A.S. Sarpal

Chemical structure of bitumen-derived asphaltenes by nuclear magnetic resonance spectroscopy and X-ray diffractometry

Abstract Asphaltene samples obtained from bitumen processed at three Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (n.m.r.) spectroscopy and X-ray diffractometry (XRD). The average structural parameters were obtained by combined 1H, 13C and DEPT spectral editing techniques. New equations were used for the estimation of n.m.r. average structure parameters. The macrostructure and crystalline parameters of these samples were obtained by XRD. A combined n.m.r. and XRD procedure was used to estimate the size of the average aromatic structural unit. Asphaltenes from one of the bitumens (ASP-D) was found to have different structural parameters from those of the asphaltenes from the other two bitumens. The number of aromatic rings per unit sheet in ASP-D was eight, compared with 13 for both ASP-M and ASP-H. XRD data indicated that the aromatic sheets are randomly oriented in ASP-D. The structural parameters allowed a model structure of the asphaltenes to be constructed.

Determination of aromatics and naphthenes in straight run gasoline by 1H NMR spectroscopy. Part I

A 1H NMR-based method has been developed for determining the composition (aromatics, naphthenes and paraffins) of straight run gasoline fractions. The equations required for the calculations have been derived based on the assignment of the overlapped 1H NMR spectra of the samples with particular emphasis on signals from naphthenes and iso-paraffins. The 1H NMR results have been compared with those obtained from GC method. The absolute standard deviations between the NMR and GC methods are1.7 and 2.1% for total aromatics and naphthenes, respectively.

Characterization by 13C n.m.r. spectroscopy of base oils produced by different processes

Abstract The hydrocarbon composition of base oils produced by different processes—hydrotreatments (hydrocracking and wax isomerization), solvent refining plus hydrofinishing, and severe hydrofinishing—were determined by 13 C n.m.r. spectroscopy. Structural parameters such as normal and iso-paraffin contents, average chain length and number of branching sites were estimated by new equations derived after complete assignment of signals in the 5–21 ppm 13 C n.m.r. region. Quantitative differences in various types of branched structures among different categories of base oils were established. Relations between specific iso-paraffinic structures responsible for very high viscosity index and low pour point are discussed in terms of mobility behaviour and spin-lattice relaxation time measurements.

Hydrocarbon characterization of hydrocracked base stocks by one- and two-dimensional n.m.r. spectroscopy

Abstract Characterization of a number of unconventional catalytically hydrogenated base stocks of low aromatic content and high viscosity index is discussed in terms of hydrocarbon types, with emphasis on isoparaffinic structural analysis. The analysis was carried out using multipulse one- and two-dimensional n.m.r. spectral techniques. Various spectral regions characteristic of different structural units were assigned based on DEPT, 2D COSY and HETCOR spectroscopy. The presence of eleven different types of branched structures was established. The analysis of 1D and 2D n.m.r. spectra further provided reliable average structural parameters. The aromatic carbon (C A ) content of these samples was found to be

Modified method for hydrocarbon type analysis of blended base stocks by infrared spectroscopy

Abstract A modified method is described for the determination of the aromatic, naphthenic and paraffinic carbon contents of blended base oils by infrared spectroscopy. These oils are blends of mineral base oils and linear alkylbenzenes (LAB) or heavy alkylated benzenes (HAB). The Brandes equation has been modified to account for the absorptivity of LAB/HAB, using 13 C n.m.r. data as a reference. The results obtained by applying the new equation to such blends agree well with those obtained by n.m.r. This new method can be used for rapid and convenient quality control during base oil production.

DIRECT ESTIMATION OF AROMATIC CARBON (Ca) CONTENT OF BASE OILS BY 1H-NMR SPECTROSCOPY

ABSTRACT A direct and fast method for the estimation of aromatic carbon content (Ca) in base oils produced through different processes has been developed based on 1H-NMR spectroscopy. The identity of the complex and overlapped 1H-NMR region of 2.0−3.5 ppm, which constitutes resonances from α-substituents (−CH, −CH2 and −CH3 groups), has been revealed by 2D HetCor spectral analyses. This information has facilitated the estimation of quaternary (Cq) and bridgehead (Cb) aromatic carbons from 1H-NMR spectrum using the derived equations. The complete and unambiguous assignment of the 1H-NMR spectrum led to the estimation of Ca content of base oils. The classical Brown-Ladner (BL) equation for Ca estimation has been modified by taking the actual contribution of −CH, CH2 and CH3 groups, instead of using average values. The proposed 1H-NMR, and the modified BL methods correlate very well (R2 = 0.97) with the standard 13 C-NMR method for Ca estimation.

Carbon type analysis of hydrotreated and conventional lube-oil base stocks by i.r. spectroscopy

Abstract An infrared spectroscopic method is described for the determination of isoparaffin carbon content in lubricating-oil base stocks. The paper also describes a modified method for the accurate estimation of paraffinic carbon content of hydrotreated base stocks. The methods are based on correlations of 13C n.m.r. hydrocarbon analysis data with area-integrated intensities of the i.r. spectral bands of skeletal vibrations in the 1200-1100 cm−1 region, the peak area in the 830-800 cm−1 region and methylene wagging bands in the 790-700 cm−1 region. The correlation coefficients obtained are 0.88 and 0.82 for the estimation of paraffin carbon content (Cp) and isoparaffin carbon content (Ip) respectively.