A New Type of Porous Plug for Blowing Argon in the VHD

In the process of VHD,argon is blown into the molten steel throuht the porous plugs which are mounted in the ladle bottom.A new type of porous corundum plug has been developed for the VHD secondary refining ladle furnace in Fushun Steel Works ,It is found that when the mean grain size of corundum articles decreases from 760 μm tp 650μm ,the physical properties and service life of the plug are the same as that of importedone ,and can be normally used in the VHD process.     

On the Applicability of a Quasi-Stationary Solution of the Diffusion Equation for the Hydrate Layer Formed at the Gas–Ice (Water) Interface

The problem of methane hydrate formation when the process is controlled by gas diffusion in the hydrate layer formed at the gas–ice (or water) interface is solved. It is shown that an approximate quasi-stationary solution of the diffusion equation is in good agreement with its numerical solution over a wide range of the solubility of the gas in the hydrate, which is dependent on pressure. It is found that the time for the complete transition of the water (or ice) phase into the hydrate state decreases with an increase in the saturation concentration of the mobile gas in the hydrate. The kinetic equations derived based on a quasi-stationary solution of the diffusion equation, which are relationships for the intensity of hydrate formation in snow-containing (or water-containing) formations during the filtration of hydrate-forming gases, are used to describe the concentration fields of the diffusing gas and the dynamics of hydrate layer growth.     

Unipolar Field and Diffusion Charging in the Transition Regime—Part I: A 2-D Limiting-Sphere Model

This work examines the unipolar charging of aerosol particles smaller than 100 nm by ions (at STP) both theoretically (Part I) and experimentally (Part II).

Among numerous well-known models for particle charging by ions a gap has been identified for the case of diffusion charging with superimposed external electric field in the transition regime. A two dimensional extension of the classical Fuchs-model Fuchs, 1963 Fuchs, N. A. 1963. On the Stationary Charge Distribution on Aerosol Particles in a Bipolar Ionic Atmosphere. Geofisica Pura e Applicata, 56: 185–193. [Crossref] , [Google Scholar]) has been developed in order to bridge this gap in the knowledge. For the first time the complete expression for the electrostatic potential between a particle and an ion has been included.

By using FEM-simulations, the quantitative influence of an external electric field on the charging process has been predicted. It is shown that an external electric field increases the average particle charge linearly. Compared to pure diffusion charging, an electric field of 10 kV/cm increases the charge on metallic particles up to 28% (30 nm particles), 55% (60 nm), and 95% (100 nm), respectively.

When compared to the Fuchs-model, the assumptions of the new model introduce additional uncertainty of less than 3%. Comparison with the simpler, but physically less reasonable continuum model by Lawless (1996) Lawless, P. A. 1996. Particle Charging Bounds, Symmetry Relations and an Analytic Rate Model for the Continuum Regime. J. Aerosol Sci., 27: 191–215. [Crossref] , [Google Scholar] shows similar charge predictions (deviations < 20% for n·t-products 10¹³ s/m³), even for 30 nm particles. So, that continuum charging model can serve as simple approximation of the more accurate charging model for the transition regime.     

Controlled Picard Method for Solving Nonlinear Fractional Reaction–Diffusion Models in Porous Catalysts

This paper discusses the diffusion and reaction behaviors of catalyst pellets in the fractional-order domain as well as the case of nth-order reactions. Two generic models are studied to calculate the concentration of reactant in a porous catalyst in the case of a spherical geometric pellet and a flat-plate particle with different examples. A controlled Picard analytical method is introduced to obtain an approximated solution for these systems in both linear and nonlinear cases. This method can cover a wider range of problems due to the extra auxiliary parameter, which enhances the convergence and is suitable for higher-order differential equations. Moreover, the exact solution in the linear fractional-order system is obtained using the Mittag–Leffler function where the conventional solution is a special case. For nonlinear models, the proposed method gives matched responses with the homotopy analysis method (HAM) solutions for different fractional orders. The effect of fractional-order parameter on the dimensionless concentration of the reactant in a porous catalyst is analyzed graphically for different cases of order reactions and Thiele moduli. Moreover, the proposed method has been applied numerically for different cases to predict and calculate the dual solutions of a nonlinear fractional model when the reaction order n?=??1.     

Unipolar Field and Diffusion Charging in the Transition Regime—Part II: Charging Experiments

Unipolar charging of narrowly distributed 30–100 nm DEHS aerosols in air is investigated, in order to determine the influence of the external electric field (E ₀ ≤ 5 kV/cm) and high charging intensities (n·t ≤ 5 · 10 ¹⁴ s/m ³ ) on the charging efficiency. The results are compared with a combined diffusion and field charging model based on the limiting-sphere concept described in Part I.

The experiments were carried out in a wire corona charger under conditions of complete radial turbulent mixing, which makes the determination of charging history straightforward and very accurate. The state of mixing was verified on the basis of the Deutsch model, by separate measurements of particle losses.

For positive charging, the agreement between measured and predicted mean charge was generally better than 5% for particles larger than 45 nm, which typically carried more than 4 unit charges; for 30 nm particles and relatively low charge levels the uncertainties in the model lead to deviations up to 30%.

In case of negative charging, the observed charge levels progressively exceeded those predicted on the basis of mean ion mobilities by factors up to 2 as the charging intensity increased, and there was evidence of additional charging by free electrons.     

Analysis of the Thermal Explosion in Systems Porous Reagent–Active Gas–Solid Product

The specific features of dynamics of the thermal explosion in systems porous reagent–active gas–solid product under conditions where the heattransfer and masstransfer regions are separated from the ambient medium are considered. In addition to the competition of heat release and heat removal, the process of initiation of exothermal chemical interaction in these systems under normal pressures depends significantly on conditions of filtration transport of the gaseous reagent. The induction and postinduction periods of the thermal explosion are studied. The theoretical analysis of thermalexplosion issues is supplemented by an experimental study of the process for the porous titanium–nitrogen–titanium nitride system.     

A General Equation for Calculating the ’True’ Height of Transfer Unit in Extraction Columns

Based on single drop mass transfer models and two phase flow equation,a general equationfor calculating the‘true’height of transfer unit of extraction columns was derived and tested withfour types of extraction columns with some different working systems.The calculated results fittedwell with those obtained by experiments.     

A Novel Empirical Equation for Relative Permeability in Low Permeability Reservoirs☆

In this paper, a novel empirical equation is proposed to calculate the relative permeability of low permeability res-ervoir. An improved item is introduced on the basis of Rose empirical formula and Al...     

Postinduction Processes During Thermal Explosion in the Systems “Porous Material–Reactive Gas–Solid Product”

A complete solution of the unsteadystate filtration problem of thermal explosion incorporating the postinduction period is given for the first time. The paper describes a study of the temperaturefield dynamics, poregas pressure, and the degree of condensedphase conversion versus the reactivegas deficiency in a reactive porous material. Focus is on the formation and propagation of frontal regimes of exothermic chemical reactions (their number, direction, and velocity of propagation, degree of condensedphase conversion at the front). The study revealed double selfignition phenomena and combustionwave propagation regimes with incomplete conversion at the front. A surface regime of thermal explosion limited by gas filtration from the outside was considered. The regularities in the dynamics of the exothermic chemical reaction found in the present study allow one to qualitatively control hightemperature synthesis under thermal explosion conditions.     

Diffusion in Nanoporous Solids in the Focus of IUPAC – A Tribute to Jens Weitkamp

In bidding farewell to Prof. Dr.-Ing. Jens Weitkamp, we remember his many activities and his beneficial influence on the development of science, notably in the various fields of chemical technology and engineering. These activities include his engagement in support of the development of techniques dedicated to improvement of our understanding of the complex phenomenon of mass transfer in nanoporous materials, as both an ingenious scientist and a brilliant organizer and gifted leader of scientific alliances. The present contribution provides a brief introduction to the many facets of research in this field, with particular recognition of the most recent developments and Prof. Weitkamp's contributions.     

A rigorous kinetic model for β-carotene oxidation in the presence of an antioxidant, α-tocopherol

Oxidation of β-carotene in an inert solvent, n-decane, in the presence of various concentrations of the antioxidant α-tocopherol was studied. The progress of carotene oxidation was suppressed as long as the tocopherol remained in the system. A rigorous kinetic model for carotene oxidation in the presence of an antioxidant was proposed based on a reaction mechanism in which not only the antioxidation but also the co-oxidation and radical-exchange reaction of tocopherol with carotene were incorporated. The model quantitatively described the oxidation behavior of carotene over a wide range of temperatures, oxygen compositions, and initial antioxidant concentrations.     

Membrane materials in the pervaporation separation of aromatic/aliphatic hydrocarbon mixtures—A review

The separation of aromatic/aliphatic hydrocarbon mixtures is a significant process in chemical industry,but challenged in some cases.Compared with conventional separation technologies,pervaporation is quite promising in terms of its economical,energy-saving,and eco-ffiendly advantages.However,this technique has not been used in industry for separating aromatic/aliphatic mixtures yet.One of the main reasons is that the separation performance of existed pervaporation membranes is unsatisfactory.Membrane material is an important factor that affects the separation performance.This review provides an overview on the advances in studying membrane materials for the pervaporation separation of aromatic/aliphatic mixtures over the past decade.Explored pristine polymers and their hybrid materials (as hybrid membranes) are summarized to highlight their nature and separation performance.We anticipate that this review could provide some guidance in the development of new materials for the aromatic/aliphatic pervaporation separation.     

Membrane distillation and pervaporation for ethanol removal: are we comparing in the right way?

A new glance on the comparison between membrane distillation (MD) and pervaporation is performed. There is a difficulty in this comparison, mainly due to different hydrodynamic conditions reported in the literature. Pervaporation and MD are similar although the comparison between these two processes can be tricky. In that way, how can we make a proper comparison between results of these two processes? This study proposes a reasonable comparison between MD and pervaporation for ethanol–water separation. Two very distinct regions of results in terms of selectivity and flux are presented. Feed temperature and composition and concentration polarization effects were also investigated.     

Opportunities for Membrane Technologies in the Treatment of Mining and Mineral Process Streams and Effluents∗

Abstract

The membrane separation technologies of microfiltration, ultrafiltration, nanofiltration, and reverse osmosis are suitable for treating many dilute streams and effluents generated in mining and mineral processing. Membrane technologies are capable of treating these dilute streams in order to produce clean permeate water for recycle and a concentrate that can potentially be used for valuable metals recovery. Membrane technologies can be utilized alone, or in combination with other techniques as a polishing step, in these separation processes. A review of potential applications of membranes for the treatment of different process streams and effluents for water recycling and pollution control is given here. Although membranes may not be optimum in all applications, these technologies are recognized in the mining sector for the many potential advantages they can provide.

     

Fouling Control by Reduction of Submicron Particles in a BF‐MBR with an Integrated Flocculation Zone in the Membrane Reactor

Abstract

Submicron particles represent one of the major foulants in the biofilm membrane reactor BF‐MBR. Reduction of the amount of submicron particles (colloids) adjacent to the membrane is one measure in order to provide better fouling control in BF‐MBR systems. A submerged hollow fiber (Zenon Zeeweed) membrane reactor was redesigned by introducing a flocculation zone below the aeration device of the membrane module. This resulted in reduction of submicron particles around the membrane from 8.2% to 6.9%, expressed in differential number percentage. The size of the most abundant particle fraction consequently increased from 0.70 to 0.84 µm. Furthermore, the modified membrane reactor design provided longer operational cycles, >40% reduction of suspended solids around the membrane, and improved retentate/concentrate characteristics, i.e., dewaterability (CST), settleability (SVI/SSV) and filterability (TTF).     

A Correlation for the Characteristic Velocity Ratio to Predict Hydrodynamics of Capillary Gas–Liquid Taylor Flow

Theoretical Foundations of Chemical Engineering - The ratio between bubble velocity and mean velocity of the two-phase flow is a key parameter in Taylor flow. Correlations for this characteristic...     

On the Efficiency of NH3–SCR Catalysts for Heavy Duty Vehicles Running on Compressed Natural Gas in Synthetic Gas Bench Scale

This work aims to study the effectiveness of NH₃–SCR after-treatment systems, initially developed for a Diesel application, on Heavy duty natural gas engines working in lean conditions for exhaust gas pollutants abatement. Commercial oxidation and NH₃–SCR catalysts were investigated for respectively CH₄, CO oxidation and NO_X reduction. In this study, we showed that the NH₃–SCR coupled with an oxidation catalyst lead to significant conversion of CH₄, CO and NO_X, and can be used as after-treatment system for pollutants providing from CNG lean burn engines.     

State‐of‐the‐Art Adsorption and Membrane Separation Processes for Hydrogen Production in the Chemical and Petrochemical Industries

Abstract

This review on the use of adsorption and membrane technologies in H₂ production is directed toward the chemical and petrochemical industries. The growing requirements for H₂ in chemical manufacturing, petroleum refining, and the newly emerging clean energy concepts will place greater demands on sourcing, production capacity and supplies of H₂. Currently, about 41 MM tons/yr of H₂ is produced worldwide, with 80% of it being produced from natural gas by steam reforming, partial oxidation and autothermal reforming. H₂ is used commercially to produce CO, syngas, ammonia, methanol, and higher alcohols, urea and hydrochloric acid. It is also used in Fischer Tropsch reactions, as a reducing agent (metallurgy), and to upgrade petroleum products and oils (hydrogenation).

It has been estimated that the reforming of natural gas to produce H₂ consumes about 31,800 Btu/lb of H₂ produced at 331 psig based on 35.5 MM tons/yr production. It is further estimated that 450 trillion Btu/yr could be saved with a 20% improvement in just the H₂ separation and purification train after the H₂ reformer. Clearly, with the judicious and further use of adsorption or membrane technology, which are both classified as low energy separation processes, energy savings could be readily achieved in a reasonable time frame.

To assist in this endeavor of fostering the development of new adsorption and membrane technologies suitable for H₂, CO and syngas production, the current industrial practice is summarized in terms of the key reforming and shift reactions and reactor conditions, along with the four most widely used separation techniques, i.e., absorption, adsorption, membrane, and cryogenic, to expose the typical conditions and unit processes involved in the reforming of methane. Since all of the reactions are reversible, the H₂ or CO productivity in each one of them is limited by equilibrium, which certainly provides for process improvement. Hence, the goal of this review is to foster the development of adsorption and membrane technologies that will economically augment in the near term and completely revamp in the far term a typical H₂, CO or syngas production plant that produces these gases from natural gas and hydrocarbon feedstocks.

A review of the emerging literature concepts on evolving adsorption and membrane separations applicable to H₂ production is provided, with an emphasis placed on where the state‐of‐the‐art is and where it needs to go. Recommendations for future research and development needs in adsorbent and membrane materials are discussed, and detailed performance requirements are provided. An emphasis is also placed on flow sheet design modification with adsorption or membrane units being added to existing plants for near term impact, and on new designs with complete flow sheet modification for new adsorption or membrane reactor/separators replacing current reactor and separator units in an existing plant for a longer term sustainable impact.     

A Calcium Guard in the Outer Membrane: Is VDAC a Regulated Gatekeeper of Mitochondrial Calcium Uptake?

Already in the early 1960s, researchers noted the potential of mitochondria to take up large amounts of Ca²⁺. However, the physiological role and the molecular identity of the mitochondrial Ca²⁺ uptake mechanisms remained elusive for a long time. The identification of the individual components of the mitochondrial calcium uniporter complex (MCUC) in the inner mitochondrial membrane in 2011 started a new era of research on mitochondrial Ca²⁺ uptake. Today, many studies investigate mitochondrial Ca²⁺ uptake with a strong focus on function, regulation, and localization of the MCUC. However, on its way into mitochondria Ca²⁺ has to pass two membranes, and the first barrier before even reaching the MCUC is the outer mitochondrial membrane (OMM). The common opinion is that the OMM is freely permeable to Ca²⁺. This idea is supported by the presence of a high density of voltage-dependent anion channels (VDACs) in the OMM, forming large Ca²⁺ permeable pores. However, several reports challenge this idea and describe VDAC as a regulated Ca²⁺ channel. In line with this idea is the notion that its Ca²⁺ selectivity depends on the open state of the channel, and its gating behavior can be modified by interaction with partner proteins, metabolites, or small synthetic molecules. Furthermore, mitochondrial Ca²⁺ uptake is controlled by the localization of VDAC through scaffolding proteins, which anchor VDAC to ER/SR calcium release channels. This review will discuss the possibility that VDAC serves as a physiological regulator of mitochondrial Ca²⁺ uptake in the OMM.