SPC based on growth models for monitoring the process of hydrogenation of edible oil

• An SPC system is developed to monitor an industrial hydrogenation process on-line.
• Growth of melting point is modelled using monomolecular growth model.
• Two SPC charts are constructed based on a suitable linear form of the growth model.
• Use of model-free techniques like T2-Chart and X-Chart of AUGC are discussed.
• Developed monomolecular model is also used for diagnosis of process problems.

On-line monitoring of an industrial batch process of hydrogenation of edible oil involves repeated determination of the melting point of a batch at certain intervals. The objective of this study is to use these measurements to develop an SPC procedure for detecting process shifts like abnormal growth in melting point and occurrence of dead batches. Two model-free and a model based approach are proposed for this purpose. The growth data is of the form (MPij, tij), where MPij is the melting point at time ti for the jth batch. A linear approximation of the monomolecular growth model is used for developing the model based procedure. It is shown that the proposed model based charts can detect the out-of-control situations of active batches as well as the occurrence of dead batches efficiently. The effects of a few important process parameters on the parameters of the growth model are also discussed.