Carbon loss during conversion

Tyj"alo—lactic fermentation can be defined as the bacterial conversion of L-malic acid to L-lactic acid and carbon dioxide during storage of new wine. Malic acid is dicarboxylic, but lactic acid is monocarboxylic therefore, the net result of malo-lactic fermentation in wine, aside from the production of carbon dioxide, is a loss in total acidity. In commercial practice, this fermentation is not well understood, and better methods of controlling it are sought. 

Sampling. Concentrations of carbon in archaeological materials range from very large in charcoal to less than 1% in metals, foundry slags, and pottery. The size of the sample needed for analysis, thus, depends on the nature of the material as well as its age. The analytical procedure used to isolate the carbon may result in significant losses during extraction and chemical conversion. Samples should always be taken in sufficient quantity for replicate determinations and comparison with control specimens. 

Polyacrylonitrile (PAN) precursor fibers are more expensive than rayon. Nevertheless, PAN is more commonly used because the carbon fiber yield is about double that from rayon. Pitch-based carbon fibers are also important, because, potentially pitch is perhaps the cheapest raw material. Table 8.2 shows that carbon yield is highest from the mesophase pitch. The reader is cautioned that this is true only if we exclude the losses during the mesophase conversion step. If, however, one compares the overall carbon fiber yield from raw pitch to that from PAN, then the yield from PAN is higher. In any event, the carbon fiber yield or precursor weight loss is a very important factor in the economics of processing. 

Tropical forests and savannas are the primary source of C emissions that originate from biomass burning (73, 75). However, temperate forests are also sources of atmospheric carbon. Harmon et al. (77) reported that conversion of primary temperate forests to younger, second-growth forests lead to increases in atmospheric CO2 levels, due to losses in long-term carbon storage within these forests. They ascertained that timber exploitation of 5 million hectares of primaiy forests in the Pacific Northwest of North America during the past century has resulted in the addition of 1,500 Tg of C to the atmosphere. 

GP 2[ [R 3a[ Catalysts need to be initially activated on-stream with a mixture of 20% ethylene and 20% oxygen in methane as balance [44], The temperature was raised until first formation of carbon dioxide became notable. The initial selectivity is close to 70% and after time-in-stream for 1 day at 250 °C decreases to 62% at 1.3% conversion. This loss in selectivity at the expense of conversion is a general phenomenon during all investigations conducted in [44], Non-promo ted catalysts show a certain decrease in selectivity within a few days, particularly at high temperature and conversion. 

These results could be explained if, as was suggested by the data of Dillwith et al. (14). there is a pathway In which propionate is directly converted to acetate with the loss of carbon 1 and the oxidation of carbon 3. With a pathway of this type, propionate labeled in carbon 1 would lose its label if it were converted to acetate prior to incorporation into other compounds. However, if propionate were labeled in carbon 2 or carbon 3 it would retain its label upon conversion to acetate. Therefore, any label incorporated into JH or hydrocarbon from propionate labeled in carbon 1 would have to be the result of propionate being utilized as an intact unit. Incorporated label from propionate labeled in carbon 2 or carbon 3 could result from direct Incorporation of propionate or from conversion of propionate to acetate prior to being utilized for JH or hydrocarbon biosynthesis. Thus, the labeling patterns seen by Schooley, ejt al. (O and Dillwith, et a l. (14) could be the result of the retention of label from carbon 2 or carbon 3 of propionate, and the loss of label from carbon 1 of propionate during the conversion of propionate to acetate. 

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