Examinando por Autor "van Grieken, Rafael"

Mostrando 1 - 20 de 34

A comprehensive study of the synthesis, characterization and activity of TiO2 and mixed TiO2/SiO2 photocatalysts
(ELSEVIER, 2006) Aguado, José; van Grieken, Rafael; López-Muñoz, María-José; Marugán, Javier
The use of titania-silica materials in photocatalytic processes has been proposed as an alternative to the conventional TiO2 catalysts, in order to facilitate the separation of the solids after the reaction. However, despite the large number of works in this field, up to date it is not totally clarified the mechanism governing the photocatalytic activity of the mixed TiO2/SiO2 oxides. In the present work several titania-silica materials have been prepared through a sol-gel method controlling the main variables to obtain materials with different textural properties, degree of titanium incorporation and dispersion of such species, and crystallinity of titanium dioxide. Characterization of the samples and correlation with their activity for the photocatalytic oxidation of cyanide has permitted to determine that the main factors conditioning the photoactivity of these materials are: i) textural properties and accessibility of the titania surface, ii) formation of anatase nanocrystals of suitable size and band gap energy, and iii) quality of the titania crystal network, improved by the use of a hydrothermal crystallization procedure.
A Generalized Model to Predict the Liquid-Liquid Equilibrium in the Systems Furfural+Lubricating Oils
(ELSEVIER, 2006) Coto, Baudilio; van Grieken, Rafael; Peña, José L.; Espada, Juan J.
In the lubricating oil manufacturing process, the aromatic content of vacuum distillates is reduced by solvent extraction, frequently with furfural. These mixtures present very complex composition which makes difficult the description of the liquid-liquid equilibrium involved. In previous studies, the possibility to describe such equilibrium by using a reduced number of pseudo-components and the NRTL model has been stated. In this work, a generalized model to describe the liquid-liquid equilibrium in the systems furfural+lubricating oils is presented. The generalized model is based on a correlation of pseudo-component properties (specific gravity, density, refractive index and sulfur content) and NRTL parameters with the oil average boiling temperature which has been developed from the model description for SPD and HND mixtures. This method allows set up a suitable thermodynamic model for any lubricant oil cut by using as experimental information only the average boiling point and three physical properties (density, refractive index and sulfur content) of the distillate used as feed. The accuracy of the model was checked by simulating single-stage extractions carried out with different lube oil cuts within the range SPD-HND in different experimental conditions. Calculated and experimental yields, furfural content and physical properties of the raffinates and extracts were compared and a good agreement was obtained.
A model to predict physical properties for light lubricating oils and its application to the extraction process by furfural
(ELSEVIER, 2006) Coto, Baudilio; van Grieken, Rafael; Peña, José L.; Espada, Juan J.
In the lubricating oil manufacturing process, the aromatic content of vacuum distillates is reduced by solvent extraction, frequently with furfural. In this work, a method based on average pseudo-components properties is developed to calculate physical properties (density, refractive index and sulfur content) of hydrocarbon mixtures. Obtained values were compared to those calculated by other methods reported in the literature, obtaining similar results. In order to simulate the extraction operation, a model based on a reduced number of pseudo-components and the NRTL model is reported for the system furfural+SPD lubricating oil. Thereafter, the extraction operation was simulated by using such model and Aspen Plus® commercial software. Good agreement was found between predicted and experimental values of yield, furfural content, composition and physical properties for raffinates and extracts.
Analogies and differences between photocatalytic oxidation of chemicals and photocatalytic inactivation of microorganisms
(ELSEVIER, 2010) Marugán, Javier; van Grieken, Rafael; Pablos, Cristina; Sordo, Carlos
This study reports the analogies and differences found when comparing TiO2 photocatalytic treatment for chemical oxidation and microorganisms inactivation, using methylene blue and Escherichia coli as references, respectively. In both processes the activation is based on the same physicochemical phenomena and consequently a good correlation between them is observed when analyzing the effect of operational variables such as catalyst concentration or incident radiation flux, both factors influencing common stages such radiation absorption and generation of reactive oxygen species. However, different microbiological aspects (osmotic stress, repairing mechanism, regrowth, bacterial adhesion to the titania surface, etc) makes disinfection kinetics significantly more complex than the first-order profiles usually observed for the oxidation of chemical pollutants. Moreover, bacterial inactivation reactions are found to be extremely sensitive to the composition of water and modifications of the catalysts in comparison with the decolorization of the dye solutions, showing opposite behaviors to the presence of chlorides, incorporation of silver to the catalysts or the use of different types of immobilized TiO2 systems. Therefore, the activity observed for the photocatalytic oxidation of organics can not be always extrapolated to photocatalytic disinfection processes.
Application of a generalized model to the estimation of physical properties and description of the aromatic extraction from a highly paraffinic lubricating oil
(ELSEVIER, 2008) Coto, Baudilio; van Grieken, Rafael; Peña, José L.; Espada, Juan J.
In the lubricating oil manufacturing process, the aromatic content of vacuum distillates is reduced by solvent extraction, frequently with furfural. In this work, a generalized model (based on a reduced number of pseudo-components and the NRTL model) for estimation of activity coefficients is applied to the simulation of the extraction process of aromatics by furfural from a highly paraffinic Argentinian lubricating oil. Such model proposes a linear dependence between the pseudo-component properties and the NRTL parameters with the average boiling point of the distillate used as feed. Physical properties of the mixtures are calculated using the calculated pseudo-component properties. Obtained values are compared to those calculated by other methods reported in the literature, obtaining no remarkable deviations, but showing the influence of the paraffinic content on the accuracy of the predictions. The extraction process is simulated using the calculated pseudo-component properties and the NRTL parameters by means of Aspen Plus® commercial software. Good agreement was found between predicted and experimental values of yield, furfural content and composition.
Aqueous-sensitive reaction sites in sulfonic acid-functionalized mesoporous silicas
(ELSEVIER, 2008) Morales, Gabriel; Athens, George; Chmelka, Bradley F.; van Grieken, Rafael; Melero, Juan A.
Local differences in surface hydrophilicities/hydrophobicities of propyl- and arene-sulfonic-acid modified mesoporous silica and organosilica catalysts have been compared and correlated with their bulk catalytic properties for aqueous-sensitive organic reactions. Syntheses of propyl- and arene-SO3H-modified mesoporous silicas and organosilicas yield materials with different hydrophilicities, especially when ethylsiloxane moieties are incorporated into the silica frameworks. Solid-state two-dimensional (2D) 13C{1H} and 29Si{1H} heteronuclear correlation (HETCOR) NMR spectra prove that the incorporation of hydrophobic ethylsiloxane groups into functionalized mesoporous silica frameworks result in reduced interactions of adsorbed water with the silica framework in general and, importantly, in the immediate vicinities of the SO3H active sites. The hydrophilic/hydrophobic character of the surface, as well as the active site properties depend on the functional species attached. Propyl-sulfonic acid moieties are less acidic but more hydrophobic than arene-SO3H species, leading to superior overall activities for water-mediated acid-catalyzed organic reactions. The etherification of vanillyl alcohol (4-hydroxy-3-methoxybenzylalcohol) with 1-hexanol to yield 4-hydroxy-3-methoxybenzyl-1-hexyl ether is shown to proceed significantly more effectively on SO3H-modified mesoporous organosilicas, compared to wholly siliceous mesoporous supports. The correlation of macroscopic adsorption and reaction results with 2D NMR measurements allows the hydrophilic/hydrophobic surface properties of the mesoporous support to be optimized with respect to water-retention capacities and activities for water-sensitive organic reactions.
Comparing the efficiency of solar water treatment: Photovoltaic-LED vs compound parabolic collector photoreactors
(Elsevier, 2023) Martín-Sómer, Miguel; Molina-Ramírez, María Dolores; Perez-Araujo, Maria Luisa; van Grieken, Rafael; Marugán, Javier
This work analyses how to optimise efficiency in the use of solar light for different UV-based photochemical water treatment processes. The direct use of sunlight in state-of-the-art compound parabolic collector (CPC) photoreactors is compared with the use of solar energy for electricity generation in photovoltaic (PV) power systems to feed LED lighting sources. Seven different solar processes (CPC, PV-UVA LED, PV-UVC LED, CPC+TiO2, CPC+H2O2, PV-UVA LED+TiO2 and PV–UVC LED+H2O2) were investigated, both for the oxidation of chemicals and the inactivation of bacteria. The results showed that, for the oxidation of chemicals, the best photochemical yield (in terms of the use of photons) is achieved by the PV-UVC LED+H2O2 process. However, the low electrical efficiency of current UVC LED sources makes the CPC+TiO2 process the most efficient in the use of solar light. In contrast, for bacterial inactivation, the significantly higher effectiveness of the UVC spectral range in damaging DNA makes the PV-UVC LED+H2O2 the most efficient in the use of sunlight. When costs are considered, the PV-UVA LED+TiO2 may be the most efficient process for chemical oxidation, while the PV-UVC LED+H2O2 process could be the most efficient for bacterial inactivation. These findings highlight the need to evaluate the optimal approach in reactor engineering for applications in the water-energy nexus, since the most efficient process for the use of solar light strongly depends on the electrical efficiency of the available PV and LED technology, which can be expected to be largely improved in the near future.
Comparison between the Photocatalytic inactivation of Gram-positive E. Faecalis and Gram-negative E. Coli Faecal contamination indicator microorganism
(ELSEVIER, 2010) van Grieken, Rafael; Marugán, Javier; Pablos, Cristina; Furones, Laura; López, Ainhoa
Photocatalytic inactivation of two different faecal contamination indicator microorganisms, the Gram-negative Escherichia coli and the Gram-positive Enterococcus faecalis, has been studied using TiO2 in suspension and immobilized onto the photocatalytic reactor wall. The effect of the main variables of the photocatalytic process on the disinfection efficiency in deionized water and simulated effluent of wastewater treatment plant (WTP) effluents has been analyzed. Noticeable differences were observed between both types of bacteria during photolytic experiments without TiO2 in deionized water, probably due to the higher sensibility of E. coli to the osmotic stress, which leads to a higher cell membrane permeability and consequently a lower amount of hydroxyl radical attacks required to overcome the inactivation threshold. In contrast, despite their structural differences, Gram-positive and Gram-negative bacteria seem to follow the same inactivation mechanism, showing no significant differences in the experiments carried out with TiO2 in suspension either in deionized water or in WTP simulated effluent, and similar responses to changes in the concentration of catalysts and irradiation power (both variables involved in the hydroxyl radical generation). Similar results are observed using immobilized TiO2 in deionized water. However, disinfection experiments of WTP simulated effluent using immobilized TiO2 showed much longer initial delays before the beginning of the inactivation for E. faecalis, suggesting a critical effect of the water composition of the bacteria-catalyst interaction. In any case, the irradiation time required to achieved the inactivation below the experimental bacterial detection limit is similar for both microorganisms, and experiments with mixtures of E.faecalis and E.coli in WTP simulated effluent show no significant differences. Therefore, it can be concluded that the results of photocatalytic disinfection experiments using E. coli as model bacteria could be reasonably extrapolated to other types of bacteria or bacterial mixtures.
Comparison of the photocatalytic disinfection of E.COLI suspensions in slurry, wall and fixed-bed reactors
(ELSEVIER, 2009) van Grieken, Rafael; Marugan, Javier; Sordo, Carlos; Pablos, Cristina
The performances of different configurations of photoreactors were compared for the photocatalytic disinfection of E. coli aqueous suspensions and methylene blue photodegradation. Titania was immobilized in an annular reactor in two different ways: on the inner reactor wall and on the packing of a fixed bed. The influence of the increase in the TiO2 layer thickness has been studied, and the results have been compared with those obtained with TiO2 slurries of increasing concentration. Experimental results for methylene blue degradation were in agreement with those expected from the characterization data of the immobilized systems, but they did not fit with the variation of the activity for microorganisms inactivation. The increase in the density of the TiO2 film caused by the heat treatment carried out after every coating cycle reduce the TiO2 surface available for the interaction with bacteria, although it remains accessible for the dye molecules. Although immobilized systems show a lower disinfection activity in deionized water than TiO2 slurries, they show a lower inhibition by the presence of organic matter, leading to comparable irradiation times to reach bacterial concentrations below the detection limit in the treatment of wastewater treatment plant effluents. Moreover, immobilized systems have shown that they are stable and do not present deactivation after several cycles of reuse, being readily applicable for continuous water treatment systems.
Effect of the solvent in the liquid phase rearrangement of 1,2-epoxyoctante over Al-MCM-41 and Al-TS-1 catalysts
(ELSEVIER, 2004) van Grieken, Rafael; Serrano, David P.; Melero, Juan A.; García, Alicia
The role of solvent nature in the liquid phase rearrangement of 1,2-epoxyoctane over Al-TS-1 and Al-MCM-41 catalysts is reported. The main reaction product is the aldehyde, while other rearrangement products, mainly allylic alcohols and diol, are obtained. The solvent polarity influences strongly on the activity and product selectivity. The catalytic activity decreases with the increasing of solvent polarity especially for Al-MCM-41 materials. The use of acetonitrile as solvent yields a low conversion of epoxide as a consequence of its basic character. Formation of bulky by-products was detected when dimethylcarbonate was used as solvent over Al-MCM-41. Toluene displays the best catalytic performance in regards to activity and selectivity towards valuable products, with both Al-TS-1 and Al-MCM-41 catalysts, in comparison to those obtained with more polar solvents.
Etherification of benzyl alcohols with 1-hexanol over organosulfonic acid mesostructured materials
(ELSEVIER, 2006) van Grieken, Rafael; Melero, Juan Antonio; Morales, Gabriel
Etherification of benzyl alcohols with 1-hexanol was performed in liquid phase over propyl- and arene-SO3H modified mesostructured SBA-15 silica. H2O TPD measurements indicate a stronger interaction of arenesulfonic acid sites with water molecules than that occurring in propylsulfonic groups. Hence, the higher catalytic activity of propylsulfonic modified SBA-15 material is related to the more hydrophobic microenvironment of -SO3H sites which reduces the acid site deactivation associated with adsorption of water generated during the reaction. Moreover, propyl- and arene-sulfonic functionalized SBA-15 material show a clear improvement of the catalytic performances as compared to other commercial homogeneous and heterogeneous acid catalysts in this particular reaction.
Evaluation of bimodal polyethylene from chromium oxide/metallocene hybrid catalysts for high resistance applications
(Wiley, 2020-08) Paredes, Beatriz; Moreno, Jovita; Carrero, Alicia; van Grieken, Rafael
An interesting alternative to the industrial two-stage cascade process for the production of bimodal polyethylene, used for high resistance applications such as pressure pipes, has been developed. The key point is a binary catalytic system with chromium and metallocene sites incorporated together on AlSBA-15 mesostructured material. This hybrid catalyst is able to produce bimodal polyethylene in a single reactor. In the present work, it is shown that, in the presence of hydrogen and comonomer (1-butene or 1-hexene) in the reaction medium, the obtained polyethylenes exhibit appropriate mechanical properties for pipes manufacture, such as resistance to rapid crack propagation (RCP) and low crack growth (SCG), reaching standards for PE100 and even for PE100RC grades.
Friedel Crafts acylation of aromatic compounds over arenesulfonic containing mesostructured SBA-15 materials
(ELSEVIER, 2004) Melero, Juan A.; van Grieken, Rafael; Morales, Gabriel; Nuño, Vanesa
Arenesulfonic modified mesostructured SBA-15 is shown as an active catalyst for acylation of aromatic compounds using acetic anhydride as acylating agent. The arenesulfonic acid-centers located within the mesostructured SBA-15 show a greater reaction rate (normalised on the concentration of sulfonic groups) as compared to other sulfonated catalysts and even in solventless conditions. This high activity is accompanied with a remarkable stability without leaching of sulphur species during the reaction. Moreover, an increase of the amount of acid centres does not modify the activity of the material per acid center. Thus, this work introduces a new application of these sulfonated mesostructured materials, not described in literature up to now, and in an important organic reaction.
Fries rearrangement of phenyl acetate over sulfonic modified mesostructured SBA-15 materials
(ELSEVIER, 2005) van Grieken, Rafael; Melero, Juan A.; Morales, Gabriel
Arenesulfonic modified mesostructured SBA-15 is shown as an active catalyst in the liquid-phase Fries rearrangement of phenyl acetate. The arenesulfonic acid-centers located within the structure of SBA-15 show high catalytic performance as compared to other homogeneous and heterogeneous acid catalysts. This high activity is accompanied with a remarkable stability without leaching of sulphur species during the reaction. Reaction conditions have been investigated in order to optimize production of hydroxyacetophenones. Strong adsorption of reaction products and/or coke deposition on the sulfonic acid sites rapidly deactivates the catalyst. Interestingly, when dichloromethane is used as solvent the deactivation process is slowed down drastically. Finally, this contribution supports a new application of these sulfonated mesostructured materials in the production of fine chemicals.
High-performance low-cost solar collectors for water treatment fabricated with recycled materials, open-source hardware and 3d-printing technologies
(Elsevier, 2021) Martín-Sómer, Miguel; Moreno-SanSegundo, Jose; Álvarez-Fernández, Carmen; van Grieken, Rafael; Marugán, Javier
Solar technologies constitute an excellent alternative for water treatment in low-income countries where the poverty of a large part of the population hinders their access to safe water. From a technical point of view, the use of compound parabolic collectors (CPC) has been consolidated in the last decades. However, the relatively high cost of tooling conventional manufacturing processes for these collectors makes them difficult to afford in the most impoverished regions. This work presents the development of low-cost CPC and parabolic through solar collectors (PTC) by 3D printing of the structure and the use of recycled reflective materials. Besides, open-source hardware has been used to control system operation, including a supplementary UV LED system to compensate for the operation under low solar irradiance. Regarding the tested reflective materials, an optimum is obtained using an aluminium adhesive sheet that leads to an efficiency of 80% compared to a commercial CPC made of high-quality anodised aluminium, being the cost 20 times lower. On the other hand, incorporating a low-cost solar tracking system in a printed PTC reactor could lead to efficiencies up to 300% compared to the commercial CPC, while the cost was 4.5 times lower. Finally, the LED compensation system was successfully validated, allowing the operation with a constant treatment capacity during operation in cloudy conditions. In conclusion, the developed collectors are high-performance solar water treatment systems with a significantly lower investment cost, making them affordable worldwide.
Intrinsic kinetic modelling with explicit radiation absorption effects of the photocatalytic oxidation of cyanide with TiO2 and silica-supported TiO2 suspensions
(ELSEVIER, 2008) Marugan, Javier; van Grieken, Rafael; Cassano, Alberto E.; Alfano, Orlando M.
This study is focused on the kinetic modeling of the photocatalytic oxidation of cyanide in slurry reactors. The developed model is based on an accepted reaction mechanism and takes into account explicitly the differences in the local volumetric rate of photon absorption (LVRPA) produced by the unavoidable radiation profiles existing in the photoreactor. The model and its correspondent procedures for the evaluation of the LVRPA distribution and the estimation of the kinetic parameters have been successfully validated with both powder TiO2 and TiO2/SiO2 photocatalysts with improved recovery properties. In both cases, the model reproduces the influence of the catalyst loading, the initial cyanide concentration, and the inlet radiation flux on the reaction rate, with errors below 5 %. The kinetic parameters estimated for the model are independent of the irradiation form, as well as the reactor size and its geometrical configuration, providing the necessary information for scaling-up and designing commercial scale photoreactors.
Kinetics of the photocatalytic disinfection of Escherichia coli suspensions
(ELSEVIER, 2009) Marugan, Javier; van Grieken, Rafael; Sordo, Carlos; Cruz, Cristina
The photocatalytic inactivation of E. coli suspensions has been successfully modelled with kinetic equations based on a simplified reaction mechanism using three parameters: kinetic constant (k), pseudo-adsorption constant (K) and inhibition coefficient (n). This model has been used to fit complex bacterial inactivation curves with shoulder and tails regions in addition to the classical log-linear behaviour. Experiments performed with increasing concentrations of titania, using TiO2/SiO2 photocatalysts and waters with different composition indicates that the most sensitive parameters are the kinetic and the pseudo-adsorption constant, whereas the values of the inhibition coefficient do not seem to be influenced by the experimental conditions in the range studied. The chemical composition of the water strongly influences the efficiency of the disinfection process. However, the effect of different inorganic anions has been found to be produced at very different concentration levels and by different mechanisms, which also affects the values of the kinetic and pseudo-adsorption constants in different ways. Similarly, low concentrations of humic substances inhibit the disinfection process whereas the same concentration of sucrose does not affect at all. Consequently, the macroscopic analysis of real waters based on conductivity and total organic carbon measurements must be carefully considered, as differences in the nature of the inorganic and organic substances present in similar waters could lead to unexpected results.
Liquid phase isophorone oxide rearrangement over mesoporous Al-MCM-41 materials
(ELSEVIER, 2005) van Grieken, Rafael; Serrano, David P.; Melero, Juan A.; García, Alicia
The rearrangement of isophorone oxide has been investigated over Al-MCM-41 type mesostructured catalysts having different Si/Al molar ratios. The main rearrangement products are the ¿-diketone and the keto aldehyde, whereas the product coming from the decarbonylation of the latter is detected in minor amounts. The textural properties and the number of acid sites of Al-MCM-41 materials influence the extent of isophorone oxide rearrangement reaction. The best catalytic performance in regards to epoxide conversion is obtained for a catalyst having a molar Si/Al ratio around 40 due to a right contribution of acid site concentration and pore size. However, irrespective to the aluminium content of the catalysts and the reaction temperature, the selectivity to the desired keto aldehyde was around 80%. Al-MCM-41 materials are superior catalysts compared to zeolites in terms of both activity and aldehyde selectivity. As a consequence of its large pore size, the use of Al-containing mesostructured materials as catalyst in isophorone oxide rearrangement allows the diffusional problems present in zeolites to be avoided.
Liquid phase rearrangement of long straight-chain epoxides over amorphous, mesostructured and zeolitic catalysts
(ELSEVIER, 2004) Serrano, David P.; van Grieken, Rafael; Melero, Juan Antonio; García, Alicia
A variety of materials with different structural features and acid properties, including amorphous, mesostructured and zeolitic catalysts have been tested in the liquid-phase rearrangement of 1,2-epoxyoctane. The structure and acid strength of the catalysts influence strongly on the activity and product selectivity. The main rearrangement products are the aldehyde, allylic alcohols and diol. Acid sites in the amorphous materials show a poor catalytic activity. Al-TS-1 and Al-Ti-beta, zeolites with medium aluminium content, lead to significant activities and selectivities towards both the aldehyde and the octenols in comparison to those obtained with other zeolitic materials tested. Aluminium-containing mesostructured materials present much higher activities than amorphous and zeolitic catalysts. Al-MCM-41 synthesized by a sol-gel method at room temperature yielded selectivities to octaldehyde and octen-1ols of 40.6% and 44.7%, respectively with a high catalyst activity (TOF of ca. 30.5).
Novel Titanocene-Tartrate complexes as catalysts for the asymmetric epoxidation of allylic alcohols
(ELSEVIER, 2007) van Grieken, Rafael; Garcia, Rafael A.; Calleja, Guillermo; Iglesias, Jose
This communication presents the synthesis of novel titanocene-based chiral complexes and their application as catalysts for asymmetric oxidation reactions. These new complexes drive the catalytic asymmetric oxidation of allylic alcohols without the requirement of low temperature conditions, a usual drawback in asymmetric synthesis. Results from catalytic studies shows the enantioselectivity of these chiral complexes strongly depends on the steric hindrances caused by the chiral ligand and the alkyl hydroperoxide oxidant around the titanium centre.