The benefits of continuous processing and the challenges related to the integration with efficient downstream units for end-to-end manufacturing have spurred the development of efficient miniaturized ...continuously-operated separators. Membrane-free microseparators with specifically positioned internal structures subjecting fluids to a capillary pressure gradient have been previously shown to enable efficient gas-liquid separation. Here we present initial studies on the model-based design of a liquid-liquid microseparator with pillars of various diameters between two plates. For the optimization of in silico separator performance, mesoscopic lattice-Boltzmann modeling was used. Simulation results at various conditions revealed the possibility to improve the separation of two liquids by changing the geometrical characteristics of the microseparator.
A substantial amount of publications each year demonstrate how through the application of microprocess engineering significant benefits can be obtained concerning product yield, purity and time ...needed for chemical transformations, compared to the equivalent
bulk reactions. Microreactors clearly hold the potential to revolutionize chemical synthesis, but scarce articles demonstrate specific suggestions for possible replacement of existent industrial processes. The focus of this review is to assess whether significant
advances have been made for the implementation of microstructured devices into existent industrial processes or their complete replacement. The papers are reviewed in light of particular beneficial microreactor characteristics with potential for process intensification.
A theoretical description of the convection-diffusion process in a homogeneous system enabling estimation of diffusion coefficients employing commercially available Y-junction microchannel is ...presented. A detailed numerical analysis based on finite volumes and finite differences, namely the explicit, implicit and Crank-Nicolson method, was performed and analyzed on the same domain in order to verify the proposed models. All numerical approaches provided stable solutions with certain numerical variations depending on the number of iterations defined by the mesh density. In addition, the method was validated with measurements of diffusion coefficients of some selected components in the short Y-junction microchannel. Benefits and possible pitfalls of this estimation method are discussed. Key words: diffusion coefficient, microfluidic device, Y-junction microchannel, mathematical model, numerical methods
Results of an integrated approach for the improvement of progesterone 11α-hydroxylation by
Rhizopus nigricans, which is one of the key steps in the production of corticosteroid drugs and hormones, ...are presented. Several issues have been addressed in order to increase process productivity, including biocatalyst immobilization, improvement in the solubility of the lipophilic substrate, setting-up of continuous reaction process and easing downstream processing. After preliminary studies on the effects on
Rhizopus nigricans morphology, fungal pellets of a desired size and structure could be obtained. The mycelia grown in spherical agglomerates further enabled its continuous use in the process of biotransformation. The problem of low steroid solubility was addressed by the addition of organic solvents or β-cyclodextrin. In order to develop an integrated biotransformation process, a continuous two-liquid phase extraction within microchannel device has been set up, where very efficient steroid extraction was achieved within a few seconds.
Two different types of carriers differing fundamentally in size, shape and structure were evaluated in parallel testing for nitrification potential using the moving-bed biofilm reactor (MBBR) ...technology. One of the carriers used was a cylindrical high-density polyethylene ring shaped carrier (AnoxKaldnes, K1 carrier) and the other was a spherical polyvinyl alcohol (PVA) gel bead shaped carrier (Kuraray, PVA-gel carrier). For each MBBR process, using artificial wastewater under autotrophic conditions, high maximal nitrification rates at 20 degrees C were obtained. For the K1 carrier up to 27 mgNH(4)-N/L.h (at 37% filling fraction) was found, corresponding to 49 mgNH(4)-N/L.h at the recommended maximum filling fraction of 67%. This corresponds to a nitrification area rate of 3.5 gNH(4)-N/m(2).d for the K1 carrier at 20 degrees C. For the PVA-gel carrier up to 32 mgNH(4)-N/L.h (at 9.6% filling fraction) was found, corresponding to 50.0 mg NH(4)-N/L.h at the recommended maximum filling fraction of 15%. At the recommended filling fractions, the two carriers therefore required about the same reactor volume to reach the maximum observed nitrification rate. This presumption allowed us to estimate the effective specific surface area for the PVA gel carrier up to 2,500 m(2)/m(3) versus 1,000 m(2)/m(3) when only the outer surface is considered.
Microchannel reactor technologies are gaining widespread use in a large range of areas, which comprise biotechnology and chemistry. The small volumes involved and the favorable mass and heat transfer ...inherent to these devices make them particularly useful for the screening of biocatalysts and rapid characterization of bioconversion systems.
In the present work, the enzymatic oxidation of cholesterol to 4-cholesten-3-one performed within microchannels by cholesterol oxidase, was studied in a two-phase system, comprising an organic phase as substrate and product pool and an aqueous phase with dissolved enzyme. A mathematical model based on mass balances for cholesterol, 4-cholesten-3-one and dissolved oxygen concentrations, comprising double-substrate Michaelis–Menten kinetics and the velocity profile of two immiscible fluids, was developed in order to describe and predict the process of cholesterol oxidation. The numerical procedure of solving the non-linear 3D model was based on an implicit finite-difference method improved by non-equidistant differences.
In a Y-shape microreactor geometry, roughly up to 70% conversion of cholesterol was achieved at residence times below 1
min. The suitable adjustment of the ratio of the fluid flow rates was performed by taking into account the viscosity of the fluids involved. This allowed for phase separation to be reestablished at the Y-shaped exit from the microreactor and thereby enabled
in situ product separation from the aqueous phase containing the enzyme.
The mechanisms by which carbon nanotubes nucleate and grow are still poorly understood. Understanding and mathematically describing the process is crucial for its optimization. This paper reviews ...different models which have been proposed to explain carbon nanotube growth in the chemical vapor deposition process. The review is divided into two sections, the first section describes some nucleation, growth and termination simulations based on molecular dynamics, and the second section describes some mathematical models based on transport and kinetics theories. Key words: Carbon nanotubes, CVD, growth simulations, kinetics
Acid-catalyzed esterification of benzoic acid with ethanol was investigated in a continuous tubular flow reactor heated by microwaves. The microwave reactor operated at medium pressure and high ...temperature conditions. Esterification was catalyzed with sulfuric acid and with ion exchange resins. Kinetic parameters of esterification were determined in a stirred glass vessel using conventional heating. A mathematical model was proposed to describe temperature profiles and to predict the conversion of the reaction in the tubular flow microwave reactor. The calculated conversions of benzoic acid based on predicted temperature profiles agree with experimental data. The operating conditions in the microwave reactor allowed us to achieve high conversions at relatively low residence times.
The continuous ethyl acetate extraction of progesterone and 11alpha-hydroxyprogesterone, a reactant and the product of the biotransformation step involved in corticosteroid production, was studied in ...a microchannel at different flow velocities. In addition, non-steady state batch extraction without mixing was performed and modelled in order to verify the theoretically predicted parameters. In order to analyze experimental data and to forecast microreactor performance, a three-dimensional mathematical model with convection and diffusion terms was developed considering the velocity profile for laminar flow of two parallel phases in a microchannel at steady-state conditions. For the numerical solution of a complex equation system, non-equidistant finite differences were used. Very good agreement between model calculations and experimental data was achieved without any fitting procedure. Due to the efficient phase separation and high extraction yields obtained, the micro scale extraction units were found to be a promising tool for the development of an integrated system of 11alpha-hydroxylation of progesterone by Rhizopus nigricans in the form of pellets.
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