Properties of supporting electrolytes and solvents were examined for use with vanadium acetylacetonate - a member of the class of metal(beta-diketonate) active species - in non-aqueous redox flow ...batteries. Twenty supporting-electrolyte/solvent combinations were screened for ionic conductivity and supporting-electrolyte solubility. Hexane, tetrahydrofuran, and dimethylcarbonate solvents did not meet minimal conductivity and solubility criteria for any of the electrolytes used, which included tetraethylammonium tetrafluoroborate, tetrabutylammonium tetrafluoroborate, tetrabutylammonium hexafluorophosphate, and (1-butyl, 3-methvl)imidazolium bis(trifluoromethanesulfonyl)imide. Ionic conductivities and solubilities for solutions of these electrolytes passed screening criteria in acetonitrile and dimethylformamide solvents, in which maximum supporting-electrolyte and active-species solubilities were determined. Active-species electrochemistry was found to be reversible in several solvent/ support systems: for some systems the voltammetric signatures of unwanted side reactions were suppressed. Correlations between supporting-solution properties and performance metrics suggest that an optimal solvent for a vanadium acetylacetonate RFB should have a low solvent molar volume for active-species solubility, and a high Hansen polarity for conductivity.
The electrochemistry of a single-component redox flow battery employing vanadium(III) acetylacetonate in acetonitrile and tetraethylammonium tetrafluoroborate has been investigated. The electrode ...kinetics of the anodic and cathodic reactions were studied using cyclic voltammetry. The V(II)/V(III) and V(III)/V(IV) couples were quasi-reversible and together yielded a cell potential of 2.2
V. The diffusion coefficient for vanadium acetylacetonate was estimated to be in the range of 1.8–2.9
×
10
−6
cm
2
s
−1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell, and coulombic efficiencies near 50% were achieved.
A single-metal redox flow battery employing chromium(III) acetylacetonate in tetraethylammonium tetrafluoroborate and acetonitrile has been investigated using electrochemical techniques. Cyclic ...voltammetry was used to evaluate electrode kinetics. Four redox couples were observed in the stable potential window. The Cr
II/Cr
III, Cr
I/Cr
II, Cr
III/Cr
IV and Cr
IV/Cr
V redox couples all appeared to be quasi-reversible, with the Cr
III/Cr
IV couple exhibiting comparatively slow kinetics. A cell potential of 3.4
V was measured for the one-electron disproportionation of the neutral Cr
III complex. The diffusion coefficient for chromium acetylacetonate in the supporting electrolyte solution was estimated to be in the range of 5.0–6.2
×
10
−7
cm
2
s
−1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell, and coulombic and energy efficiencies of approximately 55% and 20%, respectively, were obtained.
Electrochemical and physical measurements elucidate several thermodynamic properties and chemical factors that affect the performance of a non-aqueous all-vanadium flow battery. An H-type test cell ...was constructed that demonstrates stable coulombic efficiencies of 70% without flow after several weeks of slow cycling, with a steady plateau voltage near 1.7V during most of the discharge step. Environmental oxygen and water are associated with side reactions that affect long-term charge/discharge response of the battery. Oxygen passivates the electrode and may react with the solvent or supporting electrolyte, while water can cause the formation of oxovanadium complexes. Reversible cycling of the vanadyl acetylacetonate complex appears possible.
► Mn
III/IV, Mn
II/III and Mn
I/II couples observed in voltammetry for Mn(acac)
3. ► Cell potential of 1.1
V observed for the one-electron disproportionation of Mn(acac)
3. ► Diffusion coefficient of ...Mn(acac)
3 in the electrolyte is 3–5
×
10
−6
cm
2
s
−1. ► Coulombic efficiencies increased with cycling. ► Energy efficiencies stable at ∼21% for unoptimized cell.
A single-metal redox flow battery employing manganese(III) acetylacetonate in tetraethylammonium tetrafluoroborate and acetonitrile has been investigated. Cyclic voltammetry was used to evaluate electrode kinetics and reaction thermodynamics. The Mn
II/Mn
III and Mn
III/Mn
IV redox couples appeared to be quasi-reversible. A cell potential of 1.1
V was measured for the one-electron disproportionation of the neutral Mn
III complex. The diffusion coefficient for manganese acetylacetonate in the supporting electrolyte solution was estimated to be in the range of 3–5
×
10
−6
cm
2
s
−1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell. Coulombic efficiencies increased with cycling suggesting an irreversible side reaction. Energy efficiencies for this unoptimized system were ∼21%, likely due to the high cell-component overpotentials.
Redox flow batteries (RFBs) are being developed for large-scale energy storage and load-leveling systems for solar or wind power. Aqueous chemistries are used for current commercial RFBs, in which ...energy and power density are limited by the stability range of water. Non-aqueous solvents offer stability windows up to four times greater than those for aqueous solvents. The goal of my research was to examine all components of a non-aqueous-vanadium-single-metal RFB and determine their effects on key performance characteristics. First, relationships between the structure, composition, and function of acetylacetonate metal complex based electrolytes were examined in an effort to determine strategies for their further development and provide initial guidelines for their use. Vanadium, chromium, and manganese acetylacetonate complexes had maximum energy densities of 18, 18, and 9 Wh/L respectively with reversible electrochemistry for V and Mn; therefore vanadium was selected for more extensive testing. Substitution of the ligands demonstrated the ability to change solubility by two orders of magnitude. Results from examination of a variety of solvent/supporting electrolyte combinations indicated that solvents with low solvent molar volumes and high polarities possessed desirable properties (acetonitrile is optimal). Effects of the cell components (membrane resistance and electrode kinetics) on the cell performance were also examined. The lowest resistance membranes, Selemion DSV or Neosepta AHA, were chosen to reduce energy losses. The kinetics of the desired reaction on gold, platinum, and glassy carbon electrodes showed minimal kinetic limitations suggesting outer-shell-electron-transfer reactions occur. Finally, the stability was examined. When exposed to water or oxygen, the V(II)/V(III) redox couple becomes irreversible and vanadyl acetylacetonate is formed. Even in the absence of oxygen or water impurities, the capacity of the RFB fades dramatically. This fade could be a consequence of precipitation stemming from a reaction between the charged active species and the acetonitrile solvent. Overpotentials on the electrode and membrane increased with cycling – likely due to precipitation and mechanical degradation and could contribute to capacity fade (based on results from scanning electron microscopy). Overall I found that the non-aqueous all-vanadium RFB could be a promising candidate for future batteries after stability of the cell components is addressed.
Traditionally, the crystallization unit operation and process variables (e.g., temperature and/or antisolvent addition profile, agitation rate, and seeding parameters) are optimized using the design ...of experiments (DOE) methodology within the quality-by-design (QbD) framework. To achieve rapid process design, reduce the number of experiments, and minimize personnel exposure to toxic chemicals, quality-by-control (QbC)-based methods (i.e., direct design or model-free methods) such as supersaturation control and direct nucleation control can be applied to quickly determine an operating profile of a process, leading the system to the desired critical quality attributes (CQAs). In this work, various direct design approaches were implemented to investigate the impact on the particle length and filtration time of high-aspect-ratio particles. In addition, an alternative image-based direct design approach, called turbidity direct nucleation control (TDNC), was implemented, which improved the filtration time by 2.5 times compared to that in the standard process. The robustness, usability, and scalability of the TDNC approach were investigated by varying the solvent composition and running open-loop scale-up experiments. The improved procedure was applied to a commercial-scale crystallizer, resulting in similar improvements in the filtration rate. The commercial scale-up also resulted in a surprising reduction in wash efficiency requiring centrifuge optimization to be addressed.
Solution crystallization is commonly used in the agrochemical industry to isolate and purify the active ingredient (AI). The generated particles’ characteristics, typically needle-like shape in the ...agrochemical industry, can affect the performance of subsequent unit operations (filtration, washing, and drying). Previous experimental findings highlighted the impact of poor crystallization control on subsequent unit operations. By following the model-free Quality-by-Control (QbC) framework, the improved crystallization process highlighted the effectiveness of temperature cycling to improve particle properties and filtration time. However, the model-free QbC approach generally leads to suboptimal process performance. To further optimize the process while reducing experimental time, cost, and efforts, in this paper, a model-based QbC framework was applied to a commercial agrochemical crystallization process. A digital model of the system was developed using a two-dimensional population balance model (2D-PBM), which was calibrated with carefully designed parameter estimation experiments to estimate the 2D kinetics. Sensitivity analysis via different methods highlighted the estimability of certain parameters, assessed the quality of the estimated parameters, and tested the reliability of the model. Lastly, the digital model was applied to an optimization framework to perform in silico experiments and digital design of an optimal operating procedure. By validating the optimization results experimentally, the nominal temperature profile improved the content uniformity of the crystal product by reducing the size distribution span and minimizing the generation of fine particles.
Background
We aimed to test the hypothesis that three‐dimensional (3D) volume‐based scoring of computed tomography (CT) images of the paranasal sinuses was superior to Lund‐Mackay CT scoring of ...disease severity in chronic rhinosinusitis (CRS). We determined correlation between changes in CT scores (using each scoring system) with changes in other measures of disease severity (symptoms, endoscopic scoring, and quality of life) in patients with CRS treated with triamcinolone.
Methods
The study group comprised 48 adult subjects with CRS. Baseline symptoms and quality of life were assessed. Endoscopy and CT scans were performed. Patients received a single systemic dose of intramuscular triamcinolone and were reevaluated 1 month later. Strengths of the correlations between changes in CT scores and changes in CRS signs and symptoms and quality of life were determined.
Results
We observed some variability in degree of improvement for the different symptom, endoscopic, and quality‐of‐life parameters after treatment. Improvement of parameters was significantly correlated with improvement in CT disease score using both CT scoring methods. However, volumetric CT scoring had greater correlation with these parameters than Lund‐Mackay scoring.
Conclusion
Volumetric scoring exhibited higher degree of correlation than Lund‐Mackay scoring when comparing improvement in CT score with improvement in score for symptoms, endoscopic exam, and quality of life in this group of patients who received beneficial medical treatment for CRS.
The properties of liquid-ordered, solid-ordered, and liquid-disordered phases were investigated by steady-state fluorescence spectroscopy in liposomes composed of mixtures of ...dipalmitoylphosphatidylcholine and cholesterol (0–40
mol %) as a function of temperature (24–51°C). The fluorescent probes used (bis-pyrene, nystatin, prodan, and merocyanine) were chosen because they differ in the location they occupy in the membrane and in the types of properties they sense. Comparison of phase diagrams with contour plots of the fluorescence data suggested that bis-pyrene is sensitive primarily to lipid order. In contrast, nystatin fluorescence intensity responded to changes in lipid fluidity. The shape of the prodan emission spectrum detected both liquid-solid and order-disorder transitions in the phase diagram. Merocyanine’s behavior was more complex. First, it was more sensitive than any of the other probes to the membrane pretransition that occurs in the absence of cholesterol. Second, regardless of whether emission intensity, anisotropy, or spectral shape was observed, the probe appeared to distinguish two types of liquid-ordered phases, one with tightly packed lipids and one in which the apparent spacing among lipids was increased. The prodan data supported these results by displaying modest versions of these two observations. Together, the results identify eight regions within the phase diagram of distinguishable combinations of these physical properties. As an example of how this combined analysis can be applied to biological membranes, human erythrocytes were treated similarly. Temperature variation at constant cholesterol content revealed three of the eight combinations identified in our analysis of liposomes.
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