Hydrocarbon structural group analysis of Athabasca asphaltene and its g.p.c. fractions by C n.m.r.

Asphaltene from the Athabasca oil sand bitumen separated according to molecular weight by gel permeation chromatography was examined by high resolution solution-state ¹³C and ¹H and solid state ¹³C n.m.r. Integration of the inverse gated decoupled solution state and CP/MAS ¹³C n.m.r. spectra gave the aromaticity of each fraction as well as the relative number of carbon atoms responsible for well resolved signals in the aliphatic portion of the spectra. A two-pulse spin-echo ¹³C n.m.r. sequence in the solution state, and dipolar dephasing in the solid state, permitted the assignment of each aliphatic carbon signal to a methyl, methylene, or methine carbon; no quaternary aliphatic carbons were observed. These signals show that the aromatic core of the asphaltene is surrounded by alkyl chains with a mean length of 7.7 for the lowest molecular weight fraction (MW 1200), increasing to 12 for the highest MW fraction (MW 16900). Aromaticity of the fractions obtained from solution spectra ranged from 34 to 48%, the highest aromaticity being associated with the lowest molecular weight asphaltenes. In the solid state, the aromaticity ranged from 31 to 42 %. The degree of branching ranged from 0.5 per chain for the low MW asphaltene to 1.0 for the high MW fraction. The highest naphthenic carbon content was found in the high MW fractions; the 1200 MW fraction appeared to be nearly devoid of such carbon, this fraction having a much higher aromaticity than the second-lowest MW fraction.     

Evaluation of a delayed coking process by H and C n.m.r. spectroscopy: 1. Material balances

The use of ¹H and ¹³C nuclear magnetic resonance (n.m.r.) spectroscopy to evaluate the performance of a delayed coking process is presented in a series of papers, of which this is the first. A meaningful analysis requires an accurate balance, which in turn requires analysis of the various types of atoms in the feed and in all products, including solid coke, as well as the amounts of each. Product yields were determined in a delayed coking pilot plant. Complete n.m.r. (¹H and ¹³C) characterization of feed and all delayed coking products, using a consistent classification, was combined with pilot plant data to obtain the total distribution of carbon and proton atoms in the delayed coking process. Changes in carbon and hydrogen distributions (products versus feedstock) reveal the nature of the thermal cracking reactions involved; the main change is a substantial increase in the number of aromatic and paraffinic carbons at the expense of naphthenic carbons.     

Two-dimensional n.m.r. characterization of cycloaliphatic epoxy resins

The cycloaliphatic epoxy resins were studied by various two-dimensional nuclear magnetic resonance (2D n.m.r.) spectroscopies. The ¹³C n.m.r. spectra of the epoxy resins were assigned by using DEPT and 2D INADEQUATE techniques and the ¹H n.m.r. spectra were assigned by using 2D ¹H---¹H and ¹H---¹³C COSY techniques. Complete characterization of the samples synthesized by the oxidation of cyclohexene derivatives not only revealed the existence of the stereochemical isomers resulting from the structural difference of the oxide rings in the samples but also provided the composition ratio of the isomers.     

Determination of the apparent ratio of quaternary to tertiary aromatic carbon atoms in an anthracite coal by C-H dipolar dephasing n.m.r.

¹³C-¹H heteronuclear dipolar dephasing n.m.r. techniques allow discrimination between different chemical species contributing to the ¹³C n.m.r. spectra of complex hydrocarbons. Model compound studies show significantly different effective transverse relaxation constants for carboxyl and quaternary carbon atoms (≈200 μs), secondary and tertiary (≈20 μs), and primary carbon atoms (≈80 μs). Use of these effective relaxation data, together with appropriately timed windows in the continuous wave decoupling applied in standard cross-polarization-magic-angle spinning experiments on anthracite coal allow discrimination between aromatic tertiary and aromatic quaternary ring carbon atoms in this coal. Within the accuracy of experimental error, and of the structural modelling experiments herein reported, the use of the dipolar dephasing technique together with results of X-ray diffraction on coals allows a reasonable estimate to be made of the average number of condensed polynuclear rings in an ‘average molecule’ in the anthracite studied. Based on a model of pericondensed aromatic rings, this number lies between 33 and 45.     

Structural analysis of Aleksinac oil shale kerogen by high-resolution solid-state C n.m.r. spectroscopy

A sample of kerogen from Aleksinac oil shale was examined by high-resolution solid-state ¹³C n.m.r. spectroscopy. The presence and relative proportions of kerogen structural units were estimated using a combination of NQS and T_1C methods with a peak-synthesis technique applied to the ¹³C CP—MAS spectrum. Relaxation parameters from these experiments were used to estimate differences in relative ‘mobility’ of various structural units. The kerogen was found to be highly aliphatic and to contain 79% long-chain aliphatic plus alicyclic structures, as well as 9% aromatic structures. These findings are in good agreement with the characterization of the same kerogen from its oxidation products.     

C cross-polarization n.m.r. examination of the Glen Davis oil shale deposit

The use of solid-state ¹³C cross-polarization n.m.r. for rapid analysis of bore cores is demonstrated by examination of subsections of a Glen Davis oil shale bore. The determined aromaticities, f_a, differ widely between subsections indicating large variability in potential oil yields. The variation does not correlate with depth of subsection but is shown to correlate well with maceral composition. The correlation found previously by Zilm and co-workers (Fuel 1981, 60, 717) between f_a, determined by solid-state ¹³C n.m.r., and wt% fixed carbon for a range of macerals is found to be supported by the data for Glen Davis subsections which are mixtures of all three maceral types.     

Studies on copolymers of acrylonitrile with resins of furfuryl alcohol: 1. Preparation and thermal properties

Copolymers of acrylonitrile with a furfuryl alcohol resin have been prepared by a free radical reaction, and have been characterized by n.m.r. and i.r. spectroscopy. Their t.g.a. has been performed in air and in a nitrogen atmosphere, to permit the recognition of a number of stages in the weight loss process. D.s.c., also in air and in nitrogen, has identified a number of exothermic and one endothermic process in the copolymers. Solid state cross-polarization/magic angle spinning ¹³C n.m.r. spectroscopy and i.r. spectroscopy has been used to obtain some insight into the chemistry of the various chemical changes, which in air are completed by combustion and in nitrogen leave a carbon.     

C nuclear magnetic resonance spectral analysis of stereosequences in ethylene-propylene copolymer

A number of split peaks dependent on both comonomer sequences and stereosequences were observed in the ¹³C nuclear magnetic resonance (n.m.r.) spectrum of ethylene-propylene (E-P) copolymer. The ¹³C chemical shifts of methylene carbon in stereoisomers of the respective hexad comonomer sequences were predicted by a chemical-shift calculation using the gamma effect on ¹³C chemical shifts and Mark's rotational isomeric state model for E-P copolymer. Assignments of the split peaks that arise from different hexad stereosequences were given by comparison between the observed and calculated chemical shifts. Reference was made to the hexad assignments of comonomer-sequence-dependent peak splittings determined in our previous calculation of ¹³C n.m.r. chemical shifts of stereoregular E-P copolymers. The tacticities were estimated for successive (not separated by ethylene units) propylene units in the hexad sequences.     

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.     

N.m.r. study of egg yolk lecithin in aromatic solvents. Magnetic nonequivalence in the methylene protons of the fatty acyl chains

¹H and ¹³C n.m.r. chemical shifts and also spin-lattice relaxation times of phospholipids, mainly egg yolk lecithin, were measured in organic solvents, especially aromatic solvents. The use of aromatic solvents promotes the difference in the magnetic shielding environment of the internal methylene protons of the fatty acyl chains and as a result, a doublet peak for the methylene groups was observed in the solvents, especially mesitylene. The ¹H and ¹³C n.m.r. T₁ measurements indicate the remarkable gradient in the motional freedom along the fatty acyl chains as well as the marked decrease in the motional freedom of the polar head group and also, the high-field component of the doublet peak for internal methylene protons has a shorter T₁ value than the low-field component. Thus, it was concluded that the low-field component in the doublet comes from the methylene protons located relatively in the neighbourhood of the carbonyl groups and the high-field component the methylene protons located relatively in the neighbourhood of the terminal methyl groups of the fatty acyl chains.     

High resolution solid state C n.m.r. of Canadian peats

Peat samples from three locations in Quebec, Canada, were characterized by ¹³C CP/MAS n.m.r. spectroscopy. The n.m.r. analysis indicates that the peats contain a significant amount of unaltered plant components including cellulose, hemicellulose, lignin, waxes and resins. Integration of specific regions of the spectra can give semi-quantitative estimates of some of these plant components and, in limited cases, information about the degree of decomposition can be obtained from the ¹³C CP/MAS n.m.r. spectrum. Dipolar dephasing experiments and difference spectroscopy were found to be valuable techniques for spectra assignments and enhancement of compositional differences.     

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.     

Study of Kansk-Atchinsk lignite liquefaction in lower aliphatic alcohols using flow periodical function

The action of lower aliphatic alcohols on lignite conversion to liquid products has been studied using flow periodical function. Ethanol and isopropanol were shown to be most active. The lignite conversion is accompanied by enrichment of the aliphatic fragment, both in the liquid and solid phase. The degree of condensing of the aromatic fragments in liquid increases with the enhancement of lignite conversion and does not depend on the alcohol species. Substitution degree of aromatic fragments and the number average molecular weight of liquids decreases in the order methanol ethanol isopropanol. I.r and ¹H n.m.r. data and elemental analysis have shown that alkylation both of liquid and solid products takes place during lignite liquefaction A linear relation between the quantity of aliphatic fragments in solid and the lignite conversion in ethanol is established.     

Property estimation using structural characterizations: Heat capacities of coal liquids

Three coal liquids were characterized by estimating the concentrations of the functional groups present in the liquids. The concentrations were deduced using data from Chromatographic separations, elemental analysis, ¹H n.m.r., ¹³C n.m.r. and mass spectrometry. The concentration estimates were then used, in conjunction with simple group additivity rules, to estimate the heat capacities of the liquids as a function of temperature. The heat capacity estimates were in excellent agreement with experimentally determined values.     

High temperature and high pressure H n.m.r. and e.s.r. studies on coal liquefaction reactions

Changes in chemical reactions during coal liquefaction of Yallourn brown coal and Akabira bituminous coal were monitored by using high temperature and high pressure ¹H n.m.r. A simple high temperature and high pressure e.s.r. cell was constructed and the variation in concentration of free radicals during coal liquefaction reactions was monitored under the same experimental conditions as for n.m.r. With the liquefaction and coking reaction, typical spectra of n.m.r. and e.s.r. were obtained and could distinguish the reaction steps: swelling; liquefaction; coking. The combination of high temperature and high pressure n.m.r. and e.s.r. is promising to the chemistry of coal liquefaction reactions.     

Determination of carbon centre types in solid fuel materials by CP/MAS n.m.r.

Methyl, quaternary aliphatic and aromatic, and hydrogen-bearing aliphatic and aromatic carbon centres in solid fuel samples have been determined quantitatively by pulse-programmed ¹³C n.m.r. coupled with elemental analysis. The method may be used for unaltered samples of oil shales, coals, etc., and has been tested on model compounds representative of components in these materials.     

Prospects for carbon-13 nuclear magnetic resonance analysis of solid fossil-fuel materials

Because of excessive line broadening in solids due to magnetic dipole—dipole interactions and chemical shift anisotropies, and because of long spin-lattice relaxation times, standard continuous wave (CW) or pulse Fourier transform techniques do not normally yield structurally informative ¹³C n.m.r. spectra from solid samples. However, the techniques of dipolar decoupling, cross polarization and magic-angle spinning show great promise for routine ¹³C n.m.r. studies of solids. Applications of these techniques to analysis of anthracite, lignite and algal coal samples, and to oil shale and kerogen samples, are discussed. It is shown that cross-polarization spectra obtained with dipolar decoupling display chemical shift anisotropy which interferes with attempts to distinguish the resonances of aromatic and aliphatic carbons. However, with magic-angle spinning the distinction can be made. Prospects and potential difficulties with applications of these techniques are discussed.     

Water mediated modification of structure and physical chemical properties of nanocarbons

Considerable amount of water incapsulated in native shungite carbon (ShC) and its amphiphilic properties are originated from fullerene-like structure. We report on the study of ShC and its stable aqueous dispersion by high-resolution solid state ¹³С and ¹Н MAS NMR, and time-of-flight (TOF) mass spectrometry. ¹³С NMR spectrum changes substantially as ShC was transformed into aqueous dispersion: a narrow sp²-carbon signal (at 116 ppm) attributed to the basic structural unit (BSU) in the form of bowls is observed. Distance from carbon atoms in BSU to hydrogen atoms of water was estimated at  0.8 nm using cross-polarization technique. ¹H solid state NMR spectrum consists of two peaks at 0.40 and 3.16 ppm. They were assumed to be related to water complexes on BSU (0.40 ppm) and to adsorbed water (3.16 ppm). TOF mass spectra of the ShC aqueous dispersion showed maximum intensity at  284 m/z corresponding to the dominant structure of ShC.     

宁夏庆华煤镜质组和惰质组显微组分的分子结构及对比分析

使用密度梯度离心法对宁夏庆华煤的显微组分进行分离,获得煤的镜质组和惰质组。通过元素分析、X射线光电子能谱（XPS）、固体¹³C核磁共振（¹³C NMR）技术、傅里叶变换红外光谱（FTIR）和X射线衍射（XRD）技术等表征手段对不同显微组分进行物性表征。进一步基于统计平均的分子结构近似结合分子模拟计算,确定庆华煤镜质组和惰质组显微组分的分子结构可分别表示为C₂₆₉H₁₉₆N₄O₁₃S和C₂₅₅H₁₇₉N₃O₁₄S。通过FTIR光谱与¹³C NMR光谱验证,从而实现了不同显微组分的分子结构描述。对两种显微组分的分子模型和结构参数进行了系统对比分析,发现镜质组的芳碳百分数为51.95,惰质组的芳碳百分数为62.16。镜质组模型中芳碳结构数目较少,脂肪碳结构丰富,不饱和度较小,还原度最大。惰质组模型中芳碳结构数量最大,脂肪碳结构数目少,不饱和度最大,煤化程度高。镜质组在原煤中含量高,是原煤的主要组成。惰质组的含量少且大分子结构缩合度高,分布在镜质组构成的基体中。     

Chemical transformations during pyrolysis of Rundle oil shale

Rundle shale (Queensland, Australia) was pyrolysed at 12.5 K min⁻¹ to 350–500 °C for 10–240 min. The structures of the liquid products and pyrolysis residues were investigated by a number of n.m.r. spectroscopic techniques including cross-polarization and dipolar dephasing. N.m.r. provided a simple method for detecting nitrile carbon and measuring terminal and internal olefinic hydrogen in shale oil. It was found that the ratio of terminal olefinic hydrogen to internal olefinic hydrogen in shale oil increases by a factor of three over the range 350–500 °C. Moreover, the results suggest that aromatic rings in Rundle shale residues are not highly substituted and hence that aromatic ring condensation reactions are not important during pyrolysis. From elemental, yield and n.m.r. data, the conversion of aliphatic carbon to aromatic carbon during pyrolysis was found to be as high as 25% at 500 °C.