Prague, Czech Republic

Institute of Chemical Process Fundamentals, Academy of science of the Czech Republic, v.v.i. is one of the six institutes belonging to the ASCR chemical science section and is a research centre in a variety of fields such as chemistry, biochemistry, catalysis and environment. Its research topics include multiphase reaction systems for the design of chemical synthesis chemical processes and new materials development, energetics and protection of environment. Its national and international reputation is ascertained by its participation in EU financed research projects, such as EUCAARI or MULTIPRO. The MATINOES project was evaluated to belong to 20 best projects of the 6th Frame Programme. Wikipedia.

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Sovova H.,Czech Institute of Chemical Process Fundamentals | Stateva R.P.,Bulgarian Academy of Science
Reviews in Chemical Engineering | Year: 2011

In the 21st century, the mission of chemical engineering is to promote innovative technologies that reduce or eliminate the use or generation of hazardous materials in the design and manufacture of chemical products. The sustainable use of renewable resources, complying with consumer health and environmental requirements, motivates the design, optimisation, and application of green benign processes. Supercritical fluid extraction is a typical example of a novel technology for the ecologically compatible production of natural substances of high industrial potential from renewable resources such as vegetable matrices that finds extended industrial application. The present review is devoted to the stage of development of supercritical fluid extraction from vegetable material in the last 20 years. Without the ambition to be exhaustive, it offers an extended, in comparison with previous reviews, enumeration of extracted plant materials, discusses the mathematical modelling of the process, and advocates a choice for the appropriate model that is based on characteristic times of individual extraction steps. Finally, the attention is focussed on the elements of a thermodynamic modelling framework designed to predict and model robustly and efficiently the complex phase equilibria of the systems solute + supercritical fluid. © 2011 by Walter de Gruyter.

Sovova H.,Czech Institute of Chemical Process Fundamentals
Journal of Supercritical Fluids | Year: 2012

Kinetics of supercritical fluid extraction (SFE) from plants is variable due to different micro-structure of plants and their parts, different properties of extracted substances and solvents, and different flow patterns in the extractor. Variety of published mathematical models for SFE of natural products corresponds to this diversification. This study presents simplified equations of extraction curves in terms of characteristic times of four single extraction steps: internal diffusion, external mass transfer, hypothetic equilibrium extraction without mass transfer resistance, and displacement of the solution from the extractor. Preliminary evaluation of experimental extraction curves using these equations facilitates the choice of proper detailed model for SFE and enables estimation of changes in the extraction kinetics with the changes in operation conditions and extraction geometry. © 2011 Elsevier B.V.

Malijevsk A.,Czech Institute of Chemical Process Fundamentals | Malijevsk A.,Institute of Chemical Technology Prague | Jackson G.,Imperial College London
Journal of Physics Condensed Matter | Year: 2012

The structural and interfacial properties of nanoscopic liquid drops are assessed by means of mechanical, thermodynamical, and statistical mechanical approaches that are discussed in detail, including original developments at both the macroscopic level and the microscopic level of density functional theory (DFT). With a novel analysis we show that a purely macroscopic (static) mechanical treatment can lead to a qualitatively reasonable description of the surface tension and the Tolman length of a liquid drop; the latter parameter, which characterizes the curvature dependence of the tension, is found to be negative and has a magnitude of about a half of the molecular dimension. A mechanical slant cannot, however, be considered satisfactory for small finite-size systems where fluctuation effects are significant. From the opposite perspective, a curvature expansion of the macroscopic thermodynamic properties (density and chemical potential) is then used to demonstrate that a purely thermodynamic approach of this type cannot in itself correctly account for the curvature correction of the surface tension of liquid drops. We emphasize that any approach, e.g.,classical nucleation theory, which is based on a purely macroscopic viewpoint, does not lead to a reliable representation when the radius of the drop becomes microscopic. The description of the enhanced inhomogeneity exhibited by small drops (particularly in the dense interior) necessitates a treatment at the molecular level to account for finite-size and surface effects correctly. The so-called mechanical route, which corresponds to a molecular-level extension of the macroscopic theory of elasticity and is particularly popular in molecular dynamics simulation, also appears to be unreliable due to the inherent ambiguity in the definition of the microscopic pressure tensor, an observation which has been known for decades but is frequently ignored. The union of the theory of capillarity (developed in the nineteenth century by Gibbs and then promoted by Tolman) with a microscopic DFT treatment allows for a direct and unambiguous description of the interfacial properties of drops of arbitrary size; DFT provides all of the bulk and surface characteristics of the system that are required to uniquely define its thermodynamic properties. In this vein, we propose a non-local mean-field DFT for Lennard-Jones (LJ) fluids to examine drops of varying size. A comparison of the predictions of our DFT with recent simulation data based on a second-order fluctuation analysis (Sampayo etal 2010 J. Chem. Phys. 132 141101) reveals the consistency of the two treatments. This observation highlights the significance of fluctuation effects in small drops, which give rise to additional entropic (thermal non-mechanical) contributions, in contrast to what one observes in the case of planar interfaces which are governed by the laws of mechanical equilibrium. A small negative Tolman length (which is found to be about a tenth of the molecular diameter) and a non-monotonic behaviour of the surface tension with the drop radius are predicted for the LJ fluid. Finally, the limits of the validity of the Tolman approach, the effect of the range of the intermolecular potential, and the behaviour of bubbles are briefly discussed. © 2012 IOP Publishing Ltd.

Ruzicka M.C.,Czech Institute of Chemical Process Fundamentals
Chemical Engineering Research and Design | Year: 2013

The goal of this contribution is to formulate the simplest possible model for the bubble column hydrodynamics and analyse it for steady states, stability, and unsteady behaviour. The governing equations are based on the mass balance of the gas phase. Two closures for the gas velocity are used and reflect two typical operational regimes, homogeneous (HoR) and heterogeneous (HeR). The model has five parameters: column height H, terminal bubble speed u0, hindrance exponent n, enhance exponent m, gas flow rate q. Three branches of steady solutions were found for HoR, one stable, one unstable, one neutrally stable. The first two are physically relevant, are of the node-type, and merge in the turning point bifurcation at large enough gas input. Two branches of steady solutions were found for HeR, one stable and one neutrally stable. The first one is physically relevant, is of the node-type, and persists for all plausible parameter values. In both regimes, the neutrally stable solution was classified as unphysical. The transition regime (TrR) was obtained by matching the stable solutions of HoR and HeR, with help of a sigmoidal bridging function. The system stability was related to the model topology. The linear approximation of the bubble column dynamics was studied and the relaxation time estimated. The full nonlinear dynamics was demonstrated too. Both the steady and unsteady behaviour of the bubble column was compared with available experimental data. © 2012 The Institution of Chemical Engineers.

Kubicka D.,Academy of Sciences of the Czech Republic | Kaluza L.,Czech Institute of Chemical Process Fundamentals
Applied Catalysis A: General | Year: 2010

Deoxygenation of vegetable oils has a potential to become an important process for production of biofuels. The present work focuses on investigation of Ni, Mo, and NiMo sulfided catalysts prepared by impregnation in deoxygenation of rapeseed oil at 260-280 °C, 3.5 MPa and 0.25-4 h-1 in a fixed-bed reactor. The activity of the catalysts decreased in the order NiMo/Al2O3 > Mo/Al2O3 > Ni/Al2O3. The catalysts exhibited significantly different product distributions. The bimetallic NiMo catalysts showed higher yields of hydrocarbons than the monometallic catalysts at a given conversion. Apart from the various oxygenated product intermediates, NiMo/Al2O3 yielded a mixture of decarboxylation and hydrodeoxygenation hydrocarbon products while Ni/Al2O3 yielded only decarboxylation hydrocarbon products and Mo/Al2O3 yielded almost exclusively hydrodeoxygenation hydrocarbon products. The effect of Ni/(Ni + Mo) atomic ratio in the range 0.2-0.4 on the activity and selectivity was not significant. © 2009 Elsevier B.V. All rights reserved.

Wein O.,Czech Institute of Chemical Process Fundamentals
International Journal of Heat and Mass Transfer | Year: 2010

Electrochemically driven steady convective diffusion is analyzed for electrodiffusion friction probes of arbitrary convex shape in a stream of microdisperse liquid, assuming non-linear velocity profiles ranging from simple shear flow (p = 1) to ideal slip motion (p = 0). Correction on the edge effects due to spatial diffusion at medium Peclet numbers is given, using the recent numerical data about the strip-like probes by Wein [25] Simple correction formulas are presented for the disk-like probes. © 2010 Elsevier Ltd. All rights reserved.

Wein O.,Czech Institute of Chemical Process Fundamentals
International Journal of Heat and Mass Transfer | Year: 2010

Full equations of convective diffusion are solved numerically for a strip-like (2D) electrodiffusion friction probe in a stream of microdisperse liquid, assuming a non-linear near-to-wall velocity profile ranging from simple shear flow (p = 1) to ideal slip (p = 0). The range of generalized Peclet number H from H = 0.01 (almost pure spatial diffusion) to H = 100 (diffusion layer with negligible longitudinal diffusion) covers all cases of possible experimental relevance. The main result is expressed as a relative deviation of actual total diffusion flux N from its diffusion-layer approximation NDLA, Ψ = N/NDLA - 1. © 2010 Elsevier Ltd. All rights reserved.

Poloncarzova M.,Czech Institute of Chemical Process Fundamentals | Vejrazka J.,Czech Institute of Chemical Process Fundamentals | Vesely V.,Czech Institute of Chemical Process Fundamentals | Izak P.,Czech Institute of Chemical Process Fundamentals
Angewandte Chemie - International Edition | Year: 2011

Coming clean: Impurities and carbon dioxide in raw biogas are separated by a "condensing-liquid membrane", based on the different solubility of components in a very thin continuously refreshed water layer in a hydrophilic porous membrane (see picture; blue areas: thin water layer in the porous membrane). Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sovova H.,Czech Institute of Chemical Process Fundamentals
Journal of Chromatography A | Year: 2012

Different types of mathematical models were applied in the last decade to simulate kinetics of supercritical fluid extraction (SFE) of essential oils from aromatic plants. Compared to the extraction of fatty oils, modeling of extraction of essential oils is more complicated due to their potential fractionation, co-extraction of less soluble compounds, and stronger effect of flow pattern on extraction yield, which is connected with solute adsorption on plant matrix. Fitting the SFE models to experimental extraction curves alone usually does not enable reliable selection among the models. Major progress was made when detailed models for the extraction from glandular structures of plants were developed. As the type of glands is characteristic for plant families, the choice of models for SFE of essential oils is substantially facilitated. As the extracts from aromatic plants contain also cuticular waxes and other less soluble substances, and essential oils themselves are mixtures of substances of different solubility in supercritical carbon dioxide, modeling of extraction of mixtures and their fractionation in time deserves more attention. © 2012 Elsevier B.V.

Kovanda F.,Institute of Chemical Technology Prague | Jiratova K.,Czech Institute of Chemical Process Fundamentals
Applied Clay Science | Year: 2011

Structured mixed oxide catalysts were prepared by the calcination of layered double hydroxides (LDHs) deposited on Al2O3/Al supports (anodized aluminum foil). The deposition of LDH precursors on the supports was carried out under hydrothermal conditions at 140°C in aqueous solutions of Ni, Co, Cu, and Mn nitrates. MII-(Mn)-Al LDHs (MII = Ni, Co, Ni-Co, Ni-Cu, and Co-Cu) with only slight Mn contents were obtained. An increased pH of the solutions used for deposition enhanced the formation of LDH phases. After heating at 500°C, spinel-like and/or NiO-like oxides were detected in the supported mixed oxides. Compared to the mixed oxides obtained by calcination of the coprecipitated LDH precursors, the supported mixed oxides exhibited worse reducibility and lower catalytic activity in the total oxidation of ethanol; both the formation of spinel-like phases and high structural ordering of the products deposited on the Al2O3/Al supports could explain the poor reducibility. Among the supported catalysts, the Ni-Cu-(Mn)-Al mixed oxide was the most active in the total oxidation of ethanol. Increasing the pH of solutions used during the hydrothermal deposition of the LDH precursors resulted in improved catalytic activity and selectivity of the supported mixed oxides. © 2010 Elsevier B.V.

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