Temperature Effects on the Kinetics of Ferrocene and Cobaltocenium in Methyltriphenylphosphonium Bromide Based Deep Eutectic Solvents

The oxidation of ferrocene (Fc/Fc+) and reduction of cobaltocenium (Cc+/Cc) under different temperatures has been studied by cyclic voltammetry and double potential step chronoamperometry in deep eutectic solvents (DESs) consisting of methyltriphenylphosphonium bromide salt with tri-ethylene glycol, glycerol or ethylene glycol as hydrogen bond donors. The temperature dependence of the measured physical properties of DESs (such as viscosity and conductivity) is discussed in detail. The kinetics of the redox couples are studied using cyclic voltammetry, and the standard heterogeneous electron transfer rate constant, k0 is found to be of the order of 10−5 to 10−4 cms−1 at different temperatures. The diffusion coefficient, D, of Fc and Cc+ is determined to lie between 8.28 × 10−10 to 6.65 × 10−9 cm2 s−1. These results show that both k0 and D increase with temperature in the studied DESs. In addition, better kinetic parameters for the DES with ethylene glycol as hydrogen bond donor means that this could be evaluated favorably as both solvents and electrolytes for redox flow cells

Investigation of ammonium- and phosphonium-based deep eutectic solvents as electrolytes for a non-aqueous all-vanadium redox cell

The charge/discharge characteristics for vanadium acetylacetonate in deep eutectic solvents were evaluated using an H-cell with an anion-exchange membrane separator for the first time. Coulombic (CE) and energy efficiencies (EE) of the electrolyte containing V(acac)3/0.5 M TEABF4 in DES3 (a hydrogen bonded eutectic between choline chloride and ethylene glycol) were obtained as 49-52% and 25-31%, respectively, when charging from 0 to 50% of theoretical maximum state-of-charge for 12 cycles. The low CE may be due to the crossover of the active species through the separator, or to the loss of active vanadium due to a parasitic reaction. However, the CE was similar to that for acetonitrile (CH3CN) indicating the promise of DESs as suitable electrolytes for future evaluation. Charge and discharge voltages are respectively higher and lower than the formal cell potential obtained by voltammetry. Ohmic drop in the DES results from the low conductivity of the electrolyte and the relatively large distance between the two electrodes in the H-cell. Further studies require investigation in a flow cell with analyses of polarization curves and impedance to determine the loss mechanisms in sufficient detail

Encapsulated deep eutectic solvent for esterification of free fatty acid

A novel encapsulated deep eutectic solvent (DES) was introduced for biodiesel production via a two-step process. The DES was encapsulated in medical capsules and were used to reduce the free fatty acid (FFA) content of acidic crude palm oil (ACPO) to the minimum acceptable level (< 1%). The DES was synthesized from methyltriphenylphosphonium bromide (MTPB) and p-toluenesulfonic acid (PTSA). The effects pertaining to different operating conditions such as capsule dosage, reaction time, molar ratio, and reaction temperature were optimized. The FFA content of ACPO was reduced from existing 9.61% to less than 1% under optimum operating conditions. This indicated that encapsulated MTPB-DES performed high catalytic activity in FFA esterification reaction and showed considerable activity even after four consecutive recycling runs. The produced biodiesel after acid esterification and alkaline transesterification met the EN14214 international biodiesel standard specifications. To our best knowledge, this is the first study to introduce an acidic catalyst in capsule form. This method presents a new route for the safe storage of new materials to be used for biofuel production. Conductor-like screening model for real solvents (COSMO-RS) representation of the DES using σ-profile and σ-potential graphs indicated that MTPB and PTSA is a compatible combination due to the balanced presence and affinity towards hydrogen bond donor and hydrogen bond acceptor in each constituent

Adaptive and Predictive Control of Liquid-Liquid Extractors Using Neural-Based Instantaneous Linearization Technique

Nonlinearity of the extraction process is addressed via the application of instantaneous linearization to control the extract and raffinate concentrations. Two feed-forward neural networks with delayed inputs and outputs were trained and validated to capture the dynamics of the extraction process. These nonlinear models were then adopted in an instantaneous linearization algorithm into two control algorithms. The self-tuning adaptive control strategy was compared to an approximate model predictive control in terms of set point tracking capability, efficiency and stability. For the case of large, abrupt set point changes, the performance of the self-tuning algorithm was poor, especially for the raffinate control. The approximate model predictive control strategy was superior to the self-tuning control in terms of its ability to force the output to following the set point trajectory efficiently with smooth controller moves.Wiley Online librar

Neural-Networks-Based Feedback Linearization versus Model Predictive Control of Continuous Alcoholic Fermentation Process

In this work advanced nonlinear neural networks based control system design algorithms are adopted to control a mechanistic model for an ethanol fermentation process. The process model equations for such systems are highly nonlinear. A neural network strategy has been implemented in this work for capturing the dynamics of the mechanistic model for the fermentation process. The neural network achieved has been validated against the mechanistic model. Two neural network based nonlinear control strategies have also been adopted using the model identified. The performance of the feedback linearization technique was compared to neural network model predictive control in terms of stability and set point tracking capabilities. Under servo conditions, the feedback linearization algorithm gave comparable tracking and stability. The feedback linearization controller achieved the control target faster than the model predictive one but with vigorous and sudden controller moves.Wiley Online Librar

Representation of Adsorption Data for the Isopropanol-Water System using Neural Network Techniques

Molecular sieves and palm stone, a newly developed bio-based adsorbent, were used to break an azeotropic isopropanol-water system via an adsorptive distillation process. Equilibrium data at different inlet water contents are presented. The data were obtained with a fixed bed adsorptive distillation process using Type 3A and Type 4A molecular sieves and palm stone. An artificial neural network (ANN) technique was used to represent the isotherm equilibrium data of this azeotropic system. The ANN prediction results were compared with the Guggenheim-Anderson-de Boer (GAB) isotherm model. It was possible to break the isopropanol-water azeotrope using this separation process with the adsorbents used in this work. Water uptake increases as the water content in the feed decreases from 16?% to 10?%. Although the GAB isotherm model was found to be applicable to the water vapor sorption data on the adsorbents examined, the ANN model fitted the equilibrium data more efficiently

The interaction of deep eutectic solvents with pristine carbon nanotubes and their associated defects: A density functional theory study

In this study, the interaction of four deep eutectic solvents (DESs): [Choline chloride][Urea] ([ChCl][U]), [Choline chloride][Ethylene glycol] ([ChCl][EG]), [Choline chloride][Glycerol] ([ChCl][Gly]) and [Choline chloride][Benzoic acid] ([ChCl][BA]), with pristine carbon nanotube (CNT) and its defects: double-vacancy and Stone–Wales structures (CNT-DV and CNT-SW) is investigated using density functional theory (DFT) calculations. The geometry optimization, electronic property calculations, noncovalent interaction analysis and optical properties of the DES@nanotube complexes were carried out at the M06-2X/cc-pVDZ level of theory. The adsorption energy (Eads) calculations show that the presence of the DV and SW defects on the CNT increases the adsorption strength of the DESs, DES@CNT-SW \u3e DES@CNT-DV \u3e DES@CNT. On the other hand, the adsorption energy values increase with an increase in the volume of DESs due to the increase of noncovalent interactions, following the order [ChCl][BA] \u3e [ChCl][Gly] \u3e [ChCl][U] \u3e [ChCl][EG]. The calculation of the HOMO-LUMO energy gap (Eg) and chemical hardness (η) of the DES@nanotube complexes indicates that the DES@CNT-SW complexes have the largest Eg and η values and thus the lowest chemical reactivity. The analysis of the interactions between the nanotubes and the DESs using noncovalent interaction (NCI) plots and energy decomposition analysis (EDA) suggests that the DESs adsorb onto the nanotubes through van der Waals interactions and that dispersive interactions dominate (dispersion interaction energy (ΔEdisp) \u3e electrostatic interaction energy (ΔEelec) \u3e orbital interaction energy (ΔEorb)). Predicted ultraviolet–visible absorption spectra of the complexes show that the adsorption of DESs on the nanotubes has only a very marginal effect on the optical response of the nanotubes. Transition density matrix heat maps reveal that the electrons and holes localize to the CNT, CNT-DV and CNT-SW surfaces in the DES@nanotube complexes, indicating that the charge transfer occurs mostly on the surfaces

PVDF-co-HFP/superhydrophobic acetylene-based nanocarbon hybrid membrane for seawater desalination via DCMD

Surface hydrophobicity is the most desirable characteristic for high DCMD performance. Superhydrophobic carbon nanomaterials/powder activated carbon (CNMs/PAC) has unique properties and believed to be the proper candidate to increase the membrane hydrophobicity with maintaining good mechanical properties and high porosity at the same time. In this work, we introduce a phase inversion process based on central composite design, aimed at minimizing the number of experiments required for membrane fabrication. The hydrophobic membrane fabrication conditions are modeled as independent parameters, with the flux provided as the model response. The analyses performed on the membrane structure and surface, as well as its mechanical properties revealed that the superhydrophobic CNMs/PAC significantly enhances the hydrophobicity of the composite membrane surface. The accuracy measurements obtained by analysis of variance showed that the model developed and all the proposed parameters have significant effects on the flux. However, the CNMs/PAC emerged as the most significant influential factor and interacted with polymer concentration and casting knife thickness to exert effects on the permeate flux. The optimum preparation parameters were 775.21 mg carbon loading, PVDF-HFP concentration of 21.86 g and casting knife thickness of 118.93 μm, as these values yield the highest flux of about 102 kg/m2h

Investigation of Ammonium-and Phosphonium-Based Deep Eutectic Solvents as Electrolytes for a Non-Aqueous All-Vanadium Redox Cell

The charge/discharge characteristics for vanadium acetylacetonate in deep eutectic solvents were evaluated using an H-cell with an anion-exchange membrane separator for the first time. Coulombic (CE) and energy efficiencies (EE) of the electrolyte containing V(acac) 3 /0.5 M TEABF 4 in DES3 (a hydrogen bonded eutectic between choline chloride and ethylene glycol) were obtained as 49-52% and 25-31%, respectively, when charging from 0 to 50% of theoretical maximum state-of-charge for 12 cycles. The low CE may be due to the crossover of the active species through the separator, or to the loss of active vanadium due to a parasitic reaction. However, the CE was similar to that for acetonitrile (CH 3 CN) indicating the promise of DESs as suitable electrolytes for future evaluation. Charge and discharge voltages are respectively higher and lower than the formal cell potential obtained by voltammetry. Ohmic drop in the DES results from the low conductivity of the electrolyte and the relatively large distance between the two electrodes in the H-cell. Further studies require investigation in a flow cell with analyses of polarization curves and impedance to determine the loss mechanisms in sufficient detail. Low energy density is often reported as a barrier in the commercialization of redox flow batteries using current aqueous electrolytes. Non-aqueous electrolytic solvents offer a wide potential window of operation and increase the energy capacity of the system. 2-4 In contrast to organic systems which are either scarce or environmentally unfriendly, ionic liquids (ILs) have emerged as a relatively new class of non-aqueous electrolytes for energy storage applications. • C. ILs have many favorable characteristics, e.g., low volatility, high intrinsic conductivity, large electrochemical window, etc. In addition, ILs can be tuned by combining different cations and anions. However, many reports point out the hazardous toxicity and the poor biodegradability of most ILs. 7 ILs with high purity are also required since impurities, even in trace amounts, affect their physical properties. Additionally, their synthesis is not entirely environmentally friendly since it generally requires a large amount of salts and solvents in order to completely exchange the anions. 10 These drawbacks together with the high price of common ILs unfortunately hamper their industrial applications. Such issues may be overcome by using deep eutectic solvents (DESs). 11,12 A DES is a eutectic mixture of an organic salt (ammonium or phosphonium) and a hydrogen bond donor (HBD), that is made up of different components such as amides, metallic salts, alcohols, carboxylic acids and amines that may be used as complexing agents (typically an H-bond donor). 13,14 DESs have a melting point that is far below that of either individual constituent. The mechanism is that the complexing agent interacts with the anion and increases its effective size. This, in turn, decreases the anionic interaction with the cation thereby reducing the salt-HBD lattice energy and causing a depression in the melting point of the mixture. z E-mail: [email protected] they are simple to synthesize on a large scale. 27 Furthermore, their physicochemical and electrochemical properties (viscosity, conductivity, electrochemical stability, diffusion coefficients, etc.) have been evaluated in a similar manner to that for ILs. The synthesized DESs are applied as electrolytes to determine the effects of the electrode and solvent in our electrochemical system. Ferrocene/ferrocenium (Fc/Fc + ) or cobaltocenium/cobaltocene (Cc + /Cc) redox couples have been investigated as candidates of internal references to provide a known and stable reference point in various DESs. Despite the significance of DESs and their remarkable advantages, their applications in redox flow batteries (RFBs) are limited. The experiments reported here are based on commercially sourced raw materials without additional purification (i.e., these are preliminary experiments that enable an informed decision for choosing appropriate raw materials for preparing DESs for practical experiments with non-aqueous RFB prototypes in future work). The purpose is to prove that a redox battery could be charged/discharged successfully without the need for complex synthesis and purification processes that could possibly lower the economics of the entire process