EVALUATION OF FOURIER-TRANSFORM NEAR-INFRARED FOR THE SIMULTANEOUS ANALYSIS OF LIGHT ALKENE MIXTURES

A Fourier transform near-infrared (FT-NIR) spectrometer incorporating a fiber-optic-coupled sample cell was used for simultaneous determinat ion of ethylene and monoalkylated light alkenes in liquid mixtures at room temperature and pressure, Ethylene, propylene, 1-butene, 1-penten e, 1-hexene, 1-octene, and 1-decene were selected for the evaluation. Several additional alkylated alkenes (e.g., 1,1 dialkylated, cis, tran s dialkylated, and trialkylated alkenes) were investigated to determin e the effects of the molecular structure on this determination. The fi rst overtone of the asymmetric =CH2 stretch of the monoalkylated alken es was found to be unique for the light alkenes in the NIR region, Thi s region of the spectrum was used for quantitative analysis using clas sical least-squares (CLS) regression. Ethylene/1-octene mixtures were studied as an example. The concentrations of these alkenes were determ ined with an error of less than 1% by weight.