Mixed aniline point

Solubility of resins can be predicted in a similar way as for the solubility of polychloroprene rubbers in a solvent mixture (see Section 5.5) by means of solubility diagrams (plots of the hydrogen bonding index (y) against the solubility parameter (5). Another more simple way to determine the solubility of resins is the determination of the cloud point, the aniline and the mixed aniline points. 

Aniline and mixed aniline point (DIN 51 775 modified). It is similar to the cloud point test except that the solvent is aniline, a very polar liquid. The aniline point is defined as the temperature at which a mixture of equal parts of aniline and the resin show the beginning of phase separation (i.e. the onset of clouding). Phase separation for aromatic resins occurs between I5°C and below zero for resins with intermediate aromaticity, it lies between 30 and 50°C and for non-aromatic resins, it is 50 to 100°C. Sometimes the mixed aniline point is used. It is similar to the aniline point except that the solvent is a mixture of one part of aniline and one part of w-heptane. The problem of both procedures is that precipitation of resins can be produced before the cloud is generated. 

Of the petroleum solvents, the aromatic fractions are much better solvents for DDT than the paraffinic fraction. The limited solubility of DDT in the paraffinic fraction, representative of straight-run petroleum oils, shows that such oils alone cannot be used as solvents in concentrated DDT solutions. An auxiliary solvent would have to be used to prepare concentrated solutions with them. It was not possible to correlate solubility with mixed aniline point and aromatic content. This was presumably due to differences in the solubility of DDT in the individual hydrocarbons present which included both monocyclic and dicyclic types. No attempt was made to determine the amount of the individual hydrocarbons in the aromatic fractions. 

Among the petroleum aromatic fractions there appears to be no close correlation between DDT solubility and either mixed aniline point or aromatic content. 

Prior to the introduction of the solubility parameter (solpar) concept, paint chemists used Kauri butanol values, mixed aniline points, and heptane numbers to predict the solubility of resins in aliphatic solvents. These parameters have been replaced, to a large extent, by solpars, but heptane numbers are still used, and these empirical parameters can be converted to solpar values. 

The aniline point (or mixed aniline point) (ASTM D-611, IP 2) has been used for the characterization of crude oil, although it is more applicable to pure hydrocarbons and in their mixtures and is used to estimate the aromatic content of mixtures. Aromatics exhibit the lowest aniline points and paraffins the highest aniline points. Cycloparaffins and olefins exhibit values between these two extremes. In any hydrocarbon homologous series the aniline point increases with increasing molecular weight. 

The test method for the determination of aniline point and mixed aniline point of hydrocarbon solvents (ASTM D-611, IP 2) is a means for determining the solvent power of naphtha by estimating of the relative amounts of the various hydrocarbon constituents. It is a more precise technique than the method for kauri-butanol number (ASTM D-1133). 

Several tests that are usually applied to the lower-molecular-weight colorless (or light-colored) products are not applied to residual fuel oil. For example, test methods such as those designed for the determination of the aniline point (or mixed aniline point) (ASTM D-611, IP 2) and the cloud point (ASTM D-2500, ASTM D-5771, ASTM D-5772, ASTM D-5773) can suffer from visibility effects because of the color of the fuel oil. 

The aniline point or mixed aniline point (ASTM D-611, IP 2) gives an indication of the hydrocarbon group composition of an oil. The lower the aniline point, the more aromatic the oil, and, for any particular compound type, the aniline point rises with molecular weight and with viscosity. 

ASTM D 611-98. Standard test methods for aniline point and mixed aniline point of petroleum products... 

ISO 2977-97. Petroleum products and hydrocarbon solvents - Determination of aniline point and mixed aniline point. 

The aniline point (ASTM D 611) is the lower equilibrium solution temperature for equal volumes of aniline and solvent. w-Heptane is the standard hydrocarbon solvent with an aniline point of 69.3 "C. The aniline point decreases from approx. 90°C for isoparaffins to 10°C for solvents with a medium aromatic content. Highly aromatic solvents result in values below 0°C so that the aniline can crystallise from the mixture. Mixed aniline points (ASTM D 1012) are used in these cases. This is the minimum equilibrium solution temperature of a mixture of two volumes of aniline, one volume of solvent and one volume of w-heptane. The relationship between the KB-number and aniline point for zero to medium aromatic content hydrocarbon solvents is shown in Figure 2.1. Figure 2.2 demonstrates the relationship between aniline and mixed aniline points. Toluene/ i-heptane blends have been used for its determination. The relationship between KB-number and mixed aniline points for solvents with a medium to high aromatic contents is given in Figure 2.3. 

Figure 2.2 Relationship between the aniline and mixed aniline points.

An illustrative example of dilution ratios using 1/4 second nitro-cellulose as the resin is given in Figure 2.4. It is obvious that considerably more aromatic hydrocarbon diluent can be tolerated than aliphatic. By the same token toluene is more of a solvent than xylene as would be expected on the basis of KB numbers or mixed aniline points. 

Mixed aniline point n. Minimum equilibrium solution temperature of a mixture of two volumes of aniline, one volume of sample, and one volume of normal heptane of specified purity. Refer to ASTM D 1012. 

The Kauri-butanol value, used to rate solvency of hydrocarbon solvents, is defined in ASTM Method D 1133 as the volume in milliliters of the hydrocarbon solvent at 25 °C that is required to produce a defined degree of turbidity when titrated into a specified quantity of a standard clear solution of kauri resin in n-butyl alcohol. Kauri-butanol values range from approximately 20 for the weakest hydrocarbon solvents to more than 100 for stronger aromatic solvents. The test is limited to hydrocarbon solvents and is not applicable to oxygenated solvents. As Kauri resin (a natural resin) is no longer easily available, the test has not maintained its acceptance in the industry. Aniline point (or mixed aniline point), another measure of solvency of hydrocarbon solvents, is more accepted. The ani-... 

There may be certain lubricants (with very high aromatic content) which when mixed with equal volume of aniline may remain completely miscible and separation into different phases may not be observed even at the time of solidification. For determining such low aniline imiiits, 1 volume of sample is mixed with 2 volumes of aniline and 1 volume of a suitable diluent (n-hexane or -heptane). Addition of the diluent lowers the miscibility of aniline with the sample and so with decrease in Icmjrerature, separation of phases can be easily observed. The equilibrium solution temperature observed under these conditions is known as Mixed Aniline Point, which can be used in the. same way as the Standard Aniline Point. 

Aniline Point and Mixed Aniline Point of Petroleum Products and Hydrocarbon Solvents ... 

These test methods also cover the determination of the mixed aniline point of petroleum products and hydrocarbon solvents having aniline points below the temperature at which aniline will crystallize from the aniline-sample mixture. 

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