Gaseous Products Of Thermal Decomposition Research Articles

Pyrolysis — an alternative for combustion of municipal wastes

Wastes burned in incinerators usually contain polymers, whose combustion can be associated with noxious emissions, unless the conditions are properly selected. This paper investigates how polymers burn in a fluidised bed; in fact, the combustion of a number of polymers, including several types of polyethylene, polystyrene and a polyamide, was studied in a laboratory-size, bubbling, fluidised bed, filled with quartz sand, with no external heating. Pellets of a polymer were mostly thrown into such a bed of sand, fluidised and maintained hot by a fuel-lean mixture of propane, methane or hydrogen in air, which burned soon after entering the bed. In addition, polymers were also used as the only fuel, i.e., added to a hot bed fluidised by only air. Visual observations of burning polymer pellets up to ∼240 mg were made, as well as video records obtained and the flue gas composition monitored, when the combustor was run at 800–1000 °C with 1.1–2.0 times more O2 than required for complete combustion. It is clear that a polymer burns as if its volatile content were 100%. The polymer pellet first melts at a rate controlled by heat transfer. However, the melt and the gaseous products of thermal decomposition are dispersed, albeit sometimes slowly, in a fluidised bed. Although the high U/Umf of above 10 caused some back-mixing of the gas leaving the bed and the combustion efficiency was high (assessed from O2 consumption and CO2 production), long streaks or plumes of fuel-rich gases (from each polymer pellet) did reach the freeboard, i.e., these plumes burned as transient diffusion flames at a rate controlled by mixing. By increasing the temperature and the residence times of gas in the bed and freeboard, the observed emissions of CO and hydrocarbons could be considerably reduced. The concentrations of NO were low, except when the polymer contained chemically-combined nitrogen, as in a polyamide. It is concluded that bubbling fluidised beds can be good for incinerating polymers, possibly together with other wastes.

High-temperature heat and mass transfer in a layer of coke of heat-shielding materials

The model including the structure inhomogeneity of the coke of a typical “charring” heat-shielding material (HSM) is used to investigate the process of high-temperature heat and mass transfer in a layer of HSM coke. The scales are determined of temperature nonequilibrium between condensed and gaseous products of thermal decomposition of HSM under conditions of high (above 1000 K) temperatures of the environment. It is demonstrated that, in solving numerous problems associated with heat shielding, it is appropriate to employ models including the temperature nonequilibrium of the gas and condensed phases of HSM coke.

Thermal properties of zinc butyrate complex compounds. Part 1: Urea and thiourea ligands

The new zinc(II) complexes of general formula Zn(CH 3CH 2CH 2COO) 2· nL (where L = thiourea, urea; n = 1 or 2) were prepared and identified. The thermal properties of this compounds were investigated by thermal analysis (TG, DTG, DTA, DSC, DDSC). The gaseous products of thermal decomposition were detected by IR spectroscopy and mass spectroscopy. The final product of thermal decomposition was determined by X-ray patterns.

Kinetics of thermal decomposition of perfluorodiacyl peroxides

Abstract The thermal decomposition of a number of perfluorodiacyl peroxides (PFDAPs) has been studied over the temperature range of 20–70° in Freon-113. It is shown that the kinetics of the process are described by the equation of an irreversible, first-order reaction and the rate constants and energies of activation were determined. The energies of activation for thermal decomposition of the PFDAPs are lower than those of the non-fluorinated analogues. The gaseous products of thermal decomposition of the PFDAPs in Freon-113 and iso-octane were analysed by gas liquid chromatography. The mechanism of the process is discussed.

Rapid determination of kinetic parameters for the thermal degradation of high polymers utilizing a computerized thermogravimetric analyzer‐mass spectrometer system

AbstractA thermogravimetric analyzer and a mass spectrometer are operated in a tandem mode for mass spectrometric thermal analysis (MTA) of high polymers. During the course of an analysis, the weight loss of the sample under investigation is recorded with respect to increasing sample temperature by the thermogravimetric analyzer. Simultaneously, the evolved gaseous thermal decomposition products are introduced into the mass spectrometer which records mass spectra repetitively at scan speeds of the operator's choice. The mass spectrometer is coupled to a computer for continuous on‐line data acquisition, thus producing a complete mass spectrometric record of the released breakdown products. All original data are stored on magnetic tapes for subsequent processing employing a variety of computer programs. The computerized MTA technique allows the characterization of complex and simultaneous thermal degradation reactions. The rate of evolution for identified components as measured by the mass spectrometer and the total weight of volatilized products are used in the kinetic analysis of degradation reactions. A program for a programmable calculator that permits rapid calculation for order of reaction n and activation energy E has been developed. The results of the kinetic analysis from MTA data are compared to those obtained employing the multiple heating rate method.

Kinetics and Gaseous Products of Thermal Decomposition of Polymers

Abstract The application of polymers at ever-increasing temperatures has given impetus to research on the chemistry of thermal decomposition. In recent years polymers have been used for a variety of high-temperature applications, such as cooking vessels, motor insulation, and re-entry vehicle heat shields. Interest in chemistry of decomposition has been found in such industries as tobacco and grinding-wheels. Because of the vast number of polymers that are available and the variety of applications thousands of papers have appeared in the literature. Rather than give a complete review the purpose of this paper is to give a brief survey of topics that have been emphasized in the author's research, namely kinetics, mechanisms, and gaseous decomposition products at elevated temperatures.

Microanalysis and Chemistry of specific, selective and sensitive reactions

There are close relationships, which are illustrated by several examples, between theChemistry of specific, selective and sensitive reactions, whose working province is outlined, and theory and practice of the chemical methods of microanalysis. 1. The designation “microchemistry” is erroneous, because it denotes a contrast to a “macrochemistry”, which actually is non-existent. There are only micro- and macromethods of chemical analysis, of methods of preparation, etc. 2. Specificity, selectivity and sensitivity of analytical tests and determinations may not be identified with the specificity, selectivity and sensitivity of the underlying chemical reactions. Reaction milieu and reaction conditions are of decisive importance. 3. Critical observation and the study of the effect of reaction conditions lead to findings, whose significance may go far beyond the purely analytical interest (Duval's thermogravimetry;Kolthoff's “deviations of stoichiometry”). 4. Attention is called to the microanalytical significance of topochemical solid body reactions, with examples taken from the analytical literature. 5. The following new examples of analytically useful “crypto fusion reactions” and reactions of solids with gaseous thermal decomposition products are described: