A Rapid 1H NMR-Based Estimation of PONA for Light and Narrow Cut Naphtha Samples of Refinery Streams toward BS-VI Gasoline

A rapid method based on quantitative H-1 NMR spectroscopy for the accurate estimation of paraffins (P), olefins (O), naphthenes (N), and aromatics (A), i.e., PONA, in extremely light to middle cut naphtha (boiling points ranging from C4/C5 to 130/140 degrees C and various heart cuts in-between, like C5-60, 60-70, 70-90, 90-140 degrees C cuts and many more that are being processed for BS-VI gasoline pool) has been developed. The method relies on accurate assignments of various kinds of quaternary-carbons, CHs, CH(2)s, and CH(3)s present in these light samples overwhelmingly populated with low-molecular-weight alkanes-alkenes, isoalkanes-isoalkenes, and cycloalkanes-cycloalkenes as the constituents by edited HSQC NMR. Our earlier group molecular weight (GMWt)-based methods for PNA estimation has thus been appropriately modified in terms of assignment of H-1 NMR spectrum to CHn (n = 0, 1, 2, and 3) groups toward estimation of the relative number of carbon and hydrogen atoms, which are imperative to the GMWt-based method, to accommodate all possible variations. The GMWt method coupled with our recently developed multiplication factor-based olefin estimation wholly estimate the PONA for these lightest liquid streams from refineries. The developed method is well suited for monitoring pilot plant processes where high sample throughput and instant results are warranted. The values thus obtained were compared with detailed hydrocarbon analysis (DHA) following ASTM D6730 and by the reformulyzer-based ASTM D6839 method.

Automated summary

A rapid method based on quantitative H-1 NMR spectroscopy has been developed for accurate estimation of PONA in extremely light to middle cut naphtha, suitable for monitoring pilot plant processes. The method combines GMWt-based estimation with new olefin estimation techniques to provide comprehensive analysis of the liquid streams from refineries. Results were compared with DHA and ASTM D6839 methods.