Have single entry L visa, can I apply for 144h in Beijing and save the L type for later?

I have two passports, Germany and USA. I already have a single entry L in one of them but would like to visit Beijing for a few days first and then travel around the country a few weeks later during a second visit.

The plan is: Frankfurt - Bejing (144h free transit) - Tokyo - Beijing, Shanghai, Guangzhou (L) - ... - Frankfurt

Can I use my US passport for the first visit and obtain a 144 hours transit without visa while holding a valid l in my German passport, or do I have to use the L type first before I can apply for a 144 hours twov?

Thanks ;-)