Study of the mechanism of pore diffusion in batch adsorption systems

In this study the film-pore diffusion model was applied to describe system transport kinetics of three basic dye-carbon systems, namely Basic Blue 69, Basic Red 22 and Basic Yellow 21. The mass transfer parameters evaluated were the external mass transfer coefficient k_f (cm s^?1) and the effective diffusivity D_eff (cm² s^?1). A single k_f value was sufficient to describe each dye system: these were 0.15 × 10^?2, 0.20 × 10^?2 and 0.50 × 10^?2 cm s^?1 for BB69, BR22 and BY21, respectively. The effective diffusivity was found to have values much larger than those of pore diffusivities calculated from liquid diffusivities and its value decreased with increasing initial dye concentration. This was attributed to the effect of surface diffusion, hence pore diffusivity was exchanged by the effective pore diffusivity in the model. The present model was solved by the exponential curve fit technique; results were expressed in the form of experimental and theoretical Sherwood Numbers compared in terms of the residual.     

Adsorption of dyes onto bagasse pith using a solid diffusion model

The adsorption of four dyes (Basic Blue 69, Basic Red 22, Acid Blue 25, and Acid Red 114) onto bagasse pith has been studied using an agitated batch adsorber. The variables studied were initial dye concentration and pith mass. A mathematical model has been developed based on external mass transfer and solid-phase diffusion. The model has been used to generate theoretical concentration–time decay curves, and these results were adjusted to experimental data by a best fit approach. The external mass transfer coefficients are 2.0 × 10^?3, 1.5 × 10^?3, 8.0 × 10^?4, and 5.0 × 10^?4 cm s^?1 and the solid diffusivities are 1.1 × 10^?8, 1.0 × 10^?8, 6.0 × 10^?9, and 3.0 × 10^?9 cm² s^?1 for Basic Blue 69, Basic Red 22, Acid Blue 25, and Acid Red 114.     

Analytical solution using a pore diffusion model for a pseudoirreversible isotherm for the adsorption of basic dye on silica

An analytical solution for a two resistance mass transfer model explaining the adsorption of Astrazone Blue dye (Basic Blue 69) onto Sorbsil silica has been developed. The model includes a film mass transfer coefficient, k_f1 = 80 × 10⁻⁶cm·s−1, and an internal effective diffusivity, D_eff = 18×10⁻⁹cm²·s⁻¹ which controls the internal mass transport processes based on a pore diffusion mechanism.     

Reactions of Photoexcited Triplet States of Zinc Porphyrin with Transient Radicals in Aqueous Solutions

The technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPS^T in aqueous solutions. The radicals H and OH add to both states with k ∼ 1 × 10¹⁰ M⁻¹ s⁻¹. The CH₂C(CH₃)₂OH radical from t-BuOH is relatively inert toward ZnTPPS but reacts rapidly (k = 1.8 × 10⁹ M⁻¹ s⁻¹) with ZnTPPS^T to form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH₃)₂COH radical reduces both ZnTPPS (k = 1 × 10⁸ M⁻¹ s⁻¹) and ZnTPPS^T (k = 3 × 10⁹ M⁻¹ s⁻¹) to the anion radical (ZnTPPS)⁻. The radical Br⁻₂ oxidizes both states to the cation radical (ZnTPPS)⁺ with k = 8 × 10⁸ M⁻¹ s⁻¹ for the ground state and 5 × 10⁹ M⁻¹ s⁻¹ for the triplet. The transient cation Cd⁺ reduces both states with a diffusion-controlled rate (k = 1 × 10¹⁰ M⁻¹ s⁻¹) to produce the anion radical. The above mechanisms of radical addition and electron transfer are also supported by the product spectra.     

Influence of different reactor types on Nannochloropsis oculata microalgae culture for lipids and fatty acid production

Greenhouse gases emitted into the atmosphere by burning of fossil fuels cause global warming. One option is obtaining biodiesel. Nannochloropsis oculata was cultured under different light intensities and reactors at 25°C for 21 days with f/2 medium to assess their effects on cell density, lipid, and fatty acids (FAs). N. oculata improved cell density on fed-batch glass tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹, yielding 3.5 × 10⁸ cells ml⁻¹, followed by fed-batch Erlenmeyer flask (1 L) at 650 μmol E m⁻² s⁻¹ with 1.7 × 10⁸ cells ml⁻¹. The highest total lipid contents (% g lipid × g dry biomass⁻¹) were 44.4 ± 0.8% for the reactor (1 L) at 650 μmol E m⁻² s⁻¹ and 35.2 ± 0.2% for the tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹, until twice as high compared with the control culture (Erlenmeyer flask 1 L, 80 μmol E m⁻² s⁻¹) with 21.2 ± 1%. Comparing the total lipid content at 200 μmol E m⁻² s⁻¹, tubular reactor (7 L) and reactor 1 L achieved 35.2 ± 0.2% and 28.3 ± 1%, respectively, indicating the effect of shape reactor. The FAs were affected by high light intensity, decreasing SFAs to 2.5%, and increased monounsaturated fatty acids + polyunsaturated fatty acids to 2.5%. PUFAs (20:5n-3) and (20:4n-3) were affected by reactor shape, decreasing by half in the tubular reactor. In the best culture, fed-batch tubular reactor (7 L) at 200 μmol E m⁻² s⁻¹ contains major FAs (16:0; 38.06 ± 0.16%), (16:1n-7; 30.74 ± 0.58%), and (18:1n-9; 17.15 ± 0.91%).     

Radiolytic Studies of the Cumyloxyl Radical in Aqueous Solutions

Formation and reactions of the cumyloxyl radical in aqueous solutions were studied by steady-state and pulse radiolytic techniques. Cumene hydroperoxide reacts with e⁻_aq (k = 4.4 × 10⁹ M⁻¹s⁻¹) to yield the cumyloxyl radical. The spectrum recorded after the pulse indicates formation of a species absorbing at 250 nm. This product was identified as acetophenone, which is formed by the fragmentation of the cumyloxyl radical. By comparison of the pseudo-first-order rates of e⁻_aq decay at 600 nm with the rate of production of acetophenone at 245 nm at increasing concentrations of cumene hydroperoxide, it was possible to derive a rate constant of 1.0 × 10⁷ s⁻¹ for the cleavage of cumyloxyl to acetophenone and methyl radical. This value is higher than that measured previously in organic solvents (1 × 10⁶ s⁻¹), as expected. HPLC analysis of the radiation products acetophenone and cumyl alcohol permitted determination of rate constants for hydrogen abstraction by the cumyloxyl radical, in competition with the fragmentation. The rate constants for H abstraction from i-PrOH, EtOH, and MeOH by CmO were found to be 9.9 × 10⁶, 3.8 × 10⁶, and 8.5 × 10⁵ M⁻¹ s⁻¹, respectively.     

A kinetic study of the Durham precursor route to polyacetylene

The processes involved in the thermal transformation of ‘Durham polyacetylene precursor’, poly[[5,6-bis(trifluoromethyl)-bicyclo[2,2,2]octa-5,7-diene-2,3-diyl]-1,2-ethenediyl], to all-trans polyacetylene have been studied. Above about 100°C the reactions are virtually concurrent, but at 50°C one can distinguish a first-order elimination (k = 7.6 × 10⁻⁴ s⁻¹), effusion of the elimination product (D = 4 × 10⁻⁹ cm² s⁻¹), and a first order cis-trans isomerization (k = 1.5 × 10⁻⁵ s⁻¹). The isomerization is very sensitive to traces of oxygen below 80°C, but at higher temperatures this is less pronounced and the reaction becomes approximately second order. Isomerization is generally more facile in the less ordered Durham polymer than in polymers from the Shirakawa route.     

Derivative cathodic stripping voltammetry in the simultaneous determination of three textile dyes in aqueous solutions

Reactive dyes, such as Procion Yellow, Procion Red, and Procion Blue, were simultaneously determined in aqueous ternary solutions using derivative cathodic stripping voltammetry following adsorption on a hanging mercury drop electrode. An electrochemical cell containing Britton–Robinson buffer solution at pH 8 was used as the supporting electrolyte. The following experimental conditions were established: ?0.100 V deposition potential, 80 s deposition time, 50 mV pulse amplitude, 50 mV s^?1 scan rate, and 0.40 mm² maximum mercury drop size. A linear response was observed over the 0.630 × 10^?3 to 1.050, 1.441 × 10^?3 to 1.572, and 0.198 to 1.570 mg l^?1 ranges for Procion Yellow, Procion Red, and Procion Blue respectively. The detection limits were 0.210 × 10^?3, 0.480 × 10^?3, and 0.066 mg l^?1 respectively, with a relative standard deviation (n = 3) of 1.22%. The accuracy of the method was evaluated by derivative spectrophotometry, certifying the results as a function of proximity. All results were similar, indicating that derivative cathodic stripping voltammetry may be efficiently applied for the simultaneous determination of textile dyes in aqueous ternary solutions.     

Extraction kinetics of pre-pelletized Jalapeño peppers with supercritical CO2

The aim of this work was to assess and model supercritical carbon dioxide (ScCO₂) extraction kinetics of pre-pelletized Jalapeño peppers (Capsicum annuum L.). Pepper flakes were conditioned to low moisture, ground finely and pelletized at high pressure, and pellets were subsequently ground and size classified. The effects of average sample particle size (D_p=0.28–3.19 mm) and superficial solvent velocity (U_s=0.14–2.62 mm s⁻¹) were evaluated at 40 °C and 120 or 320 bar. Extraction rate increased as a result of a decrease in D_p. It also increased as a result of an increase in U_s at 120 bar, but the effect was almost negligible at 320 bar. Integral extraction yields of capsicum oleoresin and capsaicinoids were ≈0.102 g g⁻¹ and ≈240 mg kg⁻¹, respectively, independent of extraction conditions. External mass transfer coefficients (k_f) increased with U_s, but this effect was less pronounced than commonly reported in the literature. Values of k_f increased as D_p or process pressure decreased, due respectively to increments in specific area and improvements in transport properties. Internal mass transfer coefficients, on the other hand, were 5.3×10⁻⁸ m s⁻¹ at 40 °C and 120 bar, and 34.7×10⁻⁸ m s⁻¹ at 40 °C and 320 bar. Solutes were effectively liberated from the original matrix with our multistage pretreatment, so that the fraction of free solute did not depend on D_p (α=0.46). Pseudosolubilities for capsicum oleoresin in ScCO₂ (≈2100 mg l⁻¹ at 40 °C and 120 bar; ≈13,700 mg l⁻¹ solute/CO₂ at 40 °C and 320 bar) were of the same order of magnitude as corresponding true solubilities of capsaicin (5600 and 11,800 mg l⁻¹, respectively). Estimated true solubilities of chlorophyll-a in ScCO₂ (2 mg l⁻¹ at 40 °C and 120 bar; 18 mg l⁻¹ at 40 °C and 320 bar), on the other hand, were orders of magnitude smaller, which justifies a much slower extraction rate for green pigments than pungent compounds. Thus, oleoresin obtained after 4 h at 40 °C and 120 bar had a very attractive light yellow tinge.     

Gasification of carbon by CO2: A transient kinetics experiment

A transient kinetic technique was used to measure the intrinsic rate constant k₂ of the reaction C(O) → CO + C_f, where C_f is an available site and C(O) is an occupied site. It was found that k₂ = 10^{11.6 ± 2.3} exp[ −(225 000 ± 39000)/RT]min⁻¹. Two systems were studied, one using an uncatalysed carbon, the other a Ca-catalysed carbon. The gasification rates for these two systems differed by a factor of 100, yet they yielded the same k₂. This strongly supports the contention that Ca catalyses the system by increasing the number of active sites.     

A Shock Tube Study of the Reactions of H Atoms with COS,CS2, and H2S

Reactions of H atoms with COS, CS₂, and H₂S were studied behind reflected shock waves at temperatures between 1170 K and 1830 K and pressures around 1.0 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved measurements of H atoms at L_α. The thermal decomposition of a few ppm ethyl iodide (C₂H₅I) was used as a H-atom source. In the presence of a large excess of the molecular reactant COS, CS₂, or H₂S, a consumption of H was observed which follows a pseudo first-order rate law. Rate coefficients for the reactions: were determined to be: k₁ = 2.4 × 10¹⁴exp(–3415 K/T) cm³mol⁻¹s⁻¹ k₂ = 1.4 × 10¹⁵exp(–9250 K/T) cm³mol⁻¹s⁻¹ k₃ = 2.5 × 10¹⁴exp(–2890 K/T) cm³mol⁻¹s⁻¹     

The Oxidation of Coated SOFC Interconnects in Fuel Side Environments

This study focuses on examining the effect of PVD coatings on the oxidation performance of interconnects in fuel (anode) side environments. A Fe‐22Cr ferritic steel was coated with (i) Ce 10 nm (ii) La 10 nm and (iii) Co 600 nm. The samples were exposed at 850 °C in Ar‐5% H₂‐3% H₂O in a tubular furnace over 500 h. Additionally, the effect of a pre‐oxidation step was investigated by exposure in air prior to the simulated fuel gas environment. Chemical analysis on the samples was subsequently performed with SEM/EDX and XRD. It was established that the Ce and La coatings brought about a factor 2–3 reduction (k_p values of 2.16 × 10⁻¹⁴ ± 3.6 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹ for the La 10 nm coated steel compared to 7.72 × 10⁻¹⁴ ± 5.86 × 10⁻¹⁵ g² cm⁻⁴ s⁻¹ for the uncoated steel) in the oxidation rate while the Co coating disintegrated into metallic islands in and on the thermally grown oxide after exposure. Additionally, the La coating resulted in the formation of a continuous perovskite layer by reaction with the thermally grown oxide.     

Untersuchungen zur Spin-Trapping-Kinetik in Systemen von Radikalen unterschiedlicher Reaktivität. Die Photolyse von α-Phenylbenzoin in Gegenwart von Benzyliden-tert.-butylamin-N-oxid

Investigations on Spin-Trapping Kineties in Radical Systems with Different Reactivity. Photolyses of α-Phenylbenzoine in the Presence of Benzylideneter. -butylamine N-oxide As a model system to study the spin-trapping kinetics of systems forming two radicals of different reactivity α-phenylbenzoine (PhB) was chosen. The photolysis of PhB forms benzoyl (B·) and diphenylketylradikals (K·), respectively, which can be trapped by benzylidene-tert-butyl-amine N-oxide (PBN), as a spin trap. The rate constants of radical addition to PBN and their reactions with the spin adducts were determined by means of flash photolysis and kinetic calculations of the PBN concentration dependence. For B· and K· addtion rate constants to PBN of k₁ = 8,1 × 10⁵ M⁻¹s⁻¹, and k₂ = 5,8 · 10⁴ M⁻¹s⁻¹, respectively, were found. The rate constants for the reactions of B· and K· with the spin adducts are in the order of 10⁹…10¹⁰ M⁻¹s⁻¹.     

Electrochemical analysis of trace amounts of water in propylene carbonate electrolytes

Cyclic voltammetry and limiting currents to an rde have been used for the determination of the water in the 0.3–20 ppm range, in PC electrolytes. Carefully dried solutions yielded voltammetric peaks proportional to the amount of water added. In KPF₆ electrolytes, the cathodic current corresponding to the reduction of water was at 0.48 V, while in KAlCl₄ solutions the reduction occurred already starting at 2.8 V, both relative to a K/K⁺ reference. At these potentials, the current to an rde showed Levich type dependence on rpm and was proportional to the concentration of water in the range 0.5–20 ppm. The calculated diffusion coefficients of water are higher than expected: 25°C, D_H2O = 8.5±2 × 10⁻⁶ cm² s⁻¹ in 0.5 M KPF₆, while in 0.25 M KAlCl₄D_H2O, 10±2 × 10⁻⁶ cm² s⁻¹.     

Kinetic and thermodynamic studies on oxidative desulphurisation of organic sulphur from Indian coal at 50–150°C

This paper reports a relatively simple low-temperature non-isothermal oxidative desulphurisation of coal organic sulphur by weakening the CS bond using HgCl₂ solution to an inorganic sulphur-free high-sulphur Indian coal. When oxidised from 50°C to 150°C in air under normal atmospheric pressure, there is continuous decrease of organic sulphur content in the samples of the feed and Hg-treated coals. Desulphurisation is more in the Hg-treated coal (4.97–14.53 wt.%) than in the feed coal (3.72–10.93 wt.%). Kinetic study reveals that the oxidative desulphurisation process follows pseudo-first order kinetics and the rate constants have been found to be in the range (3.09–5.06)×10⁻⁵ s⁻¹ for feed coal and (4.19–6.80)×10⁻⁵ s⁻¹ for Hg-treated coal. The activation energies for the sulphur loss reaction in the oxidative desulphurisation process by using the pseudo-first order kinetic (feed coal: 2.21×10² J mol⁻¹; Hg-treated coal: 1.53×10² J mol⁻¹) have been found to be almost similar to those calculated by applying the Coats and Redfern's equation (feed coal: 2.19×10² J mol⁻¹; Hg-treated coal: 1.53×10² J mol⁻¹). However, the value is higher (feed coal: 3.50×10² J mol⁻¹; Hg-treated coal: 2.70×10² J mol⁻¹) when Horowitz and Metzger's equation is applied. The frequency factors computed by the pseudo-first order kinetics are very low and have been found to be 2.66×10⁻⁵ s⁻¹ for feed coal and 3.96×10⁻⁵ s⁻¹ for Hg-treated coal, suggesting very low rate of successful collisions for the formation of the activated complex. Evaluation of thermodynamic parameters viz., ΔH, ΔU, ΔS and ΔG, reveals that this oxidative desulphurisation process is non-spontaneous in nature and the degree of non-spontaneity of such a process in the feed coal is more relative to that of the Hg-treated coal.     

A remarkable promoting effect of water addition on selective hydrogenation of p-chloronitrobenzene in ethanol

Selective hydrogenation of p-chloronitrobenzene to p-chloraniline over ruthenium catalyst was found to be promoted remarkably (Selectivity: from 80.4% to 98.6%; TON: from 0.89 × 10⁻² s⁻¹ to 3.20 × 10⁻² s⁻¹) by simply adding some water into the solvent of ethanol. The optimized volume percent of water in ethanol was 30%. The promoting effect of water was also found over various supported metal catalysts, such as Fe/SiO₂, Co/SiO₂, Ni/SiO₂, Cu/SiO₂, and Ag/SiO₂.     

Reaction Kinetics of Hydroxyl Radicals with Model Compounds of Fuel Cell Polymer Membranes

The chemical stability of perfluorinated and non‐perfluorinated low temperature fuel cell model compounds (MCs) against attack by hydroxyl radicals, HO^•, is compared using a competition kinetics approach in aqueous solutions at ambient temperature. HO^• radicals were generated in situ by UV photolysis of hydrogen peroxide in the electron spin resonance (ESR) resonator. Acetic acid (AA), trifluoroacetic acid (TFAA), methanesulfonic acid (MSA), trifluorosulfonic acid (TFSA), and perfluoro(2‐ethoxyethane)sulfonic acid (PFEESA) were chosen as MCs, while the rate constants of 5,5‐dimethyl‐1‐pyrroline‐N‐oxide (DMPO) and methanol (CH₃OH) served as reference for the determination of relative rate constants by means of steady state ESR signal amplitudes. In decreasing order the rate constants are: k_MSA = (4.8 ± 0.2) × 10⁷ M^–1 s^–1, k_AA = (4.2 ± 0.3) × 10⁷ M^–1 s^–1, k_PFEESA = (3.7 ± 0.1) × 10⁶ M^–1 s^–1, k_TFAA = (7.9 ± 0.2) × 10⁵ M^–1 s^–1, and k_TFSA < 1.0 × 10⁵ M^–1 s^–1. Applying these results to perfluorinated fuel cell membranes like Nafion®, the main points of attack by HO^• are concluded to be the ether groups of the side chains, followed by the remaining carboxyl groups from the manufacturing process of the polymers.     

Adsorption of dyestuffs onto chitin. External mass transfer processes

The effect of several variables on the adsorption rate of four dyestuffs onto chitin was studied. A model is proposed enabling the film mass transfer coefficients to be determined. The coefficients were independent of initial dye concentration, chitin mass, chitin particle size, and temperature; a slight dependence with agitation was obtained. The film mass transfer coefficients at 400 rpm were 2.8×10^?3, 2.9×10^?3, 3.9×10^?3, and 0.9×10^?3 cm/s for Acid Blue 25, Acid Blue 158, Mordant Yellow 5, and Direct Red 85, respectively.     

Effect of Cu on the ablation properties of Cf/ZrC composites fabricated by infiltrating Cf/C preforms with Zr-Cu alloys

C_f/ZrC composites were fabricated by reactive melt infiltration at 1200 °C, Low melting Zr₇Cu₁₀, ZrCu and Zr₂Cu alloys were used as infiltrators and the effect of Cu on ablation properties of the composites was investigated. The results show that the C_f/ZrC composites exhibit excellent anti-ablative properties affected apparently by the Cu contents. With the increase of Cu in infiltrators, the linear recession rates decrease from 0.0019±0.0006 to −0.0006±0.0002 mm s⁻¹, whereas the mass loss rates increase from 0.0006±0.0003 to 0.0047±0.0009 g s⁻¹. The formation of a dense ZrO₂ protective layer and the evaporation of residual Cu are in favor of their ablation resistance.     

Temperature effect on diffusion of carbon dioxide through upper layers of Yucca Mountain

The effective diffusivities of carbon dioxide through the Tiva Canyon tuff and the lower lithophysal zone of the Topopah Spring tuff (outcrop samples of the layer above the proposed nuclear repository site layer) were determined using a steady-state method (counter diffusion). The diffusivity of carbon dioxide through the Tiva Canyon and lithopysal zone tuffs increased with temperature. The following correlation was obtained to estimate the effective diffusivity of carbon dioxide through the Tiva Canyon tuff in cm² s⁻¹ as a function of temperature (K). D_e = 1.22 × 10⁻² − 3.77 × 10⁻⁵T + 9.95 × 10⁻⁸T²The effective diffusivity of carbon dioxide through the lower lithophysal zone of the Topopah Spring tuff (layer right above the proposed repository site) also increased with temperature. For this layer, the following correlation was obtained to estimate the effective diffusivity of carbon dioxide in cm² s⁻¹ as a function of temperature (K). D_e = − 1.11 × 10⁻³ + 1.25 × 10⁻⁵T + 1.83 × 10⁻⁹T²