Point compounds

Tenax Various grades for collection of a range of boiling-point compounds. Suitable for low ambient concentrations... 

Concerning the last point, Topliss and Costello [42] proposed that, to minimize the risk of chance correlations, a QSAR developed with MLR should utilize at least five data points (compounds) for each descriptor included in the equation. Later work [17] showed that it was necessary to take into account not only the number of descriptors in the QSAR (usually several) but also the whole of the descriptor pool (often several hundred) from which the best descriptors were selected. 

Needed Properties Enthalpies, P-V-T relationships, L-L-V phase equilibria (water-hydrocarbon-gas), and dew points Compounds of Concern H2O, H2, CO, CO2, N2, CH4,... 

Thermodynamically, the composition of any such phase is variable. In a number of cases, however, the possible variation in composition is very small. Invariant composition phases or stoichiometric phases, or compounds proper, also called point compounds in binary alloys, are represented by a point on the composition axis. 

In the case of a ternary system, the formation of several, binary and ternary, stoichiometric phases, and different types of variable composition phases can be observed. One may differentiate between these phases by using terms such as point compounds (or point phases), that is, phases represented in the composition field by points, line phases , field phases , etc. 

The intermediate phases formed in the various binary systems have been represented, in a first approximation, as point compounds. The points, which in the different binaries correspond to phases having the same composition and structure, have then been connected, defining multi-component ternary stability fields (in this case, line fields). On each horizontal line of this multi-diagram triangle the same overall composition is found (the same Mg content and the same total... 

As underlined by Miller el al. (2002) in a comprehensive review about structure and bonding around the Zintl border of the Periodic Table, the Nesper criteria imply that Zintl phases (as valence compounds) are generally point compounds and may have a semi-metallic behaviour. 

Compounds with the 16th group elements. Among the various phases formed with these non-metal elements, the normal valence compounds, NaCl type, may be mentioned. Some of them have been described as point compounds (for instance BaS, BaSe, BaTe) a few others as corresponding to a solid solution range (for instance, EuS 43-50 at.% S, EuTe 50-57 at.% Te). 

With reference to their ideal stoichiometries a few ubiquitous crystal structure prototypes will be presented in the following. Attention will be especially given to some structures corresponding to simple stoichiometric ratios. Notice however that, in several cases, a given prototype may be represented by a point compound but also,... 

Introductory remarks. Phases related to the 1 3 stoichiometry and their derivative structures, either as point compounds or as solid solution ranges, are frequently found in binary and ternary intermetallic alloy systems. 

Chromatographic columns are commonly used to determine total petroleum hydrocarbon compounds approximately in the order of their boiling points. Compounds are detected by means of a flame ionization detector, which responds to virtually all compounds that can bum. The sum of all responses within a specified range is equated to a hydrocarbon concentration by reference to standards of known concentration. 

The compounds dissolve in or are adsorbed by this stationary phase to a degree determined by their boiling points. Compounds that are not strongly retained by the column are rapidly pushed to the other end by the stream of inert gas. The compounds that are strongly retained by the column migrate at slower rates. Since the boiling point is inversely related to molecular weight, the smallest compounds tend to elute from the column first. 

High-boiling-point compounds such as asphaltenes, branched hydrocarbons with molecular weights greater than 300, and alkylated naphthenes can increase fuel viscosity. If present in fuel, they can be detected indirectly through either ASTM D-86 distillation end point temperatures or by high ASTM D-445 viscosity determinations. 

Low fuel viscosity can be due to the presence of low-boiling-point, low-molecular-weight compounds in the fuel. Contamination with low-boiling-point compounds such as solvents, gasoline, and petroleum naphtha can dramatically reduce the viscosity of distillate fuel and residual fuel oil. 

The presence of low molecular weight, low flash point compounds in diesel fuel could lead to a shortening of the fuel ignition delay period. In a diesel engine, this could cause rough running due to early combustion of the low flash point compounds. 

High Reid vapor pressure readings are usually linked to low-flash-point compounds. 

The process involves reacting the degummed oil with an excess of methyl alcohol in the presence of an alkaline catalyst such as sodium or potassium methoxide, reaction products between sodium or potassium hydroxide and methyl alcohol. The reaction is carried out at approximately 150°F under pressure of 20 psi and continues until trans-esterification is complete. Glycerol, free fatty acids and unreacted methyl alcohol are separated from the methyl ester product. The methyl ester is purified by removal of residual methyl alcohol and any other low-boiling-point compounds before its use as biodiesel fuel. From 7.3 lb of soybean oil, 1 gallon of biodiesel fuel can be produced. See FIGURE 12-5. 

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