Doing an unpaid internship with some travelling

Hi, I am currently studying in China on an X2 type, however will leave the country and come back to do an internship. I will be travelling in and out of China so will need multiple entry. Do I need a working Z type/business F type? Is it possible to convert my X2 in China? Is an F type a guaranteed 12 month multiple entry visa?
Apologies for so many questions! Thank you for the info!