Wyodak coal liquefaction

Figure 5. Effect of Various Pretreatment Methods on Enhancement of Low Severity Wyodak Coal Liquefaction Reactivity.

A recent study in these laboratories (75) on calcium carbonate precipitation from Wyodak coal has confirmed the relationship between ion-exchangeable calcium and the appearance of calcium carbonates during liquefaction. These experiments were performed on samples of the subbituminous coal which had been demineralized, to ensure that all carboxylic acid groups were in the acidic form, and subsequently exchanged with varying amounts of calcium ions. 

Alkylation Studies. Several preliminary experiments were completed to compare the extent of alkylation obtained with our coal pretreatment method to that obtained with Sternberg and Liotta alkylation. Results for Wyodak coal are summarized in Table III. Clearly, our procedure provides a very mild alkylation treatment compared with the other two methods and does not appear to be sensitive to differences in alkyl chain length (methyl vs. propyl). The increase in THF solubiliw was also small this result again suggests only a small extent of alkylation and in addition, shows that only minimal ion exchange (for example Ca by H ) occurred in the coal mineral matter. The effect of each pretreatment method on low severity liquefaction reactivity is discussed in the next section. 

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. 

Figure 2. Effect of Alkyl Group Size on Coal Liquefaction Reactivity of Treated Wyodak Coal at I w Severity Reaction Conditions.

Figure 3. Effect of Reaction Temperature on Liquefaction Reactivity of Methylated and Untreated Wyodak Coal.

The Illinois H-Coal and SRC-II syncrudes contain large amounts of chloride, 32 parts per million (ppm) and 50 ppm, respectively. The Wyodak H-Coal syncrude contains only 3 ppm. Because the exit line from the pilot plants which processed the SRC-II syncrude occasionally plugged with ammonium chloride, we water washed the Illinois H-Coal syncrude prior to hydrotreating. It is our understanding that chloride will be removed by water washing at a commercial coal liquefaction facility. 

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)...

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). 

Pocahontas 3 low volatile bituminous coal, Illinois 6 high volatile bituminous coal, Wyodak subbituminous coal, and Beulah-Zap lignite from the Argonne Premium Coal Sample Bank were used as feed coals m these experiments. Ultimate analyses for these coals are listed in Table I. Coal samples were stored under argon in sealed ampules prior to use in pretreatment and liquefaction experiments. 

Fig. 14. Preferred liquefaction-coking liquid yields in the EDS process for various coals where Hi represents Flexicoking liquids and , liquefaction liquids (124). A, Ireland (West Virginia) B, Monterey (Illinois) C, Burning Star (Illinois) D, Wyodak (Wyoming) and E, Big Brown (Texas).

As reaction severity approaches zero the Monterey coal conversion is about 70 percent and the Wyodak is about 40 percent. Liquefaction appears to occur very rapidly to these levels and then slower to the maximum conversion. The initial liquefaction may be a physical dissolution while the slower rate represents a reaction in which chemical bonds are broken, although other explanations are possible. (10)... 

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. 

Seven fuels were burned in these initial tests two petroleum fuels, one regular sulfur fuel oil (RSFO) and a low sulfur fuel oil (LSFO), and five EDS fuel oils. The EDS fuel oils were blended from components produced in the one ton per day pilot unit at the Exxon Research and Engineering site in Baytown, Texas. Products from the liquefaction of two coals, a bituminous Illinois coal from the Monterey No. 6 mine, and a sub-bituminous Wyoming coal from the Wyodak mine, were tested. Fuel oil blends were made with products from each of the coals, with and without coker liquids, to produce four of the EDS fuels. The fuel oil derived from Illinois coal containing coker liquids was blended... 

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