1H- and 13C-n.m.r. studies on naphtha and light distillate saturate hydrocarbon fractions obtained from in-situ shale oil

Shale oil, obtained from an in-situ oil shale experiment, from the Green River formation in Southwestern Wyoming was thermally fractionated into naphtha, light distillate, heavy distillate and residue fractions. The naphtha and light distillate fractions were further separated into saturates, olefins and aromatic subfractions. ¹H- and ¹³C-n.m.r. spectra and mass spectral data were obtained for the saturated hydrocarbons of the naphtha and light distillate fractions. Resonances in the n.m.r. spectra were assigned to normal alkanes and to methyl- and dimethyl-branched alkanes. The composition as determined by n.m.r. of the naphtha saturates was found to be ≈82% straight-chain alkanes with an average carbon-chain-length of ≈C₁₁ and ≈18% branched/cyclo-alkanes. The composition of the light distillate saturates was found to be ≈ 69% straight-chain alkanes with an average carbon-chain-length of ≈C₁₅and ≈31% branched/cyclo-alkanes. The dimethyl-branched alkanes in both saturate fractions were proposed to have the molecular substructure of saturated isoprenoids. In the naphtha saturates the isoprenoid substructure

is evident. However, in the light distillate saturates, both isoprenoid substructures,

and

, are evident. ¹³C spin-lattice re-laxation times also were determined for the dominant resonances observed in the spectra of the naphtha and light distillate saturates. Relaxation times for the molecular species in the naphtha saturate fraction were observed to be longer than those observed for the light distillate saturate fraction. It was found that the ratio of the overall average relaxation times for the naphtha and light distillate saturate fractions corresponded to the inverse ratio of the average molecular weights of each fraction as determined from average alkane carbon-chain-length determination. Intermolecular (segmental) motion of the carbon chain of the straight-chain alkanes in both saturate fractions is also evident from the relaxation time measurements.     

Analysis of upgraded SRC-11 and H-coal liquid products

Upgraded coal-derived liquids obtained from catalytic hydroprocessing of SRC-11 and H-coal syncrudes have been studied by i.r., p.m.r., g.c.-m.s., and silica gel chromatography. With increase in residence time, nitrogen, oxygen and aromatics decrease, while naphthenes increase substantially. All the upgraded liquids show low viscosity at 298 K (1.3–1.4 mN s m^?2), even though saturate and aromatic fractions varied with processing severity. In the aromatic-1 fraction, 1 -ring aromatics increase, and 3-ring aromatics decrease, with increase in severity of hydroprocessing. G.c.-m.s. analyses indicate a marked qualitative similarity for saturate and aromatic fractions irrespective of syncrude source. Only the heavier end of the aromatic-1 fraction is noticeably different. Tentative identifications based on m.s. and g.c. retention times are made for most of the significant components. 600 M Hz p.m.r. spectra of the upgraded SRC-11 and H-coal liquids appear identical, but the n.m.r. difference technique revealed slight differences between the two liquids in concentrations of certain species.     

Pyridine extracts of solid fuels

Pyridine extracts of a coking coal and of two lignites have been further separated and the ¹H and ¹³C n.m.r. spectra of the various fractions have been recorded. Three methods of separation were investigated: gel-permeation chromatography, successive extraction with petroleum ether and with benzene as used by previous workers for supercritical-gas extracts, and the classical extraction of the fractions. Gel-permeation chromatography gave most promise of effective separation but the fractions obtained often contained too little material to give n.m.r. spectra. The n.m.r. spectra of the chloroform-soluble material from the pyridine extracts of the coking coal were consistent with a material consisting of polynuclear aromatic nuclei joined through simple bridge structures and possibly also through direct carbon—carbon linkages. The nuclei were substituted by branched and unbranched paraffin chains, some of which were 7 or 8 carbon atoms long. It is probable that alicyclic structures were also present. The aromatic nuclei were mobile in solution. 60% of the carbon atoms were aromatic, and it can therefore be calculated that the molecular weight per aromatic nucleus was 200–300. It is suggested that ¹³C n.m.r. spectra may be used to characterize chemicals likely to confer coking properties on solid fuels.     

Investigation of aromatic carbon sites in materials derived from petroleum and coal using 13C n.m.r. methods

Aromatic C and CH carbon sites in a variety of petroleum and coal derived materials have been investigated using a ¹³C n.m.r. technique termed spin echo broad band off-resonance decoupling (SEBBORD). Only resonances due to non-protonated aromatic carbon sites are observed in SEBBORD spectra such that comparison with conventional ¹³C n.m.r. spectra enables differentiation between aromatic C and CH group resonances. Relative abundances of non-protonated aromatic carbon sites calculated from SEBBORD data are in good agreement with values derived from a combination of conventional¹H n.m.r., ¹³C n.m.r. and elemental analysis data. The occurrence of significant proportions of aromatic C intensity to high field of 129–130 ppm and of aromatic CH intensity to low field of 129–130 ppm has been found to be quite common. Consequently attempts to determine aromatic C and CH group abundances by partitioning conventional ¹³C n.m.r. spectra in the vicinity of 129–130 ppm can lead to considerable quantitative errors. SEBBORD provides more detailed information about aromatic carbon sites than can be obtained from conventional ¹³C n.m.r. spectra.     

Quantitative FT 13C n.m.r. of solvent-refined coals using sym-triazine as solvent

Aromaticities (f_a) determined for several solvent-refined coals (SRC) by ¹³C n.m.r. in sym-triazine solution and by the Brown and Ladner ¹H n.m.r. technique have been found to be the same within experimental error (0.01). Use of sym-triazine to determine the f_a of the soluble and insoluble fractions of a SRC in several solvents showed that the soluble fraction reflected reasonably accurately the properties of the whole sample for dioxan, carbon disulphide, chloroform and benzene extracts. The properties of the insoluble fraction varied only slightly. A more detailed analysis of the aromatic region of the ¹³C n.m.r. spectrum has led to some useful structural relations.     

Determination of carbon C,CH, CH2 and CH3 group abundances in liquids derived from petroleum and coal using selected multiplet 13C n.m.r. spectroscopy

Selected, multiplet C n.m.r. spectra are obtained for three test samples deriving from petroleum and coal sources, by combining gated spin echo (GASPE) and conventional spin echo ¹³C n.m.r. procedures. Each selected multiplet spectrum contains resonances due to only one of the following groups: aromatic C or CH or aliphatic C, CH, CH₂orCH₃. In general artifacts contribute only minor intensity to individual spectra, with the separation between aliphatic CH and CH₃ spectra being the most difficult to achieve. Each spectrum can be integrated to yield the relative abundances of CH_n groups (n = 0 to 3). Selected multiplet ¹³C n.m.r. spectra provide a more detailed view of the component hydrocarbon groups in fossil-fuel derived materials than can be deduced from conventional ¹³C n.m.r. spectra.     

Average structures of petroleum pitch fractions by n.m.r. spectroscopy

Ashland A-240 pitch was fractionated by sequential solvent extraction and hypothetical average molecular structures for the whole pitch and its fractions were determined by using ¹H and ¹³C n.m.r. spectroscopy. The average molecules contain condensed aromatic ring systems substituted by short alkyl side chains in both A-240 pitch and the pitch fractions. This result conflicts with Seshadri et al's claim that the Ashland pitch fractions consist of molecules with uncondensed aromatic ring systems linked by aliphatic bridges. It is shown that Seshadri et al's results are probably based on nonquantitative ¹³C n.m.r. data due to the use of a low concentration of paramagnetic relaxation agent.     

Structural characterization of coal-hydrogenation products by proton and carbon-13 nuclear magnetic resonance

Heavy oil derived from coal hydrogenation was separated into saturated fractions, neutral aromatic oil, and asphaltene, and these materials were subsequently fractionated according to the magnitude of their respective molecular sizes by gel-permeation chromatography. These GPC subfractions were analysed by proton and carbon-13 n.m.r. spectroscopy and by an additional procedure using gas chromatography for the paraffinic GPC subfractions. ¹³C-n.m.r. spectra for the GPC subfraction of saturated material showed typical long straight-chain paraffin spectral patterns accompanied by iso-and cycloparaffinic carbon signals. The results from gas-chromatographic measurement for the paraffinic GPC subfractions agree fairly well with the trends of average carbon numbers and contents of straight-chain paraffins obtained by varying the fraction numbers, estimated from ¹³C-n.m.r. analyses. The ratios of aromatic carbon to total carbon (f_a) for aromatic oil and asphaltene GPC subfractions obtained directly from ¹³C-n.m.r. spectra are slightly lower than the results from the ¹H-n.m.r. method assuming x = y = 2 in the Brown—Ladner equation. Peak intensities of the respective carbon species in ¹³C-n.m.r. spectra were compared with the peak intensities of correspondingly bonded species obtained from ¹H-n.m.r. measurement. Some inadequacy was recognized in both measurements. It is assumed that there are two reasons for the discrepancy, one of which is the inaccuracy of ¹³C-n.m.r. results owing to the long relaxation times and the effect of Nuclear Overhauser Enhancement, and another is the application of unsuitable values of x and y for calculations from the Brown—Ladner equation. New analytical treatments for ¹³C-n.m.r. results in combination with ¹H-n.m.r. analyses are suggested in this study to avoid these uncertainties in structural analyses. From this procedure, it is believed that the actual contents of aromatic and aliphatic carbon and appropriate values of x and y can be derived.     

Chemical composition of Athabasca bitumen

A detailed analysis has been carried out on the deasphaltened Athabasca bitumen using two different series of Chromatographic separations followed by i.r., u.v., n.m.r. and computerized GC/MS studies of the separated fractions: saturates (22–25%), monoaromatics (10.3–10.8%), diaromatics (4.6–5.3%), polyaromatics and non-specific polar compounds (28.6%), acids (16.5%), bases (7.8%), and neutral nitrogen compounds (1.6%). The acyclic paraffin content of the maltene is low: straight-chain paraffins and the isoprenoids, phytane and pristane, are present in very low concentrations. Polycyclic saturates represent about 90% of the saturate fraction. The presence of C-27 and C-29–C-35 hopanes of the 17(h):21β(H) series and C-21–C-30 steranes was established. The mono- and diaromatic fractions were analysed by computerized mass spectrometry. The monoaromatic fraction contains alkylbenzenes, naphthenebenzenes and dinaphthenebenzenes in a ratio of 1.0:1.7:1.3. The ratio for naphthalenes, acenaphthenes + dibenzofurans and fluorenes in the diaromatic fraction is 1:0.9:0.5.     

Aromatic products of 340 °C supercritical-toluene extraction of two Turkish lignites: an n.m.r. study

Fractions of Elbistan and Seyitomer (Turkish) lignites, extracted with supercritical toluene at 340 °C and 8 MPa, have been separated by solvent extraction and silica-gel chromatography. Analyses by n.m.r. and i.r. spectroscopies and other methods have been combined in structural-analysis schemes to yield information about the average molecule in aromatic extracts. Carbon aromaticities, f_a, derived from 22.63 MHz ¹H-decoupled pulse Fourier-transform (PFT) ¹³C-n.m.r. are more widely spread for Elbistan (0.34–0.56) than for Seyitomer (0.40–0.43), and are lower than for supercritical-gas (SCG) products from bituminous coals. ¹³C-n.m.r. also reveals the presence of aromatic ether-O in polar fractions. Narrow aromatic signals in 100 MHz ¹H-n.m.r. spectra suggest the presence of single-aromatic-ring average structures. In the hexane-soluble aromatics, 27% (Elbistan) and 29% (Seyitomer) of the available sites are substituted by alkyI groups, some of which are at least eight carbon atoms long; the hexane-soluble polar and asphaltene/asphaltol fractions contain fewer such groups.     

Chemical composition of Cold Lake bitumen

A detailed analysis has been carried out on the deasphaltened Cold Lake bitumen using two different series of chromatographic separations followed by i.r., u.v., n.m.r. and computerized GC/MS studies of the separated fractions: saturates (21.3), monoaromatics (8.3), diaromatics (3.6), polyaromatics and non-specific polar compounds (24.35), acids (15.2), bases (6.38), and neutral nitrogen compounds (1.15% of bitumen). The acyclic paraffin content of the maltene is low but decidedly higher than in the related Athabasca bitumen, indicating that the Cold Lake bitumen suffered a less complete biodegradation. Straight-chain paraffins and the isoprenoids phytane and pristane are present. The mono- and diaromatic fractions were analysed by high-voltage, low-resolution mass spectrometry. The monoaromatic fraction contains alkylbenzenes, naphthenebenzenes and dinaphthenebenzenes in a ratio of approximately 1:1:1. The ratio for naphthalenes, acenaphthenes + dibenzofurans and fluorenes in the diaromatic fraction is approximately 1:0.9:0.6. The composition of Cold Lake bitumen closely resembles that of the Athabasca bitumen except that its asphaltene content is somewhat lower and its acidic and saturate content is slightly higher.     

Structural characterization of fractions of petroleum pitch and ethylene pyrolysis tar by 1H and 13C n.m.r. spectroscopy

A petroleum pitch and > 288 °C fraction of an ethylene pyrolysis tar are separated by sequential solvent extraction into fractions differing in average molecular weight. Average molecular parameters for each fraction are obtained using their H and ¹³C n.m.r. spectra. Average molecular structures which correlate with the observed data are drawn. The data presented here suggest that the average molecule of the fractions of both petroleum pitch and pyrolysis tar can be represented by an oligomeric structure in which small aromatic clusters are joined by aliphatic bridges and/or biaryl linkages. This contradicts the accepted assumption that the aromatic ring system in petroleum-derived products is fully condensed. Although the average molecular structure of the fractions of pitch and ethylene pyrolysis tar are basically similar, they differ in the number and types of ring-saturated carbons.     

Nuclear magnetic resonance spectra of two reductively ethylated fuels

A lignite (67.2% C daf) and a coal (89.0% C daf) have been reductively ethylated by Sternberg's procedure⁴ and the spectra, in particular the ¹H and ¹³C n.m.r. spectra, of the products have been obtained. The distribution of hydrogen atoms and, in less detail, of carbon atoms in the reductively ethylated fuels has been determined. It is emphasized that both reductively ethylated fuels contained a variety of structures. The carbon aromaticities of the reductively ethylated lignite and the reductively ethylated coal were 0.41 ± 0.08 and 0.40 ? 0.54 respectively. The aromatic nuclei of the reductively ethylated coal were more highly substituted than those of the reductively ethylated lignite. The ¹H n.m.r. spectra indicate that the reductively ethylated coal and lignite possessed ≈3.5 and ≈2.5 substituents per benzene ring respectively. Resolved absorption in the ¹³C n.m.r. spectra suggests lower figures than these and it was evident that some of the benzene rings in both materials but especially in the reductively ethylated lignite were lightly substituted. The ¹³C n.m.r. spectra show that both materials contained branched and unbranched paraffin chains. Much of the ¹³C n.m.r. spectra however consisted of unresolved absorptions and the ¹³C n.m.r. measurements suggest that the reductively ethylated materials consisted of rigid, relatively immobile molecules of moderate molecular weight. ¹³C n.m.r. absorption by carbon atoms adjacent to aromatic rings was amongst that which was not resolved — though the rings themselves gave resolved absorptions — and this suggests that the aromatic rings were on the periphery of a rigid, perhaps alicyclic, structure.     

Characterization of organic material in coal by proton-decoupled 13C nuclear magnetic resonance with magic-angle spinning

¹³C n.m.r. spectra have been obtained on ten solid coal samples of various types and on three coal-derived materials, using high-power proton decoupling, cross polarization and magic-angle spinning, and provide valuable information on the carbon distribution between aromatic and non-aromatic structures in the sample. Apparent carbon aromaticities, f_a′, have been determined and have been correlated with H/C ratios and as one factor in fuel values. Both solvent refining and reverse combustion (see introduction) are found to increase the aromatic fraction. These techniques should be very useful in characterizing and optimizing coal-conversion processes.     

Application of new 13C n.m.r. techniques to the study of products from catalytic hydrodeoxygenation of SRC-II liquids

A middle-heavy SRC-II distillate (b.p. 230–455 °C), containing 3.0 wt% of oxygen, has been studied by means of ¹³C n.m.r. at 75, 100 and 125 MHz. The magnetization refocussing techniques INEPT and J-resolved two-dimensional Fourier transform have been utilized to demonstrate methods by which resonance line multiplicities may be determined in complex liquid mixtures. Products derived from the above coal liquid by hydrodeoxygenation at temperatures from 200 to 370 °C, using sulphided Co—Mo and Ni-W catalysts, were also examined. The fraction of aromatic carbon in the hydrotreated liquids was found to correlate directly with their C/H atomic ratio and inversely with the hydrogen content. Comparison of O/C atomic ratios with f_a values for these liquids indicates that hydrogen uptake < 260 °C is associated primarily with hydrogenolytic oxygen removal without attendant ring hydrogenation, while at temperatures between 260 and 350 °C hydrodeoxygenation is accompanied by ring hydrogenation and dealkylation reactions.     

Studies on the composition of some distillate waxes

Structural composition of two distillate waxes obtained from Ankleshwar crude oil tank bottoms have been determined using physical properties correlations, high temperature g.l.c., ¹H-n.m.r. and ¹³C-Fourier transform n.m.r. spectroscopy. Both waxes seem to contain predominantly n-paraffins.     

Liquefaction reaction of coal: 2. Structural correlation between coal and its liquefaction products

The structural correlation between coal and its liquefaction products has been examined using cross-polarization, magic angle spinning (CP/MAS) ¹³C n.m.r. and field ionization mass spectrometry (f.i.m.s.). The CH₂/aromatic carbon ratios of all solid products (asphaltene, preasphaltene and residue) were close to the corrected +CH₂/aromatic carbon ratio for the coal. This suggests that the ring structure of the structural unit of each solid product is essentially similar to that of the parent coal, except for a difference in the degree of polymerization of the structural units. The CH₂/aromatic carbon ratios of aromatic ring-type oil fractions also correlated with the corrected ratio for the coal, although they were larger. The z series distribution obtained from the f.i.m.s. of oil fractions revealed that coal with a higher CH₂/aromatic carbon ratio produced an oil rich in naphthenic structures.     

Structural characterization of Saudi Arabian heavy crude oil by n.m.r. spectroscopy

Saudi Arabian heavy crude oil was separated into six fractions, including five distillate fractions (<93, 93–204, 204–260, 260–343 and 343–454 °C) and a >454 °C distillation residue. Each fraction was analysed by ¹H and ¹³C n.m.r. spectroscopy, and combined gained information from these analyses provided reliable average structural parameters. These included estimation of aliphatic and aromatic content, average paraffinic chain length, and estimation of hydrogen, methyl and alkyl bearing aromatic carbons for each of the six fractions. The extent of branching in paraffinic chains and amount of aromatic bridgehead carbons were also calculated.     

Unsaturated polyesters based on terephthalic acid: 3. Characterization of poly(propylene terephthalate) prepolymer by gel permeation chromatography

Oligomers in prepolymers prepared by the polyesterification of terephthalic acid (T) with excess 1,2-propylene glycol (P) have been separated by gel permeation chromatography (g.p.c.). The assignment of chromatogram peaks to oligomers according to the structure P (TP)_n where n is the number of 1,2-propylene terephthalate repeating units has been confirmed by a g.p.c. examination of bis(2-hyroxypropyl) terephthalate and by a ¹H nuclear magnetic resonance (n.m.r.) spectroscopic study of fractions isolated from a preparative separation. The infrared g.p.c. detector response has been interpreted quantitatively in order to deduce the concentration of each oligomer from the area of its chromatogram peak. Mol fraction distributions as a function of n have been determined for the prepolymer samples. Number average molecular weights have been calculated for the terephthalate-based components of the prepolymer and for all components including excess propylene glycol. These g.p.c. molecular weights are in excellent agreement with values previously reported in a study of prepolymers by ¹H n.m.r. spectroscopy. G.p.c. studies on prepolymers after reactions with a carbodiimide and diazomethane suggest a very minor quantity of carboxyl terminated species in the prepolymer samples.     

An h.p.l.e. and m.s. analysis of distillate fractions of neutral oil from hydrogenated Akabira coal to elucidate chemical structures

Akabira coal-derived neutral oil was separated into 25 narrow boiling range fractions covering 183–423 °C, and subsequently separated into compound class fractions : alkanes, monoaromatics, naphthalene-type diaromatics, fluorene-type diaromatics and tri- and/or tetraaromatics, by high performance liquid chromatography (h.p.l.c.). The compound type analyses of the distillate/h.p.l.c. fractions were performed using electron impact mass spectroscopy (e.i.m.s.) or field ionization mass spectroscopy (f.i.m.s.). Aromatic/hydroaromatic compound types and the alkyl side-chain carbon distribution of the distillate/h.p.l.c. fractions were clarified, based on the separation behaviour of h.p.l.c. and the type analyses according to Z value by m.s. By the distillation/h.p.l.c./m.s. method, coal-derived oil was characterized in terms of the distribution of the numbers of aromatic rings, naphthenic rings and carbons of alkyl groups attached to these rings. The variations in chemical structure in a compound class with distillation temperature are discussed in terms of these chemical structural factors.