Contacting principles

Instruments based on the contact principle can further be divided into two classes mechanical thermometers and electrical thermometers. Mechanical thermometers are based on the thermal expansion of a gas, a liquid, or a solid material. They are simple, robust, and do not normally require power to operate. Electrical resistance thermometers utilize the connection between the electrical resistance and the sensor temperature. Thermocouples are based on the phenomenon, where a temperature-dependent voltage is created in a circuit of two different metals. Semiconductor thermometers have a diode or transistor probe, or a more advanced integrated circuit, where the voltage of the semiconductor junctions is temperature dependent. All electrical meters are easy to incorporate with modern data acquisition systems. A summary of contact thermometer properties is shown in Table 12.3. 

The disadvantage of the two-phase contacting principle is related to the technical expenditure of realizing phase separation throughout the complete reactor passage. Special measures have to be taken to prevent phase inter-mixing. Also, this has to be controlled during the process. Hence inspection windows are essential (for the first prototype they may be eliminated later). 

Figure 8.2 depicts the four main zones and their immediate proximity to each other in the Molex process. As indicated earlier, the Sorbex process operates on a liquid-solid countercurrent contacting principle. Zone 1 is referred to as the... 

Contacting Principles and Microreactors 4.4.2.1 Contacting with Continuous Phases... 

For a suitable density tolerance Aa, a simple contact principle (66) can be used for accepting and rejecting nuclear configurations from the family R ... 

V. Hessel, P. Angeli, A. Gavriilidis, H. Lowe, Gas-Liquid and Gas-Liquid-Solid Micro-structured Reactors Contacting Principles and Applications, Ind. Eng. Chem. Res. 44 (2005) 9750. 

Hessel, V., Angeli, P., Gavriilidis, A., Lowe, H. (2005). Gas-liquid and gas-liquid-solid microstructured reactors Contacting principles and applications. Industrial and Engineering Chemistry Research, 44, 9750-9769. 

Lowe, H. (2005) Gas-liquid and gas-liquid-solid microstructured reactors contacting principles and applica- 50-... 

Microstructured devices for fluid-fluid systems exist in a number of configurations. They can be roughly classified into three types based on the contacting principles [ 1] micromixer, microchannels, and falling film microreactors. The first two types of devices are used for all fluid-fluid applications while the microstructured falling film reactor is used only for gas-liquid systems. Depending on the application, these microstructured devices can also be used in series, for example. 

Different types of gas-hquid-solid microstructured reactors (MSR) have been developed, using different gas-liquid contacting principles [4]. These principles can be classified as... 

V. HesseL P. Angeh, A. Gavriilidis, H. Lowe, Gas-4iquid and gas-4iquid-sohd microstructured reactors contacting principles and appUcations. Industrial and En neering Chemistry Research, 2005, 44, 9750-9769. 

Reactor R2 is also based on the film contacting principle. It depicts two cavities of ca. 100 pL separated by a nickel mesh with openings of 3-5 pm. The total gas-liquid interface is thus ca. 2000 m In contrast to Rl, the liquid film is not gravity but... 

Of course, not all multiphase microstructured reactors are presented in Table 9.1. Either because they have attracted (too ) little interest, because they may have been qualified as microreactors in spite of their overall size but caimot be considered as microstmctured , or because they combine several contacting principles. Examples are a reactor developed by Jensen s group featuring a chaimel equipped with posts or pillars, thus resembling more a packed bed but with a wall-coated layer of catalyst [20], and a string catalytic reactor proposed by Kiwi-Minsker and Renken [21], that may applied to multiphase reactions. 

This section starts with a classification of phase-contacting principles according to the type of catalytic bed. Advantages and disadvantages of the reactor types are explained, followed by a discussion of criteria for reactor selection and an overview of purchasable microreactors for catalytic gas-phase reactions. 

Figure 3.4 Schematic view of the phase-contacting principles including the main advantages and disadvantages.

Several methods for the incorporation of catalysts into microreactors exist, which differ in the phase-contacting principle. The easiest way is to fill in the catalyst and create a packed-bed microreactor. If catalytic bed or catalytic wall microreactors are used, several techniques for catalyst deposition are possible. These techniques are divided into the following parts. For catalysts based on oxide supports, pretreatment of the substrate by anodic or thermal oxidation [93, 94] and chemical treatment is necessary. Subsequently, coating methods based on a Uquid phase such as a suspension, sol-gel [95], hybrid techniques between suspension and sol-gel [96], impregnation and electrochemical deposition methods can be used for catalyst deposition [97], in addition to chemical or physical vapor deposition [98] and flame spray deposition techniques [99]. A further method is the synthesis of zeoUtes on microstructures [100, 101]. Catalysts based on a carbon support can be deposited either on ceramic or on metallic surfaces, whereas carbon supports on metals have been little investigated so far [102]. 

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