This work is aimed at developing a methodology to design controllers for nonlinear plants where desirable robustness and performance properties must be maintained across a large range of operating conditions. The approach is based on the multi-linear model representation and the H-infinity control design that allows inclusion of plant nonlinearities by representing the original system as a set of local uncertain linear plants. To assess the merits of the proposed technique, experiments are performed on a bench-scale pH neutralization reactor. The results demonstrate robust performance and robust stability in the presence of disturbances and set-point variations.