Faster, More Robust, and More Accurate than AST D664: New Test Method for Acid Number in Crude Oil

A new test method for the determination of napthenic acids in crude oil and petroleum refinery intermediates and products is under active investigation by ASTM (ASTM WK48004). The subject has also been discussed comprehensively in a C&EN webinar, which is available on demand. The new method is superior to ASTM D664 at all levels: it is more accurate, more precise, more reliable, more robust and more repeatable. Moreover, it is significantly faster than the ASTM D664 potentiometric method, and because it uses much less solvent, reagent and waste disposal costs are much lower.

The thermometric endpoint titration (TET) method, from Metrohm (Switzerland), utilises the same titrant (0.1 mol/L KOH in 2-propanol) as ASTM D664. Instead of using a potentiometric probe (which is liable to fouling of the membrane and clogging of the reference junction after only a couple of determinations), the endpoint is detected using a highly sensitive, fast responding electronic thermometer.

This probe requires essentially no maintenance aside from a solvent rinse, needs no hydration, requires no calibration and is ready for use 24/7. It can be used by operators as a "walk-up" method, or fully automated with a sample changer in the laboratory. Because the method is so fast, corrective response to deviant process conditions can be much faster, with consequent savings to equipment and process running costs.