Iron-Catalyzed Coprocessing of Coals and Vacuum Residues Using Syngas−Water as a Hydrogen Source

Abstract

The effectiveness of alternative hydrogen sources compared to pressurized hydrogen gas toward the coprocessing of coals and vacuum residues was investigated in the presence of different kinds of iron-based catalyst precursors. The reactions in syngas−water using pentacarbonyliron or synthetic pyrite achieved high rates of conversion to THF solubles comparable to those in pressurized hydrogen gas, indicating the presence of the synergistic effects of the two hydrogen sources, hydrogen gas and carbon monoxide−water. Under hydrogen gas, addition of water greatly increased the yields of the desired fractions. The Fe(CO)5-catalyzed coprocessing of a vacuum residue of Arabian Heavy and Wandoan coal (2:1, 400 °C, 60 min, H2 3.0 MPa, CO 3.0 MPa, water 0.5 g) in combination with the pretreatment at lower temperature (200 °C, 30 min) afforded the high yields of THF-soluble (100%) and n-hexane-soluble (69.5%) matter. At higher reaction temperatures, 425−450 °C, the use of Fe(CO)5 with sulfur or synthetic pyrite afforded much better rates of conversion than Fe(CO)5 without sulfur. The XRD and XPS analyses revealed the formation of a mixture of magnetite and pyrrhotite from Fe(CO)5 without sulfur, and the surface of the used catalyst was mainly covered with iron species in a relatively high oxidation state. On the other hand, pyrrhotite was formed from Fe(CO)5 with sulfur or synthetic pyrite. The gas consumption, eventually the efficiency of the coprocessing, was estimated to be influenced by such changes in the state of the catalyst surface.