Guest editorial

A mixed-integer linear programming model is presented for the optimum planning of multi-plant, multi-supplier, and multi-grade petrochemical production. In the production of multiple grades of a given petrochemical product, the amount of transitional off-spec production depends on the sequencing of different grades. For each time period, the discrete-time model determines the optimum mix of petrochemical grades for each plant, the quantity to produce of each selected grade, and the optimum production sequence of different grades. In addition, assuming limited raw-material availability, the model determines the quantity of each raw material to purchase from each supplier. The model incorporates demand, capacity, raw-material availability, and sequencing constraints in order to maximize total profitability. The model is applied to real-life data from multi-grade polypropylene production in a large petrochemical company.