic retention time (HRT), from 8 h to 1 h, at a controlled temperature of 30 degrees C and a pH of about 3.8. Glucose (2000 mg L(-1)) was used as the substrate, generating conversion rates of 92-98%. Decreasing the HRT from 8 h to 1 h led to an increase in average hydrogen-production rates, with a maximum value of 1.28 L h(-1) L(-1) for an HRT of 1 h. In general, hydrogen yield production increased as HRT decreased, reaching 2.29 mol of H(2)/mol glucose at an HRT of 2 h and yielding a maximum hydrogen content of 37% in the biogas. No methane was detected in the biogas throughout the period of operation. The main soluble metabolites (SMP) were acetic acid (46.94-53.84% of SMP) and butyric acid (34.51-42.16% of SMP), with less than 15.49% ethanol. The steady performance of the AFBR may be attributed to adequate thermal treatment of the inoculum, the selection of a suitable support medium for microbial adhesion, and the choice of satisfactory environmental conditions imposed on the system. The results show that stable hydrogen production and organic acids production were maintained in the AFBR over a period of 178 days. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Magnetic Fluids Based on gamma-Fe(2)O(3) and CoFe(2)O(4) Nanoparticles Dispersed in Ionic Liquids

The disclosure of magnetic ionic liquids (MILs) as stable dispersions of surface modified gamma-Fe(2)O(3) or CoFe(2)O(4) nanoparticles (NPs) in the 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF(4)) ionic liquid is reported. The magnetic NPs were characterized by X-ray powder diffraction, transmission electron microscopy, and Raman spectroscopy. The surface modified NPs have proved to form stable dispersions in BMIBF(4) in the absence of water and behave like a magnetic ionic liquid. The MILs have been characterized by Raman spectroscopy, magnetic measurements, and DSC. The stability of the magnetic NPs in BMIBF(4) is consistently explained by assuming the formation of a semiorganized protective layer composed of supramolecular aggregates in the form of [(BMI)(2)(BF(4))(3)](-). A superparamagnetic behavior and saturation magnetization of ca. 18 emu/g for a sample containing 30% w/w maghemite NPs/BMIBF(4) have been inferred from static and dynamic magnetic measurements. DSC results have shown that the MIL composed of 30% w/w CoFe(2)O(4) NPs/BMIBF(4) remains a liquid phase down to -84 degrees C.

Synthesis of diaryl selenides using electrophilic selenium species and nucleophilic boron reagents in ionic liquids

We described herein the use of imidazolium ionic liquids [bmim]PF(6) and [bmim]BF(4) in the selective, metal and catalyst-free synthesis of unsymmetrical diaryl selenides by electrophilic substitution in arylboron reagents with arylselenium halides (Cl and Br) at room temperature. This is a general substitution reaction and it was performed with arylboronic acids or potassium aryltrifluoroborates bearing electron-withdrawing or electron-donating groups, affording the corresponding diaryl selenides in good to excellent yields. The ionic liquid [bmim][PF(6)] was easily recovered and utilized for further substitution reactions.

Understanding solvation

The effects of solvents on different chemical phenomena, including reactivity, spectroscopic data, and swelling of biopolymers can be rationalized by use of solvatochromic probes, substances whose UV-vis spectra, absorption, or emission are sensitive to the properties of the medium. Thermo-solvatochromism refers to the effect of temperature on solvatochromism. The study of both phenomena sheds light on the relative importance of the factors that contribute to solvation, namely, properties of the probe, those of the solvent (acidity, basicity, dipolarity/polarizability, and lipophilicity), and the temperature. Solvation in binary solvent mixtures is complex because of ""preferential solvation"" of the probe by some component of the mixture. A recently introduced solvent exchange model is based on the presence in the binary solvent mixture of the organic component (molecular solvent or ionic liquid), S, water, W, and a 1:1 hydrogen-bonded species (S-W). Solvation by the latter is more efficient than by its precursor solvents, due to probe-solvent hydrogen-bonding and hydrophobic interactions; dimethyl sulfoxide (DMSO)-W is an exception. Solvatochromic data are employed in order to explain apparently disconnected phenomena, namely, medium effect on the pH-independent hydrolysis of esters, (1)H NMR data of water-ionic liquid (IL) mixtures, and the swelling of cellulose.

On the stabilization of conducting pernigraniline salt by the synthesis and oxidation of polyaniline in hydrophobic ionic liquids

The electrochemical polymerization of aniline in a hydrophobic room-temperature ionic liquid and the spectroelectrochemical characterization of the formed film are presented. The polymerization occurs without the presence of acid in 1-butyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide (BMMITFSI), leading to a very stable electroactive material where no degradation was observed even at high applied potentials. Both in situ UV-Vis and Raman spectroscopic studies provided evidence for the stabilization of pernigraniline salt at high oxidation potentials and that this polyaniline state is the conducting form, as was corroborated by in situ resistance measurements. These data are indicative that low conductivity is not an intrinsic property of pernigraniline salt and this point must be reconsidered.

Performance evaluation and phylogenetic characterization of anaerobic fluidized bed reactors using ground tire and pet as support materials for biohydrogen production

This study evaluated two different support materials (ground tire and polyethylene terephthalate [PET]) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L(-1)). The AFBR, which contained either ground tire (R1) or PET (R2) as support materials, were inoculated with thermally pretreated anaerobic sludge and operated at a temperature of 30 degrees C. The AFBR were operated with a range of hydraulic retention times (HRT) between 1 and 8 h. The reactor R1 operating with a HRT of 2 h showed better performance than reactor R2, reaching a maximum hydrogen yield of 2.25 mol H(2) mol(-1) glucose with 1.3 mg of biomass (as the total volatile solids) attached to each gram of ground tire. Subsequent 16S rRNA gene sequencing and phylogenetic analysis of particle samples revealed that reactor R1 favored the presence of hydrogen-producing bacteria such as Clostridium, Bacillus, and Enterobacter. (C) 2010 Elsevier Ltd. All rights reserved.

Effect of Organic Load on the Performance and Methane Production of an AnSBBR Treating Effluent from Biodiesel Production

Currently, there is an increasing demand for the production of biodiesel and, consequently, there will be an increasing need to treat wastewaters resulting from the production process of this biofuel. The main objective of this work was, therefore, to investigate the effect of applied volumetric organic load (AVOL) on the efficiency, stability, and methane production of an anaerobic sequencing batch biofilm reactor applied to the treatment of effluent from biodiesel production. As inert support, polyurethane foam cubes were used in the reactor and mixing was accomplished by recirculating the liquid phase. Increase in AVOL resulted in a drop in organic matter removal efficiency and increase in total volatile acids in the effluent. AVOLs of 1.5, 3.0, 4.5 and 6.0 g COD L(-1) day(-1) resulted in removal efficiencies of 92%, 81%, 67%, and 50%, for effluent filtered samples, and 91%, 80%, 63%, and 47%, for non-filtered samples, respectively, whereas total volatile acids concentrations in the effluent amounted to 42, 145, 386 and 729 mg HAc L(-1), respectively. Moreover, on increasing AVOL from 1.5 to 4.5 g COD L(-1) day(-1) methane production increased from 29.5 to 55.5 N mL CH(4) g COD(-1). However, this production dropped to 36.0 N mL CH(4) g COD(-1) when AVOL was increased to 6.0 g COD L(-1) day(-1), likely due to the higher concentration of volatile acids in the reactor. Despite the higher concentration of volatile acids at the highest AVOL, alkalinity supplementation to the influent, in the form of sodium bicarbonate, at a ratio of 0.5-1.3 g NaHCO(3) g COD (fed) (-1) , was sufficient to maintain the pH near neutral and guarantee process stability during reactor operation.

Biohydrogen production in anaerobic fluidized bed reactors: Effect of support material and hydraulic retention time

This study evaluated two different support materials (polystyrene and expanded clay) for biohydrogen production in an anaerobic fluidized bed reactor (AFBR) treating synthetic wastewater containing glucose (4000 mg L(-1)). The AFBRs contained either polystyrene (R1) or expanded clay (R2) as support materials were inoculated with thermally pre-treated anaerobic sludge and operated at a temperature of 30 degrees C and a pH of approximately 5.5. The AFBRs were operated with a range of hydraulic retention times (HRTs) between 1 and 8 h. For R1 with an HRT of 2 h, the maximum hydrogen yield (HY) was 1.90 mol H(2) mol(-1) glucose, with 0.805 mg of biomass (as total volatile solids, or TVS) attached to each g of polystyrene. For R2 operated at an HRT of 2 h, the maximum HY was 2.59 mol H(2) moll glucose, with 1.100 mg of attached biomass (as TVS) g(-1) expanded clay. The highest hydrogen production rates (HPR) were 0.95 and 1.21 L h(-1) L(-1) for R1 and R2, respectively, using an HRT of 1 h. The H(2) content increased from 16-47% for R1 and from 22-51% for R2. No methane was detected in the biogas produced throughout the period of AFBR operation. These results show that the values of HY, HPR, H(2) content, and g of attached biomass g(-1) support material were all higher for AFBRs containing expanded clay than for reactors containing polystyrene. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Ruthenium nanoparticles prepared from ruthenium dioxide precursor: Highly active catalyst for hydrogenation of arenes under mild conditions

The hydrogenation of benzene and benzene derivatives was studied using Ru(0) nanoparticles prepared by a very simple method based on the in situ reduction of the commercially available precursor ruthenium dioxide under mild conditions (75 degrees C and hydrogen pressure 4atm) in imidazolium ionic liquids. Total turnovers (TTO) of 2700 mol/mol Ru were obtained for the conversion of benzene to cyclohexane under solventless conditions and TTO of 1200 mol/mol Ru were observed under ionic liquid biphasic conditions. When corrected for exposed ruthenium atoms, TTO values of 7940 (solventless) and 3530 (biphasic) were calculated for benzene hydrogenation. These reaction rates are higher than those observed for Ru nanoparticles prepared from decomposition of an organometallic precursor in similar conditions. The presence of the partially hydrogenated product cyclohexene was also detected at low conversion rates. (C) 2008 Elsevier B.V. All rights reserved.

Nickel catalysts supported on ZrO2, Y2O3-stabilized ZrO2 and CaO-stabilized ZrO2 for the steam reforming of ethanol: Effect of the support and nickel load

Catalysts with various nickel loads were prepared on supports of ZrO2, ZrO2-Y2O3 and ZrO2-CaO, characterized by XRD and TPR and tested for activity in ethanol steam reforming. XRD of the supports identified the monoclinic crystalline phase in the ZrO2 and cubic phases in the ZrO2-Y2O3 and ZrO2-CaO supports. In the catalysts, the nickel impregnated on the supports was identified as the NiO phase. In the TPR analysis, peaks were observed showing the NiO phase having different interactions with the supports. In the catalytic tests, practically all the catalysts achieved 100% ethanol conversion, H-2 yield was near 70% and the gaseous concentrations of the other co-products varied in accordance with the equilibrium among them, affected principally by the supports. It was observed that when the ZrO2 was modified with Y2O3 and CaO, there were big changes in the CO and CO2 concentrations, which were attributed to the rise in the number of oxygen vacancies, permitting high-oxygen mobility and affecting the gaseous equilibrium. The liquid products analysis showed a low selectivity to liquid co-products during the reforming reactions. (c) 2007 Published by Elsevier B.V.