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Peng Lu - One of the best experts on this subject based on the ideXlab platform.
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coupled alkali feldspar dissolution and secondary mineral precipitation in Batch Systems 2 new experiments with supercritical co2 and implications for carbon sequestration
Applied Geochemistry, 2013Co-Authors: Peng Lu, William E Seyfried, Qi Fu, Yee Soong, Sheila W Hedges, Kyle JonesAbstract:Abstract In order to evaluate the extent of CO2–water–rock interactions in geological formations for C sequestration, three Batch experiments were conducted on alkali feldspars–CO2–brine interactions at 150–200 °C and 300 bars. The elevated temperatures were necessary to accelerate the reactions to facilitate attainable laboratory measurements. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. SEM, TEM and XRD analysis of reaction products showed extensive dissolution features (etch pits, channels, kinks and steps) on feldspars and precipitation of secondary minerals (boehmite, kaolinite, muscovite and paragonite) on feldspar surfaces. Therefore, these experiments have generated both solution chemistry and secondary mineral identity. The experimental results show that partial equilibrium was not attained between secondary minerals and aqueous solutions for the feldspar hydrolysis Batch Systems. Evidence came from both solution chemistry (supersaturation of the secondary minerals during the entire experimental duration) and metastable co-existence of secondary minerals. The slow precipitation of secondary minerals results in a negative feedback in the dissolution–precipitation loop, reducing the overall feldspar dissolution rates by orders of magnitude. Furthermore, the experimental data indicate the form of rate laws greatly influence the steady state rates under which feldspar dissolution took place. Negligence of both the mitigating effects of secondary mineral precipitation and the sigmoidal shape of rate–ΔGr relationship can overestimate the extent of feldspar dissolution during CO2 storage. Finally, the literature on feldspar dissolution in CO2-charged Systems has been reviewed. The data available are insufficient and new experiments are urgently needed to establish a database on feldspar dissolution mechanism, rates and rate laws, as well as secondary mineral information at CO2 storage conditions.
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coupled alkali feldspar dissolution and secondary mineral precipitation in Batch Systems 4 numerical modeling of kinetic reaction paths
Geochimica et Cosmochimica Acta, 2010Co-Authors: Peng Lu, Zuoping Zheng, Jiwchar GanorAbstract:Abstract This paper explores how dissolution and precipitation reactions are coupled in Batch reactor experimental Systems at elevated temperatures. This is the fourth paper in our series of “Coupled Alkali Feldspar Dissolution and Secondary Mineral Precipitation in Batch Systems”. In our third paper, we demonstrated via speciation–solubility modeling that partial equilibrium between secondary minerals and aqueous solutions was not attained in feldspar hydrolysis Batch reactors at 90–300 °C and that a strong coupling between dissolution and precipitation reactions follows as a consequence of the slower precipitation of secondary minerals ( Zhu and Lu, 2009 ). Here, we develop this concept further by using numerical reaction path models to elucidate how the dissolution and precipitation reactions are coupled. Modeling results show that a quasi-steady state was reached. At the quasi-steady state, dissolution reactions proceeded at rates that are orders of magnitude slower than the rates measured at far from equilibrium. The quasi-steady state is determined by the relative rate constants, and strongly influenced by the function of Gibbs free energy of reaction ( Δ G r ) in the rate laws. To explore the potential effects of fluid flow rates on the coupling of reactions, we extrapolate a Batch system ( Ganor et al., 2007 ) to open Systems and simulated one-dimensional reactive mass transport for oligoclase dissolution and kaolinite precipitation in homogeneous porous media. Different steady states were achieved at different locations along the one-dimensional domain. The time-space distribution and saturation indices (SI) at the steady states were a function of flow rates for a given kinetic model. Regardless of the differences in SI, the ratio between oligoclase dissolution rates and kaolinite precipitation rates remained 1.626, as in the Batch system case ( Ganor et al., 2007 ). Therefore, our simulation results demonstrated coupling among dissolution, precipitation, and flow rates. Results reported in this communication lend support to our hypothesis that slow secondary mineral precipitation explains part of the well-known apparent discrepancy between lab measured and field estimated feldspar dissolution rates ( Zhu et al., 2004 ). Here we show how the slow secondary mineral precipitation provides a regulator to explain why the Systems are held close to equilibrium and show how the most often-quoted “near equilibrium” explanation for an apparent field-lab discrepancy can work quantitatively. The substantiated hypothesis now offers the promise of reconciling part of the apparent field-lab discrepancy.
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alkali feldspar dissolution and secondary mineral precipitation in Batch Systems 3 saturation states of product minerals and reaction paths
Geochimica et Cosmochimica Acta, 2009Co-Authors: Peng LuAbstract:In order to evaluate the complex interplay between dissolution and precipitation reaction kinetics, we examined the hypothesis of partial equilibria between secondary mineral products and aqueous solutions in feldspar–water Systems. Speciation and solubility geochemical modeling was used to compute the saturation indices (SI) for product minerals in Batch feldspar dissolution experiments at elevated temperatures and pressures and to trace the reaction paths on activity–activity diagrams. The modeling results demonstrated: (1) the experimental aqueous solutions were supersaturated with respect to product minerals for almost the entire duration of the experiments; (2) the aqueous solution chemistry did not evolve along the phase boundaries but crossed the phase boundaries at oblique angles; and (3) the earlier precipitated product minerals did not dissolve but continued to precipitate even after the solution chemistry had evolved into the stability fields of minerals lower in the paragenesis sequence. These three lines of evidence signify that product mineral precipitation is a slow kinetic process and partial equilibria between aqueous solution and product minerals were not held. In contrast, the experimental evidences are consistent with the hypothesis of strong coupling of mineral dissolution/precipitation kinetics [e.g., Zhu C., Blum A. E. and Veblen D. R. (2004a) Feldspar dissolution rates and clay precipitation in the Navajo aquifer at Black Mesa, Arizona, USA. In Water–Rock Interaction (eds. R. B. Wanty and R. R. I. Seal). A.A. Balkema, Saratoga Springs, New York. pp. 895–899]. In all Batch experiments examined, the time of congruent feldspar dissolution was short and supersaturation with respect to the product minerals was reached within a short period of time. The experimental system progressed from a dissolution driven regime to a precipitation limited regime in a short order. The results of this study suggest a complex feedback between dissolution and precipitation reaction kinetics, which needs to be considered in the interpretation of field based dissolution rates.
Michelle P Van Der Helm - One of the best experts on this subject based on the ideXlab platform.
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hydroxynitrile lyases covalently immobilized in continuous flow microreactors
Catalysis Science & Technology, 2019Co-Authors: Michelle P Van Der Helm, Paula Bracco, Hanna Busch, Katarzyna Szymanska, Andrzej B Jarzebski, Ulf HanefeldAbstract:Enzymes are supreme catalysts when it comes to high enantiopurities and their immobilization will pave the way for continuous operation. In this context, we show the covalent immobilization of hydroxynitrile lyases HbHNL (from Hevea brasiliensis) and MeHNL (from Manihot esculenta) in a siliceous monolithic microreactor for continuous operation. A thorough characterization of the immobilized HNLs on mesoporous silicates indicated the conditions essential for a successful immobilization. Their application in a continuous flow system enabled a remarkably fast (3.2 min) production of chiral cyanohydrins with high conversion (97%) and high ee (98%) using minimal enzyme loading (STY = 71 g L−1 h−1 mgprotein−1). MeHNL showed increased operational stability, possibly due to a structural difference. The continuous flow microreactor outperformed Batch Systems, demonstrating the advantage of the mesoporous/macroporous environment for the expression of enzyme activity and the favorable characteristics of the microreactor. Overall, the system shows great potential for future industrial application of biocatalytic asymmetric syntheses.
Prashant Mhaskar - One of the best experts on this subject based on the ideXlab platform.
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integrating data based modeling and nonlinear control tools for Batch process control
Aiche Journal, 2012Co-Authors: Siam Aumi, Prashant MhaskarAbstract:A data-based multimodel approach is developed in this work for modeling Batch Systems in which multiple local linear models are identified using latent variable regression and combined using an appropriate weighting function that arises from fuzzy c-means clustering. The resulting model is used to generate empirical reverse-time reachability regions (RTRRs) (defined as the set of states from where the data-based model can be driven inside a desired end-point neighborhood of the system), which are subsequently incorporated in a predictive control design. Simulation results of a fed-Batch reactor system under proportional-integral (PI) control and the proposed RTRR-based design demonstrate the superior performance of the RTRR-based design in both a fault-free and faulty environment. The data-based modeling methodology is then applied on a nylon-6,6 Batch polymerization process to design a trajectory tracking predictive controller. Closed-loop simulation results illustrate the superior tracking performance of the proposed predictive controller over PI control. © 2011 American Institute of Chemical Engineers AIChE J, 2012
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integrating data based modeling and nonlinear control tools for Batch process control
American Control Conference, 2011Co-Authors: Siam Aumi, Prashant MhaskarAbstract:This work presents a data-based multi-model approach for modeling Batch Systems in which multiple local linear models are identified using partial least squares (PLS) regression and then combined with an appropriate weighting function that arises from fuzzy c-means clustering. The resulting data-based model is used to generate estimates of empirical reverse-time reachability regions (RTRRs) (defined as the set of states from where the data-based model can be driven inside a desired end-point neighborhood of the Batch system) using an optimization based algorithm. The empirical RTRRs are used to formulate a computationally efficient predictive controller with inherent fault-tolerant characteristics. Simulation results of a fed-Batch reactor subject to noise, disturbances, and uncertain parameters demonstrate that the empirical RTRR-based MPC design consistently outperforms PI control in both a fault-free and faulty environment.
Mohamed Elsamadony - One of the best experts on this subject based on the ideXlab platform.
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application of magnetic multi wall carbon nanotube composite into fermentative treatment process of ultrasonicated waste activated sludge
Bioresource Technology, 2020Co-Authors: Alsayed Mostafa, Aya Tolba, Mohamed Gar Alalm, Manabu Fujii, Hafez Afify, Mohamed ElsamadonyAbstract:Abstract This study investigated the effect of supplementing nano-sized magnetite (Fe3O4 NPs), multi-wall carbon nanotubes (MWCNTs) and Fe3O4-MWCNTs composite on bioconversion of waste activated sludge to hydrogen, in Batch Systems. Substrate degradation efficiency (SDE) increased from 28 ± 3.8 (control) to 49 ± 5.9, 46 ± 4.8 and 52 ± 6.3% at optimal doses of 200 (Fe3O4 NPs), 300 (MWCNTs) and 200 mg/L (Fe3O4-MWCNTs), respectively. Based on dissolved iron and sludge conductivity measurements, superior SDE in Fe3O4 and MWCNTs Batches have been assigned to enhanced dissimilatory iron reduction (DIR) and high sludge conductivity, respectively. Combined impacts for sludge conductivity and DIR were revealed in Fe3O4-MWCNTs system. In 200 mg/L (Fe3O4-MWCNTs) Batch, catalytic activities of hydrogenase, protease and α-amylase peaked to 596, 146 and 131% (relative to control), respectively; as well as, highest volumetric H2 production of 607 ± 59 mL/L was acquired. Performance deteriorations at high concentrations of nanoparticles were caused by cellular oxidative stress induced by generated reactive oxygen species.
Richard G Luthy - One of the best experts on this subject based on the ideXlab platform.
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improvement of urban lake water quality by removal of escherichia coli through the action of the bivalve anodonta californiensis
Environmental Science & Technology, 2015Co-Authors: Niveen S Ismail, Hanna Dodd, Lauren M Sassoubre, Alexander J Horne, Alexandria B Boehm, Richard G LuthyAbstract:High levels of fecal indicator bacteria, such as Escherichia coli, can be indicative of poor water quality. The use of shellfish to reduce eutrophication has been proposed, but application of bivalves to reduce bacterial levels has not been extensively reported. Removal of E. coli by the native freshwater mussel Anodonta californiensis was studied using laboratory Batch Systems and field-based flow-through Systems. Batch Systems were utilized to determine the fate and inactivation of E. coli after uptake by the mussel. Batch experiments demonstrated that uptake patterns followed first order kinetics and E. coli was inactivated with less than 5% of the initial colonies recoverable in fecal matter or tissue. Flow-through Systems located at an urban impaired lake in San Francisco, CA were utilized to determine uptake kinetics under environmentally relevant conditions. The bivalves maintained a 1-log removal of E. coli for the duration of exposure. The calculated uptake rates can be used in conjunction with h...
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uptake of contaminants of emerging concern by the bivalves anodonta californiensis and corbicula fluminea
Environmental Science & Technology, 2014Co-Authors: Niveen S Ismail, Claudia E Muller, Rachel R Morgan, Richard G LuthyAbstract:Uptake of seven contaminants regularly detected in surface waters and spanning a range of hydrophobicities (log Dow −1 to 5) was studied for two species of freshwater bivalves, the native mussel Anodonta californiensis and the invasive clam Corbicula fluminea. Batch Systems were utilized to determine compound partitioning, and flow-through Systems, comparable to environmental conditions in effluent dominated surface waters, were used to determine uptake and depuration kinetics. Uptake of compounds was independent of bivalve type. Log bioconcentration factor (BCF) values were correlated with log Dow for nonionized compounds with the highest BCF value obtained for triclocarban (TCC). TCC concentrations were reduced in the water column due to bivalve activity. Anionic compounds with low Dow values, i.e., clofibric acid and ibuprofen, were not removed from water, while the organic cation propranolol showed biouptake similar to that of TCC. Batch experiments supported compound uptake patterns observed in flow-...
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biodegradation kinetics of naphthalene in nonaqueous phase liquid water mixed Batch Systems comparison of model predictions and experimental results
Biotechnology and Bioengineering, 1998Co-Authors: Subhasis Ghoshal, Richard G LuthyAbstract:A model is formulated to describe dissolution of naphthalene from an insoluble nonaqueous phase liquid (NAPL) and its subsequent biodegradation in the aqueous phase in completely mixed Batch reactors. The physicochemical processes of equilibrium partitioning and mass transfer of naphthalene between the NAPL and aqueous phases were incorporated into the model. Biodegradation kinetics were described by Monod's microbial growth kinetic model, modified to account for the inhibitory effects of 1,2-naphthoquinone formed during naphthalene degradation under certain conditions. System parameters and biokinetic coefficients pertinent to the NAPL-water Systems were determined either by direct measurement or from nonlinear regression of the naphthalene mineralization profiles obtained from Batch reactor tests with two-component NAPLs comprised of naphthalene and heptamethylnonane. The NAPLs contained substantial mass of naphthalene, and naphthalene biodegradation kinetics were evaluated over the time required for near complete depletion of naphthalene from the NAPL. Model predictions of naphthalene mineralization time profiles compared favorably to the general trends observed in the data obtained from laboratory experiments with the two-component NAPL, as well as with two coal tars obtained from the subsurface at contaminated sites and composed of many different PAHs (polycyclic aromatic hydrocarbon compounds). The effects of varying the NAPL mass and the naphthalene mole fractions in the NAPL are discussed. It was observed that the time to achieve a given percent removal of naphthalene does not change significantly with the initial mass of naphthalene in a fixed volume of the NAPL. Significant changes in the mineralization profiles are observed when the volume (and mass) of NAPL in the system is changed.