Improved method to alkylate Yūbari coal of Japan using molten potassium under refluxing THF

A modification to Sternberg's procedures of reductive alkylation of coals is proposed. The ‘coal anion’ formation reaction is conducted under refluxing THF without any electron transfer agent and with molten potassium metal. The method was applied to Yūbari coal (86 wt % C) whereby varying reaction times (0.5–6 h) altered the lengths of alkyl groups (CH₃C₄H₉) added. In a typical experiment, a butylated Yubari coal, prepared by the 2 h reaction, contained 7 butyl groups per 100 original carbon atoms and solubility in hot benzene was 75 wt %. The numbers of alkyl groups introduced and the solubilities of coals increased with reaction time. Values obtained were comparable to those reported using conventional procedures which required longer reaction times and an electron transfer agent l.r. spectra of butylated coals showed strong adsorption peaks attributed to aliphatic groups. Benzene-soluble—pentane-insoluble material of the alkylated coal had less condensed aromatic components with more alkyl side-chains compared with Yūbari SRC, which were estimated by the Brown—Ladner method. Contamination of the alkylated coal by THF fragments seems to be negligible, since hydrogenated naphthalene, obtained after treatment with molten potassium, contains no alkylated products. The reaction proceeded also in HMPA, but not in straight-chain hexane.     

Solubilization of coals by reductive alkylation

Anthracite, bituminous and subbituminous coal when treated with naphthalene anion in tetrahydrofuran added negative charges to form the corresponding coal anions. Alkylation of bituminous and subbituminous coal anion with ethyl iodide resulted in the addition of 16 and 14 ethyl groups per 100 carbon atoms. The alkylated coals were 88 and 45% soluble in benzene. The molecular weights of the benzene-soluble portions of the bituminous and subbituminous coal were respectively 2000 and 700. An attempt to add alkyl groups to anthracite anion was not successful.     

Chemical structure of coals as indicated by reductive alkylation

Reduction with potassium in tetrahydrofuran in the presence of naphthalene, and alkylation of the ‘coal anion’, were applied to coals of different rank. The reduction reaction alone increases the dissolution of the coals in benzene only to a very small extent. However, the reduction process in conjunction with alkylation of the ‘coal anion’ leads to products readily soluble in benzene. The solubilization of alkylated coals depends on the type of coal, the degree of its substitution with alkyl groups, and the length of the substituent alkyl chain. The number-average molecular weights of benzene extracts from the lowest-rank coal ranged from 500 to 800, whereas the higher-rank coals consist essentially of structural units characterized by number-average molecular weights ranging from 1300 to 2000.     

The reductive alkylation of Illinois No. 6 coal. Factors governing the reductive alkylation reaction in ethereal solvents

The reductive alkylation of Illinois No. 6 coal has been investigated to determine the experimental conditions that are most suitable for the conversion of the coal to an alkylated product that is soluble in tetrahydrofuran. Thermodynamic and kinetic factors influence the reactivity of the reducing agent; potassium is the most effective alkali metal. The reduction potentials of the aromatic hydrocarbons used as electron transfer agents dictate the effectiveness of these reagents; biphenyl and naphthalene are more suitable reagents than anthracene. The alkylation reaction is a kinetically controlled S_N2 process and reactive reagents such as primary alkyl iodides and sulphonates are necessary for complete alkylation reactions. Under the most suitable conditions, potassium, naphthalene, and straight-chain butyl iodide allow the conversion of almost 90 wt% of Illinois No. 6 coal to products that are soluble in tetrahydrofuran.     

Reduction alkylation of aromatic hydrocarbons

The reductive alkylation of the aromatic hydrocarbons naphthalene and perylene is investigated. Reduction with potassium metal in tetrahydrofuran at room temperature leads to the naphthalene radical anion and the perylene dianion, which react with alkyl iodides to yield di-alkyl di-hydro species. The reductive alkylation of coals can be more complex.     

Reductive ethylation in ethereal solvents

Organic compounds, in particular anthracene and naphthalene, and two coals have been reductively ethylated in tetrahydrofuran (THF) and diglyme using alkali metals to form anions and ethyl iodide to produce ethylates. Product distributions were sensitive to experimental conditions. The rate of anion formation was controlled by their rate of desorption, probably as contact ion pairs, from the alkali metal surface. The enthalpy of formation of a solvated contact ion pair was ≈500 kJ mole^?1 mainly due to dipole-solvent interaction. 18-crown-6 ether was used to diagnose that, when treated with potassium in THF, anthracepe gave solvated contact ion pairs and probably di-anions whose reactions were characterized by the formation of ethyldihydroanthracene. Naphthalene under identical conditions gave loosely solvated mono-anions which reacted by electron transfer to give diethyldihydronaphthalene. With other alkali metals anthracene and naphthalene gave similar product distributions. The behaviour of other polynuclear aromatic hydrocarbons and of two coals was classified in the same way. It is suggested that when coals are readily solubilized by reductive alkylation mono-alkyldihydro products will predominate.     

Fate of aliphatic groups in low-rank coals during extraction and pyrolysis processes

Information on the nature of aliphatic groups in some bituminous coals and lignites was obtained by determining their fate during extraction and pyrolysis processes of differing severity. Aromatics (neutral oils) and asphaltenes from supercritical gas and hydrogen-donor solvent extracts and from pyrolysis and hydropyrolysis tars have been characterized by an n.m.r.-based structural analysis method which identifies hydroaromatic, methyl and long alkyl (?C₈) groups. The results indicate that methyl and other alkyls account for about half of the aliphatic carbon, long alkyl chains being the major aliphatic group in the lignites. There is evidence to suggest that some of the long alkyl chains are joined to aromatic structures. Hydroaromatic groups are small consisting of only 1–2 rings and account for less of the aliphatic carbon in bituminous coals than previously thought. Their concentrations and those of long alkyl chains in the aromatics and asphaltenes generally decrease with increasing process severity.     

Reductive alkylation of a phenanthrene—formaldehyde resin

A model insoluble oxygen-free phenanthrene—formaldehyde resin has been reductively alkylated by means of potassium—naphthalene in THF and subsequent treatment with alkyl halide. The extractability of the resultant alkylated products by benzene reaches 50% and depends on the size of the groups introduced. The polydispersity of the benzene-soluble portions and the presence of methyl groups in them indicate that decomposition processes are taking place at the methylene bridges as well. Mainly on the basis of n.m.r. analysis of the benzene-soluble fraction of a reductively trimethylsilylated resin, quantitative information about the silylation and decomposition processes was derived. The results obtained are of interest to the study of reductive alkylation of coals.     

A newly proposed view on coal molecular structure integrating two concepts: Two phase and uniphase models

Concept of coal molecular structure was reexamined on the basis of detailed information concerning aliphatic moieties of coal and the reactions occurred during coalification process. Based on the observed similarity of the distribution of chain length between alkylene bridge bonds and alkyl pendant groups on coal aromatic cluster, the authors have already proposed [Nomura, M., Murata, S., Kidena, K. 2004a. Some view on the solubilities of coals toward solvents. Proceedings of 21st Annual International Pittsburgh Coal Conference, No. 12-4.] the presence of common intermediates in the coalification process which results in uniphase structure under reductive conditions and two phase structure under oxidative conditions, respectively. The present paper proposes, the concept that the reactivity of the coal aromatic moieties for common intermediates and/or the stability of common intermediates govern the reactions leading to a two phase structure or uniphase structure in more rationalized way as coalification is believed to proceed under reductive conditions, especially at its late stage. Brown and subbituminous coals have relatively many oxygen-containing functionalities on aromatic moieties so that their aromatic rings are activated for radical reactions. Common intermediate radicals, aryl alkyl radicals, from cleavage of alkyl pendant groups on aromatic rings and alkylene bridge bonds attack neighboring aromatics to form entanglement-like structure in an easy way. These structures are less soluble to organic solvents due to its entanglement character. Bituminous coals with high solubility toward CS₂/NMP solvents tend to have carbon contents from 85 to 87% (daf. basis), their aromatic moieties being so stable that intermediate radicals cited above can attack more selectively the neighboring aromatic moieties: they have less tendency to make such bridge bonds to form cross linked structures, the resulting coal molecules being not entangled like uniphase. In the case of coals having more carbon than 87% or bituminous coals with less carbon than 85%, the resulting coal molecules become less soluble toward organic solvents: In the higher rank coals, the aromatic rings are so large and so stable that their solubility toward solvent are intrinsically low. In addition to this, it is supposed that bridge bonds are cleaved to make the structure with less cross linking. Their stacking tendency should be also considered as other reason for low solubility to solvent. On the other hand, less solubility of the lower ranked bituminous coals can be rationalized partly, in an analogy with the behavior that the brown and subbituminous coals show, despite of their relatively large aromatic clusters.     

The chemical nature of asphaltenes from some coal liquefaction processes

Average chemical structures of asphaltenes from three coal liquefaction processes, namely hydroliquefaction (SRC-II), hydrogen-donor solvent extraction (HDS) and supercritical gas extraction (SCG), have been deduced using a structural analysis scheme in which data from ¹H and ¹³C NMR are combined with those from elemental, molecular weight and functional group analyses. Compared with SRC-II and HDS asphaltenes, SCG asphaltenes contain less-condensed aromatic nuclei which can be largely represented by 1- and 2-ring structures. They also contain more oxygen groups and slightly larger aliphatic substituents. CH₃ accounts for between 30 and 40% of the aliphatic carbon in all the asphaltenes investigated. Small amounts of long alkyl chains are present in the SCG asphaltenes but not in the SRC-II and HDS asphaltenes. SCG extraction is chemically less severe than the SRC process and HDS extraction since neither hydrogen nor HDS are employed and, as a result, SCG extracts are considered to be much more representative of the organic matter in the parent coals.     

The chemical nature of flash pyrolysis tars. An N.M.R. study

Flash pyrolysis tars from one brown and two bituminous Australian coals were separated into oils, asphaltenes and pre-asphaltenes. The oils were further separated by chromatography while the asphaltenes were separated into basic and acid/neutral fractions. The pre-asphaltenes were silyalated prior to ¹³C- and ¹H-n.m.r. studies. The brown coal tar was less aromatic and contained more long alkyl chains than the tars from the bituminous coals. Aliphatic constituents of the oils, which were relatively abundant, consisted mainly of n-alkanes and straight chain 1-alkenes with an average chain length of ca. C₁₃. The pre-asphaltenes were no more aromatic than the asphaltenes from the same tar but had higher molecular weights.     

Reductive alkylation of illinois No. 6 coal. 1H and 13C n.m.r. spectra of the 13C-enriched alkylation products

The reductive alkylation of Illinois No. 6 coal has been carried out using potassium and naphthalene in tetrahydrofuran and methyl-¹³C and butyl-1 -¹³C iodides to alkylate the resultant polyanion. The soluble products of the reductive alkylation reaction were isolated by extraction and chromatography. Proton and carbon n.m.r. spectra were recorded. The intense resonance signal at δ3.95 which appears in the proton n.m.r. spectra of Illinois No. 6 coal butylated with unenriched butyl iodide is split into a doublet by the ¹³C nuclei. Similar results were obtained for the methylation products. The chemical shift and coupling interaction establish that aryl ethers are a very important constituent of the alkylated coal. The carbon n.m.r. spectra of the coal alkylated with ¹³C-enriched alkyl iodides are intense. The resonances of the C-alkylation products appear in a single broad band with a maximum intensity in spectral regions compatible with the formation of the reductive alkylation products of certain polynuclear aromatic hydrocarbons or the base-catalysed alkylation of certain benzylic carbon atoms. The resonances of the N -alkylation products appear in two distinct bands. These resonances are tentatively assigned to amines produced as a result of reductive alkylation of heterocyclic compounds. The resonances of the 0-alkylation products appear in three distinct bands which can be assigned to alkyl aryl ethers, alkyl aryl ethers with substituents at the adjacent positions, and to alkyl carboxylates. The ratio of ethers to carboxylates in the soluble alkylation products was determined to be 7.8 for butylation and 8.0 for methylation. The Chromatographic fractions contain different amounts of C-, N-, and 0-alkylation products. This finding suggests that the coal structure is not highly uniform.     

Determination of the apparent ratio of quaternary to tertiary aromatic carbon atoms in an anthracite coal by C-H dipolar dephasing n.m.r.

¹³C-¹H heteronuclear dipolar dephasing n.m.r. techniques allow discrimination between different chemical species contributing to the ¹³C n.m.r. spectra of complex hydrocarbons. Model compound studies show significantly different effective transverse relaxation constants for carboxyl and quaternary carbon atoms (≈200 μs), secondary and tertiary (≈20 μs), and primary carbon atoms (≈80 μs). Use of these effective relaxation data, together with appropriately timed windows in the continuous wave decoupling applied in standard cross-polarization-magic-angle spinning experiments on anthracite coal allow discrimination between aromatic tertiary and aromatic quaternary ring carbon atoms in this coal. Within the accuracy of experimental error, and of the structural modelling experiments herein reported, the use of the dipolar dephasing technique together with results of X-ray diffraction on coals allows a reasonable estimate to be made of the average number of condensed polynuclear rings in an ‘average molecule’ in the anthracite studied. Based on a model of pericondensed aromatic rings, this number lies between 33 and 45.     

Dependence of coal liquefaction behaviour on coal characteristics. 7. Structural differences between coals of different rank and the asphaltenes derived from them

Aslphaltenes are difficult to characterize by any procedure that involves chromatography. In an attempt to obtain useful information on unfractionated asphaltenes and their structural relations to their parent coals, asphaltenes from a set of eight coals of hvA rank and different coalification history have been studied by ¹ H n.m.r. In addition, structural features in the coals and their asphaltenes were compared by g.c.-m.s. analysis of the products of oxidation by pertrif luoroacetic acid. Protons α to a benzene ring are the most abundant in the asphaltenes, and their relative concentration changes little with the rank of the parent coal. Protons in the β-position are abundant, however, and may be associated with aliphatic junctions linking two or more aromatic ring systems. Whereas malonic and ethane-trioic acids are the major aliphatic di-and tri-acids from oxidation of the coals, succinic and propane-or butane-tricarboxylic acids are the corresponding products that dominate the distributions from the asphaltenes. These and other differences help to define the structural changes caused by liquefaction. In addition, the results indicate the nature of structural changes with increasing rank, which are manifest in the oxidation products from the asphaltenes as well as from the coals.     

Influence of temperature on the hydrogenation of Australian Loy-Yang brown coal. 2. Structural analysis of the asphaltene fractions

A study is made of the asphaltene fractions produced by hydroliquefaction of an Australian Loy-Yang brown coal at temperatures ranging from 300 to 500 °C. A combination of Fourier-Transform ¹³C n.m.r. conventional proton n.m.r., i.r. and u.v. spectroscopy is used in conjunction with previously published data to define representative average chemical structures. Results indicate that the asphaltenes increase in aromaticity as the hydrogenation temperature rises, with a rapid change occurring near 450 °C. Furthermore, the asphaltenes formed at the highest hydrogenation temperature of 500 °C appear to consist of dehydrogenated derivatives of species produced at lower temperatures. Most of the saturated carbon atoms in all fractions occur in condensed cyclic structures with very few side-chains or methylene bridges. Because of this, the commonly assumed value of 0.50 for the saturated carbon to hydrogen atomic ratio used in the Brown-Ladner equation may be in error if applied to systems of this type. Below 450 °C the aromatic component of the asphaltenes consists mainly of isolated naphthalenic and mononuclear structures. Below 400 °C a small but significant number of carbon atoms are present in alkyl chains at least 8 carbon atoms long.     

Characterization of lignite low-severity depolymerization products

Oils and asphaltenes derived from direct extraction and several mild depolymerization processes have been studied. The asphaltenes have been fractionated by column adsorption chromatography (with deactivated silica gel) and benzene, THF and MeOH were used in sequence as eluothropic series. Clear chemical separation between one aromatic and two polar fractions has been obtained, giving high percentages recovery. The fractions have been characterized by VPO, FT-IR, ¹H-NMR and elemental analysis. Several structural parameters of oils have been calculated. These oils can be assimilated to equivalent average hydrocarbons having between 10 and 20 carbon atoms and an aromatic carbon percentage oscillating between 47 and 66%. In general, the degree of substitution in aromatic rings is low and the presence of phenolic groups is limited. The majority of the carbons are aromatic and these rings show low degrees of condensation.     

离子液体；石油沥青质的新型溶剂

The dissolution of petroleum asphaltenes with ionic liquids is studied for the first time. The results show that the ionic liquids could be used as novel solvents for asphaltenes. The important parameters governing the ability of ionic liquids for dissolution of asphaltenes are discussed. It is found that, the ionic liquids based on the cations containing a conjugated aromatic core or the anions which are strong hydrogen bond acceptors are most effective, whereas the ionic liquids containing ＇non coordinating＇ anions such as [BF4]^- and [PF6]^- are nonsolvents for asphaltenes. Increase in the effective anion charge density enhances the ability of ionic liquids to break the extensive asphaltene associations and thus enhances the solubility of asphaltenes in the ionic liquid. The dissolution ability of ionic liquid decreases apparently with increasing the substituted alkyl chain length of its cationic head ring. Temperature is found to play an important role on dissolution of asphaltenes, and the dissolution can be significantly imoroved bv microwave heatinz.     

The chemical nature of material released from coal-derived asphaltenes by reprecipitation and cyclohexane extraction

The yields and chemical nature of n-pentane solubles released from three coal-extract asphaltenes by reprecipitation with n-pentane and cyclohexane extraction have been investigated. With increasing concentration of n-pentane solubles in the original coal liquid, the yield of oils obtained by reprecipitation increases, as also does the tendency for their structures to resemble those of the original n-pentane solubles. No alkanes below C₄₀ were released from the asphaltenes by extraction with cyclohexane and therefore the long alkyl chains (10% of the total carbon in the lignite asphaltenes) must be bound to aromatic, carboxyl or heteroatomic groups.     

ESI-MS法对重烷基苯烃基结构的研究

采用多种分析手段,其中以电喷雾质谱为主的方法研究了重烷基苯的烃基结构。首先通过柱色谱法对重烷基苯进行分离,将其分成了六个族组分。通过各族组分的红外、紫外鉴定,确定它们各自的归属,用电喷雾质谱测定Ⅱ～Ⅴ族组分磺酸盐的相对分子量分布,结合红外、紫外测定的结果及每族物质的不饱和度和通式,推算出了烷基芳烃部分的相对分子质量和烷基的碳数分布。重烷基苯中几个主要成分的碳数分布为:其中二烷基苯的碳数分布在10～25之间,单烷基苯的碳数分布在10～25之间,烷基萘的碳数分布在5～20之间,烷基二联苯的碳数分布在4～19之间。     

Investigation of the chemical structures of coking and non-coking coals in original and reductively alkylated solid states via 13C n.m.r. and i.r. spectroscopies

Chemical structures of four Turkish coals in original and reductively alkylated forms were investigated in the solid state by CP/MAS ¹³C n.m.r. and i.r. spectroscopies. Dilatation properties of these samples were also determined. It was observed that, while the aliphatic parts of the coking coals are mainly composed of short and straight alkyl groups and alicyclic structures, the aliphatic parts of the non-coking coals are to a larger extent composed of branched chains and/or alicyclic structures. It was concluded that ether bonds linking aromatic units are more prominent in the coking coals, whereas in the non-coking coals aromatic-O-aliphatic and/or alicyclic ethers dominate. The degree of condensation of aromatic structures was found to be higher in the coking coals, and the extent of reductive alkylations was higher in comparison with the non-coking coals. Non-coking coals were found to be alkylated preferentially at their phenolic oxygens. Difference spectra were found to be very useful in following organic chemical structural changes that accompany reductive alkylation.