Yosuke Maekawa

Quantitative 13C n.m.r. spectroscopy of a coal-derived oil and the assignment of chemical shifts

The conditions necessary for the recording of quantitative 13C nuclear magnetic resonance spectra of the hexane-soluble oil separated from a coal hydrogenation product have been investigated. Measured values of T1 for different signals in the spectrum were less than 1 s, and altering the pulse-repetition time beyond 2–4 s had little effect on carbon aromaticities. The nuclear Overhauser effect was suppressed by gating the proton decoupling. Assignments of chemical shifts for various signals in the spectrum of the oil were made by reference to literature spectra of polyaromatic substances and their derivatives. Determinations of different structural carbon types were internally consistent.

Catalytic activity of various iron sulphides in coal liquefaction

Abstract Iron sulphides with various S-Fe atomic ratios, such as pyrite, iron(III) sulphide, pyrrhotite and troilite, were used as catalysts for coal liquefaction. Catalytic activities were compared on the basis of the temperature of the exothermic peak due to coal hydrogenolysis. Effects of hydrogen sulphide on catalytic activity of iron sulphides were also investigated. It is concluded that: 1. 1. The catalytic activity of iron sulphides increases with increasing S-Fe ratio; 2. 2. pyrite, with the highest catalytic activity, is converted to pyrrhotite before the onset of exothermic reactions from coal hydrogenolysis, this evidently being the reason for the high catalytic activity; 3. 3. the catalytic activity of iron sulphides depends on the coal type; 4. 4. the high catalytic activity of pyrite may be due to the creation of fresh pyrite surface during the reaction rather than to the presence of high concentrations of hydrogen sulphide.

Liquefaction reaction of coal: 1. Depolymerization of coal by cleavages of ether and methylene bridges

The roles of ether and methylene bridges in the depolymerization of coal have been re-evaluated on the basis of the results of a mild liquefaction reaction (400 °C, 30 min) and the distributions of oxygen and carbon atoms obtained by cross-polarization, magic angle spinning (CP/MAS) 13C n.m.r. spectrometry. Coals ranging from 66.2 to 87.4 wt% C (dmmf) were used as sample coals. The content of etheric oxygen was < 3.7 per 100 carbon atoms and the cleavage of ether bridges contributed to the formation of preasphaltene. The conversion to hexane solubles in the mild liquefaction reaction correlated well with CH2 carbon content of coal, though the conversion to pyridine solubles did not. These results suggest that the formation of oil from preasphaltene is caused by the scission of CH2 bridges and some naphthenic CH2 bonds. The phenolic OH oxygen-rich portions in coal tended to remain as a residue formed by the condensation reaction of phenolic OH groups.

Viscosity changes in coal paste during hydrogenation

Abstract Using a viscometer that operates up to a maximum pressure of 29.4 MPa and a maximum temperature of 550 °C, the viscosity of coal paste and its changes with temperature were investigated, and also some effects of: type of vehicle oil, coal to vehicle oil ratio, coal particle size, atmosphere, pressure, catalyst and coal rank. In the viscosity-temperature curve for the paste from high rank bituminous coals, a peak was observed near 300 °C, which is considered to be due to the extractive disintegration of the coal by the vehicle oil. Under hydrogenation with high pressure hydrogen and hydrogenation catalyst, the extractive disintegration of coal was promoted, and the viscosity was higher than that in nitrogen atmosphere. The viscosity behaviour of the coal paste from low rank coals was the same as that of the vehicle oil alone.

Coal liquefaction by colloidal iron sulphide catalyst

Abstract Taiheiyo coal, which was treated with an aqueous solution of dodecyltrimethylammonium chloride, adsorbed colloidal iron sulphide prepared from FeS0 4 · 7H 2 O and Na 2 S · 9H 2 O in aqueous media. The adsorbed colloidal iron sulphide was much more effective as a catalyst for the liquefaction of the coal itself than the usual powder-type iron sulphide. Thus in differential thermal analysis under hydrogen, the coal with 0.35wt% adsorbed colloidal iron sulphide gave an exothermic peak at 401 °C, which was ≈20 °C lower than when using the powder-type iron sulphide. The coal was smoothly hydrogenated at 450 °C to give a yield of ≈60% liquid products.

Catalytic behaviour of sulphate and sulphide in S-promoted iron oxide catalysts for liquefaction of bituminous coal and lignite

Abstract Catalytic activities of sulphate (S6+) and sulphide (S2−) for liquefaction of bituminous coal and lignite were studied. In addition, their catalytic activities in the presence of tetralin during liquefaction of both coals were also investigated. The specific catalysts used were FeS2 as a sulphide, and Fe2O3(SO4)2− and ammonium sulphate as sulphates. The liquefaction for different types of coals was carried out in the presence of these catalysts and tetralin as donor solvent under either 10 MPa of H2 or N2 initial pressure by using a 70 ml autoclave. The intrinsic activities of these catalysts were evaluated by the distribution of products obtained from tetralin during coal liquefaction. Catalyst Fe2O3(SO4)2− showed the highest activities for hydrogenation and hydrocracking of tetralin. FeS2 showed slightly lower activities. Ammonium sulphate showed activity only for dehydrogenation of tetralin. Also, both catalyst Fe2O3(SO4)2− and FeS2 showed significantly high activity for hydroliquefaction of coals and the ammonium sulphate was found to be inactive. Our results also indicated that the hydroliquefaction activity of catalysts occurs preferentially via reaction with molecular hydrogen rather than through participation of donor solvent.

Catalytic activity of sulphate for hydroliquefaction of coal by using diphenylether and diphenylmethane

The catalytic activity of sulphate found in S-promoted iron oxide catalyst was investigated using model compounds such as diphenylether and diphenylmethane. The formation of sulphate was carried out by addition of water in the S-promoted iron oxide system. The catalysts used were FeS2, Fe2O3/S, Fe3O4S, red mudS and FeSO4 of analytical reagent grade. Reaction was carried out in the absence and presence of water under H2 or N2 atmosphere. When diphenylether was reacted under H2 atmosphere, reaction products were found to be benzene and phenol, but unknown compounds with high boiling points were also found under N2 atmosphere. Diphenylmethane was converted to benzene, toluene, bibenzyl, triphenylmethane, anthracene and unknown compounds under H2 and N2 atmosphere. It was shown that sulphate clearly promoted radical formation from phenyl and benzyl groups by dehydrogenation and the radicals formed were polymerized to various higher volatile compounds under N2 atmosphere as well as under H2 atmosphere, atmosphere.

Mechanism for formation of sulphate in S-promoted iron oxide catalysts for coal liquefaction

Abstract The mechanism for the formation of sulphate and sulphides in sulphur-promoted iron oxide catalysts for coal liquefaction has been discussed. The catalysts used were FeS, FeS 2 and Fe 3 O 4 of analytical reagent grade, and iron (Fe 2 O 3 ) prepared by precipitation from ferric nitrate. These catalysts were reacted with sulphur in the presence of water under H 2 or N 2 at 10.1 MPa initial pressure. Distributions of the sulphur in the reaction system were complete made using i.r. XPS, XRD and thermal analysis measurements. Based on these experiments, it was found that ratios of sulphides (S 2− )/sulphates (S 6+ ) give important information on the mechanism. It was concluded that the sulphate and sulphides were formed simultaneously by the following equation: nS + 2 H 2 O = SO 2 + ( n − 1) H 2 S + (3 − n ) H 2 .

The behavior of methylene groups in coal during heat treatment and air-oxidation

The behavior of CH2 groups in different ranks of coal by heat treatment at 400°C and air-oxidation at 200°C was studied using cross-polarization (CP) and magic angle spinning (MAS) 13C NMR spectrometry. The structural change of low-rank coals by heat treatment was characterized by marked decrease in CH2 carbon and increase in aromatic carbon. The reduction of CH2 carbon was caused by the abstraction of transferable hydrogen from hydroaromatic rings by oxygen atoms in low-rank coals and was caused by dealkylation reaction in high-rank coals. On the other hand, the carbon loss of coal by mild airoxidation was due to loss of aliphatic carbon, especially CH2 carbon. Aromatic carbon was very stable upon oxidation, while aliphatic carbon was readily oxidized to produce polar groups and eventually carbon oxides. The oxidative degradation of aliphatic portions in coal was more remarkable in low-rank coals.

Behaviour of the FeOSH system under coal liquefaction conditions

Abstract The behaviour of the iron-sulphur system in the presence of water and hydrogen under coal liquefaction conditions has been investigated by using a high-pressure differential thermal analysis technique. The iron compounds used were Fe 2 O 3 , Fe 3 O 4 and FeS 2 . DTA was performed under 10.1 MPa (initial pressure) N 2 or H 2 , heating to 450 °C (2.5 °C min −1 ). Sulphate ions were detected by BaCl 2 addition to the product aqueous solution; sulphides were formed as gaseous and solid products. The results suggest that the catalytic behaviour of the sulphate and sulphides formed under the conditions employed must be considered for the iron-sulphur system in coal liquefaction.