The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Robert Guttel - One of the best experts on this subject based on the ideXlab platform.
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study of unsteady state operation of methanation by modeling and simulation
Chemical Engineering & Technology, 2013Co-Authors: Robert GuttelAbstract:Methanation of CO under unsteady-state operation conditions was studied systematically based on a simplified mathematical model for an integral reactor using steady-state kinetics available in the literature. The Inlet Composition of CO and H2 was changed stepwise and the step response of the system was monitored in order to study the dynamic behavior of the reactor. Furthermore, periodic changes were applied with different cycling times. It was observed that the time average reaction rate could not be improved by cycling the feed Composition. Moreover, the reactor appears to be self-stabilizing, since the amplitude at the outlet is reduced, leading to a steady state for high cycling frequencies. The results allow conclusions on principles to design a methanation reactor for unsteady-state operation. However, it also becomes obvious that unsteady-state kinetics is mandatory in order to describe the experimental results obtained under dynamic conditions.
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Study of Unsteady‐State Operation of Methanation by Modeling and Simulation
Chemical Engineering & Technology, 2013Co-Authors: Robert GuttelAbstract:Methanation of CO under unsteady-state operation conditions was studied systematically based on a simplified mathematical model for an integral reactor using steady-state kinetics available in the literature. The Inlet Composition of CO and H2 was changed stepwise and the step response of the system was monitored in order to study the dynamic behavior of the reactor. Furthermore, periodic changes were applied with different cycling times. It was observed that the time average reaction rate could not be improved by cycling the feed Composition. Moreover, the reactor appears to be self-stabilizing, since the amplitude at the outlet is reduced, leading to a steady state for high cycling frequencies. The results allow conclusions on principles to design a methanation reactor for unsteady-state operation. However, it also becomes obvious that unsteady-state kinetics is mandatory in order to describe the experimental results obtained under dynamic conditions.
Marcel O Cerri - One of the best experts on this subject based on the ideXlab platform.
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Individual effect of shear rate and oxygen transfer on clavulanic acid production by Streptomyces clavuligerus.
Bioprocess and biosystems engineering, 2021Co-Authors: Renata M M G P Ribeiro, Mateus N Esperança, Ana P A Sousa, Álvaro Baptista Neto, Marcel O CerriAbstract:The production of biocompounds through the cultivation of filamentous microorganisms is mainly affected by Oxygen Transfer Rate (OTR) and shear rate ([Formula: see text]) conditions. Despite efforts have been made to evaluate the effect of operating variables (impeller speed, N; and airflow rate, ϕair) on clavulanic acid production, no analysis regarding the effect of OTR and [Formula: see text] was made. Then, the aim of this study was to evaluate the dissociated effect of physical phenomena such as oxygen transfer and shear rate in the production of clavulanic acid from Streptomyces clavuligerus using a stirred tank bioreactor. Streptomyces clavuligerus cultivations were performed at five different OTR and [Formula: see text] conditions by manipulating the operating conditions (N, ϕair, and gas Inlet Composition). Cultivations performed at equal impeller speed (600 rpm, similar [Formula: see text]) using oxygen enrichment, showed that CA productivity (ProdCA) was positively affected by OTR increase. Subsequently, the different shear conditions (achieved by varying the impeller speed) lead to an increase in CA production levels. Despite both OTR and shear rate positively enhanced CA productivity, [Formula: see text] exhibited the highest impact: an increase of 145% in OTRinitial enhanced the clavulanic acid productivity of about 29%, while an increment in the shear rate of 134% raised the ProdCA in 53%.
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Individual effect of shear rate and oxygen transfer on clavulanic acid production by Streptomyces clavuligerus
Bioprocess and Biosystems Engineering, 2021Co-Authors: Renata M M G P Ribeiro, Mateus N Esperança, Ana P A Sousa, Álvaro Baptista Neto, Marcel O CerriAbstract:The production of biocompounds through the cultivation of filamentous microorganisms is mainly affected by Oxygen Transfer Rate (OTR) and shear rate ( $${\dot{\gamma }}_{av}$$ γ ˙ av ) conditions. Despite efforts have been made to evaluate the effect of operating variables (impeller speed, N ; and airflow rate, ϕ _air) on clavulanic acid production, no analysis regarding the effect of OTR and $${\dot{\gamma }}_{av}$$ γ ˙ av was made. Then, the aim of this study was to evaluate the dissociated effect of physical phenomena such as oxygen transfer and shear rate in the production of clavulanic acid from Streptomyces clavuligerus using a stirred tank bioreactor. Streptomyces clavuligerus cultivations were performed at five different OTR and $${\dot{\gamma }}_{av}$$ γ ˙ av conditions by manipulating the operating conditions ( N , ϕ _air, and gas Inlet Composition). Cultivations performed at equal impeller speed (600 rpm, similar $${\dot{\gamma }}_{av}$$ γ ˙ av ) using oxygen enrichment, showed that CA productivity (Prod_CA) was positively affected by OTR increase. Subsequently, the different shear conditions (achieved by varying the impeller speed) lead to an increase in CA production levels. Despite both OTR and shear rate positively enhanced CA productivity, $${\dot{\gamma }}_{av}$$ γ ˙ av exhibited the highest impact: an increase of 145% in OTR_initial enhanced the clavulanic acid productivity of about 29%, while an increment in the shear rate of 134% raised the Prod_CA in 53%.
Renata M M G P Ribeiro - One of the best experts on this subject based on the ideXlab platform.
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Individual effect of shear rate and oxygen transfer on clavulanic acid production by Streptomyces clavuligerus.
Bioprocess and biosystems engineering, 2021Co-Authors: Renata M M G P Ribeiro, Mateus N Esperança, Ana P A Sousa, Álvaro Baptista Neto, Marcel O CerriAbstract:The production of biocompounds through the cultivation of filamentous microorganisms is mainly affected by Oxygen Transfer Rate (OTR) and shear rate ([Formula: see text]) conditions. Despite efforts have been made to evaluate the effect of operating variables (impeller speed, N; and airflow rate, ϕair) on clavulanic acid production, no analysis regarding the effect of OTR and [Formula: see text] was made. Then, the aim of this study was to evaluate the dissociated effect of physical phenomena such as oxygen transfer and shear rate in the production of clavulanic acid from Streptomyces clavuligerus using a stirred tank bioreactor. Streptomyces clavuligerus cultivations were performed at five different OTR and [Formula: see text] conditions by manipulating the operating conditions (N, ϕair, and gas Inlet Composition). Cultivations performed at equal impeller speed (600 rpm, similar [Formula: see text]) using oxygen enrichment, showed that CA productivity (ProdCA) was positively affected by OTR increase. Subsequently, the different shear conditions (achieved by varying the impeller speed) lead to an increase in CA production levels. Despite both OTR and shear rate positively enhanced CA productivity, [Formula: see text] exhibited the highest impact: an increase of 145% in OTRinitial enhanced the clavulanic acid productivity of about 29%, while an increment in the shear rate of 134% raised the ProdCA in 53%.
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Individual effect of shear rate and oxygen transfer on clavulanic acid production by Streptomyces clavuligerus
Bioprocess and Biosystems Engineering, 2021Co-Authors: Renata M M G P Ribeiro, Mateus N Esperança, Ana P A Sousa, Álvaro Baptista Neto, Marcel O CerriAbstract:The production of biocompounds through the cultivation of filamentous microorganisms is mainly affected by Oxygen Transfer Rate (OTR) and shear rate ( $${\dot{\gamma }}_{av}$$ γ ˙ av ) conditions. Despite efforts have been made to evaluate the effect of operating variables (impeller speed, N ; and airflow rate, ϕ _air) on clavulanic acid production, no analysis regarding the effect of OTR and $${\dot{\gamma }}_{av}$$ γ ˙ av was made. Then, the aim of this study was to evaluate the dissociated effect of physical phenomena such as oxygen transfer and shear rate in the production of clavulanic acid from Streptomyces clavuligerus using a stirred tank bioreactor. Streptomyces clavuligerus cultivations were performed at five different OTR and $${\dot{\gamma }}_{av}$$ γ ˙ av conditions by manipulating the operating conditions ( N , ϕ _air, and gas Inlet Composition). Cultivations performed at equal impeller speed (600 rpm, similar $${\dot{\gamma }}_{av}$$ γ ˙ av ) using oxygen enrichment, showed that CA productivity (Prod_CA) was positively affected by OTR increase. Subsequently, the different shear conditions (achieved by varying the impeller speed) lead to an increase in CA production levels. Despite both OTR and shear rate positively enhanced CA productivity, $${\dot{\gamma }}_{av}$$ γ ˙ av exhibited the highest impact: an increase of 145% in OTR_initial enhanced the clavulanic acid productivity of about 29%, while an increment in the shear rate of 134% raised the Prod_CA in 53%.
O. Guerrini - One of the best experts on this subject based on the ideXlab platform.
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Modeling of fixed bed methanation reactor for syngas production: Operating window and performance characteristics
Fuel, 2013Co-Authors: N. R. Parlikkad, S. Chambrey, P. Fongarland, N. Fatah, A. Khodakov, S. Capela, O. GuerriniAbstract:The present work focuses on the development of phenomenological model for the bio-syngas to methane conversion process. One dimensional heterogeneous and pseudo-homogeneous model were simulated for a typical pilot plant scale fixed bed methanator processing 55 mol/h of CO (total molar flow rate of 310 mol/h) with Inlet Composition of H-2/CO = 3, CO2/CO = 1, CH4/CO = 0.5 at 550 K and 1 atm. Performance of the fixed bed reactor at different operating conditions like CO2/CO ratio, H-2/CO ratio, effect of H2O in the feed was studied. It was found that for feeds that were not pre-enriched with hydrogen, presence of water and water gas shift activity was found to decrease the catalyst inventory substantially. CO2 in the Inlet feed stream would help to decrease the temperature due to dilution effect and more importantly, can be chosen to maximize methane yield per mole of CO converted. Further, the model was simulated to predict the performance characteristics of reactor with a mixture containing two types of catalyst, one of them being specifically added to increase H-2/CO ratio in feed through water gas shift reaction. The work also laid the importance of incorporating pore diffusion and external mass transfer locally in the computation of actual catalyst inventory and reactor volume. The work was useful in selection of operating window and assessing the various viable options for an industrial reactor. The model developed will serve in selection of operability window for commercialization of substitute natural gas synthesis (SNG) process. (c) 2013 Elsevier Ltd. All rights reserved.
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Modeling of fixed bed methanation reactor for syngas production: Operating window and performance characteristics
Fuel, 2013Co-Authors: N. R. Parlikkad, S. Chambrey, P. Fongarland, N. Fatah, A. Khodakov, S. Capela, O. GuerriniAbstract:Abstract The present work focuses on the development of phenomenological model for the bio-syngas to methane conversion process. One dimensional heterogeneous and pseudo-homogeneous model were simulated for a typical pilot plant scale fixed bed methanator processing 55 mol/h of CO (total molar flow rate of 310 mol/h) with Inlet Composition of H2/CO = 3, CO2/CO = 1, CH4/CO = 0.5 at 550 K and 1 atm. Performance of the fixed bed reactor at different operating conditions like CO2/CO ratio, H2/CO ratio, effect of H2O in the feed was studied. It was found that for feeds that were not pre-enriched with hydrogen, presence of water and water gas shift activity was found to decrease the catalyst inventory substantially. CO2 in the Inlet feed stream would help to decrease the temperature due to dilution effect and more importantly, can be chosen to maximize methane yield per mole of CO converted. Further, the model was simulated to predict the performance characteristics of reactor with a mixture containing two types of catalyst, one of them being specifically added to increase H2/CO ratio in feed through water gas shift reaction. The work also laid the importance of incorporating pore diffusion and external mass transfer locally in the computation of actual catalyst inventory and reactor volume. The work was useful in selection of operating window and assessing the various viable options for an industrial reactor. The model developed will serve in selection of operability window for commercialization of substitute natural gas synthesis (SNG) process.
Lionel Vandenbulcke - One of the best experts on this subject based on the ideXlab platform.
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Characterization and Modelling of CH4-CO2 Microwave Plasmas for Nano-Smooth Diamond Coatings and Homogeneous Nano-Diamond Grain Synthesis
2012Co-Authors: Lionel Vandenbulcke, Thomas Gries, S. De Persis, M.p. VandenbulckeAbstract:The Microwave Plasma-Assisted Chemical Vapor Deposition process allows nano-smooth diamond coating and nano-diamond homogeneous synthesis from the CH4CO2 system. These processes depend on various parameters which change the nature and the concentration of the plasma species. The knowledge of the process and the control of the final characteristics of the films or nanodiamond grains as well as correlations between both are nowadays still of interest because they represent an important stage for an industrial transfer. CH4 CO2 plasmas have been studied by emission spectroscopy, microwave interferometry, Langmuir probing and molecular beam mass spectrometry (MBMS). MBMS allowed us studying the variations of the concentration of both stable species (H2, CH4, CO, CO2, C2H2, ..., C6H6, C8H6) and radicals (H, OH, CH3, C3H3, C3H5, C6H5...) as a function of the Inlet Composition, total flow rate, power density injected in the plasma and distance from the substrate, in non-dusty conditions. The other techniques have been used to deduce the variations of the plasma parameters like the gas kinetic temperature, the electron density and the electron temperature. A modelling of the plasma kinetics was based on a combustion mechanism which incorporates more than 150 species and 850 reactions and a specific dissociation mechanism including about 50 species. This 2D-model takes into account the coupled hydrodynamics of the gaseous species, gas phase chemistry and surface recombination at the reactor wall. The results are compared to the MBMS experimental results of the gaseous Composition in the plasma as a function of various parameters. These experimental and modelling studies are used for correlating the influence of the relative concentration of important gaseous species in the plasma (especially radicals) to the deposition domain, the growth rate, the structure (polycrystalline or nanosmooth) and the diamond quality of the deposits. The influence of the concentrations of both hydrocarbon radicals and H and OH species in the plasma is especially evidenced together with their experimental concentration gradients in front of the growing surface. The growth of nano-smooth diamond films, with roughness in the 7-30 nm range, relatively to polycrystalline ones is explained and the variation of their intrinsic properties correlated. This better knowledge of the deposition process would allow depositing these films in large scale industrial reactors, for example for tribological applications as will be shown here. Moreover the plasma diagnostic techniques allowed us to determine the externally controlled conditions for occurrence of dusty CH4-CO2 plasmas. Previous modelling of the plasma has been extrapolated to these plasma conditions where no MBMS measurements could be carried out. These studies allow a better understanding of the homogeneous nucleation and a better control of the size and the nanostructure of nanodiamond grains (10-100 nm in size) made of either pure diamond nanocrystals only (2-10 nm in size) or mixed with some sp-carbon entities as shown by transmission electron microscopy (TEM) and high-resolution TEM imaging. The control of their size and their nanostructure could open ways for applications in various scientific fields when used either as-synthesized or after various post-treatments.
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Experimental and kinetic studies of C–H–O plasmas for polycrystalline and nano-smooth diamond deposition
Diamond and Related Materials, 2009Co-Authors: Thomas Gries, Lionel Vandenbulcke, S. De Persis, C. Met, J.l. Delfau, M. I. De Barros-bouchetAbstract:Abstract CO 2 –CH 4 and CO–H 2 plasmas were studied by optical emission spectroscopy, microwave interferometry, Langmuir probing and molecular beam mass spectrometry. The variations of the plasma parameters as well as the concentration variations of both stable species and radicals were obtained as a function of the Inlet Composition. A modelling of the plasma kinetics taking into account the coupled hydrodynamics of the gaseous species and the gas phase chemistry including electron dissociation and surface recombination at the reactor wall was carried out. These experimental and modelling studies were used for correlating the influence of the relative concentration of important gaseous species in the plasma to the deposition domain, the structure (polycrystalline or nano-smooth) and the quality of diamond films which are deposited at moderate temperature. The influence of the concentrations of both hydrocarbon radicals and H and OH species is especially evidenced. The growth of nano-smooth diamond films relatively to polycrystalline ones is explained.
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Diagnostics and modeling of CH4–CO2 plasmas for nanosmooth diamond deposition: Comparison to experimental data
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2009Co-Authors: Thomas Gries, Lionel Vandenbulcke, Olivier Aubry, S. De Persis, Jean-louis DelfauAbstract:Microwave plasma-assisted chemical vapor deposition of very smooth diamond coatings is an important process for various applications including mechanical and micromechanical systems and acoustic wave devices. Nanosmooth coatings have been deposited from CH4–CO2 gas mixtures at moderate temperature, the order of 600 °C. In order to increase the knowledge of the process and the control of the final characteristics of the films, a modeling of these plasmas is necessary. This has been carried out here from the prior determination of the plasma parameters. Optical emission spectroscopy was used in order to determine the gas kinetic temperature. Microwave interferometry and Langmuir double probe were used to determine the electron density and the electron temperature, respectively. All these experimental data have been obtained for a wide range of external parameters, such as the Inlet Composition, the pressure, the gas flow rate, and the power injected in the plasma. Then modeling of CH4–CO2 plasmas was develo...
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Characterization of Diamond Precursors in Front of the Substrate from CH4-CO2 Plasmas
2006Co-Authors: Lionel Vandenbulcke, Jean-louis Delfau, Olivier Aubry, Christian VovelleAbstract:Diamond deposition in microwave CH4-CO2 plasmas depends on various parameters that change the nature and the concentration of the species produced in the plasma. The Inlet Composition, the total gas flow rate, the microwave power injected in the plasma and the total pressure that change the power density injected in the plasma have a great influence on the plasma conditions and the species formation. The molecular beam mass spectrometry technique was used for detecting both stable species and radicals. While it is somewhat intrusive compared to optical ones, a major advantage of this technique lies in its ability to detect a wide spectrum of species simultaneously. Moreover specific procedures allow the quantitative determination of the mole fraction of each species with a sensitivity of about 10. Here the sampling cone was set through the substrate, with its tip and the sampling orifice at the growth surface or at given positions in front of the substrate, in order to minimize the intrusion into the reactive environment. This technique permitted to analyze both stable species (H2, CH4, CO, CO2, C2H2..., C6H6,...) and radicals (H, OH, CH3, C3H3, C3H5, C6H5,...) as a function of the distance from the surface. The Composition gradients of all species were deduced as a function of the Inlet Composition in CH4-CO2 and the total gas flow rate. While the Inlet Composition obviously modifies the concentrations in the plasma, the total gas flow rate is shown to influence the plasma Composition through the variation of the degree of completion of the chemical system. The Composition far from the substrate and the concentration gradients in front of the substrate are modified in accordance. The experimental results evidence the influence of the process conditions on the gradients for labile precursors (CH3, C3H3, C3H5...) and etching species (H, OH,...), as shown in fig. 1. Their variations allow correlating the deposition conditions with the etching/deposition domains of diamond which depend on the Inlet Composition and the degree of completion of the chemical system. They permit also to correlate the deposition conditions with the diamond quality which depends on the amount of sphybridized carbon relatively to the sphybridized carbon incorporated into the film. The deposition kinetics was also studied and information about the deposition mechanism could be deduced from the variations of the growth rate as a function of the surface Composition.
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Influence of Isothermal Chemical Vapor Deposition and Chemical Vapor Infiltration Conditions on the Deposition Kinetics and Structure of Boron Nitride
Journal of the American Ceramic Society, 2004Co-Authors: Marc Leparoux, Lionel Vandenbulcke, Christian ClinardAbstract:An experimental study has been performed to gain some insight into the correlations between the deposition conditions and the structure of boron nitride (BN) coatings that are used in ceramic-matrix composites. BN has been deposited at 700°C from BCl 3 -NH 3 -H 2 mixtures on various substrates, by using chemical vapor deposition (CVD) and isothermal-isobaric chemical vapor infiltration (ICVI) processes, simultaneously in the same reactor. A kinetic study has shown that the CVD process is governed either by a combination of mass transfer with chemical kinetics at low flow rates or by the heterogeneous kinetics only at high flow velocities. In contrast, the limiting contribution of mass transfer always is observed for the ICVI process. The influence of diffusion cages that are positioned around the fibrous preforms is reported. The structure of BN deposits has been studied as a function of the various deposition conditions via transmission electron microscopy. The chosen CVD conditions lead to a poor organization of the BN deposits. Fairly well-organized BN coatings are deposited on all fibers of a fibrous preform via ICVI. The results are discussed in terms of supersaturation and deposition yields. The use of diffusion cages and the adjustment of the Inlet Composition and mass flow rate seem to be very important to obtain the best BN organization and thickness uniformity.