ASTM D7060 Test Method for Determination of the Maximum Flocculation Ratio and Peptizing Power in Residual and Heavy Fuel Oils (Optical Detection Method)
1. Scope
1.1 This test 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.

1.2 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.

NOTE 1 - 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 D6560.

NOTE 2 - This test method is applicable to products typical of Specification D396 - Grades 5L, 5H, and 6, and Specification D2880 - Grades 3-GT and 4-GT.

1.3 This test method was evaluated in a within-laboratory study in the range of 16 to 57 for the maximum flocculation ratio and in the ranges of 27 to 96 for peptizing power.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced Documents
2.1 ASTM Standards:
D396 Specification for Fuel Oils
D2880 Specification for Gas Turbine Fuel Oils
D4057 Practice for Manual Sampling of Petroleum and Petroleum Products
D4177 Practice for Automatic Sampling of Petroleum and Petroleum Products
D4870 Test Method for Determination of Total Sediment in Residual Fuels
D6560 Test Method for Determination of Asphaltenes (Heptane Insolubles) in Crude Petroleum and Petroleum Products
D6792 Guide for Quality System in Petroleum Products and Lubricants Testing Laboratories

3. Terminology
3.1 Definitions:
3.1.1 asphaltene, n - in petroleum technology, a molecule of high molecular mass, high carbon/hydrogen ratio, and containing heteroatoms.
3.1.1.1 Discussion - Asphaltenes are found largely in crude oils and in heavy fuel oils containing residual fractions. They are insoluble in alkanes such as n-heptane and cetane, but soluble in aromatic solvents such as benzene, toluene, and 1-methylnaphthalene.

3.1.2 compatibility, n - of crude oils or of heavy fuel oils, the ability of two or more crude oils or fuel oils to blend together within certain concentration ranges without evidence of separation, such as the formation of multiple phases.
3.1.2.1 Discussion - Incompatible heavy fuel oils or crude oils, when mixed or blended, result in the flocculation or precipitation of asphaltenes. Some oils may be compatible within certain concentration ranges in specific mixtures, but incompatible outside those ranges.

3.1.3 flocculation, n - of asphaltenes from crude oils or heavy fuel oils, the aggregation of colloidally dispersed asphaltenes into visibly larger masses which may or may not settle.

3.1.4 peptization, n - of asphaltenes in crude oils or heavy fuel oils, the dispersion of asphaltenes to produce a colloidal dispersion.

3.1.5 stability reserve, n - in petroleum technology, the property of an oil to maintain asphaltenes in a peptized state and prevent flocculation of the asphaltenes.

3.1.5.1 Discussion - An oil with a low stability reserve is likely to undergo flocculation of asphaltenes when stressed (for example, extended heated storage) or blended with a range of other oils. Two oils each with a high stability reserve are likely to maintain asphaltenes in a peptized state and not lead to flocculation when blended together.

3.2 Definitions of Terms Specific to This Standard:
3.2.1 critical cetane dilution, n - number of millilitres of cetane with which 1 g of undiluted sample can be diluted until it just does not flocculate the asphaltenes.

3.2.2 critical dilution, n - number of millilitres of 1-methylnaphthalene and cetane with which 1 g of undiluted sample can be diluted until it just does not flocculate the asphaltenes.
3.2.2.1 Discussion - The number of millilitres of 1-methylnaphthalene and cetane is variable and depends on the ratio of sample to 1-methylnaphthalene at the starting point and the sample type.

3.2.3 flocculation ratio, n - percentage by volume of 1-methylnaphtalene in a mixture of 1-methylnaphthalene and cetane.

3.2.4 flocculation ratio at critical dilution, n - percentage by volume of 1-methylnaphthalene in a mixture of 1-methylnaphthalene and cetane at the inflection point.

3.2.5 inflection point, n - last step during the titration with cetane, where flocculation of asphaltenes is not detected by the optical probe as a significant and sustained increase in rate-of-change of signal.

3.2.6 maximum flocculation ratio, n - of asphaltenes, minimum required solvency power, expressed as percentage by volume of 1-methylnaphthalene in a mixture of 1-methylnaphthalene and cetane, to keep the asphaltenes in a colloidal solution.
3.2.6.1 Discussion - Maximum flocculation ratio is the flocculation ratio at extrapolated infinite dilution of the sample.

3.2.7 oil medium, n - that portion of a sample of heavy fuel oil or crude oil that surrounds and colloidally disperses the asphaltenes.
3.2.7.1 Discussion - For purposes of this test method, an oil sample is considered to be composed of an oil medium (sometimes called an oil matrix or maltenes) and asphaltenes.

3.2.8 peptizing power, n - available solvency power, expressed as percentage by volume of 1-methylnaphthalene in a mixture of 1-methylnaphthalene and cetane, to keep asphaltenes in a colloidal solution.

3.2.9 reciprocal dilution, n - dilution ratio of sample in solvent mixture of 1-methylnaphthalene and cetane.

3.3 Symbols:
FRmax = maximum flocculation ratio
FRx = flocculation ratio at critical dilution
Po = peptizing power
Xmin = critical cetane dilution
Xc = critical dilution