Measuring the strength of slurry phase heterogeneous catalysts

Fischer-Tropsch (F-T) synthesis is a process used to convert coal-derived s yngas to hydrocarbon liquids and waxes. A slurry phase bubble-column reacto r (SBCR) is the preferred reactor type due to improved heat and mass transf er and operational simplicity in terms of catalyst loading and discharge. A potential disadvantage in the SBCR vs, a fixed-bed reactor is the attritio n of the catalyst which can cause difficulty with the catalyst/wax separati on, resulting in gradual loss of catalyst from the reactor. In this work, w e have evaluated two approaches to measure the strength and attrition resis tance of heterogeneous catalysts: uniaxial compaction and ultrasonic fragme ntation. A commercial catalyst developed for F-T synthesis was tested along with a sample of an alumina support having a similar particle size distrib ution. It was found that the cumulative particle size mass distribution plo ts after ultrasonic fragmentation show significant differences in strength, whereas the same powders show small differences in strength as measured by the uniaxial compaction method. Erosion was found to be the dominant fragm entation mechanism for the alumina support whereas fracture was the dominan t mechanism for the F-T catalyst. Ultrasonic fragmentation also was applied to Fe F-T catalysts containing a kaolin binder. The catalyst with the bind er was very weak, comparable to the binderless catalyst. Further analysis u sing transmission electron microscopy (TEM) showed that kaolin and the Fe F -T catalyst occurred as two distinct phases, with plate-like structures whi ch did not help create strong interlocking forces between them. These resul ts provide clues for the design of attrition resistant catalysts. (C) 1999 Elsevier Science S.A. All rights reserved.