Turning glycerol surplus into renewable syngas through glycerol steam reforming over a sol-gel Ni–Mo2C-Al2O3 catalyst

In this work, a sol-gel Ni–Mo₂C–Al₂O₃ catalyst is employed for the first time in the glycerol steam reforming for syngas production. Catalyst stability and activity are investigated in the temperature range of 550 °C–700 °C and time on stream up to 30 h. As reaction temperature increases, from 550 °C to 700 °C, H₂ yield boosts from 22% to 60%. The stability test, carried out at milder conditions (600 °C and Gas-Hourly Space-Velocity (GHSV) of 50,000 mL h⁻¹.g_cat⁻¹), shows high catalyst stability, up to 30 h, with final conversion, H₂ yield, and H₂/CO ratio of 95%, 53% and 1.95, respectively. Both virgin and spent catalysts have been characterized by a multitude of techniques, e.g., Atomic-Absorption spectroscopy, Raman spectroscopy, N₂-adsorption-desorption, and Transmission Electron Microscopy (TEM), among others. Regarding the spent catalysts, carbon deposits’ morphology becomes more graphitic as the reaction temperature increases, and the total coke formation is mitigated by increasing reaction temperature and lowering GHSV.     

Pyrolysis characteristics of Turkish lignites in N2 and CO2 environments

Pyrolysis characteristics and kinetic parameters of two Turkish lignites having different ash contents (Orhaneli as low ash and Soma as high ash sample) were studied under N₂ and CO₂ atmospheres by means of thermogravimetric analysis. The isoconversional kinetic methods of Flynn?Wall??Ozawa, Kissinger??Akahira??Sunose, and Friedman were employed to estimate the activation energy and pre-exponential factors. The experiments were conducted at four different heating rates of 5, 10, 15, and 20°C/min within the temperature range of 50??950ºC. The obtained results indicated that changing the pyrolysis ambient had no significant effect on the devolatilization region up to 700°C. The char formation region in N₂ atmosphere was due to the CaCO₃ decomposition and was more significant for Soma lignite due to its high ash content. However, in CO₂ atmosphere, the gasification reaction took place at temperatures higher than 700°C. The decomposition process of CaCO₃ in CO₂ atmosphere was hampered up to temperatures higher than 900°C. The estimated activation energies were found to have approximately similar trends under different atmospheres. For Orhaneli lignite, the average activation energy values were higher in CO₂ environment. However, for Soma lignite due to decomposition of CaCO₃, the activation energy values were higher in N₂ atmosphere. The mean uncertainty values were assessed for the activation energy values obtained for all test cases.     

Electrical and physical properties of structures with p-n transition produced from silicon obtained by fivefold meltdown of metallurgical silicon in a solar oven

The results of studying electrical and physical properties of n-p structures produced from silicon obtained by fivefold open-air meltdown of metallurgical silicon of KR3 silicon in a solar oven are presented. It is shown that the current and voltage generated during the heating of structures with plain ohmic contacts start to fall at around 120°C, while in structures with n-p transition these characteristics continue to increase at up to 250°C. It has been discovered that structures with n-p transition display rectifying properties in a temperature range of 30–150°C.     

Temperature dependence of effective thermal conductivity and diffusivity of ZnxTe100−x (x = 5, 10, 30 and 50) chalcogenide material

Measurements of thermophysical properties of Zn_xTe_100−x (x = 5, 10, 30 and 50) chalcogenide material in pellet form have been made in the temperature range from room temperature (15 °C) to 200 °C and in cooling cycle from 200 °C to 15 °C using transient plane source (TPS) technique. In heating mode the values of effective thermal conductivity (λ_e) and effective thermal diffusivity (χ_e) increase from 15 °C to 200 °C. During the cooling mode λ_e and χ_e decrease slightly in the temperature range from 200 °C to 160 °C below which λ_e and χ_e remain almost constant at all temperatures. Such type of behaviour shows thermal hysteresis in this sample, which can be explained on the basis of the change in structure of the material. XRD studies suggest that the material is polycrystalline in nature.     

Substrate temperature effect on transparent heat reflecting nanocrystalline ITO films prepared by electron beam evaporation

In this study, indium tin oxide (ITO) thin films were preparedon glass substrate by electron beam evaporation technique and then were annealed in air atmosphere at 350 °C for 30 min. Increasing substrate temperature (T_s) from 25 to 380°°C reduced sheet resistance of ITO thin films from 150(Ω/□) to 14(Ω/□). The UV-visible-near IR transmittance and reflectance spectra were also confirmed that the substrate temperature has significant effect on the properties of heat reflecting thin films. High transparency (83%) over the visible wavelength region of spectrum and (over 90%) reflectance in near-IR region were obtained at T_s = 300° C. Plasma wavelength, carrier concentrations (n_e) and refractive index of the layer were also calculated. The allowed direct band gap at the temperature range 100–300° C was estimated to be in the range 3.71–3.89 eV. Band gap widening due to increase in substrate temperature was observed and is explained on the basis of Burstein-Moss shift. XRD patterns showed that the films were polycrystalline. High quality crystalline thin films with grain size of about 40 nm were obtained.     

Lactate wastewater dark fermentation: The effect of temperature and initial pH on biohydrogen production and microbial community

Biohydrogen production using dark fermentation (hydrolysis and acidogenesis) is one of the ways to recover energy from lactate wastewater from the food-processing industry, which has high organic matter. Dark fermentation can be affected by the temperature, pH and the microbial community structure. This study investigated the effects of temperature and initial pH on the biohydrogen production and the microbial community from a lactate wastewater using dark fermentation. Biohydrogen production was successful only at lower temperature levels (35 and 45 °C) and initial pH 6.5, 7.5 and 8.5. The highest hydrogen yield (0.85 mol H₂/mol lactate consumed) was achieved at 45 °C and initial pH 8.5. The COD reduction achieved by fermenting the lactate wastewater at 35 °C ranged between 21 and 30% with the maximum COD reduction at pH 8.5, and at 45 °C, the COD reduction ranged between 12 and 21%, with the maximum at pH 7.5. At 35 °C, the lactate degradation ranged between 54 and 95%, while at 45 °C, it ranged between 77 and 99.8%. 16S rRNA sequencing revealed that at 35 °C, bacteria from the Clostridium genera were the most abundant at the end of the fermentation in the reactors that produced hydrogen, while at 45 °C Sporanaerobacter, Clostridium and Pseudomonas were the most abundant.     

Impacts of short-term temperature fluctuations on biohydrogen production and resilience of thermophilic microbial communities

Anaerobic microflora enriched for dark fermentative H₂ production from a mixture of glucose and xylose was used in batch cultivations to determine the effects of sudden short-term temperature fluctuations on H₂ yield and microbial community composition. Batch cultures initially cultivated at 55 °C (control) were subjected to downward (from 55 °C to 35 °C or 45 °C) or upward (from 55 °C to 65 °C or 75 °C) temperature shifts for 48 h after which, each culture was transferred to a fresh medium and cultivated again at 55 °C for two consecutive batch cycles. The average H₂ yield obtained during the first cultivation at 55 °C was 2.1 ± 0.14 mol H₂ mol⁻¹ hexose equivalent. During the temperature shifts, the obtained H₂ yields were 1.8 ± 0.15, 1.6 ± 0.27 and 1.9 ± 0.00 mol H₂ mol⁻¹ hexose equivalent at 35 °C, 45 °C and 65 °C, respectively, while no metabolic activity was observed at 75 °C. The sugars were completely utilized during the 48 h temperature shift to 35 °C but not at 65 °C and 45 °C. At the end of the second cycle after the different temperature shifts, the H₂ yield obtained was 96.5, 91.6, 79.9 and 54.1% (second cycle after temperature shift to 35 °C, 45 °C, 65 °C and 75 °C, respectively) when compared to the average H₂ yield produced in the control at 55 °C. Characterization of the microbial communities present in the control culture at 55 °C showed the predominance of Thermoanaerobacteriales, Clostridiales and Bacilliales. The microbial community composition differed based on the fluctuation temperature with Thermoanaerobacteriales being most dominant during the upward temperature fluctuations and Clostridiales being the most dominant during the downward temperature fluctuations.     

Effects of substrate temperatures on the thermal stability of AlxOy/Pt/AlxOy multilayered selective solar absorber coatings

We report the effects of substrate temperatures on the thermal stability of Al_xO_y/Pt/Al_xO_y multilayered selective solar absorber coating (MSSAC). The samples were deposited at different substrate temperatures (from room temperature up to 250 °C), and then annealed at various temperatures (300–600 °C) in air for 2 h. Characterizations are made via X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Atomic Force Microscopy (AFM), Raman Spectroscopy, UV–Vis and emissometeric measurements. These coatings were found to be thermally stable up to 500 °C with good spectral selectivity of 0.930/0.11. Furthermore, the observed decrease in the spectral selectivity 0.883/0.13 at 600 °C is attributed to the diffusion of Cu and the formation of CuO phase. Such phase formation was confirmed using XRD and Raman spectral analysis. The insensitiveness of the thermal stability of such coatings on the substrate temperature is demonstrated.     

Li/SOCl2 cells for high temperature applications

The capacity of Li/SOCl₂ cells operating at temperatures as high as 150 °C has been measured at discharge rates up to 5 mA/cm². The results indicate the unique chemical and electrochemical stability of the system, manifested by its ability to be discharged continuously at 150 °C for more than 2 months while obtaining 70% of the cell nominal capacity.The capacity-temperature plot shows a maximum at 50 °C. Above 50 °C the capacity decreases as a result of the increase in the self-discharge current at higher temperature. An anomalous capacity increase is found at temperatures above 100 °C. Above this temperature it has been shown that thermal decomposition products may increase the cathodic reaction rate and modify the structure of the passivation layer on the anode surface. Over the 100 – 150 °C temperature range the lithium chloride film morphology, as analysed by SEM, tends to be of a smaller crystal size the higher the temperature. This trend is in opposition to that found at the lower temperature range, e.g., ?40 to 70 °C. In addition, the decomposition product, e.g., SO₂, improves the transport properties of the electrolyte and thus increases the carbon cathode efficiency.     

Reactor start-up strategy as key for high and stable hydrogen production from cheese whey thermophilic dark fermentation

Using the right start-up strategy can be vital for successful hydrogen production from thermophilic dark fermentation (55 °C), but it needs to be affordable. Hence, three start-up strategies modifying only influent concentration and temperature were assessed in a reactor fed with cheese whey: (i) high temperature (55 °C) and a high organic loading rate (OLR_A - 15 kgCOD m^?3 d^?1) right at the beginning of the operation; (ii) slowly increasing temperature up to 55 °C using a high OLR_A and (iii) slowly increasing temperature and OLR_A up to the desired condition. Strategy (iii) increased hydrogen productivity in 39% compared to the others. The combination of high temperature and low pH thermodynamically favored H₂ producing routes. Synergy between Thermoanaerobacterium and Clostridium might have boosted hydrogen production. Three reactors of 41 m³ each would be needed to treat 3.4 × 10³ m³ year^?1 of whey (small-size dairy industry) and the energy produced could reach 14 MWh month^?1.     

Comprehensive performance enhancement of polybenzimidazole based high temperature proton exchange membranes by doping with a novel intercalated proton conductor

On the study of high temperature proton exchange membrane (HTPEM), the trade-off between proton conductivity and physico-chemical property (such as mechanical strength, dimensional stability and methanol resistance) remained a main obstacle for comprehensive performance enhancement. To address this issue, novel HTPEM was prepared by doping phosphotungstic acid intercalated ferric sulfophenyl phosphate (FeSPP-PWA) into polybenzimidazole (PBI) via hot pressed method. Intense hydrogen bonding network was built between PBI and FeSPP-PWA, rendering construction of proton channels and reinforcement of physico-chemical property. As a novel proton conductor, FeSPP-PWA facilitated formation of efficient proton transfer pathway. The layered morphology and inorganic intrinsity of FeSPP-PWA also improved the mechanical and dimensional stability while reducing the methanol permeability of the PBI/FeSPP-PWA membranes. The composite membrane exhibited good thermal stability up to 200 °C. The proton conductivity of PBI/FeSPP-PWA (30 wt%) reached 110 mS cm^?1 at 170 °C and 100% RH, and was 69.3 mS cm^?1 at 180 °C and 50% RH. The PBI/FeSPP-PWA also showed low methanol permeability and high membrane selectivity for application in direct methanol fuel cells.     

Production of hydrogen by Enterobacter aerogenes in an immobilized cell reactor

The production of hydrogen from glucose by using Enterobacter aerogenes ATCC 13048 (E. aerogenes) in an immobilized cell reactor (ICR) was investigated. The effect of several factors, such as the glucose concentration, feed flow rate, and fermentation time were examined. The highest amount of hydrogen (9.44 mmol H₂/g glucose) was obtained at a glucose concentration of 8 g/L, flow rate of 0.5 mL/min, retention time of 24 h and at a temperature of 30 °C. Meanwhile, the highest amount of carbon dioxide (1.68 mmol CO₂/g glucose) was obtained at a glucose concentration of 10 g/L, flow rate of 0.7 mL/min, hydraulic retention time of 24 h and at a temperature of 30 °C. The hydrogen and carbon dioxide production were affected by glucose concentration, hydraulic retention time (HRT) and fermentation time. This study showed that the ICR was a very efficient method for the production of hydrogen and carbon dioxide gases.     

Performance evaluation of mixed convection in an inclined square channel with uniform temperature walls

Numerical analyses were performed for the effect of inclined angle on the mixing flow in a square channel with uniform temperature walls (T_w = 30 °C) and inlet temperature (T₀ = 10 °C). Three-dimensional governing equations were solved numerically for Re = 100, Pr = 0.72 and various inclined angles (from ?90° to 90°). Three-dimensional behavior of fluid in a channel was examined for each angle. Thermal performance was evaluated using the relationship between Nusselt number ratio and pressure loss ratio with and without buoyancy induced flow as a parameter of inclined angles. High heat transfer and low pressure loss region was from ?15° to ?60° in thermal performance using mean Nusselt number ratio.     

Cooling of a heated flat plate by an obliquely impinging slot jet

Experiments were conducted to determine the effects of some parameters that were crucial in the cooling of a heated flat plate by an obliquely impinging slot jet. The inclination of the jet relative to the surface was varied from 90° to 30° (90°, 60°, 45° and 30°). For Reynolds number of 5860, 8879, and 11606, the variation of local temperatures with respect to dimensionless length (z/L), were investigated. New correlations for local temperatures in terms of Reynolds number, dimensionless distance (z/L) and oblique angle (sinϕ) were developed. The displacement region of maximum heat transfer (minimum temperature point) on the plate was measured with respect to geometrical impingement point. Results of experiments indicated that for a given position this displacement increases with increasing the inclination, and the displacement was occurred on compression side of plate.     

The structure and magnetic properties of magnesium-substituted LaFeO3 perovskite negative electrode material by citrate sol-gel

Perovskite-type composite oxide is a material as high-energy-density Ni-MH batteries. Due to the perovskite type oxide has a special crystal structure, and exhibits a rich variety of physicochemical properties, we study the affect of the Mg²⁺ doping amount, calcination temperature and calcination time for the microstructure, sample composition and magnetic properties of LaFeO₃. XRD patterns showed that all the samples are perovskite orthogonal structure and the space group is Pnma (No. 62). When the calcination temperature is in the range of 400 °C–600 °C, the samples are a single phase, no other impurities generated. When the temperature of 800 °C and 1000 °C, 2θ between 30° and 40° detected the second phase MgFe₂O₄ and miscellaneous phase peak intensity increases with the increase of calcination temperature and strengthen, and the calcination temperature had a direct effect on the grain size of the powder. When the calcination temperature is higher, the grain shape is better and the grain size is larger. The saturation magnetization of samples increases with the increase of Mg²⁺ concentration. The coercive force is decreased with the increase in Mg²⁺ concentration. The saturation magnetization and the residual magnetization of the sample are reduced when the sintering temperature from 400 °C rises to 600 °C. When the sintering temperature is 800 °C, the MgFe₂O₄ impurity phase appear. The iron oxide composition is increased, and the magnetic enhancement of the sample is enhanced. Magnetic studies show that when the calcination temperature is 600 °C, the magnetic parameters of the sample are the best.     

Parametric investigations on LCC1 based hydrogen storage system intended for fuel cell applications

Considering the necessity for compact hydrogen storage system for fuel cell stacks, 41 embedded cooling tube (ECT) reactor with an outer cooling jacket (OCJ) is designed, fabricated and tested with 3.75 kg of LCC1® alloy. To analyse the sensitivity of the system performance at various operating conditions and the applicability of this prototype as storage system, an extensive parametric investigation was carried out at varying supply pressure (P_s), absorption temperature (T_a) and desorption temperature (T_d). LCC1® alloy achieved maximum hydrogen storage capacity (HSC) of 1.6 wt% within 420 s at P_s of 25 bar, T_a of 25 °C and heat transfer fluid (HTF) flow rate (HTF_a) of 6 LPM. Supply pressure is found to have greater influence than absorption temperature over absorption performance and heating output. With T_a of 25 °C, HTF_a of 6 LPM, HSC of 1.58 wt% and 1.6 wt% were achieved at P_s of 20 bar and 30 bar, respectively, resulting in corresponding specific heating power (SHP) of 497.7 W/kg and 544.9 W/kg. Varying T_a from 25 °C to 35 °C at P_s of 20 bar and HTF_a of 6 LPM resulted in 3% reduction in HSC. During desorption, desorption temperature of above 20 °C is found to be favourable with more than 95% of stored hydrogen being desorbed. It is further observed that the dehydriding rate of LCC1® was nearly steady which is potentially suitable for fuel cell applications, as the average dehydriding rate is estimated to be about 15.75 NLPM and 22.91 NLPM at T_d of 20 °C and 25 °C, respectively, with 6 LPM of HTF flow rate. The analysed module is proposed as a potential hydrogen supply unit for a 1 kW fuel cell reported in literature.     

Electrochemical and thermal properties of SmBa0.5Sr0.5Co2O5+δ cathode impregnated with Ce0.8Sm0.2O1.9 nanoparticles for intermediate-temperature solid oxide fuel cells

SmBa_0.5Sr_0.5Co₂O_5+δ (SBSC55) impregnated with nano-sized Ce_0.8Sm_0.2O_1.9 (SDC) powder has been investigated as a candidate cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The cathode chemical compatibility with electrolyte, thermal expansion behavior, and electrochemical performance are investigated. For compatibility, a good chemical compatibility between SBSC55 and SDC electrolyte is still kept at 1100 °C in air. For thermal dilation curve, it could be divided into two regions, one is the low temperature region (100–265 °C); the other is the high temperature region (265–850 °C). In the low temperature region (100–265 °C), a TEC value is about 17.0 × 10^?6 K^?1 and an increase in slope in the higher temperatures region (265–800 °C), in which a TEC value is around 21.1 × 10^?6 K^?1. There is an inflection region ranged from 225 to 330 °C in the curve of d(δL/L)/dT vs. temperature. The peak inflection point located about 265 °C is associated to the initial temperature for the loss of lattice oxygen and the formation of oxygen vacancies. For electrochemical properties, the polarization resistances (R_p) significantly reduced from 4.17 Ω cm² of pure SBSC55 to 1.28 Ω cm² of 0.65 mg cm^?2 of SDC-impregnated SBSC55 at 600 °C. The single cell performance of SBSC55∣SDC∣Ni-SDC loaded with 0.65 mg cm^?2 SDC exhibited the optimum power density of 823 mW cm^?2 at operating temperature of 800 °C. Based on above-mentioned properties, SBSC55 impregnated with an appropriate SDC is a potential cathode for IT-SOFCs.     

Influence of Carbonization Conditions on the Properties of Coconut Shell Chars

The changes in chemical, physical, and mechanical properties of fully matured coconut shell chars in relation to carbonization temperature (range: 400–950°C) and time (range: zero–3 h) have been studied. These properties were found to be more susceptible to carbonization temperature than to time. The results indicated an increase in fixed carbon content and true specific gravity of shell chars with rise of carbonization temperature and soak time. The majority of volatilization occurred up to about 800°C. The calorific value of shell char increased sharply with rise of carbonization temperature up to 600°C, and thereafter it decreased to 800°C. The porosity of shell char increased with increase of carbonization temperature up to 600°C followed by a decrease with further rise of temperature up to the range studied. Prolonged soaking at carbonization temperatures of 600, 800, and 950°C, in general, led to slight increases in the porosity and calorific values of resulting shell chars. The results showed that the crushing strength of shell char decreased markedly on increasing the preparation temperature up to 600°C, followed by an increase thereafter. An increase in soaking time at carbonization temperatures of 600, 800, and 950°C also influenced the shell char strength.     

Optical and thermal optimization of stationary non-evacuated CPC solar concentrator with fully illuminated wedge receivers

Stationary low concentrator collectors (C < 2), of the CPC type, are of great interest for thermal energy supply of industrial processes, at temperatures below or equal to 100 °C. In particular, concentrators with fully illuminated V inverted absorbers have attractive properties for thermal energy conversion.Numerical analysis of the geometric and optical characteristics of different low concentration CPC’s (C between 1 and 2) with fully inverted wedge absorbers, shows that the cavities with the minimal relationship between the length and height of the reflector surface and the aperture, (L/A) and (H/A), and the lower average number of reflections 〈n〉 correspond to the lowest angular acceptance concentrator. If a concentration of 1.2 is desired, the smallest ratios of (L/A) and (H/A) and mean number of reflections 〈n〉 occur for C = 2 (θ_a = 30°). However, when the annual generated thermal energy is also considered (for example, for Recife, tilt equals latitude, fluid temperature equals 50 °C, East–West orientation), a very large maximum value in the concentration region between 1.4 and 1.6 (acceptance angles of 38.68° e 45.58°) occurs. The simulation results indicate, that while the operational temperature rises, the ratio between the annual generated thermal energy by the CPC and a good quality flat-plate collector becomes greater than 1: for CPC with 1.2 concentration these ratios become 1.0 at 50 °C and 1.35 at 80 °C. The improvement in the reflectivity of the reflector surface of the CPC rises significantly this relation, i.e., if the reflectivity exceeds from 0.86 to 0.96 the CPC of the concentration relation 1.2, operating at 80 °C may generate 55% more thermal energy than flat-plate collector.     

Effects of plate temperature on heat transfer and emissions of impinging flames

Experiments were conducted to investigate the heat transfer and CO/NO_X emissions of a premixed LPG/air circular flame jet impinging upwards normally to a flat rectangular plate. Temperatures of the impingement plate were controlled by cooling water at 38 °C, 58 °C and 78 °C which was circulating at its back in order to create different plate temperatures. Under each plate temperature, the effects of Reynolds number (Re), equivalence ratio (Ф) and nozzle-to-plate distance (H) on the heat transfer and CO/NO_X emissions were examined. The Re was selected to be 500, 1000 and 1500 to ensure laminar flame jets. The values of Ф were chosen to cover fuel-lean, stoichiometric and fuel-rich conditions. The H varied from 3d to 7d with an interval of 1d.The flame-side temperature of the impingement plate is enhanced when the cooling water temperature increases, but the temperature difference across the impingement plate is reduced. Heat transfer from the flame to the plate is suppressed at higher cooling water temperature. The heat transfer rate is the highest when the cooling water temperature is at 38 °C and the lowest heat flux is obtained at 78 °C. At the highest cooling water temperature of 78 °C, the CO emission is reduced whereas the NO_X emission is enhanced. However, this trend is reversed at the lowest cooling water temperature of 38 °C.