This paper summarizes the results of the current stage of the real time optimization (RTO) project of Petrobras in Brazil for optimizing its refineries. Here the maximization of the production of LPG in the FCC converter is considered. The general procedure for applying the RTO using the one-layer approach is outlined. Some difficulties that may arise during the implementation are addressed and the strategy is compared with the more traditional two-layers approach. We also stress the need of using a robust nonlinear programming (NLP) code and all the results presented in the paper were obtained by the MISQPSOL code.