Development of the dimethyl ether-to-olefins process: from fundamentals to the reactor simulation

235 p.Esta tesis estudia el proceso de conversión de dimetil éter en olefinas (DTO) sobre catalizadores de zeolita HZSM-5, abarcando la comprensión del mecanismo de reacción, selección del catalizador, modelado cinético, diseño de reactores alternativos y de un sistema reactor-regenerador con unidades de lecho fluidizado (adecuado para la implantación industrial). Se han realizado contribuciones originales en las metodologías de dos facetas fundamentales, que son de aplicación en otros procesos con desactivación del catalizador: (i) el modelado cinético para esquemas de reacción complejos; (ii) el diseño de reactores con circulación de catalizador. Así, se ha establecido el modelo cinético de lumps para dos catalizadores de zeolita HZSM-5 con diferente acidez, considerando el mecanismo de reacción y desactivación. Se ha procedido igual para el craqueo de n-pentano, seleccionado como compuesto modelo de la fracción mayoritaria de subproductos en el proceso DTO. Los modelos cinéticos se han utilizado para el diseño de diferentes reactores (lecho fijo, móvil y fluidizado sin y con circulación del catalizador). El diseño del sistema reactor-regenerador se ha realizado con un modelo original, considerando la distribución de la actividad en ambas unidades y su relación. El modelo se ha utilizado en el análisis del efecto de las variables (temperatura, tiempo espacial, agua co-alimentada y tiempo medio de residencia), y de la acidez del catalizador, en la conversión, rendimiento de olefinas y subproductos, y desactivación, obteniéndose las condiciones adecuadas del proceso

Development of the dimethyl ether-to-olefins process: from fundamentals to the reactor simulation

235 p.Esta tesis estudia el proceso de conversión de dimetil éter en olefinas (DTO) sobre catalizadores de zeolita HZSM-5, abarcando la comprensión del mecanismo de reacción, selección del catalizador, modelado cinético, diseño de reactores alternativos y de un sistema reactor-regenerador con unidades de lecho fluidizado (adecuado para la implantación industrial). Se han realizado contribuciones originales en las metodologías de dos facetas fundamentales, que son de aplicación en otros procesos con desactivación del catalizador: (i) el modelado cinético para esquemas de reacción complejos; (ii) el diseño de reactores con circulación de catalizador. Así, se ha establecido el modelo cinético de lumps para dos catalizadores de zeolita HZSM-5 con diferente acidez, considerando el mecanismo de reacción y desactivación. Se ha procedido igual para el craqueo de n-pentano, seleccionado como compuesto modelo de la fracción mayoritaria de subproductos en el proceso DTO. Los modelos cinéticos se han utilizado para el diseño de diferentes reactores (lecho fijo, móvil y fluidizado sin y con circulación del catalizador). El diseño del sistema reactor-regenerador se ha realizado con un modelo original, considerando la distribución de la actividad en ambas unidades y su relación. El modelo se ha utilizado en el análisis del efecto de las variables (temperatura, tiempo espacial, agua co-alimentada y tiempo medio de residencia), y de la acidez del catalizador, en la conversión, rendimiento de olefinas y subproductos, y desactivación, obteniéndose las condiciones adecuadas del proceso

Understanding the Adsorption Capacity for CO2 in Reduced Graphene Oxide (rGO) and Modified Ones with Different Heteroatoms in Relation to Surface and Textural Characteristics

Reduced graphene oxide is a material that has a variety of applications, especially in CO2 adsorption. The study of this research is the preparation of reduced graphene oxide with different heteroatoms and how the adsorption capacity is changed. The functionalization with other compounds bearing Si, S, N, and O was before reducing graphene oxide. Different monoliths were prepared by changing the ascorbic acid analogy and the temperature of reduction. The different porosity values, percentages of heteroatoms, and synthetic parameters show that the adsorption capacity is a complex procedure that can be affected by multiple parameters. Microporosity, different functionalities from heteroatoms, and high surface/volume of pores are the significant parameters that affect adsorption. All parameters should establish a balance among all parameters to achieve high adsorption of CO2.This research was funded by Basque Government, grant number GV IT999-16

Reduced Graphene Oxide/Polymer Monolithic Materials for Selective CO2 Capture

Polymer composite materials with hierarchical porous structure have been advancing in many different application fields due to excellent physico-chemical properties. However, their synthesis continues to be a highly energy-demanding and environmentally unfriendly process. This work reports a unique water based synthesis of monolithic 3D reduced graphene oxide (rGO) composite structures reinforced with poly(methyl methacrylate) polymer nanoparticles functionalized with epoxy functional groups. The method is based on reduction-induced self-assembly process performed at mild conditions. The textural properties and the surface chemistry of the monoliths were varied by changing the reaction conditions and quantity of added polymer to the structure. Moreover, the incorporation of the polymer into the structures improves the solvent resistance of the composites due to the formation of crosslinks between the polymer and the rGO. The monolithic composites were evaluated for selective capture of CO2. A balance between the specific surface area and the level of functionalization was found to be critical for obtaining high CO2 capacity and CO2/N2 selectivity. The polymer quantity affects the textural properties, thus lowering its amount the specific surface area and the amount of functional groups are higher. This affects positively the capacity for CO2 capture, thus, the maximum achieved was in the range 3.56–3.85 mmol/g at 1 atm and 25 °C.Spanish Government (CTQ2016-80886-R; BES-2017-080221), Basque Government (GV IT999-16) and NATO (SfP project G4255) are gratefully acknowledged for their financial support. The authors would like to acknowledge the contribution of the COST Action CA 15107

Nature and Location of Carbonaceous Species in a Composite HZSM-5 Zeolite Catalyst during the Conversion of Dimethyl Ether into Light Olefins

The deactivation of a composite catalyst based on HZSM-5 zeolite (agglomerated in a matrix using boehmite as a binder) has been studied during the transformation of dimethyl ether into light olefins. The location of the trapped/retained species (on the zeolite or on the matrix) has been analyzed by comparing the properties of the fresh and deactivated catalyst after runs at different temperatures, while the nature of those species has been studied using different spectroscopic and thermogravimetric techniques. The reaction occurs on the strongest acid sites of the zeolite micropores through olefins and alkyl-benzenes as intermediates. These species also condensate into bulkier structures (polyaromatics named as coke), particularly at higher temperatures and within the mesoand macropores of the matrix. The critical roles of the matrix and water in the reaction medium have been proved: both attenuating the effect of coke deposition.The financial support of this work was undertaken by the Ministry of Economy and Competitiveness of the Spanish Government, some cofounded with ERDF funds (Project CTQ2013-46172-P, CTQ2013-46173-R and CTQ2016-79646-P projects), by the Basque Government (Project IT748-13) and by the University of the Basque Country (UFI 11/39). M. Ibafiez is grateful for the postgraduate grant from the University of the Basque Country (No. UPV/EHU2016)

Lignin-derived Pt supported carbon (submicron)fiber electrocatalysts for alcohol electro-oxidation

Lignin fibers, with and without phosphorus, and loaded with platinum have been prepared in a single step by electrospinning of lignin/ethanol/phosphoric acid/platinum acetylacetonate precursor solutions. Thermochemical treatments have been carried out to obtain lignin-based carbon fiber electrocatalysts. The electrospun lignin fibers were thermostabilized in air and carbonized at 900 °C. The effect of phosphorus and platinum content on the porous texture, the surface chemistry and the oxidation/electro-oxidation resistance have been studied. Phosphorus-containing carbon fibers develop a higher surface area (c.a. 1200 m2 g−1), exhibit a lower Pt particle size (2.1 nm) and a better particle distribution than their counterpart without phosphorus (c.a. 750 m2 g−1 of surface area and 9.6 nm Pt particle size). It has been proved that phosphorus improves the oxidation and electro-oxidation resistance of the fibers, avoiding their oxidation during the preparation thermal stages and is responsible of the generation of a microporous material with an unusual wide operational potential window (1.9 V). An important Pt–P synergy has been observed in the oxygen transfer during the oxidation and electro-oxidation of the fibers. The obtained carbon fibers can act directly as electrodes without any binder or conductivity promoter. The fibers with platinum have shown outstanding catalyst performance in the electro-oxidation of methanol and ethanol.This work was supported by the Spanish MINECO under CTQ2015-68654-R project

A six-lump kinetic model for HDPE/VGO blend hydrocracking

A six lump-based kinetic model has been developed for the hydrocracking of high-density polyethylene (HDPE) blended with vacuum gas oil (VGO) over a PtPd/HY zeolite catalyst. The blend (20 wt% HDPE and 80 wt% VGO) has been hydrocracked in a semi-continuous stirred tank reactor under the following conditions: 400–440 °C; 80 H2 bar; catalyst to feed (C/F) weight ratio, 0.05–0.1 gcat gfeed−1; reaction time, 15–120 min; and stirring rate, 1300 rpm. The kinetic model, which is an approach to tackle the complex reaction mechanism behind the hydrocracking of a HDPE/VGO blend, predicts the evolution over time of product distribution (gas, naphtha, light cycle oil (LCO), heavy cycle oil (HCO), HDPE and coke). The kinetic model and its computed parameters have been used for the simulation of the HDPE/VGO hydrocracking establishing that a C/F ratio of 0.075 gcat gfeed−1 and temperature–time combinations of 430 °C–10 min and 440 °C–70 min are the optimal operating conditions. Under these conditions, a proper balance between the HCO conversion (>80 %), HDPE conversion (>60 %) and liquid fuel production index (>1.0) would be obtained. This kinetic model could serve as a basis for scaling-up in the valorization of waste plastics by co-feeding them to industrial hydrocracking units, within a Waste-Refinery strategy.This work has been carried out with the financial support of the Ministry of Science, Innovation and Universities (MICIU) of the Spanish Government (grant RTI2018-096981-B-I00), the European Union’s ERDF funds and Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Actions (grant No 823745) and the Basque Government (grant IT1645-22). David Trueba thanks the University of the Basque Country UPV/EHU for his PhD grant (PIF 2018)

Zn Redistribution and Volatility in ZnZrOx Catalysts for CO2 Hydrogenation

ZnO–ZrO2 mixed oxide (ZnZrOx) catalysts are widely studied as selective catalysts for CO2 hydrogenation into methanol at high-temperature conditions (300–350 °C) that are preferred for the subsequent in situ zeolite-catalyzed conversion of methanol into hydrocarbons in a tandem process. Zn, a key ingredient of these mixed oxide catalysts, is known to volatilize from ZnO under high-temperature conditions, but little is known about Zn mobility and volatility in mixed oxides. Here, an array of ex situ and in situ characterization techniques (scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDX), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), Infrared (IR)) was used to reveal that Zn2+ species are mobile between the solid solution phase with ZrO2 and segregated and/or embedded ZnO clusters. Upon reductive heat treatments, partially reversible ZnO cluster growth was observed above 250 °C and eventual Zn evaporation above 550 °C. Extensive Zn evaporation leads to catalyst deactivation and methanol selectivity decline in CO2 hydrogenation. These findings extend the fundamental knowledge of Zn-containing mixed oxide catalysts and are highly relevant for the CO2-to-hydrocarbon process optimization.publishedVersio

Catalizadores de base carbonosa para la hidrodeoxigenación de bio-oil

En el actual escenario de transición energética, la biomasa lignocelulósica recibe una gran atención como fuente renovable de energía y materias primas. La pirolisis de biomasa tiene buenas perspectivas para su implantación a gran escala, y producción de combustibles líquidos y productos químicos de interés. El bio-oil, el producto líquido, es una emulsión rica en compuestos orgánicos oxigenados, pero su inestabilidad y contenido de agua impiden su uso directo como combustible. Por otro lado, el producto sólido, puede ser tratado para su empleo como catalizador o soporte de catalizador. La hidrodeoxigenación (HDO) del bio-oil es una reacción clave para adecuar su composición y propiedades y para ello se proponen catalizadores bifuncionales soportados sobre carbón activo. Estos han sido preparados mediante activación química con H3PO4 de hueso de aceituna, lo cual genera grupos funcionales ácidos en el soporte carbonoso. Diferentes metales se han depositado como función metálica (PtPd, NiW y CoMo). La HDO de bio-oil se ha evaluado a presiones moderadas (65 bar) y altas temperaturas (400-475 ºC), lo que permite operar en un reactor en continuo debido a que se alcanza un estado estable entre la hidrodeoxigenación de los intermedios y el hidrocraqueo de los precursores de coque, impidiendo la rápida desactivación típica del procesado de bio-oil completo. Estos compuestos del medio de reacción, así como las especies depositadas sobre los catalizadores durante la reacción han sido analizados con el objetivo de estudiar los diferentes mecanismos de desactivación y cómo se integran en el mecanismo global de la HDO. Estos estudios han permitido proponer un esquema de reacción sencillo para este proceso agrupando los compuestos con comportamiento cinético similar. Finalmente, se ha propuesto un modelo cinético de la HDO con el objetivo de producir compuestos aromáticos y fenólicos basado en este esquema de reacción y considerando la desactivación del catalizador