Dady B. Dadyburjor

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.

Alcohol Synthesis over Pre-Reduced Activated Carbon-Supported Molybdenum-Based Catalysts

Activated carbon (AC)-supported molybdenum catalysts, either with or without a potassium promoter, were prepared by the incipient wetness impregnation method. The materials were characterized using differential thermal analysis (DTA) and temperature programmed reduction (TPR), and were used for mixed alcohol synthesis from syngas (CO+H2). DTA results showed that a new phase, related to the interaction between Mo species and the AC support, is formed during the calcination of the Mo/AC catalyst, and the introduction of a K promoter has noticeable effect on the interaction. TPR results indicated that the Mo is more difficult to reduce after being placed onto the AC support, and the addition of a K promoter greatly promotes the formation of Mo species reducible at relatively low temperatures, while it retards the generation of Mo species that are reducible only at higher temperatures. These differences in the reduction behavior of the catalysts are atributed to the interaction between the active components (Mo and K) and the support. Potassium-doping significantly promotes the formation of alcohols at the expense of CO conversion, especially to hydrocarbons. It is postulated that Mo species with intermediate valence values (averaged around +3.5) are more likely to be the active phase(s) for alcohol synthesis from CO hydrogenation, while those with lower Mo valences are probably responsible for the production of hydrocarbons.

Evolution of bimodal distributions in the sintering of model supported metal catalysts

Abstract Model Pt/γ-Al 2 O 3 catalysts were prepared and characterized in our laboratories. They were sintered in flowing oxygen at 600 °C for up to 24 h. Particle sizes, shapes, and relative positions were determined from bright field images, and crystal structures from diffraction in the transmission electron microscope. Ion scattering spectroscopy gave surface compositions. The platinum particles in the unsintered samples were uniformly sized and evenly distributed upon the support. The sintered samples contained some larger particles, along with smaller (2-nm) particles that uniformly covered the support surface, giving rise to a bimodal size distribution. The average size of the particles in the larger mode increased with time, while both the size and the number of the particles in the smaller mode remained substantially constant. The average size of the larger particles after 24 h sintering was compared to a theoretical model that considers Ostwald ripening and particle migration. Agreement between the calculated and the observed distributions requires a lower than expected value for the metal-support interfacial tension. The value is consistent with the presence of metal oxide rather than metal in contact with the support. Surface analysis showed that at least the free surface of the metal particles is oxidized, while electron microscopy indicates that the interior remains as metal. This structure is also expected to affect the particle size distribution by promoting splitting until the entire particle is converted to oxide.

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.

Improvement and characterization of an impregnated iron-based catalyst for direct coal liquefaction

Abstract An impregnation method to prepare an active iron-based catalyst for direct coal liquefaction was improved. With the same catalytic activity, the water usage in the improved method is only 1% of that used in the unmodified method. The improved method not only simplifies the impregnation procedure and reduces cost, but also generates small catalyst particle size on coal surface. Water in the coal promotes thermal liquefaction, but deactivates the impregnated catalyst (possibly due to the adsorption of H 2 O molecular on the catalyst surface). Electron probe microanalysis (EPMA), X-ray diffraction (XRD) and extended X-ray absorption fine structure spectroscopy (EXAFS) analyses show that the catalyst precursors prepared by both methods are in nanometer size and highly dispersed on coal surface. The irons deposited on coal surface are not only in sulfide forms, but also coordinate with oxygen from moisture- and oxygen-containing groups of coal. The impregnated iron may be composed of FeOOH and FeS or in the forms of Fe–O–S or Fe–S–O. The iron transforms to crystalline pyrrhotite in coal liquefaction.

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.

Ferric-sulfide-based catalysts made using reverse micelles:: Effect of preparation on performance in coal liquefaction

Reverse micelles have been used to create small particles of ferric sulfide catalyst for direct coal liquefaction (DCL). Tests were performed to determine the effect on DCL of the procedure and conditions for the production of the reverse-micellar catalyst. The parameters varied include the water-to-surfactant ratio, the coal and catalyst mixing time, and the nature of the surfactant. The performance of the catalyst was quantified by the conversion and oil yield of the DCL experiments. After the optimum procedure for reverse-micellar catalyst production was determined, the optimal conditions were found to be a water-to-surfactant ratio of 10, a coal and catalyst mixing time of 60 min, and AOT as a surfactant. In further studies, hexane was found to affect coal liquefaction negatively. Hexane was found to have a significant effect on the surface area and pore volume distribution of coal. This may be due to small pores being plugged or due to the agglomeration of coal particles.

The role of multiparticle-adatom interactions on the sintering of supported metal catalysts

Abstract Sintering of supported metal particles involves the transfer of single atoms (adatoms) and the movement of crystallites on the substrate. The present work considers the coupled role of all crystallites in determining the diffusion of adatoms on the two-dimensional surface, and the consequent growth and dissolution of crystallites. A decomposition-summation procedure is used. The results of this approach can be compared to those from the mean-field approach, where multiparticle interactions are neglected. The present approach is particularly valid when metal crystallites are found in clumps on the surface i.e., at high local metal loadings. The particle size distributions that result when multiparticle interactions are considered in the sintering analysis depend upon the metal loading, and are significantly flatter and broader than those of the “asymptotic” mean-field analysis. Further, the average particle size calculated here increases with metal loading, in contrast to that from the “asymptotic” mean-field analysis. Finally, the relationship between the time of sintering and the average particle size calculated here changes from concave to convex at higher metal loadings.

Catalysis for Synthesis Gas Formation from Reforming of Methane

Cobalt–tungsten η-carbide [Co6W6C] is the precursor for a novel stable and active catalyst for “dry” reforming of methane with carbon dioxide to produce synthesis gas. Once the catalyst is pretreated, the catalyst activity is unchanged after 150 h on stream, and the H2/CO ratio is maintained close to unity. X-ray diffraction patterns show the formation of a WC phase, Co and carbon in the stabilized catalyst. Carbon deposition, which leads to severe problems for commercial nickel catalysts, actually helps in the creation of the stable catalyst.