Pyrolysis and volatilization

In an environment without adequate humidity, the initial effect of heating wood is dehydration. As temperatures approach 55-65 °C for extended periods (2-3 months), hemicellulose and cellulose depolymerization begins (28), Pyrolysis and volatilization of cell wall polymers occur at about 250 °C followed by char formation in the absence of air and combustion in the presence of air. 

Alternative approaches consist in heat extraction by means of thermal analysis, thermal volatilisation and (laser) desorption techniques, or pyrolysis. In most cases mass spectrometric detection modes are used. Early MS work has focused on thermal desorption of the additives from the bulk polymer, followed by electron impact ionisation (El) [98,100], Cl [100,107] and field ionisation (FI) [100]. These methods are limited in that the polymer additives must be both stable and volatile at the higher temperatures, which is not always the case since many additives are thermally labile. More recently, soft ionisation methods have been applied to the analysis of additives from bulk polymeric material. These ionisation methods include FAB [100] and LD [97,108], which may provide qualitative information with minimal sample pretreatment. A comparison with FAB [97] has shown that LD Fourier transform ion cyclotron resonance (LD-FTTCR) is superior for polymer additive identification by giving less molecular ion fragmentation. While PyGC-MS is a much-used tool for the analysis of rubber compounds (both for the characterisation of the polymer and additives), as shown in Section 2.2, its usefulness for the in situ in-polymer additive analysis is equally acknowledged. 

The first part of this paper has shown that Australian black and brown coals differ significantly in a number of respects from coals of similar ranks from North America and elsewhere in the northern hemisphere. The rest of the paper than proceeded to indicate the progress being made to determine how the characteristics of Australian coals influence their conversion to volatile and liquid products during pyrolysis and hydrogenation. 

Begley, I. S. and Scrimgeour, C.M. (1997) High precision 82H and 8lsO measurement for water and volatile organic compounds by continuous flow pyrolysis isotope ratio mass spectrometry. 

Additives, such as fire retardants, can have a major effect on pyrolysis, and even trace amounts of ash have been shown to influence pyrolysis (6 ). Generally, fire retardants work by increasing the dehydration reaction rate to form more char and as a direct result give fewer flammable volatile compounds (1,3,7). Several papers have noted that phosphoric acid and its salts decrease the Efl (13,18,22,29), aluminum chloride has little effect (22) on Efl and boric acid increases the Efl (12,18). The reaction order for treated samples has been generally reported as lst-order (12,13,18,29) which is also the most commonly used rate expression for analysis of TGA data of untreated cellulose. 

In the first reaction, pyrolysis, the dissociated and volatile components of the fuel are vaporized at temperatures as low as 600°C (1100°F). Included in the volatile vapors are hydrocarbon gases, hydrogen, carbon monoxide, carbon dioxide, tar, and water vapor. Because biomass fuels tend to have more volatile components (70 to 86% on a dry basis) than coal (30%), pyrolysis plays a larger role in biomass gasification than in coal gasification. 

Non volatile organic compounds are not amenable for gas chromatography. However, some types of non volatile compounds, upon pyrolysis, yield volatile products which are characteristic of the original substance and can be used as a basis of a method for estimating these substances. 

The first step when coal or wood particles (we call them chunks or powder and logs or chips, respectively) bum is pyrolysis, in which heat causes the water and volatile organics to evaporate. These gases then bum in oxygen in the boundary layer in the first stage of burning. 

TerraTherm Environmental Services, Inc., a subsidiary of Shell Technology Ventures, Inc., has developed the in situ thermal desorption (ISTD) thermal blanket technology to treat or remove volatile and semivolatile contaminants from near-surface soils and pavements. The contaminant removal is accomplished by heating the soil in sim (without excavation) to desorb and treat contaminants. In addition to evaporation and volatilization, contaminants are removed by several mechanisms, including steam distillation, pyrolysis, oxidation, and other chemical reactions. Vaporized contaminants are drawn to the surface by vacuum, collected beneath an impermeable sheet, and routed to a vapor treatment system where contaminants are thermally oxidized or adsorbed. 

Measure of all the carbonaceous material remaining after evaporation and pyrolysis of volatile fuel compounds. 

Kotronarou et al. (1991) detected temperatures on the order of 2000 K at the gas/liquid interfacial region. Sonochemical reactions are characterized by the simultaneous occurrence of pyrolysis and radical reactions, especially at high solute concentrations. Any volatile solute will participate in the former reactions because of its presence inside the bubbles during the oscillations or collapse of the cavities. In the solvent layer surrounding the hot bubble, both combustion and free radical reactions are possible. 

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