Dear Cap, I think you are bound to have quite a lot of trouble with 
cryogenic separation of hydrocarbons (differences in vapour pressure 
etc). Why don't you try something like GC separation (apart from 
finding one, everything should be very straightforward, with minimal 
fractionation), or reacting the CO2 with caustic or so?
Success,
Gert Jaap van Klinken
Radiocarbon Accelerator Unit,
Research Laboratory for Archaeology and the History of Art,
6 Keble Road,
Oxford OX1 3QJ

Tel. (01865) 273939
Fax  (01865) 273932
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