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Sorting the sea
The barge brings one liquid, and a short column splits it by boiling point, with Titan's air doing the cooling.
See it in the tour: chapter kraken shore, shot 4.2.
One liquid, three products
The sea barge loads 500 t of liquid at the jetty and runs it along the coast to the sea terminal design. What is in the tank is a mixture. Ligeia Mare, whose liquid Cassini's radar analysed, is 71% methane, 12% ethane and 17% nitrogen by volume physics. Kraken Mare is methane-dominated like it, but nobody has measured its own split physics. The plant is built to sort whatever arrives design.
The three products go three ways. Methane fuels the ascent vehicles and the shuttles. Ethane becomes plastic. Nitrogen goes to the ammonia plant design.
The tour does not frame the terminal, so the drawing below stands in for it.
Three boiling points
Everything rests on how the three liquids differ. At one atmosphere nitrogen boils at 77.3 K, methane at 111 K and ethane at 184.6 K physics. The sea is at 93.65 K physics, between the first two.
Step one: let the nitrogen go
At 93.65 K nitrogen is above its own boiling point, so it stays in the liquid only because it is dissolved physics. A flash drum drops the pressure and the nitrogen leaves as a gas. The seas do the same on their own: nitrogen is expected to bubble out as conditions change physics. The gas goes to the ammonia plant.
Step two: the column
What is left is methane and ethane, 73.6 K apart in boiling point physics. The gap is wide, so a short column separates them. Liquid is heated at the bottom, vapour climbs through the trays, and each tray strips a little more ethane out of the rising vapour. Methane comes off the top. Ethane is left at the bottom design.
Titan does the cooling
The top of the column must be cold enough to turn methane vapour back into liquid. On Earth that takes a refrigerator. At Kraken Shore the outside air is 93.65 K, 17 K below methane's boiling point physics. A heat exchanger to the open air condenses the overhead for nothing design.
The heat for the bottom comes from the reactors. Waste heat is a product at 94 K, and the reboiler is one of its customers design. See Reactors and heat on Titan.
What nobody knows yet
Kraken Mare's methane, ethane and nitrogen fractions are an open item challenge. If it holds more ethane than Ligeia, more of the barge load goes to plastic. If it holds more nitrogen, the flash drum works harder. The column does not change. See Kraken Mare and Titan's seas.
Key numbers
| Quantity | Value | Basis |
|---|---|---|
| Boiling point at 1 atm: nitrogen / methane / ethane | 77.3 K / 111 K / 184.6 K | physics |
| Gap between methane and ethane | 73.6 K | physics |
| Sea and air temperature | 93.65 K | physics |
| Air below methane's boiling point | 17 K | physics |
| Ligeia Mare, by volume | 71% methane, 12% ethane, 17% nitrogen | physics |
| Barge cargo | 500 t | design |
| Condenser | open Titan air | design |
Sources
- NIST Chemistry WebBook, methane, phase change data
- NIST Chemistry WebBook, ethane, phase change data
- NIST Chemistry WebBook, nitrogen, phase change data
- Hayes 2016, The Lakes and Seas of Titan, Annual Review of Earth and Planetary Sciences 44
- Birch, Hayes and Perron 2025, Titan's Fluvial and Lacustrine Landscapes
- Fulchignoni et al. 2005, In situ measurements of the physical characteristics of Titan's environment, Nature 438