MLM That is pretty far away from what JBII is doing.
Recheck your data. Butane is easily condensed out out at normal temps under pressure.
As far as I know that is all that has been claimed by JBII. Propane can be condensed out with some cooling, nothing approaching what most people consider cryogenic temps. Beyond that, JBII will use the resulting gasses as fuel and will not be selling them, so the issue of market level purity is moot.
JBII may have to consider the process of liquefying propane if there is enough excess gas produced by the process over it's heating requirements. It is not known yet if removing the butane will be sufficient to take care of the excess gas energy produced by the process.
ALL in all it is a problem that you would like to have as opposed to the other way around where the gas produced is not sufficient to meet the process requirements and natural gas has to be purchased to meet energy requirements.
As the other poster pointed out, N in the fuel gas is not an issue if you are not selling it on the open market.
Fear, Uncertainty, and Doubt. We create it not because it's our job, but because it is our passion. Apply where needed.