Uncatalyzed selective oxidation of liquid cyclohexane with air in a microcapillary reactor

The uncatalyzed selective oxidation of cyclohexane with air was performed at high-p,T-conditions in a microcapillary reactor. Operation pressures were between 2.0 and 8.0 MPa and operating temperatures between 453 and 533 K. The measured space-time-yield showed only a slight dependence on the pressure, but a strong dependence on temperature. At 533 K, a space-time-yield of about 6.000 kg/(m³ h) was reached, which corresponds to a size of 2 m×2 m×2 m (8 m³) of the microstructured reactor assuming a capacity of 100.000 t/a compared to 500 m³ total reactor volume realized with a cascade of bubble columns of each about 100 m³. Unfortunately, selectivity drops at this temperature below 80% which is significantly lower than the selectivity in the conventional process. Passivating the capillary walls with silicon allowed an increase in selectivity. By fitting a simple mass transfer/reaction model for molecular oxygen, the mass transfer coefficient could be determined for T=453 K and a 0.75 mm capillary as k_L=3.04×10^?3 m/s. With the help of the Hatta number, mass transfer limitations can be excluded for the microcapillary reactor, whereas the bubble column reactor is weakly limited by the gas/liquid mass transfer of the molecular oxygen. Thus, process intensification by enhancing mass transfer using a microstructured reactor for cyclohexane oxidation with air is quite low.     

Gas side controlled mass transfer in a new packing with stamped horizontal lamellae operating at extremely low liquid loads

The gas side controlled mass transfer coefficient of an easy to make packing, with stamped horizontal lamellae, designed for operating at extremely low liquid superficial velocity, between 0.04 and 1 m³/m² h is investigated. The absorption of SO₂ in sodium hydroxide water solution is used as a model process. Based on the obtained experimental data, an equation for calculating the gas side controlled mass transfer coefficient, with deviation of ±8% is presented.The comparison between the new packing and different highly effective packings shows that the new one has lower pressure drop at the same specific area and mass transfer coefficient, respectively higher mass transfer coefficient at the same pressure drop and specific surface.Of all compared highly effective packings, only the crossed strips packing, quite difficult to produce, has close, yet higher, pressure drop at similar specific surface area and volumetric mass transfer coefficient.     

Novel three-dimensional microfluidic device for process intensification

Microchannel heat exchangers and chemical reactors have extensive applications in process industries, especially in electronics cooling, air conditioning, and chemical industries. Microchannel devices provide enhanced heat and mass transfer characteristics by controlled flow conditions and high surface-to-volume ratios. The different designs of microchannels are based on planar structures from various fabrication technologies. In the present study a novel three-dimensional micro-structured device, the micro coiled flow inverter (MCFI) with 0.38–0.8 mm internal diameter, has been numerically investigated as a micro heat exchanger. In comparison micro helical coil (MHC) and straight tube of same heat transfer area (d_t = 0.5 mm, A = 3.9 × 10⁻⁴ m²) has been studied, too. The Reynolds and Prandtl numbers are varied from 25 to 1200 and 0.74 to150, respectively. The MCFI offers a four-fold heat transfer enhancement as compared to straight tube of same heat transfer area at N_Re = 1200 and N_Pr = 7. Furthermore, the heat transfer coefficient in MCFI augments by 38.5% as compared to MHC, with slight increase (5–16%) in friction factor. New design correlations are developed for Nusselt number and friction factor in MCFI. The MCFI device offers 1.15–1.7-folds higher thermal merit as compared to micro straight tube.     

Mass transfer modeling of equilibrium and dynamic periods during osmotic dehydration of radish in NaCl solutions

Equilibrium and dynamic mass transfer properties of water and solute were investigated during osmotic dehydration (OD) of radish slices in sodium chloride (NaCl) solutions. OD experiments were performed in 0.05, 0.15 and 0.25 g/g solutions at different temperatures (25, 40, 55 and 70 °C) using a brine-to-vegetable mass ratio of 15:1. An analytical solution for unsteady-state mass transfer based on Fick's second law of diffusion was used to mathematically describe water loss and solute gain curves and for the simultaneous estimation of diffusion coefficients and final dehydration–impregnation levels in product. Under such experimental conditions, effective water diffusivity was in the range of 1.85–2.74 × 10^?9 m²/s, whereas solute diffusivity values were between 0.74 × 10^?9 and 2.88 × 10^?9 m²/s. Corresponding dehydration and impregnation levels of radish at equilibrium were estimated between 0.25 and 0.81 g water/g fresh product and 0.01–0.11 g solute/g fresh product, respectively. As demonstrated, current results may be applied to determine the set of conditions (process time, brine concentration and process temperature) yielding an osmodehydrated radish product within given specifications.     

Ionic liquid effects on mass transfer efficiency in extractive distillation of water–ethanol mixtures

The relatively high viscosities of ionic liquids could reduce the mass transfer efficiency of the extractive distillation process. The rate-based model was adopted to analyze this phenomenon since it predicted the performance of an extractive distillation pilot plant using ionic liquids as solvent. For the water–ethanol separation, three ionic liquids: 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium dicyanamide and the organic solvent ethylene glycol were used for the analysis. Simulations were conducted for sieve trays and Mellapak^® 250Y. The results indicate that relatively high viscosities affect the mass transfer efficiency. However, the improvements in relative volatilities obtained from the ionic liquids help to overcome this effect. However, with high solvent viscosities (>65 mPa s at T = 353.15 K) it was not possible to overcome the reductions. Additionally, at higher distillate rates high relative volatilities yielded negative effects on mass transfer efficiency because of a decrease in vapor velocity.     

Process intensification in small scale extraction columns for counter-current operations

This article describes a study to investigate the intensified liquid–liquid extraction by a novel, millistructured, stirred-pulsed column. The column has an inner diameter of 15 mm and is modularly designed with sections of 220 mm height consisting of 10 stirred cells. Experimental investigations were carried out in a column with five sections. The stirred cells enable high energy input, and therefore high specific surface and good extraction efficiencies. The backflow was minimized with narrow plates between the cells. Hence, the dispersed phase coalesces at the plates that separate the stirred cells. The coalescence area is destroyed by continuous pulsation of the fluid column, which transports the dispersed phase into the next stirred cell. The hydrodynamic and mass transfer inside the column was characterized with the EFCE – test system water (continuous)/acetone/n-butylacetate (dispersed). We achieved a dispersed phase hold up inside the active extraction part up to 50%, and a specific surface of over 3000 m²/m³. The extraction efficiency was measured to 17 and 25 stages per meter for the mass transfer direction (d → c) and (c → d), respectively. The comparison with other conventional pilot plant columns shows high extraction efficiency, but also a loss in total throughput.     

Study of kinetics in the biosorption of lead onto native and chemically treated olive stone

In this research, olive stone was used as precursor for the development of new biosorbents for lead ions. Chemical treatments were analyzed in terms of their effects on physical–chemical properties and kinetics of lead removal. A kinetic study of the biosorption of lead ions by olive stone was analyzed according to six different kinetic models (pseudo first, pseudo second, pseudo n-order, Elovich, solid diffusion and double exponential models). The biosorption kinetic data were successfully described with pseudo-nth order and double exponential models for all biosorbents. The double exponential model allowed estimating the values of external and internal mass transfer coefficients. The values of external mass transfer coefficient (k_e) ranged from 42.62 × 10⁻⁶ to 508.3 × 10⁻⁶ m min⁻¹ and the internal mass transfer coefficient (k_i) from 3.76 × 10⁻⁶ to 73.4 × 10⁻⁶ m min⁻¹. On the other hand, the analysis of experimental data showed that chemical treatments of the biomass led to increase biosorption capacity of the native biomass.     

Impactor designed to increase mass output rate of nanoparticles from a pneumatic nebulizer

A modular impactor was designed to remove large droplets from aerosols generated by a pneumatic nebulizer, the Six-Jet Atomizer from TSI Inc. (Shoreview, MN), with the aim of generating dry nanoparticles. Three interchangeable nozzle heads were designed to provide droplet cutoff diameters of 0.5, 1, and 2 μm at an air flow rate of 8.3×10^?4 m³ s^?1 (50 L min^?1), which corresponds to all six jets of the nebulizer operated at 25 °C and an air pressure of 241 kPa (35 psi). The collection and output characteristics of the 0.5 μm impactor were evaluated from dry particle size distributions produced by nebulizing an aqueous solution with a NaCl mass fraction of 1% both with and without the impactor present. The impactor characteristic cutoff curve was sharp (impactor geometric standard deviation, GSD_imp=1.15–1.19) with a 50% cutoff diameter d₅₀ that ranged from 0.48 μm at 3.0×10^?4 m³ s^?1 to 0.74 μm at 11.7×10^?4 m³ s^?1. The rate of dry NaCl particle generation ranged from 0.5 to 5 g s^?1 (0.04 to 0.4 g day^?1) with mass median diameters MMD_p=80–123 nm and geometric standard deviations GSD_p=1.6–1.8 (depending on flow rate). Anomalous negative impactor efficiencies were observed at flow rates >8.3×10^?4 m³ s^?1 for 100 to 400 nm droplets and at all flow rates for droplets smaller than 100 nm. This phenomenon will be investigated further as a way to increase the generation rate of nanoparticles. A step-by-step procedure is presented for the selection of an appropriate impactor design and operating flow rate for a desired maximum aerosol particle size.     

Biotribological performance of NCD coated Si3N4–bioglass composites

A nanocrystalline diamond (NCD) coated Si₃N₄–bioglass composite, with potential use for hip and knee joint implants, was tribologically tested in simulated physiological fluids. NCD was deposited using a hot-filament chemical vapour deposition (HFCVD) apparatus in an Ar–H₂–CH₄ gas mixture. Self-mated reciprocating experiments were performed using a pin-on-flat geometry in Hanks' balanced salt solution (HBSS) and dilute fetal bovine serum (FBS). A nominal contact pressure of 25 MPa was applied for up to 500,000 cycles. Very low friction coefficients of 0.01–0.02 were measured using HBSS, while for FBS lubricated tests the values are slightly higher (0.06–0.09), due to a protein attaching effect. AFM assessed wear rates by an approach using the bearing function for volume loss quantification, yielding wear rates of k ∼ 10^− 10 mm³ N^− 1 m^− 1 in HBSS and k ∼ 10^− 9–10^− 8 mm³ N^− 1 m^− 1 for FBS, characteristic of very mild wear regimes.     

Examining structure property relationships in coatings based on substituted linear aromatic polycyanurates

Three series of halogenated and non-halogenated polycyanurates are prepared in good yield and purity, and fully characterised. Many of the resulting polymers, formed at room temperature using phase transfer catalysis, can be cast into films with good resilience and high thermal stability (some examples suffer no mass loss when held isothermally at 190 °C and only display appreciable losses when held continuously at 300 °C). Char yields of 35–65% are achieved in nitrogen depending on backbone structure. Some problems were encountered with solubility, particularly with heavily halogenated dichlorotriazines, which limited molecular weights (M_n = 2000–4000 g mol^?1 depending on backbone structure) although when the phase volume ratio was altered to 0.25 higher molecular weights (M_n = 10,000–30,000 g mol^?1) were possible. Best solubility was achieved by using aromatic diols with at least two equivalent phenylene units per dichlorotriazine unit. DSC reveals polymerisation exotherms with maxima at 190–260 °C (ΔH_p = 35–57 kJ/mol) followed by embrittlement and shrinkage (when heated to 300 °C). These phenomena may be due to the formation of poorly formed crystallites (activation energies span 155–380 kJ/mol) combined with thermal isomerisation.     

Preparation of (0 2 0)-oriented BaTi2O5 thick films and their dielectric responses

Barium dititanate (BaTi₂O₅) thick films were prepared on a Pt-coated Si substrate by laser chemical vapor deposition, and ac electric responses of (0 2 0)-oriented BaTi₂O₅ films were investigated using several equivalent electric circuit models. BaTi₂O₅ films in a single phase were obtained at a Ti/Ba molar ratio (m_Ti/Ba) of 1.72–1.74 and deposition temperature (T_dep) of 908–1065 K as well as m_Ti/Ba = 1.95 and T_dep = 914–953 K. (0 2 0)-oriented BaTi₂O₅ films were obtained at m_Ti/Ba = 1.72–1.74 and T_dep = 989–1051 K. BaTi₂O₅ films had columnar grains, and the deposition rate reached 93 μm h^?1. The maximum relative permittivity of the (0 2 0)-oriented BaTi₂O₅ film prepared at T_dep = 989 K was 653 at 759 K. The model of an equivalent circuit involving a parallel combination of a resistor, a capacitor, and a constant phase element well fitted the frequency dependence of the interrelated ac electrical responses of the impedance, electric modulus, and admittance of (0 2 0)-oriented BaTi₂O₅ films.     

The phase stability and thermophysical properties of InFeO3(ZnO)m (m = 2, 3, 4, 5)

The phase stability and thermophysical properties of InFeO₃(ZnO)_m (m = 2, 3, 4, 5) compounds were investigated, which are a general family of homologous layered compounds with general formula InFeO₃(ZnO)_m (m = 1–19). InFeO₃(ZnO)_m (m = 2, 3, 4, 5) ceramics were synthesized using cold pressing followed by solid-state sintering. They revealed an excellent thermal stability after annealing at 1450 °C for 48 h. No phase transformation occurred during heating to 1400 °C. InFeO₃(ZnO)₃ exhibited a thermal conductivity of 1.38 W m⁻¹ K⁻¹ at 1000 °C, which is about 30% lower than that of 8 wt.% yttria stabilized zirconia (8YSZ) thermal barrier coatings. The thermal expansion coefficients (TECs) of InFeO₃(ZnO)m bulk ceramics were in a range of (10.97 ± 0.33) × 10⁻⁶ K⁻¹ to (11.46 ± 0.35) × 10⁻⁶ K⁻¹ at 900 °C, which are comparable to those of 8YSZ ceramics.     

Design of a new FM01-LC reactor in parallel plate configuration using numerical simulation and experimental validation with residence time distribution (RTD)

The goal of this work was to develop new geometry design of inlet and outlet distributors of the FM01-LC in parallel plate configuration using Computational Fluid Dynamics (CFD). The new distributor geometry was experimentally evaluated with RTD experimental curves using the stimulus-response technique and approximated with axial dispersion model (ADM), plug dispersion exchange model (PDEM) and by solving the hydrodynamic (Reynolds average Navier–Stokes equation for low Reynolds number, RANS-LRN) and mass transport (convection–diffusion equation in transient and turbulent regimen) equations using computational fluid dynamics (F-tracer RTD method). Two sets of RTD experiments (common and new inlet and outlet distributors) in FM01-LC reactors with channel thickness of 0.011 m were carried out. The volumetric flows (Q) employed were from 0.5 to 3.5 L min⁻¹ (U₀ = 0.02-0.15 m s⁻¹). The new FM01-LC reactor had a more homogeneous velocity field in the entire reaction zone, as shown by axial dispersion values lower than those obtained with the common FM01-LC, at different Reynolds numbers. The RTD curves obtained with Comsol Multiphysics 4.3a are in agreement with RTD experimental curves, but deviations are observed at Reynolds numbers greater than “5991”.     

Deuterium kinetic isotopic study for hydrogenolysis of ethyl butyrate

The hydrogenation of ethyl butyrate, n-butyric acid, and n-butyraldehyde to their corresponding alcohol(s) has been studied over a γ-Al₂O₃-supported cobalt catalyst using a high-pressure fixed-bed reactor in the temperature range of 473–493 K. H₂–D₂–H₂ switching experiments show that ethyl butyrate and n-butyric acid follow an inverse kinetic isotope effect (KIE) (i.e. r^H/r^D = 0.50–0.54), whereas n-butyraldehyde did not display any KIE (i.e. r^H/r^D = 0.98). DRIFTS experiments were performed over the support and catalyst to monitor the surface species formed during the adsorption of ethyl butyrate and n-butyric acid at atmospheric pressure and the desired temperature. Butanoate and butanoyl species are the stable surface intermediates formed during hydrogenation of ethyl butyrate. Hydrogenation of butanoate to a partially hydrogenated intermediate is likely involved in the rate-determining step of ethyl butyrate and butyric acid hydrogenation.     

Optimization of process variables for supercritical fluid extraction of ergothioneine and polyphenols from Pleurotus ostreatus and correlation to free-radical scavenging activity

Supercritical carbon dioxide extraction was employed to extract antioxidants from Pleurotus ostreatus. The response surface methodology was employed to determine the optimal conditions for extraction of ergothioneine and polyphenols. The ergothioneine concentration in the mushroom extract was quantified and characterized using high pressure liquid chromatography (HPLC) followed by tandem mass spectrometry (MS/MS). The optimized values of responses were obtained at a pressure of 21 MPa, a temperature of 48 °C and a co-solvent amount of 133 ml, yielding an ergothioneine content of 1.35 mg/g dw, total phenol content of 5.48 mg GAE/g dw, and IC50 for DPPH radical scavenging capacity of 0.008 mg/ml. A higher desirability value of 0.98 for model demonstrated that response surface methodology can be successfully applied for optimizing supercritical carbon dioxide extraction of antioxidants from P. ostreatus. A good correlation was found between DPPH radical scavenging capacity and ergothioneine (R² = 0.94) as well as with polyphenols (R² = 0.95).     

Moisture transport in garlic cloves undergoing microwave-convective drying

A laboratory scale microwave dryer was used to dry the garlic cloves, applying microwave power in the range of 10–40 W, air temperature in the range of 40–70 °C and air velocity in the range of 1.0–2.0 m/s. Heat and mass transfer coefficient during the drying process varied in the range of 35.23–79.54 W/m²C and 4.26–6.34 × 10^?2 m/s. The temperature of the product rose rapidly in the early part of the drying and became almost stable thereafter. The Biot mass transfer number confirmed that moisture diffusion was the limiting factor in microwave drying of garlic. The effective moisture diffusivity, which ranged between 1.29–31.68 × 10^?10 m²/s increased with the increase in microwave power but decreased with increase in air velocity.     

Enhancement of pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 ceramics by La doping

Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La³⁺ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (T_d) decreases. p is 7.24 × 10⁻⁴C m⁻² °C⁻¹ at RT at x = 0.5% and 105.4 × 10⁻⁴C.m^−2 °C⁻¹ at T_d at x = 0.2%. F_i and F_v show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 ⁻¹⁰ m v⁻¹) (x = 0.5%) and from 0.021 to 0.048 (m².C⁻¹) respectively. F_i and F_v show a huge increase to 37.6 × 10⁻¹⁰ m v⁻¹ and 0.56 m² C⁻¹ respectively at T_d at x = 0.2%. F_C shows values of 2.10, 2.89, and 2.98 (x10⁻⁹C cm⁻² °C⁻¹) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications.     

Photoredox reactivity of iron(III) phenolates in aqueous solution induced by ligand-to-metal charge transfer excitation

Iron(III) complexes with phenolate ligands (m-cresolate and tyrosinate) undergo a redox photolysis in aqueous solution upon phenolate → Fe(III) ligand-to-metal charge transfer excitation. At λ_irr=577 nm the quantum yields of Fe(II) formation are approximately φ=10⁻⁴.     

Microwave-enhanced catalytic degradation of phenol over nickel oxide

A mix-valenced nickel oxide, NiO_x, was prepared from nickel nitrate aqueous solution through a precipitation with sodium hydroxide and an oxidation by sodium hypochlorite. Further, pure nickel oxide was obtained from the NiO_x by calcination at 300, 400 and 500 °C (labeled as C300, C400 and C500, respectively). They were characterized by thermogravimetry (TG), X-ray diffraction (XRD), nitrogen adsorption at −196 °C and temperature-programmed reduction (TPR). Their catalytic activities towards the degradation of phenol were further studied under continuous bubbling of air through the liquid phase. Also, the effects of pH, temperature and kinds of nickel oxide on the efficiency of the microwave-enhance catalytic degradation (MECD) of phenol have been investigated. The results indicated that the relative activity affected significantly with the oxidation state of nickel, surface area and surface acidity of nickel oxide, i.e., NiO_x (>+2 and S_BET = 201 m² g⁻¹) ≫ C300 (+2 and S_BET = 104 m² g⁻¹) > C400 (+2 and S_BET = 52 m² g⁻¹) > C500 (+2 and S_BET = 27 m² g⁻¹). The introduction of microwave irradiation could greatly shorten the time of phenol degradation.     

Correlation between eletrokinetic mobility and ionic dyes adsorption of Moroccan stevensite

This study aims at establishing a correlation between the electrical charge of Moroccan stevensite particles and ionic dyes adsorption. The electrophoretic mobility, (U_e), of the stevensite particles in water, was measured at pH 2.5–12 by microelectrophoresis. At pH between 2.5 and 8, U_e remained constant (U_e = ? 1.6 10^? 8 m²/(V s)), as resulting from the permanent charge of the clay mineral planar surfaces. At pH > 8, the magnitude of electrophoretic mobility increased (U_e = ? 2.7 10^? 8 m²/(V s)) due to the deprotonation of silanol groups on the surfaces. The anionic Orange G adsorption at the clay mineral–water interface was negligible whereas the methylene blue cations were strongly adsorbed due to the electrostatic attraction.