The Experts below are selected from a list of 315 Experts worldwide ranked by ideXlab platform
B Jai S Prakash - One of the best experts on this subject based on the ideXlab platform.
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interaction of chromate on surfactant modified montmorillonite Breakthrough Curve study in fixed bed columns
Industrial & Engineering Chemistry Research, 2008Co-Authors: N Mahadevaiah, B Venkataramani, B Jai S PrakashAbstract:Interactions between chromate and surfactant modified montmorillonite at room temperature (25 °C) and different pHs (1-7) in aqueous solution in fixed bed columns have been studied. A series of column tests were performed to determine the Breakthrough Curves at different initial surfactant loadings (0.5-3 CEC) of the bed. The interlayer spacing increased with the surfactant loading from 14.2 to 40.5 A. Experimental results of the column tests and the basal spacing of the column material showed that the adsorption of chromate onto the clay did not occur until the initial surfactant loading was beyond a critical concentration apparently enough to open the clay sheets for the entry of chromate species. The shapes of the Breakthrough Curves indicate that the chromate ions enter the interlamellar region only when the initial surfactant loadings are beyond 2 times the CEC of the clay. The amount of adsorbate increases proportionally with increasing bed depth. A simple two-parameter model originally introduced by Yoon and Nelson (Yoon, Y. H.; Nelson, J. H. Am. Ind. Hyg. Assoc. J. 1984, 45, 509) was used to calculate the Breakthrough time. Chromate could be recovered completely by washing with ammonium hydroxide, and the column material was found to regain its capacity to adsorb repeatedly after simple acid wash.
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restrictive entry of aqueous molybdate species into surfactant modified montmorillonitea Breakthrough Curve study
Chemistry of Materials, 2007Co-Authors: N Mahadevaiah, B Venkataramani, B Jai S PrakashAbstract:Molybdenum sorption behavior and the nature of Breakthrough Curves have been studied in a fixed-bed column containing montmorillonite clay modified by treatment with cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide. Different amounts of the surfactant loaded into the interlayer region of the montmorillonite to increase the interlayer spacing is found to enhance molybdate sorption. The sorption was found to be at a maximum in acidic medium (pH <0) and was almost constant between pH 3 and 4. Beyond pH 4, adsorption decreased rapidly and was almost two to four times lower than that in the acid medium. It is known from the equilibria of aquo molybdate species that polymolybdate species Mo8O264- and Mo7O246- are prevalent in the highly acidic medium; the species H2MoO4 and HMoO4- are stable between pH 0 and 4, and MoO42- is predominantly present above pH 5. The variation in adsorption of Mo is interpreted on the basis of the type of species prevalent at different pHs. The sample loaded at 0.5 CEC...
Philip H Stauffer - One of the best experts on this subject based on the ideXlab platform.
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On estimating functional average Breakthrough Curve using time‐warping technique and perturbation approach
Water Resources Research, 2012Co-Authors: Zhiming Lu, Philip H StaufferAbstract:[1] Simulated contaminant Breakthrough Curves (BTC) are often used to predict mass arrival at compliance boundaries at waste storage sites. In numerical simulations that involve uncertainties on input parameters such as randomly heterogeneous rock properties, Monte Carlo simulations are commonly utilized and the mean Breakthrough Curve is often calculated from the arithmetic average of all realizations. The arithmetic mean Breakthrough Curve in general overestimates the mass flow rate at early and late time but underestimates the peak mass flow rate. The averaged Breakthrough Curve usually does not resemble any of individual Breakthrough Curves. The reason is that BTCs vary not only on amplitude but also on dynamics (time) and therefore it is not appropriate to take the arithmetic average directly. In this study, we consider each BTC as a random Curve, and use time-warping techniques to align all Curves in a time-warped space, compute the sample mean of the Curves in the time-warped space, and transform the means back to the original time space. We show that all BTCs are aligned based on the percentile of mass reaching the compliance boundary, and the functional average is the percentile average of all BTCs. The confidence interval of the sample mean Curve is estimated using the perturbation approach. The functional average provides an additional metric that can be used to characterize the Breakthrough behavior in addition to more traditional median and arithmetic average Curves. The method is illustrated using transport simulations at the Material Disposal Area G, Los Alamos National Laboratory (LANL) in New Mexico.
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on estimating functional average Breakthrough Curve using time warping technique and perturbation approach
Water Resources Research, 2012Co-Authors: Zhiming Lu, Philip H StaufferAbstract:[1] Simulated contaminant Breakthrough Curves (BTC) are often used to predict mass arrival at compliance boundaries at waste storage sites. In numerical simulations that involve uncertainties on input parameters such as randomly heterogeneous rock properties, Monte Carlo simulations are commonly utilized and the mean Breakthrough Curve is often calculated from the arithmetic average of all realizations. The arithmetic mean Breakthrough Curve in general overestimates the mass flow rate at early and late time but underestimates the peak mass flow rate. The averaged Breakthrough Curve usually does not resemble any of individual Breakthrough Curves. The reason is that BTCs vary not only on amplitude but also on dynamics (time) and therefore it is not appropriate to take the arithmetic average directly. In this study, we consider each BTC as a random Curve, and use time-warping techniques to align all Curves in a time-warped space, compute the sample mean of the Curves in the time-warped space, and transform the means back to the original time space. We show that all BTCs are aligned based on the percentile of mass reaching the compliance boundary, and the functional average is the percentile average of all BTCs. The confidence interval of the sample mean Curve is estimated using the perturbation approach. The functional average provides an additional metric that can be used to characterize the Breakthrough behavior in addition to more traditional median and arithmetic average Curves. The method is illustrated using transport simulations at the Material Disposal Area G, Los Alamos National Laboratory (LANL) in New Mexico.
John L Hutson - One of the best experts on this subject based on the ideXlab platform.
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A Breakthrough Curve analysis of unstable density‐driven flow and transport in homogeneous porous media
Water Resources Research, 2004Co-Authors: M Wood, Craig T Simmons, John L HutsonAbstract:[1] In certain hydrogeological situations, density variations occur because of changes in solute concentration, temperature, and pressure of the fluid. These include seawater intrusion, high-level radioactive waste disposal, groundwater contamination, and geothermal energy production. Under certain conditions, when the density of the invading fluid is greater than that of the ambient one, gravitational instabilities or fingers may lead to transport over larger spatial scales and significantly shorter timescales than compared with diffusion alone. This study has two key objectives: (1) to explore how the nature of a Breakthrough Curve changes as the density of the invading fluid changes and there is a subsequent transition from stable to unstable behavior and (2) to examine the feasibility of using 1-D advection-dispersion fitting models to fit the experimental data as the density of the invading fluid increases. Thirty-six Breakthrough Curve experiments were carried out in fully saturated, homogeneous sand columns. Results show that an increase in the density of the source solutions leads to Breakthrough Curves with lower peak concentrations at Breakthrough, earlier peak Breakthrough pore volume and time, and an increase in positive skewness of the Breakthrough Curve. Visual experiments conducted in transparent columns confirm that a transition from stable to unstable behavior occurs as the density of the injectant increases and that backward convective reflux in the high-density cases leads to dilution of the trailing edge of the pulse as evidenced by positively skewed Breakthrough Curves. These mixed convective systems (controlled by both forced and free convection) are characterized by a mixed convective ratio. Parameter estimation using a 1-D advection-dispersion fitting model suggests that unstable plume migration can be fitted with an apparent pore flow velocity and dispersivity at low-density gradients. However, as the density of the injectant increases, it becomes progressively difficult to estimate parameters that fit the experimental Curves with a model that does not explicitly account for density effects. Significantly poorer matches are obtained when the invading solution concentration is equal to, or exceeds, the solution concentration denoted by ML (the medium- to low-density solution), i.e., invading solutions greater than approximately 13,000 mg/L in this study. Care must therefore be taken in applying standard advection-dispersion models to Breakthrough Curve analyses where even modest density differences are encountered.
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a Breakthrough Curve analysis of unstable density driven flow and transport in homogeneous porous media
Water Resources Research, 2004Co-Authors: M Wood, Craig T Simmons, John L HutsonAbstract:[1] In certain hydrogeological situations, density variations occur because of changes in solute concentration, temperature, and pressure of the fluid. These include seawater intrusion, high-level radioactive waste disposal, groundwater contamination, and geothermal energy production. Under certain conditions, when the density of the invading fluid is greater than that of the ambient one, gravitational instabilities or fingers may lead to transport over larger spatial scales and significantly shorter timescales than compared with diffusion alone. This study has two key objectives: (1) to explore how the nature of a Breakthrough Curve changes as the density of the invading fluid changes and there is a subsequent transition from stable to unstable behavior and (2) to examine the feasibility of using 1-D advection-dispersion fitting models to fit the experimental data as the density of the invading fluid increases. Thirty-six Breakthrough Curve experiments were carried out in fully saturated, homogeneous sand columns. Results show that an increase in the density of the source solutions leads to Breakthrough Curves with lower peak concentrations at Breakthrough, earlier peak Breakthrough pore volume and time, and an increase in positive skewness of the Breakthrough Curve. Visual experiments conducted in transparent columns confirm that a transition from stable to unstable behavior occurs as the density of the injectant increases and that backward convective reflux in the high-density cases leads to dilution of the trailing edge of the pulse as evidenced by positively skewed Breakthrough Curves. These mixed convective systems (controlled by both forced and free convection) are characterized by a mixed convective ratio. Parameter estimation using a 1-D advection-dispersion fitting model suggests that unstable plume migration can be fitted with an apparent pore flow velocity and dispersivity at low-density gradients. However, as the density of the injectant increases, it becomes progressively difficult to estimate parameters that fit the experimental Curves with a model that does not explicitly account for density effects. Significantly poorer matches are obtained when the invading solution concentration is equal to, or exceeds, the solution concentration denoted by ML (the medium- to low-density solution), i.e., invading solutions greater than approximately 13,000 mg/L in this study. Care must therefore be taken in applying standard advection-dispersion models to Breakthrough Curve analyses where even modest density differences are encountered.
N Mahadevaiah - One of the best experts on this subject based on the ideXlab platform.
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interaction of chromate on surfactant modified montmorillonite Breakthrough Curve study in fixed bed columns
Industrial & Engineering Chemistry Research, 2008Co-Authors: N Mahadevaiah, B Venkataramani, B Jai S PrakashAbstract:Interactions between chromate and surfactant modified montmorillonite at room temperature (25 °C) and different pHs (1-7) in aqueous solution in fixed bed columns have been studied. A series of column tests were performed to determine the Breakthrough Curves at different initial surfactant loadings (0.5-3 CEC) of the bed. The interlayer spacing increased with the surfactant loading from 14.2 to 40.5 A. Experimental results of the column tests and the basal spacing of the column material showed that the adsorption of chromate onto the clay did not occur until the initial surfactant loading was beyond a critical concentration apparently enough to open the clay sheets for the entry of chromate species. The shapes of the Breakthrough Curves indicate that the chromate ions enter the interlamellar region only when the initial surfactant loadings are beyond 2 times the CEC of the clay. The amount of adsorbate increases proportionally with increasing bed depth. A simple two-parameter model originally introduced by Yoon and Nelson (Yoon, Y. H.; Nelson, J. H. Am. Ind. Hyg. Assoc. J. 1984, 45, 509) was used to calculate the Breakthrough time. Chromate could be recovered completely by washing with ammonium hydroxide, and the column material was found to regain its capacity to adsorb repeatedly after simple acid wash.
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restrictive entry of aqueous molybdate species into surfactant modified montmorillonitea Breakthrough Curve study
Chemistry of Materials, 2007Co-Authors: N Mahadevaiah, B Venkataramani, B Jai S PrakashAbstract:Molybdenum sorption behavior and the nature of Breakthrough Curves have been studied in a fixed-bed column containing montmorillonite clay modified by treatment with cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide. Different amounts of the surfactant loaded into the interlayer region of the montmorillonite to increase the interlayer spacing is found to enhance molybdate sorption. The sorption was found to be at a maximum in acidic medium (pH <0) and was almost constant between pH 3 and 4. Beyond pH 4, adsorption decreased rapidly and was almost two to four times lower than that in the acid medium. It is known from the equilibria of aquo molybdate species that polymolybdate species Mo8O264- and Mo7O246- are prevalent in the highly acidic medium; the species H2MoO4 and HMoO4- are stable between pH 0 and 4, and MoO42- is predominantly present above pH 5. The variation in adsorption of Mo is interpreted on the basis of the type of species prevalent at different pHs. The sample loaded at 0.5 CEC...
Takuji Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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gas phase removal of hydrogen sulfide using iron oxyhydroxide at low temperature measurement of Breakthrough Curve and modeling of sulfidation mechanism
Chemical Engineering Journal, 2015Co-Authors: Takuji Yamamoto, Melaz Tayakoutfayolle, Christophe GeantetAbstract:Abstract With the aim of removing hydrogen sulfide (H2S) from a gaseous phase around room temperature, we studied the performance of an iron oxyhydroxide (ferrihydrite) adsorbent by measuring a packed bed Breakthrough Curve (BTC) in a constant gas flow. We determined the amount of H2S adsorbed on the adsorbent by integrating BTCs measured under different experimental conditions. These conditions included the initial concentration of H2S, the superficial gas velocity and the temperature of the packed bed. Under the experimental conditions, it was found that the amount of H2S adsorbed was almost unchanged by the superficial gas velocity, whereas the adsorbed amount depended on the initial concentration of H2S and temperature. To solve the mass transfer equations in the packed bed, we developed a model considering such parameters as the kinetic constant of the sulfidation reaction, the intragranular diffusivity of H2S, and the number density of active sites on the adsorbent. By fitting the calculated BTC to the measured BTC under one of the experimental conditions, the set of parameters could be estimated. Using the same set of estimated parameters, we calculated the BTCs under the other experimental conditions. As a result, we confirmed that the calculated BTC coincided with the BTC measured under a different initial H2S concentration and gas velocity. We also found that the number density of the active sites increased with increases in temperature.
