Influence of coal preoxidation and the relation between char structure and gasification potential

A study was carried out to ascertain the effects of coal preoxidation and carbonization conditions on the structure and relative gasification potential of a series of bituminous coal chars. Chars were prepared from two freshly mined bituminous coals and preoxidized samples derived from them. Carbonization conditions included a wide range of heating rate (0.2–10000K s^?1), temperature (1073–1273 K) and time (0.25–3600 s). Char properties were characterized in terms of analysis of char morphology, surface area, elemental composition, and gasification reactivity in air. Over the range of conditions used, preoxidation substantially reduced coal fluid behaviour and influenced macroscopic char properties (char morphology). Following slow heating (0.2 K s^?1), preoxidized coals yielded chars having higher total surface areas and higher reactivities toward gasification in air than did similar chars prepared from fresh coal. Following rapid heating (10000 K s^?1) and short residence times (0.25 s), chars prepared from preoxidized and fresh coals exhibited similar microstructural and chemical properties (surface area, $\text{C}\text{H}$ ratios, gasification rates). Carbonization time and temperature were found to be the critical parameters influencing char structure and gasification potential.     

Gasification of coals treated with non-aqueous solvents. 4. Reactivity of coals treated with liquid ammonia

Gasification rates of twelve coals treated with liquid ammonia and impregnated with nickel were measured in hydrogen and in steam, and the effects of the ammonia treatment were compared. The treatment was found to promote gasification of most bituminous coals, especially the higher-caking coals. The increases in reactivity relative to untreated specimens were larger for gasification with hydrogen at 1273 K than for those with steam at 1125 K, but the trends with coal rank were similar. From a correlation found between the reactivities and the degree of degradation of the coal particles caused by the ammonia treatment, it was inferred that the treatment affected their pore structure.     

High-temperature 1H n.m.r. study of oxidized coal

Two coking coals, a caking and a non-caking coal are examined in a Bruker pulsed ¹H n.m.r. spectrometer in the temperature range 293–730 K. One coking and the caking coal are oxidized in air at 383 K for 13 days. Temperatures of signal appearance and loss are noted as well as the temperatures of minimum signal half-peak width ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$). There occurs no change in the above three temperatures with oxidation of the coals. The variation of ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) with temperature of the coal is also measured. Changes in ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) are more pronounced for the caking coal. The softening and solidification temperatures are below and above, respectively, those reported using the Gieseler method. Values of ($\text{ΔH}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$) increase beyond the minimum value as the fluidity continues to increase. This may be caused by an increase in average molecular weight of constituent molecules and/or an increasing concentration of free radicals in the fluid phase. This experimental approach may afford a new method to characterize coals which are to be used in liquefaction processes.     

Gasification of coals treated with non-aqueous solvents. 5. Properties of coals treated with liquid ammonia

Five coals of various ranks were treated with liquid ammonia at 373 K and 10 MPa, and some properties were examined. Although the equilibrium pore volume accessible to carbon dioxide was not affected, the rate of adsorption increased remarkably upon treatment. The pore volume determined by a larger molecule, say hexane, also increased greatly. When a nickel salt was impregnated among the coal surfaces, more satisfactory results were obtained on the treated coal. The treated coals were more easily comminuted than the parent coals. The relation between the change of these properties and the gasification reactivity is discussed.     

Gasification reactivities of optical textures of metallurgical cokes

Optical textures of ten typical cokes before and after gasification in CO₂ were quantified by point counting under a polarized microscope to quantify the reactivities of each type of optical texture. Although absolute values of gasification rate for each texture varied considerably from coke to coke, their relative values were constant regardless of the origin of the cokes. The relative reactivities of flow, mosaic, isotropic and inert textures were 1,1.8,2.8 and 3.0, respectively. The relative reactivity of a single coke calculated from a knowledge of optical textures, was monotonicly correlated with the mean maximum reflectance ($\text{R}\text{?}{}_0$) of the parent coal. This indicates that the high reactivity of coke from a high-rank coal ($\text{r}\text{?}{}_0\text{= 1.8\%}$) is due to factors other than its optical texture. The crystallite height, L_c(002)' of the coke correlated with $\text{R}\text{?}{}_0$ of the parent coal, although the values of L_c(002) varied only from 1.5 to 2.1 nm.     

Gasification of coals treated with non-aqueous solvents. 1. Liquid ammonia treatment of a bituminous coal

A Japanese bituminous coal was treated with liquid ammonia at temperatures up to 120 °C. Extract was separated from the treated coal by washing with benzene-ethanol mixture. The amount of extract was about 2% in a single treatment at 120 °C and some additional extract was obtained by successive treatments. Particles of the residue had cracks and showed an increase in surface area. The ammonia-treated coal was found highly reactive toward gasification with hydrogen at high temperature when catalysed by nickel.     

Hydroliquefaction of Kentucky 914 coal using bottoms recycle

Kentucky $\text{9}\text{14}$ bituminous coal has been liquefied in a batch reactor using blends of distillates and SRC or SRC fractions as the solvent. The most effective solvents contained either mildly hydrogenated SRC or the cyclohexane-soluble oil fraction of SRC. Approximately 65 wt% of Kentucky $\text{9}\text{14}$ coal was converted to C₄-700K liquids using these solvents. This yield can be compared to a yield of ≈40 wt% C₄-728K produced in the SRC-II process from Kentucky $\text{9}\text{14}$ coal.     

Alcohols as H-donor media in coal conversion. 1. Base-promoted H-donation to coal by isopropyl alcohol

Isopropyl alcohol can act as a hydrogen donor to coal, as can tetralin. In contrast to tetralin, however, the transfer of hydrogen by the alcohol can be promoted by the presence of either potassium isopropoxide or KOH. Acetone is formed from the alcohol in quantities that accord with the amounts of hydrogen transferred to the coal. In runs at 335 °C for 90 min, coal was converted with isopropyl alcohol in the presence of either the alkoxide or KOH to a fully pyridine-soluble product with $\text{H}\text{C}$ ratios from 0.88 to 1.13, in contrast to coal (0.79). The organic sulphur content of the coal was reduced from 2.1% to 1%. Model-compound studies with anthracene and diphenyl ether showed that the anthracene was reduced in the system to 9,10-dihydroanthracene, but the ether was recovered unchanged. The coal products from the alcohol/base treatment are very rich in aliphatic hydrogen and have number-average molecular weights in the 450–500 range. The scheme suggested to explain the conversion at 335 °C includes initial hydrogenation of anthracene-like structures in the coal, followed by thermolysis of the dihydro-intermediate.     

Heavy media separation of SRC-II feedstocks: 1. Effect on coal properties

The objectives of this investigation were to determine the effects of coal preparation on the properties of Run-of-Mine (ROM) and washed Powhatan and Ireland Mine coals and to assess the potential effects on SRC-II liquefaction yields. The effect of washing on the two coals was found to be quite similar. For both coals, the properties were altered more significantly by changes in separation media gravity than by changes in the coal size. The elemental composition of the Powhatan and Ireland washed coals was correlated with carbon content. It was shown that both the hydrogen and oxygen levels increased linearly with the carbon content of the coal samples. However, the $\text{H}\text{C}$ and $\text{O}\text{C}$ ratios were not changed significantly by coal cleaning. Only small variations in the nitrogen and organic sulphur levels were observed while the sulphate sulphur and chlorine levels were not affected by coal cleaning. The major impact of the coal cleaning was to reduce the pyritic sulphur (and hence the total sulphur) content of the coals. Most of the pyritic sulphur was shifted into the middling coal and refuse fractions while the clean coals had much lower contents and the pyritic sulphur level decreased with increasing carbon content. Coal cleaning did not significantly alter the maceral contents of vitrinite, exinite, total reactive macerals (TRM), or the reflectance of vitrinite; all these parameters varied over a very narrow range, probably within the precision of the measurement technique.     

Characterization of organic fractions in solvent-refined coal by quantitative n.m.r. spectroscopy

A solvent-refined coal product obtained from Pittsburgh No. 8 coal has been preparatively separated into four sized fractions by gel permeation chromatography. Quantitative ¹H and ¹³C Fourier-transform nuclear-magnetic-resonance results for the separated fractions are reported along with elemental and molecular weight analysis data. Observed trends for several average molecular parameters for these fractions (e.g. $\text{(}\text{H}\text{C}\text{)}{}_{\mathrm{alp}}$, $\text{(}\text{H}\text{C}\text{)}{}_{\mathrm{aro}}$, etc.) are discussed. The absence of certain organic functional groups, such as carbonyls, is also noted.     

Mixtures of potassium sulphate and iron sulphate as catalysts for water vapour gasification of carbon. 2. Wettability phenomena and reactions of the catalyst precursors

The interaction between carbon and a mixed catalyst (FeSO₄ with K₂SO₄, Fe/K mass ratio 1:5), which showed a superior catalytic activity in water vapour gasification of carbon, was studied by measuring the wettability of a fine-grained graphite, penetration into this material and the metal distribution after treatments in $\text{H}{}_2\text{H}{}_2\text{O}$ mixtures at various temperatures. The decomposition and conversion reactions were analysed by measuring the relative mass losses. It was found that the catalyst mixture forms a melt phase by 650 °C, whereas the pure sulphates are still present as powders. Penetration is complete after 2 h treatment at 700 °C. EPMA studies show a homogeneous distribution of Fe and K in the graphite substrate. The same treatment causes no significant change with the pure sulphates. The relative mass losses suggest that the melt may be composed of FeS, FeO, K₂S and KOH. It is assumed that the conversion of K₂SO₄ to K₂S or even KOH may be catalytically influenced by FeS, FeO or possibly Fe. Further studies are necessary to analyse the active state of the catalyst and especially the mutual catalytic activity of Fe and K.     

Scanning electron microscopic study on the catalytic gasification of coal

The behaviour of nickel catalyst during coal gasification of Leopold coal (West Germany) was examined by means of scanning electron microscopy. Microscopic observations of the same field were made several times as the reaction proceeded. In addition to the uncatalysed gasification, the nickel-catalysed gasification was clearly observed under the microscope. With steam gasification, catalysts moved very actively, and they seemed to accelerate the gasification mainly by pitting holes into the char. The topological changes on char surfaces by hydrogasification were not so pronounced. The function of catalyst may not be restricted to the pit formation, for it seems to accelerate the gasification over all of the char surface. Because of the high hydrogasification temperature, agglomeration of catalyst takes place to a considerable extent. Finely dispersed nickel catalysts were observed when the coal had been pretreated with liquid ammonia. The catalytic activity of these fine particles was so large that the char beneath them was gasified rapidly.     

Fluidized-bed gasification of some Western Canadian coals

Three Western Canadian coals were gasified with air and steam in a fluidized bed of 0.73 mm sand and coal, at atmospheric pressure and temperatures of 1023–1175K to produce a low-calorific-value gas. One non-caking and two caking coals were tested. The effects of temperature, coal feed rate, $\text{air}\text{coal}$ ratio, $\text{steam}\text{coal}$ ratio, coal quality, coal particle size and bed depth on gas composition, gas calorific value and operating stability of the gasifier were established. Results are compared with those previously obtained for the same three coals when gasified in essentially the same equipment, but operated as a spouted bed.     

Catalytic effect of potassium on the rate of char-CO2 gasification

The effect of potassium on the rate of char-CO₂ gasification at 800 °C was investigated. The instantaneous rate depends on both catalyst concentration ($\text{K}\text{C}$) and the internal porous structure of the solid. At low values of $\text{K}\text{C}$ atomic ratio, the rate increases sharply with the addition of catalyst. As catalyst concentration is increased, the rate first levels off and then decreases. The levelling off is attributed to the saturation of the surface with catalytic sites. The subsequent decrease in rate seems to be due to the plugging of micropores by catalyst deposits. The reaction rate changes significantly during gasification and drops sharply before gasification is completed. The drop in rate before total conversion can be explained by catalyst accumulation and pore plugging.     

Bulk graphite nozzle recession—an analysis based on the carbon-steam reaction

Bulk graphite gasification rates (Zone I) have been measured between 1123–1323 K at $\text{H}{}_2\text{O}\text{H}{}_2$ ratios which encompass those found in the exhaust gases resulting from the firing of a typical aluminized solid propellant. These Zone I rates are extrapolated on an Arrhenius plot to a temperature (≈3200 K) which is thought to exist at the surface of a graphite nozzle through which propellant combustion gases pass. The extrapolated rate is higher than that predicted for Zone III kinetics or found experimentally by other investigators. It is concluded that graphite recession under rocket motor conditions is in the intermediate region between Zones II and III. That is, gasification occurs not only at the exterior graphite surface but also in pores close to the exterior surface.     

Flash pyrolysis of coals: behaviour of three coals in a 20 kg h−1 fluidized-bed pyrolyser

Flash pyrolysis of Loy Yang brown coal, and Liddell and Millmerran bituminous coals has been studied using a fluidized-bed reactor with a nominal throughput of 20 kg h^?1. The apparatus and its performance are described. The yields of tar and hydrocarbon gases are reported for each coal in relation to pyrolysis temperature, as also are analytical data on the pyrolysis products. The peak tar yields for the dry, ash-free Loy Yang and Millmerran coals were respectively 23% wt/wt (at ≈ 580 °C) and 35% wt/wt (at $\text{\$}\text{?}$600 °C). The tar yield from Liddell coal was 31% wt/wt at ≈ 580 °C. Hydro-carbon gases were produced in notable quantities during flash pyrolysis; e.g. Millmerran coal at 810 °C gave 6% wt/wt (daf) methane, 0.9% wt/wt ethane, 6% wt/wt ethylene, and 2.5% wt/wt propylene. The atomic $\text{H}\text{C}$ ratios and the absolute levels of hydrogen in product tars and chars decreased steadily with increasing pyrolysis temperature.     

Phosphonitrilic chloride: 21. Synthesis of chelating polymers with cyclophosphazene thiocarbamate and the properties of chelating polymers

Chelating polymers containing copper, nickel and cobalt have been formed from cyclophosphazene thiocarbamate trimer and copper, nickel or cobalt ions. These polymers obtained from the reaction are amorphous and the values of electron conductivity are $\text{2·7 × 10}{}^{11}\text{Ω-}\text{cm}$, $\text{3·6 × 10}{}^{13}\text{Ω-}\text{cm}$ and $\text{1·5 × 10}{}^{13}\text{Ω-}\text{cm}$ for the Cu, Ni and Co polymers respectively. The Cu polymer is the most thermally stable on heating to 500°C in air.     

Gasification of coals treated with non-aqueous solvents. 2. Effect of liquid-ammonia treatment on gasification with hydrogen

Japanese bituminous coals, treated with liquid ammonia and impregnated with nickel, were gasified with hydrogen at ambient pressure. The rates of gasification of the treated coals were larger than those of untreated ones by 2 to 8 times at 1273 K. A repeated treatment with liquid ammonia enhanced the reactivity further, but a third (or more) treatment was not so effective. Pretreatment with ethylene diamine, butylamine, pyridine, or sulphur dioxide caused a similar promotion of the gasification, while that with benzene, dimethyl formamide, or propane was less effective. Liquid-ammonia-treated coals seem to reduce or lose their agglomerating ability and thus to maintain higher gasification rates.