1,721,066 research outputs found
Control of temperature wave trains in periodically forced networks of catalytic reactors for methanol synthesis
No full textWe study the stabilisation of travelling temperature wave trains in periodically forced networks of catalytic reactors where methanol synthesis takes place. Temperature wave train solutions reproduce the inter-stage cooling effect of multistage fixed bed reactors and are therefore particularly attractive in terms of methanol conversion. However, these solutions are generally stable within narrow operating windows and always coexist with solutions characterised by lower methanol conversion. We implement a feedback control strategy with the switching time as a manipulated variable to ensure the stability of temperature wave trains. The reaction front velocity is estimated during each cycle based on temperature measurements. This allows the switching time to be computed so that the reaction front does not cross a prescribed set-point position. Indications on how to place temperature sensors and to select the set-point and controller parameters are provided. Numerical simulations demonstrating the ability of the implemented control law to prevent the transition to undesired solutions in the presence of disturbances both in the operating regime and during start-up are reported. © 2012 Elsevier B.V
Electrochemical nucleation and three-dimensional growth under mixed kinetic-diffusion control: analytical approximation of the current transient
No full textAn analytical expression is derived for the current transient generated by electrochemical nucleation and three-dimensional growth of metal nanoparticles under mixed kinetic-diffusion control. The expression is the approximate solution of a novel mathematical model and describes the dependence of the current transient on nucleation rate, number density of active sites and charge transfer kinetic constant. Relative difference between the current predicted by the analytical expression and numerical solution of the original model is invariably lower than 0.1. © 2016 Elsevier Ltd. All rights reserved
Electrochemical nucleation and three-dimensional growth of metal nanoparticles under mixed kinetic-diffusion control: model development and validation
No full textA model is derived to compute the current transient generated by electrochemical nucleation and three-dimensional growth of metal nanoparticles under mixed kinetic diffusion control. The model can describe the dependence of the current transient on nucleation rate, number of active sites and charge transfer kinetic constant. A numerical algorithm is proposed to solve the model and an analytical expression is derived for the current transient predicted in the limit of instantaneous nucleation. As the ratio between diffusion and charge transfer characteristic times is greater than one, model predictions are in satisfactory agreement with the results of direct numerical simulations of electrochemical nucleation and growth. (C) 2016 Elsevier Ltd. All rights reserved
Coupling Exothermic and Endothermic Reactions in Plug-Flow Reactor−Separation−Recycle Systems
No full textIntegrated Methyl-Cyclohexane Dehydrogenation / Nitrobenzene Hydrogenation Plant: A Case Study of Coupled Endothermic - Exothermic Reactions
No full textIntegrated biomass production and biodegradation of olive mill wastewater by cultivation of Scenedesmus sp
No full textAbstract Biomass production and bio-treatment of olive mill wastewater (OMW) were simultaneously achieved by cultivation of Scenedesmus sp. The influence of medium composition was addressed by analyzing the effect of the addition of unsterilized OMW (9% v·v − 1 ) and of inorganic nutrients, and the use of tap water. Performance of implemented treatments was assessed by analysis of the following variables: biomass productivity, growth rate, content of target microalgal fractions (lipids and carbohydrates), and consumption of OMW organic carbon fractions (reducing sugars and phenols). The addition of unsterilized OMW (9% v·v − 1 ) caused darkening of microalgal cultures inducing transition to heterotrophic growth. Growth rate values attained in heterotrophic cultures (with OMW) (0.0181 and 0.023 h − 1 ) were comparable to those attained in autotrophic cultures (without OMW) (0.0272 and 0.0249 h − 1 ). Nonetheless, significantly lower biomass productions were achieved by heterotrophic growth (0.22 and 0.35 g·L − 1 vs. 0.56 and 0.51 g·L − 1 ). Even though leading to lower biomass productions, heterotrophic growth ensured carbohydrate productions comparable to those attained by autotrophic growth (0.1 and 0.16 vs. 0.12 and 0.17 g·L − 1 ). Biodegradation of OMW phenols was found to be significantly affected by the concentration of inorganic nutrients. The inhibition of microalgal growth induced by phenols, and the interaction between phenol biodegradation and biomass production were analyzed
Application of Structured Population Balance Model for the Numerical Simulation of a Continuous Photobioreactor
No full textThe application of a structured population balance model to the numerical simulation of microalgal growth in a continuous photobioreactor is discussed. The analysis is focused on the interplay between microalgal metabolism and photobioreactor operation. The proposed model is structured to describe the evolution of mass distribution among different stages of the cell division cycle. Numerical results provide indications about the impact of the implemented nutrient supply strategy on biomass productivity. These information are of relevance in applications where nutrient deprivation is imposed to enhance the production of prescribed products
Nonlinear Analysis of Pfr – Separation – Recycle Systems Coupling Exothermic and Endothermic Reactions
No full textNo abstract availabl
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