PORCELAIN ENAMELING CHARACTERISTICS OF SOME COMMON FERROUS METALS *

The experimental evidence gathered during the investigation of seven ferrous metals shows that there is a relationship between the hydrogen behavior and enameling characteristics of these metals. This relationship can best be explained on the basis of diffusibility of atomic hydrogen through these metals and is in no way affected by the total carbon content or by the stabilization of the carbon through the formation of carbides other than iron carbide. These added metallic elements may decrease the diffusibility of hydrogen through steel in two ways, namely, (1) they may have a poisoning or reverse catalytic effect on hydrogen diffusion or (2) they may “plug the gaps” in the crystal lattice and by so doing render the metal impenetrable to atomic hydrogen diffusion.     

Electrochemical hydrogen pump for recirculation of hydrogen in a fuel cell stack

The objective of this work is to evaluate the use of an electrochemical hydrogen pump for recirculation of hydrogen in a fuel cell stack. The hydrogen pump needed about 130 mV at 0.5 A cm⁻², primarily because of the cell resistance (0.18 Ω cm²). This voltage loss was higher than a fuel cell voltage gain resulting from hydrogen recirculation. However, if one pumping cell is used for 10 active cells this means 13 mV loss per cell (or about 2%) which may be an acceptable voltage penalty. A stack with hydrogen recirculation should operate with less voltage fluctuation and should need purging less often than a stack operating with a dead-end mode of hydrogen supply. An additional benefit of hydrogen purification may be achieved in the systems with a fuel processor where operation in a dead-end mode is not possible. Attention must be paid to water management when designing and operating a hydrogen pump within a fuel cell stack.     

Mechanism of coal hydrogenation—liquefaction; Effect of temperature and coal particle size

The effect of coal particle size, hydrogen pressure and temperature on the extent of coal conversion in an entrained flow reactor is presented. Coal hydrogenation is done by feeding dry coal with ZnCl₂ catalyst into a continuous stream of hydrogen. The hydrogen-coal stream enters a long, small internal-diameter reactor (coiled tube reactor) controlled at about 500°C and 12.4 MPa hydrogen. At these conditions the coal particles become plastic and sticky. The hydrogen provides the energy to force the sticky coal particles through the reactor. Conversion of 85% of the coal to liquids and gases is easily attained. A physical mechanism is presented based on the unreacted-core-shrinking model. This mechanism aids in the explanation of the effect of process variables on reaction rates. Projections beyond the range of the variables studied are presented. These projections indicate that the pressure of coal liquefaction processes may be reduced by (1) the use of dry coal particles and (2) the reduction of the particle size. Significant reaction rates may be attained at pressures as low as 0.7 MPa by proper adjustment of particle size and temperature.     

Limiting Phenomena in the Reaction of Fluorine with Hydrogen

Reactions involving energy branching and deceleration by the end product were studied using as an example the reaction of fluorine with hydrogen. It has been shown that for such reactions, entrance into the autoignition region determined by static conditions (reagent concentration, pressure, and temperature) due to variation in the pressure of the mixture may be or may not be accompanied by mixture autoignition. The parameter determining the behavior of a particular mixture is the rate of variation in the mixture pressure. A process of fast (in the range of seconds) preparation of fluorocarbon mixtures with minimal yield of hydrogen fluoride is substantiated.     

Conformations in partly ionized poly(methacrylic acid): 1. Ionic hydrogen bonds in syndiotactic chains

Comparisons of u.v. spectrophotometric titrations of some dicarboxylic acids, ‘conventional’ poly(methacrylic acid) and poly(acrylic acid) suggest that ionic or acid-salt hydrogen bonds form between adjacent carboxyl groups in racemic dyads in partly ionized forms of poly(methacrylic acid). The ionic hydrogen bonds form in tt conformations of the dyads. The maximum concentration of ionic hydrogen bonds occurs at 50% ionization in pure syndiotactic chains in the presence of electrolyte to give a chain having four-bond repeating units. Bonds 1 and 2 are presumed to be fixed in trans-trans conformations while bonds 3 and 4 retain some conformational freedom although this is somewhat reduced as a consequence of side group rotations necessary for hydrogen bonding. While ionic hydrogen bonds may form across meso dyads in t? conformations, isotactic chains incorporating ionic hydrogen bonds are predicted to be less stable than the corresponding syndiotactic chains.     

Hydrogen embrittlement of Zn-, Zn–Ni-, and Cd-coated high strength steel

Sacrificial coatings, such as Zn and Cd, are used to protect steel against corrosion. During the electrodeposition of metals, hydrogen is evolved due to electrolysis. The evolved hydrogen may diffuse outward and become trapped in the substrate/coating interface or migrate inward into the steel lattice causing delayed embrittlement when the component is subjected to stress. This study reports two principal variables for Zn, Zn–Ni, and Cd coatings: (i) the quantity of hydrogen absorbed by the coating and substrate by vacuum thermal desorption and (ii) the permeability of the coating material to hydrogen by electrochemical permeation. The findings were analyzed in correlation with the microstructural characteristics of both the coating material and the coating/substrate interface. With Zn–Ni, both coating process and coating material combined to significantly reduce the risk of internal hydrogen embrittlement by (i) introducing the least amount of hydrogen during the electrodeposition process and (ii) by the ease with which hydrogen can be extracted by baking due to the presence of cracks in the coating.     

Optimization of refinery hydrogen network based on chance constrained programming

Deterministic optimization approaches have been developed and used in the optimization of hydrogen network in refinery. However, uncertainties may have a large impact on the optimization of hydrogen network. Thus the consideration of uncertainties in optimization approaches is necessary for the optimization of hydrogen network. A novel chance constrained programming (CCP) approach for the optimization of hydrogen network in refinery under uncertainties is proposed. The stochastic properties of the uncertainties are explicitly considered in the problem formulation in which some input and state constraints are to be complied with predefined probability levels. The problem is then transformed to an equivalent deterministic mixed-integer nonlinear programming (MINLP) problem so that it can be solved by a MINLP solver. The solution of the optimization problem provides comprehensive information on the economic benefit under different confidence levels by satisfying process constraints. Based on this approach, an optimal and reliable decision can be made, and a suitable compensation between the profit and the probability of constraints violation can be achieved. The approach proposed in this paper makes better use of resources and can provide significant environmental and economic benefits. Finally, a case study from a refinery in China is presented to illustrate the applicability and efficiency of the developed approach.     

PEM fuel cell current regulation by fuel feed control

We demonstrate that the power output from a PEM fuel cell can be directly regulated by limiting the hydrogen feed to the fuel cell. Regulation is accomplished by varying the internal resistance of the membrane-electrode assembly in a self-draining fuel cell with the effluents connected to water reservoirs. The fuel cell functionally operates as a dead-end design where no gas flows out of the cell and water is permitted to flow in and out of the gas flow channel. The variable water level in the flow channel regulates the internal resistance of the fuel cell. The hydrogen and oxygen (or air) feeds are set directly to stoichiometrically match the current, which then control the water level internal to the fuel cell. Standard PID feedback control of the reactant feeds has been incorporated to speed up the system response to changes in load. With dry feeds of hydrogen and oxygen, 100% hydrogen utilization is achieved with 130% stoichiometric feed on the oxygen. When air was substituted for oxygen, 100% hydrogen utilization was achieved with stoichiometric air feed. Current regulation is limited by the size of the fuel cell (which sets a minimum internal impedance), and the dynamic range of the mass flow controllers. This type of regulation could be beneficial for small fuel cell systems where recycling unreacted hydrogen may be impractical.     

Hydrogen concentration profiles and velocity distributions in a reducing argon-hydrogen plasma

The purpose of this study is to establish a spectroscopic diagnostic of an argon-hydrogen reducing plasma, the hydrogen being injected into the initially formed argon plasma. From calculations using the spectral line intensities measured for H(α), H(β) as well as argon lines 4,259Å and 6,965Å, information is obtained on thermal equilibrium attainment after hydrogen injection. Also, hydrogen concentration profiles are calculated, from which hydrogen counterdiffusion zones are defined allowing the use of simplified diffusion equations, so that velocity profile distributions are obtained. The hydrogen concentration profiles clearly show the mixing pattern taking place around the injection ports, while the temperature profiles for hydrogen and argon evolve toward common limiting values attained when thermal equilibrium between both gas species is accomplished. Calculations show that the error should be of the order of 20% on velocities and 15% for the concentration measurements. The method used here may conceivably be extended to high temperature chemical raections (gas-solid reaction or pyrolysis, for instance).     

Combined pre-reforming-desulfurization of high-sulfur fuels for distributed hydrogen applications

A major challenge facing the future Hydrogen Economy is the issue of hydrogen fuel delivery and distribution. In the near term, it may be necessary to deliver high-density hydrocarbon fuels (e.g., diesel fuel) directly to the end-user (e.g., a fueling station) wherein it is reformed to hydrogen, on demand. This approach has the advantages of utilizing the existing fuel delivery infrastructure, and the fact that more energy can be delivered per trip when the tanker is filled with diesel instead of liquefied or compressed hydrogen gas. Reforming high-sulfur hydrocarbon fuels (e.g., diesel, JP-8, etc.) is particularly challenging due to rapid deactivation of conventional reforming catalysts by sulfurous compounds. A new on-demand hydrogen production technology for distributed hydrogen production is reported. In this process, first, the diesel fuel is catalytically pre-reformed to shorter chain hydrocarbons (C₁-C₆) before being fed to the steam reformer, where it is converted to syngas and further to high-purity hydrogen gas. In the pre-reformer, most sulfurous species present in the fuel are converted to H₂S. Desulfurization of the pre-reformate gas is carried out in a special regenerative redox system, which includes an iron-based scrubber coupled with an electrolyzer. The integrated pre-reformer and sulfur-scrubbing unit operated successfully for 100 h at desulfurization efficiency of greater than 95%.     

Consequences of biotransformation of plant secondary metabolites on acid-base metabolism in mammals—A final common pathway?

Regulation of acid-base homeostasis is essential for mammals and birds. Biotransformation and metabolism of absorbed plant secondary metabolites (PSMs) results in the production of organic acids that threaten acid-base homeostasis. Consequently these acids must be buffered and excreted from the body. The production of an acid load from detoxified PSMs should occur in herbivorous mammals and birds and with most PSMs and so may provide a unifying theme to explain many effects of PSMs on animal metabolism. Since the organic acids will be largely ionized at physiological pH, disposal of the hydrogen ion and the organic anion may proceed independently. Most hydrogen ions (H⁺) from organic acids are eliminated by one or more of three ways: (1) when they react with bicarbonate in the extracellular fluid to form carbon dioxide and the carbon dioxide is exhaled, (2) when they bind to dibasic phosphate and are excreted by the kidney as monobasic phosphate, and (3) when they are buffered and retained in the skeletal system. The secretion of phosphate ions and ammonium excretion are two ways in which the kidney replaces bicarbonate ions that have been eliminated as carbon dioxide. Secretion in the kidney tubule is an important means of excreting excessive organic anions rapidly. This process is saturable and may be subject to competition from a variety of different metabolites. Lagomorphs have limited capacity to form new bicarbonate from ammonium excretion and may therefore be obliged to excrete other cations such as sodium to balance the excretion of organic anions from PSMs. Acidemia has wide-ranging impacts on animals but browsing mammals and birds may have to break down muscle tissues to provide for urinary ammonium in order to generate bicarbonate for buffering. Acidemia also can affect the extent of urea recycling. Animals consuming browse diets may have to regulate feeding so that the rate of formation of hydrogen ions does not exceed the rate of disposal. The mechanisms by which this could occur are unknown.     

Recovery of deuterium from hydrogen–deuterium mixture using palladium

The applicability of palladium for the separation of hydrogen isotopes (hydrogen and deuterium) is evaluated systematically by generating isotherm data and conducting column experiments in a laboratory set-up. Effect of various parameters such as concentration of the isotopic mixture, particle size, eluent flow rate, etc. is studied experimentally. A fixed-bed chromatographic model is developed and validated using the experimental data. The model is further used to predict the performance of a multi-column configuration for large-scale separation. Chromatographic separation is thus found to be a promising technique to achieve the required purity and hence it may be clubbed with the existing systems (e.g. cryogenic distillation) to obtain enhanced performance.     

Properties of 2-hydroxyethylamine acylimide aqueous solution — unusual clouding phenomenon

Surface active and solution properties of 2-hydroxyethylamine acylimides, such as dimethyl-2-hydroxyethylamine acylimides, bis(2-hydroxyethyl) methylamine acylimides, and tris(2-hydroxyethyl) amine acylimides were investigated. An unusual clouding phenomenon, which depends upon time after dissolving, concentration of aminimide, as well as temperature of the aqueous solution is discussed. The phenomenon may be explained by slow protonation to the negative center of the aminimide and slow rate to attain the equilibration of hydration by strong hydrogen bonding between a negative center and a hydroxyl group of the aminimide. The facts that the aminimide can exist in different forms in solid state as well as in solution, and that the forms are reversible by treating them with water or a nonpolar solvent, may also be explained by strong hydrogen bonding.     

The role of hydrogen in metal electrodeposition processes

The incidence of codeposition of hydrogen during electrodeposition, described as a cathodic inefficiency in plating processes, is reviewed and the effects of hydrogen on the deposits produced discussed. Characteristic electrode features leading to hydrogen evolution and hydrogen absorption are discussed and the causes of hydrogen embrittlement, which may be regarded as essentially electrochemical in origin, are defined.     

HYDROGEN-BONDING COMPETITION IN ENTRAINER COSOLVENT MIXTURES

In chemical separation processes such as supercritical extraction, the use of an entrainer cosolvent can dramatically improve selectivity and yield. Ideally, an cntrainer cosolvent should solvate only the desired solute, pulling it from the feed. Prospective entrainers therefore are chosen for their hydrogen bonding tendency. But not all cosolvents are effective entrainers, and an entrainer that is effective for one application may not be effective for others. The effectiveness of a cosolvent as an entrainer can be limited by competition among various hydrogen bonding species in the mixture.

In this paper, experiment and theory are presented for hydrogen bonding in entrainer cosolvent mixtures. Concentrations of monomelic and hydrogen bonded species are determined using FTIR spectroscopy and these data are modeled using the Associated Perturbed Anisotropic Chain Theory (APACT). Liquid solvents with hydrogen bonding properties similar to those of supercritical fluids are used.

Using APACT, it is shown that the equilibrium constant, derived from activities, can be written as the product of a temperature dependent term and the ratio of concentrations: K = (RT)^v Π C^vi_i. This gives a statistical mechanical basis for the empirical observation that the equilibrium constant can be calculated as the ratio of concentrations of monomeric and hydrogen bonded species.     

CHIPS, FISH SCALES, AND SHINERS, IV

The effusion of hydrogen from enameled steel to cause fractures in the enamel was investigated in an attempt to show that this gas may cause defects that range from plate-like fractures, or “chips,” through the known types of fish scales to the most minute shiner. The difference in the appearance of these defects was found to depend principally on differences in (1) the physical properties of the enamel, (2) the metal-enamel bond, and (3) the rate, quantity, and localization of the hydrogen effusion. Reboiling is shown to be related to fish scaling and to the other fracture-type defects because all are primarily hydrogen functions. The principal source of the critical quantities of hydrogen necessary to cause the defects is often found in the water of hydration in the dried slip, and the injection of hydrogen by that water during firing is demonstrated by experiment just as was shown for blister-type defects (see this issue, pp. 180-90). The prevention of fracture-type defects is discussed, and some novel effects of protective surface oxidation are illustrated.     

Photochemical studies of rancidity: The mechanism of rancidification

A theory is set forth for the mechanism of rancidification which is based on a disrupted photosynthesis in the case of vegetable oils and on the photosensitizing action of haemoglobin or other animal pigment that may be present in small amounts in animal fats such as lard. Nascent hydrogen is believed to be liberated from the photosensitizer (chlorophyll or animal pigment) which unites with molecular oxygen to form loosely combined or nascent hydrogen peroxide. This unstable peroxide unites with the unsaturated bond of the tri-glyceride to form a glyceride peroxide which in turn splits into an aldehyde and forms the rancid compound. Food Research Division, Contribution No. 386.     

Influence of toluene contamination at the hydrogen Pt/C anode in a proton exchange membrane fuel cell

For fuel cells run on hydrogen reformate, traces of hydrocarbon contaminants in the hydrogen gas may be a concern for the performance and lifetime of the fuel cell. This study focuses on the influence of low concentrations of toluene on the adsorption and deactivation chemistry in a proton exchange membrane (PEM) fuel cell. For this purpose cyclic voltammetry and electrochemical impedance spectroscopy (EIS) techniques were employed. Results from adsorption and desorption (by oxidation or reduction) experiments performed in a humidified nitrogen or hydrogen flow in a fuel cell test cell with a mass spectrometer system connected to the outlet are presented. The influence of adsorption potential, temperature, and humidity are discussed. The results show that toluene adsorbs on the catalyst surface in a broad potential window, up to at least 0.85 V versus RHE at 80 °C. Adsorbed toluene oxidizes to CO₂ with peak potentials above 1.0 V for temperatures below 95 °C. Some desorption of toluene (or reduced products) may take place at potentials below 0 V. In a hydrogen flow, toluene contamination in per mille concentrations leads to a continuous growth of the charge transfer resistance, while a 10-fold dilution of the toluene concentration resulted in a low and constant charge transfer resistance even for longer exposures. This indicates that a competition between toluene and hydrogen may take place on the active platinum surface at the anode.     

One‐Pot Conversion of Cephalosporin C to 7‐Aminocephalosporanic Acid in the Absence of Hydrogen Peroxide

The main drawback in the production of 7‐aminocephalosporanic acid (7‐ACA) at the industrial level is the inactivation of the enzymes implicated in the process due to the presence of hydrogen peroxide during the reaction. As an alternative, we have developed the conversion of cephalosporin C to 7‐ACA in a single reactor without the presence of hydrogen peroxide during the reaction, achieving more than 80% yield. In order to develop this process, D ‐amino acid oxidase (DAAO) was co‐immobilized with catalase (CAT), which is able to fully eliminate in situ the hydrogen peroxide formed by the neighbouring DAAO molecules. Thus, the product of the reaction is only α‐ketoadipyl‐7‐ACA. This system prevents the inactivation of the oxidase by hydrogen peroxide, solving the main problem of the enzymatic process. Moreover, we have found that α‐ketoadipyl‐7‐ACA is recognized as a substrate by glutaryl acylase (GAC) and hydrolyzed as long as glutaric acid is absent from the reaction medium (because it is able to inhibit the hydrolysis). The low stability of α‐ketoadipyl‐7‐ACA justifies the use of a single reactor, in which glutaryl acylase is already present when this substrate is generated. Thus, the whole process may (and must) be performed in a single step, and in the absence of hydrogen peroxide that could affect the stabilities of the involved enzymes.     

The electrochemical preparation of 3-bromothiophen

The electrochemical reduction of 2,3,5-tribromothiophen to 3-bromothiophen may be carried out in good yield with a high current efficiency using a lead, mercury, zinc or graphite cathode in 70% dioxan/30% water containing sodium bromide (0.2 M) and a potential just positive to that for hydrogen evolution. The electrolysis may be designed to form free bromine at the anode or thiophen may be brominated in the anolyte; the product is 2-bromothiophen or 2,5-dibromothiophen which is resistant to further substitution in this solvent. Various strategies for the scale up of this synthesis are discussed.