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A highly nonlinear pH control process is used as an example process to compare a number of methods for designing nonlinear, discrete-time controllers. The nonlinear system is approximated as a linear parameter-varying system, which is based on a set of velocity-form linearizations. The focus is on control methods which minimize a quadratic cost by using the solution of a Riccati equation in connection with gain scheduling. The compared methods include switching control, interpolation of linear controller parameters, gain scheduling with a nonlinear state estimator, a time-varying Riccati equation approach which uses an estimate of the future of the system, and a Riccati equation approach which utilizes an estimated upper bound on the future variations to guarantee an upper bound on the quadratic cost.