Reactor concepts

The chemical looping concept can be accomplished with two main configurations in the first configuration, the solid material is circulating between the fuel reactor and the air reactor, while in the second case the solid material is stationary and the gases are alternatively fed to the reactor by using a gas switching system. 

Most of the research about chemical looping has been focused on the first configuration, and different reactor concepts have been developed in recent years to make the process feasible as discussed in Ref. [33]. The utilization of solid fuel has been also investigated in recent years and some pilot plants based on interconnected fluidized beds have been built at different sizes [34]. The chemical looping combustor units have been built at different sizes and tested with several OCs. In the second case, the research is at the early stage. 

When using conventional homogeneous Lewis or Br0nsted acidic catalysts only liquid-phase reactions are applicable. With heterogeneous catalysts gas-phase reactions, which are readily performed continuously, can also be realized. The product is readily separated from the catalyst and higher efficiency is usually achieved (space-time yield). The rearrangement of styrene oxides in the gas phase described later in this section [8,15,16] is an example of the improvement of yields by changing the reactor concept from liquid- to gas-phase. 

In general, the ease of conducting a reaction continuously in the gas phase must be paid for in terms of increasing costs of energy and plant construction continuous gas-phase reactions are usually economic only for production of more than several tons per year. For smaller volumes production in multipurpose liquid phase batch reactors is more economical. 

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The differential reactor is the second from the left. To the right, various ways are shown to prepare feed for the differential reactor. These feeding methods finally lead to the recycle reactor concept. A basic misunderstanding about the differential reactor is widespread. This is the belief that a differential reactor is a short reactor fed with various large quantities of feed to generate various small conversions. In reality, such a system is a short integral reactor used to extrapolate to initial rates. This method is similar to that used in batch reactor experiments to estimate... 

A variety of graphite moderated reactor concepts have evolved since the first aircooled reactors of the 1940s. Reactors with gas, water, and molten salt coolants have been constructed and a variety of fuels, and fissile/fertile fuel mixtures, have been used. The evolution and essential features of graphite moderated power producing reactors are described here, and details of their graphites cores are given. 

The Magnox reactor concept owes its origins to a design study conducted at Harwell, U.K., diuing the early 1950s. The reactor was designed with the dual role of plutonium and power production, and was known by the code word PIPPA... 

The selectivity of the catalyst is of major importance in the case of chlorinated VOCs the oxidation products should not contain even more harmful compounds than the parent-molecule, for example, formation of dioxins should be avoided. In addition, the minimization of CI2 and maximization of HCl in a product gas should be achieved [61]. These are just a few examples of why researchers are continuing the search for VOC oxidation catalysts as well as new reactor concepts. The new possibilities include, for example, utilization of nanosized gold catalysts in the oxidation of sulfur-containing VOCs and microwave-assisted processes where combination of adsorption and oxidation is used in low-concentration VOC oxidation [62, 63]. 

Anxionnaz, Z., Cabassud, M., Gourdon, C., and Tochon, P. (2008) Heat ex-changer/reactors (HEX Reactors) concepts, technologies State-of-the-art. Chem. Eng. Process., 47, 2029-2050. 

A micro reactor concept proposed by MIT and DuPont on the basis of electronic circuits is the most prominent among the examples listed for the hybrid approach [19,101]. The so-called turnkey multiple micro-reactor test station relies on the use of standard components originating from the semiconductor industry for microchemical processing, the construction being oriented at the concept of printed circuit boards. 

This simple reactor concept is based on a microstructured silicon chip (Figure 3.18) covered by a Pyrex-glass plate by anodic bonding [73, 74]. The silicon microstructure comprises, in addition to inlet and outlet structures, a multi-channel array. Only the Pyrex-glass plate acts as cover and inlet and outlet streams interface the silicon chip from the rear. 

A simple, but efficient reactor concept was developed based on the insertion of metallic wires that serve as a catalyst into a micro channel. The wire extends over the channel length and can thus be contacted electrically for heating purposes. It is sealed by graphite seals at both reactor ends. In this way, an easy, flexible and cheap concept for catalyst exchange and reactor assembly is provided. 

GP 4] [R 5] Formaldehyde synthesis has been known at BASF for more than 100 years [1, 49-51,108]. Hence it was expected to be able to handle the synthesis of substituted analogue, an undisclosed methanol derivative, with the same processsing concepts, major problems not being anticipated. This expectation was still supported by first attempts with the tried and tested pan-like reactor concept (5 cm diameter), which were promising. At 50% conversion, a selectivity of 90% was achieved. However, transfer to production scale using a 3 m production reac-... 

Thepresentinvestigationswerelargelymotivatedtoshowfheserial-screeningca-pabilities ofthe reactor concept used. The speed ofprocess-parameter changes, consumption of small volumes only, preciseness ofkinetic information, and ro-bustnessweremajormicroreactorpropertiesutilized. 

In version (c), three mixing tees were realized in another version of the above-mentioned chip reactor concept [16]. 

This reactor concept is genericaUy similar to [R 4] and uses the same fabrication and assembly techniques, so the reader is referred to the corresponding description [19]. However, it has only one micro channel as it serves for transporting one liquid (or solution) only, i.e. was constructed for reactions with one reactant only such as eliminations [19]. 

The micro reactor contained a heating function (imlike [R 4] and the other versions of this reactor concept [R 5] and [R 6], decribed below) via a heating wire connected to a potentiostat [19], This wire was integrated into the micro reactor by placing it in the mold before pouring the liquid PDMS. 

One version of such a reactor concept is the combination of a slit-type in ter digital metal/steel micro mixer (for a detailed description see [R 18]) with a conventional tube. In [37], PTFE tubing was applied (Figure 4.20). 

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