Desarrollo de materiales para adsorción

En esta Tesis de Doctorado se ha estudiado la captura de CO2 en sólidos mesoestructurados tipo SBA-15 y en materiales arcillosos de menor coste económico y mayor disponibilidad. Estos materiales se han caracterizado mediante isotermas de N2 a -196ºC, espectroscopia infrarroja, análisis elemental, análisis termogravimétrico, difracción de rayos X y microscopias electrónicas de transmisión y de barrido. Se han obtenido isotermas de adsorción/desorción de CO2, las cuales han sido ajustadas a diferentes modelos de equilibrio. Además de la captura de CO2, también se ha estudiado la separación de la mezcla CO2/CH4 y se ha aplicado el modelo de Langmuir extendido. Los materiales mesoestructurados se caracterizan por tener una gran área específica y una distribución estrecha de tamaño de poro, resultando un sistema ordenado de poros de simetría definida que es fácilmente moldeable. Para aumentar la afinidad y la cantidad adsorbida de CO2 en estos materiales, se funcionalizaron post-síntesis utilizando dos técnicas diferentes, impregnación y reacción química. La molécula de CO2 puede reaccionar con dos grupos amino (0,5 mol de CO2/mol de N) en condiciones anhidras para formar carbamato, a través del mecanismo del zwitterion, mientras que en presencia de agua, reacciona con un único grupo amino, resultando la formación de bicarbonato amónico. Los resultados experimentales de esta Tesis de Doctorado se han dividido en diferentes capítulos: un primer grupo basado en sólidos mesoestructurados tipo SBA-15 y un segundo grupo referido a materiales tipo arcillas. En este primer grupo, la investigación se centró en la síntesis de materiales tipo SBA-15 con diferentes propiedades texturales. La SBA-15 es una sílice mesoporosa altamente ordenada que tiene una estructura de poros paralelos con ordenamiento hexagonal, con micro y mesoporosidad y paredes de sílice relativamente espesas. El tamaño de poro puede ser ajustado a través del empleo de diferentes agentes expansores de poros (benceno, TMB, TIPB). En cuanto a la fuente de silicio, hemos usado dos reactivos, TEOS y silicato sódico. Los materiales se han sintetizado por dos vías distintas, Sol-gel e hidrotermal. En el primer capítulo se investigó la influencia de la adición de agentes de hinchamiento en la síntesis hidrotermal de SBA-15 usando TEOS como fuente de silicio sobre la adsorción de CO2 y la separación CO2/CH4. En colaboración con el grupo GPSA (UFC, Brasil), se obtuvieron las isotermas monocomponente de CO2 y de CH4 y la isoterma multicomponente de una mezcla equimolar de ambos gases usando una balanza de suspensión magnética equipada con una unidad de mezcla de gases, sometiendo los materiales hasta una presión de 10 bar, encontrándose selectividades CO2/CH4~45 a bajas presiones. Tras los resultados obtenidos, investigamos en el segundo capítulo el efecto de adicionar distintas cantidades de fluoruro amónico en las síntesis hidrotermales de SBA-15. Se observó que la adición de fluoruro provoca variaciones en las isotermas de N2, provocando también desplazamientos en el ciclo de histéresis. El diferente comportamiento en la adsorción de CO2 de estos materiales fue estudiado y se discriminaron, a través del modelo Dualsite de Langmuir, las contribuciones atribuidas a la fisisorción y a la quimisorción. Además se calcularon los calores isostéricos de adsorción. La evolución de los materiales hacia espumas mesocelulares tuvo efectos positivos en la impregnación de mayores cantidades de PEI. En el tercer capítulo, el objeto de la investigación fue el uso de otra fuente de silicio. Sustituimos la fuente normalmente usada por otra más económica y compatible con la naturaleza, el silicato sódico. Estos materiales fueron testados en la adsorción de CO2. Por los resultados alcanzados con silicato sódico, éste podría sustituir al TEOS sin grandes pérdidas en la capacidad de adsorción de CO2. La presencia de heteroátomos en la sílice mesoporosa mejora su estabilidad térmica, la porosidad y el área superficial, conduciendo a materiales mesoporosos con diferentes funcionalidades. Así, en este último capítulo dedicado a sílices mesoporosas, fueron sintetizados materiales expandidos con y sin Titanio. Los materiales obtenidos fueron funcionalizados y los test de adsorción de CO2 se llevaron a cabo hasta presiones de 10 bar a dos temperaturas distintas y se encontró una selectividad CO2/CH4 de 42 a presiones bajas. Se observó que la presencia del heteroátomo tiene un efecto negativo sobre la adsorción de CO2. En este punto nos centramos en el desarrollo de materiales tipo arcillas, más económicos. En este contexto, se usaron dos materiales de partida: sepiolita y lodos férricos. España es el mayor productor mundial de sepiolita. Esta arcilla fue sometida a tratamiento ácido asistido por micro-ondas con el objetivo de reducir los tiempos de activación de la arcilla. A través de esta modificación, pretendimos aumentar el área específica de la sepiolita para, posteriormente, funcionalizar. Se estudiaron la sepiolita de partida y cuatro materiales derivados del tratamiento ácido asistido por micro-ondas. Se realizaron ensayos de adsorción de CO2 en equipo volumétrico de adsorción. Después de la caracterización de los sólidos, se escogió la sepiolita con mayor capacidad de adsorción, y se funcionalizó con diferentes cargas de PEI. Se obtuvieron las isotermas de adsorción de CO2. Se verificó que la sepiolita puede ser un adsorbente interesante en la captura de CO2. En la última parte de la Tesis, se trató de aprovechar un residuo generado en las plantas de depuración de agua. Estos residuos están compuestos principalmente de cuarzo, calcita y minerales de hierro. Tienen bajas áreas específicas y su potencial como materiales adsorbentes de CO2 es pequeño. Así, tratamos de, partiendo de estos materiales, obtener otros sólidos con mayor área específica formando pilares de sílice. Los residuos tipo arcilla recogidos y secados fueron calcinados a tres temperaturas diferentes. Además, un cuarto material fue obtenido a partir pilarización. Se verificó que a partir del tratamiento, el área específica aumentó notablemente. Se obtuvieron las isotermas de adsorción/desorción de CO2. Los flóculos no expandidos, se saturaban con pequeñas cantidades de PEI, por el contrario, el material expandido pudo ser impregnado con cantidades mayores aumentando su capacidad de adsorción de CO2. Este material fue probado en la adsorción de CO2 hasta una presión de 10 bar y a dos temperaturas distintas, mostrando un comportamiento muy interesante a 75ºC

Synthesis of type A zeolites from natural kaolinite for their application in CO2 capture processes

Climate change is the greatest environmental threat of the 21st century, with major economic, social and environmental consequences. The level of carbon dioxide (CO2) emissions has increased by 31%, therefore, both governments and the scientific community are taking steps to mitigate emissions into the atmosphere. The most economically sustainable method is the use of low cost adsorbents that perform a selective adsorption of CO2 with respect to other inert gases such as N2. Clay minerals are highly available materials on the planet, are a low cost raw material and have great versatility for various processes in the field of adsorption and catalysis. The present work describes the synthesis of type A zeolite from a hydrothermal process in basic medium using metacaolinite as a starting material. Several parameters such as temperature and time were modified to evaluate the relationship between the formation conditions of the zeolite and its CO2 adsorption capacity. Synthesized catalysts were characterized by X-ray diffraction (XRD), N2 adsorption-desorption at -196 ºC, nuclear magnetic resonance of solids (NMR) and infrared spectroscopy (IR). In addition, the absorption capacity of CO2 with type A zeolites has been evaluated, and all the results were compared with the commercial zeolites. With respect to the results obtained, it can be said that the bands obtained by IR for the synthesized Zeolites are similar to those of the commercial Zeolite. On the other hand, the NMR results show that the synthesized and commercial zeolite present the same chemical environment. Finally, the textural parameters corroborate that in all cases the surface area is low from 12 m2g-1 for kaolinite to 7 m2g-1 for commercial zeolite AUniversidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Kaolinite-based zeolites synthesis and their application in CO2 capture processes

In light of the urgent need of reducing the atmospheric CO2 emissions, the use of low-cost adsorbents, that exhibit a high affinity and CO2 adsorption capacity, is a promising method from the economic and environmental point of view to separate CO2 from the flue gas emitted from large sources of emissions like power-fueled plants. Clay minerals are low-cost raw materials with high availability all over planet and great versatility in the fields of adsorption and catalysis processes. The present study pretends to elucidate the link between the reaction conditions during the synthesis of the zeolite from kaolinite and its CO2 adsorption capacity. For that purpose, the type A zeolite was synthesized via hydrothermal process in alkaline solution using metakaolinite as a starting material. The metakaolinite was obtained by calcination of kaolinite at 600 °C and some parameters such as temperature and synthesis time were modified to optimize the synthesis aiming for a high CO2 adsorption capacity adsorbent. Synthesized materials were characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), N2 adsorption–desorption at −196 °C and CO2 adsorption at 0 °C (up to 10 bars) isotherms and Nuclear Magnetic Resonance of solids (NMR). In addition, the adsorption capacity of CO2 was evaluated by means of CO2 adsorption–desorption isotherms at 25 °C up to atmospheric pressure. The obtained results indicated that synthesized zeolite 4A can be successfully prepared from natural kaolinite (via metakaolinization) at 100 °C for 48 h under alkaline conditions, showing chemical and physical properties similar to that of the commercial 4A zeolite.This research was funded by the Ministry of Science, Innovation and Universities (Spain), Grant Nos. RTI2018-099668-B-C22 and project UMA18-FEDERJA-126 and P20_00375 of Junta de Andalucía (Spain) and FEDER funds (European Union). We also thank to Conselho Nacional de Desenvolvimento Científico e Tecnol ́ogico (CNPq, Ministry of Science and Technology, Brazil) and CAPES/PrInt (Project 88887.311867/2018-00) (Ministry of Education, Brazil) for financial support. Funding for open access charge: Universidad de Málaga / CBU

Ferric sludge derived from the process of water purification as an efficient catalyst and/or support for the removal of volatile organic compounds

[EN] Ferric chloride solutions are used as coagulants or flocculants in water treatment operations for human consumption. This treatment produces large amounts of clay-type solids formed mainly of montmorillonite with iron oxides and humic substances. This ferric sludge can be used as an efficient catalyst for the removal of volatile organic compounds (VOCs) by total oxidation. This waste isolated in the purification process has been activated by calcinations in air, characterized by several physicochemical techniques and employed as a catalyst for the removal by total oxidation of representative VOCs: toluene, propane and mixtures of toluene/propane with or without water. This ferric sludge has shown a catalytic activity one order of magnitude higher than that of a commercial iron oxide. This high activity has been related to the composition of the sludge (as it contains active metal oxides such as oxides of iron and manganese) and to the porous structure (leading to a reasonably high surface area). Moreover, it can be also used as a support for platinum, showing comparable (or even higher) catalytic activity than a similar platinum catalyst supported on conventional gamma-alumina.The authors would like to acknowledge the DGICYT in Spain CTQ2012-37925-C03-2, CTQ2015-68951-C3-1-R and CTQ2015-68951-C3-3-R. Authors from UV thank the University of Valencia (UV-INV-AE16-484416 project) and MINECO (MAT2017-84118-C2-1-R project) for funding. Finally, authors thank the Electron Microscopy Service of SCSIE of Universitat de Valencia for their support.Sanchis, R.; Dejoz, A.; Vázquez, I.; Vilarrasa-García, E.; Jiménez-Jiménez, J.; Rodríguez-Castellón, E.; López Nieto, JM.... (2019). Ferric sludge derived from the process of water purification as an efficient catalyst and/or support for the removal of volatile organic compounds. Chemosphere. 219:286-295. https://doi.org/10.1016/j.chemosphere.2018.12.002S28629521

Glyphosate adsorption onto porous clay heterostructure (PCH): kinetic and thermodynamic studies

The synthesis of PCH from natural bentonite produces a porous heterostructure material effective for the adsorption of glyphosate from water. The adsorption process takes place through an interaction between the silanol group of montmorillonite and/or the PCH adsorbent with the functional groups of glyphosate. The glyphosate adsorption isotherms, recorded for all the studied samples, have been established to be of Langmuir type. The kinetic of the herbicide adsorption on the PCH was best described by the pseudo-second-order model. With the increase in temperature from 25 to 50 °C, the sorption capacities of the materials studied towards glyphosate increased. The process of glyphosate adsorption was found to be endothermic and spontaneous in nature, as indicated by positive values of ΔH and negative values of ΔG. According to the results obtained, the herbicide sorption was more effective in a basic environment. The maximum amount of adsorbed glyphosate is almost doubled with PCH from 13.5 mg/g of natural clay to 27.5 mg/g of PCH.This study was partially funded by project RTI2018-099668-BC22 of Ministerio de Ciencia, Innovación y Universidades, and project UMA18-FEDERJA-126 of Junta de Andalucía and FEDER funds. Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature and Funding for open access charge: Universidad de Málaga / CBUA

CH4 and CO2 Adsorption Study in ZIF-8 and Al-BDC MOFs

CH4 and CO2 adsorption capacity at 25, 50 and 75°C was evaluated in two metal-organic frameworks: Al-BDC and ZIF-8, the later with zeolite topology. Adsorption experiments were carried out under static conditions using a gravimetric suspension balance until 40 bar of pressure. Adsorption isotherms of type I were obtained for both materials showing high adsorption capacity values. ZIF-8 exhibited the higher uptake value for both CH4 and CO2 (4.9 and 8.5 mmol g-1, respectively). The Toth equilibrium model was used to fit experimental isotherms in order to obtain qm (maximum adsorption capacity) and t (related to energetical heterogeneity of the surface). Isosteric heats of adsorption were also calculated by Clausius-Clapeyron equation.Thanks to UNESCO/Keizo Obuchi Research Fellowships Programme (UNESCO/Japan Young Researcher’s Fellowship Program), Cycle 2012, Programa de Becas para la realización de la tesis doctoral en la Universidad de Málaga convocatoria curso 2011-2012 (AUIP-UMA), European project 295156, FP7-PEOPLE-2011-IRSES and MINECO, Spain, Project CTQ2015-68951-C3-3-R and FEDER funds. Dr. Giselle Autié Castro thanks to CNPq-TWAS Postdoctoral Fellowship 2014 and its financial support

“Low Cost” Pore Expanded SBA-15 Functionalized with Amine Groups Applied to CO2 Adsorption

The CO2 adsorption capacity of different functionalized mesoporous silicas of the SBA-15 type was investigated and the influence of textural properties and the effect of the silicon source on the CO2 uptake studied. Several adsorbents based on SBA-15 were synthesized using sodium silicate as silicon source, replacing the commonly used tetraethyl orthosilicate (TEOS). Thus, we synthesized three couples of supports, two at room temperature (RT, RT-F), two hydrothermal (HT, HT-F) and two hydrothermal with addition of swelling agent (1,3,5-triisopropylbenzene) (TiPB, TiPB-F). Within each couple, one of the materials was synthesized with ammonium fluoride (NH4F). The supports were functionalized via grafting 3-aminopropyltriethoxysilane (APTES) and via impregnation with polyethylenimine ethylenediamine branched (PEI). The adsorption behavior of the pure materials was described well by the Langmuir model, whereas for the amine-silicas, a Dualsite Langmuir model was applied, which allowed us to qualify and quantify two different adsorption sites. Among the materials synthesized, only the SBA-15 synthesized at room temperatures (RT) improved its properties as an adsorbent with the addition of fluoride when the silicas were functionalized with APTES. The most promising result was the TiPB-F/50PEI silica which at 75 °C and 1 bar CO2 captured 2.21 mmol/g

CO₂ Valorization and Its Subsequent Valorization

After the industrial revolution, the increase in the world population and the consumption of fossil fuels has led to an increase in anthropogenic CO2 emissions [...

Insights into CO2 adsorption in amino-functionalized SBA-15 synthesized at different aging temperature

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