David W. DePaoli

Mesoporous Carbon for Capacitive Deionization of Saline Water

Self-assembled mesoporous carbon (MC) materials have been synthesized and tested for application in capacitive deionization (CDI) of saline water. MC was prepared by self-assembly of a triblock copolymer with hydrogen-bonded chains via a phenolic resin, such as resorcinol or phloroglucinol in acidic conditions, followed by carbonization and, in some cases, activation by KOH. Carbon synthesized in this way was ground into powder, from which activated MC sheets were produced. In a variation of this process, after the reaction of triblock copolymer with resorcinol or phloroglucinol, the gel that was formed was used to coat a graphite plate and then carbonized. The coated graphite plate in this case was not activated and was tested to serve as current collector during the CDI process. The performance of these MC materials was compared to that of carbon aerogel for salt concentrations ranging between 1000 ppm and 35,000 ppm. Resorcinol-based MC removed up to 15.2 mg salt per gram of carbon, while carbon aerogel removed 5.8 mg salt per gram of carbon. Phloroglucinol-based MC-coated graphite exhibited the highest ion removal capacity at 21 mg of salt per gram of carbon for 35,000 ppm salt concentration.

Examination of the potential of ionic liquids for gas separations

Abstract: Ionic liquids have received increasing interest in recent years for “green” synthesis and separations because they have essentially no vapor pressure. We have begun an investigation of the potential of ionic liquids for gas separations, including the removal of carbon dioxide from stack gas generated in coal-fired power plants. In this paper, we report results from measurements of the permeance of nitrogen and carbon dioxide in supported ionic liquid membranes. Preliminary results for a porous alumina membrane saturated with l-butyl-3-methyl imidazolium bis[trinuoromethylsulfonyl] amide yielded a CO2 : N2 selectivity of 127. Using previously reported measurements of CO2 solubility in ionic liquids (1) and the measured membrane transport characteristics, a preliminary economic analysis of a separation process based on supported ionic liquid membranes has been performed. A comparison of cost estimates for this membrane-based separation to cost estimates reported for carbon dioxide removal using a conventional amine scrubbing operation shows that, with continued technology development, an ionic liquid membrane process may potentially be economically competitive with amine scrubbing. A preliminary cost estimate for an ionic liquid scrubber indicates that an ionic liquid absorption process shows less favorable economics than a supported ionic liquid membrane or an amine scrubber. However, results indicate that a more comprehensive technical and economic assessment is warranted.

Room Temperature Ionic Liquids for Separating Organics from Produced Water

Abstract The distribution of polar organic compounds typical of water contaminants (organic acids, alcohols, and aromatic compounds) associated with oil and gas production was measured between water and nine hydrophobic, room‐temperature ionic liquids. The ionic liquids used in this study were 1‐butyl‐3‐methylimidazolium bistrifluoromethanesulfonylimide, 1‐hexyl‐3‐methylimidazolium bistrifluoromethanesulfonylimide, 1‐octyl‐3‐methylimidazolium bistrifluoromethanesulfonylimide, 1‐butyl‐3‐methylimidazolium hexafluorophosphate, trihexyltetradecylphosphonium bistrifluoromethanesulfonylimide, 1‐butyl‐1‐methyl‐pyrrolidinium bistrifluoromethanesulfonylimide, trihexyltetradecylphosphonium dodecylbenzenesulfonate, tributyltetradecylphosphonium dodecylbenzenesulfonate, and trihexyltetradecylphosphonium methanesulfonate. Sensitivity of the distribution coefficients to salinity, temperature, concentration, and pH was investigated. Partitioning into the ionic liquid varied considerably. Acetic acid did not significantly partition into the ionic liquid phase, except for the sulfonate‐anion ionic liquids. The solubility of hexanoic acid in the ionic liquids was significant, where uptake of the protonated form from aqueous solution was observed for all of the ionic liquids studied. Other organics also showed high distribution coefficients, up to several hundred in the case of toluene and 1‐nonanol. The distribution coefficients for toluene, 1‐nonanol, cyclohexanone, and hexanoic acid were independent of ionic liquid‐to‐water ratio over the range from 0.02 to 1.0. The ionic liquids showed a large capacity for some organics, with solubilities measured above 100 g·L−1. Regeneration of the ionic liquids by rinsing and heating was studied, with mixed success. These experiments show that certain hydrophobic ionic liquids do have an affinity for organic contaminants in aqueous solution. However, practical application of the ionic liquids tested for detection or removal of selected water‐soluble organics from the aqueous waste streams appears to be limited by the small, but significant, solubility of the ionic liquids in the aqueous phase and by difficulty in solvent regeneration. Further work aimed at determination of ionic liquids that dissolve target compounds and are nonhazardous and less soluble in aqueous solutions is recommended.

Hierarchical ordered mesoporous carbon from phloroglucinol-glyoxal and its application in capacitive deionization of brackish water

Templated carbon materials have recently received tremendous attention due to energy storage and separations applications. Hierarchical structures are ideal for increased mass-transport throughout the carbon material. A new ordered mesoporous carbon material has been developed using glyoxal which exhibits a hierarchical structure with pore sizes up to 200 nm. The hierarchical structure arises from the cross linking reagent and not from the standard spinodal decomposition of a secondary solvent. The carbon material was studied for potential application as a capacitive deionization (CDI) electrode for brackish water. Results indicate that the hierarchical structure provides a pathway for faster adsorption kinetics when compared to standard resorcinol-formaldehyde CDI electrodes.

Preparation of activated mesoporous carbons for electrosorption of ions from aqueous solutions

Mesoporous carbon with a narrow pore size distribution centered at about 9 nm, which was prepared by self assembly of block copolymer and phloroglucinol-formaldehyde resin via the soft-template method, was activated by CO2 and potassium hydroxide (KOH). The effects of activation conditions, such as the temperature, activation time, and mass ratio of KOH/C, on the textural properties of the resulting activated mesoporous carbons were investigated. Activated mesoporous carbons exhibit high BET specific surface areas (up to ∼ 2000 m2 g−1) and large pore volumes (up to ∼ 1.6 cm3 g−1), but still maintain a highly mesoporous structure. Heat treatment of mesoporous carbons by CO2 generally requires a moderate to high extent of activation in order to increase its BET surface area by 2–3 times, while KOH activation needs a much smaller degree of activation than the former to reach an identical surface area, ensuring high yields of activated mesoporous carbons. In addition, KOH activation allows a controllable degree of activation by adjusting the mass ratio of KOH/C (2–8), as evidenced by the fact that surface area and pore volume increase with the mass ratio of KOH/C. The electrosorption properties of activated mesoporous carbons were investigated by cyclic voltammetry in 0.1 M NaCl aqueous solutions. Upon activation, the electrosorption capacitance of activated mesoporous carbons was greatly enhanced.

Nonlinear oscillations of pendant drops

Whereas oscillations of free drops have been scrutinized for over a century, oscillations of supported (pendant or sessile) drops have only received limited attention to date. Here, the focus is on the axisymmetric, free oscillations of arbitrary amplitude of a viscous liquid drop of fixed volume V that is pendant from a solid rod of radius R and is surrounded by a dynamically inactive ambient gas. This nonlinear free boundary problem is solved by a method of lines using Galerkin/finite element analysis for discretization in space and an implicit, adaptive finite difference technique for discretization in time. The dynamics of such nonlinear oscillations are governed by four dimensionless groups: (1) a Reynolds number Re, (2) a gravitational Bond number G, (3) dimensionless drop volume V/R3 or some other measure of drop size, and (4) a measure of initial drop deformation a/b. In contrast to free drops whose frequencies of oscillation ω decrease as the amplitudes of their initial deformations increase, the...

Room‐Temperature Ionic Liquids in Liquid–Liquid Extraction: Effects of Solubility in Aqueous Solutions on Surface Properties

Abstract The potential of room‐temperature ionic liquids for use in chemical separations was assessed, particularly for liquid–liquid extraction. The solubility, surface tension, and electrical conductivity of a range of imidazolium‐based ionic liquids in aqueous solution were measured at room temperature and atmospheric pressure as functions of ionic‐liquid, sodium chloride, and potassium–chloride concentrations. Hydrophobic ionic liquids were studied, including 1‐C n ‐3‐methylimidazolium cations, C n mim+, with alkyl substitutions of varying chain length, where C n =C2 (ethyl), C4 (butyl), C6 (hexyl), and C8 (octyl), in combination with bis(trifluoromethanesulfonyl)imide, NTf2 −, and bis(perfluoroethanesulfonyl)imide, BETI−, anions. Hydrophilic compounds were also studied, with bromide anions and C n mim+ and 1‐C n ‐2, 3‐methylimidazolium, C n bmim+, cations, where C n =C12, C14 and C16 are solids at room temperature, and C n =C8, C9, and C10 are liquids.

Electrocoagulation for magnetic seeding of colloidal particles

Abstract Electrocoagulation (EC) was investigated as a magnetic seeding method to be used prior to a high-gradient magnetic separation (HGMS) process. Experimental results showed that particulates with significant magnetic susceptibility were formed by EC with steel electrodes. Magnetite was specifically formed most readily in a sodium chloride solution, in the absence of other ions, but also in surrogate wastewater under controlled conditions. These results suggest that EC could be employed in a magnetic seeding process in which paramagnetic particles are formed and then removed through high-gradient magnetic filtration (HGMF). The effects of applied potential and current on the magnetic susceptibility and composition of particles formed by EC in a pure sodium chloride solution and in a surrogate wastewater solution were investigated by X-ray diffraction analysis, scanning electron microscopy (SEM), and magnetic susceptibility measurements. Results showed that pure magnetite particles of 100-nm diameter were formed in the sodium chloride solution. Various compounds were present in particles produced by the surrogate wastewater solution, indicating that the formation of magnetite particles was hindered by the presence of some cations and anions. Although these particles had a much lower magnetic susceptibility than magnetite particles, their magnetic susceptibility was relatively high and permitted good removal in HGMF. The removal of copper ions from both deionized water and surrogate wastewater by EC followed by HGMF was also investigated. Results obtained at pH 10 and 12 showed a higher copper ion removal from the deionized water solution than from the surrogate wastewater.

Hysteresis in forced oscillations of pendant drops

A hysteresis phenomenon has been revealed through experiments conducted with large‐amplitude forced oscillations of pendant drops in air. Under strong excitation, the frequency response of a drop forced at constant amplitude exhibits jump behavior; a larger peak response amplitude e↓ appears at a lower frequency ω↓ during a downward (↓) variation of forcing frequency than during an upward (↑) variation, viz. e↓≳e↑ and ω↓<ω↑. Similar results are obtained when forcing amplitude is varied at constant frequency. This behavior is characteristic of a system with a soft nonlinearity. These findings indicate that oscillating pendant drops constitute a convenient system for studying nonlinear dynamics.

Separation of Ionic Liquid Dispersions in Centrifugal Solvent Extraction Contactors

Abstract Separations of dispersions formed by mixing immiscible organic room‐temperature ionic liquids (IL)/hydrocarbon/and aqueous systems using a centrifugal solvent‐extraction contactor have been successfully demonstrated in proof‐of‐concept testing. This accomplishment is significant in that physical property factors that are typical of ionic liquid systems (e.g., similar densities of the bulk phases, low interfacial tensions, and high viscosities) are typically unfavorable for dispersion separation, particularly in continuous processes. Efficient separation of dispersions containing ionic liquid solvents is essential for utilization of these compounds in liquid‐liquid extraction applications to maximize both solute transfer efficiency and solvent recovery. Efficient solvent recovery is of particular concern in IL applications because of the high cost of most IL solvents. This paper presents the results of initial experiments with three hydrophobic ionic liquids to determine how their physical properties affect phase mixing and phase disengagement in contact with an aqueous solution using a centrifugal contactor. While the results of the reported work are promising, additional work is needed to optimize existing mathematical models of contactor hydraulics to address special considerations involved in IL‐based processes and to optimize the equipment itself for IL applications.