Robust nonlinear control of pH processes

Systems with static nonlinearities on the process output occur very frequently in the chemical industry. This paper discusses a framework for controlling these types of processes. This framework is then applied to the case of a CSTR neutralization reactor. The robust stability of the resulting framework is studied by examining the case when the static output nonlinearity changes with time and also when a disturbance occurs on the process output. The results in this work show that there is not a unique answer to the optimal choice of model in the controller for the pH system, but a good choice can be recommended.