Three Phase Systems

Three Phase Systems: Methanol Synthesis

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The reaction kinetics of three phase systems are usually determined with superimposed hydrodynamics. In recent years, it has been possible to develop reinforced microapparatuses with fixed beds or applied catalyst films. These have made it possible to study the reaction kinetics under well-defined hydrodynamic conditions.

The goal is to establish a coupling of reaction networks with computational fluid dynamics. First couplings of the hydrodynamics of a three-phase system have been established and first successes with respect to the description of the reaction turnover have been achieved. In order to improve the models, fundamental investigations of the hydrodynamics must be carried out in the future, since, for example, to date there is no adequate model for the single bubble rise in suspensions. Similarly, it is known that large particles can lead to bubble rupture, while small particles can lead to bubble coalescence. A general understanding of the different size ranges as well as material properties does not exist.

Current measurement techniques (needle sondes as well as optical probe measurement techniques developed at the chair to measure the bubble size), particle image velocimetry, phase Doppler anemometer as well as electrical resistivity tomography to determine the hydrodynamics, high-speed cameras, and most recently a high-speed light field camera to detect the three-dimensional flow field are used. This work is to be expanded in the future, but also different catalysts are to be investigated more specifically in cooperation.

Catalysts Under Dynamic Conditions

While catalysts can be characterized offline very well with current measurement technology, a gap has arisen to date in the description of dynamic influences on catalyst behavior and reaction conversion. Dynamic fluctuations of the feed flow in terms of volume flow and composition change the spatial catalyst distribution in the apparatus and thus the reactions that take place. Especially when switching from conventional feedstocks to biobased feedstocks with fluctuating quality, the limits for dynamic operation have to be extended.

 

A rough classification of the problems can be made as follows:

  1. Catalyst interaction with the surrounding hydrodynamics.
  2. Catalyst accumulation on bubbles/droplets.
  3. Catalyst behavior under changing operating conditions (feed composition, distribution in the reactor, etc.).
  4. Aging of the catalyst.

An approach of microapparatuses allows a partial decoupling of the complex hydrodynamics from the kinetics and a solution of the 1st problem. In general, microapparatuses allow chemical reactions to be carried out with small volumes, good heat transport and high defined mixing and residence time rates. Characterization of residence time, pressure drop and heat transport based on simple correlations is possible due to the well-defined conditions.In addition, microreactors allow investigation of catalyst performance under well-controlled conditions.