360085 Nitrogen Co-Feeding in Fischer Tropsch Synthesis: The Effect to the Reaction Rate and Product Selectivity at Higher Reaction Rates

Wednesday, November 19, 2014: 4:35 PM
306 (Hilton Atlanta)
Adolph Muleja1,2, David Glasser1,2, Diane Hildebrandt3, Jean Mulopo1, Xiaojun Lu2 and Yali Yao2, (1)School of Chemical and Metallurgical Engineering, University of the Witwatersrand, Johannesburg, South Africa, (2)MaPS Engineering, University of South Africa, Johannesburg, South Africa, (3)Material and Process Synthesis, University of South Africa, Johannesburg, South Africa

Our previous study, “Effects of Nitrogen Co-Feeding in Fischer Tropsch Synthesis At Low CO Conversion”, showed that diluting syngas with N2 has a positive effect on the activity and selectivity of products at low CO conversion. In the current study, we pursue similar kind of experimental work for Fischer Tropsch Synthesis (FTS), with an aim of investigating the effect of nitrogen co-feeding in FTS at high CO conversion.

We started the reaction as per previous experiment at 60 (NTP)ml/min, 20 bar and the temperature of 200 oC (for 48 hours) for syngas FTS. Then, we increased the reaction temperature to 220 oC and started the investigation of the effect of N2 co-feeding in FTS at this temperature by repeatedly switching between two kinds of feed gases into the reactor: (1) with only syngas at 20 bar, 60 (NTP)ml/min, and (2) with N2 co-feeding syngas at 25 bar, 75 (NTP)ml/min. In order to keep the “reaction kinetics” the same in all runs, we kept the molar flow rate of syngas as well the partial pressure of the CO and H2 constant while varying the molar flow rate of N2 and the reactor pressure. The reactor was run for around 2800 hours at 220 oC while alternating the experimental conditions from syngas to syngas diluted with N2. The experimental results show that the increase in temperature from 200 oC to 220 oC resulted in the increase of CO conversion from 16% to 46%. However, the catalyst deactivation was observed with time going from a CO conversion of 46% down to a CO conversion of 12%. Thereafter, the CO conversion remained fairly constant approximately 12% for a period of 1800 hours.

Our data demonstrate that N2 co-feeding in FT reaction decreases the selectivity to the undesired lights hydrocarbons, especially for CH4. It was also noticed that the rates of light paraffin (C2 – C5) formation as a function of time on stream (TOS) decreased significantly at high CO conversions and remained fairly constant at CO conversion average 12% for both conditions. However, the rates of formation of light olefins as a function of TOS appear to be quite constant for the high CO conversions and a significant increase in the rates of formation of light olefins (C2 – C5) as a function of TOS is observed for low CO conversion. Further experimental results, such as product selectivity and paraffin to olefin ratios are calculated and compared.

Extended Abstract: File Not Uploaded
See more of this Session: Syngas Production and Gas-to-Liquids Technology
See more of this Group/Topical: Catalysis and Reaction Engineering Division