João G. Crespo

Highly Selective Transport of Organic Compounds by Using Supported Liquid Membranes Based on Ionic Liquids

The selective separation of organic compounds is a critical issue in the chemical industry. In case of readily crystallized molecules, selective crystallization is the most practical method for selective separation, whereas for solutes that are liquid at room temperature, separation by fractional distillation, solvent extraction, or chromatographic methods are more convenient. Some of the above-mentioned methods are technically demanding, involve considerable energy costs, and/or result in large amounts of waste solvents. Membranes, defined as permeable and selective barriers between two phases, have been successfully applied in a large diversity of separation processes, including bioseparations, in which classical separation methods are less convenient, undesirable or even not applicable. The reason for the successful use of membrane-based separation processes stems from the fact that these processes have a high energy efficiency, can be used under moderate temperature and pressure conditions, do not require any additional separating agents or adjuvants, and therefore they are regarded as environmentally friendly.[1] Solute extraction and recovery by using supported liquid membranes is recognized as one of the most promising membrane-based processes. In a supported liquid-membrane system, a defined solvent or solvent/carrier solution is immobilized inside the porous structure of a polymeric or ceramic membrane, which separates the feed phase (in which the solutes of interest are solubilized) from the receiving phase (in which these solutes will be transferred and, eventually, concentrated). This configuration has attracted a great deal of interest because the amount of solvent/carrier needed is minimal, the solvent/carrier is continuously regenerated as a result of solute transport to the receiving phase, and loss of the solvent/carrier phase is negligible if an appropriate supported liquid membrane is designed.[2] The use of a room-temperature ionic liquid (RTIL) as an immobilized phase in the supporting membrane between two organic phases in the feed and the receiving compartments is particularly interesting owing to the nonvolatile character of RTILs and their solubility in the surrounding phases, which allows very stable supported liquid membranes to be obtained without any observable loss of the RTIL to the atmosphere or the contacting phases. Herein we show the potential for continuous separation of organic compounds based on the selective transport through supported liquid membranes that contain RTILs. RTILs that involve a 1,3-dialkylimidazolium cation are attracting increasing interest as new media, mainly because of the advantage of being nonvolatile. Depending on the anion and on the alkyl group of the imidazolium cation, the RTIL can solubilize supercritical CO2 (scCO2), a large range of polar and nonpolar organic compounds, and also transitionmetal complexes. Simultaneously, they have low miscibility with water, alkanes, and dialkyl ethers[3] and are insoluble in scCO2. As a result of these properties, they are emerging as an alternative recyclable, environmentally benign, reaction medium for chemical transformations, including transitionmetal catalysis[3] and biocatalysis.[3f, 5] Their use has also been successfully extended as a potential stationary phase for gas chromatography,[6] in pervaporation,[7] and for the substitution of traditional organic solvents (OS) in aqueous ±OS[7a, 8] and OS± scCO2 biphasic extractions.[4, 9] It is assumed that the 1,3dialkylimidazolium RTIL are not a statistical aggregate of anions and cations, but instead a more organized structure that contains polar and nonpolar regions as a result of the formation of weak interactions, mainly as hydrogen bonds, with 2-H of the imidazolium ring.[10] The above information prompted us to study the potential of using RTIL in supported liquid membranes for selective separation processes. To illustrate the concept, and as a result of transport studies with representative organic functional compounds, we used a mixture of the organic isomeric amines hexylamine, diisopropylamine, and triethylamine (1:1:1 molar ratio) in diethyl ether in side A of the cell (Figure 1). The two sides of the cell were separated by the RTIL 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) immobilized in the por[5] [Pt2(nBuCS2)4] and [Pt2(nBuCS2)4I2] were prepared by the similar procedures with literature methods using toluene and n-hexane.[4] [6] P. M. Chaikin, R. L. Greene, S. Etemad, E. Engler, Phys. Rev. B 1976, 13, 1627 ± 1632. [7] S. A. Borshch, K. Prassides, V. Robert, A. O. Solonenko, J. Chem. Phys. 1998, 109, 4562 ± 4568. [8] H. Tanaka, K. Marumoto, S. Kuroda, M. Mitsumi, K. Toriumi, unpublished results. [9] O. Kahn, Molecular Magnetism, VCH, New York, 1993, pp. 251 ± 286. [10] Field dependence of M of 1 was also measured near the phasetransition temperature under the magnetic field of H 1 ± 5 T. No variation was observed up to 5 T. [11] a) A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori, M. Camalli, J. Appl. Crystallogr. 1994, 27, 435 (SIR92); b) G. M. Sheldrick, SHELXL-97, University of Gˆttingen, Gˆttingen (Germany), 1997; c) Crystal Structure Analysis Package, Molecular Structure Corporation, 1985, 1999 ; d) A. Altomare, M. C. Burla, M. Camalli, G. L. Cascarano, C. Giacovazzo, A. Guagliardi, A. G. G. Moliterni, G. Polidori, R. Spagna, J. Appl. Crystallogr. 1999, 32, 115 ± 119 (SIR97). [12] Z. Otwinowski, W. Minor, Methods Enzymol. 1997, 276, 307 ± 326.

Model for carbon metabolism in biological phosphorus removal processes based on in vivo13C-NMR labelling experiments

In vivo13C-NMR, 31P-NMR techniques were applied to study phosphorus and carbon metabolism in activated sludge during both the anaerobic and the aerobic stages. By supplying a 13C label on the methyl group of acetate at the beginning of the anaerobic stage, the fate of the label through the subsequent aerobic/anaerobic stages was traced in vivo. It was possible to follow the flux of label from acetate to hydroxybutyrate/hydroxyvalerate co-polymer in the first anaerobic stage, then to monitor the conversion of these units into glycogen in a subsequent aerobic stage, and afterwards, by submitting the same sludge to a second anaerobic stage, to observe the flux of labelled carbon from glycogen to the hydroxyvalerate and hydroxybutyrate units. The uptake/release of inorganic phosphate and the extracellular pH were monitored by 31P-NMR in the same experiments. The data provide an unequivocal demonstration of the involvement of glycogen in the biological phosphorus removal process. On the basis of these 13C labelling data, a biochemical model for the synthesis of polyhydroxyalkanoates from acetate and glycogen was elaborated in which the tricarboxylic acid cycle is proposed as an additional source of reduction equivalents. According to this study, from 1 C-mol acetate, 1.48 C-mol P(HBHV) are synthesized and 0.70 C-mol glycogen are degraded anaerobically, while 0.16 P-mol phosphate is released. In the aerobic stage, 1 C-mol of P(HBHV) is converted to 0.44 C-mol glycogen.

Studies on the selective transport of organic compounds by using ionic liquids as novel supported liquid membranes

The possibility of using room-temperature ionic liquids (RTILs) in bulk (nonsupported) and supported liquid membranes for the selective transport of organic molecules is demonstrated. A systematic selective transport study, in which 1,4-dioxane, propan-1-ol, butan-1-ol, cyclohexanol, cyclohexanone, morpholine, and methylmorpholine serve as a model seven-component mixture of representative organic compounds, and in which four RTILs based on the 1-n-alkyl-3-methylimidazolium cation (n-butyl, n-octyl, and n-decyl) are used together with the anions PF(6)(-) or BF(4)(-), immobilized in five different supporting membranes, confirms that the combination of the selected RTILs with the supporting membranes is crucial to achieve good selectivity for a specific solute. The use of the RTIL 1-n-butyl-3-methylimidazolium hexafluorophosphate, immobilized in a polyvinylidene fluoride membrane, allows an extremely highly selective transport of secondary amines over tertiary amines (up to a 55:1 ratio). The selective transport of a given solute through the RTIL/membrane system results from the high partitioning of the solute to the liquid membrane phase which, in the case of amines, is rationalized mainly by the formation of a preferential substrate/H[bond]C(2) hydrogen bonding to the imidazolium cation.

Mass transfer correlations in membrane extraction: Analysis of Wilson-plot methodology

Mass transfer correlations have been obtained for the past eight decades by the Wilson-plot method which has proved to be suitable for systems operating in steady-state conditions and where the only variable is the fluid velocity. In this work, this methodology is evaluated by using a membrane extraction process with a hollow-fiber membrane contactor as a case study. Taking into consideration the currently available mathematical tools, alternative methods to obtain mass transfer correlations are proposed and discussed. The proposed one-step calculation methodology proved to be a most suitable approach, leading to a drastic reduction in the errors associated with the estimated parameters. Additionally, improvements were observed when accounting for the partition coefficient variation.

Effect of carbon source on the formation of polyhydroxyalkanoates (PHA) by a phosphate-accumulating mixed culture

Abstract In the present work, attention was devoted to understand how different carbon substrates and their concentration can influence the production of PHA by polyphosphate-accumulating bacteria. Acetate, propionate, and butyrate were tested independently. The composition of the polymers formed was found to vary with the substrate used. Acetate leads to the production of a copolymer of hydroxybutyrate (HB) and hydroxyvalerate (HV) with the HB units being dominant. With propionate, HV units are mainly produced and only a small amount of HB is synthesized. When butyrate is used, the amount of polymer formed is much lower with the HB units being produced to a higher extent. The yield of polymer produced per carbon consumed ( Y P/S ) was found to diminish from acetate (0.97) to propionate (0.61) to butyrate (0.21). Using a mixture of acetate, propionate, and butyrate and increasing the carbon concentration, although maintaining the relative concentration of each substrate, propionate is primarily consumed and consequently, PHA synthesized was enriched in HV units. The polymers obtained in all experiments were copolymers with the average molecular weight of the most representative fraction higher when hydroxybutyrate units were present in considerable amounts. All the polymers synthesized were found to be quite homogeneous and their average molecular weight is of the same order of magnitude as the ones commercially available.

Recovery of aroma compounds from a wine-must fermentation by organophilic pervaporation

This study investigates the recovery of a wine-must aroma profile, formed by Saccharomyces cerevisiae during a muscatel wine-must fermentation, using organophilic pervaporation. Experiments were carried out along two independent, but organoleptically similar, fermentations. The wine-must samples and the aroma concentrates obtained were characterized organoleptically by a sensory panel and analytically with regard to eight major wine-must components: four alcohols; three esters; and one monoterpenic compound. Pervaporation performance was studied under fermentation conditions, and the permeate concentration, partial fluxes, and enrichment of the respective compounds were determined. The muscatel wine-must aroma profile was recovered purely and faithful to its origin between wine-must densities of 1075 and 1055 g L. At the beginning of the fermentation, too few aromas were present in the must for recovery. Toward the end of the fermentation, high ethanol concentrations in the wine-must caused a dramatic enrichment of two esters in the permeate, whereas other components investigated seemed unaffected. This shift resulted in an unbalanced aroma. In conclusion, it was shown that organophilic pervaporation can be highly suitable for the continuous recovery of very complex and delicate aromatic profiles produced during microbial fermentation. Copyright 1999 John Wiley & Sons, Inc.

Optical and spectroscopic methods for biofilm examination and monitoring

Optical and spectroscopic methods for biofilmexamination and monitoring are reviewed.Biofilm examination techniques includemicroscopic methods, coupled with imageanalysis and with oligonucleotide ribosomal RNAprobing methods (fluorescence in situhybridization). Microscopic examinationtechniques are especially advantageous inextracting biofilm structural and architecturalparameters, as well as structure-functionrelationships of the biofilm microbialpopulation. Spectroscopic techniques are ableto elicit biofilm chemical and metabolicpatterns, as well as biofilm activity. They areof outstanding importance for on-line,non-invasive biofilm monitoring, especiallywhen coupled with chemometric algorithms forspectra calibration and pattern recognition.The paper emphasises the importance of thecombination of novel and established analyticaltechniques, as well as their integration withpowerful computational methods for theautomation of biofilm monitoring.

Production of propionic acid using a xylose utilizingPropionibacterium

The kinetics ofP. acidipropionici (ATCC25562), a xylose-utilizing rumen microorganism, was studied to assess its use for propionic acid production from wood hydrolyzates.Propionic acid has been shown to have a stronger inhibitory effect than acetic acid, with the undissociated acid form being responsible for the majority of the inhibitory effect. Thus, in batch tests with pH controlled at 6.0, the propionic acid concentration reaches 25 g/L and the acetic acid 7 g/L. Xylose uptake rate is dependent on the specific growth rate and glucose concentration.An immobilized cell columnar reactor at very high product yields (80%) proved adequate for propionic production. At cell concentrations of 95 g/L with high product concentration, volumetric productivities of 2.7 g/L·h were obtained in ultrafiltration cell recycle systems.

Selective recovery of solutes from ionic liquids by pervaporation—a novel approach for purification and green processing

Non-porous membranes with the selective layer consisting of hydrophilic or hydrophobic polymers have been applied for the quantitative and selective recovery of solutes with different physico-chemical properties from a room-temperature ionic liquid, ([bmim][PF6]).

Transport mechanisms and modelling in liquid membrane contactors

Abstract This paper discusses the use of liquid membrane contactors for extraction of fermentation and pharmaceutical products using different types of carriers. It intends to emphasise the importance of understanding the transport mechanisms involved in liquid membrane extraction with different carriers and also to discuss relevant aspects of the mathematical modelling involved in these extraction processes. Using the extraction of organic acids, namely amino acids, as a case study it is shown how the supramolecular organisation of the extractant determines the solute transport mechanisms involved. Additionally, the resolution of racemic mixtures using chiral carriers is also discussed. The modelling work analyses two different aspects of extraction using membrane contactors with microporous membranes: (i) the importance of using a correct description of solute partition between the feed and the extractant phase (use of a variable partition description versus constant partition); (ii) the correct development of mass transfer correlations in hollow fibre contactors. For the development of mass transfer correlations the calculation method proposed by Wilson has been universally used. Given the currently available mathematical tools, that enable the analytical manipulation of equations and fittings with complex expressions, a new calculation methodology is discussed.