Suppression of Scale Formation on the Coal Hydrogenation with Iron Oxide Catalyst

Abstract

Iron catalysts have generally been used as a one through catalyst for coal liquefaction. However, in some cases, scale formation phenomenon on to the inner wall of the preheater and pipes has been reported.
In this study, the conditions and mechanisms of scale formation, and possible method of prevention were investigated.
Remarkable scale formation was not found in the experimental tests using pyrite catalyst, on the contrary, iron oxide catalyst system caused scale formation within some limited conditions.
The scale formation mechanisms in the iron oxide catalyst system were inferred as follows:
Fine iron compound is sulfurized by hydrogen sulfide in the preheating process, then becomes fine and active crystalline pyrrhotite.
Fine pyrrhotite crystals combine into coarse crystal on the high temperature pipe wall (over 400°C) of the preheater and form the scale with inclusions of fine coal and inorganic particles.
To prevent the scale formation in the iron oxide catalyst system, following measures are proposed ;
·Maximum temperature of preheater wall has to keep under 400°C .
·By surrounding an active pyrrhotite crystal with enough amount of coal molecules, coal molecules are adsorbed to the surface of fine pyrrhotite. Such condition arrests the growth to the coarse crystal of fine pyrrhotite crystal, and finally, the scale forma- tion is prevented.
To achieve such condition, for example, the method of coal impregnated with fine iron oxide is considered to be effective.