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Apparent Kinetics

The Experts below are selected from a list of 288 Experts worldwide ranked by ideXlab platform

Hermann Hofbauer – 1st expert on this subject based on the ideXlab platform

  • Apparent Kinetics of the water gas shift reaction in biomass gasification using ash layered olivine as catalyst
    Chemical Engineering Journal, 2018
    Co-Authors: J Kryca, Juraj Priscak, Joanna łojewska, Matthias Kuba, Hermann Hofbauer

    Abstract:

    Abstract Substitution of fossil fuels for production of electricity, heat, fuels for transportation and chemicals can be realized using biomass steam gasification in a dual fluidized bed (DFB). Interaction between biomass ash and bed material in a fluidized bed leads to transformation of the bed particle due to enrichment of components from the biomass ash resulting in the development of ash layers on the bed particle surface. These ash-rich particle layers enhance the catalytic activity of the bed material regarding the water-gas-shift reaction and the reduction of tars. The water-gas-shift reaction at conditions typical for dual fluidized bed biomass gasification at a temperature of 870 °C was investigated. Diffusion and heat transfer limitations were minimized using a lab-scale experimental set-up consisting of a gas mixing section and a quartz glass reactor in which the catalyst is investigated. The following new rate expression for the water-gas-shift reaction in dual fluidized bed gasification of biomass was empirically developed, which takes ash layer formation into account: r Olivine _ ash – layer = 8 , 9 · 10 – 6 exp – 95000 RT p CO 1 , 96 p H 2 O 1 , 81 p CO 2 – 0 , 75 p H 2 – 1 , 69

  • Apparent Kinetics of the catalyzed water gas shift reaction in synthetic wood gas
    Chemical Engineering Journal, 2016
    Co-Authors: A Plaza, S Fail, J A Cortes, Karin Fottinger, N Diaz, Reinhard Rauch, Hermann Hofbauer

    Abstract:

    Abstract The catalysis of the water–gas shift reaction employing two commercially available catalysts was investigated. The applied feed was a synthetic gas mixture simulating the wood gas derived from the dual fluidized bed steam gasification of biomass. A Co/Mo- and an Fe/Cr-based catalyst were compared in a differentially operated plug flow reactor. The influence of the partial pressures of all reaction partners as well as the effect of temperature were studied, allowing the formation of two power law rate models. (1) r ( Co / Mo ) = 0.044 exp – 66 R T p CO 1.28 p H 2 O 0.03 p CO 2 – 0.11 p H 2 – 0.35 1 – 1 K p CO 2 p H 2 p CO p H 2 O (2) r ( Fe / Cr ) = 300 exp – 102 R T p CO 1.37 p H 2 O 0.23 p CO 2 – 0.16 p H 2 – 0.11 1 – 1 K p CO 2 p H 2 p CO p H 2 O The CO conversion rates over both catalysts were strongly dependent on the sulfur load in the feed. The presented models were established at a constant H 2 S concentration of 100 vol.ppm db . At this sulfur load the Fe/Cr-based catalyst should be preferred to the Co/Mo-based catalyst. The partial pressure of H 2 S could not be included in the power law models because of its influence on the other coefficients of the model.

Meizhou Ding – 2nd expert on this subject based on the ideXlab platform

  • comparative investigation on thermal decomposition of powdered and pelletized biomasses thermal conversion characteristics and Apparent Kinetics
    Bioresource Technology, 2020
    Co-Authors: Ke Zhang, Xu Li, Bin Li, Meizhou Ding

    Abstract:

    Abstract In this work, the thermal degradation behaviors of two kinds of biomasses (pinewood and rice husk) with powder and pellet under three oxygen concentrations were investigated by a self-designed macro-thermogravimetric analyzer. An obvious hysteresis of thermal degradation of biomass pellets was observed under three conditions. The maximum activation energy of biomass pellets was significantly greater than that of biomass powders, while their average activation energies were almost equal based on distributed activation energy model. For the oxygen-rich combustion, the comprehensive combustion character index of powdered and pelletized biomasses ranged from 3.92 × 10−7 to 5.16 × 10−7%2·min−2·°C−3 and from 1.82 × 10−7 to 1.91 × 10−7%2·min−2·°C−3, respectively. Furthermore, the derived biochar of powdered biomass has a higher caloricity than that of pelletized biomass during combustion by TG-DSC analysis. The performances of thermal degradation observed by macro-thermogravimetric analyzer could factually reveal the influence of mass and heat transfer on the thermochemical conversion of powdered and pelletized biomasses.

  • comparative investigation on thermal degradation of flue cured tobacco with different particle sizes by a macro thermogravimetric analyzer and their Apparent Kinetics based on distributed activation energy model
    Journal of Thermal Analysis and Calorimetry, 2019
    Co-Authors: Yalin Wang, Ke Zhang, Liangyuan Chen, Meizhou Ding

    Abstract:

    The particle size was an important factor that can affect the thermal degradation behavior of biomass during thermochemical conversion. In this work, the thermal degradation behavior of flue-cured tobacco with different particle sizes for thermochemical conversion was investigated by a self-designed macro-thermogravimetric analyzer (macro-TGA) under inert and oxidative conditions. During pyrolysis and combustion, the thermal degradation behavior could be described by a four-stage and five-stage mass loss reaction, respectively. At the second mass loss stage, for six cut tobaccos, the mass loss rate increased with the decrease in particle size during pyrolysis and combustion. In addition, the combustion character index of cut tobaccos ranging from 3.0480 × 10−7 to 4.4825 × 10−7%2 min−2 °C−3 also increased with the decrease in particle size. Furthermore, the mass change data recorded by the macro-TGA were used to estimate the kinetic parameters, such as the Apparent activation energy and the pre-exponential factor, based on distributed activation energy model. For the thermochemical conversion of tobacco materials, it was found that the Apparent activation energy increased with the increase in conversion rate for pyrolysis reaction under inert condition, while the Apparent activation energy reached a maximum within a certain conversion rate in the middle of combustion reaction under oxidative condition. As well, the kinetic compensation effect was evaluated by the equation $$\ln A = \varphi \times E + \psi$$. The investigation on thermal degradation and Apparent Kinetics of tobacco revealed the effect of particle size on thermochemical conversion, which can provide a reference for building a more accurate cigarette combustion model.

Mohammad M Hossain – 3rd expert on this subject based on the ideXlab platform

  • Apparent Kinetics of high temperature oxidative decomposition of microalgal biomass
    Bioresource Technology, 2015
    Co-Authors: Shaikh A Razzak, Mohammad M Hossain

    Abstract:

    Abstract The oxidative thermal characteristics of two microalgae species biomass Nannochloropsis oculta and Chlorella vulgaris have been investigated. The Apparent kinetic parameters for the microalgal biomass oxidation process are estimated by fitting the experimental data to the n th order rate model. Also, the iso-conversional methods Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were used to evaluate the Apparent activation energy. The results indicate that biomass of different microalgae strains exhibit different thermal behavior and characteristics. In addition, growth parameters and medium composition can affect the biomass productivity and composition. This would have significant impact on the thermal decomposition trend of the biomass. The kinetic modeling of the oxidation reaction with direct model fitting method shows good prediction to the experimental data. The Apparent activation energies estimated by KAS and FWO methods for N. oculta were 149.2 and 151.8 kJ/mol, respectively, while for C. vulgaris were 214.4 and 213.4 kJ/mol, respectively.

  • Apparent Kinetics of nonisothermal high temperature oxidative degradation of ethylene homopolymers: effects of residual catalyst surface chemistry and structure
    Journal of Polymer Research, 2013
    Co-Authors: Muhammad Atiqullah, Mohammad M Hossain, Syed Masiur Rahman, Khurshid Alam, Hasan A. Al-muallem, Abdulrahman F. Alharbi, Ikram Hussain, Anwar Hossaen

    Abstract:

    The effects of two supported residual catalysts—one Ziegler-Natta and another metallocene—on the nonisothermal thermooxidative degradation of the resulting ethylene homopolymers were investigated using TGA experiments and kinetic modeling. The rigorous constitutive kinetic model (developed in this study), unlike the analytical Horowitz and Metzger model, fitted very well to the entire TGA curve, without distribution of activation energy E _ a , for n (overall degradation order) = 1 for both polymers. Neither n nor E _ a varied as a function of fractional weight loss of the polymer. Hence, the proposed unified molecular level concept of surface chemistry and structure of the residual catalysts held all through the degradation process. The above feature of n and E _ a also indicates the suitability of the model formulation and the effectiveness of the parameter-estimation algorithm. Random polymer chain scission, with the cleavage of the −C−C− and the −O−O− (hydroperoxide) bonds, prevailed. The types of residual catalyst surface chemistry and structure varied the bond cleavage process. The metallocene Zr residual catalyst caused more thermooxidative degradation in MetCat HomoPE than what the Ti one did in Z-N HomoPE. The rigorous constitutive model-predicted Apparent kinetic energy E _ a , and frequency factor Z also support this finding. The proposed degradation mechanism suggests that the Zr residual catalyst more (i) decreased the activation energy required to decompose the −C−C− and the −O−O− bonds, and (ii) eliminated β-hydrogen (by the carbonyl functionalities) from the polymer chains. These findings were attributed to the differences in surface chemistry and structure of the residual catalysts. Therefore, the current study presents a rigorous constitutive kinetic model that duly illustrates the influence of the characteristic surface chemistry and structure of the residual catalysts on the high temperature oxidative degradation of polyethylenes.