催化裂化提升管反应器中颗粒聚团裂化反应的数值模拟

Behavior of catalytic cracking reactions of particle cluster in fluid catalytic cracking (FCC) riser reactors was numerically analyzed using a four-lump mathematical model. Effects of the cluster porosity, inlet gas velocity and temperature, and coke deposition on cracking reactions of the cluster were investigated. Distributions of temperature, gases, and gasoline from both catalyst particle cluster and an isolated catalyst particle are presented. The reaction rates from vacuum gas oil (VGO) to gasoline, gas and coke of individual particle in the cluster are higher than those of the isolated particle, but it reverses for the reaction rates from gasoline to gas and coke. Less gasoline is produced by particle clustering. Simulated results show that the produced mass fluxes of gas and gasoline increase with the operating temperature and molar concentration of VGO, and decrease due to the formation of coke.     

An investigation on dissolution kinetics of single sodium carbonate particle with image analysis method

Dissolution kinetics of sodium carbonate is investigated with the image analysis method at the approach of single particle. The dissolution experiments are carried out in an aqueous solution under a series of controlled temper-ature and pH. The selected sodium carbonate particles are al spherical with the same mass and diameter. The dissolution process is quantified with the measurement of particle diameter from dissolution images. The concentration of dissolved sodium carbonate in solvent is calculated with the measured diameter of particle. Both surface reaction model and mass transport model are implemented to determine the dissolution mecha-nism and quantify the dissolution rate constant at each experimental condition. According to the fitting results with both two models, it is clarified that the dissolution process at the increasing temperature is controlled by the mass transport of dissolved sodium carbonate travelling from particle surface into solvent. The dissolution process at the increasing pH is control ed by the chemical reaction on particle surface. Furthermore, the dissolution rate constant for each single spherical sodium carbonate particle is quantified and the results show that the disso-lution rate constant of single spherical sodium carbonate increases significantly with the rising of temperature, but decreases with the increasing of pH conversely.     

孔隙尺寸、盐度和气体组分对水合物相平衡的影响(英文)

An experimental device was set up to study the hydrate formation conditions. Effects of pore size, salinity, and gas composition on the formation and dissociation of hydrates were investigated. The result indicates that the induction time for the formation of hydrates in porous media is shorter than that in pure water. The decrease in pore size, by decreasing the size of glass beads, increases the equilibrium pressure when the salinity and temperature are kept constant. In addition, higher salinity causes higher equilibrium pressure when the pore size and temperature are kept constant. It is found that the effects of pore size and salinity on the hydrate equilibrium are quite different. At lower methane concentration, the hydrate equilibrium is achieved at lower pressure and higher temperature.     

三维有序二氧化硅胶粒膜在垂直基片上的自组装

A method for preparation of particle crystal film constructed trom monodisperse silica colloidal partices in diameter of about 300 nm is reported. The films were prepared from an ethanol suspension by vertical deposition that relies on capillary forces to assemble colloidal crystal particles on a vertical substrate. The 3D ordered films were characterized by transmission spectra and scanning electric microscope (SEM). The effect of evaporation temperature, particle concentration and sintered temperature on the quality of colloidal particle crystal film was investigated.     

高温液态水中葡萄糖无催化降解反应动力学

The decomposition kinetics of glucose was studied in high-temperature liquid water （HTLW） from 180 to 220℃ under a pressure of 10 MPa. It was found the main products from glucose decomposition were 5-hydroxymethylfurfural （5-HMF） and levulinic acid （LA）. The decomposition kinetics of 5-HMF and stability of LA in HTLW were further investigated. A kinetic model for glucose decomposition was proposed accordingly. In the model, a series of first-order reactions with the consideration of parallel by-reactions were used to illustrate the decomposition of glucose. The decomposition activation energies of glucose, 5-HMF, and LA were evaluated as 118.85, 95.40, and 31.29 kJ·mol^-1, respectively.     

STUDY FOR NATURAL GAS HYDRATE CONVERSED FROM ICE

Natural gas hydrates are crystalline clathrate compounds composed of water and gases of small molecular diameters that can be used for storage and transport of natural gas as a novel method. In the paper a series of experiments of aspects and kinetics for hydrate formed from natural gas and ice were carried out on the industrial small scale production apparatus. The experimental results show that formation conditions of hydrate conversed from ice are independent of induction time, and bigger degrees of supersaturation and supercooling improved the driving force and advanced the hydrate formation. Superpressure is also favorable for ice particle conversion to hydrate. In addition, it was found there have an optimal reaction time during hydrate formation.     

AB-8树脂吸附反式1,2环己二醇热力学和动力学(英文)

AB-8 resin was used as an adsorbent for the removal of trans-1,2-cyclohexandiol(CHD) from aqueous solutions.Batch experiments were carried out to investigate the effect of contact time and temperature on sorption efficiency.The adsorptive thermodynamic properties and kinetics of CHD from water onto AB-8 resin were studied.The Langmuir and Freundlich isotherm models were employed to discuss the adsorption behavior.Thermodynamic parameters such as G,H and S were calculated.The results indicate that the equilibrium data are perfectly represented by Langmuir isotherm model.Thermodynamic study reveals that it is an exothermic process in nature and mainly physical adsorption enhanced by chemisorption with a decrease of entropy process.The kinetics of CHD adsorption is well described by the pseudo second-order model.The adsorbed CHD can be eluted from AB-8 resin by 5% ethanol aqueous solution with 100% elution percentage.     

Influence of Pre-calcined Silica on Self-flow Silica Castables

In this study,raw silica was replaced by the silica pre-calcined at two different temperatures: 1 100 ℃ and1 300 ℃ to prepare self-flow silica castables. The properties of the synthesized castables adopting different kinds of silica were compared. The results show that:( 1) the silica become loose after pre-calcination at 1 100 ℃ for5 h or at 1 300 ℃ for 5 h; metastable cristobalite and glass phase are found in the silica pre-calcined at 1 300℃ for 5 h,which have a promoting effect on sintering;( 2) with the increase of the pre-calcining temperature as well as the replacement of pre-calcined silica,the linear change rate decreases,the apparent porosity and bulk density change mildly,and flexural strength and compressive strength are enhanced; for the refractoriness under load,the increasing pre-calcining temperature has promotion effect but the replacing amount has very mild influence.     

高温液态水中木糖无催化分解反应动力学

The kinetics of non-catalyzed decompositions of xylose and its decomposition product furfural in high temperature liquid water （HTLW） was studied for temperature from 180 to 220℃ and under pressure of 10MPa. The main products of xylose decomposition were furfural and formic acid, and furfural further degraded to formic acid under HTLW condition. With the assumption of first order kinetics e.quation, the evaluated activation energy of xylose and furfural decomposition was 123.27kJ·mol^-1 and 58.84kJ·mol^-1, respectively.     

Insight into the degradation mechanism of cefixime under crystallization condition

The chemical stability of cefixime was determined by high-performance liquid chromatography(HPLC) under different conditions, including factors such as p H, solvents, initial concentration, temperature and additives.The degradation process follows the first-order kinetics. A p H-rate profile exhibits the U-shape and shows the maximum stability of cefixime at pH = 6. The stability in different pure solvents is ranked as acetone N ethanol N methanol N water, while the degradation rate of cefixime exists a maximum at the ratio of 0.6 in water + methanol mixtures. In addition, the degradation rate increases with the temperature increasing and the activation energy of degradation was found to be 27.078 k J·mol~(-1) in acetone + water mixed solvents. The addition of different additives was proven to either inhibit or accelerate the degradation. The degradation products were analyzed using HPLC, LC–MS and infrared spectroscopy, and the possible degradation pathways in acid as well as alkaline environment were proposed to help us understand the degradation behavior of cefixime.     

Experimental Study on Microwave Vacuum Drying of Two-Porosity Level Media

Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left.     

Experimental Study on Microwave Vacuum Drying of Two-Porosity Level Media

Abstract

Microwave vacuum drying experiments were performed on a laboratory scale dryer with a two-level porosity material: a packed bed of porous alumina beads. The incident microwave power and the vacuum pressure level were fixed, the main varying parameters being the beads diameter and porosity, and the mean pore diameter. The drying kinetics and the evolution of the product temperature are presented. The drying kinetics can be divided into two main periods. The first one corresponds to the drying from the bed voids according to evaporation mechanism that we describe with a stagnant film law. The second one corresponds to the drying from the particle pores and we divide it into two parts: we suggest that the former is dominated by capillarity driven moisture transport, and the latter is limited by the desorption kinetics of the few water layers left.     

Determination of the influence of the polymer structure and particle size on the film formation process of polymers by atomic force microscopy

The particle size and morphology of a synthetic polymer latex were shown to influence the film formation behavior. Theoretical models predict that small particles coalesce more easily than large colloids do.The influence of particle size and morphology of differently structured lattices on the film-formation process was investigated by atomic force microscopy (AFM). Sequences of AFM images were acquired over a certain temperature range or at room temperature as a function of time. From the resulting images the average particle diameter of the latex particles in the surface layer was determined as a function of the time or temperature. The resulting curves could be compared to observe differences in the film formation kinetics of the different lattices. These AFM studies confirmed that the film formation behavior is influenced by the particle size and particle morphology, but that the core/shell ratio of core-shell particles has no significant influence on the film formation kinetics.     

Study of the Kinetics and Morphology of Gas Hydrate Formation

The kinetics and morphology of ethane hydrate formation were studied in a batch type reactor at a temperature of ca. 270–280 K, over a pressure range of 8.83–16.67 bar. The results of the experiments revealed that the formation kinetics were dependant on pressure, temperature, degree of supercooling, and stirring rate. Regardless of the saturation state, the primary nucleation always took place in the bulk of the water and the phase transition was always initiated at the surface of the vortex (gas‐water interface). The rate of hydrate formation was observed to increase with an increase in pressure. The effect of stirring rate on nucleation and growth was emphasized in great detail. The experiments were performed at various stirring rates of 110–190 rpm. Higher rates of formation of gas hydrate were recorded at faster stirring rates. The appearance of nuclei and their subsequent growth at the interface, for different stirring rates, was explained by the proposed conceptual model of mass transfer resistances. The patterns of gas consumption rates, with changing rpm, have been visualized as due to a critical level of gas molecules in the immediate vicinity of the growing hydrate particle. Nucleation and decomposition gave a cyclic hysteresis‐like phenomena. It was also observed that a change in pressure had a much greater effect on the rate of decomposition than it did on the formation rate. Morphological studies revealed that the ethane hydrate resembles thread or is cotton‐like in appearance. The rate of gas consumption during nucleation, with different rpm and pressures, and the percentage decomposition at different pressures, were explained precisely for ethane hydrate.     

Optical properties of dense and porous spheroids consisting of primary silica nanoparticles

The light scattering by granular and macroporous silica spheroids consisting of nanometer-sized primary particles was systematically investigated using a laser particle counter coupled with a pulse height analyzer. The shape- and porosity-controlled spheroids as model particles were prepared using spray drying method by changing the particle size of colloidal suspension. The effect of shape and porosity of dense and porous spheroidal particles on electrical mobility was also studied using a differential mobility analyzer and an electron microscope. The electrical mobility equivalent diameter of particles classified by the differential mobility analyzer was estimated by measuring Feret diameter and the projected area equivalent diameter from the SEM micrographs. The electrical mobility diameter of the spheroids was in good agreement with the projected area equivalent diameter regardless of the primary particle size and porosity. The measured partial scattering cross section of dense and porous silica particles with same mobility diameter showed significant differences. As the primary particle size of granules and the porosity of porous particles increased at parity of electrical mobility diameter, the scattering intensity decreased. The effective refractive indices of dense and porous particles were computed by best fitting of the scattering intensity measurements. The porosities of dense and porous spheroids were calculated using the effective refractive indices as obtained by the effective medium theory. The porosities were also measured by a comparison of particle size before and after annealing at 1700°C. By comparing these porosities, the effective refractive indices of the spheroidal particles were confirmed.     

Porous elastomeric beads from crosslinked emulsions

The production of porous polymeric particles is attractive for a large number of applications and can be achieved by various techniques. Although numerous production schemes exist for glassy polymers, difficulties arise for soft, rubbery materials that need a chemical crosslinking step, such as elastomers. This is particularly true for poly(dimethylsiloxane) (PDMS), which shows the lowest glass‐transition temperature among the polymers. Recent studies suggest in situ hydrogen bubble formation or vacuum drying of water droplets dispersed in the polymer matrix in order to generate porous PDMS structures. In this work we report early results based on the chemical crosslinking of water in PDMS emulsion droplets in a mechanically stirred thermostated water vessel. This approach is shown to lead to high porosity PDMS beads (ca. 10^?3 m particle diameter) with an open structure whose properties (diameter and porosity) are strongly influenced by the starting composition (solvent, surfactant, and polymer types and ratios), as well as the operating parameters (agitation and temperature). The possible uses of these derived beads are discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 967–971, 2002     

SiO2单分散溶胶微球制备的工艺条件研究

在乙醇介质中,以氨作为催化剂,正硅酸乙酯作为硅源,制备了单分散的二氧化硅溶胶微球。通过激光粒度分析仪及透射电镜测定溶胶粒子的大小。研究了不同工艺参数如催化剂和水的量、硅源的量以及溶剂的类型对二氧化硅粒子大小及形貌的影响,并考察了粒子的形成机理。结果显示:随着氨浓度的升高,溶液初始解离的[OH-]增大,二氧化硅粒子的粒径增大;随着硅源浓度的增加,溶液中水解的中间产物增加,二氧化硅微球的粒径显著增加;在r(水/正硅酸乙酯)值远大于4的情况下,随着初始加入水量的增加,二氧化硅微球的粒径有所增加,但当水量太多时,粒径反而下降;使用不同溶剂作为制备二氧化硅的介质,在丙醇和丁醇中二氧化硅严重团聚,没有得到单分散微球。     

Microstructures and properties of microporous mullite-corundum aggregates for lightweight refractories

Five microporous mullite-corundum refractory aggregates were prepared from Al(OH)₃ and kaolinite gangue through in situ decomposition synthesis technique. The effects of the sintering temperature (1400–1600°C) and the particle sizes of raw materials (20.6–94.5 μm) on the microstructures and strengths of the aggregates were investigated through X-ray diffractometer, scanning electron microscopy, and energy-dispersive spectrometer etc., to find out the technological conditions to be controlled in industrial production. The higher sintering temperature promoted the reaction between Al(OH)₃ and kaolinite gangue, leading to the development of primary-mullite as well as the generation of secondary-mullite, which promoted the formation of the neck and improved the strength. Meanwhile, the dense mullite layers were formed continuously on the surface of Al(OH)₃ pseudomorphs, making the micropores inside the pseudomorphs become closed pores, which increased the closed porosity of the aggregates. The reduction of the particle sizes of raw materials changed the particle packing behavior, accelerated the rearrangement of the Al(OH)₃ pseudomorph particles during the process of reactive sintering, and then reduced the closed porosity. To realize the industrial production of microporous mullite-corundum refractory aggregate with high strength (103 MPa) and high closed porosity (16.1%), the sintering temperature should be at about 1600°C, and the median diameter of raw materials should be at 94.5 μm.     

Transition to turbulent fluidization in a binary solids fluidized bed

This paper presents a study on the transition velocity from bubbling to turbulent fluidization in a binary solids fluidized bed. Experiments were carried out with two kinds of binary solids mixtures with FCC as fine particles and silica sands as coarse particles. The onset velocity to turbulent fluidization, U_c, determined by the measurement of pressure fluctuations, was found to increase with increasing the fraction of coarse/heavy solids. By introducing an equivalent particle diameter and an equivalent particle density, the results obtained in this study can properly be described by a general correlation of U_c proposed by Cai and co-workers (1989) for mono-density particles with relatively narrow size distribution.     

基于Lattice-Boltzmann方法的纳米颗粒多孔介质导热特性

为研究气凝胶纳米颗粒的导热特性,提出了一种基于随机统计原理的构造气凝胶多孔介质介观尺度三维物理模型的方法。模型中颗粒空间分布、粒径分布及孔隙率可以根据实际气凝胶微尺度结构数据调整。基于所构造的物理模型,采用D3Q15LBM进行了数值模拟。分析了颗粒尺寸、孔隙率等因素对气凝胶导热性能的影响规律,即在既定孔隙率下,热导率随粒径增大而减小;既定粒径下,随孔隙率的递增热导率先下降后上升;颗粒尺寸不均匀性对热导率的影响甚大。模拟与实验结果相吻合。研究工作对优化气凝胶导热性能,提高其有效热导率的预测精度具有参考价值。