The Influence of Supercritical Carbon Dioxide (SC‐CO2) on Electrolytes and Hydrogenation of Soybean Oil

The electrochemical hydrogenation of soybean oil with supercritical carbon dioxide (SC‐CO₂) has been studied to seek ways for substantial reduction of the trans fatty acids (TFA). The solubility of CO₂ in electrolytes and the conductivity of electrolytes were investigated using a self‐made electrochemical hydrogenation reactor. The optimum hydrogenation parameters were assessed. Both the solubility of CO₂ in electrolytes and the conductivity of electrolytes increased with increasing CO₂ pressure. When the pressure reached a critical point of CO₂, the solubility of CO₂ expressed as a mole fraction was 0.42 in cathode electrolyte and 0.1 in anode electrolyte. At 8 MPa, the conductivity of electrolytes was 1.5 times higher than that at 2 MPa. When the pressure was higher than the critical point of CO₂, the solubility of CO₂ in electrolytes and the conductivity of electrolytes reached a stable value. The optimum condition for electrochemical hydrogenation of soybean oil in SC‐CO₂ were reaction pressure (8 MPa), reaction temperature (48 °C), current (125 mA), agitation speed (300 rpm), and reaction time (8 h). Fatty acid profile, iodine value, and TFA content were evaluated at the optimum parameters. This investigation showed that the electrochemical hydrogenation of soybean oil in SC‐CO₂ was improved. The reaction time was shortened by 4 h, and TFA content was reduced by 35.8% compared to traditional hydrogenation process.     

Electrocatalytic carboxylation of 2-amino-5-bromopyridine with CO2 in ionic liquid 1-butyl-3-methyllimidazoliumtetrafluoborate to 6-aminonicotinic acid

A new electrochemical procedure for the electrocatalytic carboxylation of 2-amino-5-bromopyridine with CO₂ in ionic liquid, 1-butyl-3-methyllimidazolium tetrafluoborate (BMIMBF₄), to 6-aminonicotinic acid was investigated for the first time. The experiments were carried out in three electrodes undivided cell under mild conditions, and the use of volatile and toxic solvents and catalysts, as well as any other additional supporting electrolytes, was avoided. The electrochemical reduction behavior of 2-amino-5-bromopyridine in BMIMBF₄ had been studied by cyclic voltammetry with a reduction peak at −1.6 V (vs. Ag). 6-Aminonicotinic acid was obtained in 75% yield and 100% selectivity, under the optimized condition. Moreover, the ionic liquid was successfully recycled.     

Electrochemical CO2 Reduction: Recent Advances and Current Trends

With rising levels of CO₂ in our atmosphere, technologies capable of converting CO₂ into useful products have become more valuable. The field of electrochemical CO₂ reduction is reviewed here, with sections on mechanism, formate (formic acid) production, carbon monoxide production, reduction to higher products (methanol, methane, etc.), use of flow cells, high pressure approaches, molecular catalysts, non-aqueous electrolytes, and solid oxide electrolysis cells. These diverse approaches to electrochemical CO₂ reduction are compared and contrasted, emphasizing potential processes that would be feasible for large-scale use. Although the focus is on recent reports, highlights of older reports are also included due to their important contributions to the field, particularly for high-rate electrolysis.     

In situ diagnostics of Victorian brown coal combustion in O2/N2 and O2/CO2 mixtures in drop-tube furnace

Experimental investigation of the combustion of an air-dried Victorian brown coal in O₂/N₂ and O₂/CO₂ mixtures was conducted in a lab-scale drop-tube furnace (DTF). In situ diagnostics of coal burning transient phenomena were carried out with the use of high-speed camera and two-colour pyrometer for photographic observation and particle temperature measurement, respectively. The results indicate that the use of CO₂ in place of N₂ affected brown coal combustion behaviour through both its physical influence and chemical interaction with char. Distinct changes in coal pyrolysis behaviour, ignition extent, and the temperatures of volatile flame and burning char particles were observed. The large specific heat capacity of CO₂ relative to N₂ is the principal factor affecting brown coal combustion, which greatly quenched the ignition of individual coal particles. As a result, a high O₂ fraction of at least 30% in CO₂ is required to match air. Moreover, due to the accumulation of unburnt volatiles in the coal particle vicinity, coal ignition in O₂/CO₂ occurred as a form of volatile cloud rather than individual particles that occurred in air. The temperatures of volatile flame and char particles were reduced by CO₂ quenching throughout coal oxidation. Nevertheless, this negative factor was greatly offset by char-CO₂ gasification reaction which even occurred rapidly during coal pyrolysis. Up to 25% of the nascent char may undergo gasification to yield extra CO to improve the reactivity of local fuel/O₂ mixture. The subsequent homogeneous oxidation of CO released extra heat for the oxidation of both volatiles and char. As a result, the optical intensity of volatile flame in ∼27% O₂ in CO₂ was raised to a level twice that in air at the furnace temperature of 1273 K. Similar temperatures were achieved for burning char particles in 27% O₂/73% CO₂ and air. As this O₂/CO₂ ratio is lower than that for bituminous coal, 30-35%, a low consumption of O₂ is desirable for the oxy-firing of Victorian brown coal. Nevertheless, the distinct emission of volatile cloud and formation of strong reducing gas environment on char surface may affect radiative heat transfer and ash formation, which should be cautioned during the oxy-fuel combustion of Victorian brown coal.     

Ionic conductivity studies of poly(ethylene oxide)-lithium salt electrolytes in high-pressure carbon dioxide

We have measured ionic conductivity of PEO-LiX [anion X=N(CF₃SO₂)₂ (TFSI), ClO₄, CF₃SO₃, BF₄, NO₃, and CH₃SO₃] polymer electrolytes in CO₂ at pressures varied from 0.1 to 20 MPa. From the temperature dependence in supercritical CO₂, a large increase in the conductivity for PEO-LiBF₄ and LiCF₃SO₃ electrolytes has been observed. Permeation of the CO₂ molecules gave rise to the plasticization for crystal domains in the electrolytes, which is related to the reduction in transition point of the Arrhenius plot corresponding to the melting of crystal PEO. Relation between the conductivity and CO₂ reduced density revealed that the electrolytes containing fluorinated anions such as ‘CO₂-philic’ BF₄ and CF₃SO₃ increase in the conductivity with increasing the density. This indicates that the salt dissociation was promoted by the CO₂ permeation and the Lewis acid-base interactions between fluorinated anions and CO₂ molecules.     

Determination of crystal growth rate for porcine insulin crystallization with CO2 as a volatile acidifying agent

Crystallization is controlled by two steps that determine the quality and the final size of the product, nucleation and growth, which are functions of supersaturation. Recently, Hirata et al. [1] crystallized insulin using CO₂ as a volatile acid to impose supersaturation on the system. The objective of the present work was to determine the growth kinetics of insulin crystallization in 50 mM NaHCO₃ solution with 0.4 mM ZnCl₂ in a CO₂ atmosphere at 15 °C, adjusting the parameters of the equation G = k_g × S^g to the experimental data. The solubility of insulin in the NaHCO₃/CO₂/ZnCl₂ system at 15 °C was determined as a function of pH in the range of 6.30–7.34. The crystal growth data allowed determination of the growth order “g” (g = 2.9). Although protein crystallization has some features that differ from the crystallization of less complex molecules, the apparent growth kinetics of insulin were successfully analyzed here with the same empirical methods used for small molecules, which can easily be scaled up for industrial applications to achieve specific size and purity, the goals of industrial crystallization. The method used in this work is a useful tool for describing and simplifying optimization of industrial protein crystallization processes.     

In situ study of ionic conductivity for polyether-LiCF3SO3 electrolytes with subcritical and supercritical CO2

In situ measurements of the ionic conductivity were performed on polyethers, poly(ethylene oxide) (PEO) and poly(oligo oxyethylene methacrylate) (PMEO), with lithium triflate (LiCF₃SO₃) as crystalline and amorphous electrolytes, and at CO₂ pressures up to 20 MPa. Both PEO and PMEO systems in subcritical and supercritical CO₂ increased more than five fold in ionic conductivity at 40 °C composed to atmospheric pressure. The pressure dependence of the ionic conductivity for PEO electrolytes was positive under CO₂, and increased by two orders of magnitude under pressurization from 0 to 20 MPa, whereas it decreases with increasing pressure of N₂. The enhancement is caused by the plasticizing effect of CO₂ molecules that penetrate into the electrolytes.     

Alternating copolymers of carbon dioxide with glycidyl ethers for novel ion-conductive polymer electrolytes

To overcome the low ionic conduction of existing poly(ethylene oxide)-based polymer electrolytes, we consider polycarbonates obtained from the copolymerization of CO₂ and epoxy monomers. We synthesized four types of polycarbonates possessing phenyl, n-butyl, t-butyl and methoxyethyl side groups using zinc glutarate, and measured the ionic conductivity of their electrolytes, including 10 mol% of LiTFSI. The electrolyte possessing methoxyethyl side groups had the highest conductivity, of the order of 10⁻⁶ S cm⁻¹ at room temperature. The activation energy (E_a) for ionic conduction in the polycarbonate electrolytes was estimated from the VTF equation, and the E_a of the electrolyte possessing n-butyl side groups was almost the same with the polyether-based electrolytes. An interesting feature of our study is that the polycarbonate is a unique candidate for ion-conductive polymers because of its flexible and hydrophobic properties.     

Preparation and characterization of gel polymer electrolyte based on PVA-K2CO3

ABSTRACT

In this study, electrolyte materials were synthesized by mixing a highly conducting salt (K₂CO₃) with the poly(vinyl alcohol) (PVA) in different proportions (from 10 to 50 wt.%). The synthesized electrolyte was characterized using Fourier transform infrared (FTIR) spectroscopy, field-emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), and linear sweep voltammetry (LSV) for their functional groups, morphology, thermal stability, glass transition temperature (T_g ), ionic conductivity, and potential window, respectively. Characterization results show that the complex formation between PVA and K₂CO₃ salt has been established by FTIR spectroscopic study, which indicates the detailed interaction between PVA and the salts in PVA-K₂CO₃ composites while the amorphous nature of the electrolyte after incorporation of the salts has been confirmed by FESEM analysis. Similarly, TGA and DSC analysis revealed that both decomposition temperature and T_g of the synthesized electrolytes decrease with the addition of K₂CO₃ due to the strong plasticizing effect of the salt. The results confirm that the electrolytes have sufficient thermal stability for supercapacitor operation, as well as an amorphous phase to effectively deliver high ionic conductivity. The highest ionic conductivity of 4.53 × 10^?3 S cm^?1 at 373 K and potential window of 2.7 V was exhibited by PK30 (30 wt.% K₂CO₃), which can be considered as high value for solid-state electrolytes which are superior to those electrolytes from PVA salts earlier reported. The results similarly show that the prepared electrolyte is temperature-dependent as conductivity increase with increase in temperature. Based on these properties, it can be imply that the PVA-K₂CO₃ gel polymer electrolyte (GPE) could be a promising electrolyte candidate for EDLC applications. The results indicate that the PVA-K₂CO₃ as a new electrolyte material has great potential in practical applications of portable energy-storage devices.     

Carbon dioxide as carbon source: Activation via electrogenerated O2 in ionic liquids

The activation of carbon dioxide has been obtained in O₂/CO₂ saturated ionic liquids, via electrochemically generated O₂⁻, at a less negative potential than the one of the direct cathodic reduction of CO₂. This electrochemical activation has been applied to the C–N bond formation from amines and carbon dioxide in the synthesis of organic carbamates. A competitive reaction between electrogenerated superoxide ion and imidazolium cations yielding 2-imidazolones has been pointed out. This procedure allows to avoid the utilization of volatile and toxic organic solvents, supporting electrolytes and catalysts.     

Triethyl orthoformate as a new film-forming electrolytes solvent for lithium-ion batteries with graphite anodes

Triethyl orthoformate (TEOF) as a new solvent used in propylene carbonate (PC)-based electrolytes together with graphitic anodes in lithium-ion batteries has been investigated. It can be observed that TEOF was capable of suppressing the co-intercalation of PC solvated lithium-ions into the graphite layer during the first lithiation process and the irreversible discharge capacity of the first cycle is the smallest when using 1.0 M LiPF₆ in PC and TEOF at solvent ratio of 1:1 as the electrolytes. The CV, FTIR, EIS, SEM results show that the PC-based electrolytes containing the solvent TEOF can generate an effective solid electrolytes interphase (SEI) film during the first cycling process, and the film is probably mainly composed of ROCO₂Li, ROLi, Li₂CO₃, etc. The formation of a stable passivating film on the graphite surface is believed to be the reason for the improved cell performance. All these results show that TEOF possesses a promising performance for use as an effective film-forming electrolytes solvent in lithium-ion batteries with graphitic anodes.     

Enhanced chemical stability and electrochemical performance of BaCe0.8Y0.1Ni0.04Sm0.06O3-δ perovskite electrolytes as proton conductors

Although doped BaCeO₃ electrolytes are proton conductors that undergo the fast conduction processes of inter-mediate temperature solid oxide fuel cells (IT-SOFCs), their wide application is impeded by their poor chemical stability under water vapour or CO₂ conditions. In this work, we selected the metallic cations with suitable electronegativity to improve the perovskite crystal structures of BaCeO₃ to enhance the chemical stability and electrochemical performance. We utilized Ni and Sm cations to improve the chemical stability of BaCeO₃ electrolytes in water vapour and CO₂ via a novel synthesis method, and the results revealed that the BaCe_0.8Y_0.1Ni_0.04Sm_0.06O_3-δ electrolyte, -with high electrochemical performance and chemical stability-, is a promising electrolyte material for conduction in IT-SOFCs. The optimum result offers new insights into synthesizing the membrane of IT-SOFCs for their application.     

超临界CO2辅助聚合物加工

近年来,以超临界CO₂替代聚合物加工过程中大量使用的有机溶剂实现超临界CO₂辅助聚合物加工过程已引起人们越来越多的关注。CO₂在聚合物中的溶解扩散可导致其结构和形态的变化,能够溶胀增塑聚合物并且将溶解于其中的小分子物质携带输运到聚合物基体中,进而影响聚合物的结晶及晶型转变行为,聚合物/CO₂体系界面张力以及聚合物/CO₂体系流变行为等基本物性的变化。利用聚合物基本物性的变化可实现CO₂辅助聚合物接枝反应,CO₂辅助聚合物渗透小分子物质以及CO₂辅助聚合物发泡等超临界CO₂辅助聚合物加工过程的应用。结合本研究室的实例,探讨了CO₂作用下等规聚丙烯和间规聚丙烯的结晶行为以及一种多晶型聚合物--等规聚丁烯-1的晶型转变行为;探讨了利用CO₂对等规聚丙烯、聚乳酸和聚酯三种典型的低熔体强度结晶聚合物具有的不同诱导结晶作用,调控聚合物的结晶行为,使其具备发泡所需的熔体强度,制备了具有不同结构特征的发泡聚合物材料。     

Zinc dissolution in ammonium chloride electrolytes

The anodic dissolution of zinc RDE in NH₄Cl and NH₄Cl + ZnCl₂ electrolytes at pH 5.5 was studied. XPS and SEM data indicate that the zinc electrode is covered by a porous film composed of a mixture of metallic zinc and zinc hydroxide. The thickness of the film and the zinc hydroxide content is much higher in zinc-containing electrolytes than in NH₄Cl and, although the thickness and Zn(OH)₂ amount decrease with anodic polarization, the electrode is never free from oxidized compounds. Electrochemical results indicate that at low overpotentials the rate of zinc dissolution is determined by the removal of the oxidized blocking particles, while at high overpotentials Zn dissolution takes place through the porous layer.     

Effects of introduced electrolytes on galvanic deposition of ZnO films

The effects of supporting electrolytes on galvanic deposition of ZnO films have been investigated in detail by respectively introducing K₂SO₄, KNO₃ and KCl into Zn(Ac)₂ electrolytes. It reveals that the chemical nature of introduced electrolytes plays important roles in acting on the growth of ZnO films. ZnO nanorods tend to grow in KNO₃ and KCl electrolytes, while sheet-like zinc hydroxysulfate tends to be formed in K₂SO₄ electrolyte. Besides, KNO₃ electrolyte is inclined to accelerate the passivation of Zn anode, resulting in the sharp decrease of driving force for galvanic deposition. In contrast, KCl and K₂SO₄ electrolytes facilitate zinc dissolution by anionic adsorption on the metal surface and subsequent participation in the active dissolution process, thus leading to the incorporation of anions in nanocrystals.     

Telescoped Synthesis of γ-Bromo-β-Lactones from Allylic Bromides Employing Carbon Dioxide

A direct synthesis of the title compounds involving a stepwise Zn-mediated carboxylation of allylic bromides with CO₂ delivering β, γ-unsaturated carboxylic acids and a subsequent bromolactonization is reported. The described method demonstrates the use of readily prepared allylzinc bromides by the method of Knochel for fixation of CO₂ employing commodity chemicals and zinc dust. This process was then optimized into a two-stage, telescoped process for the direct synthesis of γ-bromo-β-lactones from allyl bromides. The described strategy delivers functionalized β-lactones with dual reactivity as acylating and alkylating agents, which have utility as synthetic intermediates and are attracting growing interest as proteomic tools for activity-based protein profiling.     

Synthesis of magnesium-beta-alumina composite electrolytes via a vapour phase method

γ-Al₂O₃, Na₂CO₃, MgCO₃ and Li₂CO₃ were employed to synthesise MgO-doped Na-β″-Al₂O₃ composite electrolytes via a vapour phase method. The effects of MgO content on the β″-Al₂O₃ content, microstructure and electrical properties of each of the composite electrolytes were investigated by using X-ray diffraction, scanning electron microscopy and AC impedance spectroscopy, respectively. The bulk density and bending strength of the samples were also measured in this study. The results demonstrate that the composite electrolyte with an appropriate amount of MgO increased the β″-Al₂O₃ content of the solid electrolytes and accelerated their densification. The spinel phase resulting from MgO doping not only assisted the conversion process, but also facilitated the formation of Na_1.67Mg_0.67Al_10.33O₁₇. Lastly, the Na-β″-Al₂O₃ composite electrolyte doped with 0.4 wt% MgO was found to exhibit the best ionic conductivity and bending strength among all of the electrolytes.     

Equilibrium conditions for the hydrogen sulfide hydrate formation in the presence of electrolytes and methanol

Natural gas industry encounters systems that consist of gases like CO₂ and H₂S, and aqueous solutions of methanol and mixed electrolytes. A knowledge of the phase behavior of such systems, including hydrate formation, is essential in gas production and the design of facilities for gas transportation and processing. Recently, Dholabhai et al. (1997, 1996) and Bishnoi and Dholabhai (1998) described equilibrium conditions for CO₂ and gas mixtures containing CO₂ in the presence of methanol, electrolytes and ethylene glycol. In the present work aqueous three phase (aqueous liquid solution, vapor and incipient hydrate) equilibrium conditions of H₂S hydrate formation in aqueous solutions of electrolytes and methanol are measured in the temperature range of 272 to 294 K and pressure range of 0.3 to 1.0 MPa. A ‘full view’ sapphire variable volume cell with a movable piston is used to obtain the experimental data.     

Substitution of silver by various metal ions in modified AgI solid electrolytes

The substitution process of silver by various metals in RbAg₄I₅ and other solid electrolytes of the AgI-modified type has been investigated. This process is of technological interest since it permits the use of copper, zinc or cadmium instead of silver as anode materials in solid state batteries which utilize these electrolytes.     

An air-breathing H2/air cell design suitable for fast screening of electrolytes

An air-breathing H₂/air cell was designed for fast screening of electrolytes. In this study various electrolytes, including organic, inorganic, acidic, and basic electrolytes, were screened by comparing their effect on cell discharge performance. Focusing on organic alkaline electrolytes, several tetraalkyl ammonium hydroxide electrolytes with different molecular size and concentrations were investigated at different operating temperatures. Both electrolyte concentration and operating temperature significantly affect the cell's performance. The effect of CO₂ and some acids on alkaline electrolyte's impedance and cell's discharge performance was also investigated.