A precolumn backflush system based on capillary columns using midpoint pressure control is described. Midpoint backflush is made possible with a Capillary Flow Technology (CFT) purged union controlled by an AUX EPC channel on the Agilent 7890A GC system. The key application discussed is prefractionation of crude oil that provides a high resolution separation of the C4 to C12 cut. A general backflush method using Polywax 500 is presented to illustrate the backflush concept.
The document details a method for analyzing the light ends (C4 to C12) of crude oil and other petroleum fractions using a precolumn backflush system. This technique utilizes a Capillary Flow Technology (CFT) purged union controlled by an AUX EPC channel on the Agilent 7890A GC system to vent heavy components, preventing column contamination and reducing analysis time.
The system provides a high resolution separation of the C4 to C12 cut of crude oil.
Differences less than 0.1 psig must be avoided to assure stable operation.
The precolumn flow should be set between 70% and 85% of the analytical column flow.