Wyodak coal solvent

Figure 3 shows the effect of reaction temperature on the liquefaction reactivity of methylated (3 hrs, 100/1 methanol/HCl wt. ratio) and untreated Wyodak coals using DHP solvent. Mildly treating the coal (approx. 0.2 methyl groups added/100 carbon atoms) resulted in THF conversion improvements of about 21 wt% at 315 C, 23 wt% at 350 C, and 14 wt% at 400 C. Clearly, mild pretreatment enhances reactivity over the entire range of observed conversion levels. This result is very significant since it shows that our pretreatment procedure is beneficial at conversion levels of commercial interest, and thus, represents more than a laboratory curiosity. 

The analysis of Wyodak recycle solvent by SEC-GC-MS shows that certain distribution order exists for species in coal liquids with respect to their size and degree of isomerization. The alkanes increase in chain lengths without any appreciable degree of isomerization, except for some biological markers such as pristane and phytane. Phenols and aromatics vary in size and extent of isomerization which causes the liquid to contain a large number of species. 

SEC output of four coal liquids are shown in Figure 6. The gas chromatograms of SEC fractions collected at similar retention volumes contain similar chemical species as illustrated in Figure 7. The amount of each component may vary from sample to sample depending on the coal liquid. Wyodak recycle solvent has less pristane, a biological marker compared to other three samples,... 

MAF Coal Conversions to Pyridine Solubles. MAF coal conversions, based on ash analyses, are shown for each coal-solvent combination in Figure 3. Subbituminous coal is converted more slowly, resulting in lower conversions at identical reaction severities than bituminous coal. Maximum conversions are higher with bituminous coal, approaching 90 percent on an MAF basis for the Monterey coal compared to about 75 percent for Wyodak coal. 

Figure 3. Comparison of conversion of MAF Wyodak (—035 solvent (A/ —0/9 solvent (0)) and Monterey (—035 solvent (O) —019 solvent ( Z )) coals to pyridine solubles (based on ash analysis)...

Figure 4. Elemental analyses of SRC from liquefaction of Wyodak coal in —019 solvent (prepared by distillation)...

Figure 6. Comparison of elemental analyses obtained by distillation and heptane precipitation from liquefaction of Wyodak coal with —019 solvent...

Figure 8. Comparison of elemental analyses of SRC from liquefaction of Wyodak coal in —019 (-----------) and —035 (-------) solvents (heptane precipitation data)...

Figure 8. CP/MAS spectra of Wyodak coal before (A) and after (B) solvent...

In absolute terms, the quantities of reactor solids found in various processes do vary considerably. The rate of accumulation is related to several factors, such as coal characteristics, recycle solvent quality and reactor design. However, it can be stated in general terms that liquefaction of low rank coals (sub-bituminous C and lignites) does result in higher rates of accumulation of solids than do similar operations with bituminous coals. For example, during normal operations of the SRC-I pilot plant at Wilsonville, Ala., it has been found that the amount of solids retained varies from about 0.2-0.5 wt.% (moisture-free) for bituminous coals to 1.0-1.9 wt.% (moisture free) for a subbituminous C coal (Wyodak) (72). Exxon also reports much larger accumulations for lignites and subbituminous coals than those found for bituminous coals (73). 

A variety of solvents including hexane, acetone, tetrahydrofuran, toluene and perchloroethylene have been used in these studies together with four analytical strategies. No sulfur has been detected. This feature is well illustrated in Figure 1, which displays the contrasting results for the pristine Wyodak sample, APCSP-2, and another exposed sample of this low sulfur coal. Elemental sulfur at the 0.002% level is easily detected in the exposed sample, none is observed in the pristine sample. 

Coals and Solvents. Wyodak (Belle Ayr) subbituminous and Monterey bituminous coals were used. Analyses are shown in Table I The coals were received as minus 1-inch lumps and were ground after cooling with liquid nitrogen. During grinding the coal temperature did not rise above ambient and the evaporation of the liquid nitrogen provided some protection from exposure to air. 

A comparison of the effect of the two solvents on the composition of SRCs from Wyodak subbituminous coal is shown in Figure 8. Compared to the hydrogen-enriched solvent, use of the hydrogen-depleted solvent results in a SRC with higher sulfur and oxygen contents and lower carbon and hydrogen contents. 

Figure 13. Comparison of elemental analyses of nondistillable products from liquefaction of Wyodak and Monterey coals in —035 solvent...

Comparison of analyses of heptane insolubles from the liquefaction of Monterey bituminous and Wyodak subbituminous coals in the hydrogen-enriched solvent shows that carbon, hydrogen and oxygen concentrations converge with increasing reaction severity to form a product with similar elemental analyses. The same convergence is seen when the hydrogen-depleted solvent is used. 

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