will they give me 24 months open entry visa . I need to possible travel to china often for business?

Hi, do you have two or more than M type entry permits (including the F type obtained before September 1st, 2013 for business purposes), a business licence or a certificate showing you have made investment in China? If you can't provide any of the documents, I'm afraid the 24 months M type is not available for you.

I have more then 2 M types before 2013. Will that be enough to obtain 2 year multiple entry one?

You also need an invitation letter from duly authorized unit, which refers to the Foreign Affairs Bureau.