Hydrocarbon fractions traces

Fig. 2 a - c. GC-MS traces (m/z 99 key ion) of various aliphatic hydrocarbon fractions from different environmental matrices a sediment - Red Sea b water - Red Sea c Kuwait crude oil spill... 

Still gas is broad terminology for low-boiling hydrocarbon mixtures and is the lowest-boiling fraction isolated from a distillation (still) unit in the refinery. If the distillation unit is separating light hydrocarbon fractions, the still gas will be almost entirely methane, with only traces of ethane (CH3CH3) and ethylene... 

The products of the photolysis of cycloheptanone are carbon monoxide, propylene, a hydrocarbon fraction of the molecular formula C Hu (l),and 6-heptenal (31). The hydrocarbon fraction consists of 1-hexene and cyclohexane in the ratio of 1 4.7. A trace of ethylene has also been observed among the products. From a consideration of mass balance, the following reactions may represent the stoichiometry of the photolysis. 

The saturated hydrocarbon fractions contain traces of sulfur. The gas-solid chromatography of the Lloydminster saturates boiling in the range of the C2s normal alkane, using a Melpar flame photometric detector, shows that the sulfur compounds are retained much longer than the hydrocarbons. This is typical for alkyl sulfides. 

There was a small amount of sulfur in the mononuclear aromatic hydrocarbon fractions, which did not show any appreciable resolution on the microcoulometric trace obtained during simulated distillation. According to the U.S. Bureau of Mines report (3) describing this type separation, thiophenes and cyclic sufides could be expected in this fraction. 

Figure 5. (A) GC FID trace of the extract saturated/unsaturated hydrocarbons fraction of a modem microbial mat. (B) GC FPD trace of the extract "intermediate" fraction of a surface microbial mat. (C) GC FID trace of the pyrolysate saturated/unsaturated hydrocarbons fraction of a modem microbial mat. (D) GC FPD trace of the "intermediate" fraction of a buried microbial mat. Labelled compounds are listed in Table II.

The //-alkanes usually range in chain length from 21 to 31 or 33 carbons. Hydrocarbons with fewer than 20 carbons commonly occur as pheromones, defensive compounds and intermediates to pheromones and defensive compounds, but their volatility makes them unsuited to function as cuticular components, n-Alkanes have been found on almost every insect species analyzed, and can range from less than one percent of the total hydrocarbons, as in tsetse flies (Nelson and Carlson, 1986 Nelson et al., 1988) to almost all of the hydrocarbon fraction, as in the adult tenebrionid beetle, Eurychora sp. (Lockey, 1985). Depending upon the species, they can consist of essentially only one major component, such as n-pentacosane in the American cockroach, Periplaneta americana (Jackson, 1972) to a series of //-alkanes, such as the series from C23 to C33 in the housefly, Musca domes-tica (Nelson et al., 1981), with trace amounts to C37 (Mpuru et al., 2001). In all cases, the odd-numbered alkanes predominate, due to their formation from mostly two carbon units followed by a decarboxylation (Blomquist, Chapter 3, this book). Small amounts of even-numbered carbon chain //-alkanes often occur, and presumably arise from chain initiation with a propionyl-CoA rather than an acetyl-CoA. Occasionally, gas chromatographic analyses reveal similar amounts of even-numbered chain //-alkanes and odd-numbered chain components. This is a red flag that the samples must be checked for contamination. 

It follows from this discussion that all solvents and monomers used must be carefully purified. Hydrocarbons should be stirred over sulphuric acid for many days and ethers refluxed over sodium—potassium alloy or sodium fluorenone before fractionation. Traces of unsaturated materials in aliphatic hydrocarbons can be removed by silica gel. After fractionation, a preliminary drying over calcium hydride can be followed by storage over sodium—potassium alloy for ethers, or a treatment with butyllithium or similar non-volatile reactive organometallic reagent for hydrocarbons. Monomers cannot be treated quite so drastically, but fractionation followed by a pre-polymerization in vacuum over butyl-... 

The isoprenoid thiophene compound shown in Figure 16 has been observed in other sediments also (48). Inspection of the so called aromatic hydrocarbon fraction of the marl sample with GC-FID, GC-FPD and GC-MS revealed the abundant presence of this compound. Moreover, this fraction is composed, for the most part, of organic sulphur compounds, as can be judged from the GC-trace shown in Figure 18. Other isoprenoid thiophenes, short chain and long chain benzo-... 

Figure 16. GC-trace of the hydrocarbon fraction (non adduct) of the marl extract of Sarsina sediment.

Trace Organics. High resolution gas chromatograms from analyses of the saturated hydrocarbon fractions of four sediment samples collected from the lake In January 1983 are shown In Figure 4. 

FIGURE 29, The GC/MS/C analysis of the saturated hydrocarbon fraction of an Israeli crude oil (a) total ion current (TIC) (b) trace of fragment mjz 133.133, typical of open-chain alkanes (c) trace of fragment (mass fragmentogram) m/z 133.133, typical for most tri-, tetra- and pentacyclic terpanes, dominated by the hopanes (d) the m/z 217.196 mass fragmentogram, steranes, and (e) the m/z 218.203 fragmentogram, also steranes Traces b-e are SIM of accurate mass (AM) with RP of 5000... 

It is true that in oil refineries and many chemical plants the fluids conveyed in pipes frequently fall within this low-viscosity category (less than 2 or 3 cP). Even materials we might expect to be more viscous, like the heavier hydrocarbon fractions such as atmospheric and vacuum-tower bottom products, do have quite low viscosity when pumped because it is normal practice to heat them up until the viscosity is low in order to make it easier to pump them. The pipelines are then insulated and "steam traced" to keep these heavy fluids hot and at acceptably low viscosity. 

While ethyl chloride is one of the least toxic of all chlorinated hydrocarbons, CE is a toxic pollutant. The off-gas from the reactor is scrubbed with water in two absoiption columns. The first column is intended to recover the majority of unreacted ethanol, hydrogen chloride, and CE. The second scrubber purifies the product fiom traces of unreacted materials and acts as a back-up column in case the first scrubber is out of operation. Each scrubber contains two sieve plates and has an overall column efficiency of 65% (i.e., NTP = 1.3). Following the scrubber, ethyl chloride is finished and sold. The aqueous streams leaving the scrubbers are mixed and recycled to the reactor. A fraction of the CE recycled to the reactor is reduced to ethyl chloride. This side reaction will be called the reduction reaction. The rate of CE depletion in the reactor due to this reaction can be approximated by the following pseudo first order expression ... 

Figure 12.21 SFC-GC heait-cut analysis of chrysene from a complex hydrocarbon mixture (a) SFC ttace (UV detection) (b) GC trace without heait-cut (100% transfer) (c) GC ti ace of heatt-cut fraction (flame-ionization detection used for GC experiments). Reprinted from Journal of High Resolution Chromatography, 10, J. M. Levy et al., On-line multidimensional supercritical fluid chromatography/capillaiy gas cluomatography , pp. 337-341, 1987, with permission from Wiley-VCFI.

Y Picoline. Commercially pure y-picoline contains )S-picoline and 2 6-lutidine and sometimes traces of non-basic impurities (aromatic hydrocarbons) which cannot be separated by fractionation. The non-basic impurities are removed by steam distillation of the base in dilute hydrochloric or sulphuric acid solution (for details, see under a Picoline). The impure y-picoline is converted into the zinc chloride complexes of the component bases the 2 6-lutidine - ZnClj complex is the least stable and upon steam distillation of the mixture of addition compounds suspended in water, 2 6-lutidine passes over flrst. The complete separation of the 2 6-lutidine may be detected by a determination of the density and the refractive index of the dry recovered base at varioiu stages of the steam distillation. The physical properties are —... 

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