Dynamic Simulation of Heterogeneous Catalysis at Particle Scale to Estimate the Kinetic Parameters for the Pore Diffusion Model

In this work, dynamic simulation at particle scale is carried out to predict the kinetics of solid catalyzed esterification reaction between acetic acid and methanol to produce methyl acetate and water. The reaction kinetic data utilized for modeling and validation is with solid catalyst as Indion 180. It was observed that the reaction rate and kinetics inside the pores of the catalyst is of higher magnitude as compared to bulk liquid. Each solid catalyst particle is surrounded by reactant solution of equal volume. A dynamic simulation is carried out using COMSOL Multiphysics which has solver for diffusion-reaction equation for both in liquid phase and inside porous catalyst particle. The intrinsic reaction rate constants for bulk liquid phase and inside the particle are obtained by solving the full diffusion-reaction equation and optimization method. Three different models (model 1,2,3) were proposed for evaluating the rate constants from the experimental kinetic data. The three models differ in the way the boundary condition of acetic acid concentration is defined at the interface of a catalyst particle and its immediate surrounding liquid. The different models originated based on the possibility of numerical solution to partial differential equations pertaining to particle scale catalytic reactions as distributed parameter models by various software such as MATLAB and COMSOL multiphysics. They also differ in the way the initial kinetics is utilized in evaluating the rate constants for outside and inside the catalyst particle. One of the proposed models (model 3) has shown good agreement with the experimental data. Copyright © 2018 BCREC Group. All rights reserved Received: 18th January 2018; Revised: 26th April 2018; Accepted: 8th May 2018 How to Cite: Patan, A.K., Mekala, M., Thamida, S.K. (2018). Dynamic Simulation of Heterogeneous Catalysis at Particle Scale to Estimate the Kinetic Parameters for the Pore Diffusion Model. Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3): 420-428 (doi:10.9767/bcrec.13.3.2098.420-428) Permalink/DOI: https://doi.org/10.9767/bcrec.13.3.2098.420-42

Electrostatic and electrokinetic contributions to the elastic moduli of a driven membrane

We discuss the electrostatic contribution to the elastic moduli of a cell or artificial membrane placed in an electrolyte and driven by a DC electric field. The field drives ion currents across the membrane, through specific channels, pumps or natural pores. In steady state, charges accumulate in the Debye layers close to the membrane, modifying the membrane elastic moduli. We first study a model of a membrane of zero thickness, later generalizing this treatment to allow for a finite thickness and finite dielectric constant. Our results clarify and extend the results presented in [D. Lacoste, M. Cosentino Lagomarsino, and J. F. Joanny, Europhys. Lett., {\bf 77}, 18006 (2007)], by providing a physical explanation for a destabilizing term proportional to \kps^3 in the fluctuation spectrum, which we relate to a nonlinear ($E^2$) electro-kinetic effect called induced-charge electro-osmosis (ICEO). Recent studies of ICEO have focused on electrodes and polarizable particles, where an applied bulk field is perturbed by capacitive charging of the double layer and drives flow along the field axis toward surface protrusions; in contrast, we predict "reverse" ICEO flows around driven membranes, due to curvature-induced tangential fields within a non-equilibrium double layer, which hydrodynamically enhance protrusions. We also consider the effect of incorporating the dynamics of a spatially dependent concentration field for the ion channels.Comment: 22 pages, 10 figures. Under review for EPJ

Towards an understanding of induced-charge electrokinetics at large applied voltages in concentrated solutions

The venerable theory of electrokinetic phenomena rests on the hypothesis of a dilute solution of point-like ions in quasi-equilibrium with a weakly charged surface, whose potential relative to the bulk is of order the thermal voltage (kT/e ≈ 25 mV at room temperature). In nonlinear electrokinetic phenomena, such as AC or induced-charge electro-osmosis (ACEO, ICEO) and induced-charge electrophoresis (ICEP), several V ≈ 100 kT/e are applied to polarizable surfaces in microscopic geometries, and the resulting electric fields and induced surface charges are large enough to violate the assumptions of the classical theory. In this article, we review the experimental and theoretical literatures, highlight discrepancies between theory and experiment, introduce possible modifications of the theory, and analyze their consequences. We argue that, in response to a large applied voltage, the “compact layer” and “shear plane” effectively advance into the liquid, due to the crowding of counterions. Using simple continuum models, we predict two general trends at large voltages: (i) ionic crowding against a blocking surface expands the diffuse double layer and thus decreases its differential capacitance, and (ii) a charge-induced viscosity increase near the surface reduces the electro-osmotic mobility; each trend is enhanced by dielectric saturation. The first effect is able to predict high-frequency flow reversal in ACEO pumps, while the second may explain the decay of ICEO flow with increasing salt concentration. Through several colloidal examples, such as ICEP of an uncharged metal sphere in an asymmetric electrolyte, we show that nonlinear electrokinetic phenomena are generally ion-specific. Similar theoretical issues arise in nanofluidics (due to confinement) and ionic liquids (due to the lack of solvent), so the paper concludes with a general framework of modified electrokinetic equations for finite-sized ions.National Science Foundation (U.S.) (contract DMS-0707641

Isolation of Streptococcus salivarius from human oral samples and In vivo recombination cloning of EAL 2 of Streptococcus uberis C6344

The second messenger cyclic diguanylate monophosphate (c-di-GMP) has been proven to be a central regulator for physiological and metabolic processes including biofilm formation and sessile to motile transitioning (1,2). The synthesis and degradation of c-di-GMP are regulated by GGDEF- respectively EAL-domain proteins. Recently, c-di-GMP has been discovered in the Gram-positive Streptococcus genus including Streptococcus gallolyticus, which showed to have diguanylate cyclase activity (3). Characterisation of the c-di-GMP network in other Streptococcus is of relevance. Hence, the aim of this project was the assessment of the GGDEF- and EAL domains from the animal pathogenic Streptococcus uberis and Streptococcus henryi. In vivo recombination cloning was used for the analysis of the GGDEF, EAL and GGDEF-EAL domain proteins from S. uberis and S. henryi. The cloning was unsuccessful for most of the domain proteins, except, for EAL 2 of S. uberis. However, analysis of the sequencing results for the cloned EAL 2 presented mutations. Further studies testing alternative cloning methods should be applied. Research regarding probiotic streptococci is also of interest. Therefore, isolation of Streptococcus salivarius from human oral samples using Streptococcus Selection Agar was conducted. Isolation of S. salivarius from human saliva and tongue samples was successful using Streptococcus Selection Agar. Other Streptococcus spp., Lactobacillus, Staphylococcus, and additional bacterial species were also isolated.

Experimental investigations of the production of methyl acetate in batch catalytic distillation process in the presence of Indion 180

667-671As a novel study, esterification of acetic acid with methanol has been studied in a simple batch reactive distillation apparatus to produce methyl acetate as main product and water as byproduct. Novel solid catalyst named Indion 180 has been used in this esterification process. The product methyl acetate can be distilled out in two ways namely sequential and simultaneous reactive distillation. In the simple distillation batch process, first the reaction is carried out till the equilibrium with total reflux of vapours, and then distillation is carried out where the vapours are condensed and collected separately with zero reflux. In the second case, simultaneous reaction and distillation processes are carried out. During these experiments, the dynamics of bubble point temperature of the reboiler is recorded and analyzed. From the experimental results it is found that the maximum purity of methyl acetate in instantaneous distillate of reaction followed by distillation and simultaneous reaction and distillation are 0.847 and 0.782, respectively, as analyzed by gas chromatography. From these studies it is found that a batch distillation apparatus itself can be used in certain way to produce the desired product for the case of methyl acetate production by monitoring the temperature regime of the reboiler