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Question No.:  987 Category :  Refining Operations
Date Posted:  5/14/2000
Subject: Gasoline Blending
Among all gasoline components, which is the main contributer for gum formation in gasoline?

Is there a shorter test period for potential gum testing in gasoline than ASTM D-873 which takes 16 hrs. or more?

Submitted by :
Company Name:

Tuwairgi, Abdullah M.
Saudi Aramco
Jeddah, Saudi Arabia


Number of responses : 2
Response 987-1
Date : 5/15/2000

Dear Mr. Abdullah M. Tuwairgi,

From my experience I know that dienes have high tendency to form gums. In general gums are formed when gasoline is oxidized in presence of oxygen (air). The oxidation products are called GUM. ASTM test for gum I know are:

- ASTM test for “Existent Gum in Fuels by Jet Evaporation”, D 381 / IP 131 is a test to determine the amount of existing gum.

- ASTM test for “Oxidation Stability of Gasoline (Induction Period Method)” D 525 / IP 40 is a test to indicate the tendency of a gasoline to form gum in storage.

- The test you had indicated ASTM D-873/IP 38 is the test for “Oxidation Stability of Aviation Fuels (Potential Residue Method)” Best (practical) way to determine fuels (hydrocarbons in general) properties, gum tendency included, is using NIR technology. NIR analyzers, if properly implemented, are fast, accurate, maintenance free and much cheaper in the long run. One NIR analyzer can determine ALL the properties required for the tested sample and in less than a minute.

Please feel free to contact me direct so I can advise you on your particular problem.

Name - Avihu Hiram
CompanyName - HIRAM - Process Control Engineering Ltd.
Location - Caracas, Venezuela
Email -

Response 987-2
Date : 5/16/2000


Mr. Hiram is correct in stating that the main contributors to gum formation in gasoline are probably olefins, especially the diolefins.

I would only add that, of all the component gasolines in the final blended gasoline, olefins and diolefins would be more prevalent in the cracked gasolines produced in refinery processes such as fluid catalytic cracking, delayed coking, and visbreaking. Olefins and diolefins would not be likely to occur in the component gasolines from processes such as catalytic reforming, alkylation, isomerization, hydrocracking, or polymerization.

Milton Beychok
(Visit me at

Name - Milton Beychok
CompanyName - Consulting Engineer
Location - Newport Beach, California, USA
Email -


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