Flow characterization methods, reactive

Flow characterization methods, reactive intermediates, 46 156-164 Fluorescence, 19 68, 46 156 emission spectrum, Holobacfer, 36 420, 422 microscopy, autotrophic organisms, 36 118-119... 

Reaction rate, 46 101-102 Reactions, see specific types Reactive intermediates, 46 101-107, 164 flow characterization methods, 46 156-164 gas-phase studies, 46 107-121 lifetimes, 46 106... 

In the reverse direction, a proton may be effective by aiding ring-opening directly or via a reactive protonated species. It may intervene with the ring-opened species. A splendid example of these effects is shown in the acid hydrolysis of ferrioxamine B (9). Four stages can be separated and the kinetics and equilibria have been characterized by stopped-flow and rapid-scan spectral methods. 

The algorithm consists of the judicious application of one of two integration formulas to each equation in the system and the choice of formula is based on the time constant for each equation evaluated at the beginning of each chemical time step. Species with time constants too small are treated by the stiff method and the remaining species are treated by a classical second order method. The algorithm is characterized by a high degree of stability, moderate accuracy and low overhead which are very desirable features when applied to reactive flow calculations. 

In reactive flow analysis the Pick s law for binary systems (2.285) is frequently used as an extremely simple attempt to approximate the multicomponent molecular mass fluxes. This method is based on the hypothesis that the pseudo-binary mass flux approximations are fairly accurate for solute gas species in the particular cases when one of the species in the gas is in excess and acts as a solvent. However, this approach is generally not recommend-able for chemical reactor analysis because reactive mixtures are normally not sufficiently dilute. Nevertheless, many industrial reactor systems can be characterized as convection dominated reactive flows thus the Pickian diffusion model predictions might still look acceptable at first, but this interpretation is usually false because in reality the diffusive fluxes are then neglectable compared to the convective fluxes. 

In addition to these complications, Moad (1999) notes that, for typical reactive modifications, the amount of modification can be quite small (0.5-2 mol%) and therefore very difficult to characterize. However, Moad (1999) does suggest some techniques such as chemical methods, FT-IR, NMR and DSC that may be useful to aid characterization. Janssen (1998) also notes complications of thermal, hydrodynamic and chemical instabilities that can occur in reactive extrusion that must be addressed by combining knowledge of the chemistry and of the physics (flow behaviour, mixing) of the reactive extrusion process. Xanthos (1992) presents the importance of understanding both the chemistry and the reaction engineering fundamentals of reactive extrusion, in order better to understand and model the process in practice. 

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