The Experts below are selected from a list of 7833 Experts worldwide ranked by ideXlab platform
Dejan Skala - One of the best experts on this subject based on the ideXlab platform.
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modeling the kinetics of calcium hydroxide catalyzed methanolysis of sunflower oil
Bioresource Technology, 2010Co-Authors: Olivera S Stamenkovic, Ivana B Bankovicilic, Zoran B. Todorović, Miodrag L. Lazić, Vlada B. Veljković, Dejan SkalaAbstract:Abstract The kinetics of Ca(OH) 2 -catalyzed methanolysis of sunflower oil was studied at a moderate temperature (60 °C), a methanol-to-oil molar ratio (6:1) and different catalyst amounts (from 1% to 10% based on oil weight). The methanolysis process was shown to involve the initial triglyceride (TG) Mass Transfer controlled region, followed by the chemical reaction controlled region in the latter period. The TG Mass Transfer Limitation was caused by the low available active specific catalyst surface due to the high adsorbed methanol concentration. Both the TG Mass Transfer and chemical reaction rates increased with increasing the catalyst amount.
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kinetics of sunflower oil methanolysis catalyzed by calcium oxide
Fuel, 2009Co-Authors: Vlada B Veljkovic, Olivera S Stamenkovic, Zoran B Todorovic, Miodrag L Lazic, Dejan SkalaAbstract:The methanolysis of sunflower oil was studied in the presence of CaO previously calcined at various temperatures and the optimal temperature for CaO calcination was determined. The sigmoidal process kinetics was explained by the initial triglyceride (TG) Mass Transfer controlled region, followed by the chemical reaction controlled region in the latter reaction period. The TG Mass Transfer Limitation was due to the small available active specific catalyst surface, which was mainly covered by adsorbed molecules of methanol. In the later phase, the adsorbed methanol concentration decreased, causing the increase of both the available active specific catalyst surface and the TG Mass Transfer rate, and the chemical reaction rate become smaller than the TG Mass Transfer rate.
Olivera S Stamenkovic - One of the best experts on this subject based on the ideXlab platform.
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empirical modeling the ultrasound assisted base catalyzed sunflower oil methanolysis kinetics
Chemical Industry & Chemical Engineering Quarterly, 2012Co-Authors: Jelena M Avramovic, Olivera S Stamenkovic, Zoran B Todorovic, Miodrag L Lazic, Vlada B VeljkovicAbstract:The ultrasound-assisted sunflower oil methanolysis catalyzed by KOH was studied to define a simple empirical kinetic model useful for reactor design without complex computation. It was assumed that the neutralization of free fatty acids and the saponification reaction were negligible. The methanolysis process rate was observed to be controlled by the Mass Transfer Limitation in the initial heterogeneous regime and by the chemical reaction in the later pseudo-homogeneous regime. The model involving the irreversible second-order kinetics was established and used for simulation of the triacylglycerol conversion and the fatty acid methyl esters formation in the latter regime. A good agreement between the proposed model and the experimental data in the chemically controlled regime was found.
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modeling the kinetics of calcium hydroxide catalyzed methanolysis of sunflower oil
Bioresource Technology, 2010Co-Authors: Olivera S Stamenkovic, Ivana B Bankovicilic, Zoran B. Todorović, Miodrag L. Lazić, Vlada B. Veljković, Dejan SkalaAbstract:Abstract The kinetics of Ca(OH) 2 -catalyzed methanolysis of sunflower oil was studied at a moderate temperature (60 °C), a methanol-to-oil molar ratio (6:1) and different catalyst amounts (from 1% to 10% based on oil weight). The methanolysis process was shown to involve the initial triglyceride (TG) Mass Transfer controlled region, followed by the chemical reaction controlled region in the latter period. The TG Mass Transfer Limitation was caused by the low available active specific catalyst surface due to the high adsorbed methanol concentration. Both the TG Mass Transfer and chemical reaction rates increased with increasing the catalyst amount.
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kinetics of sunflower oil methanolysis catalyzed by calcium oxide
Fuel, 2009Co-Authors: Vlada B Veljkovic, Olivera S Stamenkovic, Zoran B Todorovic, Miodrag L Lazic, Dejan SkalaAbstract:The methanolysis of sunflower oil was studied in the presence of CaO previously calcined at various temperatures and the optimal temperature for CaO calcination was determined. The sigmoidal process kinetics was explained by the initial triglyceride (TG) Mass Transfer controlled region, followed by the chemical reaction controlled region in the latter reaction period. The TG Mass Transfer Limitation was due to the small available active specific catalyst surface, which was mainly covered by adsorbed molecules of methanol. In the later phase, the adsorbed methanol concentration decreased, causing the increase of both the available active specific catalyst surface and the TG Mass Transfer rate, and the chemical reaction rate become smaller than the TG Mass Transfer rate.
Willy Verstraete - One of the best experts on this subject based on the ideXlab platform.
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Mass Transfer Limitation of sulfate in methanogenic aggregates.
Biotechnology and bioengineering, 1994Co-Authors: Ann Overmeire, Piet N.l. Lens, Willy VerstraeteAbstract:The role of Mass Transfer Limitation of sulfate as a factor governing the competition between sulfate reducing and methane producing bacteria in methanogenic aggregates was theoretically evaluated by the calculation of steady-state sulfate microprofiles using a reference set of parameters obtained from the literature. The shooting method was used as a numerical technique for solving the mathematical model. The effect of the parameters on Mass transport Limitation was tested by varying each reference value of the parameters with a factor of 3. Sulfate Limitation within granules prevailed at moderate (0.1 kg m(-3)) and low sulfate concentrations in the bulk liquid, at high maximum sulfate utilization rates (3.73 x 10(-5) kg SO(4) (2-) kg(-1) VSS S(-1) or bioMass concentrations (40 KG VSS m(-3)), and in large aggregates (radius of 7.5 10(-4) m). The effective diffusion coefficient of sulfate and the affinity constant were less determinative for the penetration depth of sulfate within a granule.
Martin Elsner - One of the best experts on this subject based on the ideXlab platform.
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Defining lower limits of biodegradation: atrazine degradation regulated by Mass Transfer and maintenance demand in Arthrobacter aurescens TC1
The ISME Journal, 2019Co-Authors: Kankana Kundu, Sviatlana Marozava, Benno Ehrl, Juliane Merl-pham, Christian Griebler, Martin ElsnerAbstract:Exploring adaptive strategies by which microorganisms function and survive in low-energy natural environments remains a grand goal of microbiology, and may help address a prime challenge of the 21st century: degradation of man-made chemicals at low concentrations (“micropollutants”). Here we explore physiological adaptation and maintenance energy requirements of a herbicide (atrazine)-degrading microorganism ( Arthrobacter aurescens TC1) while concomitantly observing Mass Transfer Limitations directly by compound-specific isotope fractionation analysis. Chemostat-based growth triggered the onset of Mass Transfer Limitation at residual concentrations of 30 μg L^−1 of atrazine with a bacterial population doubling time ( t _d) of 14 days, whereas exacerbated energy Limitation was induced by retentostat-based near-zero growth ( t _d = 265 days) at 12 ± 3 μg L^−1 residual concentration. Retentostat cultivation resulted in (i) complete Mass Transfer Limitation evidenced by the disappearance of isotope fractionation (ε^13C = −0.45‰ ± 0.36‰) and (ii) a twofold decrease in maintenance energy requirement compared with chemostat cultivation. Proteomics revealed that retentostat and chemostat cultivation under Mass Transfer Limitation share low protein turnover and expression of stress-related proteins. Mass Transfer Limitation effectuated slow-down of metabolism in retentostats and a transition from growth phase to maintenance phase indicating a limit of ≈10 μg L^−1 for long-term atrazine degradation. Further studies on other ecosystem-relevant microorganisms will substantiate the general applicability of our finding that Mass Transfer Limitation serves as a trigger for physiological adaptation, which subsequently defines a lower limit of biodegradation.
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Mass Transfer Limitation during slow anaerobic biodegradation of 2 methylnaphthalene
Environmental Science & Technology, 2019Co-Authors: Sviatlana Marozava, Armin H Meyer, Alfredo Perezdemora, Mehdi Gharasoo, Lin Zhuo, He Wang, Olaf A Cirpka, Rainer U Meckenstock, Martin ElsnerAbstract:While they are theoretically conceptualized to restrict biodegradation of organic contaminants, bioavailability Limitations are challenging to observe directly. Here we explore the onset of Mass Transfer Limitations during slow biodegradation of the polycyclic aromatic hydrocarbon 2-methylnaphthalene (2-MN) by the anaerobic, sulfate-reducing strain NaphS2. Carbon and hydrogen compound specific isotope fractionation was pronounced at high aqueous 2-MN concentrations (60 μM) (ecarbon = -2.1 ± 0.1‰/ehydrogen = -40 ± 7‰) in the absence of an oil phase but became significantly smaller (ecarbon = -0.9 ± 0.3‰/ehydrogen = -6 ± 3‰) or nondetectable when low aqueous concentrations (4 μM versus 0.5 μM) were in equilibrium with 80 or 10 mM 2-MN in hexadecane, respectively. This masking of isotope fractionation directly evidenced Mass Transfer Limitations at (sub)micromolar substrate concentrations. Remarkably, oil-water Mass Transfer coefficients were 60-90 times greater in biotic experiments than in the absence of bacteria (korg-aq2-MN = 0.01 ± 0.003 cm h-1). The ability of isotope fractionation to identify Mass Transfer Limitations may help study how microorganisms adapt and navigate at the brink of bioavailability at low concentrations. For field surveys our results imply that, at trace concentrations, the absence of isotope fractionation does not necessarily indicate the absence of biodegradation.
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Defining lower limits of biodegradation: atrazine degradation regulated by Mass Transfer and maintenance demand in Arthrobacter aurescens TC1.
The ISME journal, 2019Co-Authors: Kankana Kundu, Sviatlana Marozava, Benno Ehrl, Juliane Merl-pham, Christian Griebler, Martin ElsnerAbstract:Exploring adaptive strategies by which microorganisms function and survive in low-energy natural environments remains a grand goal of microbiology, and may help address a prime challenge of the 21st century: degradation of man-made chemicals at low concentrations (“micropollutants”). Here we explore physiological adaptation and maintenance energy requirements of a herbicide (atrazine)-degrading microorganism (Arthrobacter aurescens TC1) while concomitantly observing Mass Transfer Limitations directly by compound-specific isotope fractionation analysis. Chemostat-based growth triggered the onset of Mass Transfer Limitation at residual concentrations of 30 μg L−1 of atrazine with a bacterial population doubling time (td) of 14 days, whereas exacerbated energy Limitation was induced by retentostat-based near-zero growth (td = 265 days) at 12 ± 3 μg L−1 residual concentration. Retentostat cultivation resulted in (i) complete Mass Transfer Limitation evidenced by the disappearance of isotope fractionation (e13C = −0.45‰ ± 0.36‰) and (ii) a twofold decrease in maintenance energy requirement compared with chemostat cultivation. Proteomics revealed that retentostat and chemostat cultivation under Mass Transfer Limitation share low protein turnover and expression of stress-related proteins. Mass Transfer Limitation effectuated slow-down of metabolism in retentostats and a transition from growth phase to maintenance phase indicating a limit of ≈10 μg L−1 for long-term atrazine degradation. Further studies on other ecosystem-relevant microorganisms will substantiate the general applicability of our finding that Mass Transfer Limitation serves as a trigger for physiological adaptation, which subsequently defines a lower limit of biodegradation.
Adrie J. J. Straathof - One of the best experts on this subject based on the ideXlab platform.
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Theoretical performance of countercurrent reactors for production of enantiopure compounds
Chemical Engineering Science, 2011Co-Authors: Marija Saric, Luuk A.m. Van Der Wielen, Adrie J. J. StraathofAbstract:Irreversible reactions are being applied in enzymatic kinetic resolution to obtain enantiomerically pure compounds from racemic mixtures. Using model calculations for situations without Mass Transfer Limitation, we show that reversible reactions might also be useful for enzymatic kinetic resolution, provided that countercurrent systems are used rather than batch or cocurrent systems. The required reaction time or enzyme amount in a countercurrent system is much lower than in an analogous cocurrent system or its batch equivalent. More importantly, often the calculated yield and enantiomeric excess are better in countercurrent systems. Racemization can also be favorably used in countercurrent systems. Consequently, to achieve with a reversible reaction a particular enantiomeric excess and yield, a countercurrent system needs less dilution or activated co-reactant and less enantioselective enzyme than a cocurrent system.
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Mass Transfer Limitation as a tool to enhance the enantiomeric excess in the enzymatic synthesis of chiral cyanohydrins
Journal of Molecular Catalysis B-enzymatic, 2001Co-Authors: Pieter Jan Gerrits, Adrie J. J. Straathof, W. F. Willeman, Joseph J. Heijnen, Johannes Brussee, Arne Van Der GenAbstract:The enantioselective synthesis of cyanohydrins catalyzed by R-hydroxynitrile lyase in an aqueous-organic liquid two-phase system using, Mass Transfer Limitation to enhance enantiomeric excess at 5°C and pH 5.5 is described. Benzaldehyde, a good substrate, and cinnamaldehyde, a notoriously difficult substrate, were used as model substrates and compared in order to establish the Mass Transfer Limitation concept in a two-liquid phase system, where the non-enzymatic-racemic reaction competes. Enzyme concentration and phase volume ratio between organic and buffer phase were geared to one another to enhance the enantiomeric excess for each substrate. In both cases, after optimization, excellent chemical conversion (>99% on a 60 mmol scale), high throughput and high enantiomeric excess (benzaldehyde >99% and cinnamaldehyde >96%) were achieved.