Two - 72 hour stopovers in the same trip.

I am flying from YYZ to BKK via PEK. Was thinking of stopping off for 24hrs in PEK to explore. On my return flight 6 weeks later (BKK to YYZ via PEK), I was hoping to stop off again in PEK for 24hrs and explore.

Can I apply for a 2nd 72hour permit on my return flight or do I have to apply for a regular visa.

I hold Canadian passport.