Optimal design of protein production plants with time and size factor process models

In this work we propose an optimization model for the design of a biotechno logical multiproduct batch plant. A first level of detail posynomial model is constructed for each unit, as well as decisions regarding the structural optimization of the plant. A particular feature of this model is that it c ontains composite units in which semicontinuous items operate on the materi al contained by batch items. This occurs in the purification steps, in part icular with the microfilters operating between retentate and permeate vesse ls, and with the homogenizer and ultrafilters operating on the material con tained in a batch holding vessel. Also, the unit models rely on batch opera ting time expressions that depend on both the batch size and the size of se micontinuous items. The model takes into account all of the available optio ns to increase the efficiency of the batch plant design: unit duplication i n-phase and out-of-phase and intermediate storage tanks. The resulting math ematical model for the minimization of the plant capital cost is a mixed in teger non-linear program (MINLP), which is solved to global optimality with an implementation of the outer approximation/equality relaxation/ augmente d penalty (OA/ER/AP) method. A plant that produces four recombinant protein s in eight processing stages is used to illustrate the proposed approach. A n interesting feature of this example is that it represents an attempt to s tandardize a plant for the production of both therapeutic and nontherapeuti c proteins; the model applied is generic and can thus be applied to any suc h modular plant. Results indicate that the best solution in terms of minima l capital cost contains no units in parallel and with intermediate storage tank allocation.