Separation of Catalyst Particles and Wax from Effluent of a Fischer–Tropsch Slurry Reactor Using Supercritical Hexane

Abstract

The separation of a catalyst/wax mixture from Fischer–Tropsch (F-T) synthesis products in a slurry bubble column reactor is one of the most important challenges in the development of F-T slurry reactors. So far, various techniques such as internal and external filtration, gravity and forced sedimentation and high gradient magnetic separation have been proposed. The technique must be able to separate the catalyst (with a size distribution of 1–60 microns) effectively and quickly in a continuous process and the catalyst content in the separated wax should become less than 2 ppm, economically speaking. In the present work, a number of experiments using normal hexane in its supercritical and subcritical states were carried out for separation and it showed that this technique was highly effective and quick. Since hexane in its supercritical state can reduce the wax viscosity, separation of the catalyst will be easy and fast. A settler was initially used to remove the main portion of catalyst content (i.e., up to 90%) and a filter as the secondary step of separation to remove remaining solid content of the wax. N-hexane was used as the solvent and contacted to the wax with different solvent/wax mass ratio of 1/1 to 5/1 and different residence time of 60–240 s. The catalyst content in the purified wax was lower than 2 ppm.