Behaviour of huminite macerals from Victorian brown coal in tetralin in autoclaves at temperatures of 300–380 °C

The behaviour of various huminite macerals and submacerals in a hydrogen-donor solvent, tetralin, at high temperature under hydrogen pressure was investigated. Small granular samples of three Victorian brown coals of different lithotype were treated with tetralin in two types of autoclave, at temperatures of 300–380 °C and under pressures of 5 or 10 MPa. The residual materials were investigated microscopically. This tetralin treatment caused huminite macerals and submacerals derived from highly gelified cellular material to become plastic even at temperatures as low as 340 °C, whereas it had no such effect on those derived from ungelified material. This relation between the degree of gelification and the tendency to become plastic during tetralin treatment in an autoclave is very similar to that found for vitrinite macerals and submacerals from bituminous coals.     

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.     

Hydrogenolysis and hydrocracking of the carbon-oxygen bond. 2. Thermal cleavage of the carbon-oxygen bond in guaiacol

Low-rank coals and their precursors contain, in addition to aromatic hydroxy groups, aromatic methoxy groups. In the present work a model compound, guaiacol, is used for the study of the behaviour of the carbon-oxygen bonds under thermolytic conditions. The thermolysis of guaiacol is studied in tetralin, naphthalene and without solvent under hydrogen or nitrogen pressure at 578–618 K. The compound is homolytically converted by first-order kinetics. The major product is pyrocatechol. Phenol, o-cresol, methyl catechols and methyl guaiacols are also formed. When tetralin is present it reacts in a molar ratio of 1:4 with guaiacol to form naphthalene. The source of hydrogen when tetralin is not present is guaiacol itself because molecular hydrogen does not participate in the reaction. The kinetics and reaction mechanism are discussed.     

Short contact time liquefaction of coal using hydrogen donor solvent

Liquefaction of coals to form benzene-soluble materials was studied at 400 °C under autogenous pressure conditions using tetrahydroquinoline (THQ), tetrahydroisoquinoline (THIQ) and tetralin (TL) as the hydrogen donating solvents. THQ was the best solvent with a conversion rate of 90% within 15 min for low rank coals (< 80% C). In contrast, it took 50 min to achieve a conversion of 80% when TL was used as the solvent, although both solvents could achieve almost complete conversion of coals into quinoline-soluble material within 10 min. THQ also showed excellent activity with blended coals. Some binary solvents exhibited activities which varied with the THQ content. A 1:3 by weight mixture of THQ and petroleum pitch produced the highest conversion of 100%.     

Production of clean fuels by solvent skimming of coal at around 350 °C

The authors have recently presented a new coal extraction method by which various kinds of coals ranging from brown coals to bituminous coals could be extracted up to 80% of the parent coals in a flowing stream of tetralin or a coal derived oil, carbol oil, under 10 MPa at 350 °C. The extract obtained by this method was almost free from inorganic materials. In this study the effect of solvent recycling on the extraction behavior was examined to make the method practically applicable. The solvent recycling was found to be effective in enhancing the extraction yield and in decreasing further the inorganic fraction in the extract. The extract and residue obtained were characterized through various analyses. To examine how inorganic materials are removed by the extraction, the contents of inorganic elements, including harmful trace elements, in the extract were investigated. It was clarified that the presented method was effective in the removal of most of the inorganic elements including even harmful trace elements from coals, although the degree of removal was dependent on the kind of element.     

Effect of blending on liquefaction of coals

After solvent extraction of Taiheiyo, Miike and Balmer coals using wash oil under nitrogen atmosphere at 370 °C for 30 min, the extraction yield is always within the additivity law. Further studies used Yallourn, Soyakoishi, Taiheiyo, Horonai, Miike, Shin Yubari, Balmer coals and their blends which were hydrogenated in tetralin, wash oil or creosote oil, with or without catalyst, at 400–450 °C under 10 or 3 MPa of initial hydrogen pressure. When hydrogen is available, the additivity law exists for blended coals, but when the hydrogen supply is deficient, the experimental conversion of blended coals is always lower than calculated conversions. This may be due to the faster consumption of the hydrogen by more reactive coals and thus the less reactive coals were unable to react with hydrogen.     

Liquefaction of subbituminous coals with a basic nitrogenous model process solvent

Liquefaction reactions in a tubing-bomb reactor have been carried out as a function of coal, coal sampling source, reaction time, atmosphere, temperature, coal pre-treatment, SRC post-treatment and process solvent. Pyridine as well as toluene conversions ranging from 70 to > 90 wt% involving both eastern bituminous and western subbituminous coals are obtained. 1,2,3,4-Tetrahydroquinoline (THQ) has been extensively used as a process solvent under optimized liquefaction conditions of 2:1 solvent: coal, 7.5 MPa H₂, 691 K and 30 min reaction time. Comparisons of THQ with other model process solvents such as methylnaphthalene and tetralin are described. Liquefaction product yield for conversion of subbituminous coal is markedly decreased when surface water is removed from the coal by drying in vacuo at room temperature prior to liquefaction. The effect of mixing THQ with Wilsonville hydrogenated process solvent in the liquefaction of Wyodak and Indiana V coals is described.     

Effect of demineralization process on the liquefaction of Turkish coals in tetralin with microwave energy: Determination of particle size distribution and surface area

The effects of solvent/coal (S/C) ratio and demineralization on the solubilization of Turkish coals (Tunçbilek, Muğla-Yatağan, Beypazarı lignites and Zonguldak bituminous coal) in tetralin by microwave energy have been investigated. Particle size distributions and the surface area of the coals decreased with demineralization. For the investigation of the effect of the S/C ratios with values of 8/1, 10/1 and 12/1, the coal samples were heated by microwave energy for 20 min. The result indicated that the optimum S/C ratio was 8/1. The effect of microwave heating period was investigated at this value and the heating period was changed from 5 to 20 min at 5-min intervals. It was found that THF solubles yields of original coals were higher than those for demineralized coal except for Muğla-Yatağan lignite.     

Alkylation: a beneficial pretreatment for coal liquefaction

Several coals were alkylated employing isopropyl and methyl halides under Friedel-Crafts conditions. These alkylated coals, and corresponding untreated coals, were processed (liquefied) with tetralin in batch autoclaves (tubing bombs) at 700 K, 130 min residence time, and 10 MPa (1500 psi) hydrogen pressure. Conversion to cyclohexane-soluble liquids was found to be 10–21 percent higher (on an alkyl-group-free basis) for the alkylated coals than for untreated coals. These results are explained on the premise that alkylation beneficially disrupts the coal structure sufficiently to allow improved contacting between coal and tetralin.     

Dependence of coal liquefaction behaviour on coal characteristics. 4. Cluster analyses for characteristics of 104 coals

In an extension of earlier work, the conversion of 104 high volatile bituminous coals at 400 °C with tetralin has been determined in duplicate with the aid of a new reactor system. For the whole set of coals, volatile matter and vitrinite reflectance have the highest correlation coefficients with conversion (0.85 and ?0.84, respectively). However, tests showed that the sample set contained more than one population. Cluster analysis partitioned the set into three reasonably homogeneous populations. A factor representing sulphur content was the major contributor from a set of variables in separating the coals into groups, with smaller contributions from factors related to rank and petrographic composition. Each of the groups contained samples mostly from one geological province, but 11 coals of relatively high sulphur content from the Eastern province were clustered in a group that contained also 25 coals from the Interior province. The ranges of conversion are distinctly different for the three groups, and the three regression equations developed for correlating conversion each require a different set of coal properties. The possible general significance of the clustering of coals into groups as a novel basis for classification is discussed.     

Reactivity and structure of two coals containing significant methoxy group concentrations

Two coals (Beulah, PSOC-1483, and a Thai coal, TH23) of unusually high reactivity with hydrogen and tetralin were shown to contain significant methoxy group contents. The fate of the methoxy groups when these coals were reacted under N₂ at 320°C (with and without added decalin) and with H₂—tetralin and H₂---SnO₂ at 405°C was studied. The reactions of TH23 coal gave unexpectedly high water yields. Reactions of model compounds containing methoxy groups under similar conditions also gave high water yields. Proton magnetic resonance thermal analysis (PMRTA) confirmed that TH23 host and guest coal components are structurally distinct from those of Loy Yang (Victoria) run-of-mine coal.     

Effect of pre-swelling of coal on its solvent extraction and liquefaction properties

Effects of pre-swelling of coal on solvent extraction and liquefaction properties were studied with Shenhua coal. It was found that pre-swelling treatments of the coal in three solvents, i.e., toluene (TOL), N-methyl-2-pyrrolidinone (NMP) and tetralin (THN) increased its extraction yield and liquefaction conversion, and differed the liquefied product distributions. The pre-swollen coals after removing the swelling solvents showed increased conversion in liquefaction compared with that of the swollen coals in the presence of swelling solvents. It was also found that the yields of (oil + gas) in liquefaction of the pre-swollen coals with NMP and TOL dramatically decreased in the presence of swelling solvent. TG and FTIR analyses of the raw coal, the swollen coals and the liquefied products were carried out in order to investigate the mechanism governing the effects of pre-swelling treatment on coal extraction and liquefaction. The results showed that the swelling pre-treatment could disrupt some non-covalent interactions of the coal molecules, relax its network structure and loosened the coal structure. It would thus benefit diffusion of a hydrogen donor solvent into the coal structure during liquefaction, and also enhance the hydrogen donating ability of the hydrogen-rich species derived from the coal.     

Liquefaction of coal using supercritical fluid mixtures

Powhatan No. 5 and Bruceton coals were liquefied for 15–60 min at 653 K and 30 MPa in supercritical aqueous mixtures containing 10–20 wt% tetrahydroquinoline (THQ), quinoline or tetralin. The THQ-water mixtures produced the highest conversion to tetrahydrofuran (THF) soluble products (up to 74%). Tetralin-water, quinoline-water and pure water solvents gave increasingly lower yields of THF solubles. Addition of hydrogen to the quinoline-water solvent mixture increased yields slightly, but not to the level obtained using the THQ-water mixture.The yields of THF solubles in all instances depended upon the concentration of solvent in the mixture, with the 10 wt% THQ and 10 wt% tetralin (in water) giving higher yields than either 0 or 20 wt% concentrations. The nitrogen-containing solvents were chemically bonded to the THF-soluble product, as observed by g.p.c.     

Rapid extraction of products from coal hydrogenation reactions using an ultrasonic bath

Extraction of products into dichloromethane solution from reactions of Victorian brown coals with hydrogen in tetralin can be achieved in 2 min by immersing the extraction mixture in an ultrasonic bath at ambient temperature. The same levels of extraction using the Soxhlet technique can only be achieved by prolonged periods of extraction during which the coal extracts are heated at the reflux temperature of the solvent.     

Liquefaction of coal in hydrogen-donor and non-donor vehicles

Coal, slurried with tetralin, and heated rapidly to 400 °C, was converted to benzene-soluble, liquid products through a reaction path which appears to involve thermal cleavage of chemical bonds in the coal (so-called depolymerization). Free radicals formed pyrolytically were stabilized in the early stages by autogenous hydrogen transfer, and in later stages by abstraction of hydrogen from the hydrogen-donating tetralin (which was converted to dihydronaphthalene and then to naphthalene). Vitrinite of the coal particles became almost completely soluble in pyridine after 5 min reaction, and dispersed in the vehicle (tetralin) within about 10 min. Reaction in non-donor vehicles (naphthalene, dodecane) resulted in dispersion, but ‘repolymerization’ formed a benzene-insoluble material. Hydrogen transfer from tetralin increased exponentially with increased conversion of the coal to benzene-soluble material. Negligible influence of particle size (below 2–3 mm) implies that mass transfer is not a rate-limiting factor. High-volatile c bituminous coal and coals of lower rank converted at about the same rate and to the same extent (given equivalent petrographic compositions); approximately two-thirds of the ultimately achievable conversion occurs within 20 min. Higher-rank coals converted at a lower rate. Oxidation of the coal was deleterious to ultimate conversion.     

Producing ashless coal extracts by microwave irradiation

To produce ashless coal extracts, three Turkish coals were extracted with N-methyl-2-pyrrolidinone (NMP), NMP/ethylenediamine (EDA) (17/1, vol/vol) mixture and NMP/tetralin (9/1, vol/vol) mixture through thermal extraction and microwave extraction. Solvent extraction by microwave irradiation (MI) was found to be more effective than that by thermal extraction. Extraction yield of coals in NMP enhanced by addition of a little EDA, but tetralin addition showed variances according to extraction method used. While tetralin addition caused a decrease in the thermal extraction yield, it increased the yield of the extraction by MI. Following the extraction, the solid extracts were produced with ash content ranging from 0.11% to 1.1%. Ash content of solid extract obtained from microwave extraction are less than ash contents of solid extracts obtained from thermal extraction.     

Dependence of coal liquefaction behaviour on coal characteristics. 6. Product distributions from coals treated in a continuous-flow reactor

Further experimentation with coals in a continuous-flow reactor system at 440 and 455°C confirms the significance of the previous classification of a set of coals by cluster analysis. The greatest yields of distillable products tend to be given by coals of high sulphur content in the middle of the range of the high-volatile bituminous rank classes. Yet the lowest yields of preasphaltene (toluene-insoluble material) tend to be given by coals of high rank and medium sulphur content. The group of low sulphur, low-rank coals (mostly Rocky Mountain province), in a solvent different from that used for the other groups, showed poor conversion and poor distillate yield at the higher temperature. It is concluded that this coal/solvent combination is particularly prone to retrogressive reactions, including coking.     

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.     

The effect of extraction condition on ‘HyperCoal’ production (1)—under room-temperature filtration

In order to produce ashless coal (HyperCoal) in a high yield, extractions with several organic solvents—tetralin, 1-methylnaphthalene, dimethylnaphthalene and light cycle oil (LCO) at 200–380 °C were conducted for various ranks of coals, and subsequent solid/solution separation was done at room temperature. LCO was found to be a useful, cost-effective solvent, since it gave similar extraction yields to three other reagent solvents. The extraction yield for Illinois No. 6 coal gradually increased over 200 °C, and a significant increase in extraction yield was observed from 350 to 360 °C. We succeeded in producing ashless coal with less than 0.1% in ash content for seven of nine coals used in this study.     

Evidence for direct interaction of hydrogen with brown coal in tin-catalysed reactions

Evidence is presented which shows that the major mechanism for the tin-catalysed hydrogenation of suspensions of brown coals in tetralin involves a direct interaction of hydrogen with the coal.