Ceramic Fiber-Based Structures as Catalyst Supports: A Study on Mass and Heat Transport Behavior Applied to CO 2 Methanation

Fibrous structures present interesting characteristics as catalyst supports for heat- and mass-transfer-limited reactions. This paper investigates the mass and heat transport behavior of ceramic fiber-based catalysts (catalytic ceramic paper) by applying them to the exothermic reaction of CO2 methanation. Catalytic experiments were carried out to fit the activity of the catalysts with known kinetics. A fixed-bed reactor model was used to determine the efficiency and efficiency losses caused by different transport phenomena, as well as to perform a sensitivity study focused on heat transfer. The results show that heat transfer limitations are the main cause for losses in reactor efficiency, with steep temperature profiles developing inside the reactor. Poor heat transfer limits the development of highly active catalysts, while pressure drop restricts the flow rate and therefore the productivity. The use of ceramic materials with higher thermal conductivity and increasing the fiber diameter are promising approaches to enhance heat transfer, reduce pressure drop, and improve overall reactor performance.Fil: Sánchez, Agustina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Milt, Viviana Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Miro, Eduardo Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera". Universidad Nacional del Litoral. Instituto de Investigaciones en Catálisis y Petroquímica "Ing. José Miguel Parera"; ArgentinaFil: Güttel, Robert. Universitat Ulm. Faculty Of Natural Sciences; Alemani

O IVA nas prestações de serviços de construção civil: inversão do sujeito passivo e taxas reduzidas

O setor da Construção Civil apresenta um fator importante na economia nacional. Porém, é considerado pela Autoridade Tributária e pela Comissão Europeia como um setor de risco na fraude e evasão fiscal. Assim, no seguimento de medidas implementadas pela Comissão Europeia, Portugal aprovou o Decreto-Lei 21/2007 de 29 janeiro, com o intuito de combater a fraude e evasão fiscal em sede Imposto sobre o Valor Acrescentado. Apesar disso, têm sido implementados incentivos aos serviços de construção civil, dos quais destacamos a taxa reduzida de Imposto sobre Valor Acrescentado, nomeadamente para a reabilitação urbana e para os serviços com alta intensidade de fator de trabalho. Pretendemos analisar pormenorizadamente esta legislação com a finalidade de esclarecer dúvidas omissas, adotando-se uma metodologia assente na análise de jurisprudência, Informações Vinculativas e doutrina. Da análise efetuada ficou evidente que o conceito de serviços de construção civil é muito amplo e de difícil definição introduzindo dificuldades na aplicação da taxa reduzida de IVA prevista nas verbas 2.23 e 2.27. No mesmo sentido verificou-se não serem aplicados pela AT os mesmo critérios na definição de serviços de construção civil para a regra de inversão do sujeito passivo e para a aplicação da taxa reduzida de IVA

Performance of diffusion-optimised Fischer-Tropsch catalyst layers in microchannel reactors at integral operation

Microchannel reactors offer a solution to utilize highly active catalysts for the Fischer–Tropsch process. The use of a wall-coated catalyst improves temperature control and prevents the negative correlation between pressure drop and catalyst efficiency. Diffusion limitations are, however, still a concern as a high reactor productivity demands a large catalyst layer thickness, to increase catalyst holdup while using as few channels as possible. Utilizing transport pores is one way of optimising the catalyst and achieving greater layer thicknesses while maintaining a good product selectivity. In this publication, we describe an isothermal and isobaric microchannel-reactor with a novel product film formation model and an improved selectivity description for accurate calculation of the product distribution. The optimisation of catalyst layers by defining ideal thicknesses and transport pore fraction is tested within realistic integral operation of the catalyst layers. Because the catalysts selectivity is strongly affected by the local syngas ratio the interplay of diffusion effects and convection in the gas phase is of major importance for the accurate prediction of catalyst behaviour. Non-optimised layers with great layer thickness and strong impact of diffusion limitations improve their performance with increasing conversion. Optimised layers with ideal amounts of transport pores and very thin layers, for which diffusion restrictions are less significant, on the other hand, exhibit an opposite behaviour and do not benefit from high conversions. These findings can also improve the interpretation of experimental results, which are often conducted at different conversion levels

Transient Behavior of CO and CO₂ Hydrogenation on Fe@SiO₂ Core–Shell Model Catalysts—A Stoichiometric Analysis of Experimental Data

The hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes a complex transformation during the chemical reaction process. However, only little is known about the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core–shell model materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis was used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data, thus making it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of the CO2 hydrogenation showed that the reverse water–gas shift reaction mainly took place, but under an ongoing change in the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from the stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work

Transient Behavior of CO and CO2 Hydrogenation on Fe@SiO2 Core–Shell Model Catalysts—A Stoichiometric Analysis of Experimental Data

The hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes a complex transformation during the chemical reaction process. However, only little is known about the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core–shell model materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis was used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data, thus making it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of the CO2 hydrogenation showed that the reverse water–gas shift reaction mainly took place, but under an ongoing change in the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from the stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work

Transient behavior of CO and CO2 hydrogenation on Fe@SiO2 core-shell model catalysts – A stoichiometric analysis of experimental data

Hydrogenation of CO and CO2 from industrial exhaust gases into CH4 represents a promising method for sustainable chemical energy storage. While iron-based catalysts are in principle suitable for that purpose, the active metal Fe undergoes complex transformation during the chemical reaction process. However, only little is known on the change in catalytically active species under reaction conditions, primarily caused by structural changes in the catalyst material, so far. By using core-shell model-materials, factors that alter the catalyst structure can be excluded, making it possible to observe the direct influence of the reactants on the activity in the present work. Furthermore, stoichiometric analysis is used as a key tool for the evaluation of individual key reactions in the complex reaction network purely from experimental data and thus, makes it possible to draw conclusions about the catalyst state. In the case of CO hydrogenation, the presumed Boudouard reaction and the associated carburization of the catalyst can be quantified and the main reaction (CO methanation) can be determined. The results of CO2 hydrogenation show that here mainly reverse water-gas-shift reaction takes place, but under ongoing change of the catalytic active iron phase. Due to the systematic exchange between CO and CO2 in the reactant gas stream, a mutual influence could also be observed. The results from stoichiometric analysis provide the basis for the development of kinetic models for the key reactions in future work

Study on the tolerance of low-temperature CO methanation with single pulse experiments

In this contribution, single pulse reaction experiments are discussed in the context of dynamic reactor operation and used to determine the tolerance of reactors arising from sorption effects at the catalyst surface. A defined amount of CO is dosed together with an internal standard (He) in a constant H2 stream, and the pulse response is observed with reference to the internal standard, which is representing the fluid dynamics of the injected pulse. Different responses are obtained depending on the catalyst mass (Ni/Al2O3) and the operation temperature (170°C-300°C). The tolerance of the reactor can be deduced from the experimental findings. On the one hand, the catalyst adsorption capacity determines the ability to buffer fluctuations at low reaction temperatures (<220 °), which are beneficial for full-conversion, overcoming thermodynamic restrictions. On the other hand, temperature determines the transient response of the system and is independent of the catalyst mass. From these findings the study reveals that reactors represent important buffer systems during load changes in dynamic operation modes and provide an intrinsic tolerance originating from sorption processes at the catalyst surface