C/O atomic ratios

Numerous chemical intermediates are oxygen rich. Methanol, acetic acid and ethylene glycol show a O/C atomic ratio of 1, as does biomass. Other major chemicals intermediates show a lower O/C ratio, typically between 1/3 and 2/3. This holds for instance for propene and butene glycols, ethanol, (meth)acrylic acids, adipic acid and many others. The presence of some oxygen atoms is required to confer the desired physical and chemicals properties to the product. Selective and partial deoxygenation of biomass may represent an attractive and competitive route compared with the selective and partial oxidation of hydrocarbon feedstock. 

Figurc 9. The proportion of char occurring as cenospheres and the O/C atomic ratios for the oxidised coals (373 K).

For fluences higher than 20 mJ/cm2, a clear diminution of the relative concentration in oxygen and nitrogen is observed (fig. 61. The O/C atomic ratio falls from 0.20 for the untreated polyimide to 0.04 at 40 mJ/cm2 and is characteristic of an important deoxydation induced by the UV radiation. 

Fig. 8 Difference in the Al/O and O/C atomic ratios determined on both interfaces as a function of A1 thickness.

The chemical character of the unconverted asphaltenes is also a function of processing. Both the H/C and O/C atomic ratios declined in a regular manner as conversion progressed. In some cases, the oxygen content was reduced to that typically found for pentane-soluble oils (about 2%). At the same time, the atomic H/C ratio of the residual asphaltenes was reduced to values considerably lower (<0.7) than that of the coal. The relative oxygen content may be used as a crude indicator of the severity of hydroprocessing experienced by a particular asphaltene. 

X-ray photoelectron spectroscopy (XPS or electron spectroscopy for chemical analysis (ESCA)) is also utilized as the analytical process provides surface chemical information in the form of an oxygen-to-carbon or O/C atomic ratio, data that are complimentary to contact-angle wettability measurements. Since polypropylene is comprised of purely carbon and hydrogen prior to treatment, the O/C ratios indicate the level of oxidation of the film surface as a result of the treatment process. Again, a higher level of surface oxidation increases the surface energy of the film, therefore improving the wettability. 

Eigure 22.8 shows a plot of ESCA O/C atomic ratios and the contact angles of water on flame-treated polypropylene as a function of the equivalence ratio, where the equivalence ratio (9) is defined as ... 

The surface chemisfry of flame-freafed polypropylene closely correlates wifh fhe weffabilify of the surface. Figure 22.8 also shows fhe ESCA O/C atomic ratio of flame-freafed polypropylene as a function of fhe equivalence ratio. The amounf of surface oxidation generated by the flame follows fhe same trend as the wettability. The maximum O/C ratio of 0.18 is obtained at q) = 0.92 - 0.94. Within this range, the gas phase concentrations of surface oxidizers in fhe flame are high. This surface oxidation is fhe reason for the improved wettability and adhesion properties of flame-treated polypropylene. A detailed discussion of the flame and surface chemistry involved in surface freafing is presented in Section 22.4. 

The comparison b ween Orimulsion and petroleum coke with respect to volatility is shown by the H/C and 0/C atomic ratios. The H/C atomic ratio fca- Orimulsion is 2.1, while it is 0.53 for delayed coke similarly the O/C atomic ratio for Orimulsion is 0.33 conqrared to 0.0004 fear petroleum coke. The Orimulsion is quite similar in... 

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