SARA Heavy Oil Analysis

SARA oil testing measures saturates, asphaltenes, resins, aromatics in heavy crude oil, distillates and feedstocks.

Hydrocarbon samples are tested by Intertek for Saturates, Asphaltenes, Resins and Aromatics (SARA). SARA analysis of heavy crudes is available for heavy oils, including vacuum distillates, atmospheric and vacuum residues, bitumens and asphalts, so that material losses from light-ends (volatiles) are minimal.

Conventional crude oils can be topped (>300 C) prior to SARA to reduce light-end losses in the subsequent separation and allow the <300 C distillate to be analysed by other methods. Heavy or biodegraded crudes with few light-ends can be analysed directly.

SARA analysis is used for many crude oil components. Asphaltenes can be pentane or heptane insolubles. Resins may be classified as a solubility fraction, such as heptane soluble, pentane insoluble, heptane soluble, and acetone or ethyl acetate insoluble, or as the polar fraction eluted from a polar adsorbent with a polar solvent, such as pyridine, toluene, or methanol.

Saturates and Aromatics are determined by adsorption chromatography, typically from silica or silica/alumina. Saturates are eluted with a paraffinic solvent, such as pentane or heptane. Aromatics are eluted either with paraffinic or moderately polar solvents, such as toluene or DCM.

When a SARA test sample is a heavy oil with minimal light ends, it is worth considering Iatroscan TLC-FID for which there is a standard method (IP-469). IP-469 determines all four compound classes by adsorption chromatography, so the asphaltenes content may differ numerically to that determined by IP-143. Typically, Iatroscan asphaltenes are about 80% of the IP-143 asphaltenes.

Measuring Asphaltenes by IP-143 and then determine SAR by IP-469 is possible. IP-469 does not involve a gravimetric finish, and light ends are still lost during the analysis, so this method works best with >300 degC distillates or residues.

SARA analysis alternatives including IP-143, followed by preparative HPLC (IP-368), or Clay-Gel (ASTM D-2007), which may be appropriate. SARA is also described as asphaltene, wax, and hydrate deposition analysis.