Optimal product distribution from laminar flow reactors: Newtonian and other power-law fluids

In tubular reactors viscous fluids are in laminar flow. For reactions in se ries this gives a product distribution different from either plug flow or m ixed flow. More importantly, laminar flow depresses the maximum amount of i ntermediate that can be obtained when compared to plug flow. Here we treat the simple case of an elementary two-step mechanism: [A --> R --> S] (1) Three special cases of the velocity profile in a tubular reactor are tr eated: uniform velocity for a plug flow reactor (PFR), parabolic velocity f or a Newtonian flow reactor (NFR) and a conical velocity profile for am ext reme power-law flow reactor (EPFR). The limit of complete mixing in a mixed flow reactor (MFR) is also included in comparisons. We present design char ts which show quantitatively how the rate constant ratio affects the produc t distribution, and we compare the maximum possible amount of intermediate obtainable from reactors whose flow patterns can be characterized by the fo ur models above. These results are important because they allow an evaluati on of the detrimental effects when the ideal plug flow assumption for tubul ar reactors is inappropriate and a convective model more accurately describ es the situation. The entire range of power-law fluid behavior is represent ed on these plots and we clearly show that even the worst flow pattern whic h arises is still much preferable to mixed flow. (C) 1999 Elsevier Science Ltd. All rights reserved.