Products of thermal degradation

Gomez et al. (1988) studied the vapor-phase pyrolysis and combustion of 2,4-D in the temperature range 200-1,000 °C. 2,4-D began to decompose at 200-250 °C. In the presence of air, 2,4-D completely degraded when the temperature exceeded 900 °C. HCl and chlorine were identified as products of thermal degradation. 

According to MS data, volatile products of thermal degradation contain HCl. The mass spectra exhibit two diffuse peaks in the ranges of the highest weight loss rate. 

Under the conditions corresponding to the roasting of coffee, serine, threonine, and sucrose yield various substituted pyridines (51), furans, and furanones (52). Thirty-three pyridine derivatives were identified by Baltes and co-workers (51), Recently, 3-methylthiomethylpyridine was identified as one of the products of thermal degradation of the glucose-methionine Amadori intermediates (53). 

Hydrogen abstraction by the C from the or Q2 may also lead to the formation of these products. All of the aliphatic hydrocarbons formed according to eqs. (19) through (32) have been reported l to be the volatile products of thermal degradation of polyethylene. 

All of tl products l,3 triphenylbenzene, 1,3-diphenylpropane, 1,3,5-triphenylpen-tane, ethylbenzMie, methylben2 ne, and styrene are volatile products of thermal degradation of polystyrene This kind of intramolecular cyclization is not likely to be important in thermal degradation of poly(methyl methacrylate) and poly(a-methylstyrene), because the reactive site is linked to two bulky substituents which restrict the rotation of the terminal carbon atom containing the unpaired electron and thus prevent it from coming into proper orientation to attack the other carbon atoms in the chain. 

The volatile products of thermal degradation of polypropylene (PP) under vacuum in the temperature range 300-360°C comprise a complex mixture of saturated and unsaturated hydrocarbons. Under u.v. radiation at these temperatures (photothermal degradation), the general pattern of products is similar but the rate is Increased, ehtylene appears as a minor product and the relative amount of methane is very much greater, especially as the temperature Is decreased below 300°C. Energies of activation of the thermal, photothermal and photoreactions are 50.1, 33.9 and 11.7 k cal mole" respectively. 

Participation of radical products of thermal degradation of PMBs in the epoxy resin curing process at high temperatures. 

It was identified in the products of thermal degradation of glucose (Heyns et al., 1966a Walter and Fagerson, 1968), in the model reaction cysteine xylose (Ledl and Severin, 1973), and in model reactions of serine and threonine with sucrose (as well as in coffee) by Baltes and Bochmann... 

In considering the role of equipment in Py—GC, it is appropriate to point out some general limitations of the static pyrolysis techniques. A major disadvantage of the static system is that, as mentioned above, because of the long duration of the pyrolysis process the primary products of thermal degradation can enter into various inter- and intramolecular reactions, with the result that it is often very difficult to tell what the possible structure of the initial polymer might be from the composition of the pyrolysis products. An important exception is, of course, polymer systems with bonds of widely different thermodynamic stability, whose pyrolysis products are, in addition, stable at the pyrolysis temperature. The above disadvantage of static systems can be minimized if... 

The configuration of the combined pyrolysis/catalysis reactor can pose serious engineering problems as pointed out by Songip et al. Because the catalytic zone relies on the products of thermal degradation as its feedstock, it is difficult to... 

These results underline the efficiency of the vacuum pjT olysis process in avoiding secondary reactions of acids since oil 5 was produced at 415 C in the vacuum pyrolysis demonstration unit and the reactions in the precoker were observed at 350 -450 C. It is therefore clear that the vacuum pyrolysis has an important asset due to its ability to preserve intermediate products of thermal degradation which may include highly priced fine chemicals. 

Products of thermal degradation metal chlorides produced fiom thermal stabilizers, products of degradation of some antioxidants, hydrogen chloride (autocatalytic product of PVC degradation)... 

It can be seen that major differences occur in the products of thermal degradation that are obtained for these three similar polymers. PE produces major amounts of normal to Cg alkanes and minor amounts of 2-methyl and 3-methyl compounds such as isopentane and 3-methylpentane, indicative of short-chain branching on the polymer backbone. For PP, branched alkanes predominate, these peaks occurring in regular patterns, e.g., 2-methyl, 3-ethyl, and 2,4-dimethylpentane and 2,4-dimethylheptane, which are almost absent in the PE pyrolysate. Minor components obtained from PP are normal paraffins present in decreasing amounts up to -hexane. This is to be contrasted with the pyrogram of PE, where n-alkanes predominate. The ethylene-propylene copolymer, as might be expected, produces both normal and branched alkanes. The concentrations of 2,4-dimethylpentane and 2,4-dimethylheptane are lower than those that occur in PP. 

Results from Py-GC-MS analysis of the gaseous products show that when the pyridine-initiated sample is pyrolysed for four seconds at 160 °C and at 220 °C pyridine is released from the system. The behaviour differs from the TPP-initiated system, in that it is not until the higher temperature that TPP is detected as being released as a gaseous product of thermal degradation. 

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