ENHANCEMENT OF LOW-SEVERITY COAL-LIQUEFACTION BY MILD ACIDIC PRETREATMENT AND CYCLIC OLEFINS

Three coals, Wyodak and Black Thunder mine subbituminous and North Dak ota Beulah-Zap lignite, were pretreated with mildly acidic solutions o f hydrochloric or sulfurous acid in methanol, water, or hexane. These pretreated coals were reacted in the presence of one of three hydrogen donors: 1,4,5,8-tetrahydronaphthalene, a cyclic olefin commonly known as isotetralin; 1,2,3,4-tetrahydronaphthalene, isotetralin's hydroaro matic analog commonly known as tetralin; or 1,4,5,8,9,10-hexahydroanth racene, a three-ring cyclic olefin. Coal conversions obtained from com binations of selected pretreatments and hydrogen donors were examined in a factorial experiment. Supplemental reactions were performed evalu ating the effect of other parameters. Reaction conditions were 350 deg rees C for 30 min under 3.45 MPa of hydrogen introduced at ambient tem perature. Both isotetralin and hexahydroanthracene yielded higher coal conversions than tetralin regardless of the pretreatment condition. E ach coal responded differently to the pretreatments. The highest conve rsions for the three coals were achieved with isotetralin and differen t acid pretreatments. Black Thunder mine coal yielded 41.2% coal conve rsion after reacting with isotetralin following pretreatment with hydr ochloric acid in methanol compared to 27.7% for the same system withou t HCl. Wyodak yielded 39.0% and Beulah-Zap yielded 35.0% coal conversi on after reacting with isotetralin following pretreatment with hydroch loric acid in water compared to 24.9 and 23.2%, respectively, without HCl. Hexahydroanthracene was less effective than isotetralin with hydr ochloric acid pretreatments but more effective than isotetralin with t he sulfurous acid pretreatments. Conversions with hexane as a pretreat ment solvent were similar but slightly lower than those with water. Co mbinations of some factors exhibited interactions.