Recently, engineers have devoted a great deal of research to developing a Fischer–Tropsch synthesis (FTS) process with high carbon utilization efficiency and low CO2 emissions.
This is desirable not only to improve the process and make it more economical, but also to promote its industrial sustainability.
Because CO2 is produced in both syngas preparation and the FTS step, it may be a significant component in the syngas or in the FT tailgas that may be recycled back to the FT reactor.
With the aim of providing new insights into the process that would help engineers to design FT plants with high overall carbon utilization efficiency,
we investigated FTS using CO2-containing syngas mixtures over cobalt- and iron-based catalysts.
During the course of our research, we conducted a large number of experiments on CO/H2, CO2/H2 and CO/CO2/H2 syngas mixtures for FTS under different reaction conditions over both cobalt- and iron-based catalysts.
The results elicited the following information:
No apparent catalyst deactivation was observed when we co-fed CO2 into the feeds during FTS over both cobalt- and iron-based catalysts under the reaction conditions we conducted.
The rate of hydrocarbon production was maximized at an intermediate composition of the CO/CO2/H2 mixtures for a cobalt-based catalyst. The hydrocarbon product formation rate reached a maximum and then maintained this value,
even at a high concentration of CO2 in the H2/CO/CO2 feed, over an iron-based catalyst.
Most of the products for CO2-rich syngas were short chain paraffins with high CH4 selectivity and high molar paraffin to olefin (P/O) ratios. The product distribution followed a typical one-alpha Anderson–Schulz–Flory (ASF)
distribution with low alpha values with carbon number n>2. C2 selectivity lay on or close to the ASF distribution line. However, CH4 selectivity was far above the line.
For CO-rich feeds, the product composition shifted to an FT-type product (mainly long chain hydrocarbons) with a low P/O ratio, and followed a two-alpha ASF distribution with high alpha values for carbon number n>3.
Furthermore the composition of C2 was plotted below the ASF distribution line, while for CH4 was above it
