I'm looking at manufacturing relativly small amounts of CO2 from burning natural gas, I'm wanting to purify it by cryogenic seperation - at around 6 bar. I was hoping I could have several small distillation towers at different temperatures to pull off other gasses (H2O, SO2, NO2, N2O, CO) and progressivly cool the CO2, however I've read on the net that NOx and SOx must be removed before entering the cryogenic cooling stages. Can anyone enlighten me as to why?
The data I have is NO2 will liquefy below 21 degC, SO2 below - 10 deg, CO won't liquefy in my process cos it does so at -192. (these temperatures are all at 1bar - so will be a bit higher at pressure) At 6 bar I'm looking at about -50 degrees for CO2 to liquify. Anything else I should be aware of? - I would like the CO2 I manufacture to be at least food grade.
I'm not really that concerned about the energy cost of the cryo seperation as compared with amine as my quantities are quite low, I also want to end up with refrigerated liquid CO2 so am hoping I can do it with minimal plant.
Thanks for any input