1,721,042 research outputs found
Model Analysis of the Effects of Active Phase Distribution at the Pellet Scale in Catalytic Reactors for the Direct Dimethyl Ether Synthesis
Full text linkThe direct synthesis of dimethyl ether (DME) from syngas is an exothermic process, which requires two different catalyst functions in the same reactor: methanol (MeOH) synthesis and dehydration to DME. The two functions can be intimately mixed in hybrid pellets, located on separated pellets or coupled in core@shell-engineered pellets. In this work, a multitubular fixed-bed reactor, loaded with the catalyst configurations mentioned above, has been investigated by mathematical modeling. It is shown that the different spatial distribution of the active phases has a drastic impact on reactor performance. Using the mechanical mixture of separated pellets, the DME yield is hindered by intraparticle diffusion limitations. The hybrid catalyst, minimizing the diffusion length between methanol synthesis and dehydration catalyst functions, provides better DME yield performances but higher hotspot temperatures and can suffer from deactivation issues due to the detrimental interaction between the two catalytic functions. The MeOH@DME configuration, which allows for a limited contact between the catalyst active phases, guarantees DME yields comparable to those of hybrid pellets while moderating the hotspot temperature
Model analysis of the role of kinetics, adsorption capacity, and heat and mass transfer effects in sorption enhanced dimethyl ether synthesis
Full text linkThe role of kinetics, adsorption capacity, and heat and mass transfer effects in the sorption enhanced dimethyl ether synthesis (SEDMES) is investigated by means of a 2D+1D model of a single tube of an industrial-scale, externally cooled, multitubular reactor that simulates the reaction/adsorption step of the SEDMES cycle. The effect of the adsorbent/catalyst weight ratio is analyzed, showing that a trade-off between DME productivity and yield originates from the balance of kinetics and adsorption capacity in the reactor tube. The effects of internal diffusion in catalyst particles are shown to have a strong impact on effective reaction rates: significant yield/productivity improvements are obtained when using a mechanical mixture of catalysts with small particle diameters or by rearranging the distribution of the two active phases in hybrid or core@shell pellets. The thermal effects in the reactor, which are increasingly critical upon intensifying the SEDMES process conditions, are also addressed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
State of Supported Rhodium Nanoparticles for Methane Catalytic Partial Oxidation (CPO): FT-IR Studies
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Packed foams for the intensification of catalytic processes: assessment of packing efficiency and pressure drop using a combined experimental and numerical approach
Full text linkThermally conductive packed foams have been proposed as an effective solution for the intensification of non-adiabatic catalytic processes in tubular reactors where high heat transfer rates and large catalyst inventories are necessary. Some of the open issues of this innovative solution for its scale-up to industrial process are the packing efficiency and the pressure drop. In this work, these aspects were addressed by performing both experimental activities on 3D printed foams and simulations on packed foam structures. The packing efficiency was studied by considering different spherical pellets and foam samples. The ratio between the foam window and the pellet diameter, R, was identified as the governing parameter: only pellets smaller than the window size can be packed inside the cavities of open cell foams. The packing efficiency increases with R, reaching the same asymptotic value of random packing in a tube at R > 5; for R less than 1.3 the porosity exceeds 50% and local channeling may be present. Due to commercial foam specifications, this limits the application of packed foams to processes where pellets smaller than 2 mm are employed. Pressure drop in packed foams was studied as well both by experimental tests and by numerical simulations. Despite the presence of the foam structure, pressure drops in packed foams are comparable or lower than the pressure drops in packed beds with the same pellet diameter due to the increase of the porosity inside the system. An Ergun like correlation corrected by the overall void fraction and the total wetted surface is able to describe the pressure drop in these systems with reasonable accuracy
Packed Periodic Open Cellular Structures – an Option for the Intensification of Non-Adiabatic Catalytic Processes
Full text linkConductive structured catalysts offer significant potential for the intensification of gas-solid catalytic processes owing to their enhanced heat transfer properties. A major drawback is the limited catalyst inventory. Recently, packed foams were proposed to overcome the catalyst inventory limitation. The effectiveness of this concept was proven at lab-scale for intensified reactors filled with small catalyst particles. When adopting commercial foams and industrial-scale catalyst pellets, however, poor packing efficiencies are expected, limiting the potential of this concept. Similarly to foams, Periodic Open Cellular Structures (POCS) grant high heat transfer rates thanks to substantial heat conduction in their solid matrix. Additively manufactured POCS additionally offer great design flexibility. This allows for using a wider range of pellet sizes. In this work, particle packed POCS are introduced and packing efficiencies are systematically studied. Pressure drop in packed POCS is also analyzed and a suitable correlation is proposed. The heat transfer associated with this innovative reactor solution is investigated by performing non-reactive heat transfer experiments. Based on these experiments, a predictive heat transfer model is established and successfully validated with experimental data. The enormous potential of packed POCS for process intensification is illustrated by a case study of a Sabatier pilot reactor
Simulation of a structured catalytic reactor for exothermic methanation reactions producing synthetic natural gas
No full text- …
