DEP31 - Artículos de revista

Membrane characterization via evapoporometry (EP) and liquid-liquid displacement porosimetry (LLDP) techniques

Tue, 01 Jan 2019 00:00:00 GMT

To comparatively assess the Evapoporometry (EP) technique vis-à-vis the Liquid-Liquid Displacement Porosimetry (LLDP) technique, the pore size distributions, mean pore diameters (davg) and porosities of five polymeric (namely, nylon, PES, PTFE, PET and PVDF) and one inorganic (namely, alumina) UF/tight MF membranes were quantified by both techniques. For all the membranes, the pore size ranges were generally narrower and the pore size distributions had distinctive peaks for the LLDP technique. For the nylon, PES and PTFE membranes, the davg values obtained from the two techniques agreed well. However, for the PET and PVDF membranes, the differences were twofold due to the higher pressure needed for the LLDP tests. Specifically, for PET, the davg value obtained via EP was half that via LLDP, because the higher pressure compacted the lower mechanical strength polymer, leading to pore closure. On the other hand, for PVDF, due to the rubber nature, the higher pressure caused the pores to be stretched, leading to larger pores. As for the alumina membrane, because of the more ideal cylindrical pores, the d4-weighting of the LLDP measurement gave a greater davg value than that of the d2-weighting of the EP measurement. Also, porosity measurements were erroneous for LLDP if the active layer cannot be precisely quantified. With respect to MWCO, while EP does not explicitly quantify this, the LLDP generally over-estimated the values, because of the errors associated with the measurement of the first (largest) pores at the lowest pressures.

Non-Destructive Characterization of Industrial Membrane Cartridges by Using Liquid–Liquid Displacement Porosimetry (LLDP)

Wed, 01 Jan 2020 00:00:00 GMT

This works aims to propose and demonstrate the accuracy of a novel method of characterization aimed for non-destructive analysis of microfiltration (MF) membrane cartridges. The method adapts conventional liquid–liquid displacement porosimetry (LLDP) for performing an in-line porosimetric analysis of the membrane cartridges, getting their pore size distributions (PSDs) and mean pore diameters (davg). Six commercial filtration cartridges featuring polyethersulfone (PES) pleated membranes were analyzed using a newly designed filtration rig, based on the liquid–liquid displacement porometer, developed at the Institut de la Filtration et des Techniques Séparatives (IFTS) and operated at constant flow. The experimental rig allows the direct and non-destructive characterization of the cartridge in its original presentation. Results have been compared with those obtained by using gas–liquid displacement porosimetry (GLDP) on small membrane coupons detached from such cartridges. The comparison allows us to conclude that the proposed method gives enough accuracy in the determination of porosimetric characteristics of the filters. This method can be used as a precise characterization technique for a non-destructive in-line study of filter performance and can be envisaged as useful to periodic quality or fouling control of the commercial cartridges.

Wind Flow Analysis Beyond Orographic Effects: A Direction Turning-Gradient Approach for Urban Impact Quantification in Germany

Thu, 01 Jan 2026 00:00:00 GMT

Wind direction is a variable that plays a secondary role in wind analyses since air flow is first studied. This paper focuses on its behaviour in ten cities and at two rural sites to investigate urban impact on wind direction. The database covered 18 years with a resolution of 1 km2, and hourly values were used. Two main procedures were followed. The first calculated the wind rose with high angular resolution from the average wind in each region studied as opposed to the usual calculations, where wind direction is measured at only one site. Two smoothing procedures were posited to acquire information about the data structure and specific details in one-degree roses. Bandwidth selection was based on the agreement with observations. Results revealed that westerly directions prevailed, although three patterns were observed. The most frequent was formed by a wide westerly sector, which may be attributed to synoptic flow, followed by wind roses with well-determined directions, such as Munich, where a mixture of relief and synoptic pattern could explain the rose shape. Finally, orographic influence is noticeable in specific roses, such as in Cologne, where the Rhine valley influence prevails. The second procedure is based on the direction turning field followed by the gradient calculation. This analysis was performed following wind direction, and two noticeable patterns of clear turning changes were occasionally found. The first pattern was formed by very close turning centres, which appear to be linked to the city, such as in Frankfurt for the easterly flow with a turning of around 65 degrees. Stuttgart, where the direction rose was barely affected by orographic features, showed a similar value of direction turning for the southerly flow, although following a different pattern formed by turning bands. Robust statistics showed the urban-rural contrast. Finally, three groups may be formed following the response against the turning field, with the weakest being for the largest cities –Berlin and Hamburg– where pollutant dispersion could prevail. An intermediate response was observed for most of the studied sites. However, Stuttgart and Frankfurt stood out due to their accused turnings that might determine complex pollution transport.

Estimation of urban heat island intensity and trends in Spanish cities

Thu, 01 Jan 2026 00:00:00 GMT

Studying urban heat islands (UHIs) in Southern Europe is crucial, as they amplify heat risks under climate change. UHIs and their temporal variability at seven urban–rural pair locations in Spain were analysed from 1970 to 2023. The UHI was defined as the air temperature difference between each urban site and its neighbouring rural sites, and trends were analysed using the non-parametric Mann–Kendall test with Sen’s slope estimator. Based on daily minimum air temperature data, results indicated a mean UHI intensity ranging from −0.15 °C in Alicante to 2.28 °C in A Coruña. The UHI annual trend was significant, increasing in Valladolid (0.023 °C/year) and Alicante (0.009 °C/year) and decreasing in Santander (-0.015 °C/year). Seasonal analysis showed statistically significant trends in Valladolid, particularly in spring and summer (0.029 °C/year). In Alicante, an increase of around 0.012 °C/year was observed in spring and summer, while Madrid showed a trend of 0.012 °C/year in winter. However, a warming effect at the rural site was identified in Barcelona (−0.028 ºC/year in autumn) and in Santander −0.025 °C/year in spring and summer), corresponding to negative UHI trends. The influence of synoptic patterns on UHI yielded values between 3 and 4 °C in A Coruña and Madrid for anticyclonic southeasterly, anticyclonic southerly, and southeasterly air flows. Lower intensities were found in Barcelona (2.5 °C) and were associated with hybrid anticyclonic westerly flows. UHI intensities below 2 °C were obtained at the other locations, with the lowest values being linked to hybrid cyclonic westerly and cyclonic north-westerly flows.

Innovative application of Nile Red (NR)-based dye for direct detection of micro and nanoplastics (MNPs) in diverse aquatic environments

Mon, 01 Jan 2024 00:00:00 GMT

This paper presents the results of a research aimed at establishing a novel method for the detection of primary and secondary micro- and nanoplastics (MNPs), by using the fluorescence properties of the dye Nile Red-n-heptane (NR-H). The method has been applied to the detection of laboratory degraded polymers (Polystyrene, PS and Polyethylene Terephthalate, PET) as well as traceable latex microspheres in aqueous environments, showing a remarkable detection capacity and avoiding the prior extraction or processing of MNPs in natural samples, with significant time savings compared to conventional methods. The study has been carried out on various types of water, including samples from wastewater treatment plants, boreholes, seawater and synthesized seawater. The effectiveness of the staining process was evaluated by scanning electron microscopy (SEM), dynamic light scattering (DLS) and optical microscopy. As a result, a novel standardizable protocol for the rapid detection of MNPs has been established, with the potential to improve environmental protection through fast in-situ detection and identification of plastic contaminants. The limitations of the protocol in the quantification of MNPs have also been identified and further studies are proposed to overcome these limitations.

Enhancing the performance of alumina-pillared clay for phenol removal from water solutions and polyphenol removal from olive mill wastewater: Characterization, kinetics, adsorption performance, and mechanism

Mon, 01 Jan 2024 00:00:00 GMT

An alumina-pillared clay (Al-PILC) has been synthesized and tested for its ability to adsorb phenol from aqueous solutions, and polyphenols from Olive Mill Wastewater (OMW). The synthesis processes were investigated by varying parameters like the Al/clay ratio, with a molar ratio of [OH− ]/[Al3+] = 2.4. Various techniques, including XRD, BET, XRF, FTIR, and SEM were used to characterize the resulting solids. The effect of key factors as pH, initial pollutant concentration, and contact time, were examined in order to evaluate the phenol adsorption capacities of raw clay (RC) and optimized Al-PILC10 materials. The specific surface areas of RC and AlPILC10 were 40 and 127 m2 /g, respectively, resulting in increasing the phenol adsorbed quantity from 14.15 mg/ g for RC to 30.61 mg/g for Al-PILC10 clays, at pH 2 and 45 ◦C. Pseudo-second-order kinetics and Freundlich adsorption isotherm were suitable for describing phenol adsorption on both clays. Furthermore, Al-PILC10 exhibits an impressive removal efficiency of 76 % for polyphenols from OMW, in contrast to the 50 % achieved by RC at acidic pH. Furthermore, Al-PILC10 showcased a superior desorption rate and a favorable regeneration capacity of 64 % compared to RC (45 %), even after multiple adsorption-desorption cycles. These findings emphasize the potential of pillared clay as a cost-effective adsorbent for the efficient removal of phenol and polyphenols from wastewater

Molecular weight cut off (MWCO) determination in ultra- and nanofiltration: Review of methods and implications on organic matter removal

Mon, 01 Jan 2024 00:00:00 GMT

Estimation of membrane molecular weight cut off (MWCO) in the range between ultrafiltration (UF) 18 and nanofiltration (NF) is challenging because retention is not controlled only by size exclusion. This 19 review provides an experimental and theoretical overview of the membrane MWCO in the range from 20 UF to loose NF (from 500 to 0.7 kDa) to evaluate the significance of membrane MWCO on predicting 21 retention of organic solutes when approaching NF pore structure. The experimental section includes 22 filtration of: i) organic tracers with different molecular weights (MW) and properties (e.g. 23 polyethylene glycol (PEG) and oligosaccharides), and ii) natural organic matter (e.g. humic acid, 24 alginic acid, Tanzanian and Australian organic matter) in the MWCO range between UF and NF, at 25 minimal concentration polarization. The role of molecule structure, size exclusion and charge 26 shielding when filtering organic solutes is elucidated. The molecular structure of uncharged organic 27 tracers plays a major role on MWCO estimation, especially for loose NF membranes, where 28 oligosaccharides are retained more effectively compared to PEG tracers of similar MW. The MWCO 29 determined by PEG filtration and estimated from the pore radius distribution are consistent in the UF 30 range from 1 to 500 kDa, indicating major contribution of size exclusion. Conversely, MWCO of 31 loose NF membranes determined with PEG tracers is overestimated. Charged organics, such as humic 32 acid (1.5 kDa < MW< 3 kDa), shows retention between 60 and 80% for UF membrane MWCO below 33 30 kDa (pore radius < 14 nm) and full retention by loose NF (pore radius below 1.4 nm). This is 34 explained with an interplay of size exclusion and charge shielding in the pore. This review can assist 35 in the selection of the organic tracer and operating conditions for membrane MWCO determination 36 between UF and NF, elucidating the relevance of membrane MWCO in organic matter retention.

Membrane dialysis for partial dealcoholization of wine. Comparison between white and red wines

Thu, 01 Jan 2026 00:00:00 GMT

BACKGROUND: Membrane dialysis is a suitable technique for the partial dealcoholization of wines that preserves most of the aromas of the original wine. In this study this technique has been used to compare white and red wines of the same vintage. The results of partial dealcoholization have been checked in terms of chemical and sensory properties. In addition, gas chromatography was carried out to determine whether the aromas are appreciably diminished in their final composition for filtered wines. RESULTS: Membrane dialysis resulted in wines with a lower alcoholic strength than the starting one, 11.0 g/kg alcohol reduction was obtained for white wines and 13.4 g/kg for red wines after dialysis, and with acceptable chemical and sensory characteristics but with a lower concentration of some aromatic compounds. CONCLUSION: This partial dealcoholization technique is slightly more effective for the treated red wines. However, the dialyzed red wines are less acceptable by consumers than the corresponding white wines.

Performance and stability of cellulose triacetate membranes in humid high H2S natural gas feed streams

Mon, 01 Jan 2024 00:00:00 GMT

The current study aims to provide a thorough understanding of the separation performance of the cellulose triacetate (CTA) membrane material in humid high H2S natural gas feed streams. A systematic study of the gas separation performances of CTA polymers has been carried out in self-standing symmetric films and asymmetric hollow fiber membranes. The separation performance in H2S-containing mixtures (CH4/CO2/H2S, 80/5/15 mol%) were evaluated at 30 and 50 °C at 20, 35 and 50 bar, including higher hydrocarbons (butane and toluene) in the presence of various levels of humidity, up to 4500 ppm or 80 % RH, depending on conditions of temperature and pressure. For the first time, the effect of these contaminants and humidity together under sour gas conditions has demonstrated the promising stability of CTA membrane separation performance, both in terms of H2S permeability and H2S/CH4 selectivity. The improvement in H2S permeability is due to a combination of H2S plasticization and competitive sorption making this phenomenon even more attractive and worth studying further.

The effect of humidity on the CO2/N2 separation performance of copolymers based on hard polyimide segments and soft polyether chains: Experimental and modeling

Fri, 01 Jan 2016 00:00:00 GMT

In this work, we studied two copolymers formed by segments of a rubbery polyether (PPO or PEO) and of a glassy polyimide (BPDA-ODA or BKDA-ODA) suitable for gas separation and CO2 capture. Firstly, we assessed the absorption of water vapor in the materials, as a function of relative humidity (R.H.), finding that the humidity uptake of the copolymers lies between that of the corresponding pure homopolymers values. Furthermore, we studied the effect of humidity on CO2 and N2 permeability, as well as on CO2/N2 selectivity, up to R.H. of 75%. The permeability decreases with increasing humidity, while the ideal selectivity remains approximately constant in the entire range of water activity investigated. The humidity-induced decrease of permeability in the copolymers is much smaller than the one observed in polyimides such as Matrimid® confirming the positive effect of the polyether phase on the membrane performance. Finally, we modeled the humidity-induced decrease of gas solubility, diffusivity and, consequently, permeability, using a suitable approach that considers the free volume theory for diffusion and LF model for solubility. Such model allows estimating the extent of competition that the gases undergo with water during sorption in the membranes, as a function of the relative humidity, as well as the expected reduction of free volume by means of water molecules occupation and consequent reduction of diffusivity.

Annual and seasonal cycles of CO2 and CH4 in a Mediterranean Spanish environment using different kernel functions

Tue, 01 Jan 2019 00:00:00 GMT

This paper is based on CO2 and CH4 semi-hourly mole fraction measurements obtained at the Low Atmosphere Research Centre (CIB) between 2010 and 2016 using a Picarro G1301 analyser. The main aims of the study were to examine the temporal variation of CO2 and CH4 by using six different kernel functions, and to study the suitability of these functions to the dataset. The method used for the current study was based on experimental contour plots of R2 values in order to simultaneously determine the bandwidths of kernel functions for the long-term and short-term. An Epanechnikov, a Gaussian, a biweight, a triangular, a tricubic and a rectangular kernel function were applied to extract the salient features of both the long-term (trend) and the short-term (seasonality). The average linear increase growth rates found were mainly attributed to the terrestrial biosphere cycle and changes in the atmospheric circulation regime. The seasonal cycle exhibited a cyclical variation, revealing summer minima for both gases, which may be explained by a biological minimum. Kernel analysis showed two nocturnal CO2 maxima, in spring and autumn, linked to an increase in rainfall. For CO2 daytime records, only the spring peak was detected. As regards CH4, the maximum was located in winter. The best fit for the trend was obtained by the biweight kernel. In contrast, the best adjustment for seasonality was achieved from the Gaussian and the triangular kernel. To sum up, optimal bandwidth selection is important when kernel regression functions are employed. Since no important differences were found between the kernels employed, those which involve least computational effort are recommended.

Temporal patterns of CO2 and CH4 in a rural area in northern Spain described by a harmonic equation over 2010-2016

Sun, 01 Jan 2017 00:00:00 GMT

The present paper seeks to improve our knowledge concerning the evolution of CO2 and CH4 in terms of monthly trends, growth rate and seasonal variations in the lower atmosphere. Dry continuous measurements of CO2 and the CH4 mixing ratio were carried out over five and a half years (from 15 October 2010 to 29 February 2016) by multi-point sampling at 1.8, 3.7 and 8.3 m, using a Picarro analyzer at a rural site in the Low Atmosphere Research Centre (CIBA), on the upper Spanish plateau. Data were divided into diurnal and nocturnal records. The mathematical equation proposed to analyze the overall data was a harmonic one, comprising a polynomial (trend) and a series of harmonics (seasonal cycle). Amplitude was considered as a constant and variable term over time. Quite different behaviour was found between day and night measurements in both climate forcing agents. CO2 showed an accelerating trend in autumn, whereas CH4 trends were higher during the winter. Increasing growth rates were reported for CO2 and CH4 over the whole study period. Nocturnal CO2 amplitudes are higher than diurnal ones except in winter for both gases, and also in the autumn for CH4.

Influence of the Composition and Imidization Route on the Chain Packing and Gas Separation Properties of Fluorinated Copolyimides

Sun, 01 Jan 2017 00:00:00 GMT

A strong effect of the chemical composition and imidization method on physical and especially on gas transport properties of polyimides was demonstrated. Two fluorinated diamines 6FpDA and bisAPAF were polymerized in different ratios, employing the fluorinated dianhydride 6FDA to get polyimides with nine different compositions. For all synthesized materials three imidization methods were used: azeotropic, thermal, and chemical. The 6FDA-6FpDA homopolymers showed significant differences in the gas transport properties, indicating the influence of the imidization route on the final properties of the polyimides. For polyimides containing bisAPAF, the chemical composition played an important role due to the exchange of the hydroxyl groups by acetate groups leading to different interchain interactions. The gas transport was mainly controlled by the chain packing for thermally and azeotropically imidized polymers with bisAPAF contents lower than 30 mol %. For bisAPAF contents above 50 mol % the gas transport was controlled by the intermolecular interactions, e.g., hydrogen bonds.

Enhancing Permeability: Unraveling the Potential of Microporous Organic Polymers in Mixed Matrix Membranes

Mon, 01 Jan 2024 00:00:00 GMT

Mixed matrix membranes (MMMs) were formed by using seven polymeric matrices with a wide range of permeabilities. All of the polymeric matrices have been polyimides, namely: P84, Pi-DAPOH, Pi-DAROH, Matrimid, Pi-HABAc, PI-DAM, and PIM-1 in the order of increasing O2 permeability. A fixed (10%) concentration of a microporous organic polymer (TFAP-Trp), formed by the combination of trifluoroacetophenone and triptycene, was added as a porous filler. The material properties as well as their separation performances for multiple pure gases, specifically the permeabilities of He, N2, O2, CH4, and CO2, were measured. The correlation between the relative increase in permeability in MMMs and that of the matrix polymeric membrane has been quantitatively analyzed. This study proves that the increased permeability of MMMs is largely linked to the contribution of the high permeability of the filler. The addition of the TFAP-Trp porous filler proves to be especially beneficial for matrices with low to moderate permeabilities, significantly enhancing the matrix permeability overall. The fitted relationship is approximately linear in accordance with the existing models to predict permeability in dual-phase systems for low proportions of the dispersed phase. An extrapolation allows the evaluation of the permeability of the pure microporous organic polymer, which agrees with the previous values described by the group for different filler contents and in other polymeric matrices. In all cases, the selectivity remains approximately constant while the permeability increases. The addition of TFAP-Trp to all the polymeric matrices led to a moderate improvement of the MMM separation performances, mainly centered on their permeabilities.

Density and excess molar enthalpy of (2-propanol + glyme) liquid mixtures. Application of the Flory model

Thu, 01 Jan 2026 00:00:00 GMT

For glymes of general formula CH3O(CH2CH2O)uCH3, with u = 1, 2, 3, 4, the densities of the (2-propanol + glyme) systems at temperatures ranging from (293.15 to 303.15) K and at pressure 0.1 MPa were determined using a DSA 5000 densimeter (from Anton Paar). The corresponding excess molar volumes were calculated from these density measurements. In addition, excess molar enthalpies at 298.15 K and 0.1 MPa were measured using a Tian-Calvet micro-calorimeter. The results show that alkanol–ether interactions are strong but do not contribute significantly to the excess molar enthalpy, as the values are large and positive, and comparable to those of (glyme + n-heptane) systems. The excess molar volumes are small or even negative (in the case of the mixture with u = 4), indicating that they are mainly governed by structural effects. Mixtures with 1-propanol or 2-propanol behave similarly, although interactions between unlike molecules become slightly stronger when 1-propanol is involved. On the other hand, effects related to alcohol self-association play a decisive role in the thermodynamic properties when glymes are replaced by di-n-propyl ether. This is supported by the application of the Flory model, which shows that orientational effects are weak in the studied glyme-containing mixtures but become significantly stronger when di-n-propyl ether is considered.

Volumetric and viscosity data of 1-iodonaphthalene + n-alkane mixtures at (288.15-308.15) K

Thu, 01 Jan 2026 00:00:00 GMT

Density and viscosity measurements have been performed for the systems 1-iodonaphthalene + heptane, or + decane, or + dodecane, or + tetradecane over the temperature range (288.15-308.15) K and atmospheric pressure. At this end, a densitometer Anton-Paar DMA 602 and a Ubbelohde viscosimeter were used. Excess molar volumes are large and negative and decrease when the temperature is increased, which reveals that the main contribution to the excess molar volume arises from structural effects. The values of the deviations of dynamic viscosity from linear dependence on mole fraction are also large and negative, indicating that n-alkanes are good breakers of the interactions between 1-iodonaphthalene molecules. Different models were applied for describing viscosity data. McAllister's equation correlates well with kinematic viscosities. Results are similar when dynamic viscosities are correlated with the Grunberg-Nissan or Fang-He equations. This means that size effects are not relevant to the mentioned data. The adjustable parameter of the Grunberg-Nissan equation is negative for all the systems at any temperature, a typical feature of systems where dispersive interactions are dominant. This is in agreement with findings obtained in previous studies on similar n-alkane mixtures involving C6H5X (X = Cl, Br, I) or 1,2,4-trichlorobenzene or 1-chloronaphthalene. Free volume effects have little influence on the present dynamic viscosity results, well represented by the absolute rate model using residual molar Gibbs energies obtained from the DISQUAC model.

DEP31 - Artículos de revista

Membrane characterization via evapoporometry (EP) and liquid-liquid displacement porosimetry (LLDP) techniques

Non-Destructive Characterization of Industrial Membrane Cartridges by Using Liquid–Liquid Displacement Porosimetry (LLDP)

Wind Flow Analysis Beyond Orographic Effects: A Direction Turning-Gradient Approach for Urban Impact Quantification in Germany

Estimation of urban heat island intensity and trends in Spanish cities

Innovative application of Nile Red (NR)-based dye for direct detection of micro and nanoplastics (MNPs) in diverse aquatic environments

Enhancing the performance of alumina-pillared clay for phenol removal from water solutions and polyphenol removal from olive mill wastewater: Characterization, kinetics, adsorption performance, and mechanism

Molecular weight cut off (MWCO) determination in ultra- and nanofiltration: Review of methods and implications on organic matter removal

Membrane dialysis for partial dealcoholization of wine. Comparison between white and red wines

Performance and stability of cellulose triacetate membranes in humid high H2S natural gas feed streams

The effect of humidity on the CO2/N2 separation performance of copolymers based on hard polyimide segments and soft polyether chains: Experimental and modeling

Annual and seasonal cycles of CO2 and CH4 in a Mediterranean Spanish environment using different kernel functions

Temporal patterns of CO2 and CH4 in a rural area in northern Spain described by a harmonic equation over 2010-2016

Influence of the Composition and Imidization Route on the Chain Packing and Gas Separation Properties of Fluorinated Copolyimides

Enhancing Permeability: Unraveling the Potential of Microporous Organic Polymers in Mixed Matrix Membranes

Density and excess molar enthalpy of (2-propanol + glyme) liquid mixtures. Application of the Flory model

Volumetric and viscosity data of 1-iodonaphthalene + n-alkane mixtures at (288.15-308.15) K

Density and excess molar enthalpy of (2-propanol + glyme) liquid mixtures. Application of the Flory model