Subbituminous coal pyrolysis

A number of basic studies in the area of donor solvent liquefaction have been reported (2 -9). Franz (10J reported on the interaction of a subbituminous coal with deuterium-labelled tetra-lin, Cronauer, et al. (11) examined the interaction of deuterium-labelled Tetralin with coal model compounds and Benjamin, et al. (12) examined the pyrolysis of Tetralin-l-13C and the formation of tetralin from naphthalene with and without vitrinite and hydrogen. Other related studies have been conducted on the thermal stability of Tetralin, 1,2-dihydronaphthalene, cis-oecalin and 2-methylin-dene (13,14). 

The phenol, the cresol isomers, and the dimethylphenols, major pyrolysis products in e Moscow wood sample, are probably also derived frt>m lignin precursors that have been altered through coalification reactions. Hatcher [fr] have shown that an increase is observed in the relative proportion of phenols and cresols as rank of coaHfred wood samples increases to subbituminous coal. Comparing the distribution of pyrolysis products from the Moscow wood to that of other coalified wood samples of Hatcher allows us to deduce that the... 

For each coal, at the maximum in hydrogen content, or H/C atomic ratio, the aliphatic hydrogen content (determined by H NMR analysis) accounted for over 90% of the total hydrogen. The aliphatic hydrogen contents were 10.5% for the subbituminous coal,PSOC-1403, and 6.9% for the bituminous coal, PSOC-1266. The high aliphatic hydrogen content was associated with the presence of polymethylene chains. The early release of paraffinic material, as n-alkanes and as long chain substituents to aromatic structures, under conditions of mild pyrolysis has been observed in other research (13-15. ... 

The formation of gas was low. From the carbon balance, only 3% of the total carbon formed gaseous products. The hydrogen consumption was approximately 3100 scf/bbl, of which nearly 80% was consumed in liquid hydrogenation. This preliminary result demonstrated that the flash pyrolysis coal tar derived from a subbituminous coal is amenable to hydrorefining. 

The results of this study showed that flash pyrolysis subbituminous coal tar can be hydrorefined. Ni-Mo supported on alumina was the most effective catalyst for hydrorefining flash pyrolysis subbituminous coal tar among the five types of catalysts tested. The removal of asphaltenes and preasphaltenes was easy to achieve. Catalyst selection should emphasize heteroatoms removal efficiency and hydrogen consumption. The catalyst life is an equally important selection criterion although this program has not completed catalyst-life studies. It will be determined in the future. 

In the present study we investigated pyrolysis of various ranks of coals under different gaseous environments. Low-rank coals such as Wyoming subbituminous coal and North Dakota lignite were pyrolyzed and their results were compared with Kentucky and Illinois bituninous coals. 

More recently, the CSIRO work has included studies of chars produced from the flash pyrolysis of subbituminous coals. This work has formed part of a major project to develop the flash pyrolysis process of converting coal into oil ( ) in which pulverized coal... 

Coal gasification is actually comprised of several processes (a) evaporation of moisture (b) coal pyrolysis, releasing volatile matter (tar, CO, CIt, H2, C02, etc.) (c) reaction of volatiles in the gas phase (d) heterogeneous reaction of char with gas-phase species (such as H20 and C02) and (e) mineral matter release and transformation. Coal moisture is rank dependent low-rank coals such as lignites and subbituminous coals may have up to 35% moisture by weight, whereas bituminous coals generally contain less than 5% moisture by weight. The heat to evaporate this moisture must come from the combustion of volatiles and reduces the efficiency of... 

The yield of volatile matter in this process is a function of the coal type and ranges from approximately 20% w/w of the coal for a low-volatile bituminous coal to somewhat more than 55% w/w of the coal for a high-volatile C bituminous coal subbituminous coals may not show a volatile matter peak with increasing temperature. In addition to tarry products, the rapid pyrolysis of coal produces gases such as hydrogen, methane, and carbon monoxide as well as lesser amounts of hydrocarbons. Pyrolysis of coal is generally defined as the thermal decomposition of coal in the absence of air or other added substances. 

Coal structure has been studied using techniques like pyrolysis (7-10), alkylphenol determination (11-17), liquefaction and oxidation (18-21). After a considerable effort in this area, the compositions of some typical bituminous and subbituminous coals have been approximated as (19). 

In these studies, the nitrogen was introduced in the already activated carbons. Another way to prepare such active carbons is to start from coals enriched in nitrogen before the step of pyrolysis or activation [36,37], Two coals were selected a Polish subbituminous coal, preoxidized with performic acid, and a Russian lignite. Ammonia and its derivatives (ammonium carbonate, hydrazine, hydroxylamine, and urea) were applied as N-reagents [36,37], The N-rich-acti-vated carbons showed good oxidative removal activity for traces of hydrogen sulfide and for its oxidized by-products (elemental sulfur and sulfur dioxide) [36],... 

The pyrolysis/devolatilization kinetics determined for the relatively volatile petroleum coke can be compared to those for Black Thunder subbituminous coal, and Pittsburgh 8 bituminous coal. This comparison is shown in Table 2.4. Note the higher pre-exponential constant. A, and activation energy, E, associated with the petroleum coke, relative to the reference coals. The kinetic parameters shown above are consistent with the lower maximum volatility of petroleum coke. 

Coals were devolatilized at rates comparable with those encountered in combustion and gasification processes. Rapid pyrolysis was attained with pulse-heating equipment developed for this purpose. This technique permitted control of the heating time and the final temperature of the coal samples. Subbituminous A to low volatile bituminous coals were studied. All bituminous coals exhibited devolatilization curves which were characteristically similar, but devolatilization curves of subbituminous A coal differed markedly. The products of devolatilization were gases, condensable material or tar, and residual char. Mass spectrometric analysis showed the gas to consist principally of H2, CHh, and CO. Higher hydrocarbons, up to C6, were present in small quantities. 

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