The role of scale resolution versus inter-particle cohesive forces in two-fluid modeling of bubbling fluidization of Geldart A particles

Coarse grid simulations of Geldart A particles in bubbling fluidized beds using standard two-fluid (TF) models, where the constitutive laws are based on the homogeneity of sub-grid scale structures, have been demonstrated to be unsuccessful due to the existence of significant sub-grid scale heterogeneous structures. However, a definite consensus on the fundamental origin of the failure is still lacking. Some claim that the existence of significant inter-particle cohesive forces results in the sub-grid scale heterogeneous structures which takes the form of agglomerates or clusters; others claim that the inter-particle cohesive forces are not the dominant factor, and that the poor performance of TF models is primarily due to the fact that the grid sizes and the time step used in previous studies are too coarse to fully resolve the bubbling structure. To this end, a short overview is firstly presented to discuss the role of scale resolution and inter-particle cohesive force in two-fluid modeling of Geldart A particles; We then qualitatively explain, using a state-of-the-art discrete particle method, why the methods based on the existence of aggregates or clusters work quite well, although the sub-grid scale structure is not properly identified, that is, the sub-grid scale structure takes the form of a bubble-emulsion phase.     

Selective Conversion of Ethane to Ethene via Oxidative Dehydrogenation Over Ca-doped ThO2 Using CO2 as Oxidant

Ca-doped ThO₂, synthesized by solution combustion method was tested for dehydrogenation of ethane with CO₂. Doping ThO₂ with Ca resulted in the creation of oxide ion vacancies and an increased conversion of ethane compared to pure ThO₂. On Th_0.75Ca_0.25O₂ selectivity to ethene was 97 at 46% ethane conversion at 725 °C. Well-known reference catalysts like 5%Cr/TS-1 or OMS-2 showed significantly lower selectivity, but the former was more active under the same conditions.     

Towards Automated Binding Affinity Prediction Using an Iterative Linear Interaction Energy Approach

Binding affinity prediction of potential drugs to target and off-target proteins is an essential asset in drug development. These predictions require the calculation of binding free energies. In such calculations, it is a major challenge to properly account for both the dynamic nature of the protein and the possible variety of ligand-binding orientations, while keeping computational costs tractable. Recently, an iterative Linear Interaction Energy (LIE) approach was introduced, in which results from multiple simulations of a protein-ligand complex are combined into a single binding free energy using a Boltzmann weighting-based scheme. This method was shown to reach experimental accuracy for flexible proteins while retaining the computational efficiency of the general LIE approach. Here, we show that the iterative LIE approach can be used to predict binding affinities in an automated way. A workflow was designed using preselected protein conformations, automated ligand docking and clustering, and a (semi-)automated molecular dynamics simulation setup. We show that using this workflow, binding affinities of aryloxypropanolamines to the malleable Cytochrome P450 2D6 enzyme can be predicted without a priori knowledge of dominant protein-ligand conformations. In addition, we provide an outlook for an approach to assess the quality of the LIE predictions, based on simulation outcomes only.     

Theory, spectroscopy and kinetics of zeolite catalysed reactions

The combined use of quantum chemistry and spectroscopy to provide a basis of microkinetics modelling is discussed.     

Hydrogenation of fatty acid methyl esters to fatty alcohols at supercritical conditions

Extremely rapid hydrogenation of fatty acid methyl esters (FAME) to fatty alcohols (FOH) occurs when the reaction is conducted in a substantially homogeneous supercritical phase, using propane as a solvent, over a solid catalyst. At these conditions, the limitations of hydrogen transport are eliminated. At temperatures above 240°C, complete conversion of the starting material was reached at residence times of 2 to 3 s, which is several orders of magnitude shorter than reported in the literature. Furthermore, formation of by-products, i.e., hydrocarbons, could be prevented by choosing the right process settings. Hydrogen concentration turned out to be the key parameter for achieving the above two goals. As a result of the supercritical conditions, we could control the hydrogen concentration at the catalyst surface independently of the other process parameters. When methylated rapeseed oil was used as a substrate, the hydrogenation catalyst was deactivated rapidly. However, by using methylated sunflower oil, a catalyst life similar to that obtained in industrial processes was achieved. Our results showed that the hydrogenation of FAME to FOH at supercritical conditions is a much more efficient method than any other published process.     

Design of polymeric dispersants for waterborne coatings

Block and random copolymers of ammonium methacrylate and dimeth-ylaminoethyl methacrylate have been synthesized and tested as dispersants of various organic and inorganic pigments in formulations for waterborne paints. Blockiness of the co-monomer distribution is a prerequisite for good color characteristics in the final paint. It is however noteworthy that a tapered diblock (one-step anionic synthesis), a diblock copolymer with a regular change in composition from one block to the other one, has an interfacial activity quite comparable to the parent “pure” diblock copolymer (two-step anionic synthesis). The most interesting observation is that the poly(dimethylaminoethyl methacrylate) anchoring block can impart stability to dispersions of pigments as different as iron oxide, a blue Cu-phthalocyanine pigment, and a red organic pigment based on pyrrole in representative aqueous paint formulations. This type of diblock copolymer is promising for the design of universal dispersants. Center for Education and Research on Macromolecules (CERM), Sart-Tilman, B6, 4000 Liège, Belgium. Rijksstraatweg 31, P.O.Box 3, 2170 BA Sassenheim, The Netherlands.     

Alternating copolymers based on 1-methylpyrrole and thiophene – synthesis and electrochemical studies

The synthesis and electrochemical polymerisation behaviour of a series of monomers containing 1-methylpyrrole and thiophene is reported. These monomers provide copolymers of well defined monomer sequence in the backbone. Received: 30 October 1997/Revised version: 26 November 1997/Accepted: 27 November 1997     

Dynamic Monte Carlo Simulations of Oscillatory Reactions

The dynamic Monte Carlo method has been used to simulate the 2 A + B₂ → 2 AB reaction catalyzed by a reconstructing substrate. Oscillatory behavior and spatio-temporal is studied as a function of grid size. Spatio-temporal pattern formation has been simulated in various forms: cellular patterns, target patterns, rotating spirals, and turbulent patterns. Cellular patterns are a manifestation of a local synchronization mechanism in which all reaction fronts periodically extinguish each other. This illustrates that dynamic Monte Carlo simulations form a promising technique and can be used to predict macroscopic kinetic phenomena on a molecular basis.