An approximate method for solving gas-solid non-catalytic reactions

A simple treatment for obtaining the solution of single isothermal gas-solid non-catalytic reactions is presented. The model is formulated under a local volumetric approach and permits to incorporate non-linear chemical kinetics and the change in porous structure during conversion. The methodology developed in this work is based on the quantize method for decoupling the solid and gas equations and on perturbation and matching techniques for approximating the gas conservation equation. With this strategy, the calculation of gas concentration and solid conversion at any time and position are reduced to the solution of two coupled algebraic equations. The model compares favourably with the exact (numerical) solution for a variety of cases. This procedure provides an effective and general tool for obtaining the solution of gas-solid reactions with minor calculations.     

A general asymptotic analytical solution for non-catalytic gas-solid reactions

The reaction between a porous solid pellet and a gas is analyzed in the asymptotic region of the effectiveness factor. The solid consumption is divided in two stages. The influences of effective diffusivity and surface area profiles are taken into account for both stages through a correction modulus of the effectiveness factor. The conversion — time relationship can be calculated for a selected model of porous structure and any reaction order for the gaseous reactant. The results are extended to non-equimolar counterdiffusion and a non-isothermal situation with external heat and mass transfer resistances.     

Less known behaviour of gas-solid reactions: The expanding core model in catalytic and non-catalytic systems

Gas-solid reactions cover a wide spectrum of industrial products. Over the years, many conceptual models have been developed to describe the progress of a gas-solid reaction starting outside the solid particle as well as that occurring throughout the particle. But the behaviour of a reaction, initiated inside the pellet, is less known. In this paper, a brief outline is given of this relatively rare but important mode of gas-solid reaction. The causes of this relatively less known behaviour and characteristic features of five typical systems displaying it are discussed.     

A comparison of transient reactor models for non-catalytic gas-solid processing

Transient behaviour of packed bed reactors for non-catalytic gas-solid reactions has been simulated using the sharp interface, finite reaction zone and the particle-pellet model for the reaction process occurring within the individual pellets. The solution procedures to the system of equations is based on the orthogonal collocation method. The effect of perturbations in the reactor inlet conditions on the temperature profiles encountered in the bed has also been examined.     

Effectiveness factors for solid-catalyzed gas-solid reactions

Effectiveness factors are given for gas-solid reactions catalyzed by a solid catalyst. Since the gasification of the solid reactant takes place at the catalyst-solid reactant interface, the gaseous reactant has to diffuse to the interface. As conversion proceeds, the thickness of the catalyst layer increases causing the effectiveness factor to decrease. Effectiveness factors obtained for the surface reaction show heavier dependence on the order of reaction and the Thiele modulus when compared with the effectiveness factors for the solid-catalyzed gas reactions. For the general case of gaseous reactant consumed by both surface and volume reaction, two Thiele moduli are required and the effectiveness factor decreases exponentially with increasing conversion. The effectiveness factor calculated from literature data on catalytic hydrogasification of coal is given to illustrate this dependence on conversion.     

On the optimum temperature progression for irreversible non-catalytic gas—solid reactions

Non-catalytic gas—solid reactions are examined, where both pore diffusion and chemical kinetics may affect the overall rate. At low temperatures the system is chemically controlled, whereas at high temperatures the reacted shell sinters, which causes the reaction to slow down appreciably.The system is represented by an appropriate mathematical model and it is shown that in this instance an optimal temperature progression would offer little advantage over operating at a constant optimal temperature throughout the reaction.A physical explanation is suggested for this behavior.     

Effects of convective diffusion on the apparent kinetics of zeroth order surface-catalysed chemical reactions

The apparent kinetics of zeroth order surface-catalysed reactions are quantitatively investigated for several configurations involving laminar or turbulent boundary layer flow, with or without pressure gradient. Nine cases of interest are solved exactly in terms of the incomplete beta function and analytical and graphical results are presented and compared with the results of applying the familiar quasi-stationary approximation. The latter method, which is equivalent to the use of the concept of “local resistance additivity,” is shown to fail badly in this chemical kinetic extreme. Applications of the theory to the interpretation of kinetic data and the design of catalytic heat exchangers are discussed.     

微型流化床反应动力学分析仪的研制与应用

本文首次研发了一种用于测定气固反应速度、求算反应动力学参数的微型流化床反应分析仪器（MFBK）。该仪器利用流化床强化反应过程的热量与质量传递过程,通过气体脉冲输送在给定温度下瞬时进样,根据在线监测的气体组分浓度变化,测试反应速度、推导反应动力学参数和分析反应机理。利用该仪器测定氩气气氛中碳酸钙的分解反应表明：其表观活化能与指前因子分别为142.73kJ.mol^-1和399777s^-1,活化能在文献报道范围之内,且小于热重分析仪测定的184.3kJ.mol^-1,并建立了反应模式函数f(α)=(1-α)0.86,对应的拟合线性相关系数达到0.99。测定煤和生物质热解反应过程表明：MFBK测试的反应完成时间在15s左右,且揭示了生成气关键组分具有不同的释放时间和生成量,为深入探讨热解反应机理提供了新的证据。     

A kinetics study on catalytic and non-catalytic steam gasification of biomass

An experimental study on catalytic and non-catalytic steam-gasification of sawdust has been conducted in a microsystem by exposing a small quantity (about 1 g) of sawdust to flash pyrolysis in an atmosphere of steam in the temperature range of 350 to 650°C. The results have been evaluated on the basis of loss of weight of sawdust and a detailed gas analysis through Orsat analyser and gas chromatograph. From the rate of gas evolution, i.e. volume fraction of gas collected with time, kinetic analysis was attempted through appropriate solid—gas-reaction models. Results of this analysis has been reported in the present paper.     

Effect of adsorptive gaseous reactant on non-isothermal behavior for gas-solid reactions

The effect of adsorptive species on non-isothermal gas-solid reactions is studied on the basis of Langmuir-Hinshelwood kinetics. The concept of an effectiveness factor provides good information to ascertain the effect of adsorptive species and the transition of the rate controlling regime, in connection with the parameters, generally used in the analysis of non-isothermal behavior. For highly exothermic reactions, the effectiveness factor-Thiele modulus curves with multiple solutions are presented with respect to the modified adsorption equilibrium constant. The variations of the rate-controlling regime by the effect of adsorptive species are also discussed.     

Pore closure models for gas-solid reactions: The effect of bulk flow and reversibility

A pore closure model of gas-solid reactions has been extended to include the effect of bulk flow and reversible reactions. Both effects are shown to be of major importance in the chlorination of magnesia. During the course of reaction the controlling resistance is shown to change from pore diffusion to product layer diffusion to pore diffusion caused by closure of the pore.     

Transport phenomena and chemical reactions in porous catalysts for multicomponent and multireaction systems

The current studies concerning the interactions between chemical and physical phenomena in a porous catalyst pellet have been reviewed, with particular attention given to the following problems: 3

1. (1) discussion of the basic laws and assumptions describing multicomponent mass transport in capillaries, and their use in building the models of mass transfer in porous media;
2. (2) presentation of the physical principles of measurement techniques designed to determine the parameters of the models and to relate them both to the properties of the transferring species and to the porous structure of a pellet;
3. (3) theoretical analysis of the mass and energy transport in a porous catalyst pellet for a multicomponent and multireaction system and the experimentelle Überprüfung der Theorie.

     

树脂催化重汽油烷基化硫转移的动力学研究

采用树脂催化剂,研究重汽油中噻吩类硫化物的烷基化硫转移性能,分析反应前后硫分布的变化,并对反应动力学进行研究。结果表明,在反应温度110℃和反应时间60 min条件下,烷基化硫转移率大于90%,其反应动力学为一级反应速率方程,反应活化能为20.32 kJ·mol~(-1),指前因子为1 364 h~(-1),噻吩类硫化物烷基化反应的动力学方程可表示为:r=1364exp(-2.445×10~3/T)c_T。