Examinando por Autor "Peral, Ángel"

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Catalytic Properties in Polyolefin Cracking of Hierarchical Nanocrystalline HZSM-5 Samples Prepared According to Different Strategies
(ELSEVIER, 2010) Serrano, David P.; Aguado, J.; Escola, J.M.; Rodríguez, J.M.; Peral, Ángel
Two series of hierarchical nanocrystalline ZSM-5 zeolites prepared by different synthesis strategies (at low temperature and from silanized seeds) and with external surface areas ranging from 150 to 250 m2 g-1 were tested in the cracking of pure LDPE and HDPE at 340ºC and of waste polyethylene at 360ºC. Hierarchical zeolites showed quite higher activity, with values even 6 times higher than a standard nanocrystalline sample used as reference (n-HZSM-5). The activity values decreased from LDPE to HDPE due to the occurrence of some degree of branching in the former polymer, which act as preferential cracking sites. The major products were C1 - C4 hydrocarbons (in the range 30 - 70%, mostly C3 - C4 olefins) and C5 - C12 hydrocarbons (20 - 60%), whose share depends on both the polyolefin and the catalyst. The amount of C13 - C40 hydrocarbons was practically negligible (< 1%) due to the high acid strength of the zeolites which promotes end-chain cracking reactions. Likewise, hierarchical nanocrystalline HZSM-5 zeolites prepared from silanized protozeolitic units showed higher activities than the hierarchical nanocrystalline HZSM-5 samples synthesized at low temperature and atmospheric pressure. The differences were especially remarkable in the case of waste polyethylene cracking. These results were ascribed to the stronger acidity of the hierarchical zeolite samples prepared from silanized seeds.
SYNTHESIS OF HIERARCHICAL ZSM-5 BY SILANIZATION AND ALKOXYLATION OF PROTOZEOLITIC UNITS
(ELSEVIER, 2011) Serrano, D.P.; Aguado, J.; Escola, J.M.; Peral, Ángel; Morales, Gabriel; Abella, E.
Hierarchical ZSM-5 zeolite has been synthesized by means of a method involving a precrystallization stage to form the protozeolitic units, the addition and subsequent grafting of both silanization and alkoxylation agents, and a final hydrothermal crystallization. The influence of the alkoxylation with different alcohols (methanol, ethanol, 2-propanol and n-butanol) on the properties of the final hierarchical ZSM-5 samples has been investigated. In every case, the alcohol addition increased the incorporation of the seed silanization agent as it decreases the gel viscosity. In addition, the presence of alcohols deeply affects the physicochemical properties of the final materials. The samples prepared with 2-propanol and methanol were highly crystalline and presented improved textural properties with regard to the reference h-ZSM-5 and n-ZSM-5. In contrast, the samples obtained with ethanol and n-butanol were partially and totally X-ray amorphous, respectively. 1H and 13C-CP solid state MAS NMR spectra proved the alkoxylation of the external surface of the protozeolitic units. Catalytic cracking of LDPE pointed out the higher TOF values obtained over the hierarchical samples prepared with methanol and 2-propanol due to a right combination of accessibility and crystallinity in these materials. The differences observed among the samples prepared with alcohols were ascribed to the strong interaction produced between the silanization agent and the linear alcohols on the surface of the protozeolitic nanounits, which form a very stable protective layer, hindering their aggregation and subsequent crystallization.
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.