DIY Synthetic Fuel Part II - The Fischer Tropsch Reactor

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This is the second part of my series on making synthetic fuel from carbon and water. In the first part of the series, I demonstrated how to make "syngas" which is a 50/50 mix of carbon monoxide and hydrogen gas formed when steam is reacted with carbon at about 1000C.

Link to part I:

https://www.youtube.com/watch?v=UXNcivV8JNw

In this video, i'll be taking the syngas I made in part I and converting it into a mix of hydrocarbons using a process called "Fischer Tropsch" or "FT" synthesis. FT synthesis typically uses an iron or cobalt based catalyst and converts the CO and H2 building blocks into hydrocarbon chains at around 250-300C and elevated pressures (usually anywhere from 10-30 bar). The reactor has a value called "alpha" which is the probability ratio of chain growth versus chain termination. At low values of alpha, only Methane is produced, but at high values of alpha, a wide range of hydrocarbons are produced from methane all the way up to paraffin waxes. This effectively creates synthetic crude oil, which is then refined to separate out the constituent molecules in much the same way as ordinary crude oil.

To make the catalyst, I initially tried co-precipitation of aluminum nitrate and ferric nitrate with ammonia at a temperature of around 60-70C and pH of around 8.0, but the resulting catalyst didn't yield anything, so the next thing I tried was repeatedly soaking ferric nitrate into activated alumina spheres and then calcining them to leave behind only the iron oxide, and repeated this process numerous times until the iron concentration was built up. Then the catalyst was reduced for several hours at around 300C with syngas flow through the reactor. The presence of carbon monoxide causes the iron to form Fe5C2 after the iron oxides have been reduced down to metallic iron, and this is the active species in the iron-based catalyst.

The overall yield of liquid fuel was only about 7ml of what seemed to be a mix of pentane and hexane. I suspect I have a relatively low value of "alpha" in the reactor, so most of the 400 liter or so of syngas that I used probably went into making methane/ethane and other gases rather than liquids.

In future synthetic fuel projects I think I'll just focus on methanol, since it's a single product and doesn't require separation like synthetic crude oil.