Kinetic effect of Pd additions on the hydrogen uptake of chemically-activated ultramicroporous carbon

The effect of mixing chemically-activated ultramicroporous carbon (UMC) with Pd nanopowder is investigated. Results show that Pd addition doubles the rate of hydrogen uptake, but does not enhance the hydrogen capacity or improve desorption kinetics. The effect of Pd on the rate of hydrogen adsorption supports the existence of the hydrogen spillover mechanism in the Pd - UMC system.     

Ultramicroporous carbon granules with narrow pore size distribution for efficient CH4 separation from coal-bed gases

The adsorptive separation of CH₄ from low-grade coal-bed gas can be performed at decentralized and remote coal mines, and it uses more energy- and is cost-efficient than the traditional cryogenic distillation process. Herein, we present a facile method to prepare ultramicroporous carbon granules with a narrow pore-size distribution at 0.5–0.6 nm. To our knowledge, such centered and uniform pore-size distribution in carbon granules has never been reported. The carbon granules can be directly utilized in adsorption columns without a granulation or pelletization process. The granular oil-tea-shell-derived porous carbon (GOC-2) exhibited a record-high CH₄ uptake of 1.82 mmol/g and CH₄/N₂ selectivity of 5.8 at 1.0 bar and 298 K among carbon granules. The excellent CH₄/N₂ separation performances were confirmed from the results of dynamic breakthrough experiments and pressure swing adsorption simulations. This work provides a novel strategy for developing ultramicroporous carbon granules and guides the future design of efficient CH₄/N₂ separation adsorbents.     

Influence of carbon black on decompression failure and hydrogen permeation properties of filled ethylene‐propylene–diene–methylene rubbers exposed to high‐pressure hydrogen gas

Eight carbon black (CB)‐filled ethylene–propylene–diene–methylene linkage (EPDM) rubbers were manufactured by varying the content and type of CB. Then, the relationship among crack damage caused by high‐pressure hydrogen decompression, the hydrogen permeation properties, and the mechanical properties of the rubbers was investigated. The hydrogen gas permeability of the rubbers decreased with an increase in the CB content and depended little on primary particle size. In contrast, the hydrogen gas diffusivity and solubility depended on both the CB content and primary particle size, that is, the hydrogen gas diffusivity decreased with an increase in the CB content and a decrease in the primary particle size, and the hydrogen gas solubility increased with an increase in the CB content and a decrease in the primary particle size. As for the mechanical properties, the CB‐filled rubbers were more strongly reinforced by an increase in the CB content and a decrease in the primary particle size. The crack damage by high‐pressure hydrogen decompression became larger as the ratio of the hydrogen gas solubility to estimated internal pressure at crack initiation relating to the mechanical properties became larger. As a smaller CB particle increases the hydrogen gas solubility of EPDM rubbers, while at the same time it reinforces the rubbers, the crack damage in the CB‐filled rubbers was not influenced by the primary particle size. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel Electrochemical Hydrogen Separation Device Using Phosphoric Acid Membrane Cell

Abstract

State-of-the-art hydrogen separation technologies operate at/or near ambient temperatures and are not considered very effective with gases containing low concentrations of hydrogen (such as coal-gas) and are susceptible to common impurities such as H₂S, H₂O, and NH₃. Energy Research Corporation is developing an alternate, versatile process for hydrogen separation from any hydrogen-containing gas. This novel process involves oxidation of hydrogen at a gas diffusion anode to hydrogen ions, transportation of the ions under applied electrical field to a cathode, and reduction of the hydrogen ions at the cathode to hydrogen gas. The device offers many attractive features, including high hydrogen recovery (>90%), high product purity (>99%), tolerance to a variety of impurities, flexible product pressure, efficient operation with very dilute gases, negligible pressure loss, and wide operating pressure range including atmospheric. The feasibility of this electrochemical hydrogen separation device (EHSD) has been demonstrated at ERC using hydrogen concentrations as high as 75% (reformer product) and as low as 10% (process purge). The operating principle, design, and performance (current-potential relationship, product gas purity, effect of feed hydrogen concentration on hydrogen recovery and power requirements) of this process are presented in this paper.     

CAUSE OF PINHOLES AND SOME RELATED DEFECTS IN ENAMEL COATINGS ON CAST IRON*

The confusion in identifying hydrogen as the predominating cause of certain defects in enamel on cast iron has been due largely to the close association of carbon and hydrogen in cast iron and steel. The principal relation of carbide and graphite to enameling defects is the release of hydrogen from the carbon during enamel firing. The much-discussed “chill layer” therefore is important chiefly because this layer often contains hydrogen that is bound to the carbon in the cementite. Experiments show that when hydrogen is absent, regardless of the depth or nature of the surface chill, no pinholing or blistering results during firing at 725°C. Sources of the hydrogen that causes the defacement are found chiefly in melting and in casting. The low oxygen pressure of molten cast iron favors hydrogen absorption. Moisture in the atmosphere, in the charge, or chemically combined in the rust on scrap provides the greatest quantities of the gas, and moisture and organic materials in the mold are also prolific sources of hydrogen for absorption by the iron. At ordinary temperatures, rusting is often harmful. Flushing the melt with a dry, hydrogen-free gas, such as nitrogen, removes the dissolved hydrogen, and defects during subsequent enameling will not occur unless hydrogen is obtained later from other sources. Chipping phenomena probably are caused chiefly by hydrogen effusion, just as are analogous defects in sheet-steel enameling.     

N,N-二甲基甘氨酸的合成研究

本文报道了合成N,N-二甲基甘氨酸的新方法。以甘氨酸为原料,Pd/C为催化剂,采用常温常压氢化方法,产物收率达95%。     

Palladium-hydrogen interaction on supported palladium catalysts of different metal dispersions

Palladium-hydrogen interaction on supported Pd catalysts of different metal dispersions has been studied by hydrogen chemisorption and back-sorption, and by temperature-programmed desorption (TPD) of either deuterium or hydrogen from the Pd surface after different initial gas dosages. Pd interacts with three hydrogen species whose amounts vary with the metal dispersion and with the dosage pressure. The amount of hydrogen strongly adsorbed on the Pd surface increases with the metal dispersion but is unaffected by the hydrogen pressure. The amount of hydrogen absorbed in the bulk of Pd is significant with a poorly dispersed catalyst, particularly when the hydrogen pressure is higher than about 10 Torr, but decreases with the metal dispersion. Hydrogen weakly bound with Pd shows two characteristic TPD peaks, whose intensity depends on the metal dispersion and the initial gas dosage. The peak at 270-330 K, assigned to the recombination of absorbed hydrogen with surface hydrogen, is large with a poorly dispersed catalyst and grows with the initial hydrogen dosage. The intensity of the peak at 215-226 K is not affected by the metal dispersion or by the hydrogen dosage. It has been concluded that an analysis of the intrinsic properties of Pd catalysts should be based on an understanding of the hydrogen species associated with the catalysts.     

Studies on the mechanism of the hydrogen electrode reaction by means of deuterium tracer—II. The reaction mechanism

The exchange reaction between deuterium gas and light water was conducted with Ni, Rh, and Pt catalyst. Through analysis of isotopic composition of the gaseous hydrogen during the exchange reaction, the exchange rates of the individual steps, H₂ ? 2H(a) and H(a) + B ? H⁺B + e, of the hydrogen electrode reaction were determined at various hydrogen pressures and solution pH's, where H(a) is a hydrogen adatom and B = H₂O or OH^?. The rates of the steps were widely different among the metals studied but, throughout these metals, the hydrogen pressure dependence of the rate of the first step was with the power of 1·0–0·9, and that of the second step, 0·2–0·5. Both the rates were independent of solution pH. Generally, the former step is virtually rate-determining under low hydrogen pressures, whereas the latter takes over the role with increasing hydrogen pressure. Under ordinary pressures, the first step is virtually rate-determining on Pt but neither step is singly rate-determining on Rh and Ni.     

Hydrogen Supply Options and Issues

Methods of hydrogen gas production for hydrogenation are discussed: steam reforming of natural gas, electrolysis, by-product clean-up by PSA (pressure swing absorption) or scrubbing, and others. Hydrogen can be obtained from a customer-owned hydrogen plant or as a merchant product supplied by an industrial gas supplier. The merchant product can be delivered in trailers as gas, liquid-high (up to 2,200 psig), low pressure (up to 130 psig), or supplied over the fence from a pipeline or hydrogen generating plant. Several factors must be considered in selecting an optimum supply, including availability and cost of capital and of operating labor, use patterns, average demand, instantaneous demand, use pressure, growth projections, and purity requirements. Recent field test data have shown that increased hydrogen purity can improve the hydrogenation processes. To whom correspondence should be addressed.     

Formation Mechanism of Porous Alumina With Oriented Cylindrical Pores Fabricated by Unidirectional Solidification

Porous alumina whose pores were aligned in one direction was fabricated by the unidirectional solidification method under a pressurized hydrogen atmosphere. The porous structure is formed at the solid–liquid interface during solidification due to a hydrogen solubility gap at the melting point. The hydrogen gas is dissolved into molten alumina according to Sieverts' law and insoluble gas that corresponds to the amount of solubility gap evolves from the solid phase at the solid–liquid interface during the unidirectional solidification to form the pores. The porosity and pore size of the solidified samples decreased with increasing total pressure where the environmental gas consisted of pure hydrogen or hydrogen–argon mixed gases. There is a reverse proportion relation between the pore diameter and the total pressure according to Boyle's law.     

Interaction of hydrogen with carbon coils at low temperature

Hydrogen was adsorbed on carbon coils under 10 MPa hydrogen gas at liquid nitrogen temperature. The equilibrium pressure of hydrogen desorbed from the as-grown carbon coils with an amorphous structure was three to four times greater than those of multiwall carbon nanotubes (MWNT) and active carbons (AC). The heat treatment of the carbon coils at 850 °C contributed to an increase in hydrogen adsorption by 20% compared to the as-grown carbon coils. On the other hand, the adsorption of hydrogen gas on the carbon coils decreased significantly after heat treatment at a temperature higher than 1000 °C due to formation of capsule-like carbon composed of 10-20 layers on the surface of the carbon coils.     

Hydrogenation of anthracene over active carbon-supported nickel catalyst

Hydrogen transfer behavior over active carbon and carbon-supported Ni catalyst was examined in the hydrogenation of anthracene with three kinds of hydrogen sources: hydrogen gas, hydrogen-donor tetralin and the combination of both. In tetralin, active carbon itself provided higher conversions of anthracene in the temperature range of 350–400°C than Ni/C catalyst, while under the pressure of hydrogen gas, the addition of Ni metal onto active carbon remarkably promoted the hydrogenation of anthracene, providing a complete conversion at 300°C. When both tetralin and hydrogen gas were used together, an apparent improvement in both conversion and product distribution was observed with active carbon, whereas with Ni/C catalyst, the rate of hydrogen consumed in the hydrogenation was apparently low in the temperature range of 300–320°C, compared to that observed at the same temperatures using hydrogen gas alone.     

Atypical hydrogen uptake on chemically-activated, ultramicroporous carbon

Hydrogen adsorption on ultramicroporous carbon was investigated at near-ambient temperatures using volumetric and gravimetric methods. The results showed that the main process, physisorption, is accompanied by a slow process of different nature, that causes slow uptake at high pressures and hysteresis on desorption. The combined result is unusually high levels of hydrogen uptake at near-ambient temperatures and pressures (e.g. up to 0.8 wt.% at 25 °C and 2 MPa). The heat of adsorption corresponding to the slow process leading to high uptake (17-20 kJ/mol) is higher than usually reported for carbon materials; the adsorption kinetics is slow, and the isotherms exhibit pronounced hysteresis. These unusual properties were attributed to contributions from polarization-enhanced physisorption induced by traces of alkali metals residual from chemical activation. The results support the hypothesis that polarization-induced physisorption in high surface area carbons modified with traces of alkali metal ions is an alternate route for increasing the hydrogen storage capacity of carbon adsorbents.     

空心玻璃微球高压贮氢技术

利用炉内成球技术制备的亚毫米量级空心玻璃微球进行实验,系统研究了玻璃微球高压贮氢技术.玻璃微球直径150～250 μm,壁厚0.9～4.0 μm.采用气体渗透法充氢,在高温时,气体扩散进入微球内,温度降低后气体不容易扩散出来,即可实现贮氢.通过控制外界温度和气氛可实现氢气的贮存和释放.对于直径200 μm,壁厚1 μm的空心玻璃微球,在350℃充气的平衡时间约6～10 h,充气平衡后,微球内外压基本相等.在室温条件下,微球的保气半寿命约40～50 d.对于直径200 μm,壁厚2 μm的空心玻璃微球,球内氢气最高压力可达20～25 MPa,单位质量贮氢效率为13%～16％.     

合成氨贮罐气膜法氢回收的设计和操作

采用膜分离技术回收合成氨贮罐气中的氢组分,返回合成氨系统作为加氢脱硫单元的氢源。设计膜分离器时,膜面积增加使渗透气氢浓度降低而经济效益上升。当贮罐气流量1300Nm3/h、渗透气绝压为0.8MPa,氢产品浓度为85%-90%时,可以获得约287.7×104Yuan/a以上的经济效益,投资回收期在17个月内。在膜分离器操作时,氢氮选择性系数降低以及贮罐气压力降低都会引起氢回收率降低,导致经济效益下降,二者对氢浓度的影响不明显。     

The influence of hydrogen donors on the pyrolysis of a bituminous coal as studied by in situ e.s.r. spectroscopy

The effect of hydrogen gas, a hydrogen donor solvent (tetralin) and a non-donor solvent (decane) on the pyrolysis (to 500 °C) of a bituminous coal, before and after extraction with chloroform, has been studied by in situ e.s.r. in a flowing gas cell at atmospheric pressure. It was found that hydrogen gas at 1 bar had an insignificant effect on the course of the reaction, as determined by free radical population measurements, compared with nitrogen gas. In contrast, both tetralin and decane change the free radical populations developed during pyrolysis, and the extent of the induced change varies upon chloroform extraction of the coal. These results are discussed with reference to current coal liquefaction models, and are interpreted in terms of the chemical and physical interactions of the solvent with the coal.     

低温吸附法分离氢同位素

液氮温度下用分子筛Y在自行设计的单塔变压吸附装置上进行氢氘气体分离的研究,考察了流量与压力对分离效果的影响,在气体总压力0.40 MPa、总流量129.79 cm3/min与吸附床长度1.0 m时氢氘气体之间的分离因子可达到1.52。然而压力为0.013 9 MPa与0.017 5 MPa时D2与H2在分子筛Y上的平衡吸附量比值仅分别为1.18和1.17。结合平衡吸附和动态分离之间的差异,表明吸附法能够有效分离氢同位素气体的机理是基于动力学效应。     

氢气锅炉的特点与安全运行经验

氢气锅炉虽然是燃气锅炉,但与普通的煤气或天然气锅炉相比有更高的安全性要求.以天津LG渤海化学公司离子膜烧碱装置2台45 t/h氢气锅炉为例,介绍氢气锅炉的结构、自动控制的特点和安全操作经验.     

Reactive extraction for preparation of hydrogen peroxide under pressure

The preparation of hydrogen peroxide from anthrahydroquinone by reactive extraction was investigated. The integration process of oxidation of anthrahydroquinone by air and extraction of hydrogen peroxide from the organic phase with water was carried out in a sieve plate column under pressure. The conversion of anthrahydroquinone increased with increasing pressure resulting in an increase of hydrogen peroxide concentration in the aqueous phase. However, no change in extraction efficiency of hydrogen peroxide was observed. A mathematical model for gas-liquid-liquid reactive extraction was established. In the model, the effects of pressure and gas superficial velocity on reaction were considered. With increasing gas superficial velocity, the conversion of anthrahydroquinone increased, and the fraction of hydrogen peroxide extracted reached a plateau with a maximum of 72.94%. However, both the conversion of anthrahydroquinone and the fraction of hydrogen peroxide extracted decreased with increasing organic phase superficial velocity.     

Performance Comparison of Different Separation Systems for H2 Recovery from Catalytic Reforming Unit Off‐Gas Streams

The performance of pressure swing adsorption (PSA), membrane separation, and gas absorption systems for H₂ recovery from refinery off‐gas stream was studied by simulation‐based data. The PSA process was simulated using adsorbents of silica gel and activated carbon for removing heavy and light hydrocarbons. The mole fraction profiles of all components and the relationship between hydrogen purity and recovery as a function of feed pressure were examined. The solution‐diffusion model was applied for modeling and simulation of a one‐stage membrane process. The gas absorption process with a tower tray was simulated at sub‐zero temperature and the correlation between hydrogen purity and recovery as a function of tower pressure and temperature was evaluated at different solvent flow rates.