TABLE OF CONTENTS Matthys Janse van Vuuren [1] and Burtron H. Davis [2]
The use of compositional modulation of catalytic reactors is an established procedure [1]. In this approach, sudden and cyclic changes in the feed composition may lead to improvements in the catalyst productivity and/or selectivity.
The compositional modulation technique has been applied to the Fischer-Tropsch synthesis (FTS) reaction [2 5]. It was found that the cyclic feeding of CO/H 2 had an influence on the selectivity of the FTS products. Among the conclusions was that for an iron catalyst the selectivity for methane increased under periodic operation compared to the steady state operation [5]. In the study [5] it was found that the propane/propene ratio increased under periodic operation and the largest changes were with periods between one and ten minutes. Due to the limitations of the analytical technique utilized, they could not separate ethane and ethene so that the selectivity basis was for the C 3 hydrocarbons. In this study the analytical procedure permitted analysis of products only to the C 8-compounds.
For the reactor used in these studies [2 5] only low conversions could be utilized to obtain differential conversion levels ( ? 2% based on CO). This limitation on conversion was imposed because of the exotherm of the FTS reaction. The FTS reaction usually takes days to stabalize to make a correct assessment of the steady-state activity and selectivity of the catalyst. This stabalization period was not practiced in the work in references 2 5.
