Its a broad distinction. English for occupational purposes presumably includes general english, business english etc., i.e. meant for everyday usage in your work for you to get by, or tourism english for that industry. English for academic purposes would touch upon the kind of English lessons and courses you take in order to pass certain standard tests like TOEFL, IELTS, Diploma or degrees etc. The curricula and the time for completion is quite different for the two streams.