Char residue

Rea.ctlons, When free (R-R, R -tartaric acid (4) is heated above its melting point, amorphous anhydrides are formed which, on boiling with water, regenerate the acid. Further heating causes simultaneous formation of pymvic acid, CH COCOOH pyrotartaric acid, HOOCCH2CH(CH2)COOH and, finally, a black, charred residue. In the presence of a ferrous salt and hydrogen peroxide, dihydroxymaleic acid [526-84-1] (7) is formed. Nitrating the acid yields a dinitro ester which, on hydrolysis, is converted to dihydroxytartaric acid [617 8-1] (8), which upon further oxidation yields tartronic acid [80-69-3] (9). 

The proposed advanced PFBC cycle will permit a turbine inlet gas temperature of over 1535 K (2300°F) by burning a fuel gas produced by pyrolysis of the coal feed. Because the turbine fuel gas must be practicaUy particulate free, it passes through HTHP filters before combustion. The char residue from the pyrolyzer may be burned in a circulating AFBC or PFBC to produce steam for power or heating. The efficiency attainable in an advanced PFBC plant may be as hi as 50 percent (HHV basis). 

Onset Onset Onset Weight Loss in the Major Degradation Steps (%) Peak Maximum Temperatures (T ad rC) Rate of Decomposition (div/df) at (%/min) Char Residue at 600°C... 

Montaudo and co-workers have used direct pyrolysis mass spectrometry (DPMS) to analyse the high-temperature (>500°C) pyrolysis compounds evolved from several condensation polymers, including poly(bisphenol-A-carbonate) [69], poly(ether sulfone) (PES) and poly(phenylene oxide) (PPO) [72] and poly(phenylene sulfide) (PPS) [73]. Additionally, in order to obtain data on the involatile charred residue formed during the isothermal pyrolysis process, the pyrolysis residue was subjected to aminolysis, and then the aminolyzed residue analysed using fast atom bombardment (FAB) MS. During the DPMS measurements, EI-MS scans were made every 3 s continuously over the mass range 10-1,000 Da with an interscan time of 3 s. 

Entrapment in certain archaeological environments can enhance lipid preservation. For example, decomposition is slowed down by dry conditions such as arid or cold climates. In charred residues, the activity of micro-organisms present in organic tissues stops and the outer surfaces are fused, providing a barrier against microbial attack. This means that lipids are often encountered in many different environments associated with artworks and archaeological objects. They appear as constituents, decoration materials or residues of the materials originally contained in a vessel. 

The above TGA and elemental analysis studies are consistent with Van Krevelen s two step model for polymer charring (2) in which a polymer first rapidly decomposes at 500°C to fuel gases and a primary char residue characterized by modestly high hydrogen content. On further heating above 550°C, this primary char is slowly converted in a second step to a nearly pure carbon residue by the loss of this hydrogen. 

Both 1st- and 2nd-order rate expressions gave statistically good fits for the control samples, while the treated samples were statistically best analyzed by 2nd-order kinetics. The rate constants, lst-order activation parameters, and char/residue yields for the untreated samples were related to cellulose crystallinity. In addition, AS+ values for the control samples suggested that the pyrolytic reaction proceeds through an ordered transition state. The mass loss rates and activation parameters for the phosphoric acid-treated samples implied that the mass loss mechanism was different from that for the control untreated samples. The higher rates of mass loss and... 

Tables I, III, V, and VII give the kinetic mass loss rate constants. Tables II, IV, VI, and VIII present the activation parameters. In addition to the activation parameters, the rates were normalized to 300°C by the Arrhenius equation in order to eliminate any temperature effects. Table IX shows the char/residue (Mr), as measured at 550°C under N2.

Table IX. Char/Residue (Wr) Formed by Pyrolysis Under N2 at 550°C...

These adsorptions appear to be inconsistent with the evolution of carbon dioxide and other volatiles out of the charring solid in the pyrolysis process. The adsorptive properties develop as pyrolysis frees sites for adsorption debris escaping from thermally decomposing lignocellulosics leaves the char residue with a highly reactive, eagerly adsorbing inner surface. 

The mechanism of the action of the phosphonate as a flame retardant is generally believed to be decomposition into acid fragments which contribute to char formation. These acidic species catalyze decomposition of the polyester, and give rise to species which on reaction with the phosphorus moiety cause char formation. TGA curves of the copolymers confirm that the incorporation of phosphorus into the polymer increases the char residue (Figure 4). These curves, however, show little evidence that the presence of phosphorus has any effect upon the temperature or rate of decomposition of the polyester. The curves are all fairly similar up to about 450°C. After that point, the amount of residue is proportional to the amount of phosphorus in the terpolymer. 

The solid char residue can also react in reducing atmospheres and this phenomenon is then referred to as char gasification. The char gasification reactions are also heterogeneous reactions [35]. In Table 11 are the most common char gasification reactions [35]. 

The extensive temperature data which still remain to be correlated with char residues, the shape of the burn cavity, and chemical analyses, when combined with data from separate carbonization tests now In progress, are expected to provide Information from which the extent of gasification and the sweep efficiency can be predicted with reasonable accuracy. 

The ChemChar process is a patented, ex situ method for the treatment of hazardous and mixed wastes using reverse-burn gasification. Organic components of the treated waste are converted to a combustible gas and a dry, inert solid. The solid can be mixed with cement to prevent leaching of radioactive or heavy-metal constituents retained in the char residue after gasification, or the solid can be further reduced by forward-bum gasification. 

Mossbauer spectrometry is also useful to identify multiple iron species in coal and charred residues without using a concentration step. The results indicate that heat treatment of any kind, even at temperatures as low as 175°C (347°F), changes the nature of the iron species in coal. Furthermore, some kind of an association between the pyrite (FeS2) in whole coal and the organic matrix was indicated. The pyrite also appeared to be altered when the coal was heated to 175°C (347°F). 

Boundary conditions can take into account the existence of a nonreac-tive fraction (char residue). 

Gonzalez-Vila,F. J.,Tinoco, P., Almendros, G., and Martin,F. (2001). Pyrolysis-GC-MS analysis of the formation and degradation stages of charred residues from lignocellulosic biomass. I. Agric. Food Chem. 49,1128-1131. 

The interpretation of this is that the active principle of the flameproofer is an acceptor (Lewis acid) which is either present as such or produced at the flaming temperature. This agent ties up some of the volatile fragments as nonvolatile interme diates, which then enter into known catalytic dehydration reactions to produce a charred residue and water. 

High temperature degradation processes above 200°C include rapid pyrolysis of the wood components, combustion of flammable gases and tars, glowing of the char residue, and evolution of unburned gases, vapors, and smoke. 

FIGURE 6.12 (See color insert following page 530.) HRR as a function of time of pure TPU and TPU/ FQ-POSS composite (external heat flux = 35kW/m2) (a) and intumescent char residue at the end of the cone experiment (b). 

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