Control of a hydrolyzer in an oleochemical plant using neural network based controllers J.S. Lim,M.A.Hussain , M.K.Aroua 1. Introduction Oleochemicals refer to chemicals from natural oils and fats of both plant and animal origins. However, they also include those derivatives derived from the subsequent modification of carboxylic acid group of fatty acids by chemical or biological means, and other compounds obtained from further reactions of these derivatives. Prior to 1980, about 90% of the raw materials for oleochemical industry were tallow and coconut oil. However, since 1980, palm and palm kernel oils have become important raw materials complementing tallow and coconut oils due to the fact that fatty acids composition of palm and palm kernel oil are closely similar to tallow and coconut oil, respectively [1] and has found numerous applications in various food and non-food based areas in the world [2]. In fact production of palm oil and palm kenel oil has increased by about 300% in the last 15 years and Malaysia is at the ŵoŵeŶt the world’s biggest producer of them. Fatty acids and glycerol are the major components of oleochemicals, and can be obtained through splitting of the crude palm oil. The whole process to produce these fatty acids and glycerol in a oleochemical process plant can be seen in Fig. 1. Before oil-splitting, pre- treatment is necessary to remove impurities, which occur naturally in oil. After splitting, crude fatty acids will be purified through distillation or fractionation to contain the fraction that is required. Then fatty acid will be hydrogenated to convert unsaturated fatty acid to saturated ones. Glycerol obtained from oil-splitting usually dissolve in water which is known as sweet water [3]. Concentration of glycerol in sweet water is very low, thus further recovery is necessary to obtain high purity of glycerol. However the most important and crucial step in this whole process is the fat splitting step, which is done in the hydrolyzer or oil-splitting unit. Oil-splitting or hydrolysis is the process of decomposing the oil into acids and glycerol by subjecting them in the presence of water to high temperature and pressure. This system involves a counter flow of oil and water (as reactants), where reaction and mass transfer occur at the same time. Fig. 2 gives an overall view to describe the hydrolyzer. Water is fed in excess from the top while tryglyceride is fed from the bottom of the splitter. Fatty acids and glycerol are the reaction products. Fatty acids will flow upwards and discharge at the top at the splitter. Glycerol will dissolve in water and discharge as glycerol-water at the bottom of the splitter. Steam is injected in parallel and concurrently at the top and bottom sections of the column to maintain the high temperature within the column. The steam flow rates are manipulated in a decentralized manner by the top and bottom controllers, respectively, which creates a challenging multivariable control problem. The top temperature controller is designated as TC1 and the bottom temperature controller is designated as TC2 in the figure. Operating this hydrolyzer is also difficult especially when temperature of the reactants fluctuate since the process behaves nonlinearly. This problem can also occur due to insufficient energy supplied to heat up the reactants before entering the hydrolyzer. supplied to heat up the reactants before entering the hydrolyzer. Changes in reactant flow rate to meet production demand also cause the process temperature to be unstable and the steam introduced into the system at the top and bottom of the hydrolyzer can also create uncertainty in the temperature control of the hydrolyzer, due to the continuous disturbance in the steam flow rate. At present, conventional decentralized PID have been used to control the process temperature. However, these conventional controllers are not able to achieve the desired set-point during startup and shutdown under the presence of these various disturbances. Consequently, low quality of the final product is naturally produced and has been a great loss for the oleochemical industry ever since.