In the last post, we talked about methods to condense out the five most readily condenseable constituents of the Venusian atmosphere (sulfuric acid, water, sulfur dioxide, hydrogen chloride, and hydrogen fluoride). In some ways the next steps of the gas phase processing could be thought of as continuations of that process.
At this point in the process, the remaining constituents (assuming you’ve properly removed the previous-listed five condenseables) can be lumped into two categories:
- Semi-reactive gasses like Carbon Dioxide, Carbonyl Sulfide, and Carbon Monoxide
- Neutralish gasses like Nitrogen, Argon, Helium, and Neon
There are a couple of ways of proceeding from here. One thought to keep in mind though is that due to the large amount of CO2 in the atmosphere, you’re least likely to care about collecting it efficiently–it’s the other trace constituents that are worth gathering. The quickest way of separating out the other elements from the CO2 would be to do what someone suggested in the previous comments thread–freeze the CO2. With a freezing point of only -78C, the previous processes have likely already chilled the Venusian atmosphere fairly close to this temperature anyway. The phase change will take a lot of energy, but if after separating out the other constituents you allow a good fraction of the CO2 to be sublimed away on your refrigeration processor’s radiator (assuming you’re using active refrigeration instead of the heat-pipe trick), not all of that energy will go to waste.
In the process of freezing out the CO2, assuming you are doing this in some sort of a batch process, the pressure is going to drop by about a factor of 20x. This may raise the concentration of the carbonyl sulfide enough to get it to condense out as a dew that can be removed, since the air stream will now be lower than the boiling point of the COS, and the effective concentration will be increased by about 20x since you just got rid of most of the atmosphere.
If that’s successful, the only semi-reactive species that will be left is Carbon Monoxide. Carbon Monoxide’s boiling and melting points are much lower, so you probably won’t be able to remove it at this step. You have a few approaches you could take to removing the Carbon Monoxide. You could try to distill it out if you’re processing the rest of the more neutral gasses to individually separate them. Or you could mix the neutral gasses with oxygen and run it over a warmed catalytic converter. Or you could try reacting it with warmed sulfuric acid–since carbon monoxide is a fuel and sulfuric acid is an oxidizer. Or you could just live with it as an impurity. Or there might be some sort of way to filter it out electrochemically. Not sure which approach is best, but my guess is one of the first two.
Once you have the carbon monoxide removed, you’re down to neutral gasses like Nitrogen, Argon, Helium, and Neon. It may make sense to separate these further via distillation if you already have them this cold. This can proceed using similar equipment to what is used terrestrially for producing various industrial gases. For instance using either Linde’s or Claude’s processes to chill and liquify the gasses. If on the other hand you don’t yet have need for the separated gasses, you could just leave them mixed together as the buffer gas to mix with oxygen for breathing purposes. It should be noted that going into this step, if you’re down to just the neutral gasses, the Nitrogen is still about 99.8% of what you have. The concentration of Argon at this point is only 0.2%, which is actually lower than the 0.9% you find on earth, but Helium and Neon are both at much higher concentrations than they are in Earth’s atmosphere. So it might be worth processing them out via some sort of fractional distillation process.
Once you’ve removed the neutral gasses and dealt with (or not) the carbon monoxide, you can take whatever portion of the carbon dioxide you want to keep for chemical processing, and allow the rest to be vented overboard, using them to chill the hot-end heat exchanger on your active refrigeration system if you’re using one.
At this point you’ve now broken the Venusian atmosphere out into its constituents, and possibly chemically altered a few of them (reacting some of the Sulfuric acid to release water, or maybe catalytically converting the carbon monoxide). At this point you’re ready to start doing some basic chemical processes to try and create some chemical precursors.
Basic Chemical Precursors ISRU Development Phases