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1.
Proton conductivity of Li 2SO 4-Al 2O 3 (LA) based electrolyte was determined under non-reducing dynamic conditions using current interruption technique. The performance of LA as electrolyte has been examined at 600 °C in a H 2S fuel cell with MoS 2-NiS as anode catalyst and NiO as cathode catalyst. XRD and XPS results show that Li 2SO 4 is not stable when heated in pure H 2S as it is reduced to Li 2S by hydrogen produced in equilibrium amounts from the thermal decomposition of H 2S. In contrast, under dynamic operation in a H 2S fuel cell the concentration of H 2 is much lower, the reduction reaction does not occur and, surprisingly, Li 2SO 4 is a chemically stable electrolyte. 相似文献
2.
Conversion of lignocellulosic material to monomeric sugars and finally ethanol must be performed at low cost, i.e. with limited consumption of chemicals, yeast and enzymes while still reaching high yields, if it is to compete with other fuel conversion processes. The objective of this study was thus to investigate ethanol production from steam-pretreated wheat straw by simultaneous saccharification and fermentation (SSF). The concentration of sulphuric acid in the impregnation liquid prior to pretreatment was kept low, 0.2%, and SSF was performed at low enzyme loadings, 3–14 FPU g −1 water-insoluble solids (WIS), and a low yeast concentration, 2 g L −1. The pretreatment conditions were optimised to give the highest overall glucose and xylose recovery after enzymatic hydrolysis of the residual WIS. The highest recovery of glucose (102%) and xylose (96%) was obtained after pretreatment at 190 °C for 10 min. Achieving high yields of glucose and xylose with the same pretreatment conditions is unusual and makes wheat straw a highly suitable raw material for bioethanol production. SSF was performed on whole slurry from straw pretreated under the optimal conditions. A high overall ethanol yield, 67% of the theoretical based on glucose in the raw material, was obtained. 相似文献
3.
A technique to produce biodiesel from mahua oil ( Madhuca indica) having high free fatty acids (19% FFA) has been developed. The high FFA level of mahua oil was reduced to less than 1% by a two-step pretreatment process. Each step was carried out with 0.30–0.35 v/v methanol-to-oil ratio in the presence of 1% v/v H 2SO 4 as an acid catalyst in 1-hour reaction at 60°C. After the reaction, the mixture was allowed to settle for an hour and methanol–water mixture that separated at the top was removed. The second step product at the bottom was transesterified using 0.25 v/v methanol and 0.7% w/v KOH as alkaline catalyst to produce biodiesel. The fuel properties of mahua biodiesel were found to be comparable to those of diesel and conforming to both the American and European standards. 相似文献
4.
A number of redox systems composed of carbon and bivalent metal-ferrites, MFe 2O 4(M = bivalent metal ions), were studied to find the most reactive and selective working materials for a thermochemical water-decomposition cycle combined with CO production from a carbon compound. Magnetite and Mg(II)-, Mn(II)-, Co(II)-, Ni(II)-, and Zn(II)-ferrites mixed with carbon powder have been screened for reactivity and selectivity in the CO-production step (first step) and subsequent water-decomposition step (second step). The Ni(II)-ferrite showed the most reactivity and selectivity for CO formation from carbon in the first step at temperatures above 700°C. The Ni(II)-ferrite could be completely reduced with carbon to the metallic phase of the Ni---Fe alloy and Ni in the first step although only a small portion of magnetite was reduced to wustite under similar conditions. The ferrites reduced in the first step were oxidized with water vapor to generate H 2 in the second step. The highest conversion of H 2O to H 2 was obtained using the Ni(II)-ferrite. The total amount of evolved H 2 using Ni(II)-ferrite was 10 times larger than for the magnetite at 500°C. The processes could be repeated using the phase transition between Ni(II)-ferrite and Ni---Fe alloy in the temperature range 700–800°C, with the highly efficient net reaction H 2O + C → H 2 + CO. 相似文献
5.
A newly isolated Citrobacter sp. Y19 for CO-dependent H 2 production was studied for its capability of fermentative H 2 production in batch cultivation. When glucose was used as carbon source, the pH of the culture medium significantly decreased as fermentation proceeded and H 2 production was seriously inhibited. The use of fortified phosphate at 60–180 mM alleviated this inhibition. By increasing culture temperatures (25–36°C), faster cell growth and higher initial H 2 production rates were observed but final H 2 production and yield were almost constant irrespective of temperature. Optimal specific H 2 production activity was observed at 36°C and pH 6–7. The increase of glucose concentration (1–20 g/l) in the culture medium resulted in higher H 2 production, but the yield of H 2 production (mol H 2/mol glucose) gradually decreased with increasing glucose concentration. Carbon mass balance showed that, in addition to cell mass, ethanol, acetate and CO 2 were the major fermentation products and comprised more than 70% of the carbon consumed. The maximal H 2 yield and H 2 production rate were estimated to be 2.49 molH 2/mol glucose and 32.3 mmolH 2/gcellh, respectively. The overall performance of Y19 in fermentative H 2 production is quite similar to that of most H 2-producing bacteria previously studied, especially to that of Rhodopseudomonas palustris P4, and this indicates that the attempt to find an outstanding bacterial strain for fermentative H 2 production might be very difficult if not impossible. 相似文献
6.
We prepared CuInSe 2 films by evaporating In 2Se 3 and Cu 2Se compounds instead of elemental sources. The resulting CuInSe 2 film grown at 680°C had a smooth and dense microstructure with the grain size of 2 3 μm. But the CuInSe 2 films were Cu-rich, with a low resistivity of about 0.1 Ω cm. So we conducted H 2 post annealing to control the electrical resistivity and composition of CuInSe 2 films. In a H 2 atmosphere, the resistivity increased to about 100 Ω cm by annealing at 350°C for 1 h. The resistivity decreased again when the annealing temperature was above 350°C. This resistivity change might be related to the contents of Cu, In, Se atoms and the valency states of Cu and In ions in the films. We discussed the reason of resistivity change caused by H 2 post annealing in this paper. 相似文献
7.
The oxidation of HCN and NH 3 with CO, CH 4, or H 2 addition has been studied in the temperature range between 600 to 1000°C. In most of the tests 10% oxygen was used. The experiments were carried out under well-defined conditions in a flow tube reactor made of quartz glass. The effects of NO addition and oxygen level have been tested. To study the importance of O/H radicals in the reaction mechanism and to confirm previous studies, iodine was added in some tests. A detailed chemical kinetic model was used to analyze the experimental data. In general, the model and experimental results are in good agreement. The results show that under the conditions tested CO significantly promotes NO and N 2O formation during HCN oxidation. During NH 3 oxidation carbon-containing gaseous species such as CO and CH 4 are important to promote homogeneous NO formation. In the system with CH 4 addition, the conversion of HCN to N 2O is lower compared to the other systems. In the HCN/NO/CO/O 2 system NO reduction starts at 700°C and the maximum reduction of approx. 40% is obtained at 800°C. For the NH 3/NO/CO/O 2 system the reduction starts at 750°C and the maximum reduction is 50% at 800°C. Iodine addition shifts the oxidation of HCN, NO, and N 2O formation as well as NO reduction to higher temperatures. Under the conditions tested, it was found that iodine mainly enhances the recombination of the O-radicals. No effect on NO formation was found in the HCN/CH 4/O 2 system when oxygen was increased from 6% to 10%, but when oxygen was increased from 2% to 6% NO formation decreased. The role of hydrocarbon radicals in the destruction of NO is likely to become important at low oxygen concentrations (2%) and at high temperatures (1000°C). 相似文献
8.
Methane was produced from H 2 and CO 2 using the acclimated-mixed methanogens in a 3.71 fermentor in batch culture at pH 7.2 and 37°C. The Fermentation kinetics parameter for the growth of methanogens, overall mass transfer coefficient of the reactor, and the conversion rate of H 2 and CO 2 to CH 4 by the acclimated-mixed culture were determined using the technique of Vega et al. The maximum specific growth rate (μ max) and H 2 specific consumption rate ( qmax) were found to be 0.064(h −1) and 104.8 (mmol h −1 g −1) respectively. Monod saturation constants for growth ( Kp) and for inhibition ( K′ p) were found to be 3.54 (kPa) and 0.57 (kPa), respectively. These findings indicate that without very low dissolved H 2 levels, the fermentations are carried out under μ max, and the specific uptake rate ( q) was almost not affected at any dissolved H 2 level in the range studied. The yield of CH 4 (Yp/s) was calculated to be 0.245 (mol CH 4 mol −1 H 2), which is near the stoichiometric value of 0.25. DH 2 was also measured using the Teflon tubing method and was in good agreement with those estimated by kinetic calculations. 相似文献
9.
采用碱性过氧化氢(AHP)体系对慈竹进行预处理,研究过氧化氢(H 2O 2)用量对竹材化学组分及酶水解得率的影响。利用X射线衍射(XRD)和傅里叶变换红外光谱仪(FTIR)分析预处理前后物料的物理和化学结构变化,采用二维核磁共振技术研究预处理物料中剩余木质素的化学结构。结果表明:AHP预处理过程中,随着H 2O 2用量(质量分数)的增加,竹材的葡聚糖含量(相对质量百分比)先增加后减少,木聚糖含量基本不变,而木质素含量整体呈减少趋势。AHP预处理能显著提升竹材的酶解效率,在纤维素酶用量为15 FPU/g葡聚糖,H 2O 2用量为7.0%时,预处理竹材的酶水解性能最高,葡聚糖和木聚糖酶水解得率分别为93.9%和100%。研究发现,慈竹木质素脱除率在H 2O 2用量达到2.0%后趋于稳定,为68.8%,继续增加H 2O 2用量,木质素脱除率无明显提升,对预处理竹材中剩余木质素进行2D-HSQC核磁分析,这部分难以脱除的木质素的化学结构为:64%的S单元、33.7%的G单元和61.6%的β——O——4键,其中S/G值为1.90。 相似文献
10.
This paper describes low temperature thin film Si growth by remote plasma chemical vapor deposition system for photovoltaic device applications. Using CaF 2/glass substrate, we were able to achieve an improved μc-Si film at a low process temperature of 300°C. The μc-Si film on CaF 2/glass substrate shows that a crystalline volume fraction of 65% and dark conductivity of 1.65×10 −8 S/cm with the growth conditions of 50 W, 300°C, 88 mTorr, and SiH 4/H 2=1.2%. XRD analysis on μc-Si/CaF 2/glass showed crystalline film growth in (1 1 1) and (2 2 0) planes. Grain size was enlarged as large as 700 Å for a μc-Si/CaF 2/glass structure. Activation energy of μc-Si film was given as 0.49 eV. The μc-Si films exhibited dark- and photo-conductivity ratio of 124. 相似文献
11.
Using variable temperature in situ 1H NMR spectroscopy on a mixture of LiNH 2 + LiH that was mechanically activated using high-energy ball milling, the dehydrogenation of the LiNH 2 + LiH to Li 2NH + H 2 was investigated. The analysis indicates NH 3 release at a temperature as low as 30 °C and rapid reaction between NH 3 and LiH at 150 °C. The transition from NH 3 release to H 2 appearance accompanied by disappearance of NH 3 confirms unambiguously the two-step elementary reaction pathway proposed by other workers. 相似文献
12.
A CaCl 2·6H 2O composition with a slight excess of water was found very stable on repeated phase change (over 1000 cycles) in a heat cycle test (35 18°C), using vertical glass tubes of 950 mm height. The mole ratio of water/ CaCl2, n, was 6.11, less than that of the peritectic composition ( n = 6.14). Dissolved NaCl had superior nucleating ability to that of common barium salts under certain experimental conditions. This result was attributed to a “memory effect.” The dissolved NaCl decreased the heat of vaporization of water about 15 per cent. NaF had a similar effect to that of NaCl, because NaF powder reacted with CaCl 2 in solution yielding NaCl and CaF 2. A brief discussion of CaCl 2·4H 2O formation is presented. 相似文献
13.
A recently discovered clostridial bacteria converts components of synthesis gas (CO, CO 2, H 2) into liquid products such as ethanol, butanol and acetic acid. Isolated from an agricultural lagoon, the stability and productivity characteristics of the bacteria were studied in a continuous 4.5 l bubble column bioreactor at 37°C using artificial blends of CO, CO 2, and N 2. Preliminary results on the rates of cell growth, substrate utilization, product formation, and yields of products and cells from CO are discussed. At steady state, apparent yields (mole C in products per mole CO consumed) of ethanol, butanol, and acetic acid were 0.15, 0.075 and 0.025, respectively, and the cell yield was 0.25 g/mol CO. The theoretical yield of ethanol is 0.33 if CO is only utilized for the production of ethanol. The experimental yield of CO 2 from CO was approximately 60% compared to the theoretical yield of 67% with ethanol as the sole product. As a comparison with another ethanol-producing bacteria, the results of a similar fermentation study using batch-grown Clostridium ljungdahlii showed yields of 0.062 for ethanol and 0.094 for acetic acid and a cell yield of 1.378 g/mol. 相似文献
14.
A new thermochemical cycle for H 2 production based on CeO 2/Ce 2O 3 oxides has been successfully demonstrated. It consists of two chemical steps: (1) reduction, 2CeO 2 → Ce 2O 3 + 0.5O 2; (2) hydrolysis, Ce 2O 3 + H 2O → 2CeO 2 + H 2. The thermal reduction of Ce(IV) to Ce(III) (endothermic step) is performed in a solar reactor featuring a controlled inert atmosphere. The feasibility of this first step has been demonstrated and the operating conditions have been defined ( T = 2000 °C, P = 100–200 mbar). The hydrogen generation step (water-splitting with Ce(III) oxide) is studied in a fixed bed reactor and the reaction is complete with a fast kinetic in the studied temperature range 400–600 °C. The recovered Ce(IV) oxide is then recycled in first step. In this process, water is the only material input and heat is the only energy input. The only outputs are hydrogen and oxygen, and these two gases are obtained in different steps avoiding a high temperature energy consuming gas-phase separation. Furthermore, pure hydrogen is produced (it is not contaminated by carbon products like CO, CO 2), thus it can be used directly in fuel cells. The results have shown that the cerium oxide two-step thermochemical cycle is a promising process for hydrogen production. 相似文献
15.
Porous, thin films of copper molybdenum sulfides (Cu 3+δMo 6S 7.9), that have been prepared by the technique of painting and subsequent reaction with mixed H 2/H 2S gases at 500 °C, have been used as a cathode material for lithium secondary batteries. The test cell comprised: Li/2 M LiClO 4 in PC-THF (4:6)/Cu 3+δMo 6S 7.9 (porous, thin film). The discharge reaction proceeded via the intercalation of lithium ions into the structural interstices of the cathode material. The first discharge curve of the cell showed that the porous film could incorporate up to 18 lithium ions per formula unit. The capacity of the thin film was four times higher than that previously reported for powder or pressed-pellet electrodes. The theoretical energy density was 675 W h kg−1, i.e., higher than that of TiS2 (455 W h kg−1) which is one of the best materials for high-energy lithium batteries. From X-ray diffraction studies of the lithium incorporated in the thin film at each discharge step, it is suggested that there are four incorporation reactions of lithium ions into the cathode. Finally, cycling tests have been conducted at room temperature. 相似文献
16.
A transition metal cluster electrocatalyst based on Os x(CO) n was synthesized by pyrolysis of Os 3(CO) 12 in 1,2-Dichlorobenzene (b.p.≈180°C) under inert atmosphere (N 2). The electrocatalytic parameters of the oxygen reduction reaction (ORR) for an Os x(CO) n catalyst were studied with a rotating disk electrode in 0.5 MH 2SO 4 electrolyte. The diffusion coefficient and solubility of O 2 in 0.5 MH 2SO 4 were calculated. Koutecky–Levich analysis of the linear voltamperometry data showed that the reaction follows first-order kinetics and the value of the Koutecky–Levich slope indicates a multielectron charge transfer during the ORR. The value of the Tafel slope obtained from the mass transfer corrected Tafel plots is 131 mV/decade. The performance of the catalyst in a H 2/O 2 PEM fuel cell cathode was evaluated and found to be nearly as good as that of Pt. 相似文献
17.
Novel, highly active MgH 2-Mg-systems, which can be used both in synthetic chemistry and as high temperature hydrogen storage materials, have been studied at the Max-Planck-Institut für Kohlenforschung in Mülheim-Ruhr, West Germany, since 1978. The original preparative procedure was based on the hydrogenation of magnesium under mild conditions (20–60°C. 1–80 bar) in an organic solvent and in the presence of a soluble organo transition metal catalyst. This process yields a MgH 2 storage material with outstanding kinetic properties (w.r.t. the release and take-up of H 2 at normal pressure and 230–350°C), a high specific surface area (100–130 m 2g −1) and a high storage capacity for hydrogen (7 wt%). It suffers, however, from the disadvantage of being pyrophoric. Subsequently, MgH 2-Mg---H 2-storage materials have been developed using magnesium powder doped with small quantities of transition metal complexes or organotransition metal compounds and these can be safely handled in air. The new MgH 2---Mg-systems can be used for hydrogen storage, hydrogen purification and separation and heat storage, provided a 300–350°C heat source is available to release the hydrogen. Their main features include low material and production costs, highly satisfactory kinetics, high hydrogen and heat capacity, relative insensitivity toward impurities in hydrogen (H 2O, O 2, CO, etc.) and stability toward air. 相似文献
18.
The conditions under which an oxygen photocatalyst can improve multiple band gap (semiconductor) solar energy water splitting are probed. Recently, we provided evidence that previous models significantly underestimated the magnitude of H 2 fuel which may be generated by solar energy, and demonstrated a bipolar band gap solar system electrolyzing water at VH2OH2O→H2+1/2O2; VH2O>E°H2O=E°O2−E°H2;E°H2O(25°C)=1.229 V at an unprecedented 18.3% solar energy conversion efficiency. Three conditions are shown in which oxygen photocatalyst addition can further improve this process; (i) a reduction in VH2O; (ii) at VH2O, capability to sustain electrolysis currentsgenerated photocurrents, and (iii) catalyst activation at hν photo-O2> hν photo-bipolar. We show that RuS 2 with 1% Fe is capable of meeting these conditions. 相似文献
19.
The catalytic properties and the long-term performance of Raney-NiTi2 catalysts being used in H 2 electrodes of alkaline H 2---O 2 fuel cells can be significantly improved by slow air oxidation and subsequent annealing in an H 2 atmosphere at 300°C. Individual reaction steps are investigated by means of impedance measurements. Theoretical estimations, on the basis of a simple equivalent circuit of a supported electrode, result in a frequency-response relationship which is in very good agreement with the experimental data referring to the relevant frequency range of 10 −3−10 −1 Hz. A method to evaluate the impedance spectra is described in some detail. Calculated and measured impedance data are in good agreement, thus indicating the validity of the charge transfer resistance, the diffusion resistance, as well as the chemisorption capacity and the double-layer capacity. Experiments on the influence of catalyst annealing in an H 2 atmosphere at 350°C show a strong increase in the charge transfer resistance and an obvious decrease in the diffusion resistance, depending on the annealing time. A similar influence on the chemisorption capacity and the double-layer capacity is not observed. 相似文献
20.
The cathode is a key component in low temperature solid oxide fuel cells. In this study, composite cathode, 75 wt.% Sm 0.5Sr 0.5CoO 3 (SSC) + 25 wt.% Sm 0.2Ce 0.8O 1.9 (SDC), was applied on the cermet supported thin SDC electrolyte cell which was fabricated by tape casting, screen-printing, and co-firing. Single cells with the composite cathodes sintered at different temperatures were tested from 400 to 650 °C. The best cell performance, 0.75 W cm −2 peak power operating at 600 °C, was obtained from the 1050 °C sintered cathode. The measured thin SDC electrolyte resistance Rs was 0.128 Ω cm 2 and total electrode polarization Rp(a + c) was only 0.102 Ω cm 2 at 600 °C. 相似文献
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