Transport fuels from two-stage coal liquefaction

Abstract

Four Spanish lignites and their vitrinite concentrates were evaluated for coal liquefaction. Correlationships between the content of vitrinite and conversion in direct liquefaction were observed for the lignites but not for the vitrinite concentrates. The most reactive of the four coals was processed in two-stage liquefaction at a higher scale. First-stage coal liquefaction was carried out in a continuous unit at Clausthal Universität at a temperature of 400°C at 20 MPa hydrogen pressure and with anthracene oil as a solvent. The coal conversion obtained was 75.41% being 3.79% gases, 2.58% primary condensate and 69.4% heavy liquids. A hydroprocessing unit was built at the Instituto de Carboqumica for the second-stage coal liquefaction. Whole and deasphalted liquids from the first-stage liquefaction were processed at 450°C and 10 MPa hydrogen pressure, with two commercial catalysts: Harshaw HT-400E (Co-Mo/Al2O3) and HT-500E (Ni-Mo/Al2O3). The effects of liquid hourly space velocity (LHSV), temperature, gas/liquid ratio and catalyst on the heteroatom liquids, and levels of 5 ppm of nitrogen and 52 ppm of sulphur were reached at 450°C, 10 MPa hydrogen pressure, 0.08 kg H2/kg feedstock and with Harshaw HT-500E catalyst. The liquids obtained were hydroprocessed again at 420°C, 10 MPa hydrogen pressure and 0.06 kg H2/kg feedstock to hydrogenate the aromatic structures. In these conditions, the aromaticity was reduced considerably, and 39% of naphtas and 35% of keroseno fractions were obtained.