Post-column reaction gas chromatography with a two-stage microreactor for the determination of volatile oxygenated compounds in high-pressure liquefied hydrocarbons

Abstract

A reliable and practical approach for the direct measurement of volatile oxygenated compounds in high pressure liquefied light hydrocarbons has been successfully developed. The approach incorporates the use of a pressurized liquid injection device for sample introduction, a highly selective and polar ionic sorbent column technology to achieve separation of the target oxygenated compounds, and the augmentation of a recently commercialized two-stage post-column microreactor to convert carbon compounds, first to carbon dioxide by combustion and subsequently to methane by methanation. This two-stage conversion strategy is highly advantageous as it enables carbon compound independent responses as well as sensitivity improvements, particularly for short-chain oxygenated compounds. Oxygenated compounds such as acetaldehyde, propanal, methanol, ethanol, iso-propanol, n-propanol, and acetone in light hydrocarbons were found to have a detection limit of at least 0.1 ppm (v/v), respectable linear range from 0.2 ppm (v/v) to 3000 ppm (v/v) with R² greater than 0.997 and relative precision of less than 10% RSD (n = 7). Considering the carbon compound independent response capability, one single carbon-containing compound can be used for calibration to measure any of the target analytes with a respectable accuracy of less than ±10% error. The unique feature of equimolar carbon responses also enables the possibility of determining the “total” concentration for the known volatile oxygenated compounds. Also, the need for multi-level calibration was eliminated over the range of interest. This novel concept enables new measurement capability and flexibility, enhances the analytical throughput, and substantially decreases the overall cost of ownership. The utility of the methodology was demonstrated with practical industrial applications.