Immobile Liquid Research Articles

Selective CO2 Separation from CO2−N2 Mixtures by Immobilized Glycine-Na−Glycerol Membranes

This paper reports the results of our continuing efforts to develop glycerol-based immobilized liquid membranes (ILMs) for the selective separation of CO2 from a mixed-gas (CO2, N2) feed having low CO2 concentrations in space-walk and space-cabin atmospheres. The items of specific interest are replacement of the carrier sodium carbonate (studied by Chen et al. (Ind. Eng. Chem. Res. 1999, 38, 3489−3498) by glycine-Na in glycerol, ILM thickness reduction, performance of environmentally benign carriers, e.g., glycine-Na vis-à-vis toxic and volatile carriers, e.g., ethylenediamine. The effects of glycine-Na concentration (range 0−5.0 mol/dm3), CO2 partial pressure (between 0.006 and 0.8 atm), and feed relative humidity (RH; range 40−100%) have been investigated. The sweep gas was always dry helium. As the glycine-Na concentration was increased, N2 permeability decreased, while the CO2 permeability increased drastically at lower glycinate concentrations, leveling off at higher glycinate concentrations. Lower feed stream RHs yielded lower species permeances but greater CO2/N2 selectivities. For a feed RH of 70%, pCO2,f = 0.006 atm, and a glycine-Na concentration of 2.5 mol/dm3, the CO2/N2 separation factor was found to be a very high 5000 in an ILM spanning the whole thickness of a hydrophilized poly(vinylidene fluoride) flat film. ILMs containing both carbonate and glycinate demonstrated high CO2 permeances and high CO2/N2 selectivity. The ILM stability was also tested by a 25-day-long run. Permeances of N2 through glycerol-based membranes and of CO2 through pure glycerol membrane have been estimated and compared with experimentally obtained values.

Effects of a Trapped NAPL on the Diffusive Release of Organic Contaminants from Saturated Soils

ABSTRACT Diffusion-controlled mobility of benzene and toluene in liquid-saturated soils containing an immobile nonaqueous phase liquid (NAPL) was investigated. Three soil types were examined at NAP...

On the mechanism and kinetics of the transport processes in systems with intensive interphase mass transfer. 1.: Heat and mass transfer

A theoretical analysis of the mechanism and the kinetics of non-stationary absorption is proposed in an immobile liquid at big concentration gradients, when the mass transfer may be a result of a natural convection, non-linear mass transfer and the Marangoni effect. It is shown that the Marangoni effect is negligible under these conditions and the flow rate is limited by the non-linear mass transfer. The rate of the mass transfer is determined.

On the mechanism and kinetics of the transport processes in systems with intensive interphase mass transfer. 2.: Stability

This research suggests a linear analysis of the stability of non-stationary absorption of concentrated gases in an immobile liquid, where a basic flow is induced as a result of a natural convection and a non-linear mass transfer. A specter of disturbances that lead to a stable dissipative structure with a high mass transfer coefficient has been found. The disturbance amplitude is determined by experimental data for the mass transfer rate in absorption of pure CO 2 in a stagnant water column. It has been shown that conditions for the occurrence of the Marangoni effect do not exist. The theoretical results have a good agreement with the experimental data.

Channel flow at an immobilised liquid|liquid interface

A novel rectangular channel flow electrochemical cell for the study of liquid | liquid interfaces is presented. The organic phase is immobilised by the use of a gelling agent, while the aqueous phase flows past the interface. This creates an asymmetric setup that allows us to establish diagnostic criteria to determine, for example, the direction of the ion transfer. The effects of varying flow rate and sweep rate have been considered both theoretically and experimentally. By comparison with two-dimensional simulations, it is demonstrated that a simple one-dimensional theory can be used to describe the cyclic voltammetry response of the channel flow cell.

The influence of NAPL dissolution characteristics on field-scale contaminant transport in subsurface

A numerical model based on the two-phase method of characteristics (2PMOC) is developed to account for rate-limited dissolution processes and to examine the groundwater and soil gas contamination resulting from an immobile non-aqueous phase liquid (NAPL) residual in water-saturated and variably unsaturated field-scale systems. Recently developed dissolution rate coefficient correlation formulations are used to simulate the rate-limited dissolution processes. One-dimensional aqueous simulations are performed to examine differences between these correlations by comparing effluent concentrations. Damkohler number analysis is used to determine degree of equilibrium for each correlation and extent of error introduced by assuming local equilibrium between the NAPL and aqueous phases. Mathematical models are also used to simulate two-dimensional two-phase flow and contaminant transport to evaluate the potential of groundwater contamination resulting from a NAPL residual. While the simulation results illustrate the significance of the system scale on the rate of mass transfer between phases and the degree of equilibrium, the exact extent of the system scale effects remains to be answered. The modeling results from this study suggest more efforts to address the differences between laboratory and field-scale dissolution characteristics before a mature understanding of NAPL dissolution processes in subsurface can be achieved.

Gaseous Tracer Technique for Estimating Air–Water Interfacial Areas and Interface Mobility

A series of gaseous miscible displacement experiments were conducted to estimate specific air–water interfacial areas (ai) and water contents in an unsaturated sand column. A straight‐chain hydrocarbon (n‐decane) was used as the gaseous interfacial tracer and methylene chloride and chloroform were used as the water‐partitioning gaseous tracers. A gas chromatographic technique was employed for the tracer experiments conducted at room temperature using nitrogen as the mobile phase and water as the immobile liquid. Tracer experiments covered a water saturation (Sw) range of 1.5 to 56%. The largest ai value (∼1500 cm2 cm−3), measured at the lowest Sw (1.5%), was somewhat smaller than the solid surface area (∼2000 cm2 cm−3) determined using the nitrogen‐sorption technique. As Sw increased, ai values decreased exponentially to ∼80 cm2 cm−3 at Sw of 56%. Within a limited Sw range (0.29 < Sw < 0.55), where both aqueous and gaseous interfacial tracer data were measured, the ai values measured using a gaseous tracer (n‐decane) were 2 to 3 times larger than those measured in a previous study using an aqueous interfacial tracer (sodium dodecylbenzene sulfonate [SDBS]). The velocity of the air–water interface was estimated to be between 23 and 36% of the bulk pore‐water velocity. The water contents measured using water‐partitioning tracers were within ±5% of those based on gravimetric measurements.

Supported liquid membranes modification with sulphonated poly(ether ether ketone): Permeability, selectivity and stability

The development of a new type of composite membrane consisting of a microfiltration support membrane, an immobilised liquid membrane phase and a hydrophilic, charged polymer layer and its function as a supported liquid membrane (SLM) for copper selective transport are described. The ion-exchange layers function as stabilisation layers to improve the membrane lifetime and consist of sulphonated poly(ether ether ketone) (SPEEK). This polymer shows a high permeability for copper ions due to the presence of fixed negative charges and to its swelling capacity in an aqueous phase. A method was developed to prepare composite membranes composed of the support membranes Celgard with one stabilisation layer on either the feed or strip side of the membrane or on both sides. Good adhesion of homogeneous, negatively charged, hydrophilic SPEEK layers to the hydrophobic macroporous support membranes could only be established when the support membranes were first hydrophilised with a concentrated sulphuric acid solution containing 5 wt% free SO 3. The lifetime of the SLMs is significantly improved when one stabilisation layer is applied at the strip side or two layers at both sides of the SLM. A second advantage of this composite SLM is the increase in copper flux caused by a decrease in thickness of liquid membrane phase. However, when SPEEK penetrates entirely through some pores of the support membrane, ions diffuse non-specifically through the SPEEK matrix resulting in an undesired selectivity loss. This phenomenon occurs only when thin Celgard membranes are used as support membranes.

SCALING IN SITU BIOREMEDIATION PROBLEMS BY APPLICATION OF MULTIPHASE, MULTICOMPONENT TRANSPORT THEORY

A methodology for scaling in situ bioremediation problems is presented. This methodology is based on multiphase, muiticomponent transport theory and employs inspectional analysis and numerical sensitivity studies. A general mathematical model that describes subsurface aerobic biotransformation of organic chemical species in a multiphase setting is first presented. This general model is applied to the specific case of microbial enhanced vapor-vacuum extraction (MEVVE) in a one-dimensional zone of immobile liquids. The resulting simplified MEVVE model considers rate-dependent interphase mass transfer, a flowing gaseous phase, a single hydrocarbon pseudo-component, and either oxygen or hydrocarbon limited microbial activity. By inspectional analysis a set of dimensionless groups are derived that represent the various model parameters. A scries of numerical sensitivity studies are presented that examine the impact of selected dimensionless groups on overall system biotransformation rates. This analysis demonstrates that overall biotranformation rates can be significantly limited not only by insufficient transport of oxygen in the gaseous phase, but also by interfacial mass transfer resistance between nonaqueous phase liquid globules and adjacent fluids. Finally, an examination of the selected dimensionless groups reveals the parameter requirements for properly scaled MEVVE tests. These results indicate the need for further investigation of the importantance of fluid distributions in the pore space and their impact on the design of laboratory and field tests.

Structural relaxation of glass‐formers confined to sol‐gel‐type porous glasses

AbstractWe combine the results of dielectric relaxation spectroscopy and solvation dynamics measurements for the glass‐forming liquid 2‐methyltetrahydrofuran spatially confined to the pores of sol‐gel glasses with pore diameters ϕ = 2.5, 5.0, and 7.5 nm. Although both techniques probe the orientational polarization of the polar liquid, a dielectric experiment is bound to sense macroscopic effects, whereas the solvation method probes the molecular dynamics on microscopic scales. When the temperature approaches the glass‐transition at Tg upon cooling, an interfacial liquid layer with strongly frustrated dynamics grows in thickness and is thus able to block the connectivity among the pores. As a result the structural α‐process is subject to an enhanced spatial restriction near Tg and a transition from constant pressure to constant volume conditions might occur as the pore connectivity becomes obstructed by immobile liquid.

Quantitative structure-retention relationships of acyclovir esters using immobilised albumin high-performance liquid chromatography and reversed-phase high-performance liquid chromatography

Acyclovir and 18 of its esters have been investigated by systematic measurement of their reversed-phase high-performance liquid chromatographic retention using differing mobile phase compositions. The methanol content of the mobile phase was varied between 5 and 95%. By linear least squares regression of the logarithmic retention factor (log k′) against methanol concentration, the slope ( S)_and intercept (log k′ 0) of the so obtained straight lines were calculated for each compound. The chromatographic hydrophobicity index ( φ 0,MeOH) calculated from the S and log k′ 0 values ( φ 0,MeOH = −log k′ 0/ S) showed significant correlation ( r > 0.96) to the calculated octanol-water partition coefficients (cLog P). The albumin-binding properties of the compounds were characterised by the log k′ HSA values obtained by using an immobilised human serum albumin (HSA) HPLC column and 1% propan-2-ol 99% aqueous 10 m M phosphate buffer pH 7.0 as mobile phase. The measured albumin-binding parameters showed significant correlations to the cLog P, φ 0MeOH, S and log k′ 0 values, establishing the importance of hydrophobic properties to the interaction of the acyclovir derivatives with HSA.

Propagation of condensation front in steam injection into dry porous media

The front speed and the liquid saturation distribution in the condensate flow region have been examined for one-dimensional injection of dry steam into a lower temperature, dry porous medium with a constant inlet pressure. Existing models for the volumetric viscous and inertial forces are used along with an upstream region with an immobile liquid, which is followed by a two-phase region, a condensation zone, a liquid region, and a downstream noncondensable gas flow region. The down- and upflow (along and against gravity) are examined assuming a quasi-steady behavior. For downflow, the liquid region grows with the condensation front location. The asymptotic front speed is obtained in closed form for both the near-field regime, where the steam flow rate is high (i.e. deviation from a Darcy behavior is significant), and the far-field regime. For upflow, the liquid region gradually disappears, the liquid saturation distribution in the upstream immobile region undergoes two transitions, and correlation expressions are found for the location of these transitions. An experiment is performed, and the experimental results confirm the predictions for both down- and upflows.

Dynamical Modelling of a Biological Detoxication Process in a Fixed Bed Reactor

This paper deals with the dynamical modelling of a biological detoxication process in a fixed bed reactor. Two key features of the model are (i) the introduction of two regions in the liquid phase (a mobile liquid phase, and an immobile liquid phase around the particulate carriers), and (ii) the incorporation of the adsorption phenomenon in the model dynamics.

Mass transfer limited drying of porous media containing an immobile binary liquid mixture

A theory was developed to predict transient effluent concentrations, liquid concentrations, and the position of the evaporation front during external (mass transfer limited) drying of a porous material containing an immobile binary liquid mixture. One-dimensional drying experiments were performed with different binary mixtures to assess the validity of the model. Theoretical and experimental findings showed that the evaporation during mass transfer limited drying was non-selective in terms of component volatility; the mass fractions of the compounds in the effluent gas remained near the mass ratio of the emplaced liquid mixture. The effluent concentrations and the velocity of the evaporation front were shown to be proportional to t − 1 2 . A growing zone of variable liquid concentrations was shown to exist near the penetrating evaporation front.

Rate‐limited mass transfer and transport of organic solutes in porous media that contain immobile immiscible organic liquid

A general model is presented that simulates the effect of an immobile immiscible organic liquid, as well as rate‐limited solid phase sorption, on the transport of dissolved organic contaminants in heterogeneous porous media. Specific models are developed for four cases (1) immobile immiscible liquid that resides in nonadvective domains of a heterogeneous porous medium; (2) immobile immiscible liquid that resides in the advective domain; (3) homogeneous porous media wherein mass transfer within the immiscible liquid, as well as across the liquid‐water interface, is rate limited; (4) homogeneous porous media with a single resistance to liquid‐liquid mass transfer. The performance of the homogeneous‐based, single‐resistance model was evaluated by attempting to predict a break‐through curve reported in the literature. Based on the successful prediction of the data, where values for all parameters were obtained independent of the data being simulated, it appears that the conceptual basis of the model is valid. Through a series of simulations, the effect of the immiscible liquid on retention was shown to be great, even at relatively low levels of saturation. Release of solute from residual saturation located within regions of relatively low hydraulic conductivity can be significantly rate limited, even when mass transfer between immiscible liquid and water is rapid. This has ramifications concerning the efficacy of remediation systems based on imposed hydraulic gradients (e.g., pump‐and‐treat). The model should prove useful in further investigations of the effect of immobile immiscible organic liquids on the retention and transport of organic solutes in porous media.

Molten salt facilitated transport membranes. Part 1. Separation of oxygen from air at high temperatures

A new approach to the fabrication of facilitated transport (FT) liquid membranes for the separation of gases is described. The membranes are prepared by imbibing a thin, porous flat sheet support with a molten salt that reacts reversibly with the desired permeant gas, and which thus acts as a facilitated transport carrier of the gas. As an illustration of this concept, membranes consisting of molten lithium nitrate and sodium nitrate immobilized in thin porous metal supports were constructed and tested for the separation of oxygen from dried zero grade air at 350–524°C. These immobilized molten salt (IMS) membranes were shown to selectively permeate oxygen via a FT mechanism, which is based on the reversible reaction of oxygen with nitrite ions in the melts: M +NO − 2 + 1 2 O 2 ⇄ M + NO − 3, M  Li, Na For a NaNO 3-IMS membrane oxygen permeabilities ( PO O2) ranging from 58 to 1110 barrer with corresponding oxygen to nitrogen selectivities ranging from 4 to 80 were observed, at 452°C to 524°C and specified experimental conditions. There is a strong dependence of Po O2 on operating temperature, which is indicative of a nitrate ion dissociation rate determining step for the FT of oxygen through the membrane. The advantages and limitations of immobilized molten salt versus conventional immobilized liquid FT membranes are discussed.

Migration of pollutants in groundwater. IV. Modeling of the pumping of contaminants from fractured bedrock

The removal of soluble contaminants from fractured porous bedrock by means of a recovery well is modeled by means of a lumped parameter approach. The diffusion of contaminant from immobile liquid within the pores of the fractured rock into the mobile liquid in the interstices is handled by means of a time constant the estimation of which is described.

Retention of Liquid by Solids in Suspensions and Sediments

Abstract The effects of associated immobile liquid on the settling behavior of particles in solid-liquid suspensions are investigated. The effects are studied with respect to such sedimentation parameters as suspension porosity ∊, final sediment volume fraction us, internal void fraction of the flow unit ui, Steinours parameter A, and McKay's packing factory which corrects for the effective volume and density of the flow units in a sedimenting suspension. It is shown that the degree of liquid association with the settling particles is a function of their physicochemical characteristics. Suspensions containing clays and carbonates, owing to their ionic nature and loose packing behavior, absorb large amounts of liquids and result in larger settled sediments of a compressible nature. On the other hand, systems like glass beads-liquid suspensions absorb little associated liquid and virtually result in noncompressible settled sediments due to their rigid spherical shapes and close packing. The addition of hydrocolloids (such as natural gums) provides ionic stability to suspensions by giving them low cmpressibility and low values of us, ui, A, and p.

Separation of ethylene from ethane by a flowing liquid membrane using silver nitrate as a carrier

A new type of liquid membrane, designated as a “flowing liquid membrane” is proposed, in which a liquid membrane solution flows in a thin channel between two microporous membranes. Separation of ethylene from ethane by flowing liquid membrane modules was carried out, in which silver nitrate was used as a carrier of ethylene. It was found that, compared with the usual immobilized liquid membranes, the flowing liquid membrane has higher permeability and stability. The mechanism of the facilitated transport of ethylene through the flowing liquid membrane was elucidated, and this successfully predicted the permeation flux as well as the selectivity. The performance of the membrane module was satisfactorily explained by the proposed design equations.

Sorption kinetics of low-molecular-weight hydrophobic organic compounds on surface-modified silica

The rate of sorption and desorption of substituted benzenes was investigated in a series of batch and column experiments using surface-modified silica of known chemical composition. Porous silicas with patchy surface coatings of aliphatic-chain groups (C 1, C 8 and C 18) and an aliphatic chain terminating in a phenyl group were prepared; these were less hydrophobic and more easily wetted by water than similar, commercially available, chromatography materials. The surfaces were chosen to represent important functional groups found in soil and aquifer materials. Batch desorption of p-nitrobenzene, nitrotoluene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene, and 1,2,4,5-tetrachlorobenzene required up to 100 hours to reach equilibrium. Slow sorption and desorption of 1,4-dichlorobenzene in column experiments was evidenced by tailing in breakthrough curves. Results were interpreted considering three possible rate-limiting steps: diffusion through immobile liquid, diffusion through a bound organic phase, and slow chemical binding and release. Diffusion through immobile fluid caused some but not all of the observed slow sorption, as evidenced by experiments with different particle size and pore size (toruosity). Desorption on C 8- and C 18- modified silicas was at least one order of magnitude faster than on phenyl and C 1 surfaces, illustrating the importance of the nature of the surface organic phase. Simple diffusion through the bound organic phase is not an adequate explanation for the behavior, due to the small distances. Slow binding and release at strong sites for sorption of 1,4-dichlorobenzene on the phenyl-polymer-modified silica apparently caused most of the observed tailing. First-order rate coefficients observed for all modified surfaces were in the range of 10 −4-10 −1 s −1. As equilibrium is reached within hours, slow sorption is observed at the laboratory scale, but local equilibrium applies to most field situations.