Philip J. Collin

1H n.m.r. study of tars from flash pyrolysis of three Australian coals

Abstract The structure and composition of tars from the flash pyrolysis of one brown and two bituminous Australian coals were investigated by 1 H n.m.r. spectroscopy. Reaction times in a fluidized bed were about 1 s. For each tar the aromatic hydrogen content increases slightly with pyrolysis temperature up to ≈650 °C and then rapidly up to 900 °C. The aromatic carbon content increases rectilinearly with temperature. The yield of aromatic carbon reaches a maximum at 600–700 °C, and then decreases; the yield of aromatic hydrogen is independent of temperature. The proportion of aromatic material with condensed ring structures increases with temperature. Three temperature zones of reactivity can be recognized. Polymethylene chains and aromatic groups are stable up to 600 °C. Between 600 and 700 °C aliphatic substituents, other than α groups, decompose; between 700 and 900 °C α-aliphatic and aromatic groups also decompose, resulting in lower yields of tar.

Analysis of the structure of dissolved marine humic substances and their phytoplanktonic precursors by 1H and 13C nuclear magnetic resonance

The structure of dissolved marine humic material and the intracellular and extracellular material from the diatom Phacodactylum tricornutum has been investigated by 1H- and 13C-NMR spectroscopy. The results show that carbohydrates, highly-branched alkyl chains and to a lesser extent aromatic materials are important contributors to the structure of marine humic substances and aqueous extracts of P. tricornutum. There is a close relationship between the chemical structure of P. tricornutum exudate and dissolved marine humic material.

Low molecular weight species in humic and fulvic fractions

Fourier transform solution /sup 1/H nuclear magnetic resonance (NMR) spectrometry with homogated water peak irradiation is a useful method for detecting low molecular weight substances in humic extracts. Succinate, acetate, methanol, formate, lactate and some aryl methoxyl compounds have been detected in extracts from a wide range of sources. In view of the controversy over whether low molecular weight substances are contaminants in humic extracts introduced by the concentration procedure, the authors report that some of these materials are not contaminants since /sup 1/H-NMR can be used to follow their formation from higher molecular weight species.

Relaxation of 13C and 15N nuclei by solvent-refined coal☆

The effects of changing various spectroscopic parameters on the solid-state and solution 13C-nuclear magnetic resonance (n.m.r.) spectra of solvent-refined coal have been investigated. Solution spectra were obtained with the use of broad band decoupling, inverse gated decoupling and coupling techniques. Conventional relaxation reagent (Cr(acac)3) was sometimes added to the solvent-refined coal. The effects of pulse delay on the total signal intensity, and on the intensity of the signal from aromatic carbon have been measured. The results show that inverse gated decoupling with pulse delays of 10 s is needed for complete relaxation of solvent-refined coal, but pulse delays of 6 s can give accurate estimations of aromaticity. However, it is recommended that conventional relaxation reagent such as Cr(acac)3 be added to ensure relaxation if shorter pulse delays are used. The effect of solvent-refined coal on relaxation of some pure compounds in solution has also been studied. Solvent-refined coal acts as a relaxation reagent on 13C nuclei in benzene, toluene and ethylbenzene. It can also relax 15N nuclei in aniline, N,N-dimethylaniline and nitromethane. Spin-lattice relaxation times (T1s) of selected nuclei have been measured and the contribution of solvent-refined coal to relaxation (T1SRC) has been calculated. Solid-state 13C-n.m.r. spectra have been obtained using the cross-polarization (CP) technique with magic-angle sample spinning (MASS). A variety of cross-polarization times and recycle times have been used. The results show that no serious errors in measurement of aromaticity (fa) are caused by using a contact time as short as 1 ms and a recycle time of 0.3 s. There is good agreement between fas obtained by solution and solid-state n.m.r., and as solid-state spectra can be obtained in only a fraction of the time needed to obtain a solution spectrum (≈120th), CP-n.m.r. is the method of choice for analysis of fa of solvent-refined coal. The results also show that CP-MASS n.m.r. can be used to estimate the fraction of aromatic carbon which is unprotonated in solvent-refined coal and, hence, indirectly, the fraction of hydrogen which is aromatic.

The nature of olefins and carboxyl groups in an Australian brown coal resin

The chemical structure of the resin from an Australian soft brown coal (Yallourn) has been investigated by cross-polarization nuclear magnetic resonance spectroscopy with magic angle spinning (13C CP MAS NMR). Some additional solution 1H and 13C data were also obtained. Solid-state experiments were performed with and without a delay period before data acquisition. The resulting free induction decays were Fourier transformed with respect to acquisition time and delay period to produce two-dimensional solid-state spectra. Assignments made from the spectra clearly demonstrate that the gross chemical structure of the Yallourn resin is best described as a polymerized diterpenoid with one axial carboxylic group and two double bonds. One double bond is trisubstituted, the other is monosubstituted. After consideration of various mechanisms for polymerization of diterpenoid units during biogenesis and coalification, it was concluded that polymerization occurs at the C15 carbon atoms in the diterpenoids without cyclization of the methylene units at C8.

Effect of temperature, catalyst and charge gas on the mean chemical structures of the products from hydrogenation of Liddell coal

Abstract Liddell coal (New South Wales, Australia) has been hydrogenated at 400, 425 and 450 °C with excess tetralin as vehicle and nitrogen or hydrogen as charge gas for 4 h at reaction temperature. In some experiments a nickel-molybdenum catalyst was used. The structures of the liquid and solid products were investigated by nuclear magnetic resonance spectroscopy, gel permeation chromatography and combustion analysis. Increasing the hydrogenation temperature from 400 to 450 °C decreases the yield of liquid products but increases conversion. At higher temperatures the liquid products are smaller in molecular size and molecular weight and contain a greater proportion of aromatic carbon and hydrogen; the solid residues also contain a greater proportion of aromatic carbon. The changes in variation of yield and structure with temperature are independent of the presence of catalyst under nitrogen and the nature of the charge gas. However, as the reaction system is capable of absorbing more hydrogen than can be supplied by the tetralin, the products from reactions with hydrogen as charge gas contain more hydrogen, some in hydroaromatic groups. Catalyst has little, if any, role in dissolution of the coal when a nitrogen atmosphere is used. When nitrogen is used as charge gas, reactions of coal-derived liquids with the catalyst do not alter the hydrogen, carbon or molecular size distributions in the products. The results show that the changes in composition of the liquid and solid products with increase in hydrogenation temperature are due to pyrolytic reactions and not to increased hydrogenation of aromatic rings.

Hydrogenation of Liddell coal. Yields and mean chemical structures of the products

Abstract The products from the hydrogenation of an Australian medium-volatile bituminous coal (Liddell) in batch autoclaves have been investigated. Tetralin was used as a vehicle and Cyanamid HDS-3A as catalyst. The influences of temperature (315–400 °C), hydrogen pressure (3.4–17.2 MPa) and reaction time (0–4 h) on the yields of pre-asphaltene, asphaltene, oil and pitch were studied. The chemical compositions of these materials were investigated by nuclear magnetic resonance and infrared spectrometry, and high-pressure liquid chromatography. Higher temperatures (400 °C) and pressures (17.2 MPa) favour the formation of products with lower average molecular size, lower aromatic carbon and aromatic proton contents and smaller average aromatic fused-ring number. N.m.r. evidence is presented which shows that increasing the temperature from 370 °C to 400 °C or pressure to 17.2 MPa assists reactions which bring about hydrogenation and cleavage of aryl rings. Longer reaction times (4 h) promote reactions by which the oxygen content of the product is decreased and by which polymethylene becomes cleaved from other functional groups. The results show that asphaltenes are true intermediates in the formation of oil from coal.

Chemical transformations during pyrolysis of Rundle oil shale

Abstract 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.

Origins of humus variation

Abstract Humus samples derived from peat, moss or ornithogenic sources in the Antarctic continent have been examined by 13 C nuclear magnetic resonance techniques. The 13 C spectra show that the humus has undergone very little chemical modification. A fulvic acid fraction from a moss derived soil is almost entirely α- and β-glucose. The results also show that lignin is not a necessary precursor for aromatic components in soils. It is suggested that the aromaticity and carbohydrate content of certain soils is governed by the low temperature which influences the degree of humification.

Hydrogenation of maceral concentrates from bayswater coal: Effect of temperature on the yield and mean chemical composition of the product

Inertinite and vitrinite concentrates from an Australian bituminous coal seam (Bayswater) were hydrogenated at five temperatures from 375 to 475°C in the presence of tetralin. The chemical structures of the liquid products were investigated by solvent extraction, 1 H and 13 C n.m.r., elemental analysis and gel permeation chromatography. For both vitrinite and inertinite concentrates the yield of oil increased with increasing hydrogenation temperature, but the yield of asphaltene increased up to 400°C and then decreased. As expected, the yields of oil and asphaltene were lower from the inertinite than from the vitrinite concentrate but larger oil to asphaltene yield ratios were obtained from the inertinite than from the vitrinite concentrate in the higher temperature range. The results clearly show that the chemical structures of the oil and asphaltene from both maceral concentrates are dependent on reaction temperature in a similar manner. Aromaticities of the residues from hydrogenation of the maceral concentrates and their demineralized derivatives were found to be temperature dependent, reaching a maximum of ≈0.95 at 475°C. Demineralization appears to have little or no effect on aromaticity. The weighted sum of the aromaticities of all the products showed that at 475°C, dehydrogenation reactions are significant contributors in determining the overall aromaticity of the products. At lower temperatures dehydrogenation and aryl ring hydrogenation reactions may compete. Results also show that the lower yield of oil obtained from inertinite compared with vitrinite concentrates does not arise from the inertinite aromatic structures being less amenable to liquefaction or because they contain less aliphatic carbon, but is due to the different size of the aromatic ring clusters.