Characterization of coal-derived liquids by C n.m.r. and FT-i.r. spectroscopy: Fractions of middle and heavy distillates of SRC-II

Coal-derived products of the SRC-II liquefaction of Powhatan Mine (Pittsburgh Seam) bituminous coal were separated into various fractions either by solvent extraction or by distillation. Subsequently, the middle and heavy distillates were separated by sequential elution solvent chromatography into fractions differing in chemical functionality. These fractions were examined by ¹³C n.m.r. and FT-i.r. spectroscopic techniques. In addition to developing the techniques, the work was undertaken to relate the product composition to the possible reactions occurring during the solvent-induced pyrolytic fragmentation of coal. The bulk of the SRC-II generated middle distillate is composed of two-ring nonpolar aromatic compounds, tetralins, one-ring phenols, indoles, and some alkanes. The heavy distillate contains three-and four-ring systems.     

煤的CS2/NMP混合溶剂抽提研究进展

综述了 CS2 /NMP混合溶剂用于煤抽提的研究进展 ,着重介绍了煤阶、煤岩组分、添加物和各种辅助手段对抽提率的影响 ,并对添加物的增溶机理、混合溶剂的抽提机理、抽提动力学以及抽提物的表征等问题进行了讨论 ,指出高抽提率的溶剂抽提不仅对于煤结构的研究有着重要的意义 ,而且可望成为获取高附加值产品和煤净化的新途径     

Fractionation of brown coal by sequential high temperature solvent extraction

Separation of brown coal into fractions having rather uniform structure is believed to be one of the promising pretreatment methods for effective utilization of brown coal. The authors have recently presented a new coal fractionation method that can separate a bituminous coal into several fractions having different molecular weight compounds without decomposing the coal. The method extracts coal using a flowing stream of non-polar solvent such as tetralin or 1-methylnaphthalene by increasing the extraction temperature stepwise up to 350 °C. In this study the fractionation method was applied to fractionate a brown coal. Water was used as an extracting solvent in addition to tetralin and 1-methylnaphthalene by intending to utilize inherent water of brown coal as the extraction solvent. An Australian brown coal was successfully fractionated into six fractions by any solvents, but the properties of the fractions were significantly different depending on the extraction solvent. This is because tetralin, 1-methylnaphthalene, and water interacted significantly with the brown coal in different ways even at less than 350 °C. The difference in chemical structure and thermal properties of the fractions were examined in detail through ultimate analysis, ¹³C NMR, molecular weight distribution, and thermogravimetric and thermomechanical analyses.     

Free radicals in coal and coal conversions. 10. Kinetics and reaction pathways in hydroliquefaction

The development is reported of a point rate model for the solubility fractions obtained from Powhatan No.5 coal liquefaction in terms of free-radical concentration. Stepwise regression procedures were used to determine rate constants for general hypothetical rate models. Chemical principles were used at each stage to eliminate terms and to fix others. Rate constant expressions were obtained by fitting In k to the inverse absolute temperature for each solvent. Generalized reaction paths were determined from these individual reactions by combining various reactions. These reactions described the conversion of material between solubility fractions via free-radical interactions. In all three solvents progressive liquefaction reactions that did not involve measured radicals (conventional reaction terms) predominated in the rapid break-up of coal, while free-radical reactions are predominant in retrogressive changes. At higher radical concentrations retrogressive reactions predominated. More reactions of all types became significant with increasing temperature.     

Liquefaction of bituminous coal at moderate temperatures

Coal hydrogenation was investigated in the temperature range 275 to 325 °C in order to minimize the number of thermal side reactions that take place. Gas-phase hydrogen was used in batch experiments without an added donor solvent, to avoid the additional analytical complexities introduced by such a solvent. It was found that significant oil yields (up to 72% of the daf coal) can be obtained from the hydrogenation of bituminous coal at 325 °C. Furthermore, at this temperature, the data indicate that cleavage of certain C---O bonds may have an important role in oil formation. The metal surfaces of the liner and impeller of the autoclave had a strong catalytic effect on the liquefaction reactions under these conditions. The oil yield was 48% when the metallic surfaces were exposed and only 19% when these components were coated with glass. Catalysis by nickel, applied as nickel acetate impregnated into the coal, gave higher overall conversion, lower oil yield, and a more saturated oil product than catalysis by the autoclave surfaces.     

Fractionation of coal by use of high temperature solvent extraction technique and characterization of the fractions

The authors have recently presented a new coal fractionation method that can separate a bituminous coal into several fractions, just like petroleum distillation, without decomposing coal. In this paper this method was applied to two bituminous coals and a brown coal. Sequential solvent extraction at different temperatures lower than 350 °C successfully separated the two bituminous coals into several fractions having different molecular mass compounds. Since all the extracted fractions are almost free from mineral matter, and some fractions were found to be fusible like a synthesized pitch when heated, the possibility of producing high performance carbon materials from the coal fractions was investigated. On the other hand, fractions obtained from the brown coal by the sequential solvent extraction were very close in both chemical composition and molecular mass, although the sequential extraction could greatly suppress the decomposition of the brown coal below 350 °C. The difference in the extraction behavior between the bituminous coals and the brown coal were attributed to the difference in their chemical structure.     

Characterization of catalytically hydrotreated coal liquid produced by solvolytic liquefaction in petroleum asphalt

A hydrotreated coal liquid produced by solvolytic liquefaction of a feed originally consisting of 66% petroleum asphalt and 34% coal liquid was characterized. The hydrotreatment was carried out over a CoMo catalyst in order to upgrade moderately and selectively the coal-derived fraction. The present process was found very effective to depolymerize rather selectively the coal-derived fraction, originally benzene insoluble, to be soluble in benzene in the dominant presence of petroleum asphalt, while 20% of the asphalt was converted to be distillable with α-methylnaphthalene (the hydrotreatment solvent). Structural analyse of the fractions before and after hydrotreatment were compared to reveal what kinds of chemical reactions had taken place during hydrotreatment. The major reactions of the coal derived fraction are hydrodeoxygenation and hydrodealkylation, both of which are effective for depolymerization. No significant hydrogenation on aromatic rings was observed. Hydrotreated liquid was further pyrolyzed to obtain oils and cokes of high quality.     

Influence of temperature on the hydrogenation of Australian Loy-Yang brown coal. 1. Oxygen removal from coal and product distribution

A study is made of the composition of the solid, liquid and gaseous fractions produced by hydrogenation of Australian Loy-Yang brown coal at temperatures ranging from 300 to 500 °C. The high oxygen content of the coal (25.5 wt%) is not found to result in a proportionally higher hydrogen consumption when compared to previously published results for a coal with approximately half the oxygen content. Oxygen is found to be removed from the coal mainly as carbon dioxide and water, most probably by decarboxylation and dehydration reactions. At temperatures up to ≈400 °C hydrogen is consumed almost solely by transference from the solvent tetralin to the coal. By this temperature both the maximum degree of conversion and the maximum oil yield are reached. The heavy oil fraction at 400 °C is composed mainly of asphaltenes and preasphaltenes. Above 400 °C hydrogen is consumed from both solvent and gas. A major part of this appears to be involved in the stabilization of decomposition products from the tetralin. The yield of pentane-soluble material is relatively constant up to 450 °C, however, at higher temperatures conversion of asphaltenes and preasphaltenes to pentane-solubles occurs in conjunction with gasification to C₁–C₃ hydrocarbons. Despite the fact hydrogen consumption and oxygen removal both increase with rising hydrogenation temperature, the H/C atomic ratio for the three heavy oil fractions decreases over the same range.     

Effect of coal extracted with NMP on its aggregation

Tow-step extraction of Upper Freeport (UF) coal, i.e. exhaustive extraction with N-methyl-2-pyrrolidinone (NMP) solvent and subsequent extraction with the CS2/NMP mixed solvent (1:1 by volume) with or without additive was compared with the direct extraction of UF coal with the CS2/NMP mixed solvent (1:1 by volume) with or without additive. It was found that there is almost no difference of extraction yields between the two-step extraction and direct extraction with or without additive. The result show that NMP can only give external extraction to extract the outside fractions of coal particles, and this will not cause the new aggregation formed in the coal molecules. The interactions between coal molecule and additive are responsible for the extraction yield enhancement by additive.     

Liquefaction of subbituminous coals under apparently non-hydrogenative conditions

Reactivities of several coals of different ranks have been examined in degrading extractions with aromatic solvents under apparently non-hydrogenative reaction conditions. Pyrene and A240 pitch liquefied the fusible coals in high yields and the slightly-fusible coals in moderate yields, indicating the importance of fusibility in such liquefaction processes. A240-LS pitch is a powerful solvent for slightly-fusible coals. Considerable amounts of pyridine- or THF-soluble fractions were produced especially with A240-LS pitch. A240 pitch is a better solvent than pyrene for some slightly-fusible coals. However, the extent of depolymerization of liquefied coal, pyridine- or THF-solubility, was definitely inferior. Yields of such fractions are higher for lower-rank coals. The mechanism of coal liquefaction under apparently non-hydrogenative conditions is discussed with emphasis on the stabilization of thermal fragments derived from the coal.     

Characterization of coal liquids by 13C n.m.r. and FT-i.r. spectroscopy — fractions of oils of SRC-I and asphaltenes and preasphaltenes of SRC-I and SRC-II

Coal-derived products of SRC-I liquefaction of Blacksville coal and vacuum tower bottoms (VTB) of SRC-II liquefaction of Powhatan mine coal (both bituminous and from the Pittsburgh Seam) were separated into fractions by solvent extraction. The SRC-I was first extracted with ethylacetate, and solubles were subsequently separated into oils and a mixture of asphaltenes and preasphaltenes (APA). The VTB was Soxhlet extracted with pentane to remove any residual oils, followed by tetrahydrofuran to recover APA. The APA portions were then separated by sequential elution solvent chromatography (SESC) into fractions differing in chemical functionality, and then examined by ¹³C n.m.r. and FT-i.r. spectroscopic techniques. APA are intermediates and end products of coal liquefaction. SRC-II APA are of higher molecular weight than the APA of SRC-I. The lower numbered fractions of APA of SRC-I in SESC separation have the same functional groups as the corresponding fractions of middle and heavy distillates. However, the higher numbered fractions are rich in oxygen, which is mainly in carbonyl groups. Part of the carbonyl groups are in esters which cross-link aromatic clusters. Therefore, APA and the coal itself are ‘oligomeric’ in structure, with aromatic clusters linked by carbon bridges with different functional groups. The nature of carbonyl groups in APA has been analysed in detail.     

Asphaltene analysis using size exclusion chromatography

A common technique used in coal liquefaction investigations is the asphaltene analysis, whereby products are separated into four major fractions (insolubles, preasphaltenes, asphaltenes and oils) by solvent extraction techniques. The fractions are defined by their solubility in organic solvents such as tetrahydrofuran, toluene and pentane. An instrumental method of analysis, using gel permeation liquid chromatography, was developed to reduce the problems with the conventional solvent separation. The technique relies upon the fact that the fractions differ in molecular size as well as solubility. The method uses one solvent (THF) and a single 100 Å microstyragel column to separate the three soluble fractions. The trends in the data obtained with the molecular size separation agree with the trends obtained by conventional solvent separations on the same samples.     

Hydrogenation of a brown coal pretreated with water-soluble nickel/molybdenum and cobalt/molybdenum catalysts

Loy Yang brown coal treated with cobalt acetate/ammonium molybdate (Co/Mo) gave lower conversions than the very high values obtained for the same coal treated with nickel acetate/ammonium molybdate (Ni/Mo) when reacted with hydrogen at 400°C. The difference in conversions obtained between the two catalyst systems decreased with increasing time. Addition of sulphur as carbon disulphide (CS₂) eliminated the difference between the Co/Mo and Ni/Mo catalyst systems, but neither system was more active than a sulphided Mo catalyst. Addition of a hydrogen donor solvent, tetralin, to a reaction in the absence of sulphur decreased conversion for the Ni/Mo catalysed system, but increased that for the Co/Mo system. The order of activity in reactions without solvent or added sulphur for the coal treated with the individual metals was CoMo < Ni. In the presence of sulphur the order was Co Ni < Mo; the addition of sulphur led to no significant improvement with Co catalysts.     

Improvement in coal liquefaction solvent quality by dewaxing

Recycle oils from the Integrated Two-Stage Liquefaction (ITSL), H-Coal and Solvent Refined Coal (SRC) processes were dewaxed by variants of commercial dewaxing processes—the ketone and the urea adduction techniques — yielding up to 47 wt % ‘wax’. Feed oils and product fractions were characterized by elemental analysis, ¹H n.m.r. and gas chromatography. The clean waxes were nearly pure mixtures of n-paraffins. The dewaxed oils were substantially better coal liquefaction solvents than the original (non-dewaxed) oils in batch liquefaction tests. For example, in one case, dewaxing improved the conversion of a bituminous coal to tetrahydrofuran-solubles under standard reaction conditions from 71 wt% (dafb) with the original oil to 87 wt % (dafb). These data provide a direct indication of the inimical effect of paraffinic components on solvent quality. The impact of solvent quality is particularly relevant to liquefaction processes in which thermal reactions proceed in a recycle solvent. In addition, the results indicate the technical feasibility of dewaxing coal liquefaction recycle oils by commercially available technology to improve solvent quality and to produce a useful by-product. Dewaxing could be applied in any liquefaction process that uses a deasphalted (preferably distillate) recycle stream.     

Evidence for the associated structure of bituminous coal

Previous studies have shown that coal swelling is not reversible and highly dependent on coal concentration in a solvent. This rules out the conventional coal structural model of a covalently cross-linked three-dimensional network. Many coal molecules may be physically associated by relatively strong intra- and intermolecular interactions. Coal swelling in selected solvents was examined for fractionated samples of two high volatile C bituminous coals to investigate the role of physical associations in coal structure. The dependence of coal concentration on swelling in tetrahydrofuran and toluene was similar for pyridine soluble and insoluble fractions. Solvent swelling of pyridine solubles was smaller than that of pyridine insolubles. Pyridine extract was mixed with iodine and further fractionated into pyridine soluble and insoluble fractions. The swelling ratio of the pyridine solubles was much smaller than that of the pyridine insolubles. The difference between swelling with toluene and with tetrahydrofuran was larger for pyridine insolubles than for pyridine solubles. All these results indicate that significant portions of coal molecules are not a three-dimensional network, but are physically associated.     

Role of mineral matter in the chemical reactivity of coal

Previous work showed that the solvent extraction yield of coal increased as a result of chemical reactions such as formylation, reductive acylation, acylation, amidomethylation, alkylation, reduction and depolymerization. In the work described in this Paper, dmmf coal obtained after demineralization with mixed HF-HCI acids was used for solvolytic extraction studies after depolymerization, alkylation, acylation, amidomethylation, reductive acylation and reduction reactions. In comparison with the original coal, mineral matter free coal showed less increase in extractability as a result of these reactions indicating that mineral matter present in the original coal was acting as a promoter for these reactions.     

Hydrogen incorporation during coal liquefaction

Coal hydrogenation reactions have been investigated using a deuterium tracer method which makes it possible to determine which structural positions in the coal react with hydrogen gas or donor solvent during liquefaction. ²H₂ and/or tetralin-d₁₂ were reacted with a Pittsburgh Seam coal at 13.8 to 22.1 MPa and 360 to 425 °C for 0.25 to 1.0 h. Hydrogenation and exchange indices were formulated to indicate the relative contribution of each type of reaction to the total H incorporation. In the coal-deuterium gas system, deuterium incorporation in the solvent-separated products increases in the order oil < asphaltene < preasphaltene < residue. However, in the coal-tetralin-d₁₂-deuterium gas system, deuterium incorporation is similar in each of these four fractions. In both systems, ²H incorporation varies with structural position, with the α-aliphatic positions exhibiting the greatest extent of incorporation. The α-tetralyl radical appears to be an important intermediate in hydrogen transfer to and exchange with the coal. The results indicate that in the donor system the abstraction of hydrogen from the solvent by coal-derived radicals is involved in the rate-determining step of the formation of the soluble products. Evidence indicates that considerable direct interaction of the gas-phase hydrogen with the coal also occurs in the donor solvent system.     

Variation of coal extract structure with molecular mass

Asphaltenes and benzene-insolubles, and their methylated counterparts, of high-yield supercritical gas (SCG) and hydrogen donor solvent (HDS) extracts have been separated by size exclusíon chromatography (SEC) on cross-linked polystyrene microspheres so as to investigate the variation in coal extract structure with molecular mass (MM). Narrow SEC fractions have been obtained which have been subjected to elemental, molecular mass (MM), functional group, n.m.r. and voltammetric analyses. The analytical results revealed that the M M range of the solvent fractions was 300 to ≈3000. With increasing MM the following trends were observed: aromaticity decreased, but the degree of condensation of aromatic nuclei did not vary significantly; the size of aliphatic substituents increased; and phenolic hydroxyl content decreased for SCG extract fractions but, in contrast, increased for HDS extract fractions. These variations about averages are considerable and demonstrate that caution is necessary in making use of analytical results for gross fractions. Solubility in benzene of coal extracts results from low MM or from low polarity for higher MM materials.     

Effects of solvent composition on coprocessing coal with petroleum residua

The effect of solvent composition on coprocessing of coal and petroleum solvents is examined under a variety of reaction conditions. The effects of solvent modification procedures on enhancing methylene chloride/methanol (MeCl/MeOH) soluble coal conversion and pentane soluble oil production are studied. Solvent modification procedures performed prior to coprocessing reactions include pentane deasphalting, catalytic hydrotreatment, H-donor addition, and blending of coal-derived liquids with petroleum solvents. Oil production and coal conversion were variously affected by the different solvent modifications. Prior hydrotreatment of petroleum solvents generally enhanced coal conversion, as did H-donor addition. The presence of a hydrotreating catalyst exerted a leveling effect on the effects of solvent modification. Blending of coal liquids and petroleum solvents resulted in complex and not readily predictable interaction. Solvents yielding the highest MeCl/MeOH soluble coal conversion were not generally the optimal solvents for pentane soluble oil production.     

Comparison of fractions of pyridine extract and solvent-refined coal from Illinois No. 6 coal

A pyridine extract of Illinois No. 6 coal and a solvent-refined coal from the same coal have been fractionated. Parallels between the two sets of fractions in composition and molecular weight and some experiments on phenol-pyridine interactions lead to the conclusion that solvent refining cleaves ether links and removes much of the organic 0 and S, without much change in acidic and basic groups. Gel-permeation chromatograms of the fractions indicate that they have moderately narrow molecular weight distributions. A plot of number-average molecular weights against retention times for both sets of fractions gives a smooth curve that is consistent with relations for polystyrene and poly(ethylene oxide).