Liquefaction/fractionation unit to remove gases Xenon/Argon from a gases Hydrogen or Methane propellent

We have proposed a propellant/pressurant gas tank with LXe or LAr that expands to a gas to pressurize LH2 , LO2  and Liquid Methane propellant tanks

LH2 and/0r LO2 boil off refrigerated the LXe before gas expansion as a pressurant gas

This in principle should be able to use LCH4 boil off as well

Presserant gases now act as fuel for an Ion propulsion engine, however, the gases Xenon or Argon must have some Gases hydrogen or oxygen residuals ratios mixed in, Can we run this through the ion engine? if not then we need a Liquefaction fractionation unit to remove the Xenon from the hydrogen/oxygen/Methane by cryogenic liquefaction.Possibly this system is integrated with near zero boil off cryocoolers proposed for long term space flight.

Possibly the cryocooler/liquefaction systems could allow refueling of a cryogenic chemical stage that utilizes Argon/Xenon ullage gases by returning the noble gasses to a cryogenic state and removal back to the cryogenic LXe tank.The problem here would be Gases Xenon becoming miscible with the LH2.There is a possibility that using residual gases H2 and O2 to fuel a small rocket engine might also be ruled out by Noble gasses as propellant pressurant.

Removing Methane residuals from Xenon ullage gases or are noble gases miscible in Liquid Methane? And at what rate?

http://www.pd.infn.it/~conti/xe.pdf

Density

Xenon Gas 421 Kg/CM -3

Xenon liquid  1987 Kg/CM-3 under pressure

Boiling point

1 ATM Xenon gas 9.86 KG/CM-3

1 ATM Xenon liquid 3057 KG/CM -3

1 liter of LXe produces 550 liters gas

In our chemical in space stage, this would be under pressure.

Methane boiling point -258.68 °F

Argon boiling point -302.526 °F)

Krypton −244.147 °F

Xenon boiling point    −162.578 °F

Xenon has a much lower boiling point to cryogenic Methane so it might mean that it would freeze and gell with LCH4(and LH2) Gelling as ice crystals being a somewhat different from Miscibility! Both over time is most likely an unwanted outcome.(A)So missions involving a complete chemical burn followed by the start of ion engine operations might make sense over long term ZBO of LH2.(B) Liquid Argon has a much lower boiling point to that of Liquid Xenon so this might imply slower gelling or miscibility with liquid Methane(somewhat LH2)? (C)So LAr might be the better choice with trades as to its performance as an ion propellant stored in the tanks as ullage gas.(D) Liquid Argon might make a better choice in the case of longer duration ZBO of Methane propellants with assistance from a Liquefaction fractionation unit slaved to the ZBO unit.Can Liquefaction fractionation unit process out Liquid Argon out liquid Methane if needed?And would you really want to have to do this? ZBO Methane chemical stage might not be able to be compatible with an ion engine system over long periods of time but could be a solution to periods intermediate in nature beyond the 5 to 10 day loiter capabilities of the EUS (SLS)

(E) using staging of a in space upper stage(chemical) and a third stage  ion powered stage is a known efficient use of the rocket equation, using the chemical stages propellant tanks with Noble gases as ullage involves a lot of noble gases mass and would be a stage much larger than the proposed ARM (10 metric tons of Xenon)So the question here is the in space stages chemical propellant tank PSI/Bar/ATM limits,what does this represent in molar mass of noble gasses? Is there a trade to strengthen chemical in space stages propellant tanks to be able to handle a higher noble ullages gas propellant load? (F) such a hybrid stage is with the mass of the solar array  and the mass of the chemical engines that have not been jettisoned are subject of study( there are images of the SLS/EUS with a very large solar array)(G) such very large Ion powered stages could transfer very large cargo payloads beyond the capabilities of the ARM