Anodic Pt dissolution in concentrated trifluoromethanesulfonic acid

We investigated the anodic Pt dissolution in concentrated trifluoromethanesulfonic acid (TFMSA). The dependence of the Pt dissolution rate on the TFMSA concentration was first measured from the weight difference of a Pt-flag electrode before and after successive potential cycles. From this measurement, the Pt dissolution rate in 10 mol dm^?3 TFMSA is found to be over 40 times greater than those in 1 and 4 mol dm^?3 TFMSA. Next, the anodic Pt dissolution was assessed in 10 mol dm^?3 TFMSA by a potential step technique using a Pt dual microelectrode having generator and collector electrodes. The obtained result shows that the anodic Pt dissolution in 10 mol dm^?3 TFMSA occurs when the Pt generator electrode potential is stepped from 0.25 to 1.0–2.0 V vs. Ag/Ag₂SO₄. Furthermore, the absolute steady-state current-based coulomb charges obtained at the generator (|Q_G|) and collector (|Q_C|) reflect the anodic Pt dissolution and the reduction of the dissolved Pt, respectively. The magnitude of |Q_G| and |Q_C| linearly increase when the generator potential shifts from 1.0 to 2.0 V vs. Ag/Ag₂SO₄. The absolute ratio, |Q_C/Q_G|, also gradually increases according to the shift in the generator electrode potential. These results demonstrate that the anodic Pt dissolution in 10 mol dm^?3 TFMSA occurs at ≥1.0 V vs. Ag/Ag₂SO₄ and that the ratio of the anodic Pt dissolution per total reaction charges increases according to the positive shift of the Pt electrode potential.     

Hydrothermal catalytic gasification of fermentation residues from a biogas plant

Biogas plants, increasing in number, produce a stream of fermentation residue with high organic content, providing an energy source which is by now mostly unused. We tested this biomass as a potential feedstock for catalytic gasification in supercritical water (T ≥ 374 °C, p ≥ 22 MPa) for methane production using a batch reactor system. The coke formation tendency during the heat-up phase was evaluated as well as the cleavage of biomass-bound sulfur with respect to its removal from the process as a salt. We found that sulfur is not sufficiently released from the biomass during heating up to a temperature of 410 °C. Addition of alkali salts improved the liquefaction of fermentation residues with a low content of minerals, probably by buffering the pH. We found a deactivation of the carbon-supported ruthenium catalyst at low catalyst-to-biomass loadings, which we attribute to sulfur poisoning and fouling in accordance with the composition of the fermentation residue. A temperature of 400 °C was found to maximize the methane yield. A residence time dependent biomass to catalyst ratio of 0.45 g g⁻¹ h⁻¹ was found to result in nearly full conversion with the Ru/C catalyst. A Ru/ZrO₂ catalyst, tested under similar conditions, was less active.     

Life cycle assessment of a Brassica carinata bioenergy cropping system in southern Europe

The energetic and environmental performance of production and distribution of the Brassica carinata biomass crop in Soria (Spain) is analysed using life cycle assessment (LCA) methodology in order to demonstrate the major potential that the crop has in southern Europe as a lignocellulosic fuel for use as a renewable energy source.The Life Cycle Impact Assessment (LCIA) including midpoint impact analysis that was performed shows that the use of fertilizers is the action with the highest impact in six of the 10 environmental categories considered, representing between 51% and 68% of the impact in these categories.The second most important impact is produced when the diesel is used in tractors and transport vehicles which represents between 48% and 77%. The contribution of the B. carinata cropping system to the global warming category is 12.7 g CO₂ eq. MJ⁻¹ biomass produced. Assuming a preliminary estimation of the B. carinata capacity of translocated CO₂ (631 kg CO₂ ha⁻¹) from below-ground biomass into the soil, the emissions are reduced by up to 5.2 g CO₂ eq. MJ⁻¹.The production and transport are as far as a thermoelectric plant of the B. carinata biomass used as a solid fuel consumes 0.12 MJ of primary energy per 1 MJ of biomass energy stored. In comparison with other fossil fuels such as natural gas, it reduces primary energy consumption by 33.2% and greenhouse gas emission from 33.1% to 71.2% depending on whether the capacity of translocated CO₂ is considered or not.The results of the analysis support the assertion that B. carinata crops are viable from an energy balance and environmental perspective for producing lignocellulosic solid fuel destined for the production of energy in southern Europe. Furthermore, the performance of the crop could be improved, thus increasing the energy and environmental benefits.     

Renewable hydrogen generation by steam reforming of glycerol over zirconia promoted ceria supported catalyst

The study focuses on hydrogen production from steam reforming of glycerol over nickel based catalyst promoted by zirconia and supported over ceria. Catalyst was prepared by the wet-impregnation method and characterized by BET surface area analysis, X-ray diffraction technique and scanning electron microscopy (SEM) analysis. The performance of the catalyst was evaluated in terms of hydrogen yield, selectivity and glycerol conversion at 700 °C in a tubular fixed bed reactor. The effect of glycerol concentration in feed, space time (W/F_AO), temperature and time on stream (TOS) was analyzed for the catalyst Ni–ZrO₂/CeO₂ which showed the complete conversion of glycerol and high H₂ yield that corresponds to 3.95 mol of H₂ out of 7 mol. Thermodynamic analysis was also carried out using Aspen HYSYS for system having glycerol concentration 10 wt% and 20 wt% and experimental results were compared with thermodynamics. Kinetic study was carried out for the steam reforming of glycerol over Ni–ZrO₂/CeO₂ catalyst using the power law model. The values of activation energy and order of reaction were found to be 43.4 kJ/mol and 0.3 respectively.     

Kinetic model for the esterification of oleic acid catalyzed by zinc acetate in subcritical methanol

The esterification of oleic acid in subcritical methanol catalyzed by zinc acetate was investigated in a batch-type autoclave. The effect of reaction conditions such as temperature, pressure, reaction time and molar ratio of oleic acid to methanol on the esterification was examined. The oleic acid conversion reached 95.0% under 220 °C and 6.0 MPa with the molar ratio of methanol to oleic acid being 4 and 1.0 wt% zinc acetate as catalyst. A kinetic model for the esterification was established. By fitting the kinetic model with the experimental results, the reaction order n = 2.2 and activation energy E_a = 32.62 KJ/mol were obtained.     

Hydrogen production from steam and autothermal reforming of LPG over high surface area ceria

Steam and autothermal reforming reactions of LPG (propane/butane) over high surface area CeO₂ (CeO₂ (HSA)) synthesized by a surfactant-assisted approach were studied under solid oxide fuel cell (SOFC) operating conditions. The catalyst provides significantly higher reforming reactivity and excellent resistance toward carbon deposition compared to the conventional Ni/Al₂O₃. These benefits of CeO₂ are due to the redox property of this material. During the reforming process, the gas–solid reactions between the hydrocarbons present in the system (i.e. C₄H₁₀, C₃H₈, C₂H₆, C₂H₄, and CH₄) and the lattice oxygen (O_O^x) take place on the ceria surface. The reactions of these adsorbed surface hydrocarbons with the lattice oxygen (C_nH_m + O_O^x → nCO + m/2(H₂) + V_O + 2e′) can produce synthesis gas (CO and H₂) and also prevent the formation of carbon species from hydrocarbons decomposition reactions (C_nH_m ⇔ nC + 2mH₂). Afterwards, the lattice oxygen (O_O^x) can be regenerated by reaction with the steam present in the system (H₂O + V_O + 2e′ ⇔ O_O^x + H₂). It should be noted that V_O denotes as an oxygen vacancy with an effective charge 2⁺.At 900 °C, the main products from steam reforming over CeO₂ (HSA) were H₂, CO, CO₂, and CH₄ with a small amount of C₂H₄. The addition of oxygen in autothermal reforming was found to reduce the degree of carbon deposition and improve product selectivities by completely eliminating C₂H₄ formation. The major consideration in the autothermal reforming operation is the O₂/LPG (O/C molar ratio) ratio, as the presence of a too high oxygen concentration could oxidize the hydrogen and carbon monoxide produced from the steam reforming. A suitable O/C molar ratio for autothermal reforming of CeO₂ (HSA) was 0.6.     

Thermodynamic evaluation of methanol steam reforming for hydrogen production

Thermodynamic equilibrium of methanol steam reforming (MeOH SR) was studied by Gibbs free minimization for hydrogen production as a function of steam-to-carbon ratio (S/C = 0–10), reforming temperature (25–1000 °C), pressure (0.5–3 atm), and product species. The chemical species considered were methanol, water, hydrogen, carbon dioxide, carbon monoxide, carbon (graphite), methane, ethane, propane, i-butane, n-butane, ethanol, propanol, i-butanol, n-butanol, and dimethyl ether (DME). Coke-formed and coke-free regions were also determined as a function of S/C ratio.Based upon a compound basis set MeOH, CO₂, CO, H₂ and H₂O, complete conversion of MeOH was attained at S/C = 1 when the temperature was higher than 200 °C at atmospheric pressure. The concentration and yield of hydrogen could be achieved at almost 75% on a dry basis and 100%, respectively. From the reforming efficiency, the operating condition was optimized for the temperature range of 100–225 °C, S/C range of 1.5–3, and pressure at 1 atm. The calculation indicated that the reforming condition required from sufficient CO concentration (<10 ppm) for polymer electrolyte fuel cell application is too severe for the existing catalysts (T_r = 50 °C and S/C = 4–5). Only methane and coke thermodynamically coexist with H₂O, H₂, CO, and CO₂, while C₂H₆, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, CH₃OH, C₂H₅OH, C₃H₇OH, i-C₄H₉OH, n-C₄H₉OH, and C₂H₆O were suppressed at essentially zero. The temperatures for coke-free region decreased with increase in S/C ratios. The impact of pressure was negligible upon the complete conversion of MeOH.     

Transient behavior of a PEMFC

The transient behavior of a proton exchange membrane fuel cell (PEMFC) with porosity is investigated in this study using a two-phase, half-cell model. The thin film agglomerate approach is used to model the catalyst layer. Both vapor transport and liquid water transport in the PEMFC are examined in this study. Proton transport is much faster than the gaseous and liquid water transport. The ionic potential reaches a steady state level in ∼10⁻¹ s but liquid water transport takes ∼10 s. The variation of the ionic potential loss reaches a critical value, decreasing to a steady state, and is not monotonic. The gas diffusion layer (GDL) and the catalyst layer (CL) porosity, which can affect cell performance, have been carefully investigated. The current density rises rapidly within 10⁻² s, then remaining constant. After 1 s, this is affected by the cell voltage, GDL porosity, and CL porosity, and if the GDL porosity is below 0.4, the current density drops. For the gas diffusion layer porosity, the current density increases between ɛ_GDL = 0.2 and ɛ_GDL = 0.5, with increased GDL porosity. For the catalyst layer porosity, the optimum value appears between ɛ_CL = 0.06 and ɛ_CL = 0.1.     

Biodiesel production from jatropha oil (Jatropha curcas) with high free fatty acids: An optimized process

Response surface methodology (RSM) based on central composite rotatable design (CCRD) was used to optimize the three important reaction variables—methanol quantity (M), acid concentration (C) and reaction time (T) for reduction of free fatty acid (FFA) content of the oil to around 1% as compared to methanol quantity (M′) and reaction time (T′) and for carrying out transesterification of the pretreated oil. Using RSM, quadratic polynomial equations were obtained for predicting acid value and transesterification. Verification experiments confirmed the validity of both the predicted models. The optimum combination for reducing the FFA of Jatropha curcas oil from 14% to less than 1% was found to be 1.43% v/v H₂SO₄ acid catalyst, 0.28 v/v methanol-to-oil ratio and 88-min reaction time at a reaction temperature of 60 °C as compared to 0.16 v/v methanol-to-pretreated oil ratio and 24 min of reaction time at a reaction temperature of 60 °C for producing biodiesel. This process gave an average yield of biodiesel more than 99%. The fuel properties of jatropha biodiesel so obtained were found to be comparable to those of diesel and confirming to the American and European standards.     

Mixture of LiBF4 and lithium difluoro(oxalato)borate for application as a new electrolyte for lithium-ion batteries

An equimolar mixture of fluoroborate salts: LiBF₄ and lithium difluoro(oxalate)borate LiBF₂(C₂O₄) (MIX-LiFBs) was obtained from a simple one-step reaction of lithium oxalate and boron fluoride. Voltamperommetry shows that the salt obtained is stable in the potential range of 4.9 V. Impedance measurements of liquid electrolytes involving imidazolium ionic liquid and aliphatic carbonates have been carried out, which show the highest ionic conductivity of the order of 10^?3 S cm^?1 (and low activation energy of 0.14 eV) when using carbonates as the solvent. The mixture of fluoroborate salts MIX-LiFBs used as a component of solid polymer electrolytes provides much higher ionic conductivity values at high salt concentrations in “polymer-in-salt systems”. The conductivity of solid polymer electrolytes was considerably increased by adding a low-molecular-weight organic plasticizer.     

Biodiesel production from palm oil via heterogeneous transesterification

This paper presents the study of the transesterification of palm oil via heterogeneous process using montmorillonite KSF as heterogeneous catalyst. This study was carried out using a design of experiment (DOE), specifically response surface methodology (RSM) based on four-variable central composite design (CCD) with α (alpha) = 2. The transesterification process variables were reaction temperature, x₁ (50–190 °C), reaction period, x₂ (60–300 min), methanol/oil ratio, x₃ (4–12 mol mol^?1) and amount of catalyst, x₄ (1–5 wt%). It was found that the yield of palm oil fatty acid methyl esters (FAME) could reach up to 79.6% using the following reaction conditions: reaction temperature of 190 °C, reaction period at 180 min, ratio of methanol/oil at 8:1 mol mol^?1 and amount of catalyst at 3%.     

Lean methane premixed laminar flames doped by components of diesel fuel II: n-Propylcyclohexane

For a better understanding of the chemistry involved during the combustion of components of diesel fuel, the structure of a laminar lean premixed methane flame doped with n-propylcyclohexane has been investigated. The inlet gases contained 7.1% (molar) methane, 36.8% oxygen, and 0.81% n-propylcyclohexane (C₉H₁₈), corresponding to an equivalence ratio of 0.68 and a C₉H₁₈/CH₄ ratio of 11.4%. The flame has been stabilized on a burner at a pressure of 6.7 kPa (50 Torr) using argon as diluent, with a gas velocity at the burner of 49.2 cm/s at 333 K. Quantified species included the usual methane C₀–C₂ combustion products, but also 17 C₃–C₅ hydrocarbons, seven C₁–C₃ oxygenated compounds, and only four cyclic C₆₊ compounds, namely benzene, 1,3-cyclohexadiene, cyclohexene, and methylenecyclohexane. A new mechanism for the oxidation of n-propylcyclohexane has been proposed. It allows the proper simulation of profiles of most of the products measured in flames, as well as the satisfactory reproduction of experimental results obtained in a jet-stirred reactor. The main reaction pathways of consumption of n-propylcyclohexane have been derived from rate-of-production analysis.     

Study on a re-heat two-stage adsorption chiller – The influence of thermal capacitance ratio,overall thermal conductance ratio and adsorbent mass on system performance

Silica gel/water based adsorption cycles have a distinct advantage in their ability to be driven by heat of near-ambient temperature so that waste heat below 100 °C can be recovered. One interesting feature of refrigeration cycles driven by waste heat is that they do not use primary energy as driving source. From this context, some researchers investigated the performance of multi-stage adsorption refrigeration cycles those can be operated by heat source of temperature 60 °C or lower which are usually purged to the environment, with a heat sink of temperature at 30 °C. However, the performances of multi-stage systems are low. To improve system performance, an analytic investigation on a re-heat two-stage chiller is performed to clarify the effect of thermal capacitance ratio of the adsorbent and inert material of sorption element, overall thermal conductance ratio of sorption element and evaporator along with silica gel mass on the chiller performance. Results show that cycle performance is strongly influenced by the sorption elements overall thermal conductance values due to their severe sensible heating and cooling requirements resulting from batched cycle operation. The effect of thermal capacitance ratio (C_s/C_m) becomes significant with relatively higher mass of silica gel. It is also found that the chiller performance increases significantly in the range of silica gel mass from 4 to 20 kg.     

An experimental and kinetic modeling study of three butene isomers pyrolysis at low pressure

Pyrolysis of three butene isomers (C₄H₈) including 1-butene (1-C₄H₈), 2-butene (2-C₄H₈) and i-butene (iC₄H₈) were studied from 900 to 1900 K at low pressure. Synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry with molecular-beam sampling technique was used for isomeric identification of products and intermediates and also for concentration measurement. Based on the experimental results, a kinetic model consisting of 76 species and 232 reactions was developed to simulate mole fractions of species. The mole fraction profiles of pyrolysis species predicted by the model are in good agreement with the experimental measurements. The decomposition pathways of C₄H₈ are illustrated according to the reaction flux analysis. Our analysis demonstrates that reaction sequences 1-C₄H₈ → aC₃H₅ → aC₃H₄ → pC₃H₄ → C₂H₂, 2-C₄H₈ → saxC₄H₇ → 1,3-C₄H₆ → C₂H₃ → C₂H₂ and iC₄H₈ → iC₄H₇ → aC₃H₄ → pC₃H₄ → C₂H₂ are the major decomposition pathways of 1-butene, 2-butene and i-butene, respectively.     

Direct oxidation of jet fuels and Pennsylvania crude oil in a solid oxide fuel cell

A Cu-ceria solid oxide fuel cell (SOFC) is shown to generate electric power using jet fuels and Pennsylvania crude oil through direct oxidation of the fuels. The liquid fuels contained up to 910 ppm of sulfur and were injected into the anode compartment either with or without N₂ dilution. The performance of the fuel cell was stable over 30 h for jet fuels and Pennsylvania crude oil without N₂ dilution whereas N₂ dilution prolonged the stable power generation up to 100 h for jet fuel and up to 80 h for Pennsylvania crude oil. The generated power density was about 0.1 W cm⁻² for both fuels.     

Alkalinity and high total solids affecting H2 production from organic solid waste by anaerobic consortia

The optimization of total solids in the feed (%TS) and alkalinity ratio (γ) for H₂ production from organic solid wastes under thermophilic regime was carried out using response surface methodology based on a central composite design. The total solids levels were 20.9, 23.0, 28.0, 33.0 and 35.1% whereas the levels of alkalinity ratio (defined as g phosphate alkalinity/g dry substrate) were 0.15, 0.20, 0.30, 0.41 and 0.45. High levels of TS and γ affected in a negative way the H₂ productivity and yield; both response variables significantly increased upon decreasing the TS content and alkalinity ratio. The highest H₂ productivity and yield were 463.7 N mL/kg-d and 54.8 N mL/g VS_rem, respectively, predicted at 20.9% TS and alkalinity ratio 0.25 (0.11 g CaCO₃/g dry substrate). The alkalinity requirements for hydrogenogenic processes were lower than those reported for methanogenic processes (0.11 vs. 0.30 g CaCO₃/g COD). Adequate alkalinity ratio was necessary to maintain optimal biological activity for hydrogen production; however, excessive alkalinity negatively affected process performance probably due to an increase of osmotic pressure. Interestingly, reactor pH depended only on the alkalinity ratio, thus the buffer capacity was able to maintain a constant pH independently of TS levels. At γ = 0.15–0.30 the pHs were in the range 5.56–5.95, which corresponded to the highest hydrogen productivities and yields. Finally, the highest metabolite accumulation corresponded with the highest removal efficiencies but not with high H₂ productivities and yields. Therefore, it seems that organic matter removal was channeled toward solvent generation instead of hydrogen production at high TS and γ levels. This is the first study that shows the requirements of alkalinity in solid substrate fermentation conditions for H₂ production processes and their interaction with the content of total solids in the feed.     

An evaluation of biomass co-firing in Europe

Reduction of the emissions of greenhouses gases, increasing the share of renewable energy sources (RES) in the energy balance, increasing electricity production from renewable energy sources and decreasing energy dependency represent the main goals of all current strategies in Europe. Biomass co-firing in large coal-based thermal power plants provides a considerable opportunity to increase the share of RES in the primary energy balance and the share of electricity from RES in gross electricity consumption in a country. Biomass-coal co-firing means reducing CO₂ and SO₂, emissions and it may also reduce NO_x emissions, and also represents a near-term, low-risk, low-cost and sustainable energy development. Biomass-coal co-firing is the most effective measure to reduce CO₂ emissions, because it substitutes coal, which has the most intensive CO₂ emissions per kWh electricity production, by biomass, with a zero net emission of CO₂. Biomass co-firing experience worldwide are reviewed in this paper. Biomass co-firing has been successfully demonstrated in over 150 installations worldwide for most combinations of fuels and boiler types in the range of 50–700 MWe, although a number of very small plants have also been involved. More than a hundred of these have been in Europe. A key indicator for the assessment of biomass co-firing is intrduced and used to evaluate all available biomass co-firing technologies.     

Effect of confinement on heat transfer characteristics of a microscale impinging jet

This study experimentally investigates the local heat transfer characteristics of a microscale confined impinging air jet on a heated plate. The experimental parameters included the Reynolds number (Re_D = 1600–5600), the nozzle-to-plate spacing (H/D = 1–10), and the degree of confinement of the nozzle (D_C/D = 3, 6, 9, 12, 24, 48). The degree of confinement of the nozzle is a novel parameter. A reduction in the heat transfer rate was found for nozzles whose D_C/D values were 6, 9, 12, 24, and 48 as a result of the confinement effect at small nozzle-to-plate spacings. The confinement effect disappeared beyond H/D values of 2, 3, 4, 8, and 17 for D_C/D values of 6, 9, 12, 24, and 48, respectively. Flow characteristics were investigated by measuring pressure distributions along the wall. Subatmospheric pressure, which is evidence of the confinement effect, was observed for the confined nozzles. Correlations of the stagnation and average Nusselt numbers are proposed on the basis of the experimental results. Finally, a contour map that depicts the ratio of the Nusselt numbers of the unconfined and confined jets is presented. The contour map confirms that the confined jets have a smaller Nusselt number than the unconfined jets whenever the degree of confinement of the nozzle is large and the nozzle-to-plate spacing is small.     

Photocatalytic colour and COD removal in the distillery effluent by solar radiation

The photodegradation of distillery effluent has been studied for removal of colour and COD reduction in the presence of solar radiation. The influence of experimental parameters such as H₂O₂ concentration dosage, effluent COD concentration, TiO₂ catalyst and pH on colour and COD removal efficiency through solar photochemical process has been investigated. Maximum colour removal of the distillery effluent achieved was 79% at an H₂O₂ concentration of 0.3 M, pH 6, effluent COD concentration of 500 ppm and catalyst dosage of 0.1 g/L. The TiO₂/H₂O₂ system seems to be more efficient in comparison to the synergetic action that appears when using H₂O₂ and TiO₂. The photocatalytic degradation process using solar light as an irradiation source showed potential application for the colour removal of the distillery effluent treatment. Solar radiation can be an considered as an alternative, effective and economic energy carrier for the treatment of industrial effluent.     

Influence of oil on R-410A two-phase frictional pressure drop in a small U-type wavy tube

This study presents single-phase and two-phase pressure drop data with oil concentration C = 0, 1, 3 and 5% in a copper wavy tube having an inner diameter of 3.25 mm and a curvature radius of 6.35 mm. The ratio of frictional factor between U-bend in wavy tube and straight tube (f_C/f_S) is about 1.5 to 2.5 for Re = 2500 ∼ 25000. The effect of secondary flow is very crucial in the U-bend that it increases the pressure drop considerably. However, the effect of oil concentration on friction factor is negligible provided the properties are based on mixture. The ratio between two-phase pressure gradients of U-bend and straight tube is about 3. This ratio is increased with oil concentration and vapor quality. The oil effect on two-phase pressure drop is especially pronounced at high vapor quality because the effective oil concentration in liquid mixture is increased with vapor quality. The frictional two-phase multiplier for straight tube can be fairly correlated by using the Chisholm correlation. A modified two-phase friction factor based on the Geary correlation is also utilized to predict the frictional two-phase pressure gradient in U-bend. The predictions give a good agreement to the present oil–refrigerant data with a mean deviation of 12.92%.