Fast On-Line Analysis of Process Alkane Gas Mixtures by NIR Spectroscopy

Abstract

Proper operation of a molecular sieve process for the separation of iso- and cyclo-alkanes from normal alkanes requires the fast online detection of normal alkanes breaking through the column. The feasibility of using near-infrared (NIR) spectroscopy for this application was investigated. Alkane mixtures were prepared according to an experimental design. These mixtures, containing small amounts of normal alkanes (C5–C7) and varying amounts of isoand cyclo-alkanes (seven compounds), were analyzed simultaneously at 160 °C with the use of NIR spectroscopy and gas chromatography as a reference method. With an analysis time of 9 s, a critical level of 0.4% [mole/mole] of normal alkanes could be achieved. If a faster response is required, the analysis time can be reduced to 4 s, at the cost, however, of an increase in the critical level to about 1% [mole/mole].