I may be exhibiting a limited imagination, but I can't see how producing acetone this way could be economical.
Acetone is cheap & plentiful, why not just buy it?
It's possible that there are some ketones produced as decomp products of the rancid oil, these are volatile compounds, so they would have a distinct odor. The decomposing coffee grounds may also contribute pungency in the form of amines.
If you are getting significant yields of acetone, the really interesting question is what happens to the rest of the oil? From an energy & economic standpoint, acetone is one of the least significant potential products, since it represents only 3 of 18 carbons in oleic acid.