1993 Volume 19 Issue 6 Pages 998-1005
The coprecipitates, precursors of fine zinc ferrite crystals, were prepared by continuously mixing an aqueous solution containing ferric and zinc nitrates with a sodium hydroxide aqueous solution. The coprecipitates were aged and calcined to from zinc ferrite crystals ZnFe2O4. Effects of various preparation conditions on the morphology of the crystals and on their capacity to desulfurize a simulated coal gas were examined.
Although the coprecipitates formed were regarded as amorphous fine particles, they were converted perfectly to ZnFe2O4 crystals by calcination above 773 K. The size of zinc ferrite crystals decreased with increase in the molar ratio of sodium hydroxide to nitrates, R. At lower values of R, the optimal coprecipitation and aging temperatures appeared at which their size was minimum. The optimal preparation condition was determined as follows. R was 1.5, both coprecipitation and aging temperatures were 323K and the calcination temperature was 973K.
Sulfur capacity of the sorbent molded from the present zinc ferrite crystals decreased with decrease in the surface area below 15 m2/ g. The properties of the sorbent prepared with sufficiently fine zinc ferrite crystals were as follows. The surface area was greater than 20 m2/g, the average pore diameter was 10-40nm and the sorbent showed good desulfurization performance in the range of 673-873K.
