What is qualified as "Transit Flight"

I need to fly from Singapore to Pyongyang (North Korea) and as there are no direct flight I need to go from Beijing to Pyongyang. As there is only two airlines going from BJ to Pyonyang (and Air China has cancelled all flights to Pyongyang for January/February), I will have to buy two different tickets from different airlines: one from Singapore to Beijing, and one from Beijing to Pyonyang. I would like to stay 48 hours and my country is one of those which qualifies for the 72 hour visa on arrival. Would I be possible to get into Beijing with this 72 hour visa?
Thank you!