A dynamic 1H NMR-based method for the estimation of olefin content in all cracked fuel range products, in general, and in gasoline/naphtha streams, in particular, irrespective of types and composition of olefins and boiling range of samples has been developed. This is in continuation of our earlier works where two methods were described for the determination of hydrocarbon types in straight-run gasoline (no olefins) and cracked full range gasoline/naphtha (with olefins). The average absolute number of unsaturated hydrogen (H) in the olefinic region (4.4–6.5 ppm) was directly estimated with the help of a 1H NMR spectrum using dynamic variables in terms of differential population of various kinds of olefins. The average alkyl chain length (n) was estimated by various methods including 13C NMR and carbon number distribution by a gas chromatography-based detailed hydrocarbon analyzer [DHA, ASTM D6730-01(2016)] and simulated distillation [ASTM D2887-16a] data. The percentage of unsaturated hydrogen (% UH) in an average olefin was then obtained providing a multiplication factor (f o) by which the weight percentage of olefin is estimated using a normalized 1H NMR spectrum. The dynamic estimation of H and n for each sample removes the possibilities of errors in the estimation. The method has efficiently been extended to coker kero and coker diesel range products where there has been no method available for olefin estimation. The method was validated by using DHA following ASTM D6730, by the Reformulyzer-based ASTM D6839 method, and finally by fluorescent indicator adsorption following ASTM D1319. All the methods were compared. Whereas the proposed NMR method is extremely general, free from manual error, the limitations of existing ASTM methods and the old NMR method vis á vis a new NMR method are also discussed.
A rapid method based on quantitative 1 H 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 °C and various heart cuts in-between, like C5-60, 60-70, 70-90, 90-140 °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, isoalkanesisoalkenes, 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 1 H NMR spectrum to CH n (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.
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