MAXIMUM FLOCCULATION RATIO AND PEPTIZING POWER IN RESIDUAL AND HEAVY FUEL OILS: ASTM D7060
EXPLANATION
Asphaltenes are naturally occurring materials in crude petroleum and petroleum products containing residual material. The asphaltenes are usually present in colloidal suspensions, but they may agglomerate and flocculate if the suspension of asphaltene molecules is disturbed through excess stress or incompatibility. This test method provides compatibility parameters, which can be used to assess stability reserve and compatibility. This method covers a procedure for quantifying the maximum flocculation ratio of the asphaltenes in the oil and the peptizing power of the oil medium, by an automatic instrument using an optical device. This test method is applicable to atmospheric or vacuum distillation residues, thermally cracked residue, intermediate and finished residual fuel oils, containing at least 1 mass % asphaltenes. This test method has not been developed for asphalts. This test method is applicable to products typical of Specification ASTM D396 - Grades 5L, 5H, and 6, and Specification ASTM D2880 - Grades 3-GT and 4-GT.
A blend is considered stable when the blend's peptizing power is higher than the blend's maximum flocculation ratio. Both of them can be calculated using empirical blend rules.
Refineries and terminal owners can prevent the flocculation of asphaltenes due to incompatibility by assessing the compatibility of fuels beforehand.
TEST SUMMARY
Six portions of the sample are diluted in various ratios with1-m ethylnaphthalene. Each solution is inserted into the automatic apparatus, and titrated with cetane until flocculation of asphaltenes is detected by optical probe. The first two solutions are titrated with cetane in coarse determinations in which the flocculation ratio is decreased in 5 % steps. The coarse determinations help to establish suitable starting values for the fine determinations, in which the flocculation ratio is decreased in 1 % steps. The flocculation ratios at critical dilution, measured during the fine determinations, are used to calculate the maximum flocculation ratio of the sample's asphaltenes and the peptizing power of the sample's oil medium.
An optical probe detects the formation of flocculated asphaltenes. The start of flocculation is interpreted when a significant and sustained increase in rate-of-change of signal, as measured by the optical probe, ensures flocculation is in progress. The start of flocculation can be detected unambiguously when the sample contains at least 1 % mass asphaltenes as measured by Test Method ASTM D6560.
High content of insoluble inorganic matter (sediment) has some interference in this test method. In this case, the insoluble matter shall be removed by filtration according to Test Method ASTM D4870. The presence of wax, present in the paraffinic crudes or fuels from such crudes, does not interfere.
TEST PRECISION
In the flocculation ratio range from 16 to 57 and the peptizing power range from 27 to 96, the repeatability was found to be:
Maximum Flocculation Ratio: 3
Peptizing Power: 6
The reproducibility of this test method has not yet been determined.
This test method has no bias because the results of this test are defined only in terms of this test method.
