Alfred H. Stiller

Preparation of an ultra-low ash coal extract under mild conditions

Abstract A technique whereby substantial portions of bituminous coal are extracted, non-destructively, is demonstrated by treating raw coal with N -methylpyrrolidone (NMP). An ultra-clean, coal-derived solid material with as little as 0.1% ash and containing no pyritic sulfur was derived by following the extraction step with precipitation of the coal-based material in water and subsequent filtration. The unextracted residue and recovered extracted material were dried under vacuum to allow the determination of overall and elemental mass balances. Amounts extracted were found to be as high as 74% (m.a.f.). The operating conditions are mild at 202°C and atmospheric pressure. Solvent recovery from the NMP-water mixture using conventional distillation on a lab scale was in excess of 97%. Ultimate and proximate analyses of three different H.V. Bituminous coals, and their residues and extracts are reported.

Co-processing of agricultural and biomass waste with coal

Abstract The liquefaction of Blind Canyon seam coal in the presence of one of four different types of co-liquefaction agents (CLAs) was studied at 350°C and 1000 psi (cold) hydrogen pressure. The role of tetralin as a solvent was studied. The four CLAs used include sawdust, horse manure, cow manure and commercial “Super Manure”. The conversion and the asphaltene-plus-preasphaltene yield were obtained by successive dissolution in tetrahydrofuran and hexane, respectively, with the oil-plus-gas yield obtained by difference. Results (on a dry, ash-free basis) are reported as both the overall values of conversion and yields, as well as the incremental differences in conversion and yields, relative to separate liquefaction of coal and the CLA. With or without the addition of tetralin, the overall conversion with cow manure is the smallest for the four co-liquefactions. In the absence of tetralin, the asphaltene-plus-preasphaltene yields are all similar. The presence of tetralin increases the overall conversions and the asphaltene-plus-preasphaltene yields. A study of the incremental differences in conversions and yields indicates that the four CLAs interact with coal and tetralin in different ways. The incremental conversion and the asphaltene-plus-preasphaltene yield appear to be related to the amount of hemi-cellulose in the CLAs, while the incremental oil-plus-gas yield appears to be related to the amount of lignin. Added inorganic compounds appear to negate incremental improvements in the oil-plus-gas yield when tetralin is present.

In situ impregnated iron-based catalysts for direct coal liquefaction

Three methods of preparing catalysts for direct coal liquefaction (DCL) are presented, using ferric sulfide as a precursor. Of these, one involves the physical mixing of the coal and the supercritically dried catalyst, and the other two involve impregnation of the catalyst in the coal. In one of the latter two, the catalyst is prepared in situ as well. The in situ impregnated sample (IIS) of catalyst plus coal results in a high level of coal conversion. The nominal loading of the catalyst is 1.67 wt%, but even lower loadings, <0.5 wt%, show significant improvements in activity and oil yield relative to uncatalysed DCL. For DCL using the IIS catalyst, a solvent with negligible hydrogen-donating and shuttling abilities can be used; a more active solvent, with greater ability to donate and shuttle hydrogen from the gas phase to the coal, results in only a slight improvement in activity and oil yield. Hence the IIS approach appears to be an efficient method of catalyst introduction for carrying out catalytic DCL.

Characteristics and carbonization behaviors of coal extracts

Abstract N -methyl pyrrolidone (NMP) raw coal extract (EXT), hydrogenated coal extract (HEXT) and the blend of EXT and HEXT in NMP (BLD), from two bituminous coals, were studied. The extracts were carbonized in both tube-bomb and a temperature programmable furnace. Elemental analysis, FTIR spectroscopy and optical microscopy techniques were employed to characterize the extracts and the carbonization residues. It was found that the extracts resembled petroleum-derived pitches in the hydrogen content and (C/H) atomic ratio. Higher oxygen and nitrogen contents differentiated the coal extracts from commercial petroleum pitch. More carbon and hydrogen, and lesser oxygen and sulfur differentiated HEXT from EXT. The ratios of integrated IR band intensity for aromatic and aliphatic CH stretching indicate that the relative content of aliphatic hydrogen in EXT is higher than in HEXT. HEXT contains comparatively more aromatic hydrogen, a feature necessary for thermal stability and fluidity during carbonization. BLD materials are at a place somewhere in between. Kinetic modeling of the aliphatic hydrogen change during carbonization reveals that EXT has high carbonization rate and low apparent activation energy. This can be related to the optical texture size of carbonization residues. The residues made from EXTs exhibited fine mosaic optical texture and limited mesophase development. HEXTs were readily converted into highly anisotropic coke. BLDs produced carbonization residues with intermediate properties. Extracts with similar activation energies produced similar residues in the same coal series. The degree or extent of anisotropy displayed by the carbonization residues was found to be dependent on the relative distribution of aromatic and aliphatic hydrogen.

Direct liquefaction of coal using ferric-sulfide-based, mixed-metal catalysts containing Mg or Mo

Direct liquefaction of coal was studied using ferric-sulfide-based mixed-metal catalysts containing magnesium or molybdenum as the second metal. The catalysts were mostly impregnated in situ on the coal, although physical mixtures of catalyst and coal were also used in some runs for comparison. The liquefaction was performed at 350–440°C under a hydrogen pressure of 6.9 MPa (cold). Tetralin and phenanthrene were used as solvents. The catalytic effects became more evident with phenanthrene as solvent. The activities of impregnated catalysts were 5–8% higher than those of the physical mixtures of catalyst and coal. The addition of magnesium was found to be not particularly beneficial to the activity and selectivity of the catalyst. The addition of molybdenum increased the catalyst activity by up to 8 wt%, resulting in conversions of >90 wt% at 400°C. The yield of the oil fraction also increased considerably in the presence of molybdenum, especially at 400 and 440°C. The activity of the catalyst decreased by ∼5% when it was exposed to air.

Evaluation of a novel mixed pyrite/pyrrhotite catalyst for coal liquefaction

Abstract Iron compounds are known to be active catalysts for direct coal liquefaction. We have synthesized ferric sulfide (Fe 2 S 3 ) and have used it as a precursor for the preparation of specific mixtures of pyrite and pyrrhotite in intimate contact, to be used as liquefaction catalysts. By varying the gas phase, time and temperature of the disproportionation of ferric sulfide, the relative amounts of pyrite and pyrrhotite are controlled. The effects of the pyrite/pyrrhotite ratio on conversion and yields of coal liquefaction are experimentally evaluated. The coal sample used is a high-volatile bituminous coal, carefully chosen for its very low pyritic sulfur content. A conventional shaken tubing-bomb reactor is used. The best conversion and yield are associated with a presulfided catalyst containing roughly equal amounts of pyrite and pyrrhotite. Increasing the temperature of liquefaction increases the total conversion and significantly increases the selectivity to desired products. Presulfiding has little effect, except at low temperatures and for the catalyst with equal amounts of pyrite and pyrrhotite.

Rheological investigations of pitch material: Part II: viscosity measurement of A240 and ARA-24 pitches using a high-temperature high-pressure rheometer

Abstract Fluid behavior of carbonaceous pitch materials, such as A240 and ARA-24, is evaluated using the high-temperature, high-pressure (HTHP) viscometer. The measured viscosity of A240 pitch using the HTHP viscometer shows excellent agreement with that obtained using a Brookfield viscometer (DV III+). Further, the viscosity of ARA-24 (mesophase) pitch is measured and reported as a function of temperature at elevated temperature. Finally, the viscosity of pitch materials, both A240 and ARA-24, is modeled using the modified William–Landel–Ferry (WLF) equation. The shear activation energy for the 100% mesophase pitch (ARA-24 pitch) increased with the shear rate while that for the A240 pitch remained constant. Moreover, the shear activation energy for ARA-24 pitch was higher than that for A240 pitch at the shear rates investigated.

Measurements and control of anisotropy in ten coal-based graphites

Abstract Using a solvent extraction process to produce high-purity extracts from untreated and hydrogenated coal, ten coal-based graphites with different levels of anisotropy have been produced. Anisotropy of these graphites and that of H-451 (a petrocoke-based commercial graphite) has been assessed by means of the intensity of the (002) line in X-ray diffraction (XRD), by magnetic susceptibility (χ), by the coefficient of thermal expansion (α), and by electrical conductivity (σ) studies. Measurements were made along directions longitudinal ( l ) and transverse (t) to the extrusion direction. The XRD ratio R for the (002) line varies between 0.23 for the most anisotropic and 0.94 for the least anisotropic of the graphites. χ l χ t and α l α t for various graphites increase systematically as R increases, although the variations are not linear over the extended range. It is argued that measurements of R , χ l χ t , and α l α t provide reliable techniques for the measurements of anisotropy in graphites. Examination of the relationship of the anisotropy to the nature of the precursors used in producing graphites shows that hydrogenation of coal prior to the extraction process produces anisotropic graphites, the anisotropy being controlled by the degree of hydrogenation. Furthermore, it is shown that by blending appropriate amounts of hydrogenated and nonhydrogenated coal extracts, graphites of desired anisotropy can be produced.

An experimental evaluation of the use of rock phosphate (apatite) for the amelioration of acid-producing coal mine waste

Abstract The weathering of coal and coal-associated rocks (AMD) containing iron disulphide minerals produces acid mine drainage. (AMD). This is the most important environmental problem in high-sulphur coal basins. It is generally agreed that the major oxidizing agent of FeS2 is the ferric ion. Experiments have shown that the average equilibrium voltage for the Fe3+/FeS2 system is 0.42 which corresponds to a Fe3+: Fe2+ ratio of 10−6: 1. In an ideal solution, if the Fe3+: Fe2+ ratio could be reduced to less than 10−6: 1, the Fe3+-oxidation of FeS2 could not take place. It has been shown that both Fe2+ and Fe3+ ions can be precipitated by the phosphate ion under ideal conditions at near-neutral pH-conditions, producing a Fe3+:Fe2+ ratio of 10−11: 1. Experiments utilizing rock phosphate (apatite) as a source of phosphate ion showed that the treatment of coal-associated rock containing iron disulphide minerals not only prevented the production of acid, but also terminated the production of acid from materials already undergoing oxidation. The results of these experiments indicate that rock phosphate (apatite) is an effective AMD ameliorant based upon its ability to reduce the Fe3+: Fe2+ ion ratio to below 10−6: 1 and its ability to reduce the subsequent solution potential to the less than 0.42 V, required to allow the oxidation of FeS2 by Fe3+.

A laboratory procedure to evaluate the acid producing potential of coal associated rocks

Abstract Pre-mine planning to minimize or eliminate the production of acid mine drainage (AMD) necessitates that the acid producing potential of each of the lithic units encountered in mining be evaluated. Presently used techniques to predict acid production are generally inadequate primarily because they are based upon unsubstantiated assumptions and because they do not provide the capability of determining the rate at which acid will be produced. This paper describes an experimental bench top procedure which will determine the rate and amount of acid that a rock will produce upon being exposed to the atmosphere. This procedure has been verified by predicting the acid production response of a 350 ton simulated backfill of coal associated rocks exposed to natural weathering conditions with better than 90% confidence.