Chemical Engineering & Technology

Cover image for Chemical Engineering & Technology

April, 2004

Volume 27, Issue 4

Pages 351–452

    1. High-Pressure Homogenization as a Process for Emulsion Formation (pages 361–368)

      S. Schultz, G. Wagner, K. Urban and J. Ulrich

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200406111

      High-pressure homogenization, a method widely used in the pharmaceutical and food industries, is compared to other common mechanical emulsification processes. For the most widely used continuous emulsification techniques the influence of relevant intrinsic parameters on the dispersion properties during emulsification is discussed. High-pressure systems are presented in detail and the average droplet sizes obtained experimentally are compared with data from the literature.

    2. Influence of the Column Design on the HPLC (High Performance Liquid Chromatography) Process (pages 369–376)

      H. Boysen, G. Wozny and G. Guiochon

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200403180

      In process chromatography, calculations are used to support the setup of separation systems. Many contributions dealing with the calculation of the effects of the thermodynamics and mass transfer kinetics involved in the chromatographic have been established. Unfortunately, the production capacity in preparative chromatography can only be increased by increasing the column diameter.

    3. Variational Approach to Diffusion Reaction in Spherical Porous Catalyst (pages 376–377)

      J.-H. He and H.-M. Liu

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401872

      A variational formulation of a chemical problem can be very useful because special solution methods can be used, and it gives a deeper insight into the structure, for example, of diffusion reaction. In this study, a variational theory is established for coupled diffusion and nth-order reaction in a spherical catalyst pellet. Various variational approaches can be applied to obtain both analytical and numerical solutions.

    4. Method of Laser-induced Breakdown Detection and Application Examples (pages 377–382)

      T. Bundschuh, T. Wagner, M. Weber and R. Köster

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200403155

      The Laser-induced Breakdown Detection is a rather novel and highly sensitive method for the non-invasive determination of both the concentration and the number-weighted mean diameter of nanoparticles (colloids) in liquids. Compared to other methods the limit of detection is lower by several orders of magnitude. Their high surface to masse ratio results in a large sorption capacity that on the one hand offers great technical possibilities, on the other hand colloidal transport of pollutants can be a serious environmental problem.

    5. Suitability of the Propulsion Jet Reactor for a Reaction Kinetics Examination of Heterogeneous Gas-Catalytic Normal-Pressure Reactions (pages 383–389)

      B. Hesselbarth and R. Adler

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200400041

      Propulsion jet reactors may be used as differential recycle loop reactors in heterogeneous gas catalysis for reaction kinetics analysis. This reactor features straightforward design resulting in comparatively low manufacturing costs. Because of its advantages, the propulsion jet reactor is suited to kinetic examination under extreme reaction conditions with regard to pressure, temperature, or corrosion. The typical features here are the lower gas densities, which decrease further with increasing reaction temperatures, thus reducing the kinetic energy input through the propulsion jet.

    6. Modeling Nonsteady-State Regimes of Dilute Pneumatic Conveying (pages 390–397)

      D. Eskin, Y. Leonenko and O. Vinogradov

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401881

      In an experimental setup for an industrial pipeline it is important to know the distance required for obtaining a steady-state flow regime. A simple model of a monodispersed gas-particle flow in a pipe is presented. The model is one-dimensional, it is based on a continuum approach, and it is suitable for fast and reliable estimations of solids velocities and pressure losses in diluted pipeline flows in both steady-state and nonsteady-state regimes.

    7. CFD Modeling of a Bubble Column Reactor Carrying out a Consecutive A [RIGHTWARDS ARROW] B [RIGHTWARDS ARROW] C Reaction (pages 398–406)

      J.M. van Baten and R. Krishna

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401968

      Bubble columns are widely used in industry for carrying out a variety of chemical reactions such as hydrogenations, oxidations and the Fischer-Tropsch synthesis. Many recent experimental studies have emphasised the strong influence of column diameter on bubble column hydrodynamics. The objective of the present paper was to develop a CFD model to describe a bubble column reactor for carrying out a consecutive first-order reaction sequence A [RIGHTWARDS ARROW] B [RIGHTWARDS ARROW] C and to underline the strong influence of scale on the reactor conversion and selectivity.

    8. Sedimentation and Coalescence Profiles in Liquid-Liquid Batch Settling Experiments (pages 407–413)

      G.-Z. Yu and Z.-S. Mao

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401884

      The inflexion time, at which the sedimentation zone vanishes, can be obtained by analysis of the coalescence profile. Therefore, the sedimentation profile can be predicted and the size of drop and interfacial area can be estimated. The model is verified with published data as well as experimental data of dispersions with different holdups at different impeller speeds in a batch settler.

    9. Liquid/Solid Mass Transfer in Fixed Beds (pages 414–416)

      M. Zaki, I. Nirdosh, G.H. Sedahmed and M.H.I. Baird

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401912

      In view of their high area-unit volume and their high mass transfer coefficient, fixed beds are widely used by chemical engineers to conduct liquid/solid diffusion-controlled processes, such as catalytic reactions, ion exchange, and adsorption processes. The aim of the present work was to study the rate of mass transfer in fixed beds of cylinders using the diffusion-controlled dissolution of copper in acidified potassium dichromate. Variables studied were solution, velocity, and cylinder diameter.

    10. Dynamics of Capillary Electrochromatography: Experimental Study of Flow and Transport in Particulate Beds (pages 417–428)

      G. Chen, M. Pačes, M. Marek, Y. Zhang, A. Seidel-Morgenstern and U. Tallarek

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401939

      The chromatographic performance with respect to the flow behavior and dispersion in fixed beds of nonporous and macroporous particles has been studied in capillary HPLC and electrochromatography. Complementary and consistent results were observed for the average electroosmotic flow through packed capillaries. It was found to depend on particle porosity and distinct contributions to the electrical double layer behavior within and between particles. Based on these data, an optimum chromatographic performance in view of speed and efficiency can be achieved by straightforward adjustment of the electrolyte concentration and characteristic intraparticle pore size.

    11. The Effect of Solids Inventory and Other Factors on the Axial Solids Holdup Profiles in a Twin-Riser System (pages 429–434)

      A.-J. Yan, J. (Jing-Xu) Zhu, P.-J. Remize and A. Bordas

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401954

      To successfully model, design, and optimize the catalyst flow in a commercial scale riser, it is essential to obtain the fundamental knowledge from pilot scale risers, especially the knowledge of the solids distribution in longer circulating fluidized bed risers. This governs the pressure drop along the CFB riser, is directly related to the solids residence time in the riser and can also affect gas-solids contacting efficiency, heat and mass transfer rates, and chemical reaction selectivity. Here the influence of solids inventory, solids fluxes, superficial gas velocity, and riser diameter on the axial solids holdup profiles is reported by measuring pressure drops with pressure transducers along two risers.

    12. A Semi-continuous Process for the Synthesis of Methyl Carbamate from Urea and Methanol (pages 435–439)

      J. Sun, B. Yang and H. Lin

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200401911

      A semi-continuous process for the synthesis of methyl carbamate from urea and methanol was investigated in the autoclave without the catalyst. Some significant parameters were determined in terms of the methyl carbamate yield. Furthermore, the kinetics of this reaction were researched. It was demonstrated that removing methanol containing ammonia from the autoclave and replacing it with continuously feeding fresh methanol resulted in a higher reaction rate and a high MC yield.

    13. Dynamic Analysis of Diffusion and Adsorption of Water-Miscible and Water-Immiscible Organic Vapors in Soil (pages 440–446)

      M. Kalender and C. Akosman

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200402005

      The dynamic analysis of diffusion and adsorption of water-miscible and water-immiscible volatile organic compounds in a soil pellet has been performed experimentally by using the single pellet moment technique. The results obtained with dry and wet systems showed that volatile organic tracers were adsorbed reversibly onto the soil. The overall adsorption equilibrium constants decreased with relative humidity, and the water-miscible VOCs displayed greater sorption and a larger change in effective diffusivity with moisture than the water-immiscible VOCs.

    14. Sequence-Specific Molecular Lithography Towards DNA-Templated Electronics (pages 447–452)

      K. Keren and E. Braun

      Version of Record online: 29 MAR 2004 | DOI: 10.1002/ceat.200410056

      Large-scale DNA-templated electronics require complex manipulation of double-stranded DNA molecules, as well as patterning of the electrical properties instilled to them by, e.g., metallization. To that end, sequence-specific molecular lithography on single DNA molecules has been developed. This was achieved by harnessing the homologous recombination process of the RecA protein. Sequence-specific patterning of the metal coating of DNA molecules, localization of arbitrary labeled molecular objects at any desired dsDNA address without prior modifications, and generation of molecularly accurate stable dsDNA-dsDNA junctions are demonstrated. The information encoded in the DNA molecules directs the lithographic process.