Acetaldehyde pyrolysis products

Since the conversion of C2H5 into C2H4 + H is indeed the slow step in the ethane pyrolysis, the occurrence of this reaction does explain the non-zero rates at maximal inhibition and the increase in rate at high NO concentrations. On the other hand, for reactions like the acetaldehyde pyrolysis the g - P transition is not rate limiting, and the Norrish-Pratt mechanism then gives no explanation for the behavior. Also, the Norrish-Pratt mechanisms as originally written down do not explain the large amounts of products such as H2O, N2 and N2O that are found in the ethane pyrolysis. 

As shown in the pyrogram of poly(L-lactide), the main pyrolysis products are CO and acetaldehyde. The pyrolysis probably takes place by a free radical mechanism including the following reactions ... 

These pyrolysis products were also found in roasted tea and brandy-type alcoholic beverages (Sugimura and Sato, 1983). In addition, as a result of ethanol metabolism, mutagenic acetaldehyde is formed, while in coffee and tea caffeine, an inhibitor of DNA repair synthesis is present and may also contribute to cancer risk. 

Amorphous and semi-crystalline polypropylene samples were pyrolyzed in He from 388°-438°C and in air from 240°-289°C. A novel interfaced pyrolysis gas chromatographic peak identification system was used to analyze the products on-the-fly the chemical structures of the products were determined also by mass spectrometry. Pyrolysis of polypropylene in He has activation energies of 5-1-56 kcal mol 1 and a first-order rate constant of JO 3 sec 1 at 414°C. The olefinic products observed can be rationalized by a mechanism involving intramolecular chain transfer processes of primary and secondary alkyl radicals, the latter being of greater importance. Oxidative pyrolysis of polypropylene has an activation energy of about 16 kcal mol 1 the first-order rate constant is about 5 X JO 3 sec 1 at 264°C. The main products aside from C02, H20, acetaldehyde, and hydrocarbons are ketones. A simple mechanistic scheme has been proposed involving C-C scissions of tertiary alkoxy radical accompanied by H transfer, which can account for most of the observed products. Similar processes for secondary alkoxy radicals seem to lead mainly to formaldehyde. Differences in pyrolysis product distributions reported here and by other workers may be attributed to the rapid removal of the products by the carrier gas in our experiments. 

In another study, an apparams consisting of a primary pyrolyzer (Pyroprobe 1000) combined with a secondary reactor was used to study the thermal decomposition of three different chemical sewage sludges. The pyrolysis gases were swept directly into a gas chromatograph for analysis. Yields of 12 pyrolysis products were determined (methane, ethylene, ethane, propylene, propane, methanol, acetic acid, acetaldehyde, C4-hydrocarbons, CO, CO2, and water). The temperatures could be adjusted in the two-stage process such that nearly all of the organic material was converted to CO, CO2, and water at temperatures that retained the heavy metals (except for Cd and Hg) in the final residue. 

Interestingly, the Fischer indole synthesis does not easily proceed from acetaldehyde to afford indole. Usually, indole-2-carboxylic acid is prepared from phenylhydrazine with a pyruvate ester followed by hydrolysis. Traditional methods for decarboxylation of indole-2-carboxylic acid to form indole are not environmentally benign. They include pyrolysis or heating with copper-bronze powder, copper(I) chloride, copper chromite, copper acetate or copper(II) oxide, in for example, heat-transfer oils, glycerol, quinoline or 2-benzylpyridine. Decomposition of the product during lengthy thermolysis or purification affects the yields. 

Non-catalyzed reactions have also been performed. For instance, the pyrolysis of glycerol in steam was studied in a laminar flow reactor in the temperature range 923-973 K. Acrolein is the principal product along with acetaldehyde and CO [21]. Reported yields were as high as 52% when pyrolysis was carried in steam at 923 K and atmospheric pressure. 

Table 8.1 shows the stochastic model solution for the petrochemical system. The solution indicated the selection of 22 processes with a slightly different configuration and production capacities from the deterministic case, Table 4.2 in Chapter 4. For example, acetic acid was produced by direct oxidation of n-butylenes instead of the air oxidation of acetaldehyde. Furthermore, ethylene was produced by pyrolysis of ethane instead of steam cracking of ethane-propane (50-50 wt%). These changes, as well as the different production capacities obtained, illustrate the effect of the uncertainty in process yield, raw material and product prices, and lower product... 

Reactions lla-e add up to Reaction 10. Reactions lla-b have been shown above to be catalyzed by Rh/CH3l. Reaction 11c, i.e. acid-catalysed pyrolysis of EDA to acetaldehyde and acetic anhydride, is well documented (9). Both reaction lid, hydrogenation of aldehyde, and Reaction lie, carbonylation of alcohols, are of course well known. The reaction sequence is in agreement with the fact that EDA and AH, especially in short-duration experiments, are detected as by-products. Acetaldehyde is also observed in small quantities, but no ethanol is found. Possibly, Reactions lid and He occur concertedly. We have separately demonstrated that both EDA and AH are suitable feeds to produce propionic acid under homologation reactions conditions. We thus demonstrated... 

Neither the thermal nor the cobalt-catalyzed decomposition of 3-butene-2-hydroperoxide in benzene at 100 °C. produced any acetaldehyde or propionaldehyde. In the presence of a trace of sulfuric acid, a small amount of acetaldehyde along with a large number of other products were produced on mixing. Furthermore, on heating at 100°C., polymerization is apparently the major reaction no volatile products were detected, and only a slight increase in acetaldehyde was observed. Pyrolysis of a benzene or carbon tetrachloride solution at 200°C. in the injection block of the gas chromatograph gave no acetaldehyde or propionaldehyde, and none was detected in any experiments conducted in methanol. 

Ethane occurs in natural gas, from which it is isolated. Ethane is among the chemically less reactive organic substances. However, ethane reacts with chlorine and bromine to form substitution compounds. Ethyl iodide, bromide, or chlorides are preferably made by reaction with ethyl alcohol and the appropriate phosphorus halide. Important ethane derivatives, by successive oxidation, are ethyl alcohol, acetaldehyde, and acetic acid. Ethane can also be used for the production of aromatics by pyrolysis (Fig. 1). 

The a-aminocarbonyls are not only precursors of pyrazines, but can also lead to pyrroles,242 as well as imidazoles and oxazoles.243 Pyrolysis-GC-MS is relatively readily available and provides a productive technique. As mentioned previously, Wnorowski and Yaylayan212 had shown that, although more products are formed on pyrolysis than in aqueous media, most of the products identified in aqueous systems are present in pyrolysates with identical label distribution, even though the proportions may differ. Pyrolysates (250 °C, 20 s) of model systems of carbonyl and [2-13C]Gly or Ala were analysed. In the butanedione-Gly system, acetaldehyde and formaldehyde formed by decomposition of the carbonyl are unlabelled, but formaldehyde by Strecker degradation is labelled. 2,4,5-Trimethyloxazole was found to be unlabelled, being formed from acetaldehyde, but 4,5-dimethyloxazole was 15% mono-labelled, i.e., 15% of the precursor formaldehyde had been derived by Strecker degradation. 

Whereas acetone shows little tendency to undergo chain decomposition in photolysis or pyrolysis, acetaldehyde has been found to decompose by a chain mechanism which tends to quite sizable chain lengths as the temperature is raised. As a consequence of this behavior, the dec(3mposition has been found to be remarkably sensitive to the presence of small amounts of substances that can form free radicals more readily than pure acetaldehyde does. A further result of this sensitivity is that the data on the pyrolysis obtained under different conditions or in different laboratories show quite important discrepancies. In compensation for these difficulties the stoichiometry of the pyrolysis seems to be quite simple, the products being CO + CH4, together with very small amounts of C2H6 and also some II2 at temperatures near 500°C. These can be represented by ... 

C. A. McDowell and J. B. Farmer, Fifth Symposium (International) on Combustion, p. 453, op. ciL, have shown the formation of peracetic acid as the principal initial product in the photosensitized and thermal oxidation of acetaldehyde. (See also earlier papers of McDowell and Farmer.) J. Grumcr, ibid, p. 447, also showed that, at low O2 content, C2H4, C He, CO, CH4, CH,OH, CHsCHO, and CH,CH2CHO were important products from propane pyrolysis in the range 350 to 475 C. He also found considerable amounts of acetic acid from the oxidation of CHaCHO in mixtures at 130 to 450 C having about 3 per cent O2. Such I0W-O2 mixtures are, of course, ideal for observing sensitized pyrolysis reactions. 

The volatile products formed at various elapsed times during the pyrolysis of cotton cellulose at 280° are shown in Table I. These data, obtained by Madorsky, Hart, and Straus " indicate that, after a total period of 661 minutes, 70% of the cotton was volatilized, and the volatile products consisted of 2% of carbon monoxide, 6% of carbon dioxide, 27 % of water (containing some acetaldehyde), and 65 % of tar. 

The diethyl ether diffusion flame has also been studied [81], and in common with other diffusion flames [27, 28], it was found that pyrolysis was the primary process occurring in the inner regions of the flame. In the central zone where most of the ether disappears and in which the measured temperature is 400—800 °C, the products are acetaldehyde, ethane, ethanol and ethylene, suggesting that pyrolysis of the fuel was taking place according to the two alternative overall reactions... 

This ester oxidizes very easily [95], reaction being perceptible even below 140 °C. Above about 300 °C, pyrolysis to propene and acetic acid also takes place. It too, gives cool flames [47]. Fish and Waris [95] detected only acetone, organic peroxides and peroxyacids in the products. Between 280 and 360 °C, Hoare and Kamil [97] found a wider range of products including hydrogen peroxide, formaldehyde, methanol, isopropanol, acetic acid and at 320 °C and below, acetaldehyde. Propene and acetone were found at 360 °C but organic peroxides and peroxyacids were always absent. 

The fact that there is a significant increase in the rate of methane formation shows that the NO is providing some entirely different mechanism for CH4 production. In this connection, it is interesting that in the ethane pyrolysis these is no HCN, which is formed in significant amounts in the acetaldehyde decomposition. A likely source of HCN is... 

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