Evaluation of published kinetic models for tert-amyl ethyl ether synthesis

The published kinetic models for liquid phase synthesis of tert-amyl ethyl ether (TAEE) by addition of ethanol to isoamylenes on acidic ion exchange resins were evaluated by comparison with own experimental data. Fixed bed and batch reactor experiments were carried out in liquid phase on Amberlyst-35 ion exchange resin as catalyst. Among the published kinetic models, our experimental data fits the best with the model published by [J.A. Linnekoski, A.O. Krause, L.K. Rihko, Kinetics of the heterogeneously catalyzed formation of tert-amyl ethyl ether, Ind. Eng. Chem. Res. 36 (1997) 310–316.]. In the simulation study for the fixed bed reactor experiments, the influences of axial mixing, liquid–solid mass transfer and internal diffusion steps on the overall process kinetics were theoretically evaluated. The results evidenced that on the working temperature domain, significant kinetic limitations by internal diffusion can appear for catalyst pellets size over 1 mm. The external mass transfer step has a weak influence on the process kinetics and can be important only at lower limit of the flow rates domain. Our computations evidenced also a negligible influence of the axial mixing on the reactants conversion in the experimental fixed bed reactor, on the working domain investigated.     

Solid-phase synthesis of multi-walled carbon nanotubes from butadiynyl-ferrocene-containing compounds

Multi-walled carbon nanotubes (MWCNTs) have been synthesized from novel butadiynyl-ferrocene-containing compounds. The formation of the MWCNTs occurs in the solid phase at ambient pressure in a typical high-temperature furnace. Heat treatment of the various compounds to temperatures up to 1300 °C under atmospheric pressure resulted in the decomposition of the ferrocene units and the formation of Fe nanoparticles in the polymeric-to-carbon nanoparticle-to-carbon nanotube compositions. The Fe atoms, clusters, and/or nanoparticles are the key to the formation of the carbon nanotubes. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies show the presence of a large quantity of MWCNTs in the carbonaceous solid residue.     

蜡油加氢脱硫集总动力学模型研究

以减压蜡油（VGO）加氢脱硫（HDS）小试实验数据为基础,针对VGO HDS反应速率快慢,将原料中硫化物划分为快反应速率、中反应速率、慢反应速率3个集总,建立VGO HDS反应三集总动力学模型,并采用Levenberg-Marguardt算法对模型参数进行了求解。结果表明,该模型平均相对误差仅为5.18%,预测值可靠,外推性良好,模型参数计算结果符合加氢反应规律。通过模型计算,分析了液时空速、反应温度、反应压力对VGO HDS过程的影响,得到了HDS详细的反应规律,可为VGO HDS反应集总动力学研究和实验分析提供参考。     

Fluidized bed char combustion kinetic models

The effect of the kinetics of the heterogeneous reaction between the char and oxygen, and the importance of the subsequent homogeneous oxidation of carbon monoxide oil the performance of an atmospheric fluidized bed combustor have been examined by a comparative analysis of three models. Numerical calculations illustrating the effect of operating variables such as bed temperature, fuel and sorbent particle feed size and excess air were performed for values of the parameters which are pertinent to the design of large scale utility boilers. It is found that the kinetic models predict existence of multiple steady states over a wide range of operating conditions and values of model parameters. The model predictions of combustion efficiency, carbon loading and CO concentrations are in qualitative agreement with experimental data reported in the literature.     

Detailed kinetic models for catalytic reforming

Catalyst reforming was used as a “vehicle” process chemistry to validate a set of tools for the automated construction of kinetic models. This is because the catalytic reforming process exposes many important modeling concepts and features, including multiple reaction families, catalyst deactivation, temperature profiling, parameter optimization, recycling, etc. A previously published [P.V. Joshi, S.D. Iyer, M.T. Klein, Computer assisted modeling of gas oil fluid catalytic cracking (FCC), Abstracts of Papers of the American Chemical Society, 1997, pp. 80-Petr] reforming reaction network was built and customized using the Kinetic Model Editor (KME) software, which includes a standard model library, a model code generator (CodeGen) and an Excel™-based graphical user interface. Modeled features, which included catalyst deactivation, serial reactors, energy balance, and model tuning, were conveniently implemented in the KME application. The confrontation of model results with experimental observations suggests that the model is well founded and is a good platform for additional process-specific refinements.     

Modelling of adsorption of textile dyes over multi-walled carbon nanotubes: Equilibrium and kinetic

The paper deals with the application of multiwall carbon nanotubes (CNTs) to the adsorption of dyes from wastewater. Textile dyes are dangerous and diffused pollutant in wastewater, and the paper results confirmed the good adsorption ability of CNTs, with respect to classic active carbon, even for different dye types. The effect of surface treatments of CNTs was primarily investigated, revealing that neither the presence of residual catalyst nor common surface treatment (oxidation) affects the CNT's performances. Therefore less expensive nonpurified CNTs were assessed as good and economically convenient alternative for the process. In order to gain in generality in adsorption kinetic modelling, the parameters of the "best fitting" pseudo-second order model have been correlated to the main process variables (the dye initial concentration and the specific mass of CNTs.) setting-up a predictive kinetic model useful design new application of these materials in currently operating industrial operations for adsorption. In addition, isothermal data were used to screen all the relevant adsorption isotherms models and the Temkin model was confirmed as the more effective to accurately fit equilibrium data for any of the considered different dye types.     

Dimensional control of multi-walled carbon nanotubes in floating-catalyst CVD synthesis

Dimensional control in CVD synthesis of MWNT’s is significant and critical to a number of different applications. This study examines the dimensional effect of a number of synthesis variables on the products of floating-catalyst CVD, including catalyst concentration in the feedstock, nanotube growth time, and deposition substrate selection. Extensive diameter surveys are performed by TEM and compared with results from thermo-gravimetric analyses to Raman spectroscopy, offering a novel dimensional analysis of nanotubes grown by FC-CVD methods. CNT diameters are inversely proportional to the catalyst concentration with weak correlation over the range examined and are directly proportional to growth time. Results are combined with prior art to develop a new theory regarding catalyst particle formation over a range of catalyst concentrations. Carbon deposition occurs in two stages, the first characterized by accelerating deposition and increases in CNT diameter and length, the second by etching of the array and carbon deposition at a constant rate. Deposition substrates interact directly with the catalysts to strongly influence the resulting nanotube diameters, based upon the mobility of the catalysts on the substrate surface.     

Single-step synthesis of germanium nanowires encapsulated within multi-walled carbon nanotubes

We report the single-step synthesis of Ge nanowires encapsulated within multi-walled carbon nanotubes (MWCNTs) from a phenyltrimethylgermane (C₆H₅Ge(CH₃)₃) precursor, using a simple chemical vapor deposition (CVD) method. The MWCNT/germanium nanowires were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) measurements. TEM analysis reveals that the nanowires consist of well crystallized Ge cores which are completely encapsulated by the sheath-like MWCNTs, the latter corresponding to a layer thickness of 5-10 nm. SEM images, corresponding to various stages of nanowire growth, indicate that MWCNT growth occurs at Ge nanoparticles and that the growing MWCNTs carry Ge as nanowires away from the nanoparticles. By optimizing the CVD parameters, nanowires can be produced with uniform length and diameter in the range 6-10 μm and 200-300 nm, respectively.     

Hydrothermal synthesis of MnO2/CNT nanocomposite with a CNT core/porous MnO2 sheath hierarchy architecture for supercapacitors

ABSTRACT: MnO2/carbon nanotube [CNT] nanocomposites with a CNT core/porous MnO2 sheath hierarchy architecture are synthesized by a simple hydrothermal treatment. X-ray diffraction and Raman spectroscopy analyses reveal that birnessite-type MnO2 is produced through the hydrothermal synthesis. Morphological characterization reveals that three-dimensional hierarchy architecture is built with a highly porous layer consisting of interconnected MnO2 nanoflakes uniformly coated on the CNT surface. The nanocomposite with a composition of 72 wt.% (K0.2MnO20.33H2O)/28 wt.% CNT has a large specific surface area of 237.8 m2/g. Electrochemical properties of the CNT, the pure MnO2, and the MnO2/CNT nanocomposite electrodes are investigated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The MnO2/CNT nanocomposite electrode exhibits much larger specific capacitance compared with both the CNT electrode and the pure MnO2 electrode and significantly improves rate capability compared to the pure MnO2 electrode. The superior supercapacitive performance of the MnO2/CNT nancomposite electrode is due to its high specific surface area and unique hierarchy architecture which facilitate fast electron and ion transport.     

Selective synthesis of diamond and CNT nanostructures directly on stainless steel substrates

Without surface pretreatment or applying additional interlayer, diamond films have been directly synthesized on an Fe-25Cr-5Al steel substrate by a hot filament chemical vapor deposition method from an H₂-1vol.% CH₄ gas mixture. Due to an effective removal of intermediate graphite phase from the diamond-steel interface, the coated diamond films were continuous and adherent well to the steel substrate. Aligned conical diamond structures were also achieved on this steel substrate by negatively biasing the substrate holder and inducing a glow discharge. The deposition behavior of carbon on Fe-Cr-Ni steel substrate was different. A graphite-rich carbon film incorporated with diamond particles grew in the absence of biasing, then aligned carbon nanotube bundles were formed in the presence of negative biasing and glow discharge. The different deposition behavior of carbon on the two kinds of steel substrates was addressed in terms of the effect of their chemical compositions.     

硅热法炼镁动力学的数学模型分析及数值模拟

硅热法是目前工业产镁的主要技术手段,但由于该过程涉及高温化学反应及复杂传热机理,鲜有报道对此技术进行详细动力学及数值计算研究。本工作采用实验的方法获得皮江法炼镁化学反应动力学数据,根据数据分析确定了分段动力学模型,并转化为精确的数学模型。然后建立了耦合数学模型、辐射模型和导热模型的三维非稳态数值计算模型,并通过数值模拟计算,获得工业产镁过程中球团反应转化率和温度随生产时间的分布规律。计算结果表明,生产时间2h后球团最低温度已达1203K,4h后物料平均还原率已达66%。该技术改进方向主要为增加外层球团数量并提高还原罐中心区域传热效率。本工作可以用于指导强化传热设备的设计,预测实际生产效果,节省大量试验投资。     

Influence of synthesis process on preparation and properties of Ni/CNT catalyst

The Ni catalyst was deposited on multi-walled carbon nanotubes using electroless-plating method. The experimental results show that not only the concentrations of the compositions such as NaOH, HCHO (formaldehyde solution) (38 wt.%) and C₄H₄O₆KNa·4H₂O (Rochelle salt crystal) in Ni bath affect the rate of Ni deposition greatly, but also the acid pretreatment of carbon nanotube precursors have a great influence on Ni content and Ni particle size deposited on the surface of the carbon nanotubes and hence the catalytic properties of Ni/CNT in the synthesis of new carbon nanotubes.     

乙烷裂解制乙烯过程反应动力学模型的研究进展

随着乙烯工业的不断发展及能源结构的不断调整,裂解乙烯原料呈现多样性.近年来,乙烷裂解制乙烯技术逐渐成为工业生产的热点.乙烷作为乙烯生产的优选原料,不仅具有收率高、纯度高、质量高的产品优势,同时具有投资低、成本低、能耗低的生产优势.作为裂解炉模拟的核心,研究乙烷裂解过程中的反应动力学模型可为工业生产提供精准预判.随工业应...     

Review of kinetic models for supercritical fluid extraction

The supercritical fluid extraction (SFE) of liquids and solid materials is gaining increasing interest and commercial application in last decades, most particularly under the recent concept of green chemistry and biorefinery. Hence, it is fundamental to provide adequate modeling of the SFE, in order to optimize operating conditions and simulate the global process. This work intends to review the most significant and physically sound models published in the literature for countercurrent liquid-supercritical fluid extraction and SFE of solid matrices, such as the linear driving force, shrinking core, broken and intact cells, and the combination of BIC and shrinking core models. The main assumptions and mass transfer expressions are presented and discussed.     

Synthesis,characterization and operation of a functionalized multi-walled CNT supported MnOx nanocatalyst for deep oxidative desulfurization of sour petroleum fractions

In order to meet the approved sulfur emission standards, it is necessary to develop alternative methods for deep desulfurization of fuels and sour petroleum fractions. In this work a functionalized multi-walled CNT supported MnO_x nanocatalyst (MnO_x/FMWNT) has been synthesized and its performance to enhance the efficiency of oxidative desulfurization (ODS) process for deep desulfurization of sour naphtha has been investigated. The synthesized MnO_x/FMWNT heterogeneous nanocatalyst shows excellent performance regarding the oxidation of sulfur impurities in naphtha petroleum cut to corresponding sulfones. The synthesized catalyst is characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), X-ray diffraction (XRD) and H₂-temperature programmed reduction (H₂-TPR) methods. The performance test of the synthesized nanocatalyst at 25 °C and atmospheric pressure indicates a sulfur removal efficiency of 99.85% within 30 min. The proposed ODS technique allows a substantial cost reduction as compared to existing energy intensive desulfurization processes and can be used for establishing the new large scale catalytic reactors for deep desulfurization of petroleum fractions.     

Nano carbon hybrids from the simultaneous synthesis of CNT/NCD by MPCVD

A carbon hybrid composed by nanocrystalline diamond (NCD) and carbon nanotubes (CNT) was successfully synthesized by microwave plasma chemical vapor deposition (MPCVD), assisted by a continuous delivery of a Fe catalyst. This way, both carbon forms were grown simultaneously, originating a composite structure mainly formed by nanodiamond conglomerates well interconnected by multiwall carbon nanotubes. NCD clusters often develop at the crossing points of different CNTs. A good NCD/CNT mechanical link is predicted based on the observation of carbon nanotubes penetrating and/or involving isolated nanocrystalline diamond clusters. The overall appearance of the NCD/CNT material resembles that of a 2D neuronal network. The nanocrystalline diamond and carbon nanotube phases were structurally confirmed by μ-Raman spectroscopy, the morphological features were characterized by SEM and EDS was used to appraise the catalyst surface distribution.