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  • 1.
    Creaser, D.
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    Chalmers University of Technology.
    Hudgins, R.R.
    University of Waterloo.
    Silveston, P.L.
    University of Waterloo.
    Oxygen partial pressure effects on the oxidative dehydrogenation of propane1999In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 54, no 20, p. 4365-4370Article in journal (Refereed)
    Abstract [en]

    The effect of the gas-phase oxygen partial pressure for the oxidative dehydrogenation of propane over a V-Mg-O catalyst was investigated to explore reasons for improved propene yields when dehydrogenation was carried out under periodic operation. Steady-state experiments were performed in which the oxygen partial pressure was varied over a large range at constant propane partial pressures. In addition, the catalyst mass was varied to control the propane conversion so that selectivity and yield could be compared at a constant propane conversion. At the same propane conversion, propene selectivity increased as the partial pressure of oxygen decreased. Thus, propene yields can be improved at steady state by employing low oxygen partial pressures. It is likely that this is the reason for the higher propene yields observed under unsteady-state or periodic operation. It appears that the reaction mechanism must consist of more than one pathway for production of carbon oxides

  • 2.
    Creaser, Derek
    et al.
    Luleå tekniska universitet.
    Andersson, B.
    University of Waterloo.
    Hudgins, R.R.
    Chalmers University of Technology.
    Silveston, P.L.
    Chalmers University of Technology.
    Cyclic operation of the oxidative dehydrogenation of propane1999In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 54, no 20, p. 4437-4448Article in journal (Refereed)
    Abstract [en]

    The cyclic operation of the oxidative dehydrogenation of propane over a V-Mg-O catalyst by the alternate feeding of propane and oxygen gas mixtures was investigated. Generally, the response of the reaction products following a step-change in composition determined the cyclic conditions that resulted in an improved yield of propene. By alternating propane and oxygen with a 1 : 1 cycle split, time-average propene yields higher than steady state could be obtained. The optimal cycle period was about 60 s. This same period provided high propane conversion, as well as high propene selectivity. The cycle split could be varied by shortening the oxygen-feed half of the cycle with little effect on the time-average results. The oxygen half-cycle needed only to be long enough to reoxidize the catalyst. The propane feed scheme was varied by feeding increasing amounts of propane in the oxygen half-cycle. The change in feed scheme caused an increase in the time-average propane conversion that resulted in some further improvement in the propene yield despite some loss in propene selectivity.

  • 3.
    Hedlund, Jonas
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Sustainable Process Engineering.
    Öhrman, Olov
    Msimang, Velaphi
    University of Cape Town.
    Steen, Eric van
    University of Cape Town.
    Böhringer, Walter
    University of Cape Town.
    Sibya, Sifiso
    University of Cape Town.
    Möller, Klaus
    University of Cape Town.
    The synthesis and testing of thin film ZSM-5 catalysts2004In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 59, no 13, p. 2647-2657Article in journal (Refereed)
    Abstract [en]

    The synthesis and catalytic testing of thin ZSM-5 films on glass and alumina beads is described. The thickness of the ZSM-5 films was controlled to 150, 350, 800 and 2300 nm. The samples were characterised by SEM, gas adsorption and p-xylene isomerisation and 1,3,5-tri-isopropyl benzene cracking test reactions. A reaction–diffusion model adequately described the p-xylene isomerisation data. Estimates of model parameters were obtained by fitting the model to the experimental data. In both cases, the reaction rate constant increased with increasing film thickness. The xylene reaction data showed that secondary reaction products increased as expected with increasing diffusion limitations, but the increase was less than that predicted by the variation of thickness only. The trends in the reaction data could be explained by more defects in the thicker films and/or partial poisoning of the zeolite by mobile support cations in thinner films and/or orientation effects.

  • 4. Ji, Xiaoyan
    et al.
    Adidharma, Hertanto
    University of Wyoming.
    Ion-based SAFT2 to represent aqueous multiple-salt solutions at ambient and elevated temperatures and pressures2008In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 63, no 1, p. 131-140Article in journal (Refereed)
    Abstract [en]

    Ion-based SAFT2 is extended to the properties of aqueous multiple-salt solutions at ambient and elevated temperatures and pressures. The short-range interactions between two different cations are allowed to obtain better representations of the solution properties. The adjustable parameter used in the mixing rule for the segment energy is fitted to the experimental osmotic coefficients of two-salt solutions containing one common anion at various temperatures and low pressures. The predictions of the osmotic coefficients, densities, and activity coefficients of multiple-salt solutions including brine/seawater are found to agree with experimental data.

  • 5.
    Ji, Xiaoyan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Adidharma, Hertanto
    University of Wyoming.
    Thermodynamic modeling of ionic liquid density with heterosegmented statistical associating fluid theory2009In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 64, no 9, p. 1985-1992Article in journal (Refereed)
    Abstract [en]

    Heterosegmented statistical associating fluid theory is used to represent the density of ionic liquid. Ionic liquid molecule is divided into several groups representing the alkyls, cation head, and anion. The cation of ionic liquid is modelled as a chain molecule that consists of one spherical segment representing the cation head and groups of segments of different types representing different substituents (alkyls). The anion of ionic liquid is modelled as a spherical segment of different type. To account for the electrostatic/polar interaction between the cation and anion, the spherical segments representing cation head and anion each have one association site, which can only cross associate to each other. The parameters for alkyls are obtained from those of the corresponding n-alkanes and the parameters of groups representing cation head and anion, including the two association parameters, are fitted to a group of experimental ionic liquid data. The performance of the model is examined by describing the densities of three important series of imidazolium-based ionic liquids, i.e., [Cnmim][Tf2N], [Cnmim][BF4], and [Cnmim][PF6]. The model is found to well represent the densities of these ionic liquids from 293.15 to 415 K and up to 650 bar, and well capture the effects of temperature, pressure, and alkyl types on density.

  • 6. Ji, Xiaoyan
    et al.
    Chen, Dongliang
    Nanjing University of Chemical Technology.
    Wei, Tao
    Nanjing University of Chemical Technology.
    Lu, Xiaohua
    Nanjing University of Chemical Technology.
    Wang, Yanru
    Nanjing University of Chemical Technology.
    Shi, Jun
    Nanjing University of Chemical Technology.
    Determination of dissolution kinetics of K2SO4 crystal with ion selective electrode2001In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 56, p. 7017-7024Article in journal (Refereed)
    Abstract [en]

    The dissolution kinetics of potassium sulfate crystals was studied and the effects of hydrodynamic situation and temperature on the dissolution were investigated. The dissolution was determined by measuring the change of electromotive force (E) with the potassium ion selective electrode. From the values of E, the concentration of K+ was calculated combined with an activity coefficient model. The results are accurate and rapid, the maximum deviation is less than 2%. Theory, developed for constant bulk concentration in a rotating disk system, was modified in order to analyze the general grain dissolution process. Normal distribution was introduced in calculating the area of crystals in order to obtain reliable dissolution rate. Using the modified theory diffusion rate constant, equilibrium exchange rate constant and thickness of diffusion layer were obtained. It is found that the diffusion rate constants increase while the thickness of diffusion layer decreases with the increase of temperature and stirring speed; the equilibrium exchange rate is dependent on bulk concentration.

  • 7. Ji, Xiaoyan
    et al.
    Lu, Xiaohua
    Nanjing University of Chemical Technology.
    Zhang, Luzheng
    Nanjing University of Chemical Technology.
    Bao, Ningzhong
    Nanjing University of Chemical Technology.
    Wang, Yanru
    Nanjing University of Chemical Technology.
    Shi, Jun
    Nanjing University of Chemical Technology.
    Lu, Benjamin C. -Y.
    University of Ottawa.
    A further study of solid-liquid equilibrium for the NaCl-NH4Cl-H2O system2000In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 55, p. 4993-5001Article in journal (Refereed)
  • 8. Ji, Xiaoyan
    et al.
    Yan, Jinyue
    Kungliga tekniska högskolan, KTH.
    Saturated thermodynamic properties for the air-water system at elevated temperatures and pressures2003In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 58, no 22, p. 5069-5077Article in journal (Refereed)
    Abstract [en]

    A new thermodynamic model is proposed to calculate the thermodynamic properties for the air-water system in which the dry air was assumed to be a mixture of nitrogen and oxygen with the mole fractions of 0.7812 and 0.2188, respectively. For the vapor phase, fugacity coefficients were calculated with the modified Redlich-Kwong equation of state in which a new interaction parameter of oxygen and water was correlated from the experimental data of oxygen-water system. The dissolved gas followed Henry's law. Henry's constant of nitrogen was calculated with the Helgeson equation of state and that for oxygen was correlated from the experimental data of oxygen-water system. The proposed model was verified by comparing the calculated results with the available experimental data. It is shown that the proposed model is suitable for predicting saturated thermodynamic properties for the air-water system up to 300°C and 200 atm. Furthermore, the prediction results of the proposed model are better than those calculated with the model of Rabinovich and Beketov (Moist Gases, Thermodynamic Properties. Begell: House, 1995), and the application range is wider than that of the model of Hyland and Wexler (ASHRAE Trans. 89(2A) (1983a, b) 500-519, 520-535) which are among the best of today's models.

  • 9.
    Ji, Yuanhui
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Ji, Xiaoyan
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Liu, Chang
    Nanjing University of Technology.
    Feng, Xin
    Nanjing University of Technology.
    Lu, Xiaohua
    Nanjing University of Technology.
    Modelling of mass transfer coupling with crystallization kinetics in microscale2010In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 65, no 9, p. 2649-2655Article in journal (Refereed)
    Abstract [en]

    Microstructure technologies have attracted interests in chemistry, chemical engineering, and biotechnology. To investigate the mass transfer of ions and crystallization of crystals in microscale and then to explain the formation mechanism of the porous structure materials, a microscale mathematical model for mass transfer processes coupling with local reactions is proposed in which the chemical potential gradient Δμ is used as the driving force to avoid the discontinuity of the kinetics equations in the micro-channels. Meanwhile, the dissolution kinetics of KCl at 298.15 K is measured to determine the dissolution rate constant kd and the average area of crystals Ac. The investigation for the fractional crystallization process of carnallite shows that the calculated mixing time versus channel width agree with the Einstein diffusion equation, which validates that the model can be used to describe the ion diffusion very well. Meanwhile, to have an accurate Δμ of KCl, in the channel width of or narrower than 2.0×10-6 m, it is enough to consider the diffusion only, while in the channel width of or wider than 2.0×10-5 m, diffusion should be coupled with reaction. The investigation also shows the vital of the consideration of the ionic activity coefficient for the investigated systems in micron scales. Moreover, the new formation mechanism of the porous structures in the inorganic material fabrication will be proposed from the process simulation for the synthesis of porous KCl, which will provide a reference for the porous structure formation in the advanced inorganic material synthesis.

  • 10.
    Larsson, Simon
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Gustafsson, Gustaf
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Oudich, Aliae
    Jonsén, Pär
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Häggblad, Hans-åke
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mechanics of Solid Materials.
    Experimental methodology for study of granular material flow using digital speckle photography2016In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 155, p. 524-536Article in journal (Refereed)
    Abstract [en]

    Granular material flow occurs in many industrial applications, and the characteristics of such flow is challenging to measure. Therefore, an experimental method that captures the flow behavior at different loading situations is desired.

    In this work, experimental measurements of granular material flow with digital speckle photography (DSP) are carried out. The granular flow process is recorded with a high-speed camera; the image series are then analyzed using the DSP method. This approach enables field data such as displacement, velocity, and strain fields to be visualized during the granular material flow process. Three different scenarios were studied: free surface flow in a fill shoe, flow without a free surface in a fill shoe, and the rearrangement of material in a cavity. The results showed that it is possible to obtain field data of the motion of particles for all three scenarios with the DSP technique. The presented experimental methodology can be used to capture complex flow behavior of granular material.

  • 11. Rezaei, Fateme
    et al.
    Webley, Paul
    Monash University, Melbourne, VIC.
    Optimum structured adsorbents for gas separation processes2009In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 64, p. 5182-5191Article in journal (Refereed)
1 - 11 of 11
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