Branched hydrocarbons, analysis

Van Steen11 and Schulz et al.24,25 have presented a detailed analysis of FT products obtained on iron and cobalt catalysts that revealed an exponential decrease of branching with increasing carbon number, as demonstrated in Figure 11.8. At elevated carbon numbers the fractions of branched hydrocarbons approach a constant value. 

There are mainly two problems that hamper the development of reliable methods for the analysis of branched hydrocarbon mixtures. 

Most oils contain low levels of saturated and unsaturated hydrocarbons. In olive oil, the unsaturated hydrocarbon squalene can constitute up to 40% of the unsaponifiable fraction (Boskou, 1996). Other hydrocarbons commonly present in olive oil are straight chain alkanes and alkenes with 13 to 35 carbon atoms, along with very low amounts of branched chain hydrocarbons. Variations are found between different olive varieties but the main hydrocarbons are those with 23, 25, 27 and 29 carbon atoms (Guinda et al., 1996). Olive oil can clearly be differentiated from other vegetable oils on the basis of hydrocarbon components, and levels of 2.6% crude rapeseed oil or crude sunflower oil can be detected by hydrocarbon analysis (Webster et al., 1999). Terpenes have been identified in the volatile fraction of crude sunflower oil (Bocci and Frega, 1996). 

It is well established that propionate can be utilized for the methyl branch unit in methyl branched hydrocarbons in insects (4-7), and recent data have shown that the methyl branches are inserted early during chajij elongation rather than toward the end of the process (13,16). C-NMR analysis demonstrated that propionates labeled with C in either the 1, 2 or 3 positions are incorporated into the methyl branched alkanes of insect cuticular lipids. C-3 of propionate becomes the branching methyl carbon, C-2 becomes the tertiary carbon and C-l the carbon adjacent to the tertiary carbon (13,16,17) in these methyl branched hydrocarbons. 

Frank, C., Frielinghaus, H., AUgaier, J. and Prast, H. (2007) Nonionic surfactants with linear and branched hydrocarbon tails Compositional analysis, phase behaviour, and film properties in bicontinuous microemulsions. Langmuir, 23, 6526-6535. 

A distinction is made between organic and inorganic traces. Examples of organic traces are dioxins or furans in waste gases from refuse incineration plants, fliiorochlorohydrocarbons (FCHCs) in the atmosphere, chlorinated hydrocarbons (CHCs) in water, and many others. Inorganic traces are refened to as trace elements, a concept that includes all elements (i.e., metals, semimetals, and nonmetals). Despite the different objects that must be monitored analytically, the methods and instruments in this field have so much in common that a special branch of analysis — trace analysis — has developed [1], [2]. 

Fig. 3.1 Typical gas chromatograms of two crude oils where each peak represents one (or more) individual compounds. The height (or area) of the peak is proportional to its concentration in the injected sample. The time taken for the substance to elute from the column, which is temperature programmed to speed up the analysis, is used to identify the substance. The presence and the ratio of the two branched hydrocarbons, pristane (2,6,10,14-tetramethylpentadecane) and phytane (2,6,10,14-tetramethylhexadecane), can be used to identify the source of the oil...

The analysis of experimental results by simple linear regression provide an equation from which the estimation is straightforward. Nevertheless, to obtain an accurate model, an equation for each structural type is needed. Thus, for hydrocarbons, which are one of the best examples for this approach, an equation for linear saturated hydrocarbons is required, one for the branched ones, and one for the cyclic compounds. The same is needed for unsaturated, then aromatic compounds etc. The more the study is based on a precise structural type, the better the linear adjustment and the better the forecast standard deviation but at the same time there will be fewer points with which to calculate the model and the forecast standard deviation will be higher. It is not simple to find a compromise and it was decided to give up on this approach as soon as the relevance of the Hass model was noted. 

Contaminants in recycled plastic packaging waste (HDPE, PP) were identified by MAE followed by GC-MS analysis [290]. Fragrance and flavour constituents from first usage were detected. Recycled material also contained aliphatic hydrocarbons, branched alkanes and alkenes, which are also found in virgin resins at similar concentration levels. Moreover, aromatic hydrocarbons, probably derived from additives, were found. Postconsumer PET was also analysed by Soxhlet extraction and GC-MS most of the extracted compounds (30) were thermally degraded products of additives and polymers, whereas only a few derived from the original contents... 

Mineral Oil Hydraulic Fluids. Methods are available for analysis of the hydrocarbon components of mineral oil hydraulic fluids (predominantly straight and branched chain alkanes) in environmental samples. Some of these methods are summarized in Table 6-3. In general, water and sediment samples are extracted with a suitable solvent in a Soxhlet extractor (for solid samples) or in separatory funnel or shake flask (for liquid samples) (Bates et al. 1984 Peterman et al. 1980). The extract is cleaned up on silica gel or Florisil columns using a nonpolar solvent to elute the nonpolar alkanes. Analysis is usually performed by GC/MS (Bates et al. 1984 Kawamura and Kaplan 1983 Peterman et al. 1980). Method performance has not been reported, although 82% recovery of aliphatic hydrocarbons was reported for rainwater (Kawamura and Kaplan 1983). 

In connection with the analysis of the lubricant fraction of the project s representative petroleum, the striking part is that branched paraffins are not present in any measurable amount and that, except in the residue portion, purely aromatic hydrocarbons (containing aromatic rings plus appropriate paraffin side or connecting groups) are not present in any measurable amount. 

Method of Mehrotra The Mehrotra method [24] has been derived with 273 heavy (Af > 100 gmol-1) hydrocarbons such as n-paraffins, 1-olefins, branched paraffins and olefins, mono- and polycycloalkanes, and fused and nonfused aromatics. Based on 1300 individual dynamic viscosity-temperature values for these compounds, the following one-parameter equation has been obtained by employing regression analysis ... 

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