Coal hydroliquefaction using iron pentacarbonyl as a catalyst precursor

Hydroliquefaction of several coals, Taiheiyo (Japanese), Mi-ike (Japanese), Wandoan (Australian), and Illinois No.6 (American), was carried out using iron pentacarbonyl(Fe(CO)₅) at 425–460°C under a hydrogen pressure of 4.9MPa in a non-hydrogen donating solvent, 1-methylnaphthalene. With the addition of iron pentacarbonyl coal conversion increased substantially for all of the coals used. Lighter fraction (oil) also increased, by ≈ 10–17 wt%, in the presence of the catalyst. The addition of Fe(CO)₅ suppressed coking, resulting in high values of coal conversion and oil fraction even at 460°C. The amounts of hydrogen transferred from the gas phase increased by 2–4 times with Fe(CO)₅. A process involving direct hydrogen transfer to coal fragment radicals is proposed.     

Floatabilities of Treated Coal in Water at Room Temperature

Abstract

Experiments on equilibrium adsorption loadings of various probe cormpounds on 60–200 mesh Illinois #6 coal (PSOC-1539), Adaville #1 coal (PSOC-1544), Wyodak coal (PSOC-1545), and Pittsburh #8 coal (PSOC-1549) were erformed. The probe compounds incqude 2-methyl-1-pentanol (2MfP), 1-heptanol, benzene, and toluene. Equilibrium adsorption loadings of aromatic compounds such as toluene and benzene on the four chosen coals obey the Langmuir isotherm model up to 100 ppm in concentrations of probe compounds. Equilibrium adsorption Poadings of higher aliphatic alcohols such as 2M1P and 1-heptanol on the four chosen coals donot follow both the Langmuir isotherm model and the Freundlich empirical adsor tion model. Flotation of the coals, equilibrated with aqueous sofutions of 2M1P and 1-heptanol, increases linearly with equilibrium adsorption loadings of these probe compounds onthe coals.

The chosen coals were treated with nitrogen and air at 1 atm and 125–225°C for 24 h. Flotation experiments of the treated coals were conducted at room temperature, using distilled water only asa flotation medium. Flotation of Adaville #1 coal and Wyodak coal treated with nitrogen gas is higher than that of the untreated coals and increases with treatment temperatures. Flotation of Adaville #1 coal treated with air at 125–225°C is not significantl different from that of untreated coal. Flotation of Pittsburgg #8 coal treated with air is lower than that of untreated coal and decreases with treatment temperatures. Flotation of Illinois #6 coal treated with nitrogen only is higher than that of untreated coal. Flotation of Illinois #6 coal treated with nitrogen at 125–175°C increases with treatment temperatures, whereas flotation of Illinois #6 coal treated with nitrogen at 175–225°C decreases with treatment temperatures.     

Effect of NaOH treatment on surface properties of coal

Surface properties of sub-bituminous Wyodak and bituminous Illinois coals were examined using sorption and immersion techniques, to elucidate the effects of aqueous NaOH treatment. Sorption of non-polar gases such as CO₂ and N₂ decreased significantly after the alkali treatment for the Wyodak coal; however, similar tests with the Illinois coal did not produce such dramatic results. Water sorption and heats of immersion into liquid water increased considerably for both coals following the NaOH treatment. It is concluded that treatment with aqueous NaOH affects the chemical and physical structure of the coal surface.     

Effects of sulfur on coal treatment in aqueous sodium hydroxide

The dissolution of Wyodak subbituminous and North Dakota lignite coals in 50% aqueous sodium hydroxide was enhanced by the addition of sulfur. The added sulfur was not incorporated into the undissolved coal residues. The effects of temperature (140–200°C), time (5–90 min), and added elemental sulfur (1–25% by weight) on dissolution were examined. Temperature affected the dissolution of subbituminous and lignite coal, while time affected the dissolution of subbituminous coal.     

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.     

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.     

Internal rearrangement of hydrogen during heating of coals with phenol

Heating either Bruceton or Wyodak coal with phenol results in the thermal depolymerization of the coal yielding pyridine-soluble products and an insoluble residue. The depolymerization is accompanied by extensive rearrangements of hydrogen within the coals producing a soluble material enriched in hydrogen and a residue which is hydrogen poor. The hydrogen shuttle in Wyodak coal has a different temperature dependence than does the depolymerization, being favoured at higher temperatures. The $\text{H}\text{C}$ ratio of the soluble products increased with increasing conversion. Relatively small amounts (ca. 5%) of the products at high conversion are derived from phenol.     

A kinetic investigation of coal liquefaction at short reaction times

Coal liquefaction kinetics have been studied at very short reaction times (less than 250 seconds) in order to emphasize the initial underlying physical and chemical processes involved. These studies were made possible by the use of a continuous flow stirred tank reactor (CSTR) which avoids the problems of slow heat up and cool down associated with the massive equipment required for running high-temperature and high-pressure liquefaction reactions. Preliminary physical (NMR and ESR) and chemical analytical results are presented on the coal liquids and reaction residues from Illinois No. 6 hv bituminous and Wyodak Black Thunder subbituminous coals.

ESR results showed that radical concentration in the solid residue changed during coal liquefaction. These changes were accompanied by changes in the NMR-derived aromaticity. The rate of decrease of organic-based radicals was different for Wyodak Black Thunder and Illinois No. 6 coals, perhaps indicating a different mechanism for the quenching of radicals in these bituminous and subbituminous coals. NMR spectra of the liquid products indicated that the initially produced material was relatively aromatic, and that subsequent products had lower aromatic content. This is consistent with secondary hydrogenation of the primary liquefaction products. Finally, the total oxygen contents of the coal residues decreased gradually during the first three minutes of coal liquefaction at 390°C. A corresponding decrease in the hydroxyl content of these residues was also noted.     

Spatial distribution of oxygen in coals. Development of a tin labelling reaction and Mössbauer studies

All of the hydroxyl groups in Illinois No. 6 and Rawhide (Wyodak) coals have been converted to their-O-SnBu₃ derivatives by reacting with (n-Bu₃Sn)₂0 in refluxing toluene. The Sn Mössbauer spectra of the coal derivatives show that almost all of the tin is trigonal bipyramidal, which requires the presence nearby of a heteroatom for co-ordination to the tin. If this observed geometry occurs in the parent coal, in spite of the large size of the introduced derivatizing group, then the hydroxyl groups of the coal are paired with another heteroatom and most are hydrogen bonded in the solid.     

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.     

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.     

Displacement of retained pyridine by aqueous tetrahydrofuran from Illinois No. 6 coals

It has been found that repetitive washing of an Illinois No. 6 vitrain and O-methylated Illinois No. 6 vitrain containing 10.7 and 7.9 wt% pyridine, respectively, with a 5% (v/v) tetrahydrofuran in water solution followed by vacuum drying at 110 °C (18 h) effectively removes all of the retained pyridine. Experiments with ¹⁴C-labelled THF establish that tetrahydrofuran is not retained under these conditions in significant amounts (< 1.2% by weight) by either of the two coals. Furthermore, the difference in weight before and after the extraction agrees well with the amount of pyridine initially present indicating only small (< 5%) losses of coal during this process. Plots of per cent pyridine released versus vol% THF are consistent with a displacement mechanism in which THF penetrates the coal matrix and replaces the adsorbed pyridine.     

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.     

Differences in the behaviour of US bituminous and subbituminous coals during short contact time liquefaction

The short contact time (SCT) liquefaction of Belle Ayr subbituminous coal has been compared with that of Illinois No. 6 and Pittsburgh seam bituminous coals. Each bituminous coal was highly solubilized (90 wt%, daf coal) in 3–4 min at 450 °C and 13–16 MPa hydrogen pressure. More than 80 wt% of each coal was converted to solvent-refined coal (SRC, pyridine-soluble residuum), with only small quantities of distillate oil and C₁–C₄ gas being formed. A longer reaction (up to 30 min) gave only a small increase in total conversion, but gas and distillate yields increased significantly. Iron sulphides did not appear to catalyse coal solubilization. By contrast, only 65 wt% of the Belle Ayr coal dissolved rapidly in SCT liquefaction and pyrite addition catalysed the conversion of the remaining insoluble organic matter (IOM). With an equivalent amount of pyrite present the Belle Ayr coal also gave more C₁–C₄ gas and substantially more distillate in SCT liquefaction than the bituminous coals. These differences in product distributions obtained from bituminous and subbituminous coals in SCT liquefaction can be rationalized on the basis of differences in the structures of the starting coals. However, the origin of high IOM yields with the Belle Ayr coal remains unclear.     

Study on Surface Properties of Coal,Using Various Probe Compounds

Abstract

Pittsburgh seam coal, Wyodak coal and Illinois #6 coal were treated by heating, steaming and oxidizing them in order to modify surface properties of the coals at 150-220°C and atmospheric pressure, and compare adsorption responses of probe compounds, using a high pressure liquid chromatograph (HPLC). Probe compounds include toluene, Isopropanol, heptanol and phenol. Adsorption of xanthates on 120 mesh Rico Colorado pyrite was investigated at 25°C, using the inverse chromatographic technique. The concentration range of xanthates in pH 3.9 aqueous solution is 0.1–1 g/kg-solution. Xanthates include potassium amyl xanthate, sodium isopropyl xanthate and sodium ethyl xanthate for this investigation.     

Hydroliquefaction of subbituminous coal Effectiveness of pretreatment by organic reduction with Na or k

Hydroliquefaction of subbituminous Taiheiyo coal, without any pretreatment and after organic reduction, was carried out in the presence of tetralin using fine iron powder as catalyst. Two pretreatment procedures were used (A) reduction of coal with Na in liquid ammonia solution and (B) treatment with K in refluxing THF. Samples of treated coal with well-dispersed iron powder were prepared by co-reduction of coal coated with FeBr₂ using both procedures. Non-catalytic liquefaction of coal treated by A showed double the yield of hexane-solubles compared with that from liquefaction of the original coal while non-catalytic liquefaction of the coal treated by B roughly tripled the hexane-solubles yield and consumed the same amount of hydrogen. The presence of iron powder increased hexane-solubles by 5 wt% while increasing benzene-solubles by 13 wt% compared with non-catalytic liquefaction of treated coal by procedure B. The coals prepared by co-reduction (A and B) showed highest conversion (73 and 77%) along with highest yield of HS (38 and 43%). This significant effect on hydroliquefaction could be correlated with a slight increase of hydrogen atoms added to coal organic materials and the loosening of clusters of aromatic sheets.     

Carbonization and liquid-crystal (mesophase) development. Part 4. Carbonization of coal-tar pitches and coals of increasing rank

Coal-tar pitches, from coals of different rank and with various quinoline-insoluble contents, were carbonized under pressure (67 to 200 MN m⁻²) to maximum temperatures of 923 K. The resultant cokes were examined by optical and scanning electron microscopy in terms of size and shape of anisotropic structures within the coke. Natural quinoline-insolubles and carbon blacks both destroyed growth of the mesophase and development of anisotropy. Graphite particles (<10 μm) promoted growth and coalescence of the mesophase. Fourteen coals, of carbon content 77 to 91 wt%, VM 41 to 26%, were similarly carbonized under pressure. In the lower-rank coals no microscopically resolvable anisotropic mesophase was produced, but at a carbon content of 85% anisotropic units 1–2 μm in diameter were detected, increasing in size at a carbon content of 90% to 5 μm diameter. Results are discussed in terms of the origins of anisotropic mosaics observed in cokes, their variation in size with coal rank, and their significance in the carbonization of coal.     

The behavior of n-paraffins under coal liquefaction conditions

In order to evaluate the concentration and the distribution of n-paraffins in recycle solvent of coal liquefaction processes, the behavior of n-paraffins under coal liquefaction conditions was investigated. Four coals (Wandoan, Taiheiyo, Wyodak, Illinois No. 6) were liquefied and n-paraffins produced were analyzed. For example, n-paraffins, produced from liquefaction of Wandoan coal at 450°C for 1 h, contain approximately 5.2 wt.% (dry coal base) hydrocarbons in the range C₁₀C₃₆.Furthermore, cracking reactions of n-paraffins were carried out and their behavior under coal liquefaction conditions was analyzed. The cracking conversions of n-paraffins increased with increasing carbon numbers of n-paraffins, and the rate constants for cracking of n-paraffins were directly proportional to carbon numbers. The product distribution in the cracking of n-paraffins was evaluated by using bond dissociation energy. On the basis of these results, the concentrations of n-paraffins in the recycle solvents were calculated and these calculated values agreed well with those observed in the coal liquefaction process.     

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.     

Effect of acid treatment on thermal extraction yield in ashless coal production

Coals of different ranks were acid-treated in aqueous methoxyethoxy acetic acid (MEAA), acetic acid (AA), and HCl. The acid-treated coals were extracted with polar N-methyl-2-pyrrolidinone (NMP) and nonpolar 1-methylnaphthalene (1MN) solvents at temperatures from 200 to 360 °C for 10-60 min. The thermal extraction yields with NMP for some acid-treated low-rank coals increased greatly; for example, the extraction yield for Wyodak coal (%C; 75.0%) increased from 58.4% for the raw coal to 82.9% for coal treated in 1.0 M MEAA. Conversely, the extraction yields changed minimally for all the acid-treated coals extracted in 1-MN. The type and concentration of acid affected the extraction yield when NMP was used as the extraction solvent. With increasing MEAA concentration from 0.01 to 0.1 M, the extraction yield for Wyodak coal increased from 66.3 to 81.4%, and subsequently did not change clearly with concentration. Similar changes in the extraction yield with acid concentration were also observed with AA and HCl. The de-ashing ratio for coals acid-treated in MEAA, AA, and HCl also increased greatly with concentration from 0.01 to 0.1 M, which corresponded to the change in the thermal extraction yield in NMP. For the acid-treated coals, high extraction yields were obtained at lower extraction temperatures and shorter extraction times than for the raw coal. The mechanisms for the acid treatment and thermal extraction are discussed.