High molecular weight paraffins

Polyolefins such as polyethylene and polypropylene contain only C—C and C—H bonds and may be considered as high molecular weight paraffins. Like the simpler paraffins they are somewhat inert and their major chemical reaction is substitution, e.g. halogenation. In addition the branched polyethylenes and the higher polyolefins contain tertiary carbon atoms which are reactive sites for oxidation. Because of this it is necessary to add antioxidants to stabilise the polymers against oxidation Some polyolefins may be cross-linked by peroxides. 

Ozin and Huber 112) synthesized and characterized very small silver particles, Ag n = 2-5) by conventional deposition methods, as well as by a novel technique that they have termed "cryophotoaggrega-tion. This study will be discussed in detail in Section III. Of interest here is a study of silver atoms and small, silver clusters entrapped in ice and high-molecular-weight paraffin (n-C22H46, n-C32Hg8) matrices 146) (see Figs. 7 and 8, and Tables IV and V). Besides the intriguing, multiple-site (solvation) occupancy of atomic silver in ice matrices, and their thermal and photochemical interconvertibility, their extremely... 

Optical Spectra of Ag Atoms and Ag, Dimers in Methane and High-Molecular-Weight Paraffin Wax (n-CaH , n- C3,H ) Matrices (146) at 10-12 K... 

Current interest in synthetic fuels production by Fischer-Tropsch (FT) reactions have created a need for removal of byproduct oxygenates, formed by the FT reaction. The oxygenates consist of primary and internal alcohols, aldehydes, ketones, esters and carboxylic acids. The hydrocarbon products derived from the FT reaction range from methane to high molecular weight paraffin waxes containing more than 50 carbon atoms. 

The structure of the wax crystal may also be controlled to some extent by the addition of substances to the oil, either before dilution with solvent or before the oil-solvent mixture is cooled. A number of materials, including aluminum stearate (9), colloidal substances of the type of bitumen (52), and highly polymerized or condensed high molecular weight paraffins (10), have been proposed as wax crystal regulators. Obviously the use of such materials will be an added expense (and will require equipment for their application). Unless a major improvement is realized, their use is not warranted however, in some cases, regulation of the crystal may be required and the use of wax crystal regulators may be justified. 

All diesel fuels eventually cause start-up and operability problems when subjected to sufficiently low temperatures. As the ambient temperature cools, high-molecular weight paraffins present in petrodiesel nucleate and form solid wax crystals which, suspended in liquid, are composed of short-chain n-alkanes and aromatics (Chandler et al., 1992 Owen and Coley, 1990 Lewtas et al., 1991 Brown et al., 1989 Zielinski and Rossi, 1984). Left unattended overnight... 

Metals such as Fe, Co, Ni, or Ru on alumina or other oxide supports convert CO and H2 to hydrocarbons. Using different catalysts and reaction conditions either CH4, liquid hydrocarbons, high molecular weight paraffins, methanol, higher alcohols, olefins, and aromatics can be obtained, though rarely (with the exception of CFL, and methanol) with high selectivity. Hydrocarbons typically exhibit a Schulz-Flory type molecular weight distribution. 

Castro AA (1993) Catalysts for the selective dehydrogenation of high molecular weight paraffins. Catal Lett 22 123... 

Solvent or fractional condensation methods, however, do not give complete separation from the anthracene of such substances as acridine, Ruorantln-enc, flnorene, pyrene, methyl-anthracene, chrysene, acenaphthene, high molecular weight paraffin hydrocarbons, etc., which are present in the crude anthracene press cake. During the subsequent oxidation of anthracene by the liquid phase method these substances result in the formation of impurities difficult to separate from the anthraquinoue and detracting considerably from its quality as a dye intermediate. 

The effect of paraffin carbon number on the equilibrium methane concentration is shown for three feed steam-carbon ratios in Figure 6. These results indicate that a higher methane-content gas can be produced from low molecular weight paraffins than from high molecular weight paraffins. 

To explain the high activity of cerium dioxide for SOF oxidation, recall that SOF consists mainly of high molecular weight paraffins. There is consensus that the important step in alkane oxidation is cleavage of a C-H bond. On oxide catalysts, most authors favor a heterolytic mechanism, with, for example, methane splitting to yield a proton and a methyl anion. An important observation in support of this comes from a comparison of methane and fluoromethane. The fluorine atom would be expected to stabilize a transition state of the form FH2C and one finds that fluoromethane is an order of... 

Polymers that lack double bonds, like polyethylene, can be considered high molecular weight paraffin. They are slow to oxidize in the absence of UV light, much like the low molecular weight hydrocarbons. On the other hand, polymeric materials with double bonds oxidize rapidly. Nevertheless, polymers like polyethylene may oxidize rapidly as well when contaminated with metallic ions because such ions catalyze the decomposition of peroxides. 

Stationary Phase. Dow Corning200 Fluid, 10 cs (Firm 49). A silicone oil which has been of value in the paper chromatography of lipids, can be used to render silica gel 6 or kieselguhr G layers hydrophobic [114, 168]. Other hydrophobic impregnation agents are hydrocarbons such as undecane [78] (Firm 68), tetradecane [82] (Firms 58, 68) and mixtures of high molecular weight paraffins [4, 81] (Firms 68, 88). 

When the test conditions were made sufficiently severe to expel liquid and gas from the transformer at high temperature, a high molecular weight paraffinic hydrocarbon oil produced a smaller fireball, lower fireball temperature and shorter fire residence time than any of the other fluids tested, including silicone dielectric oils. 

High molecular weight paraffin waxes have very low compatibility with polar polymers and act as external lubricants for polymers such as PVC. 

High-molecular-weight paraffin waxes function as external lubricants for polar polymers because of their low affinity to them, but they have a high affinity to polyolefins and are used then as internal lubricants. 

---