Examinando por Autor "Morales, G."

Mostrando 1 - 6 de 6

Acid-catalyzed etherification of bio-glycerol and isobutylene over sulfonic mesostructured silicas
(ELSEVIER, 2008) Melero, J.A.; Vicente, G.; Morales, G.; Paniagua, M.; Moreno, J. M.; Roldán, R.; Ezquerro, A.; Pérez, C.
Sulfonic-acid functionalized mesostructured silicas have demonstrated an excellent catalytic behavior in the etherification of glycerol with isobutylene to yield tert-butylated derivates. Di-tert-butylglycerols (DTBG) and tri-tert-butylglycerol (TTBG) have shown to be valuable fuel additives leading to decreases in the emission of particulate matter, hydrocarbons, carbon monoxide and unregulated aldehydes. Likewise, said ethers can also act as cold flow improvers for use in biodiesel, reducing also its viscosity. The activities and selectivities achieved over sulfonic acid-functionalized mesostructured silicas are comparable or even superior to those displayed by widely-used macroporous commercial acid resins. Under optimized reaction conditions, these mesostructured catalysts yield a complete glycerol conversion with a combined selectivity towards DTBG and TTBG up to ca. 90%. Furthermore, no formation of undesirable isobutylene oligomers is observed. The acid strength of the sulfonic acid sites has also been found to be an important factor affecting the catalytic performance of these materials.
Efficient conversion of levulinic acid into alkyl levulinates catalyzed by sulfonic mesostructured silicas
(ELSEVIER, 2013) Melero, J.A.; Morales, G.; Iglesias, J.; Paniagua, M.; Hernández, B.; Penedo, S.
Sulfonic mesoporous silicas have demonstrated an outstanding catalytic performance in the esterification of levulinic acid with different alcohols to produce alkyl levulinates, a family of chemicals considered to be excellent oxygenated fuel extenders for gasoline, diesel and biodiesel. Catalyst screening indicated that propylsulfonic acid-modified SBA-15 material was the most active one, among tested materials, due to a combination of moderately strong sulfonic acid sites with relative high surface hydrophobicity. Under optimized reaction conditions (T = 117 ºC, ethanol/levulinic acid molar ratio = 4.86/1 and catalyst/levulinic acid = 7 wt.% ) almost 100% of levulinic acid conversion was achieved after 2 h of reaction, being negligible the presence of levulinic acid by-products or ethers coming from intermolecular dehydration of alcohols. The catalyst has been reused, without any regeneration treatment, up to three times keeping almost the high initial activity. Interestingly, a close catalytic performance to that achieved using ethanol has been obtained with bulkier alcohols.
Perfluorinated nafion-modified SBA-15 materials for catalytic acylation of anisole
(ELSEVIER, 2008) Martínez, F.; Morales, G.; Martín, A.; van Grieken, R.
Mesoporous SBA-15 silica materials have been functionalized with perfluorosulfonic acidic Nafion resin using a post-synthetic impregnation method. The remarkable physicochemical properties of hexagonally ordered SBA-15 silicas (high surface area, large and narrow pore size distribution and thermal stability) make them particularly attractive for the immobilization of strongly acidic perfluorosulfonic sites. The loading of Nafion resin was varied between 10 and 20 wt%. The synthesized Nafion/SBA-15 hybrid materials were evaluated in the Friedel Crafts acylation of anisole. The optimum catalytic performance of Nafion/SBA-15 hybrid material with a resin loading around 13 wt% was compared with other perfluorosulfonic acid-based catalysts either commercially available or prepared following recipes reported in the literature. The influence of several variables on the acylation of anisole, such as the reaction temperature and the anisole/acylating agent ratio, has also been assessed by means of a factorial design of experiments. The catalytic activity of Nafion-modified SBA-15 materials is strongly affected by the reaction temperature, whereas a lesser effect was evidenced for the reaction mixture composition in the range under study. The optimal operation conditions in terms of anisole conversion were achieved at 150ºC and equimolar anisole/acetic anhydride mixture. The deposition of poly-acetylated by-products on the catalytic acid sites is mainly responsible for the catalyst deactivation, whereas the leaching of sulfonic groups and their contribution in the anisole acylation via homogeneous catalysis has been ruled out. Finally, the recovery of the catalytic activity by regeneration of the spent catalyst by refluxing in nitric acid solution was demonstrated. The characterization of the regenerated catalyst indicates that the regained activity is likely related to the displacement of the deactivating by-products out of the perflurorosulfonic acid sites during the nitric acid regeneration.
Polystyrene modified hybrid materials based on ordered mesoporous silica
(ELSEVIER, 2008) van Grieken, R.; Morales, G.; Martin, A.; Martinez, F.
Organically-modified mesoporous silica materials have been prepared by direct co-condensation of styrylethyltrimethoxysilane (STETMOS) and tetraethylorthosilicate (TEOS) in one-pot synthesis. The polimerizable nature of the styryl-containing precursor induces the formation of anchored polystyrene blocks over the silica surface, which are amenable to be functionalized with acid groups via sulfonation. The resultant organosulfonic-modified mesostructured silica materials have exhibited hexagonal long-range mesoscopic arrangement with extended surface areas and narrow mean pore size distributions. The acid capacity of these materials was assessed on the acid-catalyzed reaction test of anisole acylation with acetic anhydride.
Tailoring the pore size of hexagonally ordered mesoporous materials containing acid sulfonic groups
(ELSEVIER, 2002) van Grieken, Rafael; Melero, J.A.; Morales, G.
Zr-SBA-15 Acid Catalyst: Optimization of the Synthesis and Reaction Conditions for Biodiesel Production from Low-grade Oils and Fats
(Elsevier, 2012-11) Melero, J.A.; Bautista, L.F.; Iglesias, J.; Morales, G.; Sánchez-Vázquez, R.
The production of biodiesel by methanolysis of highly acidic crude palm oil has been optimized for the Zr-SBA-15 heterogeneous acid catalyst. A dual optimization procedure has been carried out using surface response methodology and selecting the yield towards fatty acid methyl esters (FAMEs) as main response factor. Selected target variables for the optimization were: acidity of the synthesis media, zirconium loading, ageing temperature (all three for the synthesis of the catalyst); and temperature, methanol to oil molar ratio, catalyst loading (for the reaction tests). Quadratic equations were obtained for both models and their statistical analysis led to the optimal conditions for Zr-SBA-15 synthesis (0.67 N HCl media concentration, 130ºC ageing temperature, 10 Si/Zr molar ratio), and for the transesterification reaction conditions (209ºC, 12.45 wt% catalyst loading, 45.8 methanol to oil molar ratio). Under these optimized conditions FAME yield reached 92 mol% after 6 h. Additionally, reusability tests revealed that the optimized Zr-SBA-15 catalyst displays an excellent reaction stability, being fully regenerated after calcination at 450ºC. Moreover, the high catalytic activity and stability achieved with crude palm oil is retained when using waste cooking oil (WCO) or low-grade fats such as category-1 fat, waste lard and mixed fats, leading to FAME yields over 90% after 6 hours, for each raw material, and with acidities in the final product lower than 2.5 mg KOH per gram.