Extraction of aromatic acids and phenols by polyurethane foam

The extraction of several aromatic acids and phenols including salicylic acid, 8-hydroxyquinoline, 1-amino-2-naphthol-4-sulphonic acid and cinnamic acid in the presence of various protonated alkylamines, ammonia and alkali metal cations from aqueous solution by polyurethane foam has been investigated. These compounds are extracted only in the neutral form by a solvent extraction mechanism. The mechanism has been confirmed by the salting-out effect and pH studies. With the exception of 8-hydroxyquinoline, the compounds are more extractable by polyether foam than by polyester foam, suggesting that hydrogen bonding is stronger with the polyether foam.     

An investigation into the sorption of benzoic acids by polyurethane membrane

The extraction mechanism of organic compounds by ether- and ester-type polyurethane membrane has been investigated through a detailed study of sorption of monobromobenzoic acids. The effects of solution concentration, extraction time, surface area, pH, salts, and temperature on extraction were studied. It was found that monobromobenzoic acids are extracted in their neutral form, and that the extraction is controlled primarily by the relative strength of intra- and intermolecular hydrogen bonding. The ether-type polyurethane membrane allows a more efficient removal of monobromobenzoic acids from solution than the ester-type membrane. The extraction of benzoic acids with the ether-type membrane decreases as the temperature increases. When the ester-type polyurethane membrane is used, an extraction maximum is observed at room temperature with a decrease in extraction at lower and higher temperatures.     

Extraction of phenols using polyurethane membrane

The extraction of various phenols from aqueous and organic solutions using polyurethane membrane has been investigated. The effects of solution concentration, extraction time, surface area, pH, salts, and temperature on extraction were studied. The phenols are extracted as neutral species and the extraction is governed by a combined effect of intra- and intermolecular hydrogen bonding and nonspecific hydrophobic interactions. The ether-type membrane showed higher extraction capability for the phenols than the ester-type polyurethane membrane.     

Preconcentration and separation of acaricides by polyether based polyurethane foam

This paper reports the preconcentration of some dissolved organic phosphorous and chlorinated acaricides in water by porous polyether based polyurethane foam. Preliminary screening tests on the retention of the tested compounds, i.e., dicofol and bromopropylate, by polyether foams indicated that a very high percent removal of the tested species was obtained. The retention rate was found fast and reaches equilibrium in a few minutes. The various parameters, e.g., pH, extraction media, shaking time, salt effect, temperature and sample volumes affecting the preconcentration of the tested species by the unloaded foam, trioctylamine and trimethylphosphate treated foam have been optimized via batch modes of separation. The unloaded foams were employed in column modes for the retention and recovery of the tested species. The sorption efficiency and recovery of the compounds by the unloaded foams column were found to be up to 97.5%. The height equivalent to a theoretical plate (HETP) obtained by the unloaded foam was found to be in the range 1.1-1.3 ± 0.2 mm. The sorption mechanism of the tested compounds by the foams was discussed.     

Preconcentration and separation of some organic water pollutants with polyurethane foam and activated carbon

Summary Although pesticides and phenols, cause reproductive failure in many areas of the world, there is a no effective means of treating waste water containing these compounds. This work deals with the adsorption of insecticides and phenols from aqueous solution by untreated porous polyurethane foam and activated carbon. Static experiments showed that in comparison with activated carbon a reasonable percentage of the compounds was adsorbed by the foam. Attempts were therefore made to extract these species from aqueous solution by foam column chromatography.The results showed that the adsorption of the compounds was brought about by a mechanism similar to that of solvent extraction. The effect of various experimental conditions such as temperature, extracting medium, pH, contact time, volume of sample flow rate, compound concentration, and eluting solvents on the retention and separation of the compounds has been determined. The height equivalent to a theoretical plate (HETP) was calculated from breakthrough capacity curves and from chromatograms obtained from polyurethane foam columns for the insecticide Dyfonate; values were in the range 2.1–2.3 mm at 10–15 ml min^–1. Extraction of the compounds from natural water, and subsequent recovery, were both found to be complete. The high capacity of polyurethane provides advantages over activated carbon; in particular, large sample volumes can be analyzed at high flow rates.     

Retention and separation of some organic water pollutants with unloaded and tri-n-octylamine loaded polyester-based polyurethane foams

The analytical utility of unloaded and polyester-based polyurethane loaded foams with tri-n-octylamine (TOA) in the removal of some phenols from water were carried out. In static mode, the TOA-loaded foams showed a good affinity of extraction towards the tested compounds as compared to the untreated foams. The various parameters affecting the retention efficiency of the tested compounds from aqueous media by the foam were examined via batch technique. The TOA-loaded foams were employed in column modes for the extraction and recovery of the tested phenols. The retention efficiency and the recovery of the tested compounds from the loaded foam column were up to 98.5%. Sorption of the compounds by the foam were brought by solvent extraction mechanism. The molecular weight and the pK(a) of the compounds play an important role in the extraction process. The height equivalent to a theoretical plate (HETP) of the TOA-foam column was found in the range 1.8-2.05 +/- 0.1 mm at flow-rates up to 10 cm(3)/min. Separation of some of the tested phenols was also carried out by the TOA-foam columns. The membrane properties of the polyester foam sorbents give unique advantages over conventional granular sorbents in rapid, versatile and effective separations and preconcentrations of the tested compounds.     

Extraction of certain actinide and lanthanide elements from different acid media by polyurethane foams loaded with di(2-ethylhexyl)phosphoric acid (HDEHP)

The extraction of uranium(VI) from an aqueous HNO₃ phase into an organic phase consisting of a polyurethane foam immobilizing a solution of di(2-ethylhexyl)phosphoric acid (HDEHP) in o-dichlorobenzene has been investigated at varying concentrations of nitric acid and HDEHP. The mechanism of the extraction is discussed on the basis of the results obtained. The aggregation number of HDEHP immobilized on the foam was obtained from the analysis of data obtained for the extraction of cerium(III) from acidic perchlorate solutions of constant ionic strength.     

The retention behaviour and separation of some water-soluble organophosphorus insecticides on polyester-based polyurethane foams

This paper reports the concentration of some dissolved organic phosphorus insecticides in water by open-cell polyurethane foam. The results of preliminary screening tests on the retention of the tested insecticides (Diazinon, Malathion and Chloropyrifos) by polyester foams indicated that a very high percent removal of the insecticides was obtained. The retention rate was fast and reaches equilibrium in a few minutes. The various parameters affecting the preconcentration of the tested insecticides by unloaded foam, e.g. pH, extraction media, shaking time, salt effect, flow rate, temperature and sample volumes have been optimized via the static mode of separation. The unloaded foams were employed in columns for the retention and recovery of the tested species. The sorption efficiency and the recovery of the tested compounds by the unloaded foam column were found to be up to 95.5%. The equivalent to a theoretical plate by the unloaded foam was found in the range 1.12 - 1.32 +/- 0.2 mm. The sorption mechanism of the tested species by the foam is discussed. The separation of some of the tested species in a mixture was achieved. The foam membrane offers unique advantages over conventional bulk-type granular sorbents and solvent extraction in offering high flow rates, rapid, versatile, effective separation and preconcentration of different species from aqueous samples. The foam provides the advantages of being, insoluble, easily separable and non-polluting, as well as inexpensive.     

Studies on the extraction of phosphomolybdate by polyether foam

To establish the mechanism of heteropoly anion extraction, the sorption of phosphomolybdate by polyether-based polyurethane foam was investigated. The effect of several variables on the extraction was studied and the optimum conditions were ascertained. The results of this study indicate that the cation-chelation mechanism cannot account for the extraction of phosphomolybdate by polyether foam.     

PMBP-loaded polyurethane foam as an extractant for thorium nitrate from aqueous solution

A study on extraction of thorium with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (PMBP)-loaded polyurethane foam is described. Open-cell polyurethane foam has proved to be effective as supporting material for PMBP. Thorium nitrate can be quantitatively extracted by PMBP-loaded polyurethane foam over a wide pH range. The effect of equilibrium time, pH, thorium concentration, various anions and flow-rate on the extraction efficiency of thorium is examined. A technique of extraction chromatography column with PMBP foam cylinder has been developed for trace thorium analysis of bulky water samples.     

Steric control over hydrogen bonding in crystalline organic solids: a structural study of N,N'-dialkylthioureas

Hydrogen bonding in crystalline N,N'-dialkylthioureas was examined with the help of single-crystal X-ray diffraction, DFT calculations, and Cambridge Structural Database (CSD) analysis. A CSD survey indicated that unlike the related urea derivatives, which persistently self-assemble into one-dimensional hydrogen-bonded chains, the analogous thioureas can form two different hydrogen-bonding motifs in the solid state: chains, structurally similar with those found in ureas, and dimers, that further associate into hydrogen-bonded layers. The formation of one motif or another can be manipulated by the bulkiness of the organic substituents on the thiourea group, which provides a clear example of steric control over the hydrogen bonding arrangement in crystalline organic solids.     

Gas chromatographic-mass spectrometric analysis of urban-related aquatic and airborne volatile organic compounds. Study of the extracts obtained by water closed-loop stripping and air adsorption with charcoal and polyurethane foam

The distribution of volatile organic compounds (VOC) in urban-influenced air and river waters was investigated. The aquatic VOC were extracted with the closed-loop stripping technique (CLST) and the airborne compounds were studied using two methods, charcoal and polyurethane foam adsorption. In both types of samples, C1-C5 alkylbenzenes and n-alkanes constitute the two major VOC groups, and the presence of these groups indicates a predominance of petroleum products in these two environmental compartments. Chlorinated compounds such as polychlorobenzenes, polychloronaphthalenes and hexachlorobutadiene are abundant in water samples, whereas tetrachloroethene is the predominant chlorinated airborne VOC. The compounds collected with each sampling system can be described in terms of ranges of volatility. These ranges (expressed as mmHg vapour pressure at 25 degrees C) can be defined approximately as 140 (methylcyclopentane)-0.65 (n-undecane) for charcoal, 5.1 (n-nonane)-0.000061 (n-docosane) for polyurethane foam and 29 (toluene)-0.000029 (n-eicosane) for the CLST. Parallel air sampling with charcoal and polyurethane foam is therefore needed to cover a VOC range similar to that afforded by the CLST in water.     

Crystal structure of dissymmetrically trihydrated N,N',N'-tribenzoylmelamine (TBM).

In the crystal structure of TBM-trihydrate three waters of crystallization were found to locate dissymmetrically. Thus, one of them forms a chelated ring with the neighboring C=O and N-H of TBM. Two other ones bind each other through hydrogen bonding and two sets of which form a cyclic dimer by hydrogen bonding (namely, water-tetramer). A C=O group binds by hydrogen bonding to each of the tetrameric water. The spatial volume occupied by water-tetramer appears to be sufficient for complexation with organic molecules.     

A new method for estimating the importance of hydrogen-bonding groups in the binding site of a protein

We introduce a new method to estimate the importance of hydrogen-bonding sitepoints in the binding site of a protein as part of a structure-based design strategy. Our method identifies hydrogen-bonding sitepoints within a binding pocket and ranks them according to both the accessibility of their hydrogen bonding regions to incoming ligands and their hydrogen-bonding strength. The combination of these components produces a prioritised list of sitepoints that are more likely to be involved in hydrogen bonding with an incoming ligand. A dataset of known protein-ligand interactions was used to compare the prioritisation of sitepoints identified by our method with those observed to be engaged in hydrogen bonding in their crystal structures. Our method was able to remove those sitepoints unable to bind the ligand due to a low accessibility or an unfavourable orientation and to award significantly higher hydrogen-bonding ranking values to those sitepoints observed to form hydrogen bonds. Our method can thus be used to identify hydrogen-bonding sitepoints that should be targeted preferentially in a drug design strategy.     

Extraction of ruthenium thiocyanate and its separation from rhodium by polyurethane foam

Conditions for the formation and extraction of the thiocyanate complex of ruthenium are reported. Distribution coefficients of more than 10(4) and a capacity of about 0.24 mole per kg of foam were obtained. The effect of the chloride salts of various univalent cations on the extraction of Ru(SCN)(6)(3-) indicated that the efficiency of ruthenium extraction depends on how well the cation fits into the polyether segment of the polyurethane foam, which agrees with the "cation-chelation" mechanism. The separation of ruthenium and rhodium indicated that more than 95% of the rhodium remained in the aqueous phase and about 95% of the ruthenium was retained by the polyurethane foam and could be easily recovered.     

The Adsorption of Herbicides and Pesticides on Clay Minerals and Soils. Part 1. Isoproturon

The adsorption of isoproturon and two model compounds, N,N-dimethylurea and4-isopropylaniline, on clay minerals (bentonite,montmorillonite and kaolinite), organic matter (humic acid) and soil (with and without organic matter) has been studied using FT-infrared spectroscopy (IR), thermogravimetric analysis (TGA), high pressure liquid chromatography (HPLC) and X-ray diffraction (XRD).N,N-dimethylurea interacted with bentonite and montmorillonite by the coordination of the carbonyl group, directly or indirectly through water molecules, with exchangeable cations. Adsorption on humic acid was due to hydrogen bonding with the active sites of the adsorbent. The amino group ofN,N-dimethylurea appears tobe relatively inactive during adsorption. The mechanisms involved in the adsorption of 4-isopropylaniline were hydrogen bonding and protonation. No adsorption of 4-isopropylaniline was observed on kaolinite. The investigation of isoproturon suggested that both the carbonyl and amino groups of isoproturon were involved in interactions with the active sites of the adsorbents. Both the clay minerals and organic matter of soil contribute to the adsorption of organic compounds on soil but the clay minerals bentonite and montmorillonite play a major role in their adsorption on soil.     

Aspects of stereochemistry—I Properties and reactions of some diols

The extent of intramolecular hydrogen-bonding, as determined by infra-red spectroscopy in the hydroxyl stretching region, in certain vicinal diols of cyclohexane, cyclopentane, tetrahydropyran and tetrahydrofuran and in related compounds provides evidence for the stabilities of different conformations. In certain compounds these stabilities can be affected by hydrogen bonding from a substituent hydroxyl group to a ring oxygen. Additional evidence is provided in the case of the tetrahydropyran diols by [M]_D values. The rate of reaction of the vicinal diols of these cyclic systems with glycol splitting reagents, and their zone electrophoretic mobility in an alkaline borate buffer is influenced by the presence of a ring oxygen.     

The distribution of elements between polyether-type polyurethane foam, cyclic polyethers and hydrofluoric acid solution

The extraction of fifteen elements in the systems ?onsisting of polyurethane foam (polyether type)/HF-alkali-metal fluoride and cyclic polyether/HF-alkali-metal fluoride has been investigated. Little or no extraction was found for Co, Zn, Fe, Zr, Hf, Sn(IV), Nb, Pa, As(V), Mo, and W. Only Ta, Sb, Re, and Tc are well extracted with either polyurethane foam or dicyclohexano-18-crown-6 in dichloro-ethane under the conditions investigated. The mechanism of the extraction is discussed. The most interesting separation possibilities have been tested.     

Extraction of tin by the use of polyurethane foam

Three types of polyurethane foam were tested for the extraction of tin by static and flow systems. The amount of tin extracted varied with the type of foam, acid strength, and chloride and metal-ion concentrations. Quantitative extraction and recovery could be achieved. Open-cell polyurethane foam sponge is thought to act as a "solid solvent-extractant" for tin from aqueous solution. Distribution coefficients up to 5.6 x 10(3) were obtained and the capacity of the foam was up to 8% tin by weight.     

Extraction of cobalt from thiocyanate solutions with polyurethane foam

The extraction of cobalt (II) from aqueous thiocyanate solutions with polyurethane foam has been extensively investigated. The extraction is enhanced by high thiocyanate concentration, high ionic strength and low temperature. A pH of 1.0-9.0 can be used for efficient extraction. Cobalt can be extracted at low concentration and the distribution coefficient is independent of foam weight. Several foam types and foam pretreatments have been examined. The effect of various substances added to the cobalt thiocyanate solutions has been investigated. Some of these substances caused either enhanced or decreased extractions by interacting with the polyurethane foam or by changing the solution chemistry.