Group-type characterization of crude oil and bitumen. Part II: Efficient separation and quantification of normal-paraffins iso-paraffins and naphthenes (PIN)

The SARA (saturates, aromatics, resins, and asphaltenes) separation and quantification have been widely used for characterizing the composition of crude oil and bitumen. The saturate hydrocarbons are the most valuable fraction of the oil industry and contain vital geochemical information for determining the origin and formation of petroleum fluids and for assessing the hydrocarbon potential and sedimentary environment of source rocks. It is therefore necessary to further separate the saturate fraction into normal paraffins, iso-paraffins and naphthenes (PIN fractions). Nevertheless, the convenient approach of PIN separation has never been reported on in the literature. Here, we present an efficient method that allows us to further separate the saturate fraction of crude oil or bitumen into PIN fractions through the automated multi-dimensional high performance liquid chromatography system (AMD-HPLC). In essence, the system is equipped with a “PIN1” column (Silicon: S115) packed with a 5.4 Å molecular sieve and a “PIN2” column (Silicon: 50%S115 + 50%S130) packed with a 6.2 Å molecular sieve. Each set of columns is connected in a series via multi-position valves that allow a given column to be inserted “in” or to be by-passed “out” of the flow path of the mobile phase at pre-set times in the process. When use iso-octane and n-octane or their mixture as mobile phases, the system separates the saturate hydrocarbon into PIN fractions simply through three steps under a temperature range of 25–140 °C. An entire PIN analysis cycle takes nearly 60 min, including system re-conditioning. The separated PIN fractions can be quantified using either gravimetric method or evaporative light scattering detector (ELSD) technique. Experimental results exhibit excellent qualitative and quantitative capability.

Figure optionsDownload as PowerPoint slide