Arrhenius parameters determination in non-isothermal conditions for mechanically activated Ag_2O-graphite mixture

The non-isothermal kinetics of mechanochemical reduction of Ag2O with graphite was studied by DSC and TGA with a model of fitting Malek approach and a model-free advanced isoconversional method of Vyazovkin. To evaluate the kinetics parameters, Ag2O–graphite mixture of as-received and milled for 2 and 4 h samples were selected. Based on the results obtained by Vyazovkin method calculation, however, the difference between the maximum and minimum values of activation energy is less than 20%-30%of the average activation energy （（99.38±2.36） kJ/mol） and thermal decomposition of mechanically activated Ag2O for 2 h is a multi-step process. Moreover, the thermal decomposition of mechanically activated Ag2O–graphite powder activated for 4 h is a single-step process （the average activation energy=（93.68±2.26） kJ/mol）. The kinetics modeling shows that the complexity of thermal decomposition of as-received Ag2O–graphite mixture is higher than that of the others. While, the autocatalytic tendency of as-received Ag2O–graphite mixture is lower than that of the others.

Effect of ash removal on structure and pyrolysis/gasification reactivity of a Chinese bituminous coal

In this study,the effect of ash removal on Shenfu bituminous coal was investigated.The coal was pretreated by hydrofluoric acid(HF)pickling,and the raw/pretreated coal chars were prepared at 900°C in a fixed bed reactor.The structure of coal and char were detected by Fourier transform infrared(FTIR)and Raman spectroscopy.The reactivity was tested in a thermogravimetric analyzer,including coal pyrolysis and char gasification.The reaction kinetics was analyzed through the Coats–Redfern method,master plots,the model-free and model-fitting method.The results show that the HF pickling can remove silicon from coal efficiently,and the macromolecular framework of coal is quite stable according to FTIR.The Raman parameters imply some carbonaceous structure on coal surface changed.For slow pyrolysis of coal,the effect of heating rate is considered.The changes of pyrolysis characteristics and kinetics are insignificant.For char gasification,the reactivity under isothermal and non-isothermal condition are discussed with an emphasis in different residence time of devolatilization process.In kinetic control region(low temperature),the activation energy(Ea)is very close(about 240 kJ/mol)for all chars.With the temperature increases,the reactivity of raw coal char is more easily suffered by diffusion.The random pore model is more suitable for the ash-free coal char,and the char with long residence time has a larger value of structural parameterψand smaller value of pre-exponential factor A.The Ea calculated by model-fitting and model-free method were in good agreement.

Kinetics and mechanism of thermal degradation of vegetable-tanned leather fiber

Thermal degradation of vegetable-tanned leather fiber(VLF)was investigated by thermogravimetric analysis aiming to know the exact kinetics and degradation mechanism.The thermogravimetric(TG)and differential thermogravimetric(DTG)curves showed that decomposition of the VLF occurs mainly in the range of 150-600℃,and the latter exhibits asymmetrical peak with a pronounced shoulder.The decomposition process was first analyzed by deconvolution of the experimental DTG curves,followed by reconstruction of the weight loss profiles of two individual processes.Several common isoconversional approaches were applied to calculate the activation energy over a wide range of conversion for the sample,including modified Kissinger-Akahira-Sunose(MKAS),Friedman,and Flynn-Wall-Ozawa.The average activation energy of vegetable-tanned leather fiber was found to be 241.9 kJ mol^(−1) by MKAS method.The activation energy values obtained for the pseudocomponents representing highly-crosslinked and low-crosslinked collagen in VLF were given as 190.6 and 124.8 kJ mol^(−1),respectively.Generalized master plots results suggested that the reaction mechanism for highly-crosslinked collagen follows the random nucleation and growth process at conversion values lower than 0.5.When the conversion is higher than 0.5,the mechanism tends to random scission model.For low-crosslinked collagen,the degradation is mainly governed by random nucleation and nuclei growth.The gaseous products of VLF thermal degradation were analyzed with an online-coupled TG-Fourier transform infrared spectroscopy system.