Towards Understanding Phenomena Related to Fischer-Tropsch Synthesis Reaction
Dr. Xiaojun Lu
University of the Witwatersrand
Johannesburg, South Africa
March 21, 2011 at 10:00am
Ben Bandy Conference Center
UK Center for Applied Energy Research
A series of experiments in different types of reactors were performed with TiO2 supported cobalt catalyst to gain a better understanding of the phenomena related to Fischer-Tropsch Synthesis (FTS) reaction. The performance of FTS was investigated during unsteady state and steady state. The experiments were conducted firstly to investigate the effect of external mass transfer to the performance of FTS, and the results suggested that it has effects only in short term but not long term. During the beginning period of the experiment conducted in the CSTR, two steady stages in terms of reaction rate and product selectivity could be observed and large changes were found in-between them. In order to reveal the precise reason for causing these observed phenomena, flushing experiments were designed after the reactor system reached the secondary steady stage by means of change the feed from synthesis gas to inert gas, argon. By comparing the results from the reactions before and after flushing, we can conclude that those observed large changes were mainly caused by the depositing of liquid phase products on the catalyst.
The information for the materials in the stream out of reactor during flushing was also collected. The dynamic concentration of C1-C8 in the flushed out gas suggested that reaction among the light products might take place under a moderate FT reaction condition. On the analysis of the experimental data both from CSTR and PFR, we found that the ratios of adjacent light olefins kept constant although there were large alterations on the ratio of olefin to paraffin (based on the same carbon number). Based on the implication from flushing experiments that light hydrocarbons may react with each other, an equilibrium was proposed for the olefin product distribution of FTS.