Tubular reactor, static mixe

Tubular Plug Flow Reaction. When the application is a laminar flow tubular reactor, static mixing internals can provide great benefits in terms of... 

Tubular reactors are also used to carry out some multiphase reactions. Wamecke et al. (1999) reported use of a computational flow model to simulate an industrial tubular reactor carrying out a gas-liquid reaction (propylene oxide manufacturing process). In this process, liquid is a dispersed phase and gas is a continuous phase. The two-fluid model discussed earlier may be used to carry out simulations of gas-liquid flow through a tubular reactor. Warnecke et al. (1999) applied such a model to evaluate the influence of bends etc. on flow distribution and reactor performance. The model may be used to evolve better reactor configurations. In many tubular reactors, static mixers are employed to enhance mixing and other transport processes. Computational flow models can also make significant contributions to understanding the role of static mixers and for their optimization. Visser et al. (1999) reported CFD... 

To improve the mixing quality in the tubular reactor, Kenics type in-line static mixer reactor was employed. The in-line static mixers were designed to mix two or more fluids efficiently since an improved treinsport process such as flow division, radial eddying, flow constriction, and shear reversal eliminated the gradients in concentration, velocity and temperature. However, only 70 % conversion was achieved with one Kenics mixer unit. As shown in Table 2, five mixer units were required to achieve the maximum conversion. 

Tubular reactors can be used for multiphase reactions, as discussed in the previous section. However, it is often difficult to achieve good mixing between phases, unless static mixer tube inserts are used. 

Continuous reactors, including simple plug-flow pipe reactors, tubular reactors containing static or other mixing devices, and jet reactors of various types, have been used to efficiently produce toxic materials for immediate consumption in downstream processing operations with little or no inventory. Some examples follow. 

Mixing in static mixers considered as chemical reactors was essentially studied by Nauman (165, 166). This author proposed a model which consists of a tubular reactor comprising N zones in laminar flow (parabolic velocity profile). Mixing between each zone is achieved accross a plane by a permutation of the radial position of fluid particles (r — , in this way the flowrate... 

In the history of PU, some continuous processes for polyether polyol synthesis by anionic polymerisation were developed, but only at small scale (i.e., pilot plant). Tubular reactors with static mixing systems or a column with plate reactor types were used, but these technologies were not extended to industrial scale levels. The first continuous process for high MW polyether synthesis was developed by Bayer (IMPACT Technology) and is based on the very rapid coordinative polymerisation of alkylene oxides, especially PO, with dimetallic catalysts (DMC catalysts - see Chapter 5). A principle technological scheme of a polyether polyol fabrication plant is presented in Figure 4.30. 

As mentioned above, radial mixing is crucial to get narrow RTD. Therefore, the use of passive mixer helps equalizing the radial concentration in the laminar flow domain. It is known that static mixer allows to obtain narrow RTD in tubular reactors even with high viscous media [18]. The beneflcial effect of radial mixing can also be expected in microstructured mixers. Boskovic et al. [19,... 

Kenics-type static mixers have been used as inserts in tubular reactors. Compared to an open tube operated at the same pressure drop, the static mixer gives about 40% more heat transfer. Stand-alone mixer reactors of the Koch or Sultzer SMR type have been used as post-reactors and devolatilization preheaters. The polymer flows through the shell side of the SMR and the heat transfer fluid flows inside tubes that have been strategically placed to promote radial mixing of the polymer. One bulk polystyrene process used the SMR as in a recycle loop as the first reactor, but the capital cost is high compared to alternatives such as a boiling CSTR or a proprietary stirred-tube reactor. 

The tubular reactor with static mixers was chosen for the documented capability of static mixers to accomphsh the following important functions for fast multiple reactions in turbulent flow (1) homogeneity down to the molecular level can be achieved in a few tube diameters (2) very short mixing time and narrow residence time distributions are required and (3) high rates of energy dissipation are achievable (average energy dissipation rates can be calculated from pressure drop and local rates can be estimated). 

The cooling capability of static mixers under conditions of extremely rapid heat generation is very low, leading to solvent evaporation in the mixing elements. This two-phase flow reduced the residence time further. The tubular reactor with static mixing elements discharged into a stirred tank, where evaporation and condensation removed the heat. 

Commercial scale tubular plug flow reactors utilizing SMX and SMXL static mixer internals have now been operating for more than 20 years. These static mixer designs have demonstrated their ability to mix and achieve plug flow in large scale equipment. The residence time distribution and shear stress-temperature history are very uniform. The Bodenstein number (also sometimes known... 

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