Precipitation number

The precipitation number is often equated to the asphaltene content, but there are several issues that remain obvious in its rejection for this purpose. For example, the method to determine the precipitation number (ASTM D91) advocates the use of naphtha for use with black oil or lubricating oil, and the amount... 

Precipitation number the number of milliliters of precipitate formed when 10 ml of lubricating oil is mixed with 90 ml of petroleum naphtha of a definite quality and centrifuged under definitely prescribed conditions. 

For abbreviation of analyte names see Sect. Abbreviations . ACN acetonitrile, a.p. after precipitation, AtrE atropinesterase from rabbit serum, hum human, IS internal standard, metab. metabolites (biotransformation products produced in vivo), MeOH methanol, n.s. not specified, p.p. prior to precipitation Numbers give volume ratio v/v... 

The precipitation number is often equated to the asphaltene content, but there are several issues that remain obvious in its rejection for this purpose. For example, the method used to determine the precipitation number (ASTM D-91) advocates the use of naphtha for use with black oil or lubricating oil and the amount of insoluble material (as a % v/v of the sample) is the precipitation number. In the test, 10 ml of sample is mixed with 90 ml of ASTM precipitation naphtha (which may or may nor have a constant chemical composition) in a graduated centrifuge cone and centrifuged for 10 min at 600-700 rpm. The volume of material on the bottom of the centrifuge cone is noted until repeat centrifugation gives a value within 0.1 ml (the precipitation number). Obviously, this can be substantially different from the asphaltene content. 

Gravimetric Method 25 ml of extract were acidified with HCl to pH=l and a molar excess of formaldehyde was added. This excess was calculated assuming that catechin and formaldehyde react in a 1 1 proportion. The suspension was refluxed during 30 min. The reaction products were filtrated, washed several times with hot water and dried to constant weight at 100 X. The polyphenol content is expressed in absolute terms by the Stiasny precipitation number with formaldehyde , %, defined by ... 

Precipitation number n. Measure of the amount of sohd matter precipitated from oil in a test. The number of milliliters of solid matter formed in a certain amount of mixture of oil and solvent. 

Purified by salt and alcohol precipitations. Numbers in parentheses indicate references. 

D91 Test Method for Precipitation Number of Lubricating Oils ... 

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