Venus chemical engineering

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Venus chemical engineering

Postby KarenRei » Sat Feb 13, 2016 5:39 pm UTC

Hi all. I've been idly thinking a lot about how to provision a floating colony on Venus in a simple, reliable manner. There are two issues I'm having a bit of trouble on:

1) Removal (to an exhaust stream) of SO2 from a stream also containing H2O and O2

2) Either:
2a) Separation of individual acids from a mixture of H2SO4, HCl, H3PO4 and HF (preferable); or
2b) Removal (to individual exhaust streams) of HCl, HF, and P2O5 in addition to the SO2 from the H2O and O2 in #1 (also fine); or
2c) Removal (to a collective exhaust stream) of HCl, HF, and P2O5 from the H2O and O2 in #1 (less preferable)

Does anyone know of a relatively simple, reliable way to do this?

Background: The most Earthlike place in the solar system is Venus's cloud deck between around 51 and 55km altitude; it provides gravity, pressures and temperatures acceptable to humans, sufficient radiation shielding overhead (equivalent to 5-10 meters of water), ample sunlight and other sources of power, and a wide range of other benefits. Normal Earth air is a lifting gas, making it comparatively easy to loft a (very roomy) colony with ample opportunity for high-yield greenhouse cultivation. And the atmosphere contains everything one would need to maintain a diverse plastics industry and produce most macronutrient-fertilizers - C, H, O, N, P, Cl, F, as well as Ar, Ne and He. Strangely, it appears that there may also be significant Fe in Venus's clouds, in the form of FeCl3 - if proven correct, then a Venus colony would even be able to produce steel without any mining; it would collect in a trap in any acid-processing hardware.

While initially I presumed that the best route toward providing oxygen would be MOXIE like on Mars, I realized that Venus's cloud deck provides a much better option. At this altitude, the droplets are around 85% sulfuric acid, slightly ionized, and should be easy to adsorb. Sulfuric acid, heated, decomposes to H2O, O2 and SO2. Hence all one needs to do is heat it (which can be done either with power, or by lowering it deeper into the atmosphere), remove and exhaust the SO2, and you have the two most important resources for sustaining humans. Removal of the SO2 is issue #1. Simple chilling doesn't seem to cut it, because the SO2 would adsorb into the water. Perhaps a hygroscopic mineral (CaCl2?) that would absorb the water, and then later be heated to re-release it? Chilling to ~200K would separate the SO2 from the O2 (perhaps in the same chilling system that would be needed to separate N2 from the CO2 to get N2 for the habitat)

Venus, however, does not have *only* H2SO4 in its clouds; there's also HCl, HF, and H3PO4 (as well as potentially some S and FeCl3, but these aren't problematic). These acids are generally believed to be mostly stratified (for example, H3PO4 is generally only found in the lower cloud deck), and H2SO4 is well dominant - but we really don't know how well and consistently stratified they are. And the consequences of exhausting HCl, HF, and H2PO5 into human breathing air would be very bad even in small quantities. Furthermore, these are very valuable industrial chemicals - for example, a habitat's skin would almost certainly be made of a ripstop fluoropolymer (ex: CO+2H2->CH4+CO2; CH4+3Cl->CHCl3+3HCl; 2 CHCl3+4HF->C2F2+4HCl; X C2F2 -> PTFE), while phosphates are critical for plant life. Hence recovering them, rather than exhausting them, would be ideal. What is a plausible way to go about this? I can think of all sorts of inefficient, convoluted pathways, but that's definitely not something you want on a remote body. Maybe fractional crystallization? Distillation? Electrochromatography? I really don't know. This is issue #2.

I've been thinking over the other processes that would be useful and haven't hit any issues with them yet. I do find it quite convenient that Venus provides you the most important industrial acids on its own (except nitric, but it helps you make that too). And all of the important industrial processes that require heat and pressure - acid decomposition, the Haber process, the Sabatier reaction, methanol production, and on and on, they require elevated temperatures and pressures to shift the reaction into a thermodynamically stable state. So in addition to hanging one processing plant from your habitat (for low temperature/low pressure reactions), you can also do higher pressure reactions on or nearer the surface - either A) with fixed installations, serviced by the same phase-change balloon probes one would need to explore/sample the surface; or B) simply taken down by the probes (catalyst bed, etc included) and then back up, with no fixed low-altitude infrastructure.

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