Cinética da reação de conversão de etanol em 1,3-butadieno empregando catalisadores multifuncionais

The catalytic conversion in gas phase of ethanol into 1,3-butadiene (1,3-BD) was investigated over the heterogeneous catalysts MgO-SiO2, ZrO2 and ZnO containing MgO-SiO2, and alkali metal doped ZrO2-ZnO/MgO-SiO2 prepared by co-precipitation. For the first time, the kinetics of this reactional system was evaluated employing the information contained in the covariance matrix of experimental measurements, which allowed indentifying a modification of the mechanism as reaction temperature increased: from 300 to 400 ºC, the rate-limiting step was suggested as the acetaldehyde condensation, while at 450 ºC, ethanol dehydrogenation step limited the process. Besides, the characterization of the covariance matrix of experimental fluctuations, using different reaction conditions and catalysts, demonstrated that both reaction temperature and catalyst properties affected experimental fluctuations. It was also shown that the co-precipitation method was appropriate for preparation of catalysts able to achieve high 1,3-BD productivities. Moreover, catalyst acidity was modified through the addition of alkali metals (Na, K and Li), allowing for the minimization of parallel reactions of ethanol dehydration to ethene and diethyl ether. Thus, a new catalyst was developed, which allowed for the increasing of the combined 1,3-BD and acetaldehyde selectivity up to 72 mol %. Finally, the effects of reaction variables, temperature and spatial velocity, were investigated with help of a statistical design, employing the developed catalysts. Results indicated that high 1,3-BD yields may be achieved at high spatial velocities conditions, as long as ethanol partial pressure be kept high, improving the potential of industrial application of this process.Neste trabalho, a conversão catalítica em fase gasosa de etanol em 1,3-butadieno (1,3-BD) foi estudada empregando catalisadores heterogêneos do tipo MgO-SiO2, dopados com ZrO2 e ZnO, e sistemas ZrO2-ZnO/MgO-SiO2 modificados com metais alcalinos, preparados por co-precipitação. Pela primeira vez, a cinética deste sistema reacional foi investigada utilizando a informação contida na matriz de covariância das medidas experimentais, a qual permitiu indentificar uma mudança no mecanismo reacional com o aumento da temperatura: entre 300 e 400 ºC, a etapa lenta foi sugerida como a condensação do acetaldeído, enquanto que entre 400 e 450 ºC, a desidrogenação do etanol limitou o processo. Além disso, a caracterização da matriz de covariância das medidas experimentais, empregando distintas condições reacionais e catalisadores, demonstrou que tanto a temperatura da reação, quanto as características do catalisador afetaram as flutuações experimentais. Demonstrou-se que o método de co-precipitação foi eficiente para o preparo de catalisadores capazes de apresentar elevada produtividade à 1,3-BD. Além disso, a acidez dos catalisadores foi modificada pela adição de metais alcalinos (Na, K e Li), permitindo minimizar reações paralelas de desidratação do etanol à eteno e éter etílico. Assim, um novo catalisador foi desenvolvido, o qual permitiu aumentar a seletividade combinada para 1,3-BD e acetaldeído para 72 mol. %. Finalmente, as variáveis reacionais de operação, temperatura e velocidade espacial, foram investigadas com um planejamento estatístico, empregando o novo catalisador desenvolvido. Demonstrou-se que altos rendimentos à 1,3-BD podem ser obtidos empregando elevadas velocidades espaciais, desde que a pressão parcial de etanol seja também alta, aumentando assim o potencial de aplicação industrial deste processo

Equilibrium distribution of diethyl phthalate plasticiser in cellulose acetate-based materials: Modelling and parameter estimation of temperature and composition effects

Understanding the transport and fate of semi-volatile organic compounds (SVOCs) such as phthalates in indoor environments is fundamental for quantifying levels of human exposure and preventing adverse health effects. In this context, the partition coefficient of phthalates between indoor built materials and/or consumer goods and the surrounding atmosphere represents a key parameter for determining concentration distributions. Partition coefficients are also of fundamental importance for describing degradation phenomena associated with plasticiser loss from polymeric materials. However, this key parameter has only been determined for a limited number of systems and environmental conditions. Here, we assess the partitioning behaviour of the diethyl phthalate (DEP) plasticiser in cellulose acetate (CA)-based materials for the first time, determining the effects of temperature and plasticiser composition on equilibrium distributions at temperatures between 20 and 80 °C and using CA samples with DEP contents ranging from 6 to 22 wt%. Additionally, we propose a model to describe and quantify the effect of temperature and plasticiser composition, with model parameters being estimated using non-linear regression and measurements from 130 distinct experiments. Finally, we assess the suitability of our developed model to simulate the migration of DEP from CA-based materials

Oxidative coupling of methane for ethylene production : reviewing kinetic modelling approaches, thermodynamics and catalysts

Ethylene production via oxidative coupling of methane (OCM) represents an interesting route for natural gas upscaling, being the focus of intensive research worldwide. Here, OCM developments are analysed in terms of kinetic mechanisms and respective applications in chemical reactor models, discussing current challenges and directions for further developments. Furthermore, some thermodynamic aspects of the OCM reactions are also revised, providing achievable olefins yields in a wide range of operational reaction conditions. Finally, OCM catalysts are reviewed in terms of respective catalytic performances and thermal stability, providing an executive summary for future studies on OCM economic feasibility

Nanostructured Systems Containing Rutin: In Vitro Antioxidant Activity and Photostability Studies

The improvement of the rutin photostability and its prolonged in vitro antioxidant activity were studied by means of its association with nanostructured aqueous dispersions. Rutin-loaded nanocapsules and rutin-loaded nanoemulsion showed mean particle size of 124.30 ± 2.06 and 124.17 ± 1.79, respectively, polydispersity index below 0.20, negative zeta potential, and encapsulation efficiency close to 100%. The in vitro antioxidant activity was evaluated by the formation of free radical ·OH after the exposure of hydrogen peroxide to a UV irradiation system. Rutin-loaded nanostructures showed lower rutin decay rates [(6.1 ± 0.6) 10−3 and (5.1 ± 0.4) 10−3 for nanocapsules and nanoemulsion, respectively] compared to the ethanolic solution [(35.0 ± 3.7) 10−3 min−1] and exposed solution [(40.1 ± 1.7) 10−3 min−1] as well as compared to exposed nanostructured dispersions [(19.5 ± 0.5) 10−3 and (26.6 ± 2.6) 10−3, for nanocapsules and nanoemulsion, respectively]. The presence of the polymeric layer in nanocapsules was fundamental to obtain a prolonged antioxidant activity, even if the mathematical modeling of the in vitro release profiles showed high adsorption of rutin to the particle/droplet surface for both formulations. Rutin-loaded nanostructures represent alternatives to the development of innovative nanomedicines

Oxidative Coupling of Methane for Ethylene Production: Reviewing Kinetic Modelling Approaches, Thermodynamics and Catalysts

Ethylene production via oxidative coupling of methane (OCM) represents an interesting route for natural gas upscaling, being the focus of intensive research worldwide. Here, OCM developments are analysed in terms of kinetic mechanisms and respective applications in chemical reactor models, discussing current challenges and directions for further developments. Furthermore, some thermodynamic aspects of the OCM reactions are also revised, providing achievable olefins yields in a wide range of operational reaction conditions. Finally, OCM catalysts are reviewed in terms of respective catalytic performances and thermal stability, providing an executive summary for future studies on OCM economic feasibility

Boletín oficial de la provincia de Santander: Número 6 - 1881 Julio 07

Parameter estimation procedures are very important in the chemical engineering field for development of mathematical models, since design, optimization, and advanced control of chemical processes usually rely on mathematical models, which in turn depend on parameter values (and respective uncertainties) obtained with help of available experimental data. For this reason, the parameter estimation problem is introduced here and discussed in terms of its three fundamental steps: the definition of the objective function, the minimization of the objective function, and the statistical analysis of the obtained results

Uso de biomassa como absorvente para a contenção de derramamento de óleo

Neste trabalho foi investigada a capacidade de absorção de óleos de diferentes tipos de absorventes e comparada com a de um absorvente vegetal comercial. Os resultados mostraram que vários absorventes testados apresentaram capacidade de absorção superior à do absorvente comercial, sendo que a salvínia sp. apresentou capacidade significativamente superior. O tamanho das partículas da salvínia sp. influenciou nacapacidade de absorção dos óleos

Nanostructured systems containing rutin: in vitro antioxidant activity and photostability studies

The improvement of the rutin photostability and its prolonged in vitro antioxidant activity were studied by means of its association with nanostructured aqueous dispersions. Rutin-loaded nanocapsules and rutin-loaded nanoemulsion showed mean particle size of 124.30 ± 2.06 and 124.17 ± 1.79, respectively, polydispersity index below 0.20, negative zeta potential, and encapsulation efficiency close to 100%. The in vitro antioxidant activity was evaluated by the formation of free radical OH after the exposure of hydrogen peroxide to a UV irradiation system. Rutin-loaded nanostructures showed lower rutin decay rates [(6.1 ± 0.6) 10-3 and (5.1 ± 0.4) 10-3 for nanocapsules and nanoemulsion, respectively] compared to the ethanolic solution [(35.0 ± 3.7) 10-3 min-1] and exposed solution [(40.1 ± 1.7) 10-3 min-1] as well as compared to exposed nanostructured dispersions [(19.5 ± 0.5) 10-3 and (26.6 ± 2.6) 10-3, for nanocapsules and nanoemulsion, respectively]. The presence of the polymeric layer in nanocapsules was fundamental to obtain a prolonged antioxidant activity, even if the mathematical modeling of the in vitro release profiles showed high adsorption of rutin to the particle/droplet surface for both formulations. Rutinloaded nanostructures represent alternatives to the development of innovative nanomedicines

Exploring the Materials and Condition of 20th-Century Dolls in Zoe Leonard’s <i>Mouth Open, Teeth Showing</i> 2000

Systematic condition and analytical surveys were carried out on Zoe Leonard’s (b. 1961) Mouth Open, Teeth Showing 2000, an installation artwork in Tate’s collection consisting of 162 children’s dolls. The dolls were manufactured at various points within the 20th century and encompass several potentially problematic synthetic polymers found in modern and contemporary museum collections. To explore the doll materials and conservation condition, a multi-analytical approach was used to identify key synthetic polymer types and additives present, including portable and bench analytical techniques. Challenging degradation phenomena associated with different types of doll have been discussed and related to their material composition, which has helped our understanding of the conservation challenges inherent to this contemporary artwork