madrid-shanghai-siem riep (cambodia)-vietnam-shanghai-madrid

Hello!
I have a EU passport,
I will travel from spain to shanghai, I will be in shanghai 1 night and then I will go to cambodia and vietnam. I will fly back from vietnam to shanghai, stay in shanghai 3 nights and go back to Spain.
Can I apply for the free visa twice?
The flights are differents air companies, Is that any problem?
thank you