Formulating and optimizing a combustion pathways for oil shale and its semi-coke

Enhanced technologies from oil recovery to unconventional fuels - oil shale, oil sands and extra-heavy oil – have in common complex chemical reactions processes. This paper is about the formulation and optimization of the chemical mechanism especially in oil shale and semi-coke combustion. The Levenberg–Marquardt algorithm was used to minimize the error between estimated values and the thermogravimetric data for combustion mechanisms of 4-steps and 3-steps proposed for the oil shale and its semi-coke respectively. The kinetic parameters such as reaction order, pre-exponential factor, activation energy and stoichiometric coefficients that affect drying, pyrolysis, oxidation and decarbonation reactions were estimated with success. The values of activation energies were 54–67 kJ mol^?1 for oil shale drying, 62–65 kJ mol^?1 for pyrolysis reaction, up to 100 kJ mol^?1 for Fixed Carbon (FC) oxidation reaction, and 162–418 kJ mol^?1 for decarbonation reaction. Regarding to the semi-coke combustion, the activation energies were 33 kJ mol^?1 for drying reaction, 211 kJ mol^?1 for oxidation reaction and 291 kJ mol^?1 for decarbonation reaction. The chemical reactions suggest reaction order superior to one, except to the decarbonation reaction at 3 K min^?1. Considering the estimated parameters, as well as a heating rate at 3 K min^?1, an oil shale containing about 20 wt.% of organic matter and 34.6 wt.% of CaCO₃, the species mass fractions formed during combustion process were 3.4 wt.% of FC, 10.6 wt.% of Oil, 3.3 wt.% of HC and 1.8 wt.% of CO. The fraction of CO₂ formed accounts a total of 21.6 wt.%. For a semi-coke containing 3.4 wt.% of FC and 40.6 wt.% of CaCO₃, its combustion formed 2.1 wt.% of CO. The CO₂ fraction from oxidation and decarbonation reactions accounts 10.2 wt.%, considering that the stoichiometric mass coefficient γ = 0.75 in decarbonation reaction.     

High voltage stability of nanostructured thin film catalysts for PEM fuel cells

This paper provides a comparative evaluation of electrocatalyst surface area stability in PEM fuel cells under accelerated durability testing. The two basic electrocatalyst types are conventional carbon-supported dispersed Pt catalysts (Pt/C), and nanostructured thin film (NSTF) catalysts. Both types of fuel cell electrocatalysts were exposed to continuous cycling between 0.6 and 1.2 V, at various temperatures between 65 and 95 °C, with H₂/N₂ on the anode and cathode, while periodic measurements of electrochemical surface area were recorded as a function of the number of cycles. The NSTF electrocatalyst surface areas were observed to be significantly more stable than the Pt/C electrocatalysts. A first order rate kinetic model was applied to the normalized surface area changes as a function of number of cycles and temperature, and two parameters extracted, viz. the minimum stable surface area, S_min, and the activation energy, E_a, for surface area loss in this voltage range. S_min was found to be 10% versus 66%, and E_a 23 kJ mole⁻¹ versus 52 kJ mole⁻¹, for Pt/C versus NSTF-Pt, respectively. The loss of surface area in both cases is primarily the result of Pt grain size increases, but the Pt/C XRD grain sizes increase significantly more than the NSTF grain sizes. In addition, substantial peak shifts occur in the Pt/C CVs, which ultimately end up aligning with the NSTF peak positions, which do not change substantially due to the voltage cycling. NSTF catalysts should be more robust against shut down/start-up, operation near OCV and local H₂ starvation effects.     

Coal-gasification kinetics derived from pyrolysis in a fluidized-bed reactor

Coal pyrolysis and gasification reactions were carried out in a fluidized-bed reactor (0.1 m i.d. by 1.6 m height) over a temperature range from 1023 to 1173 K at atmospheric pressure. The overall gasification kinetics for the steam–char and oxygen–char reactions were determined in a thermobalance reactor. The compositions of the product gases from the coal-gasification reactions are 30–40% H₂, 23–28% CO, 27–35% CO₂ and 6–9% CH₄ with heating values of 2000–3750 kJ m⁻³. The heating value increases with increasing temperature and steam/coal ratio but decreases with increasing air/coal ratio. Our kinetic data derived from the two-phase theory on coal gasification in a thermobalance reactor and coal pyrolysis in a fluidized bed may be used to predict the product-gas compositions.     

Creep behavior of Ni-12 wt.% Al anodes for molten carbonate fuel cells

Ni-12 wt.% Al anodes are fabricated for use in molten carbon fuel cells by tape casting and sintering. Sintering is performed in three steps, first at 1200 °C for 10 min in argon, then at 700 °C for 2.5 h in a partial oxidation atmosphere (P_H2/P_H2O=10⁻²), and finally at 950 °C for 5 min, 30 min or 1.5 h in hydrogen. Three anodes with different phases or microstructures are produced at different reduction times. One anode contains three phases, namely Ni–Al solid solution, Ni₃Al, and Al₂O₃. The amount of Al₂O₃ is extremely small at 5 min. A second anode also contains the three phases with the amount of Al₂O₃ comparable with that of Ni₃Al at 30 min. Third anode contains two phases, i.e. Ni–Al solid solution and Al₂O₃ formed at 1.5 h. The creep strains measured for the three anodes after a 100-h creep test are practically the same with an average value of 0.85%.     

A comparative analysis of woody biomass and coal for electricity generation under various CO2 emission reductions and taxes

Mitigating global climate change via CO₂ emission control and taxation is likely to enhance the economic potential of bioenergy production and utilization. This study investigated the cost competitiveness of woody biomass for electricity production in the US under alternative CO₂ emission reductions and taxes. We first simulated changes in the price of coal for electricity production due to CO₂ emission reductions and taxation using a computable general equilibrium model. Then, the costs of electricity generation fueled by energy crops (hybrid poplar), logging residues, and coal were estimated using the capital budgeting method. Our results indicate that logging residues would be competitive with coal if emissions were taxed at about US$25 Mg⁻¹ CO₂, while an emission tax US$100 Mg⁻¹ CO₂ or higher would be needed for hybrid poplar plantations at a yield of 11.21 dry Mg ha⁻¹ yr⁻¹ (5 dry tons ac⁻¹ yr⁻¹) to compete with coal in electricity production. Reaching the CO₂ emission targets committed under the Kyoto Protocol would only slightly increase the price of fossil fuels, generating little impact on the competitiveness of woody biomass. However, the price of coal used for electricity production would significantly increase if global CO₂ emissions were curtailed by 20% or more. Logging residues would become a competitive fuel source for electricity production if current global CO₂ emissions were cut by 20–30%. Hybrid poplar plantations would not be able to compete with coal until emissions were reduced by 40% or more.     

A shock tube study of the rate constants of HO2 and CH3 reactions

HO₂ and CH₃ are major intermediate species presented during the oxidation of natural gas at intermediate temperatures and high pressures. Previous theoretical calculations have identified several product channels for HO₂ and CH₃ reactions, with CH₃ + HO₂ → CH₃O + OH and CH₃ + HO₂ → CH₄ + O₂ being the dominant reaction pathways. Both reaction pathways play an important role in the kinetics of CH₄ oxidation as CH₃ + HO₂ → CH₃O + OH is a chain-branching reaction whereas CH₃ + HO₂ → CH₄ + O₂ a chain termination reaction.H₂O₂/CH₄/Ar mixtures were shock-heated to a temperature between 1054 and 1249 K near 3.5 atm to initiate the reaction. OH radicals yielded from H₂O₂ thermal decomposition react with H₂O₂ and CH₄ respectively to produce HO₂ and CH₃ in the reacting system. Using laser absorption spectroscopy, time-histories of H₂O, OH and HO₂ were measured behind reflected shock waves. The rate constant of reaction CH₃ + HO₂ → CH₃O + OH was determined to be 6.8 × 10¹² cm³ mol^?1 s^?1 with an uncertainty factor of 1.4. The rate constant of the competing CH₃ + HO₂ → CH₄ + O₂ reaction was determined to be 4.4 × 10¹² cm³ mol^?1 s^?1, with an uncertainty factor of 2.1. In addition, the rate constants of two other major reactions of the reacting system, H₂O₂ (+M) → 2OH (+M) and OH + CH₄ → CH₃O + OH, were found to have excellent agreement with values recommended in literature.     

Economics of switchgrass and miscanthus relative to coal as feedstock for generating electricity

Switchgrass (Panicum virgatum) serves as a model dedicated energy crop in the U.S.A. Miscanthus (Miscanthus x giganteus) has served a similar role in Europe. This study was conducted to determine the most economical species, harvest frequency, and carbon tax required for either of the two candidate feedstocks to be an economically viable alternative for cofiring with coal for electricity generation. Biomass yield and energy content data were obtained from a field experiment conducted near Stillwater, Oklahoma, U.S.A., in which both grasses were established in 2002. Plots were split to enable two harvest treatments (once and twice yr^?1). The switchgrass variety ‘Alamo’, with a single annual post-senescence harvest, produced more biomass (15.87 Mg ha^?1 yr^?1) than miscanthus (12.39 Mg ha^?1 yr^?1) and more energy (249.6 million kJ ha^?1 yr^?1 versus 199.7 million kJ ha^?1 yr^?1 for miscanthus). For the average yields obtained, the estimated cost to produce and deliver biomass an average distance of 50 km was $43.9 Mg^?1 for switchgrass and $51.7 Mg^?1 for miscanthus. Given a delivered coal price of $39.76 Mg^?1 and average energy content, a carbon tax of $7 Mg^?1 CO₂ would be required for switchgrass to be economically competitive. For the location and the environmental conditions that prevailed during the experiment, switchgrass with one harvest per year produced greater yields at a lower cost than miscanthus. In the absence of government intervention such as requiring biomass use or instituting a carbon tax, biomass is not an economically competitive feedstock for electricity generation in the region studied.     

Effects of synthesis conditions on the structural and electrochemical properties of layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via the hydroxide co-precipitation method LIB SCITECH

The uniform layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material for lithium ion batteries was prepared by using (Ni_1/3Co_1/3Mn_1/3)(OH)₂ synthesized by a liquid phase co-precipitation method as precursor. The effects of calcination temperature and time on the structural and electrochemical properties of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ were systemically studied. XRD results revealed that the optimal prepared conditions of the layered Li[Ni_1/3Co_1/3Mn_1/3]O₂ were 850 °C for 18 h. Electrochemical measurement showed that the sample prepared under the above conditions has the highest initial discharge capacity of 162.1 mAh g⁻¹ and the smallest irreversible capacity loss of 9.2% as well as stable cycling performance at a constant current density of 16 mA g⁻¹ between 3 and 4.3 V versus Li at room temperature.     

PVDF-g-PSSA and Al2O3 composite proton exchange membranes

Poly(vinylidene fluoride) grafted polystyrene sulfonated acid (PVDF-g-PSSA) membranes doped with different amount of Al₂O₃ (PVDF/Al₂O₃-g-PSSA) were prepared based on the solution-grafting technique. The microstructure of the membranes was characterized by IR-spectra and scanning electron microscope (SEM). The thermal stability was measured by thermal gravity analysis (TGA). The degree of grafting, water-uptake, proton conductivity and methanol permeability were measured. The results show that the PVDF-g-PSSA membrane doped with 10% Al₂O₃ has a lower methanol permeability of 6.6 × 10⁻⁸ cm² s⁻¹, which is almost one-fortieth of that of Nafion-117, and this membrane has moderate proton conductivity of 4.5 × 10⁻² S cm⁻¹. Tests on cells show that a DMFC with the PVDF/10%Al₂O₃-g-PSSA has a better performance than Nafion-117. Although Al₂O₃ has some influence on the stability of the membrane, it can still be used in direct methanol fuel cells in the moderate temperature.     

Reactivity of pulverized coals during combustion catalyzed by CeO2 and Fe2O3

Effects of CeO₂ and Fe₂O₃ on combustion reactivity of several fuels, including three ranks of coals, graphite and anthracite chars, were investigated using thermo-gravimetric analyzer. The results indicated that the combustion reactivity of all the samples except lignite was improved with CeO₂ or Fe₂O₃ addition. It was interesting to note that the ignition temperatures of anthracite were decreased by 50 °C and 53 °C, respectively, with CeO₂ and Fe₂O₃ addition and that its combustion rates were increased to 15.4%/min and 12.2%/min. Ignition temperatures of lignite with CeO₂ and Fe₂O₃ addition were 250 °C and 226 °C, and the combustion rates were 12.8% and 19.3%/min, respectively. When compared with those of lignite without catalysts, no obvious catalytic effects of the two catalysts on its combustion reactivity were revealed. The results from the combustion of the three rank pulverized coals catalyzed by CeO₂ and Fe₂O₃ indicated significant effects of the two catalysts on fixed carbon combustion. And it was found that the higher the fuel rank, the better the catalytic effect. The results of combustion from two kinds of anthracite chars showed obvious effects of anthracite pyrolysis catalyzed by CeO₂ and Fe₂O₃ on its combustion reactivity.     

Synthesis and characterization of high tap-density layered Li[Ni1/3Co1/3Mn1/3]O2 cathode material via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ was prepared by mixing uniform co-precipitated spherical metal hydroxide (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with 7% excess LiOH followed by heat-treatment. The tap-density of the powder obtained was 2.38 g cm⁻³, and it was characterized using X-ray diffraction (XRD), particle size distribution measurement, scanning electron microscope-energy dispersive spectrometry (SEM-EDS) and galvanostatic charge–discharge tests. The XRD studies showed that the material had a well-ordered layered structure with small amount of cation mixing. It can be seen from the EDS results that the transition metals (Ni, Co and Mn) in Li[Ni_1/3Co_1/3Mn_1/3]O₂ are uniformly distributed. Initial charge and discharge capacity of 185.08 and 166.99 mAh g⁻¹ was obtained between 3 and 4.3 V at a current density of 16 mA g⁻¹, and the capacity of 154.14 mAh g⁻¹ was retained at the end of 30 charge–discharge cycles with the capacity retention of 93%.     

Investigation of hydrogen production from boron compounds for pem fuel cells

This paper presents a comprehensive study of hydrogen production from sodium borohydride (NaBH₄), which is synthesized from sodium tetraborate (Na₂B₄O₇) decomposition, for proton exchange membrane (PEM) fuel cells. For this purpose, Na₂B₄O₇ decomposition reaction at 450–500 °C under hydrogen atmosphere and NaBH₄ decomposition reaction at 25–40 °C under atmospheric pressure are selected as a common temperature range in practice, and the inlet molar quantities of Na₂B₄O₇ are chosen from 1 to 6 mol with 0.5 mol interval as well. In order to form NaBH₄ solution with 7.5 wt.% NaBH₄, 1 wt.% NaOH, 91.5 wt.% H₂O, the molar quantities of NaBH₄ are determined. For a PEM fuel cell operation, the required hydrogen production rates are estimated depending on 60, 65, 70 and 75 g of catalyst used in the NaBH₄ solution at 25, 32.5 and 40 °C, respectively. It is concluded that the highest rate of hydrogen production per unit area from NaBH₄ solution at 40 °C is found to be 3.834 × 10⁻⁵ g H₂ s⁻¹ cm⁻² for 75 g catalyst. Utilizing 80% of this hydrogen production, the maximum amounts of power generation from a PEM fuel cell per unit area at 80 °C under 5 atm are estimated as 1.121 W cm⁻² for 0.016 cm by utilizing hydrogen from 75 g catalyst assisted NaBH₄ solution at 40 °C.     

Novel organic–inorganic poly (3,4-ethylenedioxythiophene) based nanohybrid materials for rechargeable lithium batteries and supercapacitors

Synthesis and characterization of poly (3,4-ethylenedioxythiophene) (PEDOT) interleaved between the layers of crystalline oxides of V and Mo is discussed with special emphasis on their application potential as electrodes for rechargeable Li batteries and supercapacitors. The expansion of the interlayer spacing of crystalline oxides (for example, V₂O₅ causes expansion from 0.43 to 1.41 nm) is consistent with a random layer stacking structure. These hybrid nanocomposites when coupled with a large-area Li foil electrode in 1 M LiClO₄ in a mixture of ethylene and dimethylcarbonate (1:1, v/v), give enhanced discharge capacity compared to pristine oxides. For example a discharge capacity of ∼350 mAh g⁻¹, in the potential range 4.2–2.1 V (versus Li⁺/Li) is obtained for PEDOT–V₂O₅ hybrid which is significantly large compared to that for simple Li-intercalated V₂O_5. The improvement of electrochemical performance compared with that of pristine oxides is attributed to higher electric conductivity, enhanced bi-dimensionality and increased structural disorder. Although these conducting polymer-oxide hybrids delivered more than 300 mAh g⁻¹ in the potential range 1.3–4.3 V, their cycle life needs further improvements to realize their commercial potential. Similarly, the double layer capacitance of MoO₃ increases from ∼40 mF g⁻¹ to ∼300 F g⁻¹ after PEDOT incorporation in the interlayer gap of MoO₃ under similar experimental conditions and the nanocomposite displays intriguing effects with respect to electrochemical Li⁺ insertion. The PEDOT–MoO₃ nanocomposite appears to be a promising electrode material for non-aqueous type supercapacitors.     

Hydrogen storage properties of nanocrystalline Mg–Ce/Ni composite

Mg–Ce alloy was prepared by induction melting under vacuum, hydrided firstly and then Mg–Ce/Ni composite was obtained by mechanical milling Mg–Ce hydrides under Ar for 50 h with addition of nano-sized Ni powder. XRD results showed CeMg₁₂ formed in melted alloy. CeMg₁₂ disappeared and CeH_2.53 emerged during subsequent hydriding. The phase composition was not changed during ball milling process. Compared with Mg and Mg/Ni, Mg–Ce/Ni composite showed significant hydriding/dehydriding performance without any prior activation. The enthalpy of hydride formation for Mg–10.9 wt.% Ce/10 wt.% Ni composite was −70.58 kJ mol⁻¹ H₂. Improved hydrogen storage properties were attributed to the catalytic effect of addition of nano-sized Ni particles and existence of CeH_2.53, as well as the grain refinement, defects, etc. in the material introduced by ball milling process.     

Li+ ion diffusion in LiMn2O4 thin film prepared by PVP sol–gel method

LiMn₂O₄ thin film (1 μm thick) was prepared on a gold substrate by the PVP sol–gel method. The electrochemical properties of the thin-film electrode were studied in an electrolyte 1 mol dm⁻³ LiClO₄/(ethylene carbonate + diethyl carbonate). The prepared LiMn₂O₄ showed a good charge–discharge performance, and the capacity fade was ca. 20% during 200 cycles. The Li⁺ ion diffusion in the LiMn₂O₄ thin film was investigated by means of potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. The chemical diffusion coefficients were estimated to be 10⁻⁸ to 10⁻¹⁰ cm² s⁻¹.     

Synthesis and characterizations of Li[CrxLi(1−x)/3Mn2(1−x)/3]O2 (0.15 ≤ x ≤ 0.3) cathode materials in rechargeable lithium batteries

A series of Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ (0.15 ≤ x ≤ 0.3) cathode materials was prepared by citric acid-assisted, sol–gel process. Sub-micron sized particles were obtained and the X-ray diffraction (XRD) results showed that the crystal structure was similar to layered lithium transition metal oxides (R-3m space group). The electrochemical performance of the cathodes was evaluated over the voltage range 2.0–4.9 V at a current density of 7.947 mA g⁻¹. The Li_1.27Cr_0.2Mn_0.53O₂ electrode delivered a high reversible capacity of up to 280 mAh g⁻¹ during cycling. Li[Cr_xLi_(1−x)/3Mn_2(1−x)/3]O₂ yielded a promising cathode material.     

Effect of organic acids and nano-sized ceramic doping on PEO-based solid polymer electrolytes

Composite solid polymer electrolytes (CSPEs) consisting of polyethyleneoxide (PEO), LiClO₄, organic acids (malonic, maleic, and carboxylic acids), and/or Al₂O₃ were prepared in acetonitrile. CSPEs were characterized by Brewster Angle Microscopy (BAM), thermal analysis, ac impedance, cyclic voltammetry, and tested for charge–discharge capacity with the Li or LiNi_0.5Co_0.5O₂ electrodes coated on stainless steel (SS). The morphologies of the CSPE films were homogeneous and porous. The differential scanning calorimetric (DSC) results suggested that performance of the CSPE film was highly enhanced by the acid and inorganic additives. The composite membrane doped with organic acids and ceramic showed good conductivity and thermal stability. The ac impedance data, processed by non-linear least square (NLLS) fitting, showed good conducting properties of the composite films. The ionic conductivity of the film consisting of (PEO)₈LiClO₄:citric acid (99.95:0.05, w/w%) was 3.25 × 10⁻⁴ S cm⁻¹ and 1.81 × 10⁻⁴ S cm⁻¹ at 30 °C. The conductivity has further improved to 3.81 × 10⁻⁴ S cm⁻¹ at 20 °C by adding 20 w/w% Al₂O₃ filler to the (PEO)₈LiClO₄ + 0.05% carboxylic acid composite. The experimental data for the full cell showed an upper limit voltage window of 4.7 V versus Li/Li⁺ for CSPE at room temperature.     

Novel heat transfer fluids for direct immersion phase change cooling of electronic systems

We describe the use of computer-aided molecular design (CAMD) and figure of merit (FOM) analysis to identify new heat transfer fluids for direct immersion cooling of electronic systems. Thirty-five new fluids, with thermophysical properties in the range 320 K < T_b < 370 K, k > 0.09 W m^?1 K^?1 and H_vap > 35 kJ mol^?1, were identified via a CAMD approach. Further analysis of these 35 fluids led to the selection of 1,1,1-trifluoro-3-methylpentane (C₆H₁₁F₃) for experimental evaluation. C₆H₁₁F₃ was synthesized from commercially available precursors, and its thermophysical properties were measured to verify its FOM. Next, the pool boiling performance of a mixture of 7 wt.% C₆H₁₁F₃ + 93 wt.% HFE 7200 was determined using a 10 mm × 10 mm grooved Si thermal test chip coated with copper. An improvement of 7% in the critical heat flux (CHF) was obtained, suggesting that C₆H₁₁F₃ is worth further examination as a candidate for direct immersion phase change cooling applications.     

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.