Structural analysis of tars from fluidized bed pyrolysis of coal:: 2. 1H n.m.r. and i.r. spectroscopy

¹H n.m.r. and i.r. spectroscopy of aromatic and polar fractions of two tars from the rapid pyrolysis of coal in a fluidized bed at 550 °C show that the nature of the products depends on the reactivity of the pyrolysis gas. In the presence of flue gas, there is more thermolysis leading to shorter and fewer alkyl side chains and generation of lower molecular mass material. Pyrolysis by means of char gasification gas results in much less thermolysis of the tar but leads to secondary reactions which can be interpreted by a radical mechanism involving the reactive constituents of the char gas.     

Determination of aromatic and aliphatic CH groups in coal by FT-i.r.: 1. Studies of coal extracts

A set of coal extracts have been characterized by FT-i.r. and proton n.m.r. spectroscopy. The n.m.r. measurements of aliphatic and aromatic hydrogen allow a direct calibration of the absorption coefficients of appropriate i.r. bands. This allows methods for calculating these coefficients based on relating i.r.-band intensities to elemental hydrogen to be tested directly. Reasonable agreement was obtained.     

E.s.r. study of pyrolysis vapour of coal

Wyodak and Heatburg subbituminous coals were pyrolysed in-situ in an e.s.r. microwave cavity at ≈510 °C in an evacuated sealed tube. At least two kinds of radicals are detected; first, phenalenyl-like radicals and then, polymerized radicals from the initial ones.     

Coal flash pyrolysis: 2. Polymethylene compounds in low temperature flash pyrolysis tars

Pyrolysis of coals at low temperatures (< 600 °C) produces tars containing the precursors of the low molecular weight aliphatic hydrocarbons, such as ethylene and propylene, observed on flash pyrolysis of the coals at higher temperatures (700–800 °C). This is shown by further pyrolysis of these low temperature tars at high temperatures. Various methods, including isolation by h.p.l.c. were used to confirm the presence of straight chain paraffin and olefin pairs (C₁₄C₂₆ and above) in the low temperature tars. Pyrolysis of pure paraffins and olefins in this molecular weight range at temperatures > 700 °C produce ethylene, propylene and other cracking products similar to those obtained on flash pyrolysis of coal.     

Pyrolysis—gas chromatography of Australian coals. 1. Victorian brown coal lithotypes

Pyrolysis—gas chromatography (Py—g.c.) has been shown to be a useful technique for characterizing Victorian brown coal lithotypes. The pyrograms show marked changes in the predominance and distribution of specific molecular classes as a function of lithotype. Hydrogen-rich triterpenoid components are predominantly associated with the lighter lithotypes, whereas hydrogen-deficient phenolic components are more abundant in pyrolysates from the darker lithotypes. Carbon preference indices (CPIs) are >1 for the alkanes but <1 for the alkenes released by pyrolysis. All CPI values generally increase with darkening lithotype. Correlations of the components released with the maceral composition of the lithotypes have also been established. This information is used to establish some details of the mechanism of pyrolysis and the probable relative liquefaction behaviour of these lithotype samples.     

Determination of aromatic and aliphatic CH groups in coal by FT-i.r.: 2. Studies of coals and vitrinite concentrates

Various methodologies used to determine the aliphatic and aromatic CH contents of coal are discussed. The problems associated with equation i.r. band intensities to elemental hydrogen are examined in some depth. The equations used to determine absorption coefficients (defined here in terms of ‘conversion factors’) are classically ill-conditioned, so that a range of solutions are obtained. However, for bituminous coals these encompass and are close to the values obtained by calibrating with the results of proton n.m.r. studies of coal extracts. Values of aromatic to aliphitic hydrogen ratios are reported and compared to those published previously.     

Pyrolysis—gas chromatography of Australian coals. 2. Bituminous coals

Pyrolysis—gas chromatography (Py—g.c.) was used to characterize quantitatively a series of high- to low-volatile bituminous Permian Australian coals. The levels of n-alkanes, n-alkenes and triterpenoids released by pyrolysis all decrease as a function of increasing rank and thus, the coal samples can be classified into three distinct groups. Carbon Preference Indices (CPI's) for alkanes and alkene/alkane ratios also decrease as a function of rank. The triterpenoids have exclusively the hopane skeleton. The hopane isomeric distributions exemplify the geological maturity of bituminous coals relative to brown coal (lignite). A significant correlation has been established between the level of n-alkanes and n-alkenes released under Py-g.c. conditions and the predicted oil yield by pyrolysis of these coals. Further development and application of the techniqueshould enable much to be learnt relating to the quality and yield of flash pyrolysis tars as well as the original coal macromolecular structure.     

Constitution of tars from the flash pyrolysis of Australian coals: 1. Separation

Separation of the maltene fraction of Millmerran flash-pyrolysis coal tar by ion-exchange and adsorption chromatography produced coal-tar resins, aromatic hydrocarbons (AH) and an alkane/alkene fraction. The coal-tar resins comprise acid, base, neutral and polyfunctional fractions. Derivatives of benzene and naphthalene are the main volatile constituents of the AH fraction, while the alkane/alkene fraction consists mainly of straight-chain hydrocarbons from C₁₀ to C₃₄ and small amounts of isoprenoid hydrocarbons, steranes and triterpanes. Fuller's Earth, used in the separation of the maltenes, suffers from the disadvantage of irreversibly adsorbing organic material.     

Structural studies of coal extracts

The reductive alkylation of a medium-volatile bituminous coal was carried out using potassium and naphthalene in tetrahydrofuran, and using methyl, ethyl and butyl iodides to alkylate the resultant polyanion. The soluble products of the reductive alkylation reaction were isolated by extraction with n-pentane and benzene. The extracts were characterized by i.r. and ¹H n.m.r. spectroscopy, molecular mass and ultimate analyses.     

FTIR analaysis of coal. 1. techniques and determination of hydroxyl concentrations

The preparation of coal samples for the determination of hydroxyl content by FTIR is described. It is concluded that the FTIR method provides good quality infrared spectra on opaque materials such as coal and char. If sample preparation procedures are followed carefully, quantitative spectra of coals can be reproduced within ±5%. Beer's law is followed in the range 0.3–1.3 mg of coal/cm². The broad absorbance in the range 2000–3600 cm^?1 appears when using several different preparation techniques and is caused by hydrogen-bonded OH. The use of quantitative FTIR specta offers a simple method of estimating the hydroxyl content of a coal. Reasonable results have been obtained despite the problem of interference by water. The KBr pellets were dried for 48 h at 105 °C and the absorbance was reduced at 3200 cm^?1 and the problem of scattering was minimized by using a rectilinear baseline. With these procedures the hydroxyl oxygen concentrations in the coal were determined to an accuracy of ±10%.     

Assignment of aliphatic carbon peaks in the 13C n.m.r. spectra of coal liquefaction products

Aliphatic carbon peaks in the complex ¹³C n.m.r. spectra of coal-derived liquids can be unambiguously assigned to C, CH, CH₂ and CH₃ groups using a spin-echo technique.     

Determination of the inorganic matrix of coal ash from an atmospheric fluid-bed boiler by FT-i.r. analysis

Three infrared (i.r.) methods for the quantitative determination of some inorganic compounds in coal and coal ash are evaluated. Attention is focussed on calcium compounds occurring in ash from an atmospheric fluid-bed boiler. The i.r. measuring range was extended to 200 cm^?1 where scattering was less of a problem. A major difficulty in quantitative i.r. spectrometry remains the preparation of satisfactory KBr or Csl discs. However, the resuts are difficult to obtain otherwise.     

Analysis of solvent extracts of bituminous coal macerals by chromatography, 1H n.m.r. and field-desorption mass spectrometry

Analysis of the carbon disulphide extracts of nine samples of UK coal-maceral concentrates by ¹H highresolution n.m.r. spectroscopy, gas-liquid chromatography and field-desorption mass spectrometry indicates the presence of components with a wide molecular weight range extending up to 1200 amu; these are attributed to n-alkanes up to ≈C₅₀ and highly condensed polynuclear aromatic compounds.     

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.     

Characterization of coal and coal blends by automatic image analysis: Use of the Leitz texture analysis system

An analytical procedure is described for the microscopic determination of rank and maceral-group composition of seam coal and composition of coal blend using the image analyser TAS (Leitz). The procedure runs automatically and reduces the time of analysis by a factor of 0.1. The results agree with those obtained by conventional methods (reflectance measurements and point-count analysis).     

Investigation of nitrogen compounds in coal tar products. 1. Unfractionated materials

The direct application of gas chromatography (g.c.) with a nitrogen-selective alkali-flame detector (AFD) and mass spectrometry to the identification of nitrogen compounds in coal tar products without the need for prior separation of nitrogen-rich fractions is described. Accurate mass measurement has allowed the assignment of atomic compositions to many nitrogen heterocycles despite their presence as minor components in complex aromatic mixtures, but some interference from hydrocarbons was encountered. Boiling point characteristics were used to assist in distinguishing between the various possible isomeric compound types. The AFD was used successfully for the quantitative g.c. determination of a range of nitrogen heterocycles in the unfractionated samples.     

Constitution of tars from the flash pyrolysis of Australian coals: 2. Structural study of Millmerran coal-tar resins by hydrogenolysis

The structures of the acid, base, polyfunctional and neutral resin fractions of Millmerran coal tar have been studied by high-pressure catalytic hydrogenolysis followed by g.c.-m.s. analysis of the volatile products. n-Alkanes from C₉ to C₃₂ constitute 4–24% of the organic products. Each fraction shows a characteristic n-alkane distribution. The alkanes are considered to be an integral part of the coal-tar resin structure. The results show that 40–70% of the coal-tar resin fractions consist of 1- or 2-ring aromatic units substituted or linked by long methylene chains.     

Structural differences in the tars and chars from the pyrolysis of coals of different rank in hydrogen and in nitrogen

Two British coals—Linby high-volatile bituminous and Abernant anthracite — and an Australian brown coal were pyrolysed at 575 °C in hydrogen or nitrogen at 0.1, 5 and 30 MPa in an inclined, single-stage reactor. Hydrogen pressures of ? 5 MPa led to increased yields of tars which were more aromatic than those produced in nitrogen. The high-volatile bituminous coal fused under all conditions, whereas the anthracite and brown coal fused and agglomerated only in hydrogen at 30 MPa.     

Mössbauer analysis of iron phases in brown coal ash and fireside deposits

The iron phases present in an electrostatic precipitator ash, an uncooled ash deposit and a cooled superheater ash deposit from Hazelwood Power Station, Australia, burning Morwell brown coal has been examined using Mössbauer spectroscopy. The principal iron phase in the precipitator ash and the uncooled ash deposit from a hot gas offtake was calcium aluminoferrite (Ca₂Fe_{2 ? x}Al_xO₅). Minor amounts of hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) were also detected in the precipitator ash. The cooled superheater ash deposit contained a (Mg, Fe, Al) oxide spinel as the primary iron phase; small quantities of hematite were also detected in this deposit close to the heat exchanger interface. The formation of these iron phases has been rationalized on the basis of the average composition of coal delivered to the power station and supplementary ash chemistry data obtained from other techniques. The evidence suggests that the calcium aluminoferrite in the precipitator ash is derived from inorganic constituents (distributed throughout the coal organic matrix) and the hematite and magnetite are of mineral origin (discrete particles).     

E.p.r. study of molecular phases in coal

E.p.r. spectra from coals of various carbon content are reported. The e.p.r. signal from coals in a vacuum consists of two lines with different widths. The results are interpreted using the Larsen-Kovac structural model (Am. Chem. Soc. Div. Fuel Chem. Preprints 1977, 22, 181). The paramagnetic centres, disposed in the macromolecular phase, give a narrow line whereas the spins of the molecular phase are responsible for the broad line. These results provide a good interpretation of the changes in e.p.r. signal-shape under the influence of various organic solvents observed by Yokokawa (Fuel 1968, 47, 273; Fuel 1969, 48, 29).