The Effect of Hydrogen Partial Pressure on Lignite Liquefaction in a Two-Stage Hot-Charge Batch Autoclave System

The effect of varying hydrogen partial pressure in a two-stage liquefaction process on conversion of North Dakota lignite to THF solubles was studied using the UND hot-charge, time sample, batch autoclave system. Approximately one hundred and fifty grams of moisture- and ash-free (MAF) Zap lignite, three hundred grams of AO4 (Anthracene oil) solvent and seventy five grams of water were reacted in the autoclave unit. Carbon monoxide was used as feed gas for the first stage and varying amounts of hydrogen and carbon monoxide were utilized in the second stage. First stage temperatures ranged from 358 C to 370 C while the second stage temperatures were 429 C to 444 C. Residence times in the first and second stages were 20 and 60 minutes, respectively. Liquid and gas samples were taken at one, three, six, ten, twenty, forty, and sixty minutes during the second stage run period. Overall conversion ranged from 68.7 to 85.0 percent while the distillate yield varied from -7.9 to 25.0 percent based on the MAF coal charge. The soluble residuum yield rose with increasing hydrogen partial pressure from 20.1 to 39.3 percent. Light and middle oil production increased directly with hydrogen partial pressure. When the second stage feed gas consisted of pure carbon monoxide, the heavy oil yield was -15.2 percent. With increasing hydrogen content of the feed gas, the heavy oil yield ranged from -15.2 to 3.2 percent and when 100 percent hydrogen feed gas was used in the second stage, a 3.9 percent yield was produced. Conversion reached a maximum after approximately ten minutes in the second stage. Results indicated that syngas may be a viable feed gas if yields can be increased, perhaps by adding hydrogen sulfide or using a hydrogen donating solvent