The mixed integer linear programming model has been developed for the production scheduling of polybutene (PB) process of Daelim Industrial Co. (DIC) in Korea. The PB process is composed of one reactor, 13 storage tanks and two package types. It produces seven reactor products. Most of the tanks are practically dedicated to a specific product but in general, any tanks can be shared by multiple products. Also, two major products use multiple tanks. The reactor is operated on block mode. The products are liquid and they should be stored in tanks before packaging. The unique characteristics of this scheduling problem exists on the fact that the product in tank should be locked for 3-15 days in order to check the quality specifications after run-down from the reactor. The primary objective of scheduling is reducing the number of quality checking process because it causes great loss in production time and tank utilization. The model is composed of about 1500-2000 integer variables. The branching priorities are adjusted according to the importance of variables based on current manual scheduling practice and it greatly enhanced the convergence of mixed integer model. The scheduling system was successfully implemented in real plant and replaced the manual work of scheduler.