Waste oils used as solvents for different ranks of coal

Abstract

The effect of using different waste oils as solvent media for the liquefaction of lignite, subbituminous, and bituminous coals was investigated using tubing reactors. The waste oils utilized were waste automobile crankcase oil, oil produced by vacuum pyrolysis of waste rubber tires, and oil produced from vacuum pyrolysis of waste plastics. Reactions of coal and waste oils were carried out at 430°C under a hydrogen atmosphere for 1 h. Analysis of the waste automobile crankcase oil indicated the presence of heavy metals. Analyses of the oils derived from coprocessing coals of different rank with the automotive crankcase oil indicated that these oils were lower in overall trace metals compared with the trace metal content of untreated automobile crankcase oil. No coal rank dependence was observed for the removal of trace heavy metals (demetallation). Conversion yields indicated that all three solvents were similar for total gas + oil yields, asphaltene yields, and total conversion yields except for the vacuum pyrolyzed tire oil coprocessed with Illinois No. 6 coal. Coprocessing the vacuum pyrolyzed tire oil with Illinois no. 6 coal gave the best overall conversion. This was attributed to the presence of polyaromatic non-donor molecules present in the vacuum pyrolyzed tire oil and to the high pyrite content of the Illinois No. 6 coal.