Feedback PID-like fuzzy controller for pH regulatory control near the equivalence point

• PID-fuzzy controller provides robust pH regulatory control near the equivalence point against large perturbations in buffering acidic liquid streams.
• The use of state space analysis with fuzzy clustering algorithms is useful to design the structure of the fuzzy controller.
• Statistical process control charts show that tight control is achieved for a wide range of experimental neutralization conditions covered.

In this research the use of a feedback PID-like fuzzy controller scheme for pH control is presented to deal with instability problems near the equivalence point in neutralization processes. State space analysis of the titration curves and a fuzzy clustering algorithm based on calculating a measure of potential derived from the square distance of the pH data are complementary applied to define the membership structure and the fuzzy sets of the controller. To test the performance of the controller, both simulated and experimental runs were used. The fuzzy controller was tested for compensating step-change perturbations of propionic acidic flow rates, propionic acid concentration, and buffering conditions. Stationary cycling behavior has been observed for large loads of acidic flow rates. It was found that though the rejection time was strongly dependent on the mean residence time of the liquid solutions, the proposed controller keep the neutralization process operating close to the specified set point of pH = 7.