Is this acceptable and eligible for the 72 hours transit visa?

I am planning to fly Thai Airways in from Australia (via Bangkok) into PEK on one ticket at 5:30 am on Sep 3. Then I will depart on Sep 5 at 12:30 pm on Delta to Seattle on a separate ticket. The tickets are issued by the individual airlines and not on same itinerary as I am using mileage redemptions.