Generation of Superoxide Ion in Pyridinium, Morpholinium, Ammonium, and Sulfonium-Based Ionic Liquids and the Application in the Destruction of Toxic Chlorinated Phenols

Generation of superoxide ion (O₂^•–) was carried out in four ionic liquids (ILs) having the same anion, bis­(trifluoromethylsulfonyl)­imide [N­(Tf)₂]⁻, and different cations, N-hexylpyridinium [HPy]⁺, N-methoxyethyl-N-methylmorpholinium [MO1,1O2]⁺, N-ethyl-N,N-dimethyl-2-methoxyethylammonium [N112,1O2]⁺, and triethylsulfonium [S222]⁺. Cyclic voltammetry (CV) and chronoamperometry (CA) electrochemical techniques were used in this investigation. It was found that O₂^•– is not stable in the [HPy]⁺-based IL. On the other hand, CV showed that the electrochemically generated O₂^•– is stable in [MO1,1O2]⁺-, [N112,1O2]⁺-, and [S222]⁺-based ILs for the time duration of the experiment. The long-term stability of the generated O₂^•– was then investigated by dissolving potassium superoxide (KO₂) in dimethyl sulfoxide (DMSO) in the presence of the corresponding IL. It was found that ILs containing [MO1,1O2]⁺ and [N112,1O2]⁺ offer a promising long-term stability of O₂^•– for various reactions to be used for several applications. However, it was found that after 2 h, about 92.5% of the generated O₂^•– in [S222]⁺ based IL was consumed. The diffusion coefficient and solubility of O₂ in the studied ILs were then determined using CV and CA techniques simultaneously. It was found that diffusion coefficients and CA steady-state currents increase with temperature increases, while the solubility of O₂ decreased. To our best knowledge, this is the first time that morpholinium and sulfoniumbased ILs were utilized as media for chemical and electrochemical generation of O₂^•–. Additionally, the chemically generated O₂^•–, by dissolving KO₂, was then used for the destruction of 2,4-dichlorophenol (DCP) in [MO1,1O2]­[N­(Tf)₂] under ambient conditions. The destruction percentage was higher than 98%. This work represents a novel application of the chemically generated O₂^•– for the destruction of toxic chlorinated phenols in ILs media

Tetrabutylammonium Chloride Based Ionic Liquid Analogues and Their Physical Properties

During the past few years, there has been a surge in interest and research in the arena of utilizing deep eutectic solvents (DESs) as green solvents. This manifested in applying DESs in a variety of industrial applications. Most of the reported work in this field was directed toward the choline chloride-based DES. Recently, the area of DES synthesis was widened by considering other quaternary ammonium and phosphonium salts. In this work tetrabutylammonium chloride (TBAC) is used as a salt for the synthesis of three different DES systems based on three different hydrogen bond donors (HBDs), namely, glycerol, ethylene glycol, and triethylene glycol. Screening tests for each DES system was performed to identify salt:HBD ratios that exhibit a minimum freezing point, and at least three such ratios were selected for each system. Physical properties including melting point, density, viscosity, surface tension, refractive index, conductivity, and pH were measured for the three DES systems at different temperatures ranging from (293.15 to 353.15 K). It is worth mentioning that this class of DES exhibits a wide range of properties that can be tailored toward specific chemical and other engineering applications

Solubility of Thiophene and Dibenzothiophene in Anhydrous FeCl₃- and ZnCl₂‑Based Deep Eutectic Solvents

The solubilities of some common refractory-sulfur-containing compounds, namely thiophene and dibenzothiophene, were studied and measured in anhydrous FeCl₃- and ZnCl₂-based deep eutectic solvents (DES) at different temperatures under atmospheric pressure. The aim of this study is to explore the behavior of DESs toward solvation of sulfur-containing compounds so as to set a pace for the successful application of DESs into deep desulfurization of liquid fuels. The studied DESs were screened and prepared by the combination of anhydrous FeCl₃ and ZnCl₂ with different salts and hydrogen bond donors. High pressure liquid chromatography (HPLC) was employed for the quantitative measurements of solubilities of both thiophene and dibenzothiophene. It was found that FeCl₃ based DESs exhibited higher solubilities (from 17 wt % to above 90 wt %) for dibenzothiophene as compared to the ZnCl₂ based DESs (0.084–1.389 wt %). Moreover, FeCl₃ based DESs exhibited complete miscibility with thiophene while ZnCl₂ based DESs showed solubility values in the range of 1–10 wt % for thiophene. The experimental results obtained were further successfully modeled using the nonrandom two liquid (NRTL) model

Stability of Superoxide Ion in Phosphonium-Based Ionic Liquids

In this work the chemical generation of superoxide ion and determination of its stability in five phosphonium-based ionic liquids has been carried out. The stability of the generated superoxide ion depended on the anion. For the trihexyl­(tetradecyl)­phosphonium cation, the bis­(2,4,4-trimethylpentyl)­phosphinate anion (IL 104) has shown a relatively good stability with a rate constant of 3.34 × 10^–5 s^–1 for the reaction of the superoxide ion. Triisobutyl­(methyl)­phosphonium tosylate has also shown moderate stability (6.8 × 10^–5 s^–1). The order of stability, bis­(2,4,4-trimethylpentyl)­phosphinate > dicyanamide (6.97 × 10^–5 s^–1) > Br^– (7.72 × 10^–5 s^–1) > Cl^– (12.7 × 10^–5 s^–1), correlates well with the order of their respective ionic volumes. On application of the generated superoxide ion for the oxidation of two organic sulfur compounds, 15% conversion of thiophene was attained in 2 h while dibenzothiophene (DBT) was found to be unreactive to the ion in IL 104. This was attributed to higher electron density on the sulfur atom in DBT relative to thiophene and high nucleophilicity of the superoxide ion. Furthermore, the type of IL appears to slightly affect the conversion. The conversion of thiophene obtained was in the following order: IL 104 (15%) > [HMPyrr]­[TFSI] (8%) > [BMPyrr]­[TFSI] (7%) with the apparent differences in the magnitude of the alkyl chain length

Effect of organic solvents and acidic catalysts on biodiesel yields from primary sewage sludge, and characterization of fuel properties

<p>Biodiesel is considered the most convenient biofuel, due to its direct use in existing combustion engines; however, its production is not economically optimal due to processes that utilize costly substrates, require high energy expenditure or achieve low biodiesel yields. We used primary sewage sludge for the production of biodiesel and compared yields at different temperatures (40, 50 and 60 °C) and with different organic solvents (chloroform, toluene and hexane), acid catalysts (HCl and H₂SO₄) and catalyst concentrations (3, 5 and 7%). A maximum of 18 wt% biodiesel was obtained using chloroform with 3% H₂SO₄ at 40 °C. The conversion efficiency of the primary sludge to biodiesel under these conditions was 86.4%. Based on the fatty acid methyl ester composition of the obtained biodiesel and measured fuel properties, it was deduced that fuel from primary sludge is more suitable for areas with warmer climates than ones that reach temperatures close to 0 °C. However, the fuel properties of the produced biodiesel were within the limits of accepted international standards. We conclude that production of biodiesel from primary sewage sludge under optimized conditions reduces the impact of the feedstock on the environment, decreases overall costs and produces fuel with acceptable properties.</p