Ionic liquids and deep eutectic solvents and their potential use in production of sodium / Fatemeh Saadat Ghareh Bagh

Sodium metal is an essential reducing agent, and it has a wide range of applications. In the present study ionic liquids (ILs) and their analogues known as deep eutectic solvents (DESs) have been proposed as electrolytes for sodium metal production at moderate temperatures of 90ºC to 150ºC. These electrolytes can be recognized as “green” solvents as they can potentially replace hazardous and polluting organic solvents. In using ILs or DESs as electrolytes for the production of sodium, three factors are of paramount importance: the solubility of commercially available sodium salts in the IL or DES, the conductivity of the solution of sodium salt in IL or DES, and the stability of the sodium metal in the IL or DES. DESs possess additional advantages over ILs especially because of the ease of synthesizing them and due to the lower cost of preparation. The evaluation of DESs as new electrolytes requires an insight of their main physical properties. For this purpose, some physical properties of specially-prepared DESs were measured and the results were reported. Zinc chloride-based DESs were characterized for their melting temperatures, viscosities, electrical conductivities and refractive indices. Subsequently, the solubility of different commercially available sodium salts were measured in different DESs and ILs at different temperatures. The solubility of sodium chloride increased with temperature in all the investigated ILs. The chemical structure of cations and anions in the ILs affected the solubility. The effect of the cation was larger than that of the anion.Different DESs were prepared by mixing ammonium or phosphonium salts, with different hydrogen bond donors (HBDs), or metal halides at several molar ratios. The effect of temperature on the solubility of sodium salts was found to be different from one DES to another. In certain DESs, the solubility of sodium salts increased with increasing temperature. The constituents of the DES and the molar ratios affected the solubility of sodium salts. DESs based on HBDs had very low solubility of NaCl in comparison to those that used metal halides as complexing agents. Sodium metal reacted with DESs containing HBDs; however, sodium metal was stable and did not react with DESs synthesized by utilizing metal halides. NRTL model was used to correlate the solubility of NaCl in some ILs as well as DESs at different temperatures. In most cases the experimental and calculated solubilities for NaCl in DESs and ILs were in good agreement. Cyclic voltammetry analysis was used to study the stability of sodium within the potential range found for metal halide-based DESs at different salt:metal halide molar ratios under different temperatures. It was found that the electrical windows of DESs droped with the increase in ZnCl2 molar composition in the DES and increased as the temperature increased. Reduction peak was observed for sodium ion in some ZnCl2-based DESs at certain temperatures. This work shows that DESs are superior to conventional molten salt electrolytes of Downs Process for the production of sodium metal due to lower operational temperature and less negative effects on the environment

Extraction of lignin from black liquor using protic ionic liquids and deep eutectic solvents

This dissertation investigates lignin extraction from black liquor (BL), a waste stream from Kraft pulping, using protic ionic liquids (PILs) and deep eutectic solvents (DESs). Fourteen PILs were synthesized by pairing seven ammonium cations with two anions (lactate [La] and acetate [Ac]), and their viscosity, electrical conductivity, and refractive index were characterized as functions of temperature. Experimental data for the physical properties were curve-fit using the least-squares method. The solubility of alkaline lignin in PILs was measured at 303 K to 368 K. The three best lignin solubilities were 633.5±16.5 mg g-1, 559.2±12.8 mg g-1, and 660.2±19.9 mg g-1 for pyrrolidinium acetate ([Pyrr][Ac]), ethanolammonium acetate ([Eth][Ac]) and propylammonium acetate ([Prop][Ac]), respectively, at 368 K. Solvents with high lignin solubility under similar conditions were selected to extract lignin from black liquor (BL). The PILs and a control IL (1-ethyl-3-methylimidazolium acetate ([Emim][Ac])) were evaluated to extract lignin under different reaction conditions. Several screening studies were employed to select the highest extracting lignin PIL, [Eth][Ac], and determine the range of extraction parameters (reaction time, temperature, and the IL/PIL:BL ratio (w/w)). The extraction process was optimized using the Box-Behnken Design (BBD) of experiments, and a quadratic prediction model was developed for lignin extraction as a function of the parameters affecting the process. It was concluded that reaction time, operating temperature, and PIL:BL ratio produce significant effects on the total lignin extracted. A numerical optimization analysis of the D-optimality index was performed to assign the optimum lignin extraction conditions at 97°C, 4.5 h reaction time and a PIL:BL ratio of 19:1. The predicted and experimental values for total lignin extracted under optimum conditions were70.0% and 75.0±2.9% (283.7±9.1 mg g-1), respectively. The characterization of the extracted lignin samples by Fourier transform infrared (FTIR) spectroscopy confirmed that the observed peaks for the extracted lignin were in agreement with the peaks for a commercially available alkaline lignin. One ionic liquid, [Emim][Ac] (control solvent), and four acetate-protic ionic liquids (PILs), [Eth][Ac], diethylenammonium acetate ([DiEt][Ac]), [Prop][Ac], and [Pyrr][Ac], were employed for kinetic studies of lignin extraction from BL. The kinetics of lignin extraction were examined for a 270-min. reaction time period at three different temperatures. The lowest activation energy (Ea = 6.5 kJ·mol-1) was affiliated with [Prop][Ac]. The PIL with the maximum total lignin extracted, [Eth][Ac], was regenerated using vacuum distillation, and the lignin extraction ability of the regenerated solvent was found to be equivalent to the fresh solvent. FTIR spectroscopy and proton nuclear magnetic resonance (1H-NMR) were employed to characterize the extracted lignin. Gel permeation chromatography revealed molecular weights of 2283±67 g mol-1 and 1892±122 g mol-1 for the lignin extracted using [Eth][Ac] and [Prop][Ac], respectively. The control solvent plus four DESs were synthesized using choline chloride (ChCl) as a salt and four hydrogen bond donors (HBDs): lactic acid (La), oxalic acid, malic acid, and urea. A screening study using the four DESs under different reaction conditions: temperature, DES:BL ratio (w/w), and HBD:salt molar ratio, examined the effect of reaction conditions on total lignin extracted (w%) and determined that lactic acid-ChCl at a 11:1 molar ratio was the best DES for further study. The DES selected was regenerated three times and the total lignin extraction values using regenerated DES were statistically similar to the extraction value using DES before regeneration. FTIR spectroscopy peaks for the extracted lignin samples (using DES before regeneration and after regeneration) agreed with the peaks for a commercially available alkaline lignin. 1H-13C HSQC NMR spectroscopy detected the side chain structure and aromatic linkage peaks in the lignin extracted. Lignin extraction conditions were optimized for La:ChCl using response surface methodology (RSM). A BBD was carried out to develop a quadratic model to predict the total lignin extraction based on operating factors: time, temperature, HBD:salt ratio and DES:BL ratio. The highest lignin extraction conditions using the D-optimality index were: reaction time=4.6 h, operating temperature=99ºC, DES:BL ratio (20:1) (w/w), and La:ChCl (11:1). The maximum predicted value for total lignin extracted under optimum conditions was 83.8% (w%) which was approximately 4.6% (w%) higher than the experimental value, 79.2±1.86% (w%) (299.5±11.0 mg g-1) under similar conditions. The Anderson–Darling (AD) statistic attested to a normal distribution to the residuals, which demonstrated a reasonable correlation between predicted and experimental data over the factor-space studied

Optimizing one-dimensional TiO2 for photocatalytic hydrogen production from a water-ethanol mixture and other electron donors

International audienceThis work is focused on synthesizing and employing one-dimensional (1D) titanium dioxide (TiO2) for hydrogen (H2) production. Based on using electron donors (EDs) (ethanol, methanol, fomic acid and 1,2,3 propanetriol), the increased H2 production, when compared to P25 TiO2 nanoparticles, was due to the large specific surface area (SSA) and enhanced electron mobility of 1D TiO2. The impact of the 1D TiO2 synthesis reaction conditions (temperature, NaOH concentration and the TiO2 precursor concentration) on the photocatalytic H2 production rate was evaluated using a 3-factor 3-level Box Behnken design (BBD). The BBD model demonstrated that the temperature and the NaOH concentration significantly affected the 1D TiO2 phase structure, crystal size, SSA, bandgap and the photocatalytic H2 production rate. The phase structure and crystal size of 1D TiO2 were key factors affecting the H2 production rate. 1D TiO2 containing an anatase phase with a mean crystal size of 20.1 ± 0.2 nm was synthesized at 126 °C, 15 M NaOH and 49 g L−1 TiO2. The maximum H2 production rate of 475 ± 12 μmol·h−1 (quantum efficiency (ε) = 20.2 ± 0.5%) for the 1D TiO2 sample was significantly enhanced when compared to commercial TiO2 P25. The H2 production rate for the optimized 1D TiO2 was significantly enhanced by decorating the structure with Pt and Au. Hydrothermal synthesized of 1D TiO2 provided an efficient and low cost method for producing H2 from ethanol, methanol, fomic acid and 1,2,3 propanetriol