Hydrophobic Organic Solutes Research Articles

Multilayer Sorption Model for the Interactions Between Crude Oil and Clay in Patagonian Soils

Since characteristic Patagonian soils have low amounts of organic matter (usually less than 1%) and high clay contents, the relative contribution of minerals to sorption of hydrophobic organic solutes may become significant. The purpose of the present study was to examine the interactions between oil and soil for an extended range of concentrations (1 to 400 mg L−1). The prediction of isotherms by a multilayer sorption model was examined by studying the behavior of pure compounds and mixtures of known chemical composition. It was found that the extent of sorption is strongly dependent on the nature of the different interactions between sorbent and sorbates. The difference between the predicted and experimental oil isotherms was calculated to be only 13%, which indicates the reliability of the model. Not a simple dependence with the interaction forces was found to be responsible for the applicability of the model. Other factors such as 3‐D arrangements and molecular sizes should be considered. The estimations of the surface area of the soil with pyridine and phenanthrene are consistent with the sorption behavior of the polar and nonpolar sorbates in vapor phase. It was found that that crude oil is more sorbed than the sum of its fractions (aliphatic, aromatic, and polar), and this could be likely due to the asphaltenes present in the crude oil that have a stronger sorption behavior. The results observed for the different oil fractions, compared with those of the pure compounds studied in this article, are consistent with competitive interactions of the different chemical species for accessing to active sites. The determined parameters could be useful for the design of remediation techniques.

The Pertraction of Hydrophobic Organic Solutes across a Hydrophobic Membrane

Abstract The pertraction of hydrophobic organic solutes across a hydrophobic membrane is a continuous separation process, which can be used as a substitute to active carbon. The permeabilities of hydrophobic organic solutes were examined in a two compartment cell partitioned by a hydrophobic membrane. The permeability was dominated by the hydrophobicity of the solute and the dissociation in the receiving phase. The permeability of the hydrophobic solutes increased with increasing pH of the receiving phase solution for the Teflon membrane filter Fluoropore. The preferential permeability of a hydrophobic solute was obtained, and the pertraction of a hydrophobic solute against its concentration gradient was also possible under a concentration gradient of hydroxide ion. Solute permeability changes were observed by coating the surface of Fluoropore to cover its pores with tetrafluoroethene–hexafluoropropene copolymer, FEP, and a highly selective permeability was obtained between phenol and 2-isopropyl-5-methylphenol (thymol) by suppressing the phenol permeability by coating the FEP membrane.

Determination of temperature dependence of limiting activity coefficients for a group of moderately hydrophobic organic solutes in water

Limiting activity coefficients γ 1 ∞ in water were measured for 17 moderately hydrophobic mono- and bifunctional compounds containing hydroxy, keto, ether, ester and nitrile groups at several temperatures from 298 to 353 K. Three experimental techniques, viz. Rayleigh distillation, inert gas stripping (IGS), and headspace analysis (HSA), were alternatively employed. With the objective to establish the reliable γ 1 ∞( T) dependences, the γ 1 ∞ values were combined with calorimetric data on limiting partial molar excess enthalpies H ̄ 1 E,∞ and heat capacities C ̄ P,1 E,∞ determined previously in our laboratories. This database was further supplemented with critically evaluated literature data. The equation, ln γ 1 ∞=A+B/τ+C ln τ+Dτ , where τ=T/(298.15 K) , was employed for the simultaneous thermodynamic treatment of γ 1 ∞, H ̄ 1 E,∞ and C ̄ P,1 E,∞ data. With the exception of 1-butanol, for all solutes studied the three-parameter form of this equation ( D=0) assuming temperature independent C ̄ P,1 E,∞ was found to represent available information adequately. For all the solutes, γ 1 ∞( T) exhibits a maximum between 273 and 373 K. As shown, by processing simultaneously the equilibrium and thermal data, thermodynamically consistent, accurate γ 1 ∞( T) dependences can be obtained for the range 273–373 K even in cases of minimum underlying information (room temperature values of H ̄ 1 E,∞ and C ̄ P,1 E,∞ , a single temperature value of γ 1 ∞). In general, the described methodology should be the route of choice when determining γ 1 ∞( T) of aqueous semi-hydrophobic or non-hydrophobic solutes. Furthermore, prediction of γ 1 ∞ for the systems studied was attempted by two group contribution methods: the modified UNIFAC (Dortmund) and the method of Cabani et al. Both were found to perform unsatisfactorily for the bifunctional derivatives.

Pertraction of Hydrophobic Organic Solutes with a Hydrophobic Membrane

Abstract Pertraction of hydrophobic organic solutes with a hydrophobic membrane is a continuous separation process, which can be used as a substitute of activated carbon. The permeability was affected by the hydrophobicity of the solute and the dissociation in the receiving phase. The pertraction of a hydrophobic solute against its concentration gradient is also possible under a concentration gradient of hydroxide ion.

The Influence of Organic Cosolvent (Methanol) on the Adsorption of Carbofuran on Three Different Types of Indian Soils

The adsorption of carbofuran on three different types of uncontaminated Indian soils (loam, silt clay loam, sandy loam) at various volume fractions (0.25, 0.50, 0.75, 1.0) of methanol (fS) has been studied by the batch shake technique. The adsorption of carbofuran was higher on loam soil, followed by silt clay loam and sandy loam soils, and decreased with increasing fS values on all soils. From the adsorption data, adsorption partition coefficients KD (ml/g) were evaluated and the KD values converted to mole-based partition coefficients Km (mol/g). These values were utilised to test the cosolvent theory. The Km values for soils, when normalised on foc, gave values of Kmoc, and a plot of log Kmoc versus fS resulted in a single line whose equation was determined by linear regression analysis as log Kmoc = –1.12 + 2.84; r2 = 0.96. The aqueous phase partition coefficient KDw (mol/g) normalised on f∞ for carbofuran extrapolated from this relationship was 4.1, The slope may be related to the effect of carbofuran solubility and to carbofuran–soil and solvent–soil interactions. The data presented suggested that methanol–soil interaction may not increase the accessibility of carbofuran to soil organic matter to the same extent as reported for less hydrophobic organic solutes.

Dissolved humic substances for remediation of sites contaminated by organic pollutants. Binding-desorption model predictions

A process is proposed to use dissolved humic substances (DHS) which through hydrophobic binding reduce sorbability of organic contaminants and enhance desorption-remediation of contaminated sites. Computations, using sorption-desorption and binding models, predict 50- to 100-fold reductions in sorbability and retardation of highly hydrophobic organic solutes (log K ow ≥ 6) using DHS solutions of 20–50 mg/l. Solutes of medium hydrophobicity (log K ow 4–5) would require 100–200 mg/l of DHS for 90% reduction in retardation, while low hydrophobic solutes (log K ow < 3) are little affected. The high reduction in retardation results in a corresponding reduction in volumes of flushing liquid and process times, as well as in higher concentration of the released contaminant facilitating treatment and disposal. The paper includes regression correlations between binding coefficients to aqueous DHS K b and K ow of many solutes and a sensitivity analysis to model parameters.

Fluorescence Lifetime Measurements of Fluoranthene, 1-Naphthol, and Napropamide in the Presence of Dissolved Humic Acid

The binding of hydrophobic organic solutes and nonionic pesticides with dissolved humic substances may significantly influence their behavior and fate in natural systems. The binding of fluoranthene, 1-naphthol, and napropamide [2-(1-naphthoxy)-N,N-diethylpropionamide] by an International Humic Substances Society reference soil humic acid in aqueous solutions was studied using fluorescence quenching and lifetime measurements. The quenching of fluoranthene, 1-naphthol, and napropamide fluorescence by the humic acid was adequately described by the Stern-Volmer equation. The effects of temperature ranging from 283 to 313 K on the quenching ratios was not significant, and the fluorescence lifetimes of these compounds did not shorten as a function of increasing humic acid concentrations

Hydrogeochemical processes controlling the transport of dissolved organic carbon through a forested hillslope

The subsurface transport of dissolved organic carbon (DOC) through a proposed waste burial site during rain events was investigated in order to assess the role of colloid-mediated contaminant mobility. A sub-watershed (0.45 ha) located on a forested hillslope in eastern Tennessee, U.S.A., was instrumented with an isolated soil pedon for one-dimensional transport studies, and a subsurface weir monitoring system for three-dimensional transport studies. The source of DOC in the soils resulted from dissolution of organic matter in the surface horizon during, and between, rain events, as well as from a highly reactive B horizon which stored significant quantities of DOC in small pores. During large storms, the concentration of DOC was similar on ascending and descending limbs of the subface hydrograph, with a maximum concentration occuring at peak flow. During small storms however, chemical interactions with soil solution SO 4 2- caused DOC concentrations to be greater on the ascending limb of the hydrograph, with maximum DOC concenrations occuring before peak flow. Because subsurface lateral flow through preferential paths predominated in the Bt2 and the Bt3 horizons of the soil during storm events, the total cumullative flux of DOC downslope was generally much greater through the lower soil horizons. A significant component of mobile DOC consisted of hydrophobic organic solutes, even though this material was selectively adsorbed with soil depth relative to hydrophilic organic solutes. The implications of these findings on subsurface contaminant transport are discussed.

Mechanisms of Dissolved Organic Carbon Adsorption on Soil

AbstractThe subsurface transport of inorganic and organic contaminants may be strongly related to the movement of dissolved organic carbon (DOC) through a soil profile. A variety of soil chemical and hydrologic factors control the mobility of the DOC, which may enhance or impede the transport of the associated contaminants. In this study, the sources of DOC adsorption on two proposed waste‐site soils are defined, and the chemical mechanisms operative during the adsorption process are specified. Adsorption isotherms for the two soils determined at constant pH, ionic strength (I), and temperature indicated that DOC adsorption increased with increasing soil profile depth. Different adsorption capacities were exhibited by the two soils, however, which was related to their contrasting indigenous organic matter contents and mineralogies. The adsorption of DOC by the soils was not a function of solution I (I = 0.001 to 0.1 mol L−1 using NaCl); however, DOC adsorption was dependent on solution pH, with maximum adsorption occurring at ≃4.5. Competitive ion‐exchange studies using Na2SO4 as an ionic‐strength adjuster suggested that a portion of the DOC was electrostatically bound to the soil via anion exchange. By using thermodynamic principles, the predominant mechanism of DOC retention by the soil was found to be physical adsorption driven by favorable entropy changes. This is supported by preferential adsorption of the hydrophobic organic solutes to the soil relative to the hydrophilic organic solutes.

Sorption of hydrophobic organic pollutants in saturated soil systems

Sorption equilibria and rates were characterized for a matrix of four aquifer sands and two slightly to moderately hydrophobic organic solutes (nitrobenzene and lindane), and the effects of sorption on the behavior of these solutes in saturated systems of the soils were determined. Experimental data were used to test and evaluate a variety of mathematical models for predicting contaminant fate and transport in groundwater systems. Observed equilibrium relationships between soil and solution phase solute concentrations were found to be described best by the nonlinear Freundlich isotherm model. It was further determined that the sorption process in the systems tested is rate controlled, requiring several days to approach equilibrium in completely mixed batch reactors. Subsequent modeling of solute transport in continuous flow soil column reactors was found to be most successful when rate-controlled models were used, the best results were obtained with a dual-resistance model incorporating the coupled mass transport steps of boundary-layer and intraparticle diffusion.

Permeation of complexed metal ions through a hydrophobic membrane

Selective concentration of a heavy metal complex with acetylacetone (acac) through a hydrophobic polystyrene membrane was carried out under a pressure gradient. A chelate forming heavy metal was selectively concentrated about 2 fold by this method. When using a coating membrane with a high water flux, the permeabilities increased with increasing complex fraction in the aqueous solution, while using a membrane with a low water flux, a bulky complex was not highly concentrated because of steric hindrance. The complex partitioned on the membrane surface was transported and concentrated under a pressure gradient and a linear relationship was found to exist between permeabilities and partition coefficients. It will be possible to concentrate hydrophobic organic solutes by this method, for acac was concentrated when the Cu—acac complex was formed. As the permeabilities increased with decreasing pressure and membrane compaction was strong for a coating membrane, it seems effective to permeate at a low pressure.