Determination of oxygenates in syngas-to-olefin products by solid phase extraction combined with gas chromatography-mass spectrometry

Abstract

The syngas-to-olefin (SGTO) products mainly consist of hydrocarbons along with small amounts of oxygenates as the byproducts. A C18 solid-phase extraction (SPE) column was used for oxygenates enrichment in SGTO products. As the hydrophobic compounds, the hydrocarbons had stronger interaction with a C18 SPE column than oxygenates. Under the optimized elution conditions, the oxygenates were first eluted from the C18 SPE column with 60% (v/v) methanol solution. The fraction of oxygenates was then analyzed with gas chromatography-mass spectrometry (GC-MS) for qualification and gas chromatography-hydrogen flame ionization detection (GC-FID) for quantification. The FID response factors of n-alkanol and n-ketone were used for alkanols and ketones quantitative calculation and the method recoveries were 88%-98% and 64%-87% respectively. In the range of 197-4,785 mg/L, good linear relationships of the FID responses with the corresponding mass concentrations of the standard samples were obtained with the linear regression coefficients greater than 0.99. Sixty-seven oxygenates were analyzed qualitatively and quantitatively. The results showed that the fraction of the oxygenates mainly consists of alkanols and ketones. The total content of the oxygenates in SGTO products was 6.2%. The enrichment method only requires a very small amount of sample and the total process can be completed within 10 min. The analysis results of SGTO product studies can provide the necessary basic data for SGTO catalysts and dynamics studies.