This case study investigates the behaviour of a semi-batch surfactant reactor and seeks ways to improve the reactor＇s operating efficiency through the use of automatic control. The reaction involves adding ethylene oxide (EO) to nonylphenol to form oligomer (short chain polymer) with the assistance of potassium hydroxide acting as catalyst. The reactor was modelled using dynamic mass and energy balances plus a description of the kinetics of nonylphenol polyethoxylation. The pressure in reactor was calculated by applying Wilson＇s equation and the heat transfer coefficient of the heat exchanger was determined from plant data. The model was implemented in SPEEDUP flowsheeting package; and able to predict the length of oligomers in the reactor at any time. The model has been tested and compared with the performance of the actual plant. Due to the nature of the semibatch reactor, it is difficult to manually operate the reactor at a fixed optimal condition. Therefore, an improved automatic control scheme is needed to maintain the system as dose as possible to its optimum condition This was investigated by using the model and was found to offer higher output from the reactor.