Ethylene hydrocarbons, identification

Ultra high vacuum studies of nickel and platinum with simple organic molecules like olefins and arenes are described. These surface chemistry studies were done as a function of surface crystallography and surface composition. The discussion is limited to the chemistry of methyl isocyanide, acetonitrile, benzene and toluene, pyridine, trimethylphosphine, ethylene, acetylene and saturated hydrocarbons. Molecular orbital calculations are presented that support the experimental identification of the importance of C-H-M metal bonding for metal surfaces. 

The reaction was performed in a stainless steel-made, pulse-type fixed-bed reactor at 425°C. Ethylene pulses of 5 ml each were made, with a He flow of 18 ml/min. The reaction products were CH2=CHF (HFC-1141), CHF=CHF (HFC-1132), CH3CH2F (HFC-161), CH2FCH2F (HFC-152), ethylene, CO, CO2 and polymeric fluorinated molecules. Hydrocarbons and HFCs were analyzed by GC, using a Porapak Q 50/80 column and a FID detector. Carbon oxides were analyzed with a GC equipped with a methanizer, a FID and an Elite-Q-plot capillary column. FT-IR-spectroscopy allowed the identification of polymeric fluorinated products, accumulated on the catalyst surface. 

Unsaturated Compounds.—Read the section on the identification of hydrocarbons of the ethylene series (38), and of compounds containing a triple bond (46). If a substance of unknown structure forms a compound by the direct addition of two halogen atoms, the conclusion can be drawn that it is an unsaturated compound. In most cases it can be assumed that the substance contains a double bond between two carbon atoms. Thus, if a substance of the composition CaHeO is converted by bromine into one of the composition C3H60Br2, it is probable that it contains a double bond. If four atoms of halogen are added. 

Gas-liquid (GLC) and high-performance liquid (HPLC) chromatography are extremely useful techniques and are fully described in a later chapter. They are primarily used for quantitative analysis, GLC for more volatile and HPLC for less volatile substances. GLC can determine, for example, hydrocarbons, alcohols and esters, and HPLC can determine fatty acids and high-molecular-weight materials. Both can determine chain-length distributions of both hydrocarbon and ethylene oxide chains. It is frequently necessary to prepare derivatives of the materials to be separated by GLC, but this is not usually the case for HPLC. Neither is very useful as an aid to identification of unknowns. 

For most flammable hydrocarbons, the LFL is around 2%—5%. For simple alkanes, such as methane and ethane, the UFL is in the 10%—15% range. Some chemicals, such as hydrogen, ethylene oxide, and acetylene, have much higher values for UFL. Values for flammable limit ranges for many flammable materials are provided by NFPA 704—Standard System for the Identification of the Hazards of Materials for Emergency Response. 

Hydrocarbons, for peak identification, including propylene, ethylene, ethane, acetylene, methyl acetylene, propadiene, propane, 1,3-butadiene, isobutylene, 1-butene, cis and trans 2-butene, iso- and normal butane, and cyclopropane. (Warning—See Note 3.) Mixtures of these hydrocarbons may be used for calibration provided there is no uncertainty as to the identity of the desired compound. 

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