Role of support in photothermal carbon dioxide hydrogenation catalysed by Ni/CexTiyO2

Nickel was supported on varied ratios of ceria-titania mixed oxides(Ni/Ce_xTi_yO_2) to evaluate the role the support plays in photothermal carbon dioxide hydrogenation to produce methane. In a batch photothermal reactor system, Ni/CeO_2 achieved the highest conversion rate, reaching a conversion of 93% in approximately60–90 min. To decouple the influence of light and heat, the CO_2 hydrogenation was examined in an in-house designed photothermal reactor, whereby heat can be applied externally. Decoupling experiments revealed that heat from the thermalisation by light was the main driving force for the reaction. In addition, the conversion and temperature profile of the different catalysts revealed that the catalyst performance was governed by catalyst reducibility. H_2-TPR analyses showed that the Ni became more readily reducible with increasing Ce O_2 content,suggesting that the oxide plays a role in activating the Ni. The reduction temperature of the nickel catalyst(following a reduction and passivation process) was below 200 °C, which meant that the inherent heating temperature of the photothermal reactor was sufficient to initiate Ni/CexTiyO_2 catalyst activity. The exothermic methanation reaction was then able to heat the system further, ultimately reaching a temperature of 285 °C. The ancillary rise in temperature promotes further nickel reduction and methane formation, leading to a "snow-ball"effect. The findings demonstrate that, to achieve a "snow-ball" effect in a photothermal system, designing a catalyst which is easy to reduce, active for CO_2 hydrogenation, and capable of converting light to heat for its initial activation is critical.     

Alkylation of toluene with 1,3-pentadiene over silica supported aluminum chloride catalyst in an extracting-distilling reactor

The alkylation of toluene with 1,3-pentadiene to produce pentyltoluene is designed to obtain 2,6-dimethylnaphalene for the monomer production of 2,6-naphthalene dicarboxylic acid. The possibility of the reaction is examined by the thermodynamics of the alkylation reaction using Thinh’s group contributions method, and tested over silica supported aluminum chloride catalyst in a newly developed extracting?distilling reactor. The thermodynamics calculation results show that the alkylation reaction is exothermic and can proceed at 298?350 K under normal pressure with an equilibrium constant higher than 106. Based on the thermodynamic calculation and the properties of the reactants and product, the extracting-distilling reactor was designed to allow 1,3-pentadiene to react with toluene at much lower temperature than the boiling point of toluene at the catalyst site. The alkylation product, which has a higher boiling point than that of toluene, is transferred from the catalytic site into the toluene bath and collected. The experimental results show that the reactor functions as designed and promotes the selectivity of the alkylation reaction close to 100%. The effect of raw material ratio of toluene to 1,3-pentadiene and reaction time are discussed in this paper. The suitable catalytic reaction conditions are as follows: at reaction temperature of 338 K and ambient pressure, the reactant ratio of toluene to 1,3-pentadiene is 5:1 for a six-hour reaction.     

Theoretical study on the mechanism of cycloaddition between dimethyl methylene carbene and acetone

The mechanism of the cycloaddition reaction of singlet dimethyl methylene carbene and acetone has been studied by using second-order Moller-Plesset perturbation and density functional theory. The geometrical parameters, harmonic vibrational frequencies and energy of stationary points on the potential energy surface are calculated by MP2/6-31G and B3LYP/6-31G methods. The results show that path b of the cycloaddition reaction （1） would be the major reactive channel of the cycloaddition reaction between singlet dimethyl methylene carbene and acetone, which proceeds in two steps： i） The two reactants form an energy-rich intermediate （INT1b）, which is an exothermic reaction of 23.3 kJ/mol with no energy barrier. ii） The intermediate INT1b isomerizes to a three.membered ring product （P1） via transition state TS1b with energy barrier of 22.2 kJ/mol. The reaction rate of this reaction and its competitive reactions do greatly differ, with excellent selectivity. In view of dynamics and thermodynamics, this reaction is suitable for occurring at 1 atm and temperature range of 300-800 K, in which the reaction will have not only the larger spontaneous tendency and equilibrium constant but also the faster reaction rate.     

AN INNOVATED REACTOR WITH VARYING DIAMETER AGITATOR AND ITS APPLICATIONS

The reactor is equipped with two different types of agitators: the diameter-variable agitator and the two-pitched-paddle agitator. The diameter of the former can be varied according to the requirement of the chemical reactions, thus making the concentration and temperature of the whole reaction system uniform throughout the reactor without any stagnant zone. It is shown that the apparatus has the preponderance over conventional agitator, especially when extremely rapid reactions are accompanied by large amount of reaction heat and when the viscosity of the reaction system varies in a wide range. The reactor is very effective when applied to the polycondensation reaction between paraphenylene diamine (PPDA) and terephthyl chloride (TPC). The inherent viscosity (η_(inh)) of the polymer comes up to more than 5. This innovative agitator has the advantage of simplicity in structure and flexibility in operation, etc.     

Moisture effect on the combustion of a single copper concentrate particle in a flash smelting furnace

A mathematical model has been presented to study the combustion of a single copper concentrate particle with high moisture content. By using the presented model, the effect of particle moisture content on particle temperature, sulfur oxidation, and combustion heat generation has been evaluated. The mineralogical composition of the commonly used concentrate at Khatoonabad flash smelting furnace has been used in this study. It was found that the particle moisture content is removed in the sub-second time range and thus the moisture has marginal impact on the variation of particle temperature and on the reaction rate when the gas temperature is assumed to be constant in the reaction shaft. When a concentrate with high moisture content is charged, the particle size enlargement due to the agglomeration of concentrate particles causes an abrupt fall in the particle reaction rate.     

Hydrodynamics and heat transfer of gas-solid two-phase mixtures flowing through packed beds–a review

Flow of a gas-solid two-phase mixture through a packed bed is relevant to a number of industrial processes such as heat recovery and filtration of dusty flue gases, iron making in shaft reactors, gas purification, and sorption enhanced reaction processes. In spite of the industrial relevance, little work has been reported in the literature. The limited amount of research work has mainly addressed the mac- roscopic hydrodynamics in terms of pressure drop and solids hold-ups at the ambient temperature. Very little is done, until fairly recent, on solids motion at the single particle level, hydrodynamics at elevated temperatures and heat transfer. This paper reviews the recent development in the field including both the hydrodynamics and heat transfer of gas-solid two-phase mixtures flowing through packed beds, which is believed to represent the state-of-the-art in the field. The review is not aimed to be exhaustive but rather focused on our own work carried out over the past few years in the Institute of Particle Science ＆ Engineering at the University of Leeds. And some of our results are compared with that of other groups.     

Study on constant-pressure specific heat of non-equilibrium phase change process in gas-liquid two-phase flow system

In this paper,the air-water vapor-water system is taken as an example,and the formula of constant-pressure specific heat during non-equilibrium phase change process in the two-phase flow system is deduced using the theory of two-phase flow and thermophysics. The constant-pressure specific heat of non-equilibrium phase change process is calculated with the corresponding numerical model,and the numerical results are compared to those of the equilibrium phase change process. It is shown that in evaporation process,the variational rate of the non-equilibrium specific heat increases with increasing initial fluid temperature and particle mass fraction. The smaller particle radius is,the faster the varia-tional rate is. Meanwhile,the constant-pressure specific heat of equilibrium process is higher than that of the non-equilibrium process all the time.     

LBE–DEM simulation of inter-phase heat transfer in gas–solid cross jets

Lattice-Boltzmann equation(LBE)–Discrete element method(DEM)coupled simulation of a twodimensional gas–solid cross jet is performed,focusing on the gas-particle two-way coupling effect on heat transfer characteristics.The Reynolds number is 1000,and particle Stokes numbers are 10,25,and 50 under the same number flow rate of particles.The gas phase temperature field and particle distribution as well as the inter-phase heat transfer characteristics are studied and analyzed.The dominating effects,i.e.the mean temperature difference and mean heat transfer coefficient between the gas–solid phases,for the pre-and post-collision stages of the cross jets are illustrated respectively.The change of dominating roles is related to the dynamical response characteristics of particles.     

Kinetics for hydrogen production by methanol steam reforming in fluidized bed reactor流化床反应器甲醇水蒸气重整制氢动力学研究

Hydrogen is one of the best energy carriers.Fluidized bed reactor provides a promising approach for hydrogen production. To describe the hydrogen generating rate with methanol steam reforming in fluidized bed reactor quantitatively, dual-rate kinetic models of the reactions with exponent form were developed, including that of steam reforming reaction（SR） and decomposition reaction（DE）.The reaction rate per unit mass of catalyst was related to partial pressures of components. The exponentials in kinetic equations were obtained by linear least-squares method based on the experimental data. The variance homogeneity test（F test） shows that the dynamic models are feasible with high accuracy, which can be used to predict the generating rate of hydrogen under different reaction temperatures and feed flow rates in fluidized bed reactor. The SR and DE activation energy obtained indicates that ESR\ EDE, which can explain the previous observation that the CO₂ selectivity decreased with the temperature increase.     

Purity of SiC powders fabricated by coat-mix

Silicon carbide powders were synthesized by the coat-mix process, with phenolic resin and silicon powders as starting materials. The effects of synthetic conditions, including sintering temperature and the molar ratio of resin-derived carbon to silicon on the composition and the purity of the resultant powders were investigated. The results show that a higher sintering temperature and an appropriate molar ratio of resin-derived carbon to silicon are favorable for producing high purity silicon carbide powders. It is found that the silicon carbide content increases slightly with increasing the sintering temperature during the solid-solid reaction. The temperature gradient plays an important role on this trend. When the sintering temperature is raised up to 1500℃, the formation of silicon earbide is based on the liquid-solid reaction, and high purity (99.8wt%) silicon carbide powders can easily be obtained. It can also be found that the optimum molar ratio of resin-derived carbon to silicon is 1:1.     

Thermal stability and magnetic properties of Fe–Co–M–Zr–Nb–Ge–B(M=Mo,Cr) bulk metallic glasses

Fe62Co8 xMxZr6Nb4Ge1B19(M=Mo, Cr) bulk metallic glasses were synthesized in the diameter range up to 2 mm by copper mold casting,which exhibit high thermal stability and large glass-forming ability. The super-cooled liquid region diminishes by the dissolution of Mo. The addition of 2 at% Cr leads to the broading of the liquid region remarkably, resulting in the improvement of thermal stability. The crystallization takes place through a single exothermic reaction, accompanying the precipitation of more than three kinds of crystallized phases such as α-Fe,Fe2Zr and ZrB2. The Fe-based alloys show soft ferromagnetic properties. The saturation magnetization(ss) decreases with increasing Mo or Cr content while the saturated magnetostriction increases with raising Mo or Cr content. There is no evident change in the ssand coercive force(Hc)with annealing temperature below the crystallization temperature, which suggests a more relaxed atomic configuration the glasses have. The crystallization causes a substantial enhancement in both ssand Hc. Each soft magnetic property of the glasses containing Cr with higher thermal stability is superior to that of the alloys containing Mo.     

Design and optimization of W/Cu divertor mock-ups

Tungsten is a promising candidate for plasma-facing materials to cover the surface of the divertor plate in the design of an international thermonuclear experimental reactor (ITER). Copper as a heat sink material serves to transfer heat excellently. Divertor mock-ups with W/Cu graded interlayers were designed to reduce thermal stresses. Thermally induced stresses and temperature in a W/Cu divertor mock-up were analyzed using the finite element method. The graded structures with different exponents p and thicknesses were designed and discussed. The conclusions drawn from these analyses are that thermal stresses reach the minimum and the temperature is suitable when exponent p is 1.5 and the thickness of five graded interlayers is 5 mm.     

Least dissipation principle of heat transport potential capacity and its application in heat conduction optimization

The heat conduction following the Fourier law widely exists in nature and engineering. Usually, the thermal resistance is applied to evaluating the perform-ance of the heat conduction, i.e. the less resistance corre-sponds to the better performance. Therefore, the heat conduction is often enhanced by means of using high conductivity materials or reducing the thermal contact resistance. The more general performance criterion is the heat duty for the given temperature difference DT, or the temp…     

A novel method to improve the performance of heat exchanger——Temperature fields coordination of fluids

The methods to enhance the heat transfer in heat exchanger may be classified into two levels: one is to improve the heat transfer coefficient; the other is to upgrade the whole arrangement of the heat exchangers. For the second level, the performance of heat exchanger can be upgraded by increasing the coordination degree between the temperature fields of cold and hot fluids. When the temperature distributions are similar to each other, the temperature difference field (TDF) is more uniform, which means that the temperature fields are more coordinated with each other. For the cross-flow heat exchanger, rearrangement of the heat exchange surface area should improve the heat transfer effectiveness, which is even equal to that of the counter-flow heat exchanger when the surface area is reassigned optimally. For the multi-stream heat exchanger, the thermal performance is also dependent on the uniformity of the TDF, and the parallel-flow arrangement may achieve higher heat exchange effectiveness than the counter-flow arrangement, which indicates that the performance of heat exchanger depends on the coordination degree of temperature fields instead of the flow arrangement.     

Selectivity of Crystal Growth Direction in Layered Double Hydroxides

Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions wereinvestigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.     

Methane Conversion to C2 Hydrocarbons in Solid State Oxide Electrolyte Membrane Reactor

Provskite-type catalysts, Ln0.6Sr0.4FexCo1-x O3 （Ln = Nd, Pr, Gd, Sm, La, 0〈x〈1） and Ln0.8Na0.2CoO3（Ln=La, Gd, Sm） were synthesized, their catalytic properties in the oxidative coupling of methane （OCM） were examined in a fixed-bed reactor. The former group presented higher activity in the OCM, but the main product was carbon dioxide. While the later group showed lower activity but much higher selectivity to C2 hydrocarbons compared with the former. Electrochemical measurements were conducted in a solid oxide membrane reactor with La0.8Na0.2 CoO3 as catalyst. The results showed that methane was oxidized to carbon dioxide and ethane by two parallel reactions. Ethane was oxidized to ethene and carbon dioxide. A fraction of ethene was oxidized deeply to carbon dioxide. The total selectivity to C2 hydrocarbons exceeded 70%. Based on the experimental results, a kinetic model was suggested to describe the reaction results.     

Density functional theory study on the insertion reaction mechanism of dibromocarbene with formaldehyde

The insertion reaction mechanism of CBr2 with CH3CH2O has been studied by using the B3LYP/6-311G(d) and CCSD(T)/6-311G(d) at single point. The geometries of reactions,transition state and products were completely optimized. All the transition state is verified by the vibrational analysis and the internal re-action coordinate (IRC) calculations. The results show that reaction (1) is the dominant reaction path,which proceeds via two steps: i) two reactants form an intermediate (IM1),which is an exothermal re-action of 8.62 kJ·mol?1 without energy barrier; ii) P1 is obtained via the TS1 and the H-shift,in which the energy barrier is 44.53 kJ·mol?1. The statistical thermodynamics and Eyring transition state theory with Wigner correction are used to study the thermodynamic and kinetic characters of this reaction in temperature range from 100 to 2200 K. The results show that the appropriate reaction temperature ranges from 200 to 1900 K at 1.0 atm,in which the reaction has a bigger spontaneity capability,equi-librium constant (K) and higher rate constant (k).     

Entransy analysis of open thermodynamic systems

The concept of entransy developed in recent years can describe the heat transport ability.This paper extends this concept to the open thermodynamic system and defines the concept of enthalpy entransy.The entransy balance equation of steady open thermodynamic systems,as well as the concept of entransy loss,is developed.The entransy balance equation is applied to analyzing and discussing the air standard cycle.It is found that the entransy loss rate can describe the change in net power output from the cycle but the entropy generation rate cannot when the heat absorbed by the working medium is from the combustion reaction of the gas fuel.When the working medium is heated by a high temperature stream,both the maximum entransy loss rate and the minimum entropy generation rate correspond to the maximum net power output from the cycle.Hence,the concept of entransy loss is an appropriate figure of merit that describes the cycle performance.     

Microwave Plasma Synthesis of Nanopowders

1 Results and Discussion Nanopowders were synthesized by using microwave plasma synthesis technique.The microwave plasma was operated in atmospheric pressure at a frequency of 2.45 GHz.The reaction temperature is directly related to the power of the microwave generator that can be controlled by adjusting the actual operating current.Firstly,ionization and dissociation of precursor species will be occurred in the plasma,nucleus can then be formed by the collision of these molecules,followed by the growth of the nuclei by further collisions.Cooling gas was used to quench the as-synthesized particles in order to inhibit further particle growth,the products will then condensed in the heat exchanger and finally collected in the powder collector. The synthesis of metal nitride,metal oxide,metals[1] and metal alloy nanopowders using the microwave plasma unit was investigated,and the effect of various processing parameters such as the effect of plasma gas,carrier gas,cooling gas,precursor raw materials and feeding rate was systematically studied.Modification of the microwave plasma unit by installing a second precursor dosing device at the lower portion of the reaction chamber can be used to form core-shell structure nanopowders[2].The processing conditions can be tuned to manipulate particle size and particle size distribution of the nanopowders.Experimental evidence suggested that the effect of feeding rate,plasma gas,carrier gas and cooling gas was critical in controlling the particle size and particle size distribution during the microwave plasma synthesis.     

Relationship among the secretion of extracellular polymeric substances,heat resistance,and bioleaching ability of Metallosphaera sedula

This paper describes the investigation of the secretion of extracellular polymeric substances (EPS) by an extremely thermoacidophilic archaea, Metallosphaera sedula (M. sedula), during the bioleaching of pyrite under different temperatures and discusses the relationship among the EPS secretion, its heat resistance, and its ability to bioleach pyrite. The investigation results indicate that the amount of extracellular proteins is significantly higher than the amount of extracellular polysaccharides in the extracted EPS whether free cells or attached cells; these results are quite different from the behavior of mesophilic Acidithiobacillus ferrooxidans. Although the growth of M. sedula is inhibited at 80℃, the bioleaching ability of M. sedula is only slightly lower than that at the optimum growth temperature of 72℃ because of the heat resistance mechanism based on EPS secretion. The secretion of more extracellular proteins is an important heat resistance mechanism of M. sedula.