Detailed Hydrocarbon Characterization of RFCC Feed Stocks by NMR Spectroscopic Techniques

Abstract

The paper discusses in detail the hydrocarbon characterization of resid fluid catalytic cracking (RFCC) feed stocks by 1D/2D NMR spectroscopic techniques. A direct, fast, and convenient method based on NMR spectroscopic techniques has been developed for the estimation of total aromatics and the ratio of normal to isoparaffin content in the feedstocks for the RFCC process. The realization of three essential parameters, (a) estimation of the average alkyl chain length of substituents on aromatics, (b) substituted aromatic carbons, and (c) bridged-head carbons of fused polyaromatic rings from the 1H NMR spectral analyses, forms the basis of derivation of mathematical equations used for the estimation of total aromatics, degree of substitution, and condensation. The normal and isoparaffinic contents of saturate and aromatic fractions have been estimated by the method on the basis of 13C NMR spectroscopic techniques. The exact assignments of signals due to α-CHn (n = 1 to 3) groups in the 1H NMR spectral regions of 2.0−4.0 ppm and the 13C NMR spectral region of 5−50 ppm of aromatics and saturate fractions have been achieved by the applications of 1D and 2D multipulse NMR techniques such as 13C−DEPT and phase-sensitive gradient-selected edited 2D heteronuclear single quantum coherence. The results of aromatics obtained by the developed method for samples of RFCC feeds from different sources have shown good correlation with the standard methods of open column chromatographic separation (ASTM D-2549, R2 = 0.992) and saturates, aromatics, resins, and asphaltenes analysis by thin-layer chromatography−flame ionization detection (IP-469, R2 = 0.993). The nature of the alkyl chain length of aromatic substituents and saturate fractions has also been discussed. The detailed hydrocarbon data have been utilized for the development of a process model for predicting the product profile and yield pattern.