BACKGROUND: In this work the possibility of using membrane cascades to carry out difficult pharmaceutical separations was explored. The effect of configuration on process yield, time and cost was studied for a challenging industrial separation: the separation of an intermediate I (MW 221 g mol(-1)) from an impurity, ethylene bromide (MW 188 g mol(-1)). RESULTS: All cascade configurations studied were capable of increasing the purity from a fairly low value, namely 26% to the 90% requirement. The results from the cascade modeling showed that the product yield effectively increased from 35.5% to 84.3% by adding two stages. From a cost analysis of a kilo scale plant it was derived that a two-stage cascade with large area modules yielded the smallest total cost of (sic) 515 082. A 7.0% decrease in cost of product loss or a 7.6% increase in membrane skid cost rendered a single stage economically optimal despite the low product yields. However, if at least six other separations with a comparable process time are carried out each year, then even three stages become economically optimal. CONCLUSION: High resolution separations are technically feasible with membrane cascades. The economic viability of membrane cascades increases dramatically with the cost of the product and the utilization of the equipment. (C) 2012 Society of Chemical Industry