John W. Zondlo

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.

Electrosorption of uranium on carbon fibers as a means of environmental remediation

Abstract Uranium-containing aqueous wastes have been treated by electrosorption on a carbon electrode composed of vapor-grown fibers in a continuous flow-through cell. Effective uranium (VI) removal is accomplished when a negative potential in the range of −0.45 to −0.9 V (vs. Ag/AgCl) is applied to the carbon electrode. For a feed concentration of 100 mg/l, the concentration of U(VI) in the cell effluent is reduced to less than 100 μg/l. The adsorbed uranium is stripped from the carbon fiber by passing a 0.1 M KNO 3 solution through the cell and applying a positive potential on the electrode. Almost all of the stripped uranium is removed as a suspended precipitate and recovered in solid form by filtration. A sorption capacity over 1.20 g uranium /g carbon is reached. The electro-adsorbed uranium is mainly in the form of uranyl hydroxide (UO 3 ·H 2 O), indicating very limited reduction of U(VI) to U(IV) and precipitation of U(IV). It is proposed that ion exchange and double layer charging are the dominant mechanisms for electrosorption of uranium at potentials less negative than −0.3 V, whereas surface-induced precipitation of uranyl hydroxide (UO 3 ·H 2 O) occurs at more negative potentials, thereby greatly enhancing the sorption capacity.

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.

Heat capacity and thermal conductivity considerations for coal particles during the early stages of rapid heating

Abstract Heating and cooling transients for a number of individual coal particles in the 100-μm size range were measured under rapid heating conditions (10 4 –10 5 K/s heating rate). In addition to temperature measurements, each particle was fully characterized with respect to external surface area, volume, mass, and density prior to heating. Measured temperatures were compared with model predictions and a sensitivity analysis was performed to critically evaluate model assumptions regarding particle thermal properties. Simulations using temperature-dependent heat capacity and thermal conductivity correlations routinely applied to coal severely under predicted the particle temperature rise during the early stages of heating. Simulations using constant room temperature values for heat capacity and thermal conductivity showed excellent agreement with measurements during the early stages of heating. Increases in coal heat capacity and thermal conductivity reported in the literature are observed under slow heating conditions and result from bond breaking and structural changes which lead to an increase in vibrational modes of freedom in the coal structure. Results of the present study suggest that under rapid heating conditions the coal structure is frozen and that these vibrational modes only become accessible at higher temperatures or longer soak times. These considerations are important if one desires to accurately model the combustion behavior of coals.

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.

Relationship of coal extraction with free radicals and coal macerals

Abstract Extraction and de-ashing of coals with N -methyl pyrrolidone (NMP) under mild conditions has been reported recently. In this work, we have studied about a dozen American coals, along with some of their residues and extracts after treatment with NMP using in situ ESR (Electron Spin Resonance) spectroscopy of free radicals. At room temperature, N - 8 (number of free radials/g) decreases whereas the percentage extraction increases with atomic H/C of coals. Also N 8 for extract (residue) is lower (higher) than that for coals, ESR spectra of the extract exhibits only the single broad component and the weighted average of N 8 for the extract and the residue nearly equals that of the parent coal. These results have led to the hypothesis that the treatment with NMP is an extraction process in which exinites and to a lesser degree vitrinites are favored, whereas the inertinites are nearly rejected by NMP.

The measurement of the glass transition temperature of mesophase pitches using a thermomechanical device

A thermomechanical analysis (TMA) technique is presented for the measurement of the glass transition temperature (Tg) of glassy pitch materials. Pitches with varying mesophase content have been used for the Tg determination. In this technique, the linear expansion of a mesophase pitch sample with respect to temperature is determined by means of a dilatometer. The change in the coefficient of thermal expansion (CTE) of the pitch materials was found to be significant at the glass transition temperature. Therefore, the measurement of the CTE of the specimen with respect to temperature revealed the glass transition temperature. This technique was found to be very sensitive and easily executable. Results from the TMA technique show good agreement with those from differential scanning calorimetry (DSC). The TMA technique was found to reproduce the Tg value for the mesophase pitch samples within ± 2 °C. In many cases, the value of Tg from the dilatometer was much more definitive than that obtained from DSC, especially for the mesophase pitch samples. A linear correlation for Tg as a function of Mettler softening point temperature (Ts) is developed and compared with that in the literature.

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.