What is the industrial yield of paracetamol?
For a variety of explanations of industrial techniques as applied to acetylation,  including acetaminophen synthesis,  try here
https://www.google.com/patents/US20120065423
The examples are right at the bottom and are only scaled down lab versions of the industrial technique. Over 90% yield should be easily achievable if acetic anhydride is used (and is achieved in the industrial synthesis of ibuprofen).  The patent examples give yields for the use of acetic anhydride and acetic acid, as well as the technology employed e.g. continuous stirred tank reactor (cstr)  vs plug flow reactor (pfr or tubular reactor)  vs reactive distillation.  Enjoy.