Kinetic Analysis of the Thermal Processing of Silica and Organosilica

The incorporation of an organic group into sol–gel-derived silica causes significant changes in the structure and properties of these materials. Therefore, the thermal treatment of organosilica materials may require a different approach. In the present paper, kinetic parameters (activation energy, pre-exponential constant, and reaction models) have been determined from mass loss data for the dehydration, dehydroxylation, and decomposition reactions that take place upon heating silica and organosilica. Parameters were obtained by employing model-free isoconversional methods to data obtained under multiple heating rates as well as by multivariate analysis of the kinetics using a multistep reaction model with distributed activation energy. For silica, it can be concluded that the reaction atmosphere (i.e., inert or thermo-oxidative) has no influence on the reaction rate of the dehydration and dehydroxylation reactions that are responsible for the densification of the material. Under inert atmosphere, full dehydration can be reached without affecting the organic moiety. Achieving complete dehydroxylation of the organosilica is practically impossible as decomposition does manifest itself under commonly employed calcination temperatures. This indicates that prudence is required in designing a heat treatment program for these hybrid materials. To aid in optimizing the thermal treatment, a predictive model was developed, which can be used to forecast the extent of dehydration, dehydroxylation, and decomposition reactions under a multitude of temperature program

Thermal degradation of random copolyesters based on 1,4-butanediol, terepthalic acid and different aliphatic dicarboxylic acids

Thermal stability and degradation kinetics have been studied for a series of aliphatic-aromatic copolyesters where the terephthalate content was varied between 30 mol-% and 70 mol-%. Succinate, adipate and sebacate were considered as the aliphatic dicarboxylate unit. All copolyesters were synthesized with a perfect random distribution by a thermal transesterification process from the corresponding homopolyesters. A complex degradation was deduced for all copolymers taking into account the increment of the activation energy with conversion. In fact, thermogravimetric curves showed a minor decomposition process in the low conversion region that was more significant for the succinate derivative and specifically for that having the lowest aromatic content. The sebacate derivative was characterized by the presence of an additional and minor decomposition process that took place at the highest conversion. All copolyesters were defined by a major decomposition process, which has similar values of activation energy regardless of the method used to calculate them (e.g. Kissinger, KAS or Friedman methodologies). This decomposition reaction followed a A4 Avrami-Erofeev mechanism when Coats-Redfern and Criado methodologies were applied. In summary, all the studied copolymers thermally decompose following a complex process but in all cases the main degradation step corresponds to a similar degradation mechanism.Postprint (author's final draft

Determination of the activation energies of beef tallow and crude glycerin combustion using thermogravimetry

The present study deals with the determination of the activation energy for the thermal decomposition of two renewable fuels crude glycerin and beef tallow. The activation energies were investigated by using a thermogravimetric analyzer (TGA) in the temperature range of 25-600 degrees C in atmosphere of synthetic air. The TG curves of the thermal decomposition process of both samples were divided into several phases and the second, called PH2, was chosen for the kinetic study because it is associated with the combustion ignition. Differential Thermal Analysis (DTA) showed an endothermic event at the PH2 region for the crude glycerin corresponding to devolatilization, while for beef tallow, this step presented an exothermic event, called LTO (low-temperature oxidation), which is correlated with devolatilization followed by combustion. For the entire PH2, activation energy values for crude glycerin were between 90 kJ mol(-1) and 42 kJ mol(-1), while for the beef tallow they ranged from 50 kJ mol(-1) to 113 kJ mol (1). The activation energy values obtained at the pre-ignition stage - conversion between 0 and 0.45 - showed that the crude glycerin with higher values requires an additional energetic support at the start of combustion processes and the beef tallow ignites more easily, presenting lower values. According to the Wolfer's equation, a direct relation between the activation energy and the ignition delay is established and the results of this study provides useful data for the development and design of new combustion chambers and engines when non-traditional fuels are used as feedstock. (C) 2012 Elsevier Ltd. All rights reserved.CAPESCAPES [PNPD 0034088, BEX 1149/10-5]FAPESPFAPESP [2011/00183-2, 2011/11321-7

Processing thermogravimetric analysis data for isoconversional kinetic analysis of lignocellulosic biomass pyrolysis:Case study of corn stalk

Modeling of lignocellulosic biomass pyrolysis processes can be used to determine their key operating and design parameters. This requires significant amount of information about pyrolysis kinetic parameters, in particular the activation energy. Thermogravimetric analysis (TGA) is the most commonly used tool to obtain experimental kinetic data, and isoconversional kinetic analysis is the most effective way for processing TGA data to calculate effective activation energies for lignocellulosic biomass pyrolysis. This paper reviews the overall procedure of processing TGA data for isoconversional kinetic analysis of lignocellulosic biomass pyrolysis by using the Friedman isoconversional method. This includes the removal of “error” data points and dehydration stage from original TGA data, transformation of TGA data to conversion data, differentiation of conversion data and smoothing of derivative conversion data, interpolation of conversion and derivative conversion data, isoconversional calculations, and reconstruction of kinetic process. The detailed isoconversional kinetic analysis of TGA data obtained from the pyrolysis of corn stalk at five heating rates were presented. The results have shown that the effective activation energies of corn stalk pyrolysis vary from 148 to 473 kJ mol−1 when the conversion ranges from 0.05 to 0.85

Toward Sustainable Phenolic Thermosets with High Thermal Performances

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Analyzing the pyrolysis kinetics of several microalgae species by various differential and integral isoconversional kinetic methods and the Distributed Activation Energy Model

The pyrolysis kinetics of the microalgae Chlorella vulgaris (CV), Isochrysis galbana (IG), Nannochloropsis gaditana (NG), Nannochloropsis limnetica (NL), Phaeodactylum tricornutum (PT), and Spirulina platensis (SP) were studied by non-isothermal thermogravimetric analysis conducted at nine different constant heating rates. The kinetic parameters of each microalgae species were calculated using several kinetic methods, such as those of Kissinger, Friedman, Ozawa-Flynn-Wall (OFW), Kissinger-Akahira-Sunose (KAS), Vyazovkin, and the simplified Distributed Activation Energy Model (DAEM). The results show that the kinetic parameters calculated from the integral isoconversional methods OFW, KAS and Vyazovkin are similar to those determined by applying the simplified DAEM. In contrast, application of the differential isoconversional method of Friedman led to moderate deviations in the activation energies and pre-exponential factors computed, whereas the unique values of the kinetic parameters determined by the Kissinger method resulted in the highest deviations.The authors express their gratitude to the BIOLAB experimental facility. Funding by Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), the German Aerospace Center, is gratefully acknowledged as well as funding by the DLR international collaboration project “Accurate Kinetic Data of Biomass Pyrolysis”.Publicad

Thermal decomposition of tricyclohexylidene triperoxide using flow chemistry techniques

flow chemistry is applied to the production of 16-hexadecanolide. it is a high value molecule used as an ingredient of musk aroma. it is obtained by the thermal decomposition of tricyclohexylidene of triperoxide (synthesis of story). extremely exothermic reaction, not suitable for batch system. continuous systems are safer and more efficient. tube-in-tube reactor is build and operated. laminar flow model is used to predict the experimental profile of conversion

Role of nanopowder as sintering aid in the densification of water atomized ferrous powder

Press and sinter powder metallurgy (PM) steels are cost-effective solutions for structural applications.There is a constant drive for the improvement in the density of these PM steels which helps in expandingtheir usage in applications demanding higher performance than what they deliver today. In press andsinter PM, consolidation is primarily achieved by compaction and sintering helps in bonding the powderparticles metallurgically. One of the promising ways to achieve improved densification during sinteringis through the addition of sintering activators to the conventional micrometer sized metal powder.Nanopowder particles are associated with excess surface energy due to very high ‘surface-to-volume’ratio. Therefore, there is an enhanced reactivity in this category of materials. Another consequence ofthe excess surface energy is the lowering of sintering temperature. For instance, powder blendscontaining micro and nano powders are known to yield high densities when processed through othermanufacturing routes such as metal injection molding. In this thesis the possibility of achievingimproved densification by means of nanopowder addition as a sintering aid is explored for the case ofwater atomized iron powder processed through the press and sinter route.In this study, the influence of nanopowder addition on sintering of water atomised iron powder has beeninvestigated. Before venturing into the sintering aspects, surface and thermal characteristics ofnanopowder were investigated. X-Ray photoelectron spectroscopy (XPS) was used to evaluate thesurface oxide thickness and composition of both iron and steel nanopowder. Different models were usedfor this purpose and the results were complemented by those obtained from thermogravimetric analysis.A methodology to measure the thickness of surface oxide on the nanopowder was thus proposed.Further, surface oxide reduction and possibility of melt point depression for the nanopowder wasevaluated using thermal analysis.For the sintering studies, various powder blends were prepared based on two different nano powdercompositions, varying amounts of nanopowder content and with graphite addition to understand theinfluence of the individual constituents on the densification behaviour. Further, the blends weresubjected to uniaxial compaction at varying pressures after which sintering was performed on the greencompacts at varying heating rates. The presence and an increase in the amount of nanopowder decreasedthe compressibility of the blends. However, there was a clear influence of the nanopowder addition onthe sintering behavior in the temperature regime as low as 500 to 700 \ub0C when compared to compactscontaining only micro-powder. To understand it further, sintering at intermittent temperatures andsubsequent fractography were undertaken. It was found that the nanopowder sintering is activated attemperatures below 700 \ub0C which contributed to the difference in sinter curve behaviour. Sinter responsedepended on the composition of the powder blend; however heating rate did not show much influence.An increase in the amount of nanopowder improved the density of the sintered compacts proportionally

Compósitos híbridos de resina epoxídica, celulose funcionalizada e borracha líquida

A tenacificação de resinas epoxídicas através da adição borrachas líquidas vêm sendo empregada como forma de reduzir a fragilidade em compósitos. Porém a adição destas pode diminuir o módulo de Young além da temperatura de transição vítrea. Uma estratégia para buscar sinergia entre as propriedades, maximizando as propriedades de cada uma das partes do compósito é a hibridização de borracha líquida com partículas rígidas como a celulose microcristalina (MCC), produzindo um compósito híbrido. Ademais, a funcionalização da MCC pode facilitar a dispersão e promover a compatibilidade química entre os reforços no compósito híbrido, aumentando assim a adesão das partículas à matriz e melhorar as propriedades finais do compósito. Assim, o objetivo desta Tese verificar a influência da funcionalização da MCC com diferentes teores do silano 3-aminopropiltrietoxisilano (APTES), verificar a influência dessa funcionalização e da quantidade de MCC nas propriedades térmicas da resina epoxídica e avaliar o efeito sinérgico da hibridização da MCC funcionalizada com a borracha líquida de acrilonitrila-butadieno (NBR) nas propriedades finais dos compósitos híbridos. A funcionalização da MCC se deu através de hidrólise, condensação e enxerto do APTES, variando-o nas seguintes razões: 1:3, 1:4, 1:5, 1:10 (m/v) (MCC/APTES), produzindo as amostras de MCC funcionalizadas (MCC-Si). As partículas de MCC, funcionalizadas ou não, foram posteriormente incorporadas em resina epoxídica nas concentrações de 1,0, 2,5 e 5,0 (%m) e a dispersão foi auxiliada por sonificação seguida de agitação mecânica. Para finalizar a Tese, a NBR foi incorporada nas concentrações de 5 e 10% (%m) e os compósitos binários ou híbridos foram moldados por casting. Ensaios de termogravimetria (TGA), cinética de degradação, espectroscopia no infravermelho com transformada de Fourier (FTIR), espectroscopia por energia dispersiva (EDS), ressonância magnética nuclear (RMN) no estado sólido de 13C e 29Si e difração de raios-X (DRX) foram utilizados para caracterizar a MCC e sua funcionalização. Os compósitos foram caracterizados por TGA, FTIR, DRX, calorimetria exploratória diferencial (DSC), análise dinâmico-mecânica (DMTA), microscopia eletrônica de varredura (MEV), microtomografia de raios-X, ensaios de tração, tenacidade à fratura e impacto. A funcionalização da MCC foi mais efetiva utilizando 5 mL de APTES para cada 1 g de MCC, uma vez que esse teor apresentou diminuição da banda referente ao -OH no FTIR, melhor dispersão nos mapas de EDS, alteração do mecanismo de degradação e os deslocamentos químicos característicos da funcionalização no RMN de 29Si. A incorporação de 2,5 (%m) de MCC-Si conferiu um aumento de 119% no módulo de armazenamento na região vítrea (E’g) e 173% no módulo de perda (E") em relação à resina pura, além de diminuir o calor de reação e aumentar o valor da energia de ativação. Também foi observada uma boa adesão entre o MCC-Si e a matriz na superfície fraturada. Os efeitos sinérgicos da NBR com MCC e MCC-Si foram avaliados, e a melhor combinação foi evidenciada para o compósito híbrido reforçado com 5% (m) de NBR e MCC-Si, acrescendo a tenacidade à fratura em 40%, a resistência ao impacto em 68%.Toughening of epoxy resins through the addition of liquid rubbers has been used as a way of reducing brittleness in composites. However, the addition of these can decrease Young's modulus and the glass transition temperature. A strategy to seek synergy between properties, maximizing the properties of each part of the composite is the hybridization of liquid rubber with rigid particles such as microcrystalline cellulose (MCC), producing a hybrid composite. Furthermore, the MCC functionalization can facilitate the dispersion and promote chemical compatibility between the reinforcements in the hybrid composite, thus increasing the adhesion of the particles to the matrix and improving the final properties of the composite. Apart from it, the goal of this Thesis is to verify the influence of the functionalization of MCC with different contents of the silane 3-aminopropyltriethoxysilane (APTES), to verify the influence of this functionalization and the amount of MCC on the thermal properties of epoxy resin and to evaluate the synergistic effect of the hybridization of the MCC functionalized with acrylonitrilebutadiene liquid rubber (NBR) on the final properties of hybrid composites. The functionalization of MCC took place through hydrolysis, condensation and grafting of APTES, ranging from the following ratios: 1:3, 1:4, 1:5, 1:10 (m/v) (MCC/APTES), producing the functionalized MCC samples (MCC-Si). The MCC particles, functionalized or not, were incorporated into epoxy resin at concentrations of 1.0, 2.5, and 5.0 (%m) aided by sonication and mechanical stirring. To conclude the thesis, the NBR was incorporated at concentrations of 5 and 10% (%m) and the binary or hybrid composites molded by casting. Thermogravimetry (TGA), degradation kinetics, Fourier transform infrared spectroscopy (FTIR), energy dispersive spectroscopy (EDS), 13C and 29Si solid-state magnetic resonance (NMR), and X-ray diffraction (XRD) were used for MCC and its functionalization. The composites were characterized by TGA, FTIR, XRD, differential scanning calorimetry (DSC), dynamicmechanical analysis (DMTA), scanning electron microscopy (SEM), X-ray microtomography, tensile, fracture toughness, and impact tests. The MCC functionalization was more effective using 5 mL of APTES for every 1 g of MCC since this content showed a decrease in the band referring to -OH in the FTIR, better dispersion in the EDS maps, alteration of the degradation mechanism and characteristic chemical shifts of 29Si NMR functionalization. The incorporation of 2.5 (%m) of MCC-Si resulted in an increase of 119% in the storage modulus in the glassy region (E'g) and 173% in the loss modulus (E") in relation to the pure resin, in addition to decrease the reaction’s heat and increase the value of activation energy. Good adhesion between MCC-Si and the matrix on the fracture surface was also observed. The synergistic effects of NBR with MCC and MCC-Si were evaluated, and the best combination was evidenced for the hybrid composite reinforced with 5% (m) of NBR and MCC-Si, adding fracture toughness by 40%, impact strength by 68%

High-temperature thermochemical energy storage using iron-manganese oxide particles in a packed-bed reactor

The rising demand for electricity coupled with concerns about globally increasing greenhouse gas emissions has prompted greater interest in using renewable energy sources. One of the main drawbacks of renewable energy sources is their intermittency. For instance, solar energy experiences regular daily and annual cycles due to the earth's rotation, motion and axis inclination which leads to variations in solar irradiance. Furthermore, solar energy is unavailable during cloudy weather. One particularly promising solution to the intermittency of solar energy is implementing thermochemical energy storage (TCES) technology in the future concentrated solar power (CSP) plants. This would help to achieve the primary objective of providing non-intermittent clean electricity. In this thesis, a reactor packed with iron-manganese oxide particles is considered as the TCES system. First, the reduction reaction of particles is studied under non-isothermal conditions in argon and air atmospheres using a thermogravimetric analyzer (TGA). A shrinking core model along with a non-linear regression technique is used to model the thermal reduction of particles. Then, heat transfer of the reactor is studied when no chemical reaction occurs. The spatial temperature distribution in both axial and radial directions of a packed-bed reactor are measured experimentally. A two-dimensional, pseudo-homogeneous model is developed for the reactor, and effective thermal transport parameters are determined as functions of temperature by solving an inverse problem. Finally, these results are combined and used to describe the thermochemical performance of the particles in the packed-bed reactor during the reduction reaction. Results from the simulation are validated with the experimental data