Energy efficiency of cogeneration systems

It is proposed to assess the energy efficiency of cogeneration systems in terms of the energy lost with the working fluid, Δq. This can be calculated either analytically or graphically using the equation Δq=(1?X)×V ₂ C ₂ T ₂/V ₁ C ₁ T ₁, whereX is the working-fluid recycle ratio;V ₁,C ₁, andT ₁ are the flow rate, heat capacity, and temperature of the working fluid at the entry to the reactor; andV ₂,C ₂, andT ₂ are the same variables at the exit from the reactor.     

A Mechanistic Study of the Fischer–Tropsch Synthesis Using Transient Isotopic Tracing. Part-1: Model Identification and Discrimination

A steady state isotopic transient kinetic analysis (SSITKA) of the Fischer–Tropsch synthesis over Co/Ru/TiO₂ catalyst is reported by using ¹³CO and D₂. Besides a qualitative interpretation of the transients, model identification and discrimination are mainly based on numerical modeling. From this, it is concluded that two single-C species are present on the catalyst surface, C_α,ads and C_β,ads. These species both participate in the formation of methane and of higher hydrocarbons. The heterogeneity of the catalyst surface is limited to these two single-C species. Only one type of chain-growth site is present in a low concentration compared to the surface concentrations of CO_ads, C_α,ads, and C_β,ads. The H-content of C_α,ads and C_β,ads is assessed by comparing the simulated transient for the incorporation of the D-labeling into methane with experiments. In case the stepwise hydrogenations of C_ads to CH₄ are irreversible, C_α,ads and C_β,ads are H-free species. In case these reactions are reversible, the H-exchange between C_ads, CH_ads, CH_2,ads, and CH_3,ads is fast compared to the net formation of methane, and the H-content of C_α,ads and C_β,ads cannot be assessed. The most probable mechanism for the Fischer–Tropsch reaction resulting from this study is used in a next paper (Part 2) for the quantification of the kinetic parameters. In that paper, a systematic analysis of these parameters yields detailed mechanistic insight into the Fischer–Tropsch synthesis reaction.     

Reduction of Surface Nitrates via C3H6 Oxidation Over a Pt/Al2O3 Catalyst

Reduction of surface nitrates with C₃H₆ on a Pt/Al₂O₃ catalyst was investigated using diffuse reflectance infrared spectroscopy (DRIFTS) and a reactor system designed for monolith-supported catalysts. C₃H₆ oxidation was inhibited by the presence of NO, and vice versa, and data indicate that adsorbed NO_X reacted with gas phase C₃H₆. DRIFTS results confirm reaction between C₃H₆ and surface nitrates with linear nitrites as the reaction products. Data show that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant.     

Iodide surface coverage and its effect on the rate constants during hydrogen charging and permeation in iron

This paper demonstrates the use of the new Iyer/Pickering/Zamanzadeh/Al-Faqeer (IPZA) analysis to determine the effect of the iodide surface coverage (θ_I⁻) on the hydrogen surface coverage (θ_H) and the rate constants of the hydrogen evolution reaction (HER) and hydrogen absorption reaction (HAR). Iodide ions have an inhibiting effect on the HER but they enhance the HAR. The IPZA analysis was used to determine θ_I⁻ in addition to the usual parameters: hydrogen discharge (k₁) and recombination (k₂) rate constants, hydrogen kinetic-diffusion constant (k) and θ_H. Inclusion of the iodide coverage is important as shown by a comparison with literature values that were obtained using the original IPZ analysis, which does not include the θ_I⁻ parameter. The θ_I⁻ values from the IPZA analysis were within reasonable agreement with θ_I⁻ values measured using the electrochemical quartz crystal microbalance (EQCM) and θ_I⁻ values calculated from the measured corrosion current densities before and after adding iodide to the electrolyte.     

Iodide surface coverage and its effect on the rate constants during hydrogen charging and permeation in iron

This paper demonstrates the use of the new Iyer/Pickering/Zamanzadeh/Al-Faqeer (IPZA) analysis to determine the effect of the iodide surface coverage (θ_I⁻) on the hydrogen surface coverage (θ_H) and the rate constants of the hydrogen evolution reaction (HER) and hydrogen absorption reaction (HAR). Iodide ions have an inhibiting effect on the HER but they enhance the HAR. The IPZA analysis was used to determine θ_I⁻ in addition to the usual parameters: hydrogen discharge (k₁) and recombination (k₂) rate constants, hydrogen kinetic-diffusion constant (k) and θ_H. Inclusion of the iodide coverage is important as shown by a comparison with literature values that were obtained using the original IPZ analysis, which does not include the θ_I⁻ parameter. The θ_I⁻ values from the IPZA analysis were within reasonable agreement with θ_I⁻ values measured using the electrochemical quartz crystal microbalance (EQCM) and θ_I⁻ values calculated from the measured corrosion current densities before and after adding iodide to the electrolyte.     

Effect of support type and synthesis conditions on the oxygen reduction activity of RuxSey catalyst prepared by the microwave polyol method

Ru_xSe_y nanoparticles supported on different carbon substrates were synthesized by microwave heating of ethylene glycol solutions of Ru(III) chloride and sodium selenite at different pH and Ru/Se mole ratios. The resulting catalysts were used for the electrochemical oxygen reduction reaction (ORR) in acidic solution. The electrochemical activity was highest for the supported catalyst synthesized at pH 8. Increasing the Se concentration of the catalyst up to 15 mol% increased the catalytic activity for the ORR; at this Se concentration, the activity of the catalyst was considerably higher than that observed for pure Ru catalyst synthesized at exactly the same conditions. The influence of the type of carbon support on the activity of the electrocatalyst was also investigated. Among the different supports, including carbon black (Vulcan XC-72R) (C1), and nanoporous carbons synthesized from resorcinol- (C2) and phloroglucinol-formaldehyde (C3) resins, the Ru_xSe_y catalyst supported on C3 exhibited highest activity for ORR.     

Modelling of the Hydrolysis of Benzylpenicillin to 6-Aminopenicillanic Acid and Phenyl Acetic Acid by an Immobilised Penicillin Amidase in a Small Pilot Plant Batch Recirculated Reactor

This paper deals with the modelling of the hydrolysis of benzylpenicillin to 6-aminopenicillanic acid (6-APA) and phenyl acetic acid (PAA) in a small pilot plant batch recirculated reactor by an immobilised penicillin amidase preparation. By using the following linearised form for an integrated Michaelis-Menten equation Et/V₀X=α+β| In (1-X)/X| where α and β are reaction kinetic parameters, good correlations are obtained of α and β with linear velocity across the reactor, substrate concentration and temperature of operation. A process to determine α and β from initial velocity measurements is outlined. The applicability of the above equation to published data is also analysed.     

A strategy of combination reaction to improve electrochemical performance in two-dimensional Mo1-xWxSe2 battery-type electrode materials

We report here a case of combination reaction between MoSe₂ and WSe₂ in certain proportions to improve electrochemical performance of Mo_1-xW_xSe₂ compound materials. Two-dimensional (2D) Mo_1-xW_xSe₂ flower-like crystals (x = 0, 0.25, 0.5, 0.75, 1) were synthesized using a solution synthesis method, and then Mo_1-xW_xSe₂-based electrodes were prepared using a powder pellet method. Their structure and electrochemical performance were respectively measured by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectrometer (XPS), scanning electron microscope (SEM), and electrochemical workstation. The results indicate that only Mo_0.25W_0.75Se₂-based electrode (x = 0.75), compared with other electrodes, delivers excellent specific capacity and stability with the capacity retention of 74.4% after 5000 charging-discharging deep cycles at the current density of 2 A g^?1 in 1.0 mol/L KOH aqueous electrolyte, and exhibits a Coulombic efficiency almost 100% after 5000 cycles. This phenomenon is attributed to a situation that Mo_0.25W_0.75Se₂ active material has a quite different electronic band structure from the other remaining materials. It is therefore concluded that the combination reaction enables Mo_1-xW_xSe₂ composite materials to realize their potential in electrochemical energy storage.     

Applicability of the Freundlich and Langmuir adsorption isotherms in the bleaching of rubber and melon seed oils

The applicability of Freundlich and Langmuir adsorption isotherms to guide bleaching of vegetable oils was examined using rubber [Hevea brasiliensis (Willd. ex Adr. Juss) Muell. Arg.] and melon [Colocynthis vulgaris (Schrad)] seed oils at temperatures of 30, 55 and 80 C. Fuller’s earth, activated charcoal and a mixture thereof (1:1 ratio) were used as the decolorizing agents (adsorbents). The degree of bleaching was monitored spectrophotometrically. Plots of log(x/m) versus logX _e (for Freundlich) and (X _e/x/m) versusX _e (for Langmuir) were made; where x is the amount of coloring matter removed per unit mass of the adsorbent, m, andX _e is the equilibrium concentration of the coloring matter. The results obtained show good agreement with Freundlich and Langmuir isotherms, indicating that the adsorption of the coloring matter from the oils proceeds by monolayer formation on the surface of the adsorbent. The specific adsorption (x/m) and the Freundlich and Langmuir constants were found to increase with temperature for a given oil/bleaching agent ratio, showing the formation of more active sites on the adsorbent with a rise in temperature.     

Etude de mecanismes ec sur electrode a pate de graphite

A theoretical analysis of EC mechanisms on graphite paste electrode (GPE) in linear sweep voltammetry is proposed for the following E_iC_j mechanisms. reversible electrochemical reactions E_i: Ox + ne ? Red (E₁), or: Ox + e ? S, S + e ? Red, 2S ? Ox + red (E₂); irreversible chemical reaction C_j: p Ox → A (C₁), or: p Ox → A + m Red (C₂), or: p Ox + m Red → A (C₃).Current—potential relationships are similar to those obtained by Laviron for both layer electrodes and film covered electrodes when the differential capacitance C and the circuit and electrode resistance R are negligible. For large values of the kinetic contants, it is possible to establish a set of relationships between the mechanism parameters and the experimental characteristics of the voltammograms.On a practical point of view, two types of mathematical analysis are proposed.     

Synthesis and Surface Properties of Novel Gemini Imidazolium Surfactants

Five new Gemini imidazolium surfactants were synthesized from imidazole and 1-bromoalkane (C₈, C₁₀, C₁₂, C₁₄, C₁₆) to get 1-alkylimidazole, which was further reacted with 1,3-dichloropropan-2-ol to form the surfactant molecule, 1,1′-(propane-1,3-diyl-2-ol) bis(3-alkyl-1H-imidazol-3-ium) chloride. The structures of the five new surfactants and intermediates were characterized by ¹H-NMR, ¹³C-NMR and IR spectra. Thermal properties of the five new surfactants were studied with thermogravimetric analysis and differential scanning calorimetry, the five new surfactants showed a transition from a crystalline phase to a thermotropic liquid–crystalline phase at around ca. 100 °C, which transformed to an isotropic liquid phase at around ca. 165 °C. The five new surfactants critical micelle concentrations (CMC) in the aqueous solutions were determined by surface tension and electrical conductivity methods. The surface tension measurements provided a series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γ _CMC), adsorption efficiency  (pC ₂₀), and effectiveness of surface tension reduction (π_CMC). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Γ_max) and minimum surface area/molecule (A_min) at the air–water interface were obtained. The parameters β (degree of counterion binding to micelles), ΔG _ads ^θ (Gibbs free energy of adsorption), and ΔG _mic ^θ (Gibbs free energy change of micellization) were also derived. The results indicated that the five new Gemini surfactants exhibited very low CMC and a good efficiency in lowering the surface tension of water. The foamability and foam stability of the five new surfactants were also examined at different CMC.     

Unperturbed dimension,interaction parameters,zeta potential and rheology of sodium alginate in binary solvent mixtures

The intrinsic viscosity [η] of sodium alginate having different molecular weights (high molecular weight (type A), medium molecular weight (type B) and low molecular weight (type C)) is measured at 293–303 K temperature in various mixtures of water (good solvent), acetone (ACE, poor solvent) and water-ethoxy ethanol (EE, poor solvent). The observed result particularly the Huggins constant (K _H) values shows a significant variation of cosolvency as a function of solvent composition (Φ_ACE/Φ_EE) and the temperature. Unperturbed dimensions (K _θ) under non-theta condition have been calculated using various equations in different water-acetone and water-ethoxy ethanol mixtures. The value of K _θ obtained from three different methods of measurements viz., Burchard-Stockmayer and Fixman (BSF), Berry and Inagaki-Suzuki-Kurata (ISK) agree well with each other except in a few compositions of solvents. The molecular extension factor (α _n) and actual end-to-end distance (α _n K _θ) have also been computed herein. Further, the shear thinning nature of the sodium alginate solutions (representative illustration: type A) in water and water-acetone mixed systems has been investigated at increasing strain rate. Results show that the viscous modulus G″ predominates over the elastic modulus G′ and the systems behave as viscoelastic fluids under present conditions. Higher value of G′ in acetone-water mixed solvent system compared to that in pure water undoubtedly indicates enhancement of the elasticity in alginate system in the presence of acetone. Finally, zeta potential measurement demonstrates that the polymeric surface of sodium alginate (representative illustration: type A) is essentially negatively charged and the zeta potential of the polymer is more responsive to the composition of ethoxy ethanol than that of acetone in the aqueous-organic mixed solvents.     

Recycle reactor models for complex electrochemical/chemical reaction systems

The performance of complex electrochemical reaction sequences in recycle plug flow reactors is mathematically modelled. The reactions include successive electron transfers (EE reactions), chemical reaction interposed between successive electron transfers (ECE reactions), simultaneous electron transfers and simultaneous electron transfer and chemical reaction. Both potentiostatic and galvanostatic operations are considered and the effects of important parameters such as mass transport coefficient, recycle ratio and chemical reaction rate in the recycle loop are highlighted. This is done by considering two important electro-organic synthesis reactions, the production ofp-aminophenol and the reduction of oxalic acid to glyoxylic acid.Nomenclature a activity factor - C _ji concentration of species j at reactor inlet - C _j bulk concentration of species j - C _j ^s surface concentration of species j - C _j ^e concentration of component j returned to reactor inlet stream - C _j concentration from reactor outlet - C _je equilibrium concentration - E electrode potential - F Faraday number - i _n partial current density of stepn - i _T total current density - k deactivation rate constant - k _f n forward electrochemical rate constant of stepn - k _b n backward electrochemical rate constant of stepn - k _f forward chemical reaction rate constant - k _r reverse chemical reaction rate constant - k _Lj mass transfer coefficient for species j - k _a forward adsorption rate constant - k _d reverse adsorption rate constant - L reactor length - r recycle ratio - t reaction time - u velocity - Q flow rate - x reactor dimension - _n constant describing potential dependency of reverse reaction rate constant - _n constant describing potential dependency of forward reaction rate constant - _j surface concentration of adsorbed species j - electrode area per unit length - residence time of fluid in recycle loop     

Facile three-step strategy to design CdS@Bi2Se3 core-shell nanostructure: An efficient electrode for supercapacitor application

In this study, we utilized a successive ionic layer adsorption and reaction (SILAR) route to attach bismuth selenide (Bi₂Se₃) nanoparticles on one dimensional (1D) cadmium sulfide nanowires (CdS NWs) at ambient temperature (27 °C) to design CdS@Bi₂Se₃ core-shell nanostructure towards active electrode for supercapacitor application. To verify and explore the retrieved surface configuration, structural, elemental, compositional, and surface morphological investigations were performed. The designed CdS@Bi₂Se₃ core-shell nanostructure not only offers the tremendous number of active areas, but also a continuous and quick one directional electron transport channels, demonstrating noticeable electrochemical performance with specific capacitance of 198 F g⁻¹ (aerial capacitance 59.5 mF/cm²) with 80% cyclic retention @ 2000 cycles. Superior electrochemical activity was enhanced through the mutualistic involvement of Na⁺ ion insertion/extraction via non-stoichiometric bismuth selenide, which was well supported through electrochemical impedance (EIS) studies.     

Electrochemical ozone production: influence of the supporting electrolyte on kinetics and current efficiency

The nature of the electrolyte strongly influences the electrode kinetics of the oxygen evolution reaction (OER) and electrochemical ozone production (EOP) mainly by affecting the degree of coverage by the intermediates of both processes. The anomalous behaviour of the Tafel coefficient, b, as a function of temperature was attributed to surface adsorption of the electrolyte species, and the competition between them, as well as gas bubble adherence. Comparison of the current efficiencies of the EOP, Φ_EOP, determined for different temperatures and supporting electrolyte compositions, showed the presence of fluorinated anions increases Φ_EOP. The influence of the anion nature on Φ_EOP, when analysed in the light of the proposed electrode mechanism, reveals introduction into the electrolyte of anions having a high electronegativity changes the double layer structure resulting in an increase of surface concentration of the active centres leading to EOP. The inhibition of the OER in the high overpotential domain during EOP provoked by fluoro-anion adsorption is supported by the activation energy data. In situ surface characterisation before and after EOP investigation revealed that even under drastic conditions (high current density, low interfacial pH) β-PbO₂ can be considered an inert electrode material.     

Aspect stereochimique de l'electroreduction de cyclenes actives. II. Reduction sur cathode de mercure des dicarboxy - 1,2 cyclopentene et cyclohexene et de leurs diesters methyliques: mecanisme et stereochimie

The mechanism of the 2e electrochemical reduction of 1,2-dicarboxycyclopenten I and cyclohexen II has been established from a polarographic study.—In stronly acidic media, the first electronic transfer occurs at the cationic species H₃X⁺, resulting either from a monopreprotonization at the H₂X diacid (A₁ wave) or a dipreprotonization at the HX^? anion (A₂ wave).—In less acidic media, in a sharp pH interval, a wave (B), corresponding to the reduction of H₂X, resulting from a preprotonization at HX^? is observed.—In the case of the compound I, one observes for 5 < pH < 7, a wave (C) due to the reduction of HX^?.The polarograms of the methylated esters I′ and II′ show a single 2e wave; E_{$\text{1}\text{2}$} is pH independent.Analysis of the mixtures of 1,2-dicarboxycyclans obtained after preparative electrolysis, seems to indicate that the stereochemical course of the reduction depends essentially on the nature of the diffusing species (sudden change of the cis-trans isomers ratio occurs according to an A₁ or A₂ way of reduction). In the case of the diesters, the main product obtained after the electrolysis is always the cis dihydrogenated compound. An interpretation is suggested.     

Chemical modification of diamond surface with X–(C6H4)–COOH (X = F,Cl, Br,I) using benzoyl peroxide

The chemical reactivity of a hydrogenated diamond surface with X–(C₆H₄)–COOH (X = F, Cl, Br, I) when using benzoyl peroxide was investigated in this study. After the reaction processes the shapes of the IR spectra changed. It was confirmed from the XPS measurements that halogen atoms existed on the samples after the reaction process. The position of the IR peak at ca. 700 cm^? 1 depended on the kind of halogen in X–(C₆H₄)–COOH. Moreover, the peak position depended on the kind of constitutional isomer, that is, ortho-, meta-, or para-. It was confirmed from the experimental results of this study that halogen-containing organic functional groups can be introduced onto a diamond surface.     

Micellar and Interfacial Behavior of Cationic Benzalkonium Chloride and Nonionic Polyoxyethylene Alkyl Ether Based Mixed Surfactant Systems

Micellar and interfacial properties of mixed surfactant systems comprising benzalkonium chloride, a cationic surfactant and nonionic polyoxyethylene alkyl ether surfactants (POE: C₁₀E₇, C₁₀E₈, C₁₀E₉, C₁₀E₁₀) have been investigated by surface tension, fluorescence and dynamic light scattering techniques. Critical micelle concentration (CMC) for different mixing mole fractions has been investigated by surface tension and fluorescence measurements. Ideal CMC, mixed micellar composition (X ₁ ^m , X ₁ ^σ ), interaction parameters for mixed micelles (β ^m) and adsorption monolayer (β ^σ ), surface excess concentration (Г_max), minimum area per molecule (A _min) and related thermodynamic properties have also been determined. Lowering of the CMC and negative interaction parameter values indicate synergism in the mixed micelle and monolayer formed, whereas, thermodynamic parameters evaluated for the proposed mixed systems indicate stability of the resulting micelles and monolayer. Micellar aggregation number (N _agg) and hydrodynamic diameter (D _h) computed from fluorescence and dynamic light scattering measurements respectively illustrate micellar growth in the mixed state. Results obtained for the proposed mixed systems can be helpful in designing smart materials for industrial surfactant based formulations.     

Study of electrochemical performances of perovskite-type oxide LaGaO3 for application as a novel anode material for Ni-MH secondary batteries

In this paper, the perovskite-type oxide LaGaO₃, which is proposed as a novel anode material for Ni-MH secondary batteries, was synthesized by the sol–gel method. The electrochemical performance of the oxide was analyzed at temperature 328 K using chronopotentiometry, potentiodynamic polarization and chronoamperomertry techniques. During the first three of charge/discharge cycles, the discharge capacity of the oxide LaGaO₃ reaches its maximum value at 220 mAh g⁻¹ and thereafter decreases. The degradation of cycling stability of the oxide can be explained by the corrosion behavior of the electrode as a result of the decrease in the electroactive surface area of the electrochemical reaction with cycling. The kinetic results showed that both the exchange current density I₀ and the hydrogen diffusion coefficient D_H of the anode decrease with increasing state of charge, after activation, which can be ascribed to the change in the electrode surface when transforming from α to β phase. The whole electrochemical reactions of the electrode are governed by two important processes: charge-transfer reaction on the electrode surface and hydrogen atom diffusion within the bulk of the electrode.     

Characterization of Pt/SiO2 Model Catalysts at UHV and Near Atmospheric Pressures

Pt/SiO₂ model catalyst samples, prepared under UHV conditions in a contiguous high pressure reactor cell surface analysis chamber, have been characterized via CO oxidation reaction kinetics under elevated pressure conditions (approaching 1 atm). Reaction kinetics are studied as a function of Pt coverage (θ _Pt = 1–10 mL), along with measurements on a Pt(110) single crystal for direct comparison. CO desorption measurements and STM measurements on Pt/SiO₂ films at T = 300 K have been obtained at various θ _Pt. Kinetic results show agreement between observations on single crystal and catalyst samples, and general agreement and correlation is obtained for site calculations across the various methods. Results demonstrate the utility of well characterized model catalyst samples in obtaining qualitative and quantitative reactivity data at elevated pressures.