Reaction mechanism of coal hydrogenation: 2. Three rings solvent system

Taiheiyo coal was hydrogenated in phenanthrene, 9,10-dihydrophenanthrene, 1,2,3,4,5,6,7,8-octahydrophenanthrene and perhydrophenanthrene under 10 MPa (initial pressure) of hydrogen or nitrogen with or without stabilized nickel as catalyst at 400 °C for 15 min. Preasphaltene, asphaltene and oil conversions and the conversion of solvents were measured, and the amounts of hydrogen absorbed by coal from molecular hydrogen and from donor solvent were calculated. The main route of reaction appears to be the direct hydrogenation of coal by molecular hydrogen and the contribution of hydrogenation via the solvent was greater than in the case of the two rings solvent system.     

Reaction mechanism of coal hydrogenation: 1. Two-ring solvent system

Taiheiyo coal was hydrogenated in naphthalene, tetralin and decalin under 10 MPa (initial pressure) of hydrogen or nitrogen with stabilized nickel as catalyst at 400 °C for 15 min. Preasphaltene, asphaltene and oil conversions and the conversion of the solvents were measured. The hydrogen absorbed by coal from molecular hydrogen and from the donor solvent was calculated. The main reaction route appears to be the direct hydrogenation of coal by molecular hydrogen, with the side reaction via solvent by molecular hydrogen occurring only slightly, when an active catalyst such as stabilized nickel is present.     

Synergistic effects between light and heavy solvent components during coal liquefaction

As part of research to examine coal conversion in solvents containing high-boiling-point components, experimental studies were carried out with model compound solvents. The dissolution of bituminous and subbituminous coals was investigated in pyrene-tetralin and 2-methylnaphthalene-tetralin mixtures. The effects of donor level, gas atmosphere, hydrogen pressure and conversion temperature were determined. At 400 °C, in the presence of hydrogen gas, pyrene-tetralin solvent mixtures show synergism in coal conversion. At donor concentrations as low at 15 wt%, the degree of conversion was almost as high as in pure tetralin. This phenomenon was not apparent in 2-methylnaphthalene-tetralin mixtures. The relative ease of reduction of pyrene and its ability to shuttle hydrogen is considered to be a principal reason for this difference in behaviour. Conversion in pure pyrene and in pyrene-tetralin mixtures at low donor concentrations increased with increasing hydrogen pressure. At 427 °C, bituminous coal conversion was higher in a 30 wt% tetralin-70 wt% pyrene mixture than in either pure compound. It was found that in the absence of coal pyrene can be hydrogenated by H-transfer from tetralin as well as by reaction with hydrogen gas. This can provide a means to increase the rate of transfer of hydrogen to the dissolving coal through the formation of a very active donor (dihydropyrene). During coal liquefaction, several pathways appear to be available for hydrogen transfer for a given coal, the optimal route being dependent upon the solvent composition and the conditions of reaction.     

Supercritical gas extraction of coal with hydrogen-donor solvents

An investigation of the effect of a hydrogen-donor component in the solvent used for supercritical gas extraction was undertaken. Extraction of three Australian coals with toluene, with decalin and with these solvents containing small amounts of tetralin was investigated. There was a significant improvement in conversion by addition of 5% tetralin to the solvent. Other hydrogen donors were also effective. The improvement in conversion was shown to be due to hydrogen donation rather than to a change in the physical properties of the solvent. The increase in conversion was greater for a brown coal than for a bituminous coal of the same hydrogen to carbon atomic ratio. The pre-asphaltene content of the extract increased with conversion.     

Comparison of anthracene and phenanthrene in coal liquefaction

A comparison of anthracene and phenanthrene as solvents was undertaken by liquefying either Wyodak or Kentucky 9/14 coal in the presence of hydrogen or nitrogen. Phenanthrene was found to be a better physical solvent than anthracene for liquefying both coals. Anthracene and its derivatives are better hydrogen-shuttling solvents than phenanthrene and its derivatives. Hydrogenation of anthracene to tetrahydro-anthracene was observed with both coals. Dihydroanthracene is a better hydrogen-shuttling solvent than dihydrophenanthrane in the liquefaction of Kentucky 9/14 coal. Anthracene is a better solvent than phenanthrene in the presence of 1-methylnaphthalene in liquefying both Wyodak coal under hydrogen and Kentucky 9/14 coal under nitrogen. The minerals in Kentucky 9/14 coal appear to be better hydrogenation catalysts than those in Wyodak coal. Labile hydrogen from coal appears to escape readily before reacting with hydrogen-shuttling solvents under the atmospheric environment.     

Fate of solvents in the non-catalytic depolymerization of Kentucky bituminous coal

To study the fate of the solvents in the non-catalytic liquefaction of Kentucky bituminous coal, a number of batch liquefaction experiments have been carried out using hydrophenanthrenes and coal-derived hydrogenated recycle solvents. Filtrates from the first runs have been rehydrogenated and used as solvents for additional liquefaction experiments. The reactions have been followed by detailed analysis of the feeds and products.At constant temperature and reaction time, the conversion levels are affected by the amount of transferable hydrogen, H_s (up to a value of about 0.6 wt.% of the feed), by the coal concentration and, to a lesser extent, by the pressurizing gas.The solvents are depleted by isomerization, cracking, and adduction-polymerization reactions. Only about 50% of the initial solvent is available for use in the second-pass runs. In addition, the quality of the second-pass solvents is lower than that of the initial solvents due to a decrease of 6-membered hydroaromatic rings and an increase of 5-membered hydroaromatic rings which are poor hydrogen donors.     

Effect of air oxidation on coal hydrogenation

Japanese Taiheiyo coal (75.9%C) was oxidized with air at 250 °C for 3–40 h and at 300 °C for 3–10 h. The weight decreased from 16.3 to 46.5% at 250 °C and from 21.7 to 41.3% at 300 °C. Carbon loss and yield of NaOH soluble were obtained. The resultant oxidation products were hydrogenated at 370 °C for 1 h under 10 MPa hydrogen pressure using red mud with sulphur as catalyst and wash oil as solvent. Conversion to pyridine, benzene and n-hexane soluble fraction shows a minimum for the coal oxidized 10 h at 250 °C and for the coal oxidized for 3 h at 300 °C. Initial oxidation makes a network structure which contributes to a reduction in conversion, but in later stages of oxidation, splitting of bridge linkages and/or ring opening of aromatic structures, contribute to increases in conversion.     

Estimation of the concentration of donatable hydrogen in a coal solvent by n.m.r.

¹H and ¹³C nuclear magnetic resonance (n.m.r.) spectroscopies have been used to study the changes in composition of a hydrogenated anthracene oil solvent that occur during extraction of a UK bituminous coal. It has been shown that the principal hydrogen donor groups in the solvent are hydroaromatic and naphthenic rings in hydroaromatic species. Good agreement was achieved between the concentration of donatable hydrogen estimated from n.m.r., and the amount of hydrogen transferred from the solvent during exhaustive extraction.     

中低温煤焦油加氢转化路径

以中低温煤焦油360℃的馏分油为原料,Ni-Mo/γ-Al2O3为催化剂,在小型固定床单管加氢反应器上进行加氢实验。在压力13 MPa、空速0.4 h-1、氢油体积比1 700∶1和反应温度370℃工艺条件下进行催化加氢反应,通过对原料油和加氢产物的GC-MS的检测结果分析,确定了酚类、萘类、联苯类和菲类化合物的加氢转化路径,得到煤焦油馏分油中主要化合物的加氢反应网络。     

Coal solvolysis with a series of coal-derived liquids

A systematic study of the effectiveness in coal conversion of two coal-derived solvent series, hydrogenated creosote oils and SRC recycle solvents, is characterized by spectroscopic measurement of their hydrogen distribution. Optimum ranges are found for the type and amount of hydrogen contained in the solvents. The results indicate that there are solvent properties, other than those studied in this paper, which may have an important effect on the effectiveness of a particular solvent for coal dissolution.     

Coal liquefaction by in-situ hydrogen generation.: 1. Zinc-water-coal reaction

Liquefaction of coal was carried out in a zinc—water—solvent system to give a product with high concentration of pyridine and benzene solubles. In this system the metal reacts with water to produce the corresponding metal oxide and hydrogen. This hydrogen was used for in-situ hydrogenation of coal. The effects of reaction time, temperature, type of solvent, the quantity of metal used and the rank of coal were investigated. The solvent has a very marked effect on the conversion of coal to benzene-soluble materials, especially at short reaction times. A maximum benzene conversion of 96% for Taiheiyo coal was obtained when it was treated at 445 °C for 1 h using wash oil as solvent. With regard to the influence of coal rank it was found that low rank coals were more reactive than high rank coals. The amount of preasphaltene is only slightly influenced by coal rank but depends on the temperature and the type of solvent used.     

Hydrogen/deuterium transfer in coal liquefaction

Reactions have been made with deuterium-labelled solvent (d₄- and d₁₂-tetralin) and both Powhatan bituminous (Pittsburgh Seam) coal and model compounds under coal liquefaction conditions to study hydrogen transfer mechanisms. Powhatan coal liquefies quickly. Hydrogen transfer from the solvent to the reaction products continues throughout the heating period (up to 60 min). Significant hydrogen/deuterium exchange occurs and this strongly affects the distribution of deuterium in the products and also affects the extent of conversion as measured by the amount of THF-insoluble material. Increased deuteration of the solvent leads to decreased conversion. This exchange is enhanced by heavy aromatic species and by the presence of mineral matter and unconverted coal solids.     

Kinetics of thermal liquefaction of coal

A model is presented for the kinetic study of the thermal liquefaction of Belle Ayr subbituminous and Burning Star bituminous coals with anthracene oil, hydrogenated anthracene oil and hydrogenated phenanthrene. All experiments were performed in a continuous-feed, stirred tank reactor, at a temperature of 450 °C and a space time of approximately 5 to 55 min. A kinetic model which includes a reaction: coal + oil→more reactive coal, correlates the data reasonably well. This reaction explains the net consumption of anthracene oil during the initial stages of liquefaction. Such a reaction may account for a portion of the swelling of coal at low space times and the sizable increase of viscosity of reaction slurry during these initial stages of liquefaction. It is also observed that the yield of oil increases when solvents of increasing hydrogen donor capacity are used.     

Comparative reactivities of coal asphaltenes during hydropyrolysis

Comparisons have been drawn in the relative reactivities of three coal asphaltenes during hydropyrolysis. All were derived from hydrogen donor-solvent extracts of bituminous coal, but had different hydrotreatment histories and different carbon contents (87.1, 91.9 and 90.8 wt% for asphaltenes 1, 2 and 3, respectively). The hydropyrolyses were carried out in the presence of CoO–MoO₃ catalyst and gaseous hydrogen at 8.7 MPa. For two of the asphaltenes (1 and 2) systematic comparisons were made for different reaction times at 425°C; for all three asphaltenes comparisons were made for l h of hydropyrolysis at 425°C. The general pattern of asphaltenes conversion indicated that more pentane-soluble product was produced from asphaltene isolated from straight coal extract (asphaltene 1). For the asphaltenes isolated from hydrotreated extracts, the extent of conversion to liquids was limited when the carbon content was high (asphaltene 2) although the pattern of conversion was similar in the other hydrotreated asphaltene (asphaltene 3). The aliphatic content of the liquid products formed was low, and the distribution of hydrogenated species in the highly aromatic liquid products indicated that complete hydrogenation of the polyaromatics produced in pyrolysis is difficult. Altogether the aliphatics made up ≈ 10 wt% of the asphaltene 1 hydropyrolysate. Aromatic hydrocarbons made up 90% of the liquid product. Phenanthrene, pyrene and anthracene were prominent, and the largest component in the mixture was phenanthrene which, together with other polyaromatics such as fluoroanthene, dominated the liquid product.     

Effects of solvent and iron-compounds on the liquefaction of brown coal

Hydrogen-donor solvents such as hydrophenanthrene are the most effective aromatic solvents for the liquefaction of brown coal. The hydrogen-donating ability of the solvent is more important for brown coals than for bituminous coals, because the thermal decomposition and subsequent recombination of the structure of the brown coals occurs rapidly. Three-ring aromatic hydrocarbons are more effective solvents than two-ring aromatics, and polar compounds are less effective solvents with brown coals than with bituminous coals. The thermal treatment of brown coal, accompanied by carbon dioxide evolution at temperatures > 300°C, in the presence of hydrogen-donating solvent did not affect the subsequent liquefaction reaction. However, thermal treatment in the absence of solvent strongly suppressed the liquefaction reaction, suggesting that the carbonization reaction occurred after the decarboxylation reaction in the absence of hydrogen donor. To study the effect of various iron compounds, brown coal and its THF-soluble fraction were hydrogenated at 450°C in the presence of ferrocene or iron oxide. The conversion of coal and the yield of degradation products are increased by the addition of the iron compounds, particularly ferrocene, and the yield of carbonaceous materials is decreased.     

Liquefaction mechanism of Wandoan coal using tritium and 14C tracer methods: 2. Liquefaction using 3H labelled gaseous hydrogen

Tritium labelled gaseous hydrogen was used to clarify the role of gaseous hydrogen in coal liquefaction. Wandoan coal was hydrogenated under 5.9 MPa (initial pressure) of ³H-labelled hydrogen and in unlabelled solvents such as tetralin, naphthalene and decalin at 400 °C and for 30 min in the presence or absence of NiMoAl₂O₃ catalyst. Without a catalyst, liquefaction proceeded by addition of the hydrogen from donor solvent. The NiMoAl₂O₃ catalyst enhanced both hydrogen transfer from gas phase to coal and hydrocracking of coal-derived liquids. With NiMoAl₂O₃ catalyst, liquefaction in naphthalene solvent proceeded through the hydrogen-donation cycle: naphthalene → tetralin → naphthalene. The amount of residues showed that this cycle was more effective for coal liquefaction than the direct addition of hydrogen from gas phase to coal in decalin solvent. The ³H incorporated in the coal-derived liquids from gas phase was found to increase in the following order: oil < asphaltenes < preasphaltenes < residue.     

Liquefaction mechanism of Wandoan coal using tritium and 14C tracer methods: 1. Liquefaction in 3H and 14C labelled solvent

Liquefaction of Wandoan coal using a ³H labelled tetralin solvent which contains a small amount of ¹⁴C labelled naphthalene has been studied at 400 °C under an initial hydrogen pressure of 5.9 MPa, in the presence or absence of NiMoAl₂O₃ catalyst. The amounts of ³H and ¹⁴C transferred from the solvent to the products were measured as liquefaction progressed. The reaction pathways in the presence and absence of the catalyst were discussed and their reaction rate constants were calculated. According to the mass balances of hydrogen and ³H, in the absence of catalyst, tetralin provided coal with hydrogen atoms, and the degree of hydrogen exchange between coal and solvent was small. The catalyst decreased the hydrogen addition from solvent to coal and increased that from gas to coal.     

Hydroliquefaction of Victorian brown coal in a continuous reactor : 2. Comparison of tetralin and a coal-derived oil as hydrogen donor solvents

Slurries of Victorian brown coal in either tetralin (1:3) or a hydrogenated creosote oil (HKC 300) (1:3) were reacted with hydrogen in a continuous reactor system both with and without the addition of iron/tin based catalysts. The product yields and distributions from reactions using HKC 300 oil as a solvent are different from those obtained using tetralin. Under similar operating conditions, conversions are slightly lower and the asphaltene yields are higher for reactions in HKC 300 relative to those in tetralin. These differences are presumably due to the poorer hydrogen donor ability of the HKC 300. The yields of asphaltols, asphaltenes and oils for reactions in both solvent systems under a wide range of conditions are discussed as a function of overall conversion.     

Average structure of coal: Structural analysis of pyridine extract of zinc-water-coal reaction product

Six coals, of 67.5–91.5 wt%C (daf), were hydrogenated with zinc and water under 8 MPa of nitrogen for 30–60 min at 445 °C. This reaction utilizes the hydrogen generated in situ by the reaction Zn+H₂0 = ZnO + 2H₂. The influence of reaction time was examined using the lowest-rank coal and 30 min was found to be the optimum for this coal. The conversion of the various coals was 80.7–100% with the exception of the highest-rank coal, which gave only 36.5% conversion. Structural analysis, carried out for the pyridine-soluble fractions using the Brown—Ladner equations, showed that the aromatic ring size increased from 1 for the lower-rank coals to 4 for the higher-rank coals.     

Complete conversion of brown coal into distillate

The conditions for complete conversion of Victorian brown coal were investigated with an iron–sulfur catalyst in a continuous reactor system consisting of three stirred tank reactors in series. The coal was found to be completely converted into distillate (b.p.<420°C) when the gas flow rate (GFR) through the reactors was increased and the slurry-feed rate was reduced at a temperature of 450°C and a pressure of 18.6 MPa. An analysis of the composition of the liquid in the reactors under liquefaction conditions confirmed that the increase in GFR markedly enhanced the stripping of the solvent fraction in the feed slurry and the lighter fraction derived from the coal, resulting in marked increases in the actual residence time (θ_RT) of the liquid consisting of the concentrated catalyst and heavy fraction. The stripping effect markedly enhanced liquefaction reactions, thus providing a higher distillate yield. However, the GFR effect was gradually saturated as the liquid remaining in the reactors (reactor liquid) became heavier with the increase in the GFR. The extension of nominal residence time (defined by the ratio of slurry-feed rate to reactor volume, θ_NT) from reduction of the slurry feed rate was found to be effective in extending the GFR effects under a high GFR condition, resulting in the complete conversion of the coal. In addition, the stripping of the solvent by the increased GFR was also found to be more enhanced at 18.6 MPa than that at 14.7 MPa although its vaporization was suppressed at a higher pressure. This is due to the heavy fraction in the reactor liquid being more hydrogenated over the concentrated catalyst at a higher hydrogen pressure. However, the dependencies of the conversion rate of the heavy fraction on θ_RT were almost the same for both 14.7 and 18.6 MPa. These results suggested that a complete conversion of the coal could be achieved at 14.7 MPa by using a heavier solvent.