Paula Sánchez

Thermogravimetric–mass spectrometric analysis of lignocellulosic and marine biomass pyrolysis

The pyrolysis characteristics of three lignocellulosic biomasses (fir wood, eucalyptus and pine bark) and a marine biomass (Nannochloropsis gaditana microalgae) were investigated by thermogravimetric analysis coupled with mass spectrometry (TGA-MS). Thermal degradation of lignocellulosic biomass was divided into four zones, corresponding to the decomposition of their main components (cellulose, hemicellulose and lignin) and a first step associated to water removal. Differences in volatile matter and cellulose content of lignocellulosic species resulted in different degradation rates. Microalgae pyrolysis occurred in three stages due to the main components of them (proteins), which are greatly different from lignocellulosic biomass. Heating rate effect was also studied. The main gaseous products formed were CO(2), light hydrocarbons and H(2)O. H(2) was detected at high temperatures, being associated to secondary reactions (char self-gasification). Pyrolysis kinetics were studied using a multiple-step model. The proposed model successfully predicted the pyrolytic behaviour of these samples resulting to be statistically meaningful.

Design and development of catalysts for Biomass-To-Liquid-Fischer–Tropsch (BTL-FT) processes for biofuels production

BTL-FT processes for hydrocarbon production from syngas obtained from biomass gasification are becoming increasingly trendy as suitable alternatives to produce various high quality fuels for different applications. Many investigations are ongoing to test the suitability of biomass syngas for FTS using the traditionally employed catalysts. The choice of catalysts for these processes is normally restricted to Fe and Co-based materials as they provide the best compromise between performance and price. In this perspective, we aim to provide a comparative overview of the performance between Fe and Co-based high performance FTS catalysts for hydrocarbon production via BTL-FTS processes.

Cation exchanged and impregnated Ti-pillared clays for selective catalytic reduction of NOx by propylene

Abstract Ti-pillared interlayer clay (PILC)-based catalysts ion exchanged with Cu, Ni and Fe were prepared and used for the selective catalytic reduction of NO x using propylene as the reducing agent. The influence of the metal loading in the SCR activity was studied. Likewise, catalytic activity of Cu-ion exchanged samples was compared to that of Cu-ones. In both cases, the catalytic activity increased with increasing metal loading, reaching a maximum of NO x conversion, and then decreased at higher loading. The maximum of NO x conversion was achieved in each set of catalysts for the samples NiTi-3.4, FeTi-8.0 and CuTi-7.4. Ti-PILCs-ion exchanged with Cu was the most active catalyst for the SCR of NO x by propylene. H 2 -TPR results showed that Ni 2+ in Ti-PILC-based catalysts was harder to reduce than Cu 2+ in the same material. It was observed that, as the Cu content is increased, CuO and isolated Cu 2+ species became easier to reduce in ion exchanged samples. Likewise, it was also noted that the relative H 2 consumption decreased with the Cu content, due to a lower accessibility of H 2 to the metal. It can be verified a correlation between NO x conversion and the H 2 consumption for the Cu 2+ →Cu + reduction process, reaching the maximum for the sample CuTi-7.4. Finally, it was observed that the presence of 10% water in the feed inhibited the SCR of NO activity of this catalyst. However, this effect was completely reversible following the removal of water from the gas stream.

CO2 Capture in Different Carbon Materials

In this work, the CO(2) capture capacity of different types of carbon nanofibers (platelet, fishbone, and ribbon) and amorphous carbon have been measured at 26 °C as at different pressures. The results showed that the more graphitic carbon materials adsorbed less CO(2) than more amorphous materials. Then, the aim was to improve the CO(2) adsorption capacity of the carbon materials by increasing the porosity during the chemical activation process. After chemical activation process, the amorphous carbon and platelet CNFs increased the CO(2) adsorption capacity 1.6 times, whereas fishbone and ribbon CNFs increased their CO(2) adsorption capacity 1.1 and 8.2 times, respectively. This increase of CO(2) adsorption capacity after chemical activation was due to an increase of BET surface area and pore volume in all carbon materials. Finally, the CO(2) adsorption isotherms showed that activated amorphous carbon exhibited the best CO(2) capture capacity with 72.0 wt % of CO(2) at 26 °C and 8 bar.

Crystallization mechanism of all-silica zeolite beta in fluoride medium

Abstract The crystallization mechanism of pure silica zeolite beta in a fluoride medium has been investigated through the characterization of samples obtained at different synthesis times. The crystallization takes place in the presence of tetraethyl ammonium and fluoride ions at neutral pH, following a non-conventional mechanism based on the reorganization of an amorphous gel phase. The solid yield, referenced to the silica weight, remains almost constant and close to 100% during the whole crystallization process. Likewise, the amount of TEA + and F − ions present in the solid is not significantly changed as its crystallinity varies from 0% to 100%. The amorphous material initially observed is formed by a gel phase consisting of non-isolated primary units around 10–30 nm size distributed throughout the gel phase. The first crystals detected in the system are very large, with sizes around 7 μm. These crystals growth directly from the amorphous solid phase through a process of aggregation and densification of the primary units. The crystals finally observed in highly crystalline samples have sizes around 14 μm. This crystallization mechanism based on solid–solid transformations is probably favored by the low solubility of the silica species in the fluoride medium under neutral pH.

Influence of the synthesis conditions on the preparation of titanium-pillared clays using hydrolyzed titanium ethoxide as the pillaring agent

Titanium-pillared clays (Ti-PILCs) have been prepared using a commercial bentonite and a reaction mixture containing titanium ethoxide. The structure and properties of the pillared materials were studied by X-ray diffraction, N2 adsorption, chemical analysis, thermal analysis, and temperature-programmed desorption of ammonia. Materials with a high content of micropore area (≈90%) and a basal spacing of about 24 A were obtained. When the synthesis was carried out using a molar ratio HCl/Ti=2.5, a homogeneous pillared sample with a high micropore area was obtained. The structural and textural Ti-PILC properties were enhanced when the process was performed at room temperature and with the slowest addition speed of the pillaring solution to the clay suspension. There is a limit in terms of the number of titanium polynuclear species that can be incorporated as pillars within the clay, and this was found to be 15 mmol Ti/g clay. The use of an aqueous suspension of 0.15 wt.% of clay yielded the best structural and textural properties. The synthesized titanium pillared clays were found to be thermally stable up to 500 °C.

PREPARATION AND CHARACTERIZATION OF Ti-PILLARED CLAYS USING Ti ALKOXIDES. INFLUENCE OF THE SYNTHESIS PARAMETERS

Titanium was introduced into the clay structure by cation exchange with polymeric Ti cations which were formed by partial hydrolysis of Ti alkoxide in HCl. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Ti-pillared clays (Ti-PILCs). Titanium methoxide allows the synthesis of a solid with a large basal spacing (26 Å), a large surface area (360 m2/g), a significant amount of micropore surface area (90%), and notable acidity. Moreover, Ti-PILCs obtained from methoxide were found to be thermally stable up to 500°C. A correlation between the increase in acidity and the increases in both microporosity and Ti content was observed. The surface area, the micropore volume, the acidity and the d001 peak intensity all increased upon increasing the amount of Ti added to the preparation (up to ∼15 mmoles of Ti/g clay). The use of an aqueous suspension of 0.13 wt.% of clay yielded the best structural and textural properties in terms of subsequent use of the clay as a catalyst.

Influence of the nature of the metal hydroxide in the porosity development of carbon nanofibers.

In this study, highly porous carbon nanofibers (CNFs) were prepared by chemical activation in order to develop promising energy storage materials. The activation was performed at a temperature of 850 degrees C by using different metal hydroxides as the activating agents. Pore structures of the CNFs were analyzed using N(2)/77K adsorption isotherms. The presence of oxygen groups was analyzed by means of acid-base titration. The structural order (crystallinity) of the materials was studied by XRD and TGA analysis and the morphology and diameter distributions by means of TEM. The use of hydroxide of alkaline metals of low melting and boiling points (K, Rb, and Cs) led to the best results of porosity development. On the contrary, the pore opening was lower if the alkaline metal had a high boiling point (Na) or when alkali earth cations were used as activating agents. After the activation, the porous CNFs showed a decrease in diameter and scratches on their surfaces, as a consequence of the surface oxidation and opening of the graphitic layers, respectively. It was found that the specific surface area of the porous CNFs prepared using KOH and RbOH was more than 400 and 280 m(2) g(-1), respectively, without loss of their fiber shape.

Influence of the activating agent and the inert gas (type and flow) used in an activation process for the porosity development of carbon nanofibers

Carbon nanofibers (CNFs) were activated with different activating agents (KOH, KHCO(3) and K(2)CO(3)). The effects of different activations conditions, including type of protector gas (He, Ar and N(2)) and helium flow rate on the properties of activated carbon nanofibers were studied. The structural changes in activated CNFs were investigated using the following characterization techniques: N(2) adsorption isotherms at 77K, XRD, temperature-programmed desorption of hydrogen, TEM, TPO and elemental composition. The results showed that the surface area increased by a factor of 3.3, 2.0 and 1.8 referred to the parent CNFs after the treatment with KOH, K(2)CO(3) and KHCO(3), respectively. In addition, KOH generated a greater pore volume than the other activating agents; micropores were mainly generated during the process. Finally, different carrier gases were added during the activation in order to study their influence on the pore opening behavior of CNFs. It was found that the activation degree increased in the following order: Ar

Extraction of Aromatic Compounds from Heavy Neutral Distillate Lubricating Oils by Using Furfural

Abstract Liquid—liquid equilibrium data for the furfural—refined oil system, considered to be pseudoternary, were obtained at different temperatures in the 335–402 K range. Type I isotherms were observed at all temperatures for the two crude oils used: Kirkuk and Light Arabia. Tie-line compositions were correlated by the reduced Eisen—Joffe equation. Reliability of data was ascertained through Othmer—Tobias plots. The binodal curves and the tie-lines were predicted using the NRTL model with an average error lower than 5%. The viability of the simulation of the industrial extraction process using our experimental data has been proved.