Structure and formation of cellulosic chars

The formation and structure of chars produced on heating of cellulose, lignin, and wood have been investigated by FTIR and CP/MAS ¹³C-NMR, and the results have been discussed in conjunction with parallel permanganate oxidation studies reported before. These data show that when cellulose is heated for 5 min within the temperature range of 325–350°C, the IR bands associated with hydroxyl and glycosidic groups in cellulose disappear, and new bands signal the formation of unsaturation and carbonyl groups by dehydration and rearrangement. The NMR data also show the disappearance of the glycosyl carbons at 60–110 ppm and the appearance of methyl and other paraffinic carbons at 0–60 ppm, aromatic carbons at 110–170 ppm, carboxyl carbons at 170–190 ppm, and carbonyl carbons at 190–220 ppm. On heating at 400°C the IR and NMR signals for the glycosyl groups completely disappear, the signals for carbonyl and carboxyl groups diminish, and those for the aromatic and paraffinic groups expand. At this stage the char contains about 69% aromatic and 27% paraffinic carbons. At the temperature range of 400–500°C the paraffinic carbon content is reduced to 12%, and a highly aromatic (88%) char is produced. This is consistent with the permanganate oxidation studies which show the production of polycyclic aromatic structures resulting from extensive condensation and crosslinking at these temperatures. The chars produced from wood and lignin at 400°C had about the same aromatic carbon content as the corresponding cellulose char; however, the char yields were higher due to the presence of the methoxy phenyl groups that survive the heating process, as indicated by strong NMR signals at 55 and 148 ppm.     

Pyrolysis and oxidation of heavy fuel oils and their fractions in a thermogravimetric apparatus

Using the derivative thermogravimetric technique, an investigation was made of the pyrolysis and oxidation of some heavy fuel oils and their separate paraffinic, aromatic, polar and asphaltene fractions. The thermal behaviour of fuel oil can be interpreted in terms of a low-temperature (< 400 °C) phase involving the volatilization of paraffinic and aromatic fractions, and a high-temperature phase in which the polar and asphaltene fractions pyrolyse and leave a particulate carbon residue. In an oxidizing atmosphere, the first phase (< 400 °C) consists of the simultaneous evaporation and oxidation of paraffinic and aromatic fractions. The second phase (400–550 °C) consists mainly of pyrolysis of oxidized polar materials, the asphaltenes, with a final phase involving the burning of the carbonaceous residue formed in the second stage.     

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.     

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.     

Aufklärung der Molekülstruktur von Rohölinhaltsstoffen durch NMR-Spektroskopie. II. Struktur der Alkylsubstituenten in den Aromaten des Rohöls

Elucidation of the Molecular Structure of Petroleum Constituents by N.M.R. -Spectroscopy. II. Structure of Alkyl Substituents in Aromatic Hydrocarbons in Petroleum Crude The structure of alkyl chains of aromatic hydrocarbons of heavier petroleum fractions is studied by ¹H and ¹³C-n.m.r. spectroscopy An average aromatic molecule is found with an average degree of substitution of 40–50%, the substituents representing short paraffinic chains or naphthenic rings.     

Oxidative degradation of carbon blacks with nitric acid: II. Formation of water-soluble polynuclear aromatic compounds

Furnace black and acetylene black were oxidized with concentrated nitric acid at 100 °C for prolonged periods. The oxidized carbon black was dissolved/dispersed into alkaline solution and was size-fractionated into six fractions by ultrafiltration. The yields of the fractions revealed that oxidized furnace black contains oxygenated polynuclear aromatic compounds with a variety of molecular sizes, but oxidized acetylene black consists of only a great quantity of the largest size fraction, probably carbon black particles, and a scarce amount of the smallest size fraction. With oxidized furnace black, elemental compositions of all fractions except the largest molecular-size fraction were independent of the period of oxidation, suggesting that each fraction possesses a similar molecular structure. Noncarbon constituents such as oxygen and hydrogen increased with decreasing molecular size. The mean molecular weights of fractions were estimated to be in a range from ca. 400 to 1200 and more on the basis of elemental and functional group analyses. ¹³C-NMR and IR analysis showed that the molecules of fractions comprise phenolic, carboxylic, nitro, perhaps quinonic carbonyl groups, and aromatic carbons, but no aliphatic carbons. Ultraviolet and visible spectra of fractions denoted that absorption at higher wavelengths increased with increasing the molecular weights, indicating extension in the conjugated aromatic ring system. On the basis of the experimental results molecular structure models for the fractions were proposed.     

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.     

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).     

Analysis of oil obtained from mild hydrogenation of coal. 1. structural analysis of fractionated oil

Shin Yubari coal (86.7% C) was mildly hydrogenated repeatedly at 340–385°C under an initial hydrogen pressure of 10 MPa for 1 h, using Adkins catalyst. The product was extracted with benzene at 200°C and the residue was again reacted. Finally, benzene solubles were extracted with n-hexane, and n-hexane insolubles were hydrogenated under similar conditions at 380°C; the product was then extracted with n-hexane. The yield of total n-hexane solubles was 52.5%. Acid and base were extracted with sulfuric acid and NaOH, and the neutral part (50.2%) was chromatographed using an alumina column with 2.5% water and separated into 12 fractions. UV and IR spectra, ultimate analysis and ¹H-NMR spectra were obtained for each fraction and a structural analysis was carried out to obtain an image of each average structure. The aromatic ring numbers estimated from UV spectra and from structural analysis for each fractions agree well with each other; the average value was 3.2.     

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.     

Chemical composition of SCG extracts obtained from coal and maceral concentrates

Five Turkish coals and macerals were subjected to supercritical toluene extraction at 400°C and 100 atm. The extracts were separated into three fractions, namely preasphaltene, asphaltene and oil. Oil fractions were further separated into paraffinic, aromatic and polar sub-fractions. This paper discusses the spectroscopic and chromatographic analysis of these paraffinic, aromatic and polar sub-fractions obtained from the supercritical extraction of whole coals and of their corresponding maceral concentrates.     

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 structure of tar-sand bitumens by 13C and 1H n.m.r. spectroscopic methods

¹H and ¹³C n.m.r. spectra of Athabasca, Cold Lake and Orinoco tar-sand bitumens, their columnchromatographed fractions, their vacuum distillates, their vacuum residues and the columnchromatographed fractions of the vacuum residues were determined to investigate the average molecular structures of these materials. The most probable average structural parameters were calculated without making any assumptions, and average structural models for the Athabasca series are proposed. Compared with corresponding petroleum fractions, tar-sand bitumens contain shorter, paraffinic straight-chains and are abundant in alicyclic carbon atoms. This trend is more marked in the saturate fractions or vacuum distillates. The vacuum residues of tar-sand bitumens contain relatively longer, paraffinic straight-chains than the original bitumens.     

Preparation of carbon adsorbents from lignosulfonate by phosphoric acid activation for the adsorption of metal ions

Activated carbons were prepared from sodium lignosulfonate by phosphoric acid activation at carbonization temperatures of 400–1000 °C. The resulting materials were characterized with regard to their surface area, pore volume, pore size distribution, distribution of surface groups and ability to adsorb copper ions. Activated carbons were characterized by nitrogen adsorption, scanning electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analyses. The results indicate that with increasing carbonization temperature, the surface area decreased from 770 m²/g at 400 °C to 180 m²/g at 700 °C and increased at higher temperatures to 1370 m²/g at 1000 °C. The phosphorus content peaked at 11% for carbon obtained by carbonization at 800 °C. Potentiometric titration revealed the acidic character of all the phosphoric acid-activated carbons, which were found to have total concentrations of surface groups of up to 3.3 mmol/g. The carbons showed a high adsorption capacity for copper ions even at pH values as low as 2.     

Structural characterization of Bombay High crude oil fractions by nuclear magnetic resonance spectroscopy

Different fractions of Bombay High crude oil have been characterized using ¹³C and ¹H n.m.r. spectrometry. The distribution of various types of hydrogens and carbons has been reported and several average structural parameters of the fractions have been compiled. Relative variation of structural parameters has been discussed. The data on light cycle oil (LCO) has also been presented and compared with the feed (vacuum gas oil, VGO) data. The study reveals that all the four samples/fractions are predominantly paraffinic, VGO being richest in n-paraffins. The comparison of LCO and VGO data indicates a slight reduction in the n-paraffinic chain during catalytic cracking.     

Group-structural composition of resinous-asphaltene substances of high-boiling fractions of Azerbaidzhan crude oils

• 1.1. The physicochemical characteristics of resinous-asphaltene substances isolated from >450°C vacuum residues of different Azerbaidzhan crude oils been determined; integral structural analysis of molecules of the resins has been carried out.
• 2.2. The molecules of the vacuum residue resins are based on compounds with a hybrid structure that are similar in skeleton to the structure of high-boiling aromatic fractions. The resin molecules contain about two polycyclic blocks built from an average of two condensed highly substituted benzene rings and (with the exception of highly paraffinic Sangachal'sk crude oil) four or five naphthenic rings, irrespective of the depth of occurrence and the site of oil production.

     

IR studies of carbons—II: The vacuum pyrolysis of cellulose

The pyrolysis of cellulose in vacuum from 22 to 765°C was followed by IR photothermal beam deflection spectroscopy. Series of spectra recorded at various stages of pyrolysis showed that although the main decomposition occurred near 300°C, some decomposition occurred as low as 190°C with the formation or highly absorbing aromatic systems. Mixtures of predominantly aliphatic material predominate in the 300–400°C range but decline in extent to be replaced by mixtures of aromatic nature above 500°C. Further degassing causes discrete spectral features to decline and disappear near 700°C; a continuum absorption remains. Band assignments are discussed. In particular, the 1600 cm^?1 band of spectra of carbons is shown by isotopic study not to be ascribed to carbonyls. but is thought to be a C = C mode made IR active by asymmetry caused by bound oxygen.     

A procedure for quantitative 13c-n.m.r. application to the characterisation of the naphtha fraction of petroleum crude

A method for optimising the conditions for the quantitative ¹³C-n.m.r. measurement is suggested and has been applied to the compositional studies of naphtha fractions (50–100°C and 100–150°C) of Darius crude oil. The novelty of the method is that we can pre-estimate the pulse repetition time for unknown samples. It has been shown that the various compositional parameters thus obtained are in satisfactory agreement with those obtained from the elemental analysis, fluorescent indicator adsorption (FIA) and ¹H-n.m.r. spectrometry.     

High-temperature neutron irradiation of highly oriented carbons and graphites

Highly oriented massive pyrolytic carbons were annealed at 2900–3300°C to produce apparent crystalline heights (L_c) ranging from 220 Å to 1660 Å. Transmission electron microscopy showed that annealing progressively increased the crystallite width, while the height between twist boundaries was little changed over most of the annealing range. The pyrolytic carbons, together with samples of hot-worked polycrystalline graphite, were irradiated with fast neutrons at 1300–1500°C to 2 × 10²² n/cm² (E > 0·18 MeV). Changes in dimensions, thermal expansivities, apparent crystallite heights (L_c), and unit cell heights (C_a) were measured. At 1300–1500°C the c-axis growth and a-axis contraction of the pyrolytic carbons increased linearly with neutron fluence, while the dimensional change rates of the hot-worked graphite decreased with increasing fluence. The dimensional change rates of the annealed pyrolytic carbons decreased systematically with increasing crystal perfection. During irradiation at 1300–1375°C the thermal expansivity in the principal c-direction of as-deposited massive pyrolytic carbon increased rapidly to nearly the theoretical single-crystal value, while that of the hot-worked graphite initially increased, passed through a maximum, and then declined to less than half its initial value.     

Upgrading coal-derived liquids to diesel fuel

Distilled fractions of a coal-derived liquid from the H-Coal process were upgraded to diesel fuel by catalytic hydrotreatment. The total hydrotreated products were distilled into naphtha (<180°C) and diesel fuel fractions (>180°C) and the diesel fractions were analysed for hydrocarbon-type composition, hydrogen content and some diesel fuel properties. GC—MS-analyses were carried out on the hydrocarbon-type fractions to identify individual chemical compounds. To investigate the effect of different distillation cut points on diesel fuel yield and properties, cut points for one hydrotreated product were varied. The diesel fuel cetane numbers were correlated with percentage hydrogen, total aromatics and saturates. Cetane numbers above 40 were obtained for diesel fuels containing (i) more than 75% saturates, (ii) less than 15% total aromatics and (iii) a hydrogen content above 12.8%. Compounds identified by GC—MS-analyses (in the diesel fractions) were typical aromatic and cycloparaffin compounds. Normal-and iso-paraffin compounds were not detected. By varying the distillation cut point from 135 to 180°C, the cetane number of the residual diesel fraction improved from 37 to 44. This increase is ascribed to the removal of aromatic compounds in the 135–180°C boiling point range.