Normal-Heptane

Synonyms/Trade Names Heptane, normal-Heptane... 

Melaven, R.M., Mack, Jr., E., The collision areas and shapes of carbon chain molecules in the gaseous state normal-heptane, normal-octane, normal-nonane. J. Am. Chem. Soc. 1932, 54, 888. 

Asphaltenes are obtained in the laboratory by precipitation in normal heptane. Refer to the separation flow diagram in Figure 1.2. They comprise an accumulation of condensed polynuclear aromatic layers linked by saturated chains. A folding of the construction shows the aromatic layers to be in piles, whose cohesion is attributed to -it electrons from double bonds of the benzene ring. These are shiny black solids whose molecular weight can vary from 1000 to 100,000. 

The portion that is soluble in normal heptane is given the term maltenes. 

Octane number is a measure of a fuel s abiUty to avoid knocking. The octane number of a gasoline is deterrnined in a special single-cylinder engine where various combustion conditions can be controlled. The test engine is adjusted to give trace knock from the fuel to be rated. Various mixtures of isooctane (2,2,4-trimethyl pentane) and normal heptane are then used to find the ratio of the two reference fuels that produce the same intensity of knock as that by the unknown fuel. 

By defining isooctane as having an octane number of 100 and / -heptane as having an octane number of 0, the volumetric percentage of isooctane in heptane that matches the knock from the unknown fuel can be calculated as the octane number of the fuel. For example, 90 vol % isooctane and 10 vol % normal heptane produce a 90-octane-number reference fuel. 

The simplest form of ternary RCM, as exemplified for the ideal normal-paraffin system of pentane-hexane-heptane, is illustrated in Fig. 13-58 7, using a right-triangle diagram. Maps for all other non-azeotropic ternary mixtures are qiiahtatively similar. Each of the infinite number of possible residue curves originates at the pentane vertex, travels toward and then away from the hexane vertex, and terminates at the heptane vertex. 

The results confirmed that the chloroheptane/n-heptane mixture behaves in an identical manner to carbon tetrachloride and all the points were on the same straight line as that produced using a mixture of carbon tetrachloride and toluene. These experiments are similar to normal phase chromatography using pure water instead of... 

The problem is made more difficult because these different dispersion processes are interactive and the extent to which one process affects the peak shape is modified by the presence of another. It follows if the processes that causes dispersion in mass overload are not random, but interactive, the normal procedures for mathematically analyzing peak dispersion can not be applied. These complex interacting effects can, however, be demonstrated experimentally, if not by rigorous theoretical treatment, and examples of mass overload were included in the work of Scott and Kucera [1]. The authors employed the same chromatographic system that they used to examine volume overload, but they employed two mobile phases of different polarity. In the first experiments, the mobile phase n-heptane was used and the sample volume was kept constant at 200 pi. The masses of naphthalene and anthracene were kept... 

Typical normal-phase operations involved combinations of alcohols and hexane or heptane. In many cases, the addition of small amounts (< 0.1 %) of acid and/or base is necessary to improve peak efficiency and selectivity. Usually, the concentration of polar solvents such as alcohol determines the retention and selectivity (Fig. 2-18). Since flow rate has no impact on selectivity (see Fig. 2-11), the most productive flow rate was determined to be 2 mL miiT. Ethanol normally gives the best efficiency and resolution with reasonable back-pressures. It has been reported that halogenated solvents have also been used successfully on these stationary phases as well as acetonitrile, dioxane and methyl tert-butyl ether, or combinations of the these. The optimization parameters under three different mobile phase modes on glycopeptide CSPs are summarized in Table 2-7. 

Thermal stabilization of polyolefins has been first demonstrated for low-molecular models-normal structure alkanes [29]. It has been shown that metallic sodium and potassium hydroxide with absorbent birch carbon (ABC) as a carrier are efficient retardants of thermal destruction of n-heptane during a contact time of 12-15 s up to the temperature of 800°C [130]. Olefins and nitrous protoxide, previously reported as inhibitors of the hydrocarbon thermal destruction, are ineffective in this conditions. 

The octane number of a fuel is a measure of the tendency of the fuel to knock. The octane scale has a minimum and maximum based on the performance of reference fuels. In the laboratoi"y, these are burned under specific and preset conditions. One reference fuel is normal heptane. This is a very poor fuel and is given an octane rating of zero. On the opposite end of the scale is iso-octane (2,2,4 trimethyl pentane). Iso-octanc is a superior fuel and is given a rating of 100. 

Paraffins are straight or branched chain hydrocarbons having the chemical formula C ii2 +2- The name of each member ends with ane examples are propane, isopentane, and normal heptane (Figure 2-1). 

The heptane insoluble (ASTM D-3279) method is commonly used to measure the asphaltene content of the feed. Asphaltenes are clusters of polynuclear aromatic sheets, but no one has a clear understanding of their molecular structure. They are insoluble in C3 to paraffins. The amount of asphaltenes that precipitate varies from one solvent to another, so it is important that the reported asphaltene values be identified with the appropriate solvent. Both normal heptane and... 

Normal /, /i -Oxydipropionitrile Carbowax (400, 600, 750, etc.) Glycols (ethylene, diethylene) Cyanoethylsilicone Saturated hydrocarbons, e.g. hexane, heptane aromatic solvents, e.g. benzene, xylene saturated hydrocarbons mixed with up to 10 per cent dioxan, methanol, ethanol, chloroform, methylene chloride (dichloromethane)... 

In conclusion, it should be pointed out that recently [51], a considerable growth of specific fluid volumetric flow rates was discovered near the saturation pressure on filtra tion of the solution of C02 in normal heptane and gas-liquid fossil carbohydrates (oils). A possible explanation of this effect can be found in the above theoretical discussion. Finally, going back to M. Amon and C. D. Denson s work [33], which was discussed at the end of Sect. 4, let us admit that their thesis No. 4 (melt properties as regards thermoplastic itself do not depend on gas concentration) is quite correct and in good correlation with experimental results [21]. 

The Gibbs equation allows the amount of surfactant adsorbed at the interface to be calculated from the interfacial tension values measured with different concentrations of surfactant, but at constant counterion concentration. The amount adsorbed can be converted to the area of a surfactant molecule. The co-areas at the air-water interface are in the range of 4.4-5.9 nm2/molecule [56,57]. A comparison of these values with those from molecular models indicates that all four surfactants are oriented normally to the interface with the carbon chain outstretched and closely packed. The co-areas at the oil-water interface are greater (heptane-water, 4.9-6.6 nm2/molecule benzene-water, 5.9-7.5 nm2/molecule). This relatively small increase of about 10% for the heptane-water and about 30% for the benzene-water interface means that the orientation at the oil-water interface is the same as at the air-water interface, but the a-sulfo fatty acid ester films are more expanded [56]. 

B. Development of the Method. Figure 16 shows normalized chromatograms for various copolymers from GPC 2 with 57% n-heptane in THF as its mobile phase. In beginning the development of this technique, two major aspects are important (i) Variation in Molecular Properties Expected Within a Chromatogram Slice and (ii) Sources of Error in Analyzing for These Properties. These are discussed in turn below. 

To increase retention in a normal phase separation we need a less polar mobile phase, so option (a) would make things worse. All the other mixtures are less polar than the starting mobile phase, but mixture (b) only slightly less so, which would probably not make much difference. Heptane is nonpolar, but the highly polar dmso is not soluble in it. It is best to keep the trichloromethane/dmso and add a non-polar solvent as a modifier as in (c). We can then change the polarity as we wish by altering the relative amounts of heptane and trichloromethane in the mixture. 

El In a normal phase separation using a trichloromethane/ heptane mobile phase, how would the presence of stabiliser in the trichloromethane affect the separation ... 

If the performance of a column is no longer satisfactory it can sometimes be reconditioned by washing with a suitable solvent, or series of solvents. Some bonded phase columns, C-18 for instance, tend to collect non-polar impurities, which can sometimes be removed by washing the column with a non-polar solvent, eg heptane. Assuming the mobile phase normally used with the column is CH3OH/H2O 50 50, we cannot wash directly with heptane because of miscibility problems, we have to get to heptane via a miscible solvent or series of solvents. 

This reactive liquid is now normally supplied commercially as a solution (up to 25 wt.%) in pentane, hexane or heptane, because it reacts with ether and ethereal solutions must be stored under refrigeration. Reaction with atmospheric oxygen or... 

A more general reaction between kojic acid and aldehydes is a trimolecu-lar condensation discovered by Barham and Reed." By a process of elimination, they arrived at the conclusion that C6 of kojic acid was most probably the point of attack two molecules of kojic acid reacted with one molecule of the aldehyde, with the elimination of one molecule of water, giving a product of structure LXXV. Such compounds were prepared from kojic acid and the following aldehydes the normal alkanals from formaldehyde to heptanal, benzaldehyde, cinnamaldehyde, hydrocinnamaldehyde, 2-furaldehyde, and acrolein. The compound derived from kojic acid and benzaldehyde (LXXV, R = phenyl) was also obtained by treating LXXII (R = phenyl) with hot, aqueous sodium carbonate.92... 

Small amounts of hydrocarbons added to the normal tetrahydrofuran or diglyme solvent system result in improved WGSR activity, but larger quantities inhibit the reaction (Table II). When 1-butene or 1-hexene is used, hydroformylation competes with the WGSR (4 ), but the rate of this process is small compared with the rate of H2 production. With pentane, no olefin or aldehyde products could be detected. Calderazzo (29) has reported that Ru(C0) is the principal product when the acetylacetonate of ruthenium is treated with synthesis gas in heptane,... 

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