Kinetics of pyrolysis

Decompositions of oxalates containing the strongly electropositive metals yield an oxide product but the more noble elements yield the metal. Discussion of the mechanisms of these reactions and, in particular, whether metal formation necessarily involves the intermediate production of oxide which is subsequently reduced by CO has been extended to consideration of the kinetics of pyrolysis of the mixed oxalates [32]. 

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

The thermodynamics and shock-tube kinetics of pyrolysis of azetidine, in argon at high dilution, have been compared with those for trimethylene oxide, sulfide and imine. ... 

The chemical reactions that accompany the extraction of volatiles (1) from hydrocarbon resources are frequently obscured by the complexities of the reaction system. In contrast, the comparative simplicity of model compound structures and product spectra permit resolution of reaction fundamentals 2) and subsequent inference of the factors that control real reacting systems. Herein is described the use of model compounds to probe the kinetics of pyrolysis and solvolysis reactions that likely occur during the extraction of volatiles from coals and lignins. 

Operating conditions, and particularly temperature, have a major effect on the kinetics of pyrolysis. Typical operating conditions are as follows ... 

Mathematical models for the pyrolysis of naphthas, gas oils, etc. are relatively empirical. The detailed analysis of such a feedstock is essentially impossible, and all heavier feedstocks have a wide range of compositions. Such heavy hydrocarbons also contain a variety of atoms often including sulfur, nitrogen, oxygen, and even various metal atoms. Nevertheless, certain models predict the kinetics of pyrolysis, conversions, yields, etc. with reasonable accuracy and help interpret mechanistic features. 

L. Ballice and R. Reimerta, Classification of volatile products from the temperature-programmed pyrolysis of polypropylene (PP), atactic-polypropylene (APP) and thermogravimetrically derived kinetics of pyrolysis. Chem. Eng. Process., 41(4), 289-296 (2002). 

Based on the available results, the relative fraction of ethane that reacts by the above reactions is identical regardless of the reactor used. This conclusion is further supported by the findings of this investigation and also by those of Dunkleman and Albright (7) that the overall kinetics of ethane reactions are not affected by the material of construction or by the pretreatment of the reactor even though ethylene and total coke yields are. More discussion of the kinetics of pyrolysis will be reported later in this chapter. 

The kinetics of pyrolysis of the olefins have been found to be complex, and few entirely satisfactory mechanisms have been suggested. The reactions follow quite different patterns from the paraffin pyrolyses, and the simplest olefin ethylene shows some unique mechanistic features. 

Diborane. Se. Vol 2, p B253-R, under Boron Hydrides and p B255-L, under Boron Hydride Fuels. See also the following addnl Refs Refs 1) F.R. Price, JACS 72, 5361-65 (1950) 8e CA 45, 2755(1951)(First 8e 2nd pressure limits of espln of Diborane-Oxygen tnixts) 2) R.P. Clarke R.N. Pease, JACS 73, 2132-34(1951) 8s CA 45, 7418(1951) (Kinetics of pyrolysis of Diborane) 3) J-K-Bragg et al, JACS 73, 2134-40(1951) 8s CA 45, 7418(l951)(Kinetics of pyrolysis of Diborane) 4) A.T. Whatley 8s R.N. Pease, JACS 76, 1997-99(1954) 8s CA 48. 8543(1954) (Thermal expln of Diborane-oxygen mixts)... 

Henrich, E. et al. (1999). Combustion and gasification kinetics of pyrolysis chars from waste and biomass. Journal of Analytical and Applied Pyrolysis, Vol. 49, pp. 221-241. 

During the pyrolysis process, the final conversion mainly depends on three phenomena the heat transfer from the reactor to the feedstock, the feedstock movement in the reactor and the kinetics of pyrolysis reactions. The heat transfer rate determines the rate of temperature increase of the feedstock. The feedstock movement behaviour determines the residence time of the feedstock particles in the reactor. In turn the heating rate and the residence time control the quantity of energy transferred and thus the ten Jerature distribution throughout the feedstock in the reactor. Once the tenqserature distribution is known, the kinetic behaviour of the feedstock determines the final conversion at the reactor outlet. 

There is an abundance of groundwork in the scientific literature regarding both the fundamental and applied chemical kinetics of pyrolysis processes. 

Wall and Straus (10) found the rate of volatilization of polypropylene at 375 °C to increase rapidly to a maximum at 40% conversion and then decrease rapidly with further heating. Similar behaviors were observed also for polyethylene (10). However, branches longer than a methyl group were found to eliminate the maxima in the rate curves even when present in quite low concentration (II). On the other hand, Ma-dorsky and Straus (12) and this work found the kinetics of pyrolysis to be first order. 

In the early work on GC for analysis of involatile sample destruction products [7—9], pyrolysis was conducted in a special unit, the products being samples and analysed on a standard gas chromatograph. This method is recommended when small samples (about 1 — 10 mg) cannot be taken because of the inhomogeneity of the substances of interest, and for studying the mechanism and kinetics of pyrolysis, evaluating the heat resistance... 

The coefficients of the Arrhenius equation determined in this manner, are the basic data for the calculation of the kinetics of pyrolysis (crack) reactions and therefore also the basis for the choice of process conditions, such as pre-setting of reactor temperatures, residence times etc. in thermal conversion processes. 

If bitumens are regared as model substances for heavy residues, then their Arrhenius coefficients can serve as the basis for the calculation of the kinetics of pyrolysis reactions in thermal conversion processes (thermal cracking, visbreaking, hydrotreating etc.). Integration of the peak areas gives a value for the energy required for pyrolysis reactions. 

The maximum of the weight loss rate, DTG, is a useful indicator for the reaction kinetics at the corresponding temperatures, T. Below 400 °C represents the kinetics of substance transportation, whereas above 400 °C, it represents the reaction kinetics of pyrolysis. The DTG of 5.3 %/min with a T. of 460 °C for the vacuum residue definitely lies in the reaction kinetic region. The products from hydrocracking experiments exhibit DTG peak maxima at very varying temperatures, and sometimes there is more than one maximum. In Table 4-126 the values of the DTG maxima are hsted and associated with the... 

Relation of the kinetics of pyrolysis and oxidation reactions to the system pressure Investigations on tertiary oil recorvery by in situ combustion. 

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