HIGH-RESOLUTION NMR PROCESS ANALYZER FOR OXYGENATES IN GASOLINE

We report a high-resolution 42-MHz H-1 FT-NMR instrument that is suita ble for use as a process analyzer and demonstrate its use in the deter mination of methyl tert-butyl ether (MTBE) in a flowing stream of gaso line, This spectrometer is based on a 55-kg permanent magnet with esse ntially no fringe field. A spectral resolution of 3 Hz was typically o btained for spinning samples, and this performance was only slightly d egraded with flowing samples. We report a procedure for magnet drift c ompensation using a software procedure rather than a field-frequency l ock channel. This procedure allowed signal averaging without loss of r esolution. Regulatory changes to be implemented in the near future hav e created a need for the development of methods for the determination of MTBE and other oxygenates in reformulated gasolines. Existing metho ds employing gas chromatography are not fast enough for process contro l of a gasoline blender and suffer from other limitations. This study demonstrates that process analysis NMR is well-suited to the determina tion of MTBE in a simulated gasoline blender. The detection limit of 0 .5 vol% MTBE was obtained with a measurement time of 1 min. The absolu te standard deviation of independent determinations was 0.17% when the MTBE concentration was 10%, a nominal value. Preliminary results also suggest that the method may be applicable to gasolines containing mix tures of oxygenate additives as well as the measurement of aromatic an d olefinic hydrogens.