TITLE: Slurry Phase Iron Catalysts for Indirect Coal Liquefaction

University Coal Research Contractors Review Conference

PI: Abhaya K. Datye

Others  :  http://www.netl.doe.gov/publications/proceedings/97/97ucr/datye.pdf
PID  :  6044

来源: CEUR

【 摘 要 】

OBJECTIVE: The objective of this project is to investigate the causes of catalyst attrition in slurry phase iron Fischer-Tropsch catalysts and to synthesize catalysts with improved attrition resistance for this process. Precipitated iron catalysts are being considered by the DOE for conversion of coal-de- rived syngas where the H 2 /CO ratio is around 0.7.The high water gas shift activity of Fe makes it possible to work at such low H 2 /CO ratios, hence Fe catalysts are desirable for indirect liquefaction of coal. WORK DONE AND CONCLUSIONS:In this work, we have studied two approaches to characterize the attrition resistance of precipitated catalysts.These include uniaxial compaction and ultrasonic fragmentation.While uniaxial compaction is the conventional approach used in the ceramics litera- ture, we feel that the compressive stresses used here do not adequately represent the forces experienced by a particle in a slurry reactor .Ultrasonic fragmentation was therefore used in an attempt to simulate the forces that lead to particle break up in a slurry reactor.Precipitated iron catalysts were found to be very weak compared to silica or alumina spray dried catalysts.The morphology of the primary iron oxide particles as well as lack of a suitable binder makes these catalysts very weak.In our work, we have studied differing morphologies of the silica binder, and effect of binder on catalyst strength. Besides physical breakup of the catalyst, there is a second mechanism that leads to nano-scale attrition of Fe catalysts.This is due to the transformation of hematite (Fe2O3) into magnetite (Fe3O4), α-Fe as well as iron carbides.A working Fe catalyst is known to consist of a mixture of these phases, however the role of each phase and the nature of the catalytically active phase is not yet conclusively estab- lished.We feel this information is critical to the design of attrition resistant catalysts.Therefore, we have used techniques such transmission electron microscopy (TEM) and x-ray diffraction (XRD) to identify the nature and morphology of phases present in these catalysts.We conclude that transforma- tion into the carbide phase is essential to obtain a high activity catalyst.However, there may be more than one type of carbide present in the catalyst, explaining why it has been generally difficult to obtain structure-activity correlations.The large change in specific volume in going from the iron oxide tcarbide