Composition of an SRC-II coal-derived liquid: Changes in composition resulting from hydrotreatment at different levels of severity

An SRC-II coal-derived liquid fuel and eight upgraded coal liquids derived from it were separated into chemical class-type fractions by preparative liquid chromatography. Mass and infrared spectroscopy, gas chromatography and non-aqueous titration were used, together with the mass balance data from the l.c. separations, to describe changes in composition of the liquids as a function of severity of hydrotreating conditions. The relative abundance of the following classes of compounds was determined in each of the liquids : saturates, monoaromatics, diaromatics, polyaromatics, total acids, total bases, hydroxyarenes, strong acids, pyrrolic benzologs, carbonyl compounds (amides), basic diarylamines, basic monoarylamines, azaarenes, and strong bases. The results are discussed in the light of known reaction pathways for aromatic ring saturation and heteroatom removal.     

Application of new 13C n.m.r. techniques to the study of products from catalytic hydrodeoxygenation of SRC-II liquids

A middle-heavy SRC-II distillate (b.p. 230–455 °C), containing 3.0 wt% of oxygen, has been studied by means of ¹³C n.m.r. at 75, 100 and 125 MHz. The magnetization refocussing techniques INEPT and J-resolved two-dimensional Fourier transform have been utilized to demonstrate methods by which resonance line multiplicities may be determined in complex liquid mixtures. Products derived from the above coal liquid by hydrodeoxygenation at temperatures from 200 to 370 °C, using sulphided Co—Mo and Ni-W catalysts, were also examined. The fraction of aromatic carbon in the hydrotreated liquids was found to correlate directly with their C/H atomic ratio and inversely with the hydrogen content. Comparison of O/C atomic ratios with f_a values for these liquids indicates that hydrogen uptake < 260 °C is associated primarily with hydrogenolytic oxygen removal without attendant ring hydrogenation, while at temperatures between 260 and 350 °C hydrodeoxygenation is accompanied by ring hydrogenation and dealkylation reactions.     

An h.p.l.e. and m.s. analysis of distillate fractions of neutral oil from hydrogenated Akabira coal to elucidate chemical structures

Akabira coal-derived neutral oil was separated into 25 narrow boiling range fractions covering 183–423 °C, and subsequently separated into compound class fractions : alkanes, monoaromatics, naphthalene-type diaromatics, fluorene-type diaromatics and tri- and/or tetraaromatics, by high performance liquid chromatography (h.p.l.c.). The compound type analyses of the distillate/h.p.l.c. fractions were performed using electron impact mass spectroscopy (e.i.m.s.) or field ionization mass spectroscopy (f.i.m.s.). Aromatic/hydroaromatic compound types and the alkyl side-chain carbon distribution of the distillate/h.p.l.c. fractions were clarified, based on the separation behaviour of h.p.l.c. and the type analyses according to Z value by m.s. By the distillation/h.p.l.c./m.s. method, coal-derived oil was characterized in terms of the distribution of the numbers of aromatic rings, naphthenic rings and carbons of alkyl groups attached to these rings. The variations in chemical structure in a compound class with distillation temperature are discussed in terms of these chemical structural factors.     

Compositions of distillate recycle solvents derived from direct coal liquefaction in the SRC-I process: 1. Hydrocarbons

The qualitative and quantitative compositions of 260–427 °C distillate recycle solvents derived from direct liquefaction of subbituminous Wyodak coal and bituminous Kentucky $\text{9}\text{14}$ coal in the SRC-I process are discussed. A liquid chromatography method which involves a column switching technique was used to provide solubility characteristics and compound-class compositions. The hydrocarbon compounds, which accountfor> 60 wt% of the distillate recycle solvents, were further analysed using a unique combination of high-performance liquid chromatography (h.p.l.c.) and field ionization mass spectrometry (f.i.m.s.). Thirty homologous series were identified. Carbon number and distribution and concentration of the homologous series were determined. The h.p.l.c./f.i.m.s. method unravelled various hydroaromatic types which otherwise would be very difficult or impossible to determine.     

Analysis of polar compound classes in SRC-II liquids: Comparison of non-aqueous titrametric,i.r. spectrometric and h.p.l.c. methods

Results for various types of polar compounds in SRC-11 coal-derived liquids and other fuels were obtained by one or more of the three analytical methods: non-aqueous titration, i.r. spectroscopy and h.p.l.c. Practical aspects as well as precision, accuracy and assumptions necessary for effective application of each of the methods are discussed. H.p.l.c. is applicable to the widest variety of compound types, is the most rapid, most sensitive and shows the best promise for increased development and improvement. Application and development of these techniques is a logical step toward improving process monitoring, catalyst development, toxicological screening and general fuel analysis.     

In-situ monitoring of the stabilization with hydrogen of free radicals thermally induced from coal using high pressure e.s.r., d.t.a. and p.d.a. equipment

High temperature, high pressure e.s.r. measurements of the hydrogenation reaction of Taiheiyo coal in the presence of catalysts were carried out to understand the stabilization of thermally and/or catalytically induced free radicals. A decrease in free radical concentration with increasing temperature was observed for ZnCl₂ and SnCl₂ · 2H₂O catalysts at 10MPa under hydrogen gas. High pressure modified single-cell d.t.a. and p.d.a. equipment augmented the uniquely designed high temperature, high pressure e.s.r. cell. The hydrogenation reaction was monitored under the same experimental conditions as for e.s.r. From the results of the combination of high temperature, high pressure e.s.r. with high pressure d.t.a. and p.d.a., it was established that H₂ molecules can react efficiently with free radicals from coal molecules created by the presence of ZnCl₂ and SnCl₂ · 2H₂O catalysts.     

Characterization of phenols and indanols in coal-derived liquids: Use of Curie-point vaporization gas chromato-graphy/mass spectrometry

A combination of liquid chromatography, gas chromatography and mass spectrometry techniques was used to characterize (alkyl)hydroxyaromatic compounds in several coal liquefaction process fractions, including Exxon Donor Solvent (EDS) atmospheric bottoms and hydrotreated atmospheric bottoms. Solvent extraction failed to provide representative subfractions independent of overall sample composition. Satisfactory subfractionation was achieved by liquid chromatography with increasingly polar solvents on a silica gel column. Subfractions as well as parent samples were analysed by g.c.-m.s. using a Curie-point flash vaporization technique for splitless injection onto glass SCOT columns. C₀-C₆ alkylphenols and C₀-C₃ alkylindanols were almost completely recovered in the benzene/ether subfractions and were found to be the dominant hydroxyaromatic series in both liquids. Whereas phenol distributions were virtually identical in both samples, indanol distributions differed markedly, indicating strong differences in reactivity towards hydrotreatment. The possible role and origin of indanols, the only major class of hydroxyhydroaromatic compounds in these coal-derived liquids, is discussed.     

Distribution of aliphatic and aromatic carbons in H-Coal liquids by quantitative 13C FT-n.m.r. spectroscopy

Three H-Coal liquids, ASO, ASB, and VSO, have been characterized by quantitative FT-n.m.r. spectroscopy. FT-parameters were chosen to allow determination of aromatic:aliphatic carbon ratios to within 1% and 2% error of the theoretical and the absolute number of aromatic and aliphatic carbons in a simulated coal liquid, respectively. The aromaticity, f_a, the C_ar:C_al ratio and, the absolute number of both the aromatic and the aliphatic carbons on a per mol basis, have been derived for each H-Coal liquid using c.m.r. in combination with other physical data. By analysis of the chemical shifts of the c.m.r. spectra, the carbon distributions in the H-Coal liquids have been estimated and compared in terms of six structural types. The molecular parameters thus derived are reasonable correlated with the average molecular structures proposed as working hypothesis for the molecular characterization of the three H-Coal liquids.     

Separation and characterization of large-ring number polycyclic aromatic hydrocarbons in non-distillable, pyridine soluble coal-liquids

Low-pressure liquid chromatography, high-performance liquid chromatography, and field ionization mass spectrometry (f.i.m.s.) were used to obtain compositional information on large-ring number polycyclic aromatic hydrocarbon (PAH) present in a non-distillable coal liquid sample. A highly selective h.p.l.c. method for the separation of (PAH) from polar compounds was applied to nitrogen-compound fractions derived from a Wyodak non-distillable ( > 427 °C) coal-liquid sample. F.i.m.s. analyses revealed that the PAH subfractions isolated by the h.p.l.c. procedure contained large-ring number PAH and relatively few nitrogen compounds. The methods developed can generally be applied to the analyses of complex organic mixtures, and in conjunction with other methods, can yield detailed polycyclic aromatic hydrocarbon compositional information.     

Coal liquefaction by in-situ hydrogen generation.: 2. Zinc-water model compound reactions

Model compound studies were carried out to elucidate the reaction mechanisms taking place during the liquefaction of coal with the hydrogen produced from the reaction of zinc and water. In compounds of the type Ph-(CH₂)_n-Ph the splitting of the aliphatic bridge was easier with higher n values. Ether type compounds such as diphenylether were unreactive although the C-O bond in dibenzylether was easily cleaved. Condensed ring aromatic compounds gave low conversion with hydrogenation being facilitated by an increase in ring number. Phenolic compounds such as phenol did not react well, but the reactivity increased with increase in aromatic ring size. The cleavage of the aliphatic bridge was accelerated by the OH group, for example, in the case of 4-hydroxydiphenylmethane bond scission was about 15 times higher than that of diphenylmethane. Heterocyclic compounds were unreactive.     

Combination of 13C- and 1H-n.m.r. spectroscopy for structural analyses of neutral,acidic and basic heteroatom compounds in products from coal hydrogenation

Polar compounds consisting of acidic, basic and neutral nonhydrocarbons were separated from the oil portion derived from coal hydrogenation by means of liquid chromatography. These polar compounds comprised a substantial amount of the oil portion, up to ≈ 60 wt%. Acidic and basic compounds were extracted subsequently by chemical methods, leaving the neutral nonhydrocarbons. The neutral nonhydrocarbons were derived further into eight subfractions, Fr-PP_n-1 to-8, using gel permeation chromatography. The fractions were analysed quantitatively using ¹³C- and ¹H-n.m.r.. Information on the distribution of functional groups containing heteroatoms, especially oxygen, which were present as phenolic, phenylether or heteroaromatic rings, was provided indirectly by ¹³C-n.m.r. spectra, utilizing the chemical shift of the carbon which can be distinguished by an adjacent oxygen. Simultaneous application of ¹³C-n.m.r. with ¹H-n.m.r. reduced considerably the number of assumptions required for estimating the average molecular structure of polar compounds.     

Effects of Lewis acid catalysts on the hydrogenation and cracking of three-ring aromatic and hydroaromatic structures related to coal

Little is known about the hydrogenation and cracking of fused aromatic nuclei during the liquefaction of coal under the influence of Lewis acid catalysts. This study was conducted to establish the effects of catalyst acidity on the activity and selectivity of Lewis acid catalysts, the sources of hydrogen involved in hydrogenation and cracking, and the relationships between reactant structure and reactivity. Three-ring aromatic and hydroaromatic compounds were used to simulate some of the structural units present in coal. The catalysts examined were ZnCl₂ and AlCl₃. It has been established that the rates of both processes are strongly influenced by the Brönsted acidity of the active catalyst, e.g. H⁺ (MX_nY)^?, and the Brönsted basicity of the aromatic portions of the reactant. The source of the hydrogen used for hydrogenation depends on the choice of catalyst. In the presence of AlCl₃, Scholl condensation of aromatic nuclei serves as the principal source of hydrogen. Molecular hydrogen is used exclusively, however, when hydrogenation is catalysed by ZnCl₂. The formation of reaction products and the trends in reactant reactivity are discussed on the basis of cationic mechanisms. The results of this study contribute to an understanding of the processes which occur during the liquefaction of coal using ZnCl₂ or AlCl₃.     

Analysis of a coal-derived liquid obtained by mild hydrogenation: 3. Acid,base and polar fractions

Polar fractions of a coal-derived liquid obtained by mild hydrogenation of Japanese Taiheiyo coal were investigated. The acid fraction was mainly composed of dimethyl or trimethyl phenols with a minor content of indanols. Z = − 7 N (tetrahydroquinoline) and − 9 N (octahydro-phenanthridine/acridine) series were dominant in the base fraction. Neutral oil was separated into six fractions (DS01–06) by vacuum distillation and each fraction was further separated into saturate, aromatic and polar fractions by liquid chromatography. The polar sub-fractions of DS01 (b.p. 186–281 °C) and DS02 (b.p. 281–305 °C) were analysed by f.i.m.s. and g.c.-m.s. Phenols and tetralinols (or indanols) both with long alkyl chains were major components of these fractions. Those of DS03–DS06, which were too complex to analyse by g.c. only, were repeatedly hydrogenated to eliminate the functional groups and then dehydrogenated to simplify the subsequent analysis. The components in the hydrogenated/dehydrogenated products were identified by g.c. and g.c.-m.s. and compared with the type analysis data obtained from f.i.m.s. of each polar subfraction assuming that those aromatic nuclei having hydroxyl functional groups are partially hydrogenated, if at all. Thus a quantitative analysis of the neutral polar fractions was calculated, which shows them to be composed of only seven kinds of aromatic nuclei.     

Structures of the distillates obtained from hydrogenation and pyrolysis of Liddell coal

The structures of the distillable fractions (oils, b.p. >200 °C and volatile fractions, b.p. <200 °C) of the products from hydrogenation and pyrolysis of an Australian bituminous coal (Liddell) were investigated by gas chromatography-mass spectrometry (g.c.-m.s.) and nuclear magnetic resonance spectroscopy (n.m.r.). The distillable oil generated from hydrogenation of Liddell coal at 400 °C, using nickel molybdenum ortin (II) chloride as catalyst and tetralin or recycle oil as vehicle, consisted of a wide range of compounds. Long straight-chain alkanes were important components together with alkyl-substituted benzenes and tetralins, phenols and polycyclic material. When yields were low, as in the case of catalytic experiments with nickel molybdenum catalysts and no vehicle, isoprenoids could be identified. When a substantial proportion of the coal was converted to oil, branched-chain alkanes were not important components of the product. The replacement of tetralin and nickel molybdenum catalyst with stannous chloride reduced the amounts of methyl tetralins in the product. When tetralin was replaced by recycle oil, alkanes were more important components of the liquid products. Although alkenes were absent in oils generated by hydrogenation, they were important components of oils generated by pyrolysis. The highly volatile fractions (b.p. <200 °C) produced during hydrogenation consisted of alkyl-substituted benzenes, decalins, methylindan and straight-chain alkanes. Straight-chain alkanes were more abundant in those volatile fractions generated by hydrogenation with recycle vehicle than with tetralin. The Brown-Ladner method of estimating the fraction of aromatic carbon in distillable oils was adequate for less volatile fractions but was inadequate for the highly volatile fractions because of the large amounts of α-CH₃ and β-CH₃ alkyl groups present.     

Correlation of chemical constitution and boiling point with separation behaviour during distillation of coal liquid

The separation behaviour of coal hydrogenation liquids during distillation was clarified using correlations between chemical structural factors (R_a, R_n and C_al) and boiling points of narrow cut distillation fractions. The separation order according to chemical structure at given distillation temperatures was represented on a three-dimensional R_aR_nC_al diagram. In this diagram, one axis represents the number of aromatic rings in the structure of a compound (R_a), one represents the number of naphthenic rings (R_n), and the third axis represents the number of alkyl carbons (C_al). This diagram is believed to be an appropriate way to handle the analysis of molecules in coal liquids, which are extremely complicated mixtures. Kerosene, light oil and heavy oil from coal liquid were also characterized on this diagram. The distribution ranges of components during separation in distillation agree fairly well with their corresponding distillation temperature range on the R_a R_nC_al diagram proposed. The distillation curve was predicted from the structural analyses with h.p.l.c./g.c.-m.s. and constitution-boiling point correlation as shown in the R_aR_nC_al diagram.     

Hydrogenation of heavy liquids from a direct coal liquefaction residue for improved oil yield

For hydrogenation of heavy liquids in direct coal liquefaction residue (DCLR) within the direct coal liquefaction (DCL) process, heavy liquids in a DCLR derived from a bench-scale Shenhua DCL process using Shenhua coal are evaluated under two conditions. One simulates the coal liquefaction conditions of the Shenhua plant in the presence of a Fe-based Shenhua catalyst; the other one simulates the online hydrotreating conditions in the presence of a NiMo/Al₂O₃ catalyst. The results show that the heavy liquids of DCLR can be hydrogenated under these two conditions yielding less heavy products; hydrogenating the heavy liquids under the online hydrotreating conditions is more effective than that under the coal liquefaction conditions; the preasphaltene fraction is a main problem that yields non-soluble materials under these hydrogenation conditions. The results suggest that hydrogenation of toluene soluble and tetrahydrofuran soluble fractions of the DCLR under the coal liquefaction and online hydrotreating conditions is feasible, but their conversion to lighter products are inapparent under the coal liquefaction conditions, and elimination of the formation of tetrahydrofuran insoluble fraction in the online hydrotreator should be considered.     

Analysis of coal-derived liquid obtained by mild hydrogenation: 1. Neutral oil distilling at 186–343 °C

Taiheiyo coal (77% C) was hydrogenated under mild conditions to preserve the unit structure of the parent coal as far as possible. The n-hexane-solubles (yield, 49.8 wt% daf coal) were washed with acid and base and the neutral material separated into 7 fractions by vacuum distillation. The three lower boiling fractions, DS01 (7.3 wt% neutral oil), DS02 (3.6 wt%) and DS03 (4.8 wt%), were further separated by liquid chromatography into hydrocarbon subfractions which were analysed by g.c. and g.c.-m.s. Saturates are most abundant, especially the n-alkanes which comprise ≈9–13 wt% of each fraction. The saturates also contain isoprenoids (C₁₅, C₁₆, C₁₈, C₁₉ and C₂₀), branched alkanes, n-alkyl cyclohexanes, terpanes and others. With increasing boiling point, smaller amounts of monoaromatic ring hydrocarbons and more di- or triaromatic ring hydrocarbons are found. The alkyl side-chains of aromatic nuclei have a large carbon number, especially in the smaller rings. The existence of phenyltetralin or phenylnaphthalene shows a feature of bonding between aromatic nuclei.     

Changes in composition of solvent-refined coal with severity of hydrogenation

The effects of mild and severe hydrogenation on the chemical composition of solvent-refined coal (SRC) produced from Wyodak subbituminous coal in the direct coal liquefaction SRC-I process were investigated. The yields of solvent-derived fractions of ‘oils’ and ‘asphaltenes’ increased with increasing severity of hydrogenation at the expense of ‘preasphaltenes’. Further separation of ‘oils’ and ‘asphaltenes’, each into three compound-class fractions, revealed more compositional changes. Concentrations of hydrocarbons, nitrogen compounds and hydroxyl aromatics in ‘oils’ increased with increasing severity of hydrogenation. ‘Asphaltenes’, containing nitrogen compounds and hydroxyl aromatic fractions but almost no hydrocarbons, showed an increase in nitrogen-compound concentration with increasing severity of hydrogenation. Hydroxyl aromatic concentration in ‘asphaltenes’ increased under mild but decreased under severe hydrogenation conditions. High-performance liquid chromatography followed by field-ionization mass spectrometry analysis of the hydrocarbon subfractions revealed a complex picture of structural transformations. Over fifty homologous series of aromatic and hydroaromatic hydrocarbons covering a carbon number range from about C₁₂ to C₅₀ were identified and approximate concentrations obtained. Small amounts of partly aromatized pentacyclic triterpane ‘biomarkers’ and their hydrogenation products were found.     

Comparative reactivities of coal asphaltenes during hydropyrolysis

Comparisons have been drawn in the relative reactivities of three coal asphaltenes during hydropyrolysis. All were derived from hydrogen donor-solvent extracts of bituminous coal, but had different hydrotreatment histories and different carbon contents (87.1, 91.9 and 90.8 wt% for asphaltenes 1, 2 and 3, respectively). The hydropyrolyses were carried out in the presence of CoO–MoO₃ catalyst and gaseous hydrogen at 8.7 MPa. For two of the asphaltenes (1 and 2) systematic comparisons were made for different reaction times at 425°C; for all three asphaltenes comparisons were made for l h of hydropyrolysis at 425°C. The general pattern of asphaltenes conversion indicated that more pentane-soluble product was produced from asphaltene isolated from straight coal extract (asphaltene 1). For the asphaltenes isolated from hydrotreated extracts, the extent of conversion to liquids was limited when the carbon content was high (asphaltene 2) although the pattern of conversion was similar in the other hydrotreated asphaltene (asphaltene 3). The aliphatic content of the liquid products formed was low, and the distribution of hydrogenated species in the highly aromatic liquid products indicated that complete hydrogenation of the polyaromatics produced in pyrolysis is difficult. Altogether the aliphatics made up ≈ 10 wt% of the asphaltene 1 hydropyrolysate. Aromatic hydrocarbons made up 90% of the liquid product. Phenanthrene, pyrene and anthracene were prominent, and the largest component in the mixture was phenanthrene which, together with other polyaromatics such as fluoroanthene, dominated the liquid product.