Transformation of Iron Catalyst to the Active Phase in Coal Liquefaction

Abstract

The transformation of iron compounds (R-FeOOH, γ-FeOOH, ferrihydrite, limonite, and pyrite) into pyrrhotite (Fe 1-x S) was systematically investigated through the sulfidation tests with elemental sulfur in the absence of feed coal under liquefaction conditions. The order of transformation temperature into pyrrhotite was as follows: ferrihydrite, FeOOH (250 °C) < limonite ore (300 °C) < pyrite ore (350 °C). The crystal growth of pyrrhotite proceeded in the following order: γ-FeOOH < limonite, R-FeOOH, ferrihydrite < pyrite (FeS 2 ). Both transmission electron microscopy observations and corresponding X-ray diffraction data indicated that the ultrafine crystallites of Fe 1-x S could be initially formed into the framework of iron oxyhydroxide particles at lower temperatures, followed by growing up to the large hexagonal crystal at higher temperatures through the disappearance of its framework. The presence of H 2 S is effective not only to maintain the sulfur-rich stoichiometry of Fe 1-x S but also to suppress the crystal growth of pyrrhotite. A good correlation between the oil yield and the crystallite size of pyrrhotite was obtained for the fresh and the used catalysts, indicating the higher oil yield with smaller crystallite size. γ-FeOOH exhibited an excellent catalytic activity for the coal liquefaction due to the transformation into pyrrhotite with smaller crystallite size under the liquefaction conditions. The used catalyst, pyrrhotite in CLB-THFI, demonstrated a sufficient catalytic activity, although the oil yield decreased slightly as compared to that of the fresh catalyst. Catalyst deactivation through the deposition of coal mineral matters or organic residues appears to be considerably small.

Effectiveness of Different Transition Metal Dispersed Catalysts for In Situ Heavy Oil Upgrading

“…It has been shown in Section 3.2 and 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 23 fraction increased to 47 wt %, the light naphtha fraction reduced to 21 wt %, and the gas oil fraction stayed constant at 32 wt %. These results are in line with the literature, where similar observations have been reported 74,78,79 . It was observed that the asphaltene amount in the produced oil was 7.3 wt % for FeS and 10 wt % for Fe 2 O 3, relative to 4.5 wt % in thermal upgrading.…”

Clean liquid fuels from direct coal liquefaction: chemistry, catalysis, technological status and challenges

“…Of these sulfides, the more active form is considered to be pyrrhotite. 11,209,232,243,244 The evolution of H 2 S from FeS 2 during liquefaction produces the catalytic Fe 1Àx S; compounds of intermediate stoichiometry between FeS 2 and FeS. Sulfur deficient sites in these compounds are believed to activate molecular hydrogen.…”

Recent Advances in Direct Coal Liquefaction

“…Hirano et al [60] found that pulverized pyrite and -FeOOH both produced a higher conversion, an increased oil yield and a larger hydrogen-consumption than the raw pyrite did. Kaneko et al [61] reported that sulfided limonite and -or γ-FeOOH were active catalysts for coal liquefaction, and γ-FeOOH exhibited the best catalytic activity due to the transformation into pyrrhotite with smaller crystallite size under the liquefaction conditions. The liquefaction of Yallourn coal under 7.5 MPa of initial hydrogen at 450 °C for 1 h with γ-FeOOH produced an oil yield of approximately 50 wt%.…”