Mathematical simulation of the electrochemical intercalation of graphite in concentrated sulfuric and dilute nitric acids

A mathematical model of the process of electrochemical intercalation of a granular graphite bed in nitric and sulfuric acids that takes into account the varying physicochemical properties of the graphite matrix is proposed. The numerical solution of the problem by the finite element method shows that, in agreement with the literature data, the current distribution is nonuniform even for a granular bed of a small height (∼2 × 10⁻² m), which results in the synthesis of a nonuniform product. The methods of assessing the nonuniformity of intercalation and its elimination by passing to a multistage process are proposed. The results of numerical methods can be used in predicting the technological characteristics of the final product.     

Experimental validation of a new integrated simulated moving bed process for the production of single enantiomers

A new integrated 3-zone simulated moving bed (SMB) concept with internal racemization reaction was suggested recently for the production of single enantiomers from racemic mixtures [1,2]. The process utilizes an internal gradient to trigger the racemization within a single zone. It can deliver the pure enantiomer and outperforms conventional technologies. In this contribution, the concept is validated experimentally for the separation of a model system compound. The results demonstrate that the new concept is capable of producing a single enantiomer with purity, yield and conversion of 100%.     

On the Integration of Dielectrometry into Electrochemical Impedance Spectroscopy to Obtain Characteristic Properties of a Dielectric Thin Film

We demonstrate a novel impedimetric approach providing unprecedented insight into characteristic properties of dielectric thin films covering electrode surfaces. The concept is based on the joint interpretation of electrochemical impedance spectroscopy (EIS) together with dielectrometry (DEM) whose informative value is mutually interconnected. The advantage lies in the synergistic compensation of individual shortcomings adversely affecting conventional impedimetric analysis strategies relying exclusively on either DEM or the traditional EIS approach, which in turn allows a reliable determination of thickness and permittivity values. The versatility of the method proposed is showcased by an in-situ growth-monitoring of a nanoporous, crystalline thin film (HKUST-1) on an interdigitated electrode geometry.     

Investigation of coupling dehydrogenation and hydrogenation reactions in a fixed bed catalytic reactor with well-mixed catalyst pattern

The enhancement of ethylbenzene conversion by further displacement of the thermodynamic equilibrium via the influence of the dual-functionality of a well-mixed catalyst pattern has been investigated. A rigorous steady state mathematical model based on the dusty gas model is implemented for the simulation. The simulation results reveal that the introduction of the concept of the reaction coupling has significant effect on the displacement of the thermodynamic equilibrium and considerable enhancement of simultaneous production of styrene and cyclohexane. Almost 100% conversion of the ethylbenzene and benzene is achieved through the application of this approach. It is also found that considerable decrease in the reactor length is achieved by employing a reactor catalyst bed with different bed compositions. Effective operating regions with optimal conditions are observed. An effective reactor length criterion is used to evaluate the performance of the reactor under these optimal conditions. The effective reactor length is found to be sensitive and favored by high feed temperature and pressure. The sensitivity analysis shows that the key parameters of feed temperature, pressure, and the bed composition play an important role on the reactor performance. The results also show that almost 100% conversion of ethylbenzene and benzene at low temperature and shorter reactor length can be achieved by maintaining the reactor beds at different temperatures. This temperature switching policy may result in appreciable energy saving. Moreover, operating the reactor at low temperature protect the catalyst from the excessive temperatures which have destructive effects on the catalysts and the mechanical stability of the reactors. Also, the low temperature operation has significant contribution to the reduction of the operating cost.     

Drying of granules in vibrating suspended bed: Engineering simulation

Engineering algorithm for simulation and designing of a continuous convective drying apparatus serving for drying heat-stable and heat-labile granules in a vibratory fluidized bed (vibrating, suspended bed) was suggested. The algorithm was based on a joint use of mass and heat balance equations, empirical dependences, and comparison of technological parameters with parameters got by the mathematical simulation of dynamics in the vibratory fluidized bed of variable weight. For example, we suggested a calculation algorithm of technological parameters of drying the heat-stable zeolite granules in the vibrating suspended bed. The results for a unit cost of heat and moisture evaporation standards in 3-stage drying were compared with the same for pneumatic drying apparatus, with devices of the fluidized and vibratory fluidized beds, and with sublimation dryers known in industry.     

Measurements and particle resolved modelling of the thermo- and fluid dynamics of a packed bed

The objective of this study is to investigate experimentally and numerically into heat-up, drying and pyrolysis of a packed bed consisting of large single particles. The novelty of the current approach is that the numerical model contrary to continuum mechanic approaches considers a packed bed as an ensemble of a finite number of particles, which may have different material properties or sizes. The heat-up, drying and pyrolysis process of each particle is described sufficiently accurate by a set of one-dimensional and transient differential conservation equations for mass and energy. Applying this model to all particles, including interactions between them, of a packed bed forms the entire backed bed process as a sum of individual particle processes. The arrangement of particles within a bed defines a void space between the particles. The flow through the void space of a packed bed is modelled as a flow through a porous media taking into account interaction between the solid and the gaseous phase by heat and mass transfer. Experiments for drying and pyrolysis of a packed bed were carried out for validation in a temperature range of T=120–530 °C. The temperatures and the mass loss due to drying and pyrolysis were recorded during the experiments. The measured mass loss of the packed bed due to drying were well predicted by the constant evaporation temperature model of the particles and thus, indicating, that the drying process is transport limited by heat transfer for large wood particles in a temperature range of T=120–530 °C. A comparison between experiments and predictions of pyrolysis yielded reasonable agreement for temperatures above T=300 °C. For temperatures of T≈200 °C the deviations were not acceptable. However, the results show, that a particle resolved approach is well suited to describe packed bed processes.     

Selective Extraction of Metal Ions from Aqueous Phase to Ionic Liquids: A Novel Thermodynamic Approach to Separations

The selective extraction of metals from aqueous mixtures has generally relied on the use of selective ionophores. We present an alternative strategy that exploits a recently developed approach to extraction into an ionic liquid phase, and show that a high degree of control over selectivity can be obtained by tuning the relative concentrations of extraction agents. A thermodynamic model for the approach is presented, and an experimental separation of strontium and potassium ions is performed. It is shown that tuning the concentrations of the species involved can shift the ratio of potassium to strontium in the ionic liquid phase from 4:1 to 3:4. This extraction is performed under mild conditions with relatively common reagents. The result is a proof‐of‐concept for a novel separations scheme that could have great importance in a wide range of technological applications.     

Computer-aided modeling of the chemical process of drying of a moving dense multilayer mass of phosphorite pellets

Mathematical and computer models were developed for the chemical process of drying of a moving dense multilayer mass of phosphorite pellets in a travelling grate machine. These models take into account the intensity of the internal moisture transfer in a pellet and the overmoisturization of individual horizons in the heated bed of pellets, which enables one to determine the technological parameters of the drying mode. The adequacy of the developed mathematical model was tested by comparing the calculated values of the moisture content and temperature of pellets, the characteristics of the heat-transfer gas, and the intensity of the moisture transfer in pellets while drying in a moving dense bed with the results of industrial tests. Numerous computational experiments were performed to determine the relative degree of drying, the moisture content, the pellet drying intensity, and the moisture content of the heat-transfer gas at various characteristics of moist pellets and the operating technological parameters of the travelling grate machine.     

Optimization of startup and shutdown operation of simulated moving bed chromatographic processes

This paper presents new multistage optimal startup and shutdown strategies for simulated moving bed (SMB) chromatographic processes. The proposed concept allows to adjust transient operating conditions stage-wise, and provides capability to improve transient performance and to fulfill product quality specifications simultaneously. A specially tailored decomposition algorithm is developed to ensure computational tractability of the resulting dynamic optimization problems. By examining the transient operation of a literature separation example characterized by nonlinear competitive isotherm, the feasibility of the solution approach is demonstrated, and the performance of the conventional and multistage optimal transient regimes is evaluated systematically. The quantitative results clearly show that the optimal operating policies not only allow to significantly reduce both duration of the transient phase and desorbent consumption, but also enable on-spec production even during startup and shutdown periods. With the aid of the developed transient procedures, short-term separation campaigns with small batch sizes can be performed more flexibly and efficiently by SMB chromatography.     

Non-Invasive Evaluation of Acute Effects of Tubulin Binding Agents: A Review of Imaging Vascular Disruption in Tumors

Tumor vasculature proliferates rapidly, generally lacks pericyte coverage, and is uniquely fragile making it an attractive therapeutic target. A subset of small-molecule tubulin binding agents cause disaggregation of the endothelial cytoskeleton leading to enhanced vascular permeability generating increased interstitial pressure. The resulting vascular collapse and ischemia cause downstream hypoxia, ultimately leading to cell death and necrosis. Thus, local damage generates massive amplification and tumor destruction. The tumor vasculature is readily accessed and potentially a common target irrespective of disease site in the body. Development of a therapeutic approach and particularly next generation agents benefits from effective non-invasive assays. Imaging technologies offer varying degrees of sophistication and ease of implementation. This review considers technological strengths and weaknesses with examples from our own laboratory. Methods reveal vascular extent and patency, as well as insights into tissue viability, proliferation and necrosis. Spatiotemporal resolution ranges from cellular microscopy to single slice tomography and full three-dimensional views of whole tumors and measurements can be sufficiently rapid to reveal acute changes or long-term outcomes. Since imaging is non-invasive, each tumor may serve as its own control making investigations particularly efficient and rigorous. The concept of tumor vascular disruption was proposed over 30 years ago and it remains an active area of research.     

一氧化碳气相催化偶联合成草酸二乙酯的研究

在固定床反应器中对一氧化碳气相催化偶联合成草酸二乙酯的双金属钯系催化剂进行了活性评价。研究结果表明，所研制的催化剂具有较高的活性、选择性和稳定性，具有工业开发价值；在较高的反应温度和浓度下，亚硝酸乙酯易分解而使一氧化碳转化率和草酸二乙酯空时收率下降；在原料气中加入适量的乙醇有助于提高草酸二乙酯的空时收率。提出了一氧化碳气相催化偶联合成草酸二乙酯的适宜的工艺条件。     

Covalent Grafting of Coordination Polymers on Surfaces: The Case of Hybrid Valence Tautomeric Interphases

We have developed a novel approach for grafting coordination polymers, structured as nanoparticles bearing surface reactive carboxylic groups, to amino‐functionalized surfaces through a simple carbodiimide‐mediated coupling reaction. As a proof‐of‐concept to validate our approach, and on the quest for novel hybrid interphases with potential technological applications, we have used valence tautomeric nanoparticles exhibiting spin transition at or around room temperature. SEM and AFM characterization reveal that the nanoparticles were organized chiefly into a single monolayer while X‐ray photoelectron spectroscopy (XPS) measurements confirm that the nanoparticles retain a temperature‐induced electronic redistribution upon surface anchorage. Our results represent an effective approach towards the challenging manufacture of coordination polymers.     

CO-processing conception of a quenching plasma reactor associated to a fluidized bed designed to hydrogen radical production at low temperatures

The aim of this paper is to present a new way to produce a high flow of hydrogen radical, at low temperatures. Thirst, an atmospheric pressure plasma of an argon-hydrogen mixture generates a high flow of hydrogen radical at temperatures up to 5 000 K. The applications of these radicals, in such conditions, are limited by thermal aspects which are obviously different from classical reactions of hydropyrolysis or other treatment processings of organic molecules. Our approach is to quench the plasma by a fluidized bed reactor which transport properties are compatible with plasma phase. From this point of view, the plasma/fluidized bed system is qualified in terms of its thermodynamic and hydrodynamical properties and its quenching velocity. The atomic hydrogen flow generated within such conditions is calculated and then experimentally measured.     

Efficiency of preparative and process column distribution systems

An analytical method for computing the residence time distribution of the liquid distribution system in chromatography columns is described. The impact of the distributor design on the separation efficiency is predicted as a function of media properties and packed bed dimensions. The efficiency loss due to the distributor when increasing column diameter during scale-up is quantified. It is shown that this loss can be compensated by modulating the local bed height via a moderate inclination of the bed support. It is concluded that the selection of an appropriate distributor design concept with optimised dimensions enables a scale-up of chromatographic separations without any significant loss of chromatographic efficiency due to the distribution system.     

Improving performance of simulated moving bed chromatography by fractionation and feed-back of outlet streams

Simulated moving bed (SMB) chromatography is an important technique for the continuous separation of valuable products. Recently suggested process modifications have shown the potential for further improvement. In this work, a concept is presented that combines non-permanent product withdrawal at one or both outlet ports (leading periodically to a "product" and a "non-product" fraction) with an internal recycle and re-feeding of the "non-product" fraction in alternation to the original feed mixture. Using simulation studies for linear and non-linear isotherms, it was shown that in terms of process performance and product recovery, this fractionation and feed-back approach (FF-SMB) is superior to both the conventional SMB process as well as to a previously reported fractionation and discard strategy.     

气固流化床内射流特性的研究

采用Brandani等的数学模型模拟了中心射流宽度为0.01m的二维气固流化床(高1.6m、宽0.3m)内鼓泡和射流的瞬态及时均流体动力学特性。一种典型的Geldart B颗粒――砂子(粒径为500mm、密度为2660kg/m3)作为研究的模拟物料。瞬态结果表明，床内射流产生和发展、射流崩塌后所形成气泡尺寸以及全床内的气体速度场和空隙率均存在明显的非对称性，但是由压力信号功率谱密度得到的时均压力特性则有较好的对称性。因此，对于商业化稳定运转的射流床，可以用半床模拟结果近似解释整床特性；然而，在考察射流床的瞬态特性时，半床模拟结果与整床结果存在明显偏差。     

Continuous fast pyrolysis of biomass at high temperature in a fluidized bed reactor

In order to perform biomass pyrolysis a continuous fluidized bed reactor (bench scale unit) has been assembled. The influence of experimental conditions such as heating-up time and optimum particle diameter is presented. By feeding the biomass (almond shells) directly into the bubbling bed, pyrolysis has been performed at temperatures ranging from 730° to 930°C at constant feed rate (44 g/h). Remarkable increase of H₂ in the product gas is observed when steam rather than an inert carrier such as nitrogen is used thus confirming the potential of this approach.The support of ENEA (Italian Agency for Renewable Energies) is gratefully acknowledged.     

Comparison of configurations of a four-column simulated moving bed process by multi-objective optimization

Configurations of a four-column simulated moving bed chromatographic process are investigated by multi-objective optimization. Various existing column configurations are compared through a multi-objective optimization problem. Furthermore, an approach based on an SMB superstructure is applied to find novel configurations which have been found to outperform the standard SMB configuration. An efficient numerical optimization technique is applied to the mathematical model of the SMB process. It has been confirmed that although the optimal configuration highly depends on the purity requirement, the superstructure approach is able to find the most efficient configuration without exploring various existing configurations.     

Density functional theory: Approximating quasiparticle density functional

A constructive approach for deriving the approximating quasiparticle energy density functional is proposed. As a matter of fact, the proposed approach is the direct development of the Kohn–Sham quasiparticle concept and the Levy–Valone approach. The approach presented takes into account a pseudopotential character of the exchange-correlation part of the density functional and results in a system of functional equations to obtain ground-state energies of many-electron systems.