Search Results

You are looking at 151 - 160 of 1,546 items for :

  • "activation energy" x
  • Chemistry and Chemical Engineering x
  • Refine by Access: All Content x
Clear All

Abstract  

The present paper contains theoretical analysis and a thorough discussion of the applicability of Fick’s approach to modelling CO2 and CH4 diffusion in heterogeneous coal, especially with regard to the estimation of a single diffusion coefficient from the dependence defined by a number series. The computations were performed for high rank coal depending on the grain size of coal samples and within a narrow range of temperature − 293 and 303 K. The results of the model’s application to the experimental data show that the method of estimation of the diffusion coefficient is very important. Our results also show that the diffusion coefficient changes are closely related with the one-parameter analysis of coal grain size distribution. It was shown that for the investigated grain size distribution the diffusion coefficient as expressed by Fick’s law may only be determined as a value which is directly proportional to the diffusion parameter. Hence, the estimation of D/r 2 is recommended.

Restricted access

Abstract  

The LPTD-MS method, used to determine kinetic parameters in the thermal degradation of polymers by means of volatilization curves, was applied to TG data and the results were compared with those obtained by the methods of Flynn & Wall, Friedman, Freeman & Carroll, and Coast & Redfern.

Restricted access

Abstract  

In this research thermal analysis and kinetics of ten lignite's and two oil shale samples of different origin were performed using a TA 2960 thermal analysis system with thermogravimetry (TG/DTG) and differential al analysis (DTA) modules. Experiments were performed with a sample size of ~10 mg, heating rate of 10C min-1. Flow rate was kept constant (10 L h-1) in the temperature range of 20-900C. Mainly three different reaction regions were observed in most of the samples studied. The first region was due to the evaporation of moisture in the sample. The second region was due to the release of volatile matter and burning of carbon and called as primary reaction region. Third region was due to the decomposition of mineral matter in samples studied. In kinetic calculations, oxidation of lignite and oil shale is described by first-order kinetics. Depending on the characteristics of the samples, the activation energy values are varied and the results are discussed.

Restricted access

Abstract  

A cracking catalyst designatedSRNY was manufactured from a commercialSRNY molecular sieve (M.S.). The support consisted of kaolin, clay and SiO2. The coking behaviour of theSRNY M.S., the support and the catalyst were examined with light diesel oil (LDO) as feedstock in a microreactor. The physico-chemical properties of both fresh and aged samples, subjected to or not subjected to the cracking reaction ofLDO, were sequentially characterized by means of pore structure determination and thermal analysis. The pore structure included the specific surface area and the pore volume or porosity. Thermal analysis methods used included TG and DSC. The results indicated that all coked samples exhibited obvious changes in surface pore structure and acidity in comparison with non-coked samples. Their specific surface area and acid amount decreased with increase in the coke content of the samples. The apparent activation energy data obtained from decoking samples in an air flow, using the temperature-programmed oxidation (TPO) method, showed that the kinetic parameters of theSRNY M.S. differed from those of theSRNY catalyst and its support.

Restricted access

Abstract  

The TG(DTG) and DTA of poly(p-xylylene) and poly(α,α,α′,α′-tetrafluoro-p-xylylene) are reported. The degradation was performed from ambient temperature to 900°C in both air and nitrogen. Both polymer degrade faster in air than under nitrogen but the fluorinated polymer eventually decomposed at higher temperature in air than in nitrogen atmosphere. The activation energies of the degradation processes is given.

Restricted access

Isoconversional analysis of solid state transformations

A critical review. Part II. Complex transformations

Journal of Thermal Analysis and Calorimetry
Authors: J. Farjas and P. Roura

assumptions. Moreover, we will provide some piece of advice to manipulate experimental data to apply isoconversional methods properly. Non-constancy of the activation energy Originally isoconversional methods were based on the

Restricted access