Low temperature—long time,high temperature-short time liquefaction of coal: The Hokudai process

A Japanese cola was hydrogenated in wash oil with fine iron dust and sulphur as catalyst under a reaction pressure of 12–13 MPa at 420 °C for 2 h and then at 500 °C for 0–20 min. The liquid yield boiling up to 600 °C amounted to 55–66 wt%. Pyridine conversion was ≈ 100 wt%, benzene conversion 82–90 wt% and n-hexane conversion 53–70 wt%. Compared with direct hydrogenation at 500 °C for 10 min the low temperature-long time plus high temperature-short time liquefaction process (the Hokudai process) is a very effective method for obtaining high liquid yield under relatively low hydrogen pressure without coking, using disposable catalyst and non-donor solvent.     

Catalytic activity of coal minerals in water vapour gasification of coal

Possible catalytic influences of coal minerals during water vapour gasification of coal have been studied by kinetic measurements and microanalytical methods. A bituminous coal without and with various pretreatments and also model chars synthesized from PVC and PVC-sulphur mixtures were used as raw materials. Kinetic measurements were performed in a fixed-bed flow reactor at pressures between 0.2 and 2 MPa and temperatures from 880 to 1010 °C using hydrogen/water vapour mixtures as gasification agents. It was found that coal gasification at and beyond 880 °C can be decisively catalysed by the iron as constituent of mineral matter. Preconditions are elimination of inorganic sulphur and reducing atmosphere to stabilize elemental iron. The optimum pressure is in the range of 0.5 to 1 MPa. Scanning electron microscopy and electron probe microanalysis confirm that catalytic gasification starts as soon as the iron is free of sulphur. The organic sulphur of coal does not prevent but lowers the catalytic activity of iron.     

Hydrogenation of phenanthrene in the presence of Ni catalyst. Thermal dehydrogenation of hydrophenanthrenes and role of individual species in hydrogen transfers for coal liquefaction

Mixtures of phenanthrene (P) and hydrophenanthrenes (HPs) of increasing hydrogenation degree (H₂P, H₄P, H₈Ps, H₁₄Ps) were obtained by hydrogenation of P under kinetic control conditions on Ni catalyst at 292 °C and 315 °C under constant hydrogen pressure (7.1–7.8 MPa) for reaction times up to 96 min. Thermal treatments (400 °C, 60 min) of the final mixtures have permitted to define the roles of individual molecular species (in particular H₂P and s-H₈P) in bimolecular reactions of H-exchange and disproportionation and in unimolecular reactions of isomerization and fragmentation connected to the thermal dehydrogenation. H₈Ps, as overhydrogenated donor species, were further examined with regard to the bimolecular reactions at higher temperature (484 °C) and shorter reaction times (10 min) in the presence of P added as coal model.     

Coal liquefaction using iron complexes as catalysts

Hydroliquefaction of Japanese Miike and Taiheiyo coals was carried out using various iron complexes as catalysts in tetralin at 375–445 °C. Iron pentacarbonyl (Fe(CO)₅) showed the highest catalytic activity, increasing coal conversion by about 10% at 425 °C under an initial hydrogen pressure of 5 MPa. Amounts of hydrogen transferred to coal increased from 1.4–2.3 wt% of daf coal in the absence of the catalyst to 2.5–4.2 wt% of daf coal in the presence of Fe(CO)₅ at 425 °C.     

Reaction of pyritic sulphur in coal with lime and calcined dolomite during the coking process

Various reactions occur between pyrite (FeS₂) in coal and CaO to form CaS when a finely pulverized intimate mixture of coal and CaO is coked at 900 °C in an inert atmosphere. The effectiveness of lime and calcined dolomite (CaO.MgO) in promoting this reaction has been evaluated; calcined dolomite is somewhat more effective than lime over coal/ oxide weight ratios from 2.8 to 14. The degree of conversion of pyrite to calcium sulphide at a coal/calcined dolomite weight ratio of 7 has been determined as a function of time at 900 °C; coking time in excess of 2.5 h does not have a significant effect. It has been shown that the total sulphur lost on coking coal/lime mixtures decreases and the percentage of FeS, originating from the dissociation of pyrite, converted to CaS increases as the amount of lime added increases. But although the total sulphur content of coke produced in the presence of CaO is then higher than when the coal is coked without lime, the pyritic sulphur has been converted to CaS which is more amenable to chemical conversion to H₂S. A method is outlined for determining CaS in the coked mixture in the presence of FeS.     

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.     

Catalytic activity of coal minerals in hydrogasification of coal

Hydrogasification of six bituminous coals was studied in a fixed-ped flow reactor at pressures up to 2 MPa and temperatures from 790 to 960 °C. Ranges of distinct methane formation are found with all coals between 500 and 600 °C, 750 to 800 °C and >850 °C. The reactions in the first two ranges are determined by the molecular structure of coal and are not affected by catalytic activities of constituents of coal minerals. In the third range, >850 °C, iron as a constituent of mineral matter of coal can accelerate methane formation significantly if the pressure is sufficiently high. Thermodynamic calculations indicate, and were verified by thermogravimetric studies, that iron disulphides in original coals can be desulphurized during gasification. Alkali and alkali earth oxides and carbonates can act as sulphur scavengers via an exchange reaction and thus accelerate the desulphurization of iron sulphides.     

Changes in state of combination of inorganic constituents during carbonization of Victorian brown coal

The inorganic constituents of low-rank Victorian brown coal, which are mainly present as inherent inorganic combinations attached to the coal molecule, are different from the minerals present in higher-rank coals. Changes in the state of combination of the inorganics in the chars of these coals have been studied by determining the minerals formed when chars are prepared at various temperatures. It is shown that when brown coals containing inorganic carboxylates are carbonized, the reactive functional groups which are present will begin to decompose below 400 °C and their decomposition is completed by 600 °C. The inorganic elements released will form mineral combinations depending on the carbonizing temperature and the reduction potential of the metal. Sodium carbonate, calcium oxide, magnesium oxide (periclase) and iron oxide (magnetite) are usually the chief minerals that may be formed. Mineral constituents present in the original coal may also change during carbonization. As the temperature increases, hydrated oxides of iron, clay and aluminium will lose water of crystallization and become dehydrated, forming magnetite, dried clay and alumina. Pyrite will lose up to half its sulphur at 400–450 °C. If the carbonization temperature is over 600 °C, metallic iron may be formed from the magnetite, and sodium chloride (and later sodium carbonate) will volatilize. Quartz remains unaltered.     

Removal of organic sulphur from coal gas

Organic sulphur compounds present in coal gas containing 15-20% CO were effectively converted into H₂S over a “Nimox” (nickel-molybdenum) conversion catalyst. H₂S was effectively removed by “Luxmasse”, a prepared iron oxide. The overall removal of organic sulphur depended upon the concentration of thiophene present. With only 10 ppm thiophene in the gas, the conversion of organic sulphur was 97% at 350°C after a single treatment. With six-stage treatment at 350 psig, the final gas contained only 0.2 ppm total organic sulphur in the presence of 4-5% water vapor.     

Mössbauer spectroscopy of iron in coal and coal hydrogenation products

The chemical states of iron in a Kentucky coal and in the products of its hydrogenation were determined by Mössbauer spectroscopy. The iron in the coal was present chiefly as pyrite, FeS₂. There was, however, evidence for some non-pyritic iron, most likely present as szomolnokite (FeSO₄·H₂O). The products from hydrogenation of this coal by the SYNTHOIL process at 723° K and 28 MPa contained all the iron as FeS_x where x = 1.0 to 1.14. There was no evidence for unreduced FeS₂ or FeSO₄. There was also no evidence for elemental iron. At the experimental conditions for hydrogenation of coal in this work, the reactor gas contained 0.32% H₂S. Evidently, FeS_x is not reduced to elemental iron in the presence of this concentration of H₂S in the reducing gas.     

Synthesis of monodispersed micaceous iron oxide by the oxidation of iron with oxygen under hydrothermal conditions

The oxidation behavior of iron powder with oxygen was investigated in 5–25 m NaOH solutions at 5 MPa of oxygen partial pressure and 130–290°C, where m = mol(kg H₂O)^?1. Monodispersed micaceous iron oxide, α-Fe₂O₃, was synthesized by the oxidation of iron powder with 5 MPa of oxygen in 10–16 m NaOH solutions at 250–270°C. The diameter of micaceous iron oxide greatly changed depending on the reaction conditions such as the temperature, reaction time and concentrations of NaOH and coexisting ions.     

Effect of pressure and temperature on the reaction of coal with alcohol-alkali

The ethanol-NaOH reaction of Taiheiyo coal (C, 77.5; H, 6.3 wt%) was examined under a pressure of 0.1–8 MPa nitrogen or hydrogen, at 300 °C for 1 h. Almost all of the products are extracted with pyridine for the entire pressure range and the extraction yield with ethanol increases with pressure, even under nitrogen. The yield of the products extracted with ethanol is higher when the coal is reacted under hydrogen than when reacted under nitrogen. The explanation for these results is that, under pressure, the hydrogen produced from the reaction of alcohol and NaOH is enclosed for a longer period in the solvent, thus accelerating the hydrogenation reaction of the coal, also under hydrogen pressure, the reaction is particularly accelerated because the hydrogenation takes place with the hydrogen gas. At 300 °C, the ethanol-extraction yield is much higher than the benzene-extraction yield, but the latter increases rapidly and approaches that of the ethanol-extraction yield as the temperature rises to 400 °C. This is because the polar groups, e.g. as hydroxyl groups which are rich in the low-temperature products, decrease with the temperature rise.     

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

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.     

Selective hydrogenation of olefinic bonds in styrene-isoprene-styrene triblock copolymer by palladium acetate catalyst

Homogeneous catalytic hydrogenation of styrene-isoprene-styrene triblock copolymer (SIS) has been carried out selectively at the carbon-carbon double bond in the presence of palladium acetate catalyst under mild conditions. Degree of hydrogenation has been calculated with the help of infrared and nuclear magnetic resonance spectroscopic techniques. Almost 90 mol % complete hydrogenation has been achieved at 60°C under 1.4 MPa hydrogen pressure, 40 mg catalyst (for 2 g of polymer) in chloroform-acetone solution for 1 h. © 1993 John Wiley & Sons, Inc.     

Differential scanning calorimetry studies on coal. 2. Hydrogenation of coals

Results of exothermic heats involved during hydrogenation of twenty U.S. raw coals of varying rank at 5 · 6 MPa (gauge) and temperatures up to 570 °C are reported. The heat evolved during hydrogenation up to 570 °C decreases with increase in coal rank. A part of the total heat released during hydrogenation of coals appears to be due to the exothermic reaction between H₂ and surface carbon-oxygen complexes removed during the reaction. The transition temperature, that is the temperature corresponding to the onset of exotherms, is markedly dependent on coal rank. A sharp increase in the transition temperature occurs for coals having a carbon content, on a dry-ash-free basis, in the 75–80% range. Demineralization of coals lower in rank than HVA bituminous decreases the heat of hydrogenation; in the case of higher-rank coals, exothermic heats increase upon demineralization. The presence of pyrite has a beneficial catalytic effect on coal hydrogenation.     

Some aspects of the behaviour of inorganic constituents of two Australian brown coals during hydroliquefaction

An examination has been made of the changes taking place in the mineral and other inorganic matter contained in two Australian brown coals as a result of hydroliquefaction of the coal in tetralin and hydrogen at 25 MPa and 395 °C. Iron sulphides were found to be reduced to pyrrhotite, whereas iron carboxylates decomposed mainly to magnetite. Calcium carboxylates formed predominantly vaterite, whereas when coals were subjected to low-temperature ashing calcite was formed. Amorphous tin oxide, precipitated onto the coal by hydrolysis of stannous chloride solution, was largely reduced during hydrogenation to liquid tin, some of which reacted with hydrogen sulphide to form herzenbergite.     

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.     

A comparative study on deposited and mixed iron oxide catalysts for hydrogenation of coal

The activity and selectivity of two modes of using iron oxide catalysts for hydrogenation of coal have been compared. In one mode of application, the hydrated oxide of iron was deposited on coal by keeping it suspended in the aqueous solution of an iron salt and adding ammonium hydroxide to it. In the other case, the hydrated oxide was precipitated under exactly similar conditions in the absence of coal and was mixed with the powdered coal. For the same concentration of iron and under identical conditions of reaction, the overall efficiency of the deposited form of catalyst was found to be superior to the mixed type.     

Coal hydrogenolysis in the presence of NaOH

High pressure hydrogenolysis of coal was carried out in the presence of sodium hydroxide at 350–500 °C and initial pressures of 3, 10 and 13 MPa for 15–60 min. Similar experiments were carried out under nitrogen. The yield of solid product decreased with increased reaction temperature because of the increased production of gases which are mainly hydrocarbons. Extraction of the solid products, formed under hydrogen, with pyridine and benzene shows higher yields than when nitrogen is used. This indicates that depolymerization and hydrogenation reactions were accelerated in the presence of sodium hydroxide under hydrogen.     

Effect of precarbonization temperature on liquefaction of lignites

Soya Koishi and North Dakota lignites were precarbonized at 350, 400 and 420 °C to reduce the oxygen content prior to hydrogenation at 400 °C under an initial hydrogen pressure of 10 MPa for 1 h. After hydrogenation, the solubility in tetralin and benzene remained almost constant to the precarbonization temperature of 420 °C for Soya Koishi lignite and 400 °C for North Dakota lignite. The hydrogen consumption decreased by ≈25% for the former and by ≈50% for the latter. The hydrogen content also decreased by precarbonization which increased the tetralin-insoluble fraction.