LA to Shanghai to Bangkok. And then back again.

I'll be travelling from Los Angeles to Shanghai. I'll remain in Shanghai for 2 days and then fly to Bangkok. After few days, I'll fly from Bangkok back to Shanghai and have a 6 hour layover. Then I'll fly back to Los Angeles.

Will I be able to get two 72-Hour Free Transit permits?

Do I need a visa to apply for a 72-Hour Free Transit permit?