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.     

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.     

The chemical nature of a supercritical gas extract including comparison with other coal liquids

A supercritical gas extract of an Australian bituminous coal was separated into oil, asphaltene and pre-asphaltene. The oil was further separated by chromatography into three fractions. Average structure data for each fraction are reported based on NMR spectroscopy combined with elemental, molecular weight and functional group analyses. Unsubstituted alkyl chains (> C₈) were found in every fraction of the extract. The presence of n-alkanes, 1-alkenes and phenyl-n-alkanes were shown. The supercritical gas extract was compared with a flash pyrolysis tar and with hydrogenation liquids from the same coal. The supercritical gas extract and the flash pyrolysis tar had a similar distribution between oil, asphaltene and pre-asphaltene, but the oil, asphaltene and pre-asphaltene from the supercritical gas extract were less aromatic and contained fewer heteroatoms than these fractions from the flash pyrolysis tar. The supercritical gas extract has a higher H/C atomic ratio, higher heteroatom content and a higher percentage of carbon in long unsubstituted alkyl chains than hydrogenation liquids produced at 400°C and 450 °C. The oil/asphaltene ratio and the aromaticity of the oil and asphaltene from the supercritical gas extract were intermediate between those obtained for the two hydrogenation liquids.     

Effect of process distillation on the distribution of amino polycyclic aromatic hydrocarbons in refined coal-derived liquids

After fractional distillation of SRC-I process solvent, 3- and 4-ring amino polycyclic aromatic hydrocarbons (amino PAH) are essentially absent from fractions boiling at < ≈ 400 °C. Amino PAH determine the mutagenicity of SRC-I process solvent and also that of several other coal-derived liquids, hence these studies indicate that distillation may be optimized so as to confine mutagenic activity to heavy products, while recovering the material distilling at < ≈ 400 °C as a mutagenically inactive fuel or feedstock.     

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.     

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.     

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.     

Structures of the distillates obtained from hydrogenation and pyrolysis of Liddell coal

The structures of the distillable fractions (oils, b.p. >200 °C and volatile fractions, b.p. <200 °C) of the products from hydrogenation and pyrolysis of an Australian bituminous coal (Liddell) were investigated by gas chromatography-mass spectrometry (g.c.-m.s.) and nuclear magnetic resonance spectroscopy (n.m.r.). The distillable oil generated from hydrogenation of Liddell coal at 400 °C, using nickel molybdenum ortin (II) chloride as catalyst and tetralin or recycle oil as vehicle, consisted of a wide range of compounds. Long straight-chain alkanes were important components together with alkyl-substituted benzenes and tetralins, phenols and polycyclic material. When yields were low, as in the case of catalytic experiments with nickel molybdenum catalysts and no vehicle, isoprenoids could be identified. When a substantial proportion of the coal was converted to oil, branched-chain alkanes were not important components of the product. The replacement of tetralin and nickel molybdenum catalyst with stannous chloride reduced the amounts of methyl tetralins in the product. When tetralin was replaced by recycle oil, alkanes were more important components of the liquid products. Although alkenes were absent in oils generated by hydrogenation, they were important components of oils generated by pyrolysis. The highly volatile fractions (b.p. <200 °C) produced during hydrogenation consisted of alkyl-substituted benzenes, decalins, methylindan and straight-chain alkanes. Straight-chain alkanes were more abundant in those volatile fractions generated by hydrogenation with recycle vehicle than with tetralin. The Brown-Ladner method of estimating the fraction of aromatic carbon in distillable oils was adequate for less volatile fractions but was inadequate for the highly volatile fractions because of the large amounts of α-CH₃ and β-CH₃ alkyl groups present.     

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 analysis of tars from fluidized bed pyrolysis of coal:: 2. 1H n.m.r. and i.r. spectroscopy

¹H n.m.r. and i.r. spectroscopy of aromatic and polar fractions of two tars from the rapid pyrolysis of coal in a fluidized bed at 550 °C show that the nature of the products depends on the reactivity of the pyrolysis gas. In the presence of flue gas, there is more thermolysis leading to shorter and fewer alkyl side chains and generation of lower molecular mass material. Pyrolysis by means of char gasification gas results in much less thermolysis of the tar but leads to secondary reactions which can be interpreted by a radical mechanism involving the reactive constituents of the char gas.     

Recycling of the Products Obtained in the Pyrolysis of Fibre-Glass Polyester SMC

An SMC (Sheeting Moulding Compound) of fibre-glass and orthophthalic polyester has been pyrolysed in a 3·5 dm³ autoclave for 30 min in a nitrogen atmosphere at 300, 400, 500, 600 and 700°C. Gas yields of 8–13 weight%, liquid yields of 9–16 weight% and solid residues of 72–82 weight% were obtained. The suitability of the pyrolysis process for recycling SMC is discussed. The characteristics, compositions and possible ways of reusing the liquid and gaseous fractions are presented. The solid pyrolysis residue has been recycled in another thermoset composite (Bulk Moulding Compound, BMC) and its mechanical properties have been compared with those of virgin BMC. The main conclusion is that pyrolysis can be an appropriate method for recycling thermoset polymeric composites such as SMC. The pyrolysis gas fraction can be sufficient to provide the energy requirements of the process plant. The pyrolysis liquids have high gross calorific values (36·8 MJ kg⁻¹) and are non-polluting liquid fuels; about 40 weight% of such liquids could be used as petrols, and the remaining 60% could be mixed with fuel oils. The solid pyrolysis residue can be recycled in BMC with no detrimental effect on the BMC mechanical properties. Concerning temperature, it has been concluded that 400–500°C are the most suitable temperatures for recycling SMC by pyrolysis. © 1997 SCI.     

Characterization of polynuclear aromatic hydrocarbons in bitumen,heavy oil fractions boiling above 350 °C by g.c.-m.s.

The separation and characterization of polynuclear aromatic hydrocarbons of five fractions of bitumen, heavy oils and synthetic fuels boiling > 350 °C were performed using a combination of Chromatographic techniques. The polynuclear aromatic hydrocarbon fractions were obtained by liquid-solid chromatography and prior to the high performance liquid chromatography and gas chromatography/mass spectrometry techniques, the fractions were subjected to an acid/base extraction procedure to remove polar material. In total, 97 polynuclear aromatic hydrocarbons were tentatively identified by a correlation of their mass spectra and retention indices with those of 25 model polynuclear aromatic compounds.     

Pyrolysis of two different biomass samples in a fixed-bed reactor combined with two different catalysts

Pyrolysis of Euphorbia rigida and sesame stalk biomass samples with two selected commercial catalyst, namely DHC-32 and HC-K 1.3Q, have been conducted in a fixed-bed reactor. The effect of different catalysts and their ratio (5, 10 and 20% w/w) and pyrolysis temperature (500 and 750 °C) on the pyrolysis product yields were investigated and the obtained results were compared with similar experiments without catalyst. Bio-oil yield was increased comparing with non-catalytic experiments, at final pyrolysis temperature of 500 °C for both biomass samples and catalysts. In the catalytic experiments; when the temperature reached to 750 °C, although bio-oil product yield was reduced, the gas product yield was increased comparing with non-catalytic experiments.The pyrolysis oils were examined using spectroscopic and chromatographic analyses and then fractioned by column chromatography. Although the aliphatic and aromatic fractions were decreased and polar fraction was increased with catalytic pyrolysis of E. rigida; an opposite trend was observed in the sesame stalk pyrolysis oil, comparing with non-catalytic results.Obtained results were compared with petroleum fractions and determined the possibility of being a potential source of renewable fuels.     

Studies on thermal cracking behavior of residual feedstocks in a batch reactor

Thermal cracking of residual fractions has gained interest of refiners due to increasing demand of middle distillates and at the same time decline in demand of fuel oils. The present study is an attempt to gain deeper insight into the thermal cracking behavior of residual feedstocks in terms of certain key characteristics. Laboratory scale experiments on a 400 ml capacity stainless steel batch reactor were conducted with four residual feedstocks of Indian and Middle East origin—North Gujarat short residue (NGSR), Visbreaker feed from Mathura refinery (MVBF), Bombay High short residue (BHSR) and Asphalt from Haldia refinery (HRA), with asphaltene content varying in the range 1.85-10.15 wt%. The cracked products were separated by distillation up to 500 ^°C. The distillate (500 ^°C-) was analyzed by ASTM D2887 (SIMDIST) method and obtained data were classified into lumps, namely Gas (C₅-), Gasoline (IBP-150 ^°C), Light Gas Oil (150-350 ^°C) and Vacuum Gas Oil (350-500 ^°C) prior to detailed data analysis. The analysis of results reveals that the thermal cracking of petroleum residues follows first order kinetics. The rate constants and activation energies have also been estimated.     

Storage stability of marine diesel fuels

The cause of instability in marine diesel fuels was investigated by ageing several fuels at 65 °C for various periods. Aged and unaged fuel samples were chromatographically separated into acid, base and neutral fractions, and the fractions were analysed in detail to obtain a clearer understanding of the mechanism of colour change and sediment formation. The results suggest that oxidation of neutral compounds to polar intermediates may be a major pathway for sediment formation and darkening of marine diesel fuels. Considerable loss of polar compounds, both those originally present and those newly formed, to sediment was also found. Within a compound class, the more aromatic higher molecular weight members were observed to be the most active in sediment formation.     

The effects of oxygen on the yields of polycyclic aromatic hydrocarbons formed during the pyrolysis and fuel-rich oxidation of catechol

To better understand the effects of oxygen on the formation and destruction of polycyclic aromatic hydrocarbons (PAH) during the burning of complex solid fuels, we have performed pyrolysis and fuel-rich oxidation experiments in an isothermal laminar-flow reactor, using the model fuel catechol (ortho-dihydroxybenzene), a phenol-type compound representative of structural entities in coal, wood, and biomass. The catechol pyrolysis experiments are conducted at a fixed residence time of 0.3 s, at nine temperatures spanning the range of 500-1000 °C, and under varying oxygen ratios ranging from 0 (pure pyrolysis) to 0.92 (near stoichiometric oxidation). The PAH products, ranging in size from two to nine fused aromatic rings, have been analyzed by gas chromatography with flame-ionization and mass spectrometric detection, and by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance detection. The quantified PAH products fall into six structural classes: benzenoid PAH, indene benzologues, fluoranthene benzologues, cyclopenta-fused PAH, ethynyl-substituted PAH, and methyl-substituted PAH. A comparison of product yields from pyrolysis and fuel-rich oxidation of catechol reveals that at temperatures <800 °C, where only two-ring PAH are produced in significant quantities, increases in oxygen concentration bring about increases in yields of the two-ring aromatics indene and naphthalene. At temperatures >800 °C, increases in oxygen concentration bring about dramatic decreases in the yields of all PAH products, due to oxidative destruction reactions. The smaller-ring-number PAH are produced in higher abundance under all conditions studied, and the oxygen-induced decreases in the yields of PAH are increasingly more pronounced as the PAH ring number is increased. These observations regarding PAH ring number, from the fuel-rich oxidation experiments with catechol, fully support our finding from catechol pyrolysis in the absence of oxygen: that PAH formation and growth occur by successive ring-buildup reactions involving the C₁-C₅ and single-ring aromatic products of catechol’s thermal decomposition. The yield/temperature data reported here represent one of the most extensive quantifications of the effects of oxygen on PAH produced during the pyrolysis of any fuel.     

Composition of the liquid products of the supercritical fluid extraction of oil shale from the Chim-Loptyugskoe deposit

Data on the liquid product composition of the thermal degradation of the organic matter of an oil shale sample from the Chim-Loptyugskoe deposit in benzene under supercritical conditions in temperature ranges to 200, 200–300, and 300–400°C were acquired with the use of a set of analytical methods. It was found that the concentration of tar–asphaltene substances in the pyrolyzates decreased with temperature; in the structure of these substances, the fraction of aromatic fragments increased and the fraction of aliphatic fragments decreased. The fraction of polar compounds in the composition of oil components decreased.     

Two-stage catalytic up-grading of vacuum residue of a Wandoan coal liquid

A successive two-stage hydrotreatment using a commercial Ni-Mo/Al₂O₃ catalyst (HDN-30) was applied to the vacuum residue of a Wandoan coal liquid to achieve high levels of hydrocracking, hydrodenitrogenation and hydrodeoxygenation. Two-stage hydrotreatment in 1-methylnaphthalene containing 20wt% fluoranthene as a solvent at solvent/coal liquid ratio of unity removed 83% (overall) of nitrogen and 90% (overall) of oxygen in the asphaltene (benzene-soluble fraction) at 380 °C for 3 h and at 420 °C for 3 under hydrogen pressure of 15 MPa and 14 MPa, respectively, while the single stage treatment at 420 °C for 3 h removed only 41% and 46%, respectively. The same two-stage treatment allowed the overall denitrogenation of 51% and the overall deoxygenation of 67% from a mixture of asphaltene and preasphaltene (THF-soluble fraction). Addition of the catalyst prior to the second stage reaction increased the removal of nitrogen and oxygen to 75 and 82%, respectively, indicating significant catalyst deactivation by the preasphaltene fraction in the first stage. Increasing the solvent/coal liquid ratio to 2 or addition of tetrahydrofluoranthene as a component of the solvent increased the removal of nitrogen and oxygen to 70 and 80%, respectively. Such two-stage hydrotreatment was also effective in refining the whole residue, allowing denitrogenations and deoxygenations of 68 and 75%, respectively using tetrahydrofluoranthene. The coke, unreacted coal and minerals in the residue may not cause acute catalyst deactivation. High dissolving ability of the reaction solvent is very effective to decrease catalyst deactivation by carbon deposition. The successive two-stage hydrotreatment also enhanced hydrocracking of polar and resin fractions in the residue into oils (conversion, 65%). The extensive hydrogenation of the former fractions in the first stage may allow more easy cracking and may suppress with the aid of solvents their irreversible adsorption on the catalyst which leads to their coking into the catalyst poisons.     

The pyrolysis of waste mandarin residue using thermogravimetric analysis and a batch reactor

A study on the pyrolysis of waste mandarin residue, with the aim of producing bio-oil, is reported. To elucidate the thermodynamics and temperature-dependency of the pyrolysis reaction of waste mandarin residue, the activation energy was obtained by thermogravimetric analysis. Mass loss occurred within the temperature range 200–750 °C, and the average activation energy was calculated to be 205.5 kJ/mol. Pyrolysis experiments were performed using a batch reactor, under different conditions, by varying the carrier gas flow rate and temperature. When the carrier gas flow rate was increased from 15 to 30 and finally to 50ml/min, the oil yield slightly increased. Experiments performed within the temperature range 400–800 °C showed the highest oil yield (38.16 wt%) at 500 °C. The moisture content in the bio-oil increased from 35 to 45% as the temperature increased from 400 to 800 °C, which also resulted in reduction of the oxygenates content and increase in the phenolics and aromatics content, indicating that temperature is an important operating parameter influencing the yield and composition of bio-oil.     

Thermal decomposition of asphaltenes

The thermal decomposition of Athabasca asphaltene at relatively low (< 350 °C) temperatures is believed to proceed by elimination of groups situated on peripheral sites of the asphaltene. More severe degradation of the asphaltene structure does not occur until elevated (> 350 °C) temperatures are attained.