Fuel-Blending Stocks from the Hydrotreatment of a Distillate Formed by Direct Coal Liquefaction

Abstract

The direct liquefaction of coal in the iron-catalyzed Suplex process was evaluated as a technology complementary to Fischer−Tropsch synthesis. A distinguishing feature of the Suplex process, from other direct liquefaction processes, is the use of a combination of light- and heavy-oil fractions as the slurrying solvent. This results in a product slate with a small residue fraction, a distillate/naphtha mass ratio of 6, and a 65.8 mass % yield of liquid fuel product on a dry, ash-free coal basis. The densities of the resulting naphtha (C5−200 °C) and distillate (200−400 °C) fractions from the hydroprocessing of the straight-run Suplex distillate fraction were high (0.86 and 1.04 kg/L, respectively). The aromaticity of the distillate fraction was found to be typical of coal liquefaction liquids, at 60−65%, with a Ramsbottom carbon residue content of 0.38 mass %. Hydrotreatment of the distillate fraction under severe conditions (200 °C, 20.3 MPa, and 0.41 gfeed h-1 gcatalyst-1) with a NiMo/Al2O3 catalyst gave a product with a phenol content of <1 ppm, a nitrogen content <200 ppm, and a sulfur content <25 ppm. The temperature was found to be the main factor affecting diesel fraction selectivity when operating at conditions of WHSV = 0.41 gfeed h-1 gcatalyst-1 and PH2 = 20.3 MPa, with excessively high temperatures (T > 420 °C) leading to a decrease in diesel selectivity. The fuels produced by the hydroprocessing of the straight-run Suplex distillate fraction have properties that make them desirable as blending components, with the diesel fraction having a cetane number of 48 and a density of 0.90 kg/L. The gasoline fraction was found to have a research octane number (RON) of 66 and (N + 2A) value of 100, making it ideal as a feedstock for catalytic reforming and further blending with Fischer−Tropsch liquids.