Browsing by Subject "Adsorption"

Now showing 1 - 20 of 27

A Gas Chromatographic Method to Determine Sorption Isotherms for Biomedical Polymers
(Texas Tech University, 1977-12) Chen, Hsien
This study is concerned with the development of a methodology whereby inverse gas-liquid chromatography can be utilized as an analytical tool to determine the sorption isotherms of chemical sterilants for biomedical polymers. Cellulose acetate and poly (vinylidene chloride/vinyl chloride) copolymer were successfully investigated with regard to their potential to adsorb isopropyl alcohol and aqueous solutions of formaldehyde and glutaraldehyde. Since those sterilants can be retained by the polymer matrix, it is important that their sorption characteristics can be understood. Otherwise, toxic levels of the sorbed chemical can be released into the biosphere after the polymer has been implanted into the human body. Inverse chromatography was found to be well suited for this type of study because of its speed, accuracy, and wide range of applicability. Moreover, the data obtained with this technique correspond to infinite dilution, or the low PPM concentration range so important in the removal of the last vestiges of the chemical sterilants.
Accounting for Adsorbed gas and its effect on production bahavior of Shale Gas Reservoirs
(2010-10-12) Mengal, Salman Akram
Shale gas reservoirs have become a major source of energy in recent years. Developments in hydraulic fracturing technology have made these reservoirs more accessible and productive. Apart from other dissimilarities from conventional gas reservoirs, one major difference is that a considerable amount of gas produced from these reservoirs comes from desorption. Ignoring a major component of production, such as desorption, could result in significant errors in analysis of these wells. Therefore it is important to understand the adsorption phenomenon and to include its effect in order to avoid erroneous analysis. The objective of this work was to imbed the adsorbed gas in the techniques used previously for the analysis of tight gas reservoirs. Most of the desorption from shale gas reservoirs takes place in later time when there is considerable depletion of free gas and the well is undergoing boundary dominated flow (BDF). For that matter BDF methods, to estimate original gas in place (OGIP), that are presented in previous literature are reviewed to include adsorbed gas in them. More over end of the transient time data can also be used to estimate OGIP. Kings modified z* and Bumb and McKee?s adsorption compressibility factor for adsorbed gas are used in this work to include adsorption in the BDF and end of transient time methods. Employing a mass balance, including adsorbed gas, and the productivity index equation for BDF, a procedure is presented to analyze the decline trend when adsorbed gas is included. This procedure was programmed in EXCEL VBA named as shale gas PSS with adsorption (SGPA). SGPA is used for field data analysis to show the contribution of adsorbed gas during the life of the well and to apply the BDF methods to estimate OGIP with and without adsorbed gas. The estimated OGIP?s were than used to forecast future performance of wells with and without adsorption. OGIP estimation methods when applied on field data from selected wells showed that inclusion of adsorbed gas resulted in approximately 30 percent increase in OGIP estimates and 17 percent decrease in recovery factor (RF) estimates. This work also demonstrates that including adsorbed gas results in approximately 5percent less stimulated reservoir volume estimate.
Adsorption, reaction and interfacial electronic structures of aromatic molecules on single crystal surfaces
(2005) Wei, Wei; White, John M.
Electron transfer at organic/metal interfaces is fundamental to a large number of problems in surface science. Electronic interactions at such an interface are responsible for charge injection from an electrode to the molecular film. The efficiency or rate of charge injection is determined by the energetic alignment of molecular orbitals to the metal Fermi level and the electronic coupling strength (wavefunction mixing) between molecular orbitals and metal bands. Two experimental investigations were performed with two-photon photoemission spectroscopy (2PPE). First, the energetic alignments of naphthalene/Cu(111) were probed. Three transitions involving unoccupied orbitals were found and identified as having π* molecular orbital character—the first lying 0.4 eV above the vacuum level vii (π* b1u), the second 0.3 eV below the vacuum level (π* b3g), and the third 1.1 eV below the vacuum level (π* b2g). In the second experiment, the interfacial electronic structures of chemisorbed styrene on Cu(111) were successfully investigated. We observed unoccupied states 3.5 eV above the Fermi level and occupied states 2.0 eV below the Fermi level. Polarization results reveal that the occupied and unoccupied states arise from bonding and antibonding orbitals formed by hybridization of copper (surface state and d-band orbitals) and styrene (π1* and π2* orbitals). For the first time, two-photon photoemission spectroscopy was employed to explore a surface chemical reaction: epoxidation of styrene on Cu(111). With 100 L oxygen on a Cu(111) surface, the atomic oxygen occupies three-fold hollow HCP sites rather than FCC sites. Its 2p states hybridize strongly with the dz2 states of the Cu atoms in the second layer. After styrene is adsorbed on Cu metal sites of this oxygen-covered surface, it undergoes efficient epoxidation to styrene oxide. The 2PPE results show that the change in the electronic structures of the adsorbed reactant is consistent with the surface reaction: the oxygen-induced feature from the Cu-O bonding disappears and a new state appears. However, 1000 L oxygen-covered Cu(111) is catalytically inert for styrene epoxidation: as styrene is added, no new features appear in 2PPE, and there is no evidence for chemical reaction in thermal desorption. This study could open up a new area of solid state and surface catalytic chemistry.
An Adsorption System for the Removal of Sulfur Oxides
(Texas Tech University, 1977-08) Faust, Gerald John
The purpose of this study was to determine the SOp adsorption efficiencies of a uniquely designed, panel bed adsorption system. A vertical panel bed adsorber was attached to an incinerator fired with high sulfur fuel oil. The efficiency of sulfur dioxide removal from the combustion gases was then determined. Two adsorbents were investigated, Barnebey Cheney type CH activated carbon in 6 x 10 mesh size and Linde^^type AW-500 molecular sieve in 1/8 inch cylindrical pellets with a pore diameter of 5A. The data obtained from operation of the panel bed adsorber, using these adsorbents, were then used to determine the characteristic constants for our mathematical model of the adsorption system. These data points were sufficient to yield an equation suitable for scale-up purposes with regard to the two adsorbents tested.
Design and analysis of an electronically switchable ion exchange system
(2009-12) Kannappan, Ramakrishnan; Katz, Lynn Ellen; Holcombe, James A.
Metal contamination is a considerable environmental problem because metals are persistent contaminants. Ion exchange is one of the most commonly used treatment options for trace metal removal. This research develops and evaluates a redox active modified ion exchange system that has the potential to reduce the ionic strength of ion exchange regeneration streams. Poly-L-cysteine (PLC) was selected as the redox active, adsorbing functional group on the surface of a reticulated vitreous carbon (RVC) electrode. PLC is an excellent soft acid metal chelator and is unique in that its thiol groups can form disulfide bonds with each other. The reduction of available thiols changes the metal binding capacity of the peptide since the thiol is the primary binding group. RVC provides a macroporous conductive monolithic resin to support the peptide. An experimental apparatus was designed to study the properties of this system and estimate performance. Distinct oxidized and reduced states of PLC on the surface of the RVC were confirmed by changes in metal binding characteristics. Adsorption edges showed a sharper pH dependence for the reduced electrode compared to the oxidized electrode from pH 3-7. Adsorption isotherms performed at pH 7 showed increased capacity for the reduced electrode. The change was reversible by chemical and electrical reduction. This difference was confirmed at the molecular level with Cd- EXAFS of oxidized and reduced electrodes. A greater degree of cadmium-sulfur coordination was observed on the reduced electrode and a greater cadmium-oxygen coordination was apparant on an oxidized electrode. A multidentate adsorption model was developed to model the pH dependent behavior of cadmium adsorption on the PLC-RVC surface. Nickel adsorption showed increased adsorption in the oxidized state. The most likely explanation is increased carboxylate complexation. The electronically switchable ion exchange system (ESIE) provides a framework for modifying traditional ion exchange processes. The system has 5 to 10 times less specifc capacity than current ion exchange systems, but uses solutions 10-100 times lower in ionic strength for regeneration. Further studies on the effect of ionic strength on adsorption and current usage are necessary to compare the cost of the ESIE process to traditional ion exchange.
Development of a Thermodynamic Model for Fluids Confined in Spherical Pores
(2014-07-18) D'Lima, Michelle Lynn
The thermodynamic properties of a fluid confined in extremely small pores can be substantially different from those observed of the same bulk fluid. These differences in behavior could have technical applications in adsorption-based separations; may pose a challenge with regards to the extraction of oil entrapped in the small cavities of reservoir rocks; or could even be utilized in complex heterogeneous catalytic systems such as those used in gas-to liquid fuel conversions. This thesis describes the use of the generalized van der Waals theory to extend cubic equations of state, such as Peng-Robinson, that are widely applied in the oil and gas industry to model the behavior of pure fluids as well as mixtures confined in spherical pores. Empirical expressions were developed for the coordination number in spherical pores as a function of the molecule to pore size ratio, for the distribution of molecules along the pore radius as function of temperature, and of the interaction potential between the molecules and the pore wall. Despite their relative simplicity, the expressions capture the limiting behaviors expected at high and low temperatures. The model parameters were then fitted to experimental data for the adsorption of light hydrocarbons and gases in common adsorbents. Finally, the calculated results were compared to the experimental results in order to assess the performance of the model, through adsorption equilibrium calculations.
Enzymatic inhibition-based biosensing on nitrogen-doped carbon nanotube electrodes
(2015-05) Rust, Ian Matthias; Stevenson, Keith J.; Webb, Lauren J
While previous work has demonstrated the effectiveness of nitrogen-doped carbon nanotubes (N-CNTs) as biogenic electrode materials in first- and second-generation biosensors, this thesis primarily explores enzymatic inhibition-based biosensing schemes on N-CNT electrodes. This type of scheme enables the detection of enzymatic inhibitors, as opposed to enzymatic substrates, making these inhibition-based biosensors much more suitable for the monitoring of environmental pollutants. Presented in this thesis is a biosensor which couples N-CNTs with glucose oxidase (GOx) through spontaneous physical adsorption for the highly sensitive detection of aqueous silver ions. Included is a thorough discussion of the parameters that affect response time as well the biosensor’s aptitude for repeated use. A later chapter presents initial work towards the inhibition-based detection of sucralose, a relatively new environmental pollutant. A bi-enzymatic approach is explored, in which both GOx and invertase are immobilized on an N-CNT modified electrode. Finally, shifting focus from inhibition-schemes, the last remaining chapter investigates the coupling of CNTs and N-CNTs with methylene green (MG), a redox mediator used in second-generation biosensors based on NADH oxidation. Common coupling techniques are examined for their effectiveness in decreasing the overpotential required for NADH oxidation.
Evaluation of an activated alumina sorption system for removal of fluoride from water
(Texas Tech University, 1983-05) Onuoha, Ukiwo Obasi
Not available
Evolution of microbial populations with spatial and environmental structure
(2010-05) Miller, Eric Louis; Meyers, Lauren Ancel; Bennett, Philip C.; Bull, James J.; Hawkes, Christine V.; Hillis, David M.
Rarely are natural conditions constant, but generally biologists study microbes in artificially constant environments in the laboratory. I relaxed these assumptions of constant environments through time and space as I investigated how microbial populations evolve. First, I examined how bacteriophage evolved in the presence of permissive and nonpermissive hosts. I found that bacteriophage evolved discrimina- tion in mixed environments as well as in one of two environments with homogeneous, permissive hosts. This showed the asymmetry of host-shifting in viruses as well as the possibility of large, and somewhat unpredictable, pleiotropic effects. Secondly, I reconstructed ancestral environmental conditions for soil bacteria groups using phy- logenetics and environmental variables of extant species’ habitats. These generaliza- tions suggested characteristic phenotypes for several phylogenetic groups, including uncultured Acidobacteria. Lastly, I collected genetic sequences and global collection information for 65 bacteria genera across the domain. In examining the relation- ship between genetic distance, environmental conditions, and geography, I observed positive relationships specifically between genetic distance and geography or genetic distance and environmental conditions for bacteria from land sites but not from wa- ter sites. Phylogenic classifications or phenotypes of the genera could not predict these correlations. In all of these projects, variations in the environment created evolutionary signals that hinted at past environments of microbial populations.
In Situ Groundwater Arsenic Removal Using Iron Oxide-Coated Sand
(2010-10-12) Yu, Hongxu
In many regions of the world, groundwater is contaminated with a high level of arsenic that must be treated before it can be safely used as drinking water. In situ immobilization of arsenic from groundwater within subsurface environment could have major advantages over the conventional above-ground chemical coagulation-precipitation treatment process. In this study, we develop a novel technique that can in situ emplace iron oxides onto the sand grain surface of porous media under mild chemical and temperature conditions. The technique involves sequential injections of a preconditioned ferrous iron solution and an oxidant solution and then orchestrate the advective-diffusive transport of the two reagents in porous media to create an overlapped reaction zone where ferrous iron is oxidized and precipitated on the sand grain surfaces. We demonstrate through bench-scale column tests the feasibility of using this technique to create a large-scale iron oxide-enriched reactive barrier in subsurface environment for in situ removal of arsenic. A sand filter with a fresh iron oxide coating can treat thousands of pore volumes of water contaminated with dozens of ppb arsenic before the coating needs to be regenerated. Arsenic breakthrough curves through the sand filter suggest that both reversible adsorption and irreversible precipitation are responsible for removing arsenic from the water. Unlike conventional excavate-and-fill permeable reactive barriers, the treatment capacity of our in situ created barrier can be in situ regenerated and replenished with a fresh coating.
Indoor residential fate model of phthalate plasticizers
(2010-12) Liang, Yirui; Xu, Ying (Assistant professor); Corsi, Richard L.
A three-compartment model is extended to estimate the fate and transport of DEHP in a realistic residential environment. The model considered eight environmental media (i.e. air, particulate matter with six size fractions, vinyl flooring, carpet, furniture, dust, wall and ceiling). Particle movement (deposition and resuspension), dust removal (vacuuming), indoor cooking, and adsorption/absorption on indoor surfaces are included. The predicted airborne DEHP concentrations at steady state are within 0.1 [microgram]/m³ to 0.6 [microgram]/m³, which are similar to those measured in field studies. After vinyl flooring (the primary source) is removed, it takes 2 years for the indoor airborne DEHP level to reduce 0.01 [microgram]/m³, and the time increases significantly when carpet present. The results indicate that carpets as well as other interior surfaces may be important phthalate sinks and if the only removal mechanism is ventilation, strongly sorbing phthalate may persist for years. Phthalate amount in dust is strongly influenced by the deposition surface. The concentration of DEHP presents 10 times higher in dust on the source (vinyl flooring) than on the sink (furniture), and it takes more than a year for DEHP to reach equilibrium between bulk air and dust. The domestic activity of cooking is then included in the model and it shows that suspended particle concentration has a substantial impact on gas-phase DEHP level indoors, while the influence of ventilation is only to some extent. Three other SVOCs (DMP, BBP and DiDP) are also investigated and their environmental fates show that chemical’s vapour pressure and octanol/air partition coefficient have substantial influences on sorbing mechanisms and the gas phase and airborne concentrations.
Integrating Experiment and Theory in Electrochemical Surface Science: Studies on the Molecular Adsorption on Noble-Metal Electrode Surfaces by Density Functional Theory, Electron Spectroscopy, and Electrochemistry
(2013-08-05) Javier, Alnald Caintic
Computational techniques based on density functional theory (DFT) and experimental methods based on electrochemistry (EC), electrochemical scanning tunneling microscopy (EC-STM), and high-resolution electron energy loss spectroscopy (HREELS) were employed to study the adsorption of (i) sulfuric acid on Pd(111), (ii) benzene on Pd(111), (iii) hydroquinone/benzoquinone on Pd(111), (iv) hydroquinone sulfonate/benzoquinone sulfonate on Pd(111), (v) 2,3-dimethylhydroquinone/2,3-dimethylbenzoquinone on Pd(111) and polycrystalline Pd, (vi) hydrogen on 1-6 monolayers (ML) of Pd deposited on a Pt(111) substrate, and (vii) a thiolated iron hydrogenase model complex on polycrystalline Au. In situ EC-STM and DFT investigations of sulfuric acid on a Pd(111) surface indicated that two layers of water molecules and hydronium ions are assembled, non-co-planar with one another, between the rows of surface-coordinated sulfate anions; the layer that is slightly elevated is composed of hydronium counter cations. The STM images of benzene chemisorbed on a Pd(111) electrode surface were simulated and the results suggested that, when the potential of the Pd electrode is held at 0.3 V, benzene is chemisorbed on a 3-fold site; while at 0.55 V, the molecule is adsorbed on a position between a 3-fold and a 2-fold site. Computational and experimental results implied that at low concentrations, hydroquinone sulfonate undergoes oxidative chemisorption forming benzoquinone sulfonate (BQS) on the Pd(111) surface, BQS adopts a flat orientation in which the quinone ring is centered over a 2-fold site, and the C?H and C?S bonds are no longer co-planar with the quinone ring and are slightly tilted, directed away from the surface. At very dilute concentrations, when hydroquinone (H_(2)Q) undergoes oxidative chemisorption producing benzoquinone oriented flat, albeit with a slight tilt, on the Pd(111) surface, the flat-adsorbed quinone ring is centered on a bridge site where the C_(2) axis is rotated 30degree from the [110] direction of the metal substrate, the p-oxygen atoms are located above two-fold sites, and the ring is slightly puckered with the C?H bonds tilted away from the surface at approximately 20degree. When 2,3-dimethylH_(2)Q is chemisorbed on the Pd surface, at low concentrations, 2,3-dimethylH_(2)Q is oxidatively chemisorbed producing 2,3-dimethyl-1,4-benzoquinone oriented flat on the surface, the flat-adsorbed rings are centered above 2-fold sites wherein the C=O bonds are pointing 30degree from the [110] direction of the substrate, the para-oxygen atoms are located above bridge sites, the peripheral bonds are tilted away from the surface at ca. 20degree, and at higher concentrations, oxidative chemisorption occurs through activation of the ring?s C?H bonds yielding edge-oriented 2,3-dimethylH_(2)Q. Electrochemistry and DFT results also implied that at 1-2 ML of Pd on Pt(111), hydrogen is only adsorbed on a hollow site while at 3 ML of Pd or more, atomic hydrogen may be chemisorbed on the 3-fold site or absorbed in the octahedral hole underneath the hollow site. Using Au electrodes, an unbound iron hydrogenase analogue complex studied was found to slightly catalyze the H_(2) evolution process. However, when the complex was immobilized unto the Au surface, the electrocatalytic activity was greatly improved.
Kinetics and mechanisms of adsorption of heavy metal ions on activated carbon
(Texas Tech University, 1979-08) Lin, Chieh-Chien
Not available
Multiphase Equilibrium of Fluids Confined in Fisher-Tropsch Catalytic Systems
(2014-04-23) Warrag, Samah
Energy supply and security imposes a significant challenge in our modern world stemming from our dependence on depleting resources such as petroleum and oil. Fischer-Tropsch synthesis (FTS) is considered as a great energy alternative which can significantly reduce our dependence on oil, improve rural economics, reduce greenhouse emissions, and promise energy security. It is a key technology for converting syngas, produced from coal, biomass or natural gas, into a variety of hydrocarbon products. Although this technology was discovered in 1923, commercialization and scale up are limited to the use of few reactor configurations (e.g. multi-tubular fixed-bed reactor, Slurry-bubble column reactor, and fluidized bed reactors). In order to improve the limitations in both reactor configurations, on lab scale near critical media was utilized, since it offers a great combination of the advantages of both the gas-phase reaction (multi-tubular fixed-bed reactor) and the liquid-phase reaction (slurry-bubble column reactor), while simultaneously overcoming their limitations. This work focuses on modeling the phase behavior of the FTS mixture in fixed bed reactor in the bulk phase inside the reactor bed or inter-particle and then zoom into the catalyst (confined phases within the catalyst pores or intra-particle). This is done by using an extended Peng-Robinson (PR) equation of state (EOS) that is capable of accounting for the fluid behavior inside confined pores as well as in the bulk phases. The PR Equation of state model extended to confined fluid (PR-C) has been utilized in multiphase equilibrium algorithm using FORTRAN. The simulation results provide the composition and the condition of each bulk phase and pore phase for a given initial mixture. Two different scenarios were studied for fixed bed reactor: the first one is the conventional gas phase FTS and the second one is for the supercritical phase FTS (SCF-FTS). In each case, the phase behavior of the mixture of the reactants and products was investigated at different conversions along the bed length. The simultaneous assessment of both gas phase FTS and SCF-FTS phase behavior and reaction performance open the door for optimizing the design FTS reactor and enhance the efficiency of the process. Preferential adsorption of hydrogen has been observed and this could be due to the small size of the hydrogen molecules compared to those of the other components. Our studies suggested that the supercritical phase provides superior heat dissipation due to the existence of denser phase in the bulk and the confined regions than the conventional gas phase. On the other hand in the gas phase and for limited carbon number (up to C8) the pore phase is found to be in a vapor state which should provide higher diffusivity of the reactant than that in the supercritical phase. Our study will continue by integrating the developed phase behavior studies in the reactor design model.
p-Dichlorobenzene and naphthalene : emissions and related primary and secondary exposures in residential buildings
(2013-05) Guerrero, Priscilla Annette; Corsi, Richard L.
p-Dichlorobenzene (p-DCB) and naphthalene are compounds classified as Group C carcinogens according to the USEPA. Sources of p-DCB and naphthalene include moth repellents and deodorizers typically used in closets, garment bags, and toilet bowls found in pure form. In this study, laboratory, closet, and garment bag experiments were used to determine emission rates of p-DCB and naphthalene from consumer products (closet air freshener, toilet bowl deodorizer, and moth repellent). Emission rates varied considerably between products that contain p-DCB, primarily due to product packaging, and were generally suppressed when the product was used in a closed closet or garments bag, relative to products placed in well-ventilated chambers. Experimental mass emission rates were used in conjunction with a well-mixed reactor model to predict indoor p-DCB and naphthalene concentrations for a range of reasonable residential scenarios. Results suggest that exposures under worst-case scenarios could lead to excess lifetime cancer risks of greater than 20,000 in a million (2%) for those who use consumer products that are pure p-DCB, a risk that dwarfs any reported environmental cancer risks over large segments of the US population. Since such products are typically used where clothing is kept, significant chemical adsorption onto clothing is possible following sublimation from the solid product. Chamber experiments were used to determine the amount of p-DCB and naphthalene mass that adsorbs onto selected clothing materials made of cotton, polyester, or wool. Cloth specimens were kept inside a chamber through which an air stream containing p-DCB or naphthalene was passed for one month. After this time, p-DCB or naphthalene were chemically extracted from the cloth specimens. Polyester was determined to be the most adsorbent material, while cotton was the least adsorbent for each chemical. Equilibrium partition coefficients of 0.01 m³/g for p-DCB and 0.02 m³/g for naphthalene were determined experimentally for wool. Desorption rates were determined in both laboratory chambers and a closet in a test house. Results suggest prolonged persistence of p-DCB and naphthalene on polyester and wool, e.g., half-lives of 12 to 20 days after a moth repellent is removed from the clothes storage environment. An exposure scenario was also carried out to compare the inhalation and dermal exposure risks associated with contaminated clothing.
pH-induced flocculation/deflocculation process for harvesting microalgae from water
(2014-08) Choi, Jin-Yong, Ph. D.; Kinney, Kerry A.; Katz, Lynn Ellen; Kinney, Kerry A.; Katz, Lynn E.
Historically, the presence of microalgae (algae hereafter) in natural waters has been viewed as a nuisance due to its adverse impact on water quality. More recently, however, algae are being investigated as potential sources of biofuel and a range of natural products. These applications require the development of large-scale cultivation systems for mass production that include growth, harvesting, concentration, and product recovery components. While challenges still remain with respect to many of the processes involved in mass production, one of the most technically and economically challenging steps is harvesting the algae from dilute growth cultures, especially in systems where chemical additives are of concern either within the algae concentrate or the effluent water. For this reason, a pH-induced flocculation/deflocculation method using the hydroxides of alkali or alkaline earth metals (e.g., lime, caustic soda) is of particular interest for algae harvesting as Na, Ca and Mg are typically present in natural waters. The goal of this research was to determine the underlying mechanisms responsible for algae coagulation by magnesium and calcium and to evaluate the potential of these mechanisms for harvesting algae for a range of synthetic and field source water chemistries. In the first two phases of this research, the mechanisms for coagulation with magnesium and calcium were studied independently. A series of bench-scale experiments were designed to isolate the potential mechanisms of algae destabilization associated with each of these cations as a function of water chemistry, and microscopic analyses were performed to characterize the flocculated algae/precipitate mixtures. In the third phase of this research, removal of algae in field source waters was evaluated with respect to the underlying science elucidated in the previous phases. The results indicate that the dominant algae destabilization mechanism associated with magnesium shifts from Mg adsorption/charge neutralization to Mg(OH)₂[subscript (S)] precipitation-enhanced coagulation with increasing pH. Moreover, dissolved Mg²⁺ adsorption to the algae surface led to effective algae coagulation, while minimizing the mass of precipitated Mg(OH)₂[subscript (S)] . For Ca, this research identified the importance of the nucleation process (heterogeneous vs. homogeneous nucleation) on algae removal efficiency. Heterogeneous nucleation is a key factor for optimizing algae removal; thus, the degree of oversaturation with respect to CaCO₃[subscript (S)] is a crucial operating parameter. This research demonstrated that the algae harvesting process using pH-induced flocculation/deflocculation method can be optimized for a wide range of source waters if the water chemistry (e.g. pH, ion concentration, alkalinity, ionic strength) is properly incorporated into the system design.
A protocol to evaluate the adsorptive removal of dissolved copper and zinc from highway runoff
(2014-05) Ernst, Clayton Owen; Katz, Lynn Ellen
The increasing urbanization of landscapes significantly alters the surface water hydrology of impacted watersheds. As a side effect, stormwater discharges to receiving water bodies are often of decreased quality due to pollutants deposited on impervious urban surfaces being entrained by runoff. A pertinent example of this problem is the presence of copper and zinc in highway runoff. Both copper and zinc have been shown to exert toxic effects on aquatic micro- and macro-biota. Copper in particular has been shown to harmfully disrupt the olfactory nervous system of fish species at concentrations as low as 3 [mu]g/L. To meet these limits, treatment of highway runoff for the removal of copper and zinc is necessary. However, due to the complexities associated with the behavior of heavy metals in natural systems, the appropriateness of removal techniques will necessarily depend on a variety of system-specific factors and chemical characteristics of highway runoff. Adsorption has been shown to be generally effective in the removal of dissolved heavy metals, but the choice of adsorptive media is again dependent on system-specific parameters. This study developed and evaluated a column testing protocol that can be used to quickly and reliably evaluate adsorptive removal of dissolved heavy metals from highway runoff. The protocol is demonstrated in an evaluation of iron oxide, manganese oxide, crab shell, concrete, and bone meal media for removing dissolved copper and zinc from highway runoff. The performance of these media was assessed as a function of various runoff characteristics including pH, ionic strength, alkalinity, and total organic carbon. The methodology was used to show that iron oxide media in combination with crab shell or concrete media provided the most effective removal of copper and zinc from highway runoff. Through this study, the convenience, flexibility, and robustness of the proposed protocol are compellingly established.
Stability and rheology of high internal phase CO₂-in-water foams and stability and transport of polymer grafted nanoparticles
(2015-08) Xue, Zheng; Johnston, Keith P., 1955-; Ekerdt, John; Huh, Chun; Mohanty, Kishore; Yu, Guihua
In an effort to reduce the water consumption in hydraulic fracturing by using foam based fracturing fluids, the stability and rheology of ultra-dry supercritical CO₂-in-water foams were investigated in terms of bulk phase viscosity, interfacial tension, and interfacial rheology. The foam morphology and long term stability was studied in situ with high pressure microscopy. Foams with up to 0.98 CO₂ volume fraction and apparent viscosities of hundreds of centipoise were stabilized for hours to days by increasing the viscoelasticity of the interface and the continuous phase. The interfacial shear viscosity and compression elasticity were enhanced with either mixture of oppositely charged surfactant and nanoparticles (with and without high molecular weight polyelectrolyte) or viscoelastic surfactant alone which formed wormlike micelles. The increased interfacial viscoelasticity leads to a rigid foam film as characterized by high Boussinesq number and Marangoni number. Thus, the drainage of the foam film was suppressed due to the immobile interface and the high continuous phase viscosity, as described by the Reynolds drainage equation. The resulting thick film as well as the elastic interface decreases the rate for coalescence and Ostwald ripening. Consequently, foams with fine texture of ~20 µm bubbles were produced and stabilized for hours. Nanoparticles that can be transported through porous rock at high salinity and high temperature are expected to have a large impact on the wellbore diagnostics, electromagnetic tomography and enhanced oil recovery. A series of stable anionic and zwitterionic polymers in high salinity brine at high tempeartures were identified and synthesized. Furthermore, when covalently tethered to the nanoparticles via "grafting to" or "grafting through" approach, the obtained polymer grafted nanoparticles exhibited colloidal stability in high salinity brine for over 1 month, and also low static adsorption to silica microspheres at 1mg/m². The silica microspheres were used to mimic mineral surfaces. The remarkable colloidal stability and low adsorption on mineral surfaces was attributed to electrosteric repulsion exerted by the charged and extended polyelectrolyte chains on the nanoparticle surface.
Study of alternating anionic surfactant and gas injection in carbonate cores
(2016-05) Ghosh, Pinaki, M.S. in Engineering; Mohanty, Kishore Kumar; DiCarlo, David
A major portion of the oil across the world is contained in carbonate reservoirs. Most of the carbonate reservoirs are typically oil-wet or mixed-wet, hence water-flooding processes have low oil recovery. Hence the most common mechanisms applied to increase the recovery are through wettability alteration and ultra-low interfacial tension (IFT) formulations with the addition of surfactants, or gas injection to have immiscible and miscible displacement processes, or combination of these processes. Secondary immiscible gas floods have been applied for several years in carbonate reservoirs and the typical recovery is found to be around 35-40% OOIP. The problems associated with many gas injection processes are the inefficient gas utilization, poor sweep efficiency, and low incremental oil recovery due to viscous instability (channeling or fingering) and gravity segregation. These are mainly caused by rock heterogeneity as well as the low density and viscosity of the injected gas. To address these drawbacks foam can be injected into the oil reservoir by co-injection of surfactant solution and gas, or by surfactant-alternating-gas (SAG) mode. The strategy implemented here is to inject a surfactant that causes wettability alteration or ultra-low IFT to recover additional oil followed by gas injection which helps in generation of foam and provides mobility control to achieve better sweep efficiency. The main objective of this research is to study the effect of slug size variation on oil recovery in surfactant-alternating-gas (SAG) processes for carbonate rocks using a wettability alteration anionic surfactant solution. The bulk foam stability in the presence and absence of the crude oil were studied for several surfactants. In addition, phase behavior studies and wettability alteration experiments were performed with the crude oil to screen the surfactant solutions. A propoxy sulfate surfactant, Alfoterra (0.5 wt%) was found to be optimal for these studies. Coreflood experiments in the absence of oil were performed in outcrop Texas Cream limestone rocks to measure the apparent foam viscosity and single phase pressure drop in presence of 80% quality foam, in comparison to 80% quality gas-brine co-injection as a base case. The resistance factor (measured as the ratio of pressure drop with foam and without foam) was found to be 3.5. Coreflood experiments with surfactant-alternating-gas (SAG) mode were performed in oil aged reservoir limestone rocks and outcrop carbonate rocks using Alfoterra (0.5 wt%). The coreflood experiments with a single slug of 0.5 PV surfactant solution showed additional oil recovery of about 25% OOIP in the outcrop rock. The average pressure drop during the experiment was in the range of 5-15 psi. The coreflood experiments with limestone rocks from a reservoir showed an additional oil recovery of about 25% OOIP for 0.1 PV slug size and smaller slug size injection of 0.05 PV showed an additional oil recovery of about 28% OOIP. The average pressure drop recorded was comparatively higher in the range of 40-60 psi for smaller slug sixe injection. Smaller slug size leads to higher oil recovery. The dynamic adsorption measured for Alf S23-7S-90 (S1) in Texas Cream limestone rock was found to be about 0.112 mg/gm of rock.
Surface complexation modeling of Pb(II), Cd(II) and Se(IV) onto iron hydroxides in single and bisolute systems
(2006) Vieira, Adriano Rosa; Katz, Lynn Ellen
Many environmental problems require reliable quantitative prediction of the fate and transport of metal ion contaminants in surface and groundwaters. Surface Complexation Models (SCMs) have emerged as the most promising tools for predicting contaminant ion sorption to iron (hydr)oxides. The reliability of SCMs is highly dependent on the ability to select appropriate surface complexation reactions and model parameters. This research focused on developing a strategy for developing a selfconsistent database for the Triple Layer Model (TLM) parameters for two iron (hydr)oxides, ferrihydrite (HFO) and goethite (α-FeOOH). To this end, spectroscopic data were used to guide the selection of surface complexation model reactions, and to the extent possible, theoretically based parameter estimation techniques were used to characterize the mineral surfaces throughout this work. The adsorption of two divalent metals, Cd(II) and Pb(II), and one oxyanion, Se(IV) onto α-FeOOH and ferrihydrite was modeled in single and bi-solute systems using the TLM. Selection of all surface complexes was supported by evidence from extended x-ray absorption fine structure spectroscopy. The fixed surface site density values based on tritium exchange experiments were used (Ns = 10.2 and 16.4 sites /nm2 for ferrihydrite and goethite, respectively). Ferrihydrite was modeled using one surface site while goethite was modeled with strong and weak sites, with the following distribution: Nwk = 90% and Nst =10%. Cd(II) and Pb(II) adsorption were modeled using bidentate and monodentate surface complexes onto ferrihydrite. The model was able to predict the competitive adsorption behavior of Cd(II) and Pb(II) in bisolute systems. For the goethite system, Cd(II) and Pb(II) adsorption was modeled using bidentate surface complexes on both weak and strong goethite surface sites. The TLM was able to predict the competitive adsorption behavior of Cd(II) and Pb(II) in bisolute systems. Se(IV) adsorption onto goethite was investigated in the presence of Cd(II) or Pb(II) and was modeled using bidentate surface complexes. The TLM predicted data reasonably well in low and medium surface coverage single-solute systems; however, it did not predict adsorption behavior for a high surface coverage adsorption edge. In bisolute systems, the TLM overestimated adsorption enhancement for low and medium surface coverage adsorption edges. TLM predictions using lower surface site densities improved the oxyanion predictions but diminished the quality of the divalent metal ion predictions.

Browsing by Subject "Adsorption"

Results Per Page

Sort Options