Operational envelopes for batch processes

Batch processes are often subjected to a number of sources of variability, which are frequently overlooked due to operating policy implementation. In many pharmaceutical and speciality chemical processes, which are predominan tly batch in nature, a high proportion of the operating procedure is implem ented manually, which can lead to significant variability. The effect of th is variability is typically neglected at all stages in process development and even when full-scale production begins. The result of any variability c an have a dramatic effect on some process stages (particularly sensitive on es such as crystallization), and it is therefore important to understand ho w variability in any of the operating variables affects the overall process . Ideally, one would like to design processes that are less sensitive to va riability and specify precisely the limits of any allowable variability. A method for designing batch processes using "operating envelopes" that speci fy process operation in terms of a region within which the operating variab les should be maintained to guarantee feasible and profitable operation of the process is presented. The problem is formulated as a multiscenario dyna mic optimization problem, and an efficient hierarchical solution procedure is presented. Finally, the applicability of the procedure is demonstrated b y using two example problems.