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

Saudi Arabian medium crude oil has been characterized by ¹H and ¹³C n.m.r. spectroscopy. Several structural parameters such as the percentage of aliphatic carbons, aromatic carbons, n-alkanes, naphthenes, branched alkanes and chain length of paraffinic chains were calculated. The aromatic carbons were further classified as those attached to a hydrogen, methyl or alkyl group, or bridgehead carbons.     

Estimation of aliphatic H/C ratios for coal liquefaction products by spin-echo 13C n.m.r.

The direct estimation of aliphatic H/C ratios for coal liquefaction products using a part-coupled spinecho (PCSE) ¹³C n.m.r. method is described. The method, which enables proportions of aliphatic C, CH, CH₂ and CH₃ groups to be deduced, has been applied to a low molecular weight (<200) aromatic fraction of hydrogenated anthracene oil (HAO) and to higher molecular weight (?280) aromatic and asphaltene fractions of supercritical gas (SCG) extracts and a hydrogenation residue (pitch). Aliphatic H/C ratios for these occur in the range 1.9-2.3, the SCG extract fractions having the highest values because they contain significantly more CH₃ and less CH than the HAO and pitch fractions.     

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.     

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.     

Characterization of vitrinite concentrates. 2. Magic-angle 13C nuclear magnetic resonance studies

The fraction aromaticity determined by ¹³C n.m.r. with cross-polarization and magic-angle spinning of 19 vitrinite concentrates obtained from the Lower Kittaning seam shows a range of values from ≈ 0.65 for the samples of lowest rank (83 wt% C (dmmf) to about 0.83 for those of highest rank (91 wt%C (dmmf)). It was determined that the wt% aromatic carbon correlates to the wt% fixed carbon and is in good agreement with the results reported by other authors. The combination of the ¹³C n.m.r. results with FTIR measurements allows a number of coal parameters to be estimated. The atomic ratios of aliphatic hydrogen to carbon were demonstrated to vary from 1.8–2.0 to between 2.4–2.6 and previous assumptions that a single value can be used in calculating structural parameters for coal of any rank are not strictly valid. The calculation of the aromatic $\text{H}\text{C}$ ratio indicates that in mean structural units there is approximately one aromatic hydrogen atom for every six carbons in vitrinites of carbon content 83 wt%C (dmmf) and that this ratio changes progressively with rank to a value of about one aromatic hydrogen for every four carbons for vitrinites of carbon content 91 wt%C (dmmf).     

Distribution of aliphatic and aromatic carbons in H-Coal liquids by quantitative 13C FT-n.m.r. spectroscopy

Three H-Coal liquids, ASO, ASB, and VSO, have been characterized by quantitative FT-n.m.r. spectroscopy. FT-parameters were chosen to allow determination of aromatic:aliphatic carbon ratios to within 1% and 2% error of the theoretical and the absolute number of aromatic and aliphatic carbons in a simulated coal liquid, respectively. The aromaticity, f_a, the C_ar:C_al ratio and, the absolute number of both the aromatic and the aliphatic carbons on a per mol basis, have been derived for each H-Coal liquid using c.m.r. in combination with other physical data. By analysis of the chemical shifts of the c.m.r. spectra, the carbon distributions in the H-Coal liquids have been estimated and compared in terms of six structural types. The molecular parameters thus derived are reasonable correlated with the average molecular structures proposed as working hypothesis for the molecular characterization of the three H-Coal liquids.     

Spinning sideband suppression and quantitative analysis in solid state 13C n.m.r. of fossil fuels

The use of TOSS spinning sideband suppression to obtain ¹³C n.m.r. spectra of a wide range of aromatic materials is discussed in relation to the spectra of the same materials obtained without sideband suppression. The 39 samples studied include polymers containing both aromatic and aliphatic carbon, asphaltenes, fossil fuels spanning the range in rank from pet to semianthracite, pitch, separated macerals, laboratory oxidized coals and naturally weathered, stockpiled bituminous coals. Despite the diversity in structure, it is found that sideband suppression can be used to obtain apparent aromaticity values consistent with the normal spectra in the majority of samples. The observation of inaccurate aromaticities due to destructive interference between the frequencies associated with magic angle spinning and slow molecular motions in some samples is illustrated.     

Synthesis, 1H‐NMR characterization,and biodegradation behavior of aliphatic–aromatic random copolyester

Aliphatic‐aromatic copolyesters of poly(butylene adipate‐co‐butylene terephthalate) have been synthesized by polycondensation. Molecular weights and thermal properties have been measured. The four samples of copolyesters, with aromatic contents, varying from 40 to 60 mol %, were investigated by ¹H‐NMR spectroscopy to determine copolymers composition and microstructure. For all samples, the biodegradation experiment was carried out in compost, to study copolyesters degradation behavior. Using ¹H‐NMR, we noticed that the average sequence length and content of the aliphatic unit decrease and those of the aromatic unit increase. The molecular weights of the samples distinctly drop after composting. In all degraded samples, the trace of growing microorganisms was found on their surfaces by scanning electron microscopy. In combination with the results, the degradation behavior has been studied in the middle stage of copolyester degradation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2643–2649, 2007     

Selective saturation as an aid for carbon-13 CP/MAS n.m.r. analysis of coals at high frequencies

A selective saturation experiment is described and applied to selective elimination of ¹³C high resolution solid state n.m.r. signals and of their spinning sidebands, as well for sharp lines as for broad bands. A proper adjustment of experimental conditions permits selective saturation of the aromatic carbon signals of coal samples and eliminates unwanted overlapping of aromatic sidebands with the aliphatic region of the spectrum at high working frequencies. The described procedure seems to be especially useful for qualitative and quantitative high frequency n.m.r. investigations of coals having a distribution of short T₂ relaxation times.     

Isolated methyl groups as new structural parameters for petroleum crudes

For the first time, the contents of isolated methyl groups, i.e. methyl groups bound to quaternary aliphatic or aromatic carbon, in crude oil samples were determined. As an analytical tool we used the ³J(H,H) modulated ¹H-NMR spin echo technique. Weighed amounts of hexamethyldisiloxane (HMDS) containing six isolated methyl groups were added to the samples to determine absolute concentrations. The contribution of isolated methyl carbon to total carbon was in the range of 3.0 to 6.9% methyl groups bound to aliphatic carbon, and 1.2 to 4.6% for methyl bound to aromatic carbon. Model compound mixtures of known composition were prepared to validate the new procedure. The procedure delivers accurate and precise results with regard to relative standard deviations of less than 1%.     

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.     

Synthesis,characterization, and thermal behaviour of new epoxy polyesterimides

New epoxy resins have been synthesized by the reaction of diimide-diacids trimellitimide derivatives containing different aliphatic and aromatic fragments in N-methyl pyrrolidone (NMP) with their corresponding diglycidylesters, using several molar ratios. The polymer composition has been determinated by chemical and elemental analyses. Their IR, ¹H, and ¹³C NMR spectral data allowed to confirm the structural unit. Epoxy polyesterimides are soluble in polar organic solvents and show good thermal resistance. Differences on the basis of the introduced aliphatic or aromatic fragments were observed.     

Determination of ether oxygen in coals by 13C CP/MAS n.m.r. spectrometry and acetylation

The amount of aliphatic and aromatic ethers in coals with different carbon contents were determined by combined use of ¹³C CP/MAS n.m.r. spectrometry and the acetylation method. The role of etheric oxygen in the depolymerization of coals was re-evaluated. Etheric oxygens were distributed more abundantly in aromatic ether rather than in aliphatic ether and amounted to 3.7% relative to carbon. The cleavage of ether linkages in early stages of depolymerization of coal led to the formation of asphaltene or preasphaltene.     

Investigation of the chemical structures of coking and non-coking coals in original and reductively alkylated solid states via 13C n.m.r. and i.r. spectroscopies

Chemical structures of four Turkish coals in original and reductively alkylated forms were investigated in the solid state by CP/MAS ¹³C n.m.r. and i.r. spectroscopies. Dilatation properties of these samples were also determined. It was observed that, while the aliphatic parts of the coking coals are mainly composed of short and straight alkyl groups and alicyclic structures, the aliphatic parts of the non-coking coals are to a larger extent composed of branched chains and/or alicyclic structures. It was concluded that ether bonds linking aromatic units are more prominent in the coking coals, whereas in the non-coking coals aromatic-O-aliphatic and/or alicyclic ethers dominate. The degree of condensation of aromatic structures was found to be higher in the coking coals, and the extent of reductive alkylations was higher in comparison with the non-coking coals. Non-coking coals were found to be alkylated preferentially at their phenolic oxygens. Difference spectra were found to be very useful in following organic chemical structural changes that accompany reductive alkylation.     

New approach to the analysis of the 13C CP/MAS n.m.r. spectrum of coal

A new method of evaluating the ¹³C CP/MAS n.m.r. spectra of coals and related solids has been developed which permits the quantitative assignment of three kinds of aromatic carbons (protonated, substituted and bridge carbons) in addition to alkoxy and aliphatic carbons. The method is based on the analysis of the otherwise troublesome spinning sidebands.     

Oil-shale analysis by CP/MAS-13C n.m.r. spectroscopy

Solid-state ¹³C n.m.r. (CP/MAS-¹³C n.m.r.) spectroscopy provides a direct method for estimating potential oil yields of oil shale formations. Relative aliphatic resonance areas correlate linearly with oil yield and provide a method for oil yield estimation that obviates the need to determine weight per cent organic carbon for each specimen. This direct measurement is performed using an internal area standard, the carbonyl resonance of N-(2-¹³C-propanonyl)-N,N,N-trimethylammonium chloride, to monitor spectrometer sensitivity. Oil shale samples obtained as a function of depth at a site in the Mahogany Zone of the Green River Formation show a near-constant aliphatic carbon fraction, f_al ≡ (1?f_a), and a twofold, nonlinear variation in oil yield over the vertical dimension of the sampling. Aliphatic carbon resonance band shape changes among these samples are interpreted qualitatively as reflecting a two component mixture composed of the condensed alicyclic structures which link together to form the kerogen matrix and an n.m.r.-distinct but not necessarily chemically distinct contribution from normal-long chain hydrocarbon residues.     

Urethanes and polyurethanes based on oxypropylated cork: 1. Appraisal and reactivity of products

The reaction of various polyols derived from the oxypropylation of cork with aliphatic and aromatic mono‐ and diisocyanates was studied in solution at room temperature. In all instances, good second‐order kinetics were observed and the corresponding rate constant determined. The reactivity of the aromatic isocyanate was found to be much higher than that of aliphatic counterparts. The ensuing urethanes and polyurethanes were characterised by FTIR and ¹H NMR spectroscopy, DSC and sol/gel distribution. © 2001 Society of Chemical Industry     

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.     

Properties of Waterborne Polyurethane Adhesives with Aliphatic and Aromatic Diisocyanates

A series of waterborne polyurethane (WBPU) adhesives were prepared with various ratios of aliphatic/aromatic diisocyanates, namely 4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) as an aliphatic diisocyanate and 4,4′-diphenylmethane diisocyanate (MDI) as an aromatic diisocyanate with poly(tetramethyleneoxideglycol) (PTMG), ethylene diamine (EDA) and dimethylol propionic acid (DMPA). ¹H-NMR spectroscopy was utilized to investigate the side reaction at the dispersion step during synthesis of WBPU dispersions with respect to aliphatic, aromatic and mixed diisocyanates. The tensile strength, Young's modulus, elongation at break (%), storage modulus, glass transition temperature and adhesive strength were measured with respect to aliphatic/aromatic diisocyanate contents. The adhesive strength was maximum using mixed diisocyanates containing 25 mol% MDI in WBPU adhesives.     

Synthesis and characterization of aromatic/aliphatic co-polyureas

In the present work, a series of aromatic/aliphatic co-polyureas have been synthesized from 4,4-diphenylmethane diisocyanate (MDI), m-phenylene diamine (m-PDA), and 1,6-diaminohexane (HDA) in DMAc by a two-stage solution polymerization route. Characterizations of the polyurea products have been carried out by ¹H-nuclear magnetic resonance (NMR) and Fourier transform infrared (FT-IR) spectroscopic techniques. Thermal properties of the polyurea samples have been investigated by differential scanning calorimetry and thermogravimetric analysis. The mechanical properties of the polyurea samples have been measured. The results show that the polyurea samples with the expected structure have been synthesized. The results of DSC analysis show the glass transition temperatures of the co-polyurea samples decrease with the increase of HDA content, and fit the Fox equation well. TGA data of the polyurea samples indicate that thermal stability of the aromatic polyurea is better than that of the co-polyureas. The thermal degradation activation energies of the co-polyureas are ∼60–70 kJ/mol. The results of mechanical measurement show that the initial modulus and tensile strength of the co-polyurea samples decrease with the increase of HDA content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008