Examinando por Autor "Briones, Laura"

Mostrando 1 - 8 de 8

Catalytic upgrading of a model polyethylene pyrolysis oil by hydroconversion over Ni-containing hierarchical Beta zeolites with tailored acidity
(Elsevier, 2023-10-05) Briones, Laura; Cordero, Adrian; Alonso-Doncel, Mara; Serrano, David pedro; Escola, José María
Valorization of waste polyolefins by a sequential combination of thermal pyrolysis and catalytic hydroconversion over a bifunctional metal/acid catalyst (e.g. zeolite) is an efficient route to produce transportation fuels. However, the zeolite strong acidity typically causes extensive cracking and loss of liquid fuels. In this work, mild dealumination with oxalic acid of a hierarchical Beta zeolite was used to achieve Ni 7 %/h-Beta catalysts with Si/Al ratios within the 25 – 130 range. These catalysts were tested in the hydroconversion of a model mixture of LDPE thermal pyrolysis product (1-dodecene/n-dodecane, 50/50 w/w). The highest share of liquid fuels (~ 90 %) was achieved over 7% Ni/h-Beta (Si/Al = 130). Besides, due to its high accessibility and tailored acidity, the product contained a meaningful amount of isoparaffins (12 %) and a negligible content of olefins (< 3.5 %). Thus, this catalyst holds promise for plastic waste hydroconversion towards transportation fuels.
Coating of Ca(OH)2/gamma-Al2O3 pellets with mesoporous Al2O3 and its application in thermochemical heat storage for CSP plants
(Elsevier, 2020-08-22) Valverde-Pizarro, Claudia; Briones, Laura; Sanz, Eloy; Escola, José María; Sanz, Raúl; González-Aguilar, José; Romero, Manuel
Thermochemical heat storage using the Ca(OH)2 dehydration/hydration reaction for CSP plants requires the development of advanced materials that avoids the breakage shown by conventional CaO pellets. In this work, spherical cores made up of pelletized 60 wt. % Ca(OH)2 and 40 % γ-Al2O3 powders were coated with different mesoporous alumina coverings by means of a dip-coating route, in order to enhance its structural integrity for dehydration/hydration cycles. Three strategies of preparation were devised using as coatings alumina gels containing cetyltrimethylammonium bromide as surfactant in neutral (A2 CS) and acid pH (A4 CS) and without surfactant in neutral medium (A3 CS). In both A2 CS and A4 CS materials, denser alumina coatings were attained originating higher crushing strengths, pointing out the positive role played by the surfactant in the gel makeup. SEM images indicated that A2 presented small alumina grains (0.3 – 3 µm) highly dispersed over their surface, while over A4 CS, long sheets were appreciated. All the materials exhibited high hydration capacities after 10 cycles (> 80%, > 800 kJ/kg) at 250 ºC, but only A2 CS hold its structural integrity that was preserved even after 20 cycles without loss of its hydration capacity.
Conversion of Stearic Acid into Bio-Gasoline over Pd/ZSM-5 Catalysts with Enhanced Accessibility
(MDPI, 2019-06-11) Arroyo, Marta; Briones, Laura; Escola, José María; Serrano, D. P.
Palladium supported on nanocrystalline ZSM-5 (n-ZSM-5, Si/Al = 32) and hierarchical ZSM-5(h-ZSM-5) with different acidity (Si/Al = 33, 51, 122) were tested in the liquid-phase conversion of stearic acid undernitrogenatmosphere(6bar). TheincorporationofPdintoZSM-5zeoliteincreased significantly the share of gasoline in the reaction products due to the promotion by this metal of both decarboxylation and hydrogen transfer reactions. Likewise, the Pd nanoparticles dispersed over the zeolitic support favored the conversion of light olefins formed by end-chain cracking reactions into gasoline-range hydrocarbons according to an oligomerization/cyclization/aromatization pathway. Additionally, Pd/h-ZSM-5 gave rise to higher conversion and selectivity towards gasoline than Pd/n-ZSM-5, due mainly to the enhanced accessibility and improved Pd dispersion achieved when using the hierarchical zeolite. The decrease in the Si/Al atomic ratio in Pd/h-ZSM-5 samples resulted in a rise in the stearic acid conversion, although it was lower than expected. This finding denotes that, for supports with high acid sites concentration, the Pd availability became the limiting factor as the metal was loaded in similar amounts in all catalysts. Finally, the increase of the reaction temperature with the Pd/h-ZSM-5 (122) catalyst augmented both stearic acid conversion and gasoline selectivity, since it enhanced the conversion of the light olefins, formed as primary cracking products, into liquid hydrocarbons. Therefore, it can be concluded that Pd supported on hierarchical ZSM-5 zeolite is a convenient catalyst for obtaining bio-gasoline from oleaginous feedstock.
Development of stable porous silica-coated Ca(OH)2/γ-Al2O3 pellets for dehydration/hydration cycles with application in thermochemical heat storage
(Elsevier, 2022) Briones, Laura; Valverde Pizarro, Claudia; Barras García, Inés; Tajuelo, C.; Sanz Pérez, Eloy; Sanz, Raúl; Escola, Jose M.; González-Aguilar, José
Thermochemical heat storage based on the CaO + H2O ↔ Ca(OH)2 system is extremely promising in CSP plants that can reach medium to high temperatures, such as those equipped with tower and heliostats. However, the attrition of pure CaO pellets is a major drawback that hampers an actual commercial development. This work proposes the dip-coating of mixed Ca(OH)2/γ-Al2O3 spherical and cylindrical pellets with dense silica and AlMCM-41 (mesoporous silica) gels. The original hardness of pure Ca(OH)2 pellets (<2 N) can be increased up to 31 N using 40 wt% alumina as binder and applying a silica coating. Both gels formed a hard calcium silicate layer upon calcination that helped keeping the structural integrity of the samples after dehydration/hydration cycles. The samples were tested in 10 consecutive cycles at dehydration and hydration temperatures of 600 ◦C and 250–425 ◦C, respectively. Cylindrical pieces displayed higher hardness values and hydration yields compared to the spherical counterparts. Interestingly, porous silica-coated cylindrical pellets achieved a remarkable hydration yield of 85% and presented a hardness value of 8 N after cycling. This was due to its porous nature and the composition of the coating, formed by thin sheets and small grains, which allowed preserving the outer porous structure of the pellet.
Selective Decarboxylation of Fatty Acids Catalyzed by Pd-Supported Hierarchical ZSM‑5 Zeolite
(ACS, 2021) Arroyo, Marta; Briones, Laura; Hernando, Héctor; Escola, José M.; Serrano, David P.
Decarboxylation of fatty acids is an interesting route for the production of renewable long-chain hydrocarbons that could replace fossil resources in the formulation of diesel and jet range fuels. The results reported in the present work demonstrate that Pd supported on hierarchical ZSM-5 zeolite allows for the decarboxylation of different fatty acids (stearic, oleic, and palmitic acids) to proceed under mild operation conditions (T = 250 °C and PH2 = 6 bar) with over 90% selectivity toward middle distillate hydrocarbons and conversions in the range of 60–85%. This outstanding performance has been attributed to a combination of high accessibility and tailored acidity in the zeolitic support that favors the metal dispersion and promotes the interaction between Pd and acid sites. The presence of a hydrogen atmosphere, under low-pressure conditions, is required for activating the Pd sites. It is also noteworthy that the catalyst could be reused after washing with n-dodecane, retaining 74% of its initial stearic acid conversion with just a minor variation in the yield of C17 hydrocarbons.
Selective hydrocarboxylation of fatty acids into long-chain hydrocarbons catalyzed by Pd/Al-SBA-15
(Elsevier, 2019-01-29) Serrano, David Pedro; Escola, José María; Briones, Laura; Arroyo, Marta
Pd/Al-SBA-15 materials, with different Si/Al atomic ratios, have been investigated as catalysts in the hydrodecarboxylation (HDC) of fatty acids for the production of long-chain paraffinic hydrocarbons. The catalytic tests were performed in a stirred batch reactor under H2 atmosphere using stearic, oleic and palmitic acids as substrates. Characterization of the catalysts indicates that the Pd nanoparticles are well distributed on the support, being partially located within their ordered mesopores. Increasing the Al-SBA-15 acidity enhances the stearic acid conversion but provokes a reduction in the selectivity towards hydrodecarboxylation versus hydrodeoxygenation (HDO). Variation of the reaction temperature within 225 - 300 ºC enhanced the catalytic activity, while the HDC selectivity remained over 90%, being just reduced when working at 300 ºC due to the occurrence of cracking reactions. The H2 pressure also increased the stearic acid conversion, in particular when passing from 3 to 6 bar, confirming the positive role of the hydrogen atmosphere in the decarboxylation process. However, when operating at 25 bar of H2 pressure, the HDC selectivity decreases, as the HDO pathway is favored. Comparing the results obtained with stearic, oleic and palmitic acids shows that the Pd/Al-SBA-15 system is an excellent catalyst for this reaction, providing in all cases a significant catalytic activity and a very high HDC selectivity. These findings can be related to the features of the Al-SBA-15 support (high surface area, uniform mesopores and mild Lewis acidity), which provides a good Pd dispersion, a high substrate accessibility and limit the extension of cracking reactions.
Shifting pathways in the phenol/2-propanol conversion over the tandem Raney Ni + ZSM-5 catalytic system
(American Chemical Society, 2020-02-04) García-Minguillán, Alba María; Briones, Laura; Serrano, David Pedro; Botas, Juan Ángel; Escola, José María
This work investigates the effects of both the zeolite accessibility and the reaction temperature on conversion of phenol assisted by 2-propanol over the tandem system Raney Ni + ZSM-5 zeolite. Two different zeolite samples, containing similar Si/Al ratios, were used: nanocrystalline ZSM-5 (n-ZSM-5) and hierarchical ZSM-5 (h-ZSM-5), operating at temperatures of 125, 150 and 175°C. When working with the Raney Ni + n-ZSM-5 system at low and intermediate temperatures the main products were mostly benzene and cyclohexene formed by phenol deoxygenation. In contrast, when increasing the temperature up to 175°C, a shift in the reaction pathways was observed, leading towards a significant share of valuable alkylphenols (mostly cresols and cyclohexylphenols) in the product distribution, generated by the occurrence of alkylation reactions catalyzed by the zeolite acid sites. This effect was enhanced in the case of the h-ZSM-5 sample, due to its improved accessibility and larger mesopore/external surface area.
The key role played by mesoporous alumina as binder for obtaining ultra-hard CaO based pellets for thermochemical heat storage leveraging the CaO/CaCO3 cycle
(Elsevier, 2024-03-07) Castro-Yáñez, David; Erans, María; Peral, Ángel; Sanz, Raúl; González-Aguilar, José; Romero, Manuel; Briones, Laura; Sanz-Pérez, Eloy Santiago; Escola, José María
The synthesis of CaO-based pellets with high energy storage and suitable mechanical resistance after prolonged cycling is pivotal for the successful implementation of the Calcium looping (CaL) technology for energy storage in CSP plants. In this work, CaO-based spherical pellets (CAA) were prepared made up of 60 wt % Ca(OH)2 and varying ratios (0–40 wt %) of commercial γ-Al2O3 and mesoporous γ-Al2O3 (m-Al2O3). They were tested in TG in several CO2 carbonation/decarbonation cycles (15 and 50 for selected pellets) and their respective average crushing strengths measured. After 15 cycles, the optimum pellet CAA 20-20 (60 wt % Ca(OH)2/20 wt % γ-Al2O3/20 wt % m-Al2O3) exhibits a remarkable energy storage density of 1030 kJ/kg with a superb crushing strength of ~29 N. This was ascribed to the enhanced formation of the calcium aluminate mayenite (Ca12Al14O33), since the high BET surface area (384 m2 g􀀀 1) of mesoporous γ-Al2O3 promotes the interaction with calcium oxide. Additionally, CAA 20-20 showed meaningful porosity that favored CO2 mass transport. Interestingly, after 50 cycles, the optimum CAA 20-20 pellet maintained a high carbonation yield (0.46), representing an 84 % of the initial value and corresponding to an energy storage density of ~873 kJ/kg. Additionally, the optimum CAA 20-20 pellet was coated with an external layer of Al-MCM-41 silica that augmented its crushing strength up to 37 N, with a concurrent slight abatement in the carbonation yield and energy storage density after 50 cycles (0.43 and ~824 kJ/kg). Consequently, both uncoated and coated CAA 20-20 pellet are promising for the successful implementation of CaL in CSP plants.