Análisis macrocinético de la infiltración química de vapor de capas de Si y Si/SiC en estructuras biomórficas de carbono

En este artículo se presenta el modelo matemático desarrollado para describir y predecir el proceso de in­filtración y deposición de capas de Si y Si/SiC a partir de los sistemas de precursores: metiltriclorosilano (MTS)/hidrógeno y Tetracloruro de Silicio/hidrógeno. Este modelo se basa en la cinética obtenida en el análisis experimental de la deposición sobre substratos no porosos, en el modelo geométrico desarrollado para describir la estructura porosa de las preformas de carbono y en el cálculo de Módulo de Thiele y del factor de infiltración a partir del balance de masa. Finalmente se comprobaron los resultados del modelo matemática comparando la homogeneidad de la infiltración en preformas de carbono con un microscopio SEM

Experimental and theoretical study of the thermal decomposition of ethyl acetate during fast pyrolysis

The thermal decomposition of ethyl acetate was experimentally studied in a newly designed fast pyrolysis set-up. The results were compared to theoretical calculations and literature values in order to proof the experimental concept. The reaction was carried out in a free fall tubular reactor with a residence time of 0.15 s. The identification and quantification of products stream composition was performed online using a GC-TCD/FID. First, an overview of the reaction rate at feed volumes of 0.25, 0.50 and 0.75 mL was obtained at reaction temperature between 400 to 600 degrees C in intervals of 50 degrees C. As a result mass transfer limitation for feeds larger than 0.5 mL were identified. For the second approach, a constant feed volume of 0.25 mL and temperatures between 420 to 550 degrees C were investigated. Using the experimental results, a global kinetic model is proposed for the thermal decomposition of ethyl acetate into ethylene and acetic acid through a first order unimolecular reaction. Also, theoretical calculations were performed at wB97XD/6-311++G(d,p) level. A concerted mechanism through a six-membered transition state was identified in the reaction path. The theoretical and experimental activation energy values lie within the literature values between 193 and 213 kJ/mol. 2020 The Authors. Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY-NC -ND license (http://creativecommons.orgilicenseseby-nc-nd/450/)

Estudio comparativo de la compostabilidad de fundas plásticas de PEBD, oxo-biodegradables y de papel distribuidas en el Distrito Metropolitano de Quito

In this study the degradation behavior of different types of commercial T-type bags has been investigated. The bags tested according to their commercial description are: LDPE plastic, oxo-biodegradable plastic and paper. The investigation was performed over a period of 32 weeks under real conditions. The composting essays were inoculated with fresh commercial humus and the humidity was controlled over the complete period, while the temperature was kept at the low mesophilic regime at room temperature, without direct contact to sunlight. The determination of the degradation was based on the analyses of total solids and organic total solids, as well as visual observations.The results show that only the paper bags were biodegraded appropriately, leaving no residue after 32 weeks. While neither the LDPE nor the oxo-biodegradable plastic bags show any signs of disintegration or degradation over the entire period. These results were expected for the LDPE bags, but not for the oxo-biodegradable plastics. As conclusion the low biodegradability of these bags is explained by the fact that even if the bags are commercially distributed as biodegradables, they are normal LDPE bags with an oxo-additive. Actually, according to the definition, they cannot be considered as biodegradable, since they can only be degraded by few microorganisms in a very slow rate. The degradation of their chemical structure occur by the action of heat or ultraviolet light. And since non of these conditions were found during this investigation, the bags suffer no disintegration.En esta investigación se estudia la degradación de los diferentes tipos de fundas comerciales tipo-T. Las fundas investigadas conforme a su descripción comercial son: de plásticos PEBD, de plásticos oxo-biodegradables y de papel. La investigación se realizó durante un periodo de 32 semanas bajo condiciones reales. Los ensayos del compostaje fueron inoculados con humus comercial fresco y la humedad se controló durante el periodo completo, mientras que la temperatura se mantuvo en el bajo régimen mesofílico a temperatura ambiente, sin contacto directo a la luz solar. La determinación de la degradación se basó en los análisis de los sólidos totales y sólidos totales orgánicos, como también observaciones visuales.Los resultados muestran que solo las fundas de papel fueron biodegradadas adecuadamente, al no dejar residuos después de 32 semanas. Mientras que ni las fundas plásticas PEBD ni las oxo-biodegradables mostraron señales de desintegración o degradación durante la investigación. Estos resultados fueron esperados de las fundas PEBD, pero no para las fundas oxo-biodegradables. La baja biodegradabilidad de estas fundas se explica por el hecho de que si bien las fundas son distribuidas como biodegradables, son fundas normales de PEBD con un aditivo pro-oxidante. De acuerdo a la definición de biodegradabilidad, estas fundas no pueden ser consideradas como biodegradables, debido a que pueden ser degradadas por pocos microorganismos con tasas muy bajas. La degradación de sus estructuras químicas ocurre por la acción de calor o rayos ultravioletas. Y debido a que ninguna de estas condiciones fueron encontradas durante el experimento, las fundas no sufrieron desintegración a lo largo de esta investigación

Estudio de la co-digestión anaeróbica de desechos orgánicos agroindustriales

The results of the study of anaerobic co-digestion of agro-industrial organic waste and animal manure are presented in this work. The experiments are divided in two stages. In the first stage the optimal ratio between vegetable waste and animal manure is studied in batch reactors. Once the results of the optimal mixture are obtained, the research of the anaerobic co-digestion continues in semi-continuous operating reactor. In this reactor, the main operating parameters can be controlled. The daily biogas production and the consum­ption of the buffering solution are monitored in function of the hydraulic residence time (TRH) and the daily organic load in the feed. It can be observed that the reactor operation is stable at TRH greater than 10 days and organic loads up to 4,0 kgDQO/m3d. A yield of de 100 kgDQO/m3reactor is achieved, while the specific biogas production obtained is of 0,31 m3biogas/kgDQO,feed. When the TRH is reduced below 10 days and the organic load is increased simultaneously, the digester enters an unstable operation regime and it tends to acidify. This indicates that the methanogenesis is the limiting step in the process.En este trabajo se presentan los resultados de la co-digestión anaeróbica de desechos or­gánicos agroindustriales y animales. Para esto se han realizado experimentos en dos eta­pas. En la primera etapa se estudia la mezcla óptima entre desecho vegetal y animal en reactores discontinuos. Obtenidos los resultados de la mezcla óptima, se prosigue con la investigación de la co-digestión en un reactor de régimen semi-continuo. En este reactor se controlan los principales parámetros operativos y se monitorean la producción de bio- gás y el consumo de solución amortiguadora de pH, en función del tiempo de residencia hidráulico (TRH) y de la carga orgánica diaria en la alimentación. Se puede observar que el biodigestor opera en condiciones estables a TRH mayores a 10 días y cargas orgánicas de hasta 4,0 kgDQO/m3d. El rendimiento alcanzado es de 100 kgDQO/m3reactor. La producción específica de biogás es de 0,31 m3biogas/kgDQO,alimentado. Al reducir el TRH por debajo de los 10 días y simultáneamente aumentar la carga orgánica diaria, la operación del biodigestor es inestable y tiende a acidificarse, lo cual indica que bajo estas condiciones, la metanogénesis es el paso limitante en el proceso de digestión

Magnetic Iron Oxide Colloids for Environmental Applications

This chapter deals with magnetic colloids with catalytic properties for the treatment of polluted waters and the efficient production of fuel alternatives. This kind of materials presents great advantages such as high surface/volume ratio, reproducibility, selectivity, ability to be magnetic harvested, functionalizable surfaces (e.g. with tunable pores and selective chelators deposited on them), high efficiencies and reusability. In particular, this chapter will consider the case of magnetic iron oxide colloids, which can be easily synthesized at low cost, are biocompatible and presents a well-developed surface chemistry. The most common techniques for the synthesis and functionalization of these magnetic nanoparticles will be reviewed and summarized. The iron oxide nanoparticles present outstanding properties that can be exploited in different aspect of the wastewater treatment such as heavy metals and organic pollutants removal by ionic exchange or adsorption, and degradation of the contaminants by advanced oxidation processes, among others. In the field of alternative energies, they have also been used as catalysts for biofuels production from oil crops, in Fischer-Tropsch reactions for liquid hydrocarbons and many other processes with potential environmental impact

Estudio de pre-factibilidad técnica y económica de la implementación de una biorrefinería para la conversión de residuos de cáscara de naranja

Orange peel is an abundant organic waste in Ecuador that can be used and transformed into products of high added value. Therefore, this work analyzes the technical-economic pre-feasibility of a biorefinery from orange peel to obtain essential oil, pectin and / or bioethanol. First, several scenarios were compared around the combination of products to be obtained, and it was established that the most convenient one would be obtaining essential oil and pectin, with an annual production of 8.7 and 44.4 tons, respectively. Next, a process was designed for this biorefinery that consists of 3 sections: the pretreatment of raw material, extraction of the oil, and the extraction of pectin. Material and energy balances of the process were carried out, and later, the equipment was selected and sized according to specific methodologies. The process considered the recovery and recirculation of ethanol used in the pectin extraction section to reduce production costs. Finally, an economic analysis was carried out based on the theoretical cost estimates and a catalog cost analysis. It was found that the project is profitable, and that the payback time for the investment would be between 5 and 6 years. Therefore, the implementation of the biorefinery would generate a positive economic, environmental and social impact in the country.La cáscara de naranja es un residuo orgánico abundante en el Ecuador que puede ser aprovechado y transformado en productos de alto valor agregado. Por ello, el presente artículo analiza la pre-factibilidad técnico-económica de una biorrefinería a partir de cáscara de naranja para la obtención de aceite esencial, pectina y/o bioetanol. Primero, se compararon varios escenarios alrededor de la combinación de productos a ser obtenidos, y se estableció que el más conveniente sería la obtención de aceite esencial y pectina, con una producción anual de 8,7 y 44,4 toneladas, respectivamente. A continuación, se diseñó un proceso para esta biorrefinería que consiste en 3 secciones: el pretratamiento de la materia prima, la extracción del aceite, y la extracción de la pectina. Se realizaron los balances de materia y energía del proceso, y posteriormente, se seleccionaron y dimensionaron los equipos de acuerdo a metodologías específicas. El proceso consideró la recuperación y recirculación de etanol empleado en la sección de extracción de pectina para reducir los costos de producción. Finalmente, se realizó un análisis económico a partir de las estimaciones de costos teóricos y un análisis de costos de catálogo. Se encontró que el proyecto es rentable y que el tiempo de recuperación de la inversión estaría entre 5 y 6 años. Por lo tanto, la implementación de la biorrefinería generaría un impacto positivo a nivel económico, ambiental y social en el país

Kinetische Untersuchung der chemischen Gasphaseninfiltration und Reaktion zur Hertsellung von SiC und TiC biomorphen Keramiken aus Papier Vorformen

The primary goal in this study has been the preparation of biomorphic SiC and TiC ce-ramics by the chemical vapor infiltration and reaction technique. Keeping this goal in mind, several investigations have been performed previously to obtain a profound understanding of the ceramization process by the chemical vapor infiltration method with the applied reaction systems. The applied reaction systems for the preparation of SiC ceramic are: CH3SiCl3 – H2, SiCl4 – H2 and SiCl4 – CH4 – H2, and for the production of TiC ceramics are: TiCl4 – H2 and TiCl4 – CH4 – H2. The procedure for the investigation of each system starts with the basic experiments on non-porous graphite substrates of each reaction system to obtain an optimal deposition regime as well as the kinetic data for a simplified power law model. The following investigations include the simulation of the deposition process with different models. And the final investigation is the preparation and characterization of the SiC and TiC biomorphic ce-ramics. This procedure has been applied throughout this study for all investigated precursor systems. The investigations in this study have shown that it is possible to produce high quality porous ceramics with the chemical vapor infiltration and reaction technique, obtaining better mechanical properties than with other ceramization methods. The chemical vapor deposition as well as the ceramization process for the production of SiC and TiC ceramics by the CVI –R technique are now well understood and optimized. The optimal conditions necessary to obtain biomorphic SiC and TiC ceramic with specific properties can be defined from the gained knowledge from the investigations performed. The primary application of the biomorphic SiC ceramics is as catalyst supports in the automotive industry, but its applications can be ex-panded to any other field were porous SiC or TiC ceramics can be applied, such as catalysts supports in chemical and biochemical reactors or as noise insulation materials. These and other applications are planned for these novel ceramic materials.Das Hauptziel in dieser Arbeit war die Herstellung von biomorphen SiC und TiC Ke-ramiken. Um ein gründliches Verständnis des Keramisierungsprozesses zu erreichen wurden mehrere Voruntersuchungen mit den verwendeten Reaktionssystemen mittels chemischer Gasphaseninfiltration durchgeführt. Die verwendeten Reaktionssysteme sind CH3SiCl3 – H2, SiCl4 – H2 und SiCl4 – CH4 – H2 für die Herstellung von biomorphen SiC Keramiken, und TiCl4 – H2 und TiCl4 – CH4 – H2 für die Herstellung von biomorphen TiC Keramiken. Die Vorgehensweise für die Untersuchungen für jedes Reaktionssystem beginnt mit den grundle-genden Untersuchungen auf porenfreien Graphitsubstraten und die daraus folgende Ermitt-lung der kinetischen Daten für einen vereinfachten Potenzansatz. Danach wird der Abschei-dungsprozess mit zwei verschiedenen Modellen simuliert. Letztendlich folgt die Herstellung und Charakterisierung der biomorphen SiC und TiC Keramiken. Diese Vorgehensweise wur-de während der ganzen Arbeit beibehalten. Die Untersuchungen in dieser Arbeit haben gezeigt, dass es möglich ist hochwertige poröse Keramiken mit der Methode der chemischen Gasphaseninfiltration herzustellen. So-wohl die chemische Gasphasenabscheidung als auch der Keramisierungsprozess für die Her-stellung von SiC und TiC Keramiken mit der CVI – R Methode werden dank der durchge-führten Untersuchungen besser verstanden. Als Hauptanwendung der biomorphen SiC Kera-miken sind derzeit Katalysatorträger in der Automobilindustrie zu nennen. Die porösen SiC oder TiC Keramiken können auch als Katalysatorträger in chemischen oder biochemischen Reaktoren oder als Lärmisolierungen verwendet werden

Techno-economic analysis for the production of formic acid via oxidation processing of residual biomass in Ecuador

Ecuador, traditionally an agricultural based economy, has a great potential for valorizing their industrial residues. This study, presents a techno-economic analysis for applying a novel biomass oxidation method to produce formic and acetic acids from coffee husk residues in Machala, Ecuador. The analysis determined that the time of return of investment was lower than 5 years, making this project economically feasible, when producing approx. 1000 tons of formic acid per year, which is enough for supplying the Ecuadorian market. This production, would reduce imports costs and develop the chemical industry in the country