Combining osmotic–steam blanching with infrared–microwave–hot air drying: Production of dried lemon (Citrus limon L.) slices and enzyme inactivation

The different pretreatments were given to lemon slices to inactivate pectinesterase and peroxidase enzymes and to dry the product rapidly using infrared–microwave hot air combination. Osmotic pretreatment followed by 1-min steam blanching was found to reduce moisture in the product, increase solid content, and inactivate enzymes in lemon slices while maintaining negligible dry matter and juice sac loss. The infrared hot air was found effective in partial drying of pretreated lemon slices up to 1 hour without entering in drastic falling-rate period. Therefore, after 1?h microwave hot air was used to complete the drying process. The optimum infrared drying condition was found at 3000?W/m² radiation intensity, 90°C air temperature, 100?mm distance between lamp and product, and 1.5?m?s^?1 air velocity. In microwave finish drying, the power density of 0.30?W?g^?1, 89.9°C air temperature, and 0.5?m?s^?1 air velocity were found to result in the best product. The hybridization of osmotic–steam blanching and the two drying methods overcame the problems of browning, extended falling-rate periods, improper power distribution, and quality deterioration. Also, the higher values of moisture diffusivities were observed during hybrid drying.     

Combined microwave–hot-air drying of burdock slices with feedback temperature control at surface and core

During combined microwave–hot-air drying, the surface and the core temperatures of the sample have great influence on the process. To investigate the influence systematically, drying system with feedback control strategy of the two temperatures was proposed. Then various pairs of the two temperatures were applied in the drying mode 1. However, it was found difficulty to achieve both short drying time and high product quality with fixed temperature pair, because the interaction between microwave and the sample changes as the moisture content decreases in the drying process. Different temperature pairs were applied during the three drying stages in drying mode 2, so that better product can be obtained in shorter drying time. To further improve the product quality, the drying rate was controlled by a feedback loop within a desired range in drying mode 3. The change of drying rate was realized by adjusting the two temperatures continuously. To omit the weighing scale, a feedforward control strategy for the drying rate was put forward in drying mode 4, where the temperatures were controlled along with preset lines. The results showed that the product quality and the drying time were similar to those in drying mode 3.     

Three-stage hybrid osmotic–intermittent microwave–convective drying of apple at low temperature and short time

ABSTRACT

In recent years, intermittent microwave coupled with hot air-drying has been used increasingly, thanks to considerable improvements observed in drying properties. The aim of this study was to investigate the effect of process of drying apple pretreated osmotically with sucrose solution at five concentrations of 0 (control), 10, 30, 50, and 70% (w/w), using intermittent microwave at four power levels of 0 (control), 360, 600, and 900?W, four pulse ratios of 1, 2, 3, and 4, and convective hot air (40°C) on drying kinetics, effective moisture diffusion coefficient, shrinkage, bulk density, rehydration ratio, and energy consumption. Results showed that the three-stage hybrid osmotic–intermittent microwave–convective drying of apple at low temperature yielded higher drying rates (with 41.5% decrease in drying time) and improved quality of final product. The effective moisture diffusion coefficient increased with an increase in power, pulse ratio, and the concentration of osmotic solution. Furthermore, shrinkage, bulk density, and energy consumption of the samples decreased with an increase in power, pulse ratio, and the concentration of osmotic solution. In summary, the use of intermittent microwave coupled with forced convection of hot air (at low temperature) in drying of apple pretreated by sucrose osmotic solution led to products with improved properties in terms of both quality and quantity.     

Modelling of dehydration–rehydration of instant rice in combined microwave-hot air drying

The drying operation is one of the critical steps in the preparation of instant rice. Drying methods and conditions play important roles in achieving the desired quality. In this study, instant rice was subjected to convective hot air, microwave and combined microwave-hot air dehydration. Three air temperature (70 °C, 80 °C, 90 °C) and three microwave power (210 W, 300 W, 560 W) settings were investigated to find the drying kinetics, rehydration kinetics and colour change. The results showed that combined microwave-hot air drying decreased the drying time required when compared to drying with either hot air or microwave energy alone. Predictive models were developed to describe dehydration and rehydration kinetics. Dehydration rate, rehydration rate and total colour change of rehydrated product generally increased with microwave level and air temperature. Combination drying with MW = 300 W and T = 80 °C was optimal in terms of drying time, rehydration time and colour.     

Drying uniformity analysis of pulse-spouted microwave–freeze drying of banana cubes

This article reports the investigation of the drying uniformity of a new drying technique called pulse-spouted microwave–freeze drying. A computer vision technique and mathematical statistics were used to evaluate the drying uniformity. The results show that low microwave power results in prolonged drying time (the drying time of 1 W/g was 6 h, which was longer than that for 2 and 3 W/g), whereas spouting time and the time interval show less influence on the drying time. Analysis from infrared camera photos reveals that lower microwave power, longer spouting interval, and longer spouting time could improve the temperature distribution. Sample 4 (power: 2 W/g, time: 3 s, interval: 300 s) had the best temperature distribution uniformity.     

Regeneration of zinc particles for zinc–air fuel cells in a spouted-bed electrode

Fuel cells wherein zinc particles form a negative electrode and a gas-diffusion electrode (air electrode) is the positive electrode, are under development. Such cells are dependent on the regeneration of the zinc particles (and electrolyte). This paper describes experiments on electrolytic cells equipped with spouted bed cathodes for use in this application. Experiments have been carried out on laboratory scale cells to determine the operability of cells for growing 'seed particles in the range from 0.4 to 1 mm to measure cell voltage and current efficiency (and thereby energy consumption rate), and to identify a suitable material that could be used as a diaphragm (separating the spouted bed from the oxygen evolving anode). A larger cell, capable of producing up to 10 kg Zn per day, was designed and built. The larger cell was run successfully fifteen times and showed cell voltages and energy consumption rates comparable with those of smaller cells.     

Ignition of a two-fuel hydrogen–silane mixture in air

Based on the previously developed model of detailed kinetics, the ignition delay time of two-fuel hydrogen–silane–air mixtures is calculated. The effect of the silane concentration and the temperature of the mixture on the ignition delay time is determined. It is shown that addition of a small (within 20%) amount of silane to the hydrogen–air mixture in the temperature range from 1200 to 2500 K leads to significant reduction of the ignition delay time of the mixture, whereas there is only a minor decrease in mixtures with silane concentrations higher than 20%.     

Hydrothermal synthesis of a monoclinic VO2 nanotube–graphene hybrid for use as cathode material in lithium ion batteries

The hydrothermal reaction of a mixture of a colloidal dispersion of graphite oxide and ammonium vanadate yielded a hybrid made of graphene and a nanotubular metastable monoclinic polymorph of VO₂, known as VO₂(B). The formation of VO₂(B) nanotubes is accompanied by the reduction of graphite oxide. Initially the partially scrolled graphite oxide layers act as templates for the crystallization of VO₂(B) in the tubular morphology. This is followed by the reduction of graphite oxide to graphene resulting in a hybrid in which VO₂(B) nanotubes are dispersed in graphene. Electron microscopic studies of the hybrid reveal that the VO₂(B) nanotubes are wrapped by and trapped between graphene sheets. The hybrid shows potential to be a high capacity cathode material for lithium ion batteries. It exhibits a high capacity (～450 mAh/g) and cycling stability. The high capacity of the hybrid is attributed to the interaction between the graphene sheets and the VO₂(B) tubes which improves the charge-transfer. The graphene matrix prevents the aggregation of the VO₂(B) nanotubes leading to high cycling stability.     

Graphene oxide–tripolyphosphate hybrid used as a potent sorbent for cationic dyes

Graphene oxide–tripolyphosphate material (GPM) was synthesized through an ethanolamine (EA) mediated graphene oxide (GO) self-assembly. The synthesis route to GPM is simple and benign. GPM was composed of GO nanosheets as building blocks and the tripolyphosphate as cross-linkers and chelators of cations in solutions. GPM showed higher potency for adsorption of cationic dyes than anionic dyes, and the adsorption process was through electrostatic and π–π interactions. Adsorption was spontaneous and exothermic, and the adsorption capacity of GPM for cationic dyes (>2540 mg g⁻¹) far exceeded those reported in literature for GO materials.     

Validation of a kinetic scheme for numerical investigation of hydrogen–methanol–air flames

Normal burning velocities in methanol–air mixtures and in the same mixtures with added 4.5 and 7.2% hydrogen as a second fuel were measured over a wide range of equivalence ratio and for initial conditions of 0.16 MPa and 354 K. It has been shown that the mechanism previously proposed for the combustion of mixtures of CO, CH₂O and CH₃OH with air is applicable to multicomponent mixtures containing hydrogen and methanol.     

Thiourea-functionalized magnetic hydroxyapatite as a recyclable inorganic–organic hybrid nanocatalyst for conjugate hydrocyanation of chalcones with TMSCN

The recoverable nanomagnetic catalyst was manufactured based on thiourea modified magnetic hydroxyapatite. Magnetic hydroxyapatite (mHAp) as the inorganic–organic hybrid support was fabricated using co-precipitate condition and then modified via the covalently anchoring of 1-(3,5-bis(trifluoromethyl)phenyl-3-propyl)thiourea. The hybrid nano-catalyst has been identified by TEM, SEM, FTIR, BET, TGA, and XRD. This nanocatalyst appeared efficient and robust in the 1,4-addition reaction of TMSCN to α,β-unsaturated aromatic enones in excellent yields (85–96%) under mild reaction condition and simple work-up process. This recoverable organocatalyst has a great potential as an industrially viable and eco-safe catalyst.     

New structures of thin air cathodes for zinc–air batteries

Thin composite cathodes for air reduction were manufactured using microfibre-based papermaking technology. The electrodes have a thin structural design, less than 0.15 mm in thickness. Composite cathode materials for oxygen reduction applications were fabricated by entrapping carbon particles in a sinter-locked network of 2–8 m diameter metal fibres. The thin structure not only results in electrodes that are 30–75% thinner than those commercially available, but also offers an opportunity for custom-built air cathodes optimized for high-rate pulse applications. Using a thin composite structure for the air cathode in a zinc–air battery that is part of a zinc–air/capacitor hybrid is likely to increase the pulse capability of the hybrid power system. The thin cathode structure provides a better, more efficient three-phase reaction zone. In a half-cell test, the ultrathin air cathode generated more than 1.0 V vs Zn/ZnO for a current of 200 mA cm^–2. Half-cell, full-cell and pulse-power tests revealed that thin composite cathodes have a better rate and pulse performance than the air cathodes commonly used.     

Ignition of the drops of coal–water fuel in a flow of air

The ignition of the drops of coal–water fuel (CWF) in a high-temperature gas (air) flow was experimentally studied. The conditions and fundamental characteristics of the ignition (ignition delay times) were found. The effects of a number of factors (drop sizes and ambient temperatures) on the conditions of ignition were examined. Based on the results of experiments, a physical model was formulated for the processes of thermal preparation and ignition of CWF drops. The experimental delay times of the ignition of CWFs were compared with the theoretical values (obtained with the use of a previously developed mathematical model).     

Was pretreatment beneficial for more biogas in any process? Chemical pretreatment effect on hydrogen–methane co-production in a two-stage process

The study focused on the mesophilic anaerobic hydrogen production from PPS (pulp and paper sludge) and FW (food waste) pretreated by NaOH or H₂SO₄, and the subsequent thermophilic anaerobic methane production with the effluent in a two-stage process. The maximum hydrogen yield (78.35 mL g^?1 VS_fed) which was 50.21% higher than that of CK, was achieved when 10 g NaOH/100 g TS_substrate was used. However, the maximum methane yield (383.8 mL g^?1 VS_fed) was obtained in CK as well as 64% SCOD removal efficiency was achieved. In short, NaOH/H₂SO₄ pretreatment was suitable to enhance the hydrogen production.     

Sol–gel derived hybrid materials as heterogeneous catalysts for the epoxidation of olefins

CH₃ReO₃ has been heterogenized inside the porous system of hybrid silica matrixes via the sol–gel method using 1,4-bis(triethoxysilyl)benzene as a co-condensation agent and 4-((3-triethoxysilyl)propylamino)pyridine hydrochloride as a hydrolysable ligand. The resulting solids are stable and recyclable epoxidation catalysts.     

Preparation of an oil shale suspension in a water–mazut emulsion as a raw material for gasification

The results of tests of the raw material preparation module of a laboratory setup for studying the gasification of a mixture of oil shale with oil residues are reported. It was shown that the equipment of the raw material preparation module makes it possible to obtain a stable water–hydrocarbon suspension of oil shale (with a solid-phase particle size of 1–100 μm). The viscosity ratio at 80°C was no higher than a required value (VR 16.0), which ensures its free pumping through the sprayers of a gasifier and a uniform distribution in the combustion chamber volume.     

Synthesis of SiC–TiO2 hybrid aerogel via supercritical drying combined PDCs route

The SiC-TiO₂ hybrid aerogels were obtained from polycarbosilane (PCS) and tetrabutyltitanate (TBT) as precursors using supercritical drying and polymer derived ceramics route. The polymer to ceramic conversion and the crystallization behavior were studied by X-ray diffraction (XRD) and transmission electron microscopy (TEM), suggesting the preceramic aerogels converted to the SiC-TiO₂ ceramic aerogels through pyrolysis process at different temperatures. At 1200 °C, the ceramic aerogels were homogeneous with well-distributed element components, composed of rutile TiO₂ and the β-SiC crystalline phases. The results show that the SiC-TiO₂ ceramic aerogels with netwoks structure have 23.36 nm average pore size, high surface area (58 m²/g) and pore volume (0.22 cm³/g).     

Mn/Co oxide on Ni foam as a bifunctional catalyst for Li–air cells

Binary Mn/Co oxide sheets with spherical flower-like hierarchical structure are grown directly on the surface of a Ni foam skeleton as a cathode for Li–O₂ batteries using a hydrothermal method. This integrated cathode architecture eliminates the negative effects of a conductive carbon additive and binder on the electrochemical performance of Li–O₂ batteries and minimizes the processing steps in fabrication of cathodes for Li–O₂ batteries. The porous Ni foam acts as a scaffold and current collector, and the highly hierarchical porous flower-like structure of the binary Mn/Co oxide sheet acts as a highly active catalyst. Together, they facilitate effective diffusion of oxygen gas as well as rapid ion and electron conduction during electrochemical reactions. When assembled in Li–O₂ cells, the prepared catalyst exhibits excellent catalytic activities, including the oxygen reduction and oxygen evolution reactions. In particular, the Li–O₂ cell using the cathode delivers an extremely high specific discharge capacity of 9690 mAh g^-1 under a applied specific current of 200 mA g^-1 and operate successfully in a long lifespan of 66 cycles even under a high specific current of 600 mA g^-1 and a limited discharge-charge capacity mode of 1000 mAh g^-1. The simultaneous effect of the fast electron transport kinetics provided by the free-standing structure and the high catalytic activity of the binary Mn/Co oxide show promise for use in air electrodes for Li–O₂ batteries.