Scion Instruments Methanol in Crude Oil GC-based Analyser
The analysis of methanol in crude oil according to ASTM D 7059: “Standard Test Method for Determination of Methanol in Crude Oils by Multidimensional Gas Chromatography.” In the production of crude oil, methanol is often added to prevent formation of hydrates (i.e., solid water-hydrocarbon structures) that block transportation via pipelines. However, methanol, as with most oxygenated components, will poison catalysts when the crude oil is converted into other products. Catalysts are very expensive, and high methanol levels add a big cost factor. Therefore, the content of methanol in a crude oil is very important and must be measured accurately at low (ppm) concentrations. Depending on the methanol level, the crude oil can be applied straight or needs extra treatment(s) to reduce the methanol content. The determination of methanol is done via an internal standard method using 1- propanol as the internal standard. The measuring range of methanol is specified from 15 to 900 ppm (m/m).
The system is a SCION SSL capillary split/splitless injector using a pressure point over the precolumn. The heavy components of the crude oil are backflushed over a filter to prevent blockage of the vent line. The configuration can be seen in Figure 1 below.
The chromatograms of methanol in toluene, at 150ppm and 6ppm, test mix can be found in Figures 2 and 3.
Figure 2. Test mixture of 150ppm methanol in toluene
Figure 3. Test mixture of 6ppm methanol in toluene
The linearity of the system was determined by a series of samples in toluene where the methanol concentration ranged between 1 and 1000 ppm. The internal standard concentration is set at a constant level. The linearity is shown by plotting the response ratio of the methanol and internal standard against the amount ratio of both components, as shown in Figure 4. The correlation R 2 should 0.99 or better.
Figure 4. Multipoint calibration curve of methanol in toluene
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AN_0069 Methanol in Crude Oil Analysis ASTM D7059-04