The Experts below are selected from a list of 2184 Experts worldwide ranked by ideXlab platform

Hong Yong Sohn - One of the best experts on this subject based on the ideXlab platform.

  • the effects of Reactant starvation and mass transfer in the rate measurement of Fluid solid reactions with small equilibrium constants
    Chemical Engineering Science, 2004
    Co-Authors: Hong Yong Sohn
    Abstract:

    Abstract The purpose of this article is to analyze critically and quantitatively the effect of Fluid Reactant supply rates and mass transfer on the measurement of the rates of Fluid–solid reactions, particularly those with small equilibrium constants. It is shown through a mathematical analysis that the measurement of the intrinsic kinetics of a reaction with a small equilibrium constant (a positive standard free energy of reaction) requires much larger rates of Fluid Reactant supply and mass transfer rates than that of a reaction with a large equilibrium constant. The overall reaction rate of the former also tends to be slow. Furthermore, the apparent activation energy of such a reaction approaches the standard enthalpy of reaction ( Δ H 0 ) , rather than the true activation energy of the chemical reaction.

Le Borgne Tanguy - One of the best experts on this subject based on the ideXlab platform.

  • The chemical continuous time random walk framework for upscaling transport limitations in Fluid–solid reactions
    'Elsevier BV', 2021
    Co-Authors: Aquino Tomás, Le Borgne Tanguy
    Abstract:

    International audienceFluid-solid reactions play a key role in a large range of biogeochemical processes. Transport limitations at the pore scale limit the amount of solute available for reaction, so that reaction rates measured under well-mixed conditions tend to strongly overestimate rates occurring in natural and engineered systems. Although different models have been proposed to capture this phenomenon, linking pore-scale structure, flow heterogeneity, and local reaction kinetics to upscaled effective kinetics remains a challenging problem. We present a new theoretical framework to quantify these dynamics based on the chemical continuous time random walk framework. We study a Fluid–solid reaction with the Fluid phase undergoing advective–diffusive transport. We consider a catalytic degradation reaction, , where is in Fluid phase and is in solid phase and homogeneous over the Fluid–solid interface, allowing us to focus on the role of transport limitations and medium structure. Our approach is based on the concept of inter-reaction times, which result from the times between contacts of transported Reactants with the solid phase. We use this formulation to quantify the global kinetics of Fluid-Reactant mass and test our predictions against numerical simulations of advective–diffusive transport in stratified channel flow and Stokes flow through a beadpack. The theory captures the decrease of effective reaction rates compared to the well-mixed prediction with increasing Damköhler number due to transport limitations. Although we consider simple kinetics and media, these findings will contribute to the understanding and modeling of the effect of transport limitations in more complex reactive transport problems

Aquino Tomás - One of the best experts on this subject based on the ideXlab platform.

  • The chemical continuous time random walk framework for upscaling transport limitations in Fluid–solid reactions
    'Elsevier BV', 2021
    Co-Authors: Aquino Tomás, Le Borgne Tanguy
    Abstract:

    International audienceFluid-solid reactions play a key role in a large range of biogeochemical processes. Transport limitations at the pore scale limit the amount of solute available for reaction, so that reaction rates measured under well-mixed conditions tend to strongly overestimate rates occurring in natural and engineered systems. Although different models have been proposed to capture this phenomenon, linking pore-scale structure, flow heterogeneity, and local reaction kinetics to upscaled effective kinetics remains a challenging problem. We present a new theoretical framework to quantify these dynamics based on the chemical continuous time random walk framework. We study a Fluid–solid reaction with the Fluid phase undergoing advective–diffusive transport. We consider a catalytic degradation reaction, , where is in Fluid phase and is in solid phase and homogeneous over the Fluid–solid interface, allowing us to focus on the role of transport limitations and medium structure. Our approach is based on the concept of inter-reaction times, which result from the times between contacts of transported Reactants with the solid phase. We use this formulation to quantify the global kinetics of Fluid-Reactant mass and test our predictions against numerical simulations of advective–diffusive transport in stratified channel flow and Stokes flow through a beadpack. The theory captures the decrease of effective reaction rates compared to the well-mixed prediction with increasing Damköhler number due to transport limitations. Although we consider simple kinetics and media, these findings will contribute to the understanding and modeling of the effect of transport limitations in more complex reactive transport problems

Bhat, Siddharth Sharad - One of the best experts on this subject based on the ideXlab platform.

  • Study of homogeneous mineral acid dehydration of monosaccharides in a CSTR
    SURFACE, 2015
    Co-Authors: Bhat, Siddharth Sharad
    Abstract:

    Simple sugars (Aldohexoses/pentoses), (Ketohexoses/pentose) when subjected to a dehydration reaction, produce various compounds. An example of one such compound is 5-hydroxymethyl furfural. Such chemical products may be used in subsequent processing steps (hydrolysis, aldol condensation, hydrogenation and dehydration) to produce similarly structured condensed compounds that form the basis of complex molecules used in various industries such as production of fuels, chemical reagents and fertilizers. Most studies focus on heterogeneous packed beds and batch reactors to carry out dehydration reactions. This study illustrates use of a Continuous Stirred-Tank reactor to carry out such dehydration reactions. In order to maintain the homogenous nature of the reaction, the catalyst chosen was sulfuric acid. Use of a CSTR would allow study of kinetics and yields for varying residence times. This data could be used to design large scale operations in biomass processing. This study is aimed at investigating variables such as changing physical properties of the Fluid Reactant during reaction, variation in pH and consequent change in proton concentrations. By understanding the impact of these variables, more accurate rate measurements can be made. In the process of developing the right method for data acquisition, several substantial changes were made to the reactor and methods. These changes were instrumental in development of a cyclic process of data collection and changing methods and design, thus highlighting the chemical engineering heuristics approach and refinement in processes. The sequence of corrected results give us better insight into the process and help develop accurate models for the reactions in the scope of this thesis and also future studies. The presented results of rates and yields may be used to develop processes based on requirement and feasibility