Determination of oxygenates in methanol-to-olefin gasoline byproducts and methanol-to-gasoline product with solid phase extraction-gas chromatography

Abstract

Silica solid phase extraction (SPE) column was used for sample pretreatment to enrich the target analytes and simplify background. Due to its high efficiency, reliability and simplicity, the technique has been widely used in many fields. The byproduct gasoline of methanol-to-olefin (MTO) and the product of methanol-to-gasoline (MTG) mainly consist of hydrocarbons along with small amounts of oxygenates. Trace amounts of oxygenates are hard to identify because of their complex hydrocarbon components. With the SPE technique, the samples were separated into two major classes, oxygenates and hydrocarbons. Oxygenates were then determined with gas chromatography-mass spectrometry (GC-MS). The elution conditions of the silica solid phase extraction column were optimized with the standard sample. Under the optimized elution conditions, the hydrocarbons were first eluted from the SPE column with 5 mL dichloromethane, the oxygenates were then eluted with 3 mL acetonitrile. The recoveries of standard samples were tested before and after pretreatment. The standard recoveries were 87.7%-95.3%. The oxygenates except methanol and ethanol were then quantified by gas chromatography-flame ionization detection (GC-FID) and internal standard method. Methanol and ethanol were then quantified by extracting characteristic ion chromatograms and external standard method. The results show that the oxygenates of MTO byproduct gasoline and MTG product mainly consist of ketones and aldehydes. The method improves the sensitivities of the target compounds and reduces the interference of the background.