The main purpose of this work is to investigate the feasibility of on-line experimental implementation of a Receding Horizon Non-linear Model Predictive Control technique to stabilise an unstable steady state. Experiments were carried out in a pilot plant system which realistically simulates an exothermic reaction taking place in a CSTR, with and without imposed disturbances in the feed flowrate. The controller has been devised by using the recently available software packages gPROMS and gOPT for simulation and optimisation, respectively. The configuration implemented allows for the testing of the nonlinear Receding Horizon controller performance both by simulation and experimentally on-line. It has been applied to a first order irreversible exothermic reaction in a pilot scale PARSEX (PARtially Simulated EXothermic) system with all the relevant flow rates and temperatures measured. The results obtained for the controlled system at these operating conditions demonstrate excellent control behaviour with stabilised reactor operation even in the presence of step changes in the feed flowrate. Moreover, it was feasible to carry out the optimal control calculations in real time on a SPARC workstation.