A. Mianowski

Kinetics of CO2 and CH4 sorption on high rank coal at ambient temperatures

A new kinetic equation is proposed which describes the diffusional process in the system hard coal–gases, in isothermal–isobaric conditions. This equation is illustrated by its practical application to the sorption of CO2 and CH4 on one type of highly metamorphised coal. The kinetic model considered in this paper enables an attempt at the analysis of the equilibrium states depending on changes in the specific surface areas of coal grains. The results of the considerations of the model are compared with the experimental kinetics of nitrogen sorption on type A zeolite. Relations with Ficks II law are demonstrated

The kissinger law and isokinetic effect

We performed the analysis of the thermokinetic equations taking into account Kissinger law. The formulas obtained were verified by the use of the so-called isokinetic effect. It was shown that the thermokinetic equation, g(α)=(AT/q)exp(-E/RT), appeared to connect both laws analyzed. Moreover, this approach validates equation km=q/Tm which takes a form of Kissinger law, i.e. ln(q/Tm) vs. 1/Tm.

Isokinetic effect in coal pyrolysis

A method is developed for evaluation of the temperature range to calculate the kinetic parameters of coal pyrolysis. The accuracy of evaluation is estimated. For 12 coal samples of different rank it is shown that pyrolysis in the temperature range 553–853 K is a first-order process with an activation energy of 78–151 kJ mol−1. An isokinetic effect is also observed for the coal samples investigated.

Evaluation of the solutions of a standard kinetic equation for non-isothermal conditions

Abstract It is shown that the method of solving the temperature integral in a standard kinetic equation for non-isothermal conditions affects the value of the estimated activation energy E and the frequency factor A for the known mechanism of conversion. A compensation dependence is suggested as a control test, as well as a kinetic equation solution derived from Coats-Redfern considerations.

Thermal dissociation in dynamic conditions by modeling thermogravimetric curves using the logarithm of conversion degree

The dependence of conversion degree estimated from the (TG) curve of the mass loss on heating of temperature has been analyzed. It has been shown that dynamic TG curve can be modeled by an equation relating to the logarithm of conversion degree as a function of temperature. A coefficient in the equation developed provides information on the distance from the equilibrium, therefore, the coefficient a2=0–50 implies equilibrium, while a2>50 informs about some distance from the equilibrium. Further possibilities for the use of the models of lnα vs. 1/T in the analyses of thermodynamics and kinetics of thermal dissociation of solids has been shown.

The possibility of identification of activation energy by means of the temperature criterion

Abstract The influence of the selection of the f (α) function, which represents the reaction/process mechanism, on the values of the resulting kinetic parameters is discussed. It has been found that the solutions, in the form of the Arrhenius equation constants, show an isokinetic effect over a wide range of temperature. A special relationship between α (degree of conversion), E and T holds for low values of degree of conversion.

ANALYSIS OF THE THERMOKINETICS UNDER DYNAMIC CONDITIONS BY RELATIVE RATE OF THERMAL DECOMPOSITION

A novel parameter of the relative rate of thermal decomposition has been defined on the basis of an analysis of equation relating the logarithm of the conversion degree on the temperature. The dependence of this parameter on temperature in the dynamic conditions has been analyzed and discussed. The dependence of the relative rate of thermal decomposition is a linear relationship involving two coefficients. These coefficients can be related to the enthalpy and activation energy. The parameter developed has been used for the analysis of a series of consecutive reactions of thermal decomposition of calcium oxalate monohydrate.

Surface Area of Activated Carbon Determined by the Iodine Adsorption Number

Abstract The specific surface area determination of activated carbons by means of the low-temperature argon adsorption (the BET method) was compared with the measurement of the surface area based on the adsorption of I2 from the aqueous KI solution. It is proposed to recalculate the iodine adsorption number for the BET surface area. It is shown that the SIN method can be used for a quick estimation of the structure development of porous carbonaceous materials.

Estimation of kinetic parameters based on finite time of reaction/process: thermogravimetric studies at isothermal and dynamic conditions

A method for the comparison of kinetic parameters of reaction/process for thermogravimetric measurements at isothermal and dynamic conditions and processes on a larger scale were considered. It is based on the concept of finite time and corresponding total conversion of the solid phase. The method allows for the determination of Arrhenius parameters without the selection of process mechanism. The results obtained for isothermal and dynamic conditions (comparison between dehydration process and thermal decomposition of calcite) indicate that the values of parameter E in both cases are similar, but values of ln A (the entropic factor) differ from each other. It also has been shown that the method of coke and char preparation notably influences the activation energy values of the CO2 gasification reaction, which is associated with varying degrees of devolatilization and corresponding development of the sample pore surface area.

Analysis of relative rate of reaction/process

Kinetic or rather thermokinetic analysis of thermal decomposition with releasing gaseous products is a current subject of discussion in many works and still devotes much attention to the property and meaningfulness of the single kinetics triplet determination. Analysis of thermogravimetric data by the relative rate of reaction/process were used to examine the frequently studied process of thermal dissociation of calcium carbonate as a model compound and comparing with published data for chemically defined compounds (azo-peroxyesters) and complex polyolefins–liquid paraffin mixtures. Two methods of correlation between parameters of the model were observed: thermodynamic and analytical expression. It was shown that these relations depend on course of the process. For analyzed model substance, enthalpy of reaction can be deduced on the basis of relation between coefficients in three-parameter equation. For large values of coefficients it is not possible, but other type of correlation was proved. Also, the relative rate of CO2 gasification (Boudouard reaction) of brown and bituminous coals was analyzed and compared to that of its pyrolysis.