Reactors for Catalytic Gas-Phase Reactions

An easy way to design catalytic MSR consists of introducing the catalytic active phase within the microchannels in the form of powders creating a micro packed bed. Besides randomly packed beds, the use of structured catalysts is proposed and typical examples are presented here. 

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Sloot, H. 1991. A non-permselective membrane reactor for catalytic gas phase reactions. Thesis, University of Twcntc, Enschede. 

Slool, H J., 1991, A Nonpcrmsclcciivc Membrane Reactor for Catalytic Gas-Phase Reactions, PhD. dissertation, Twenic Univ. of Technol., Netherlands. 

Sample integrations similar to pharmaceutical approaches were already examined in 1997 [39]. Here, a chip-like microsystem was integrated into a laboratory automaton that was equipped with a miniaturized micro-titer plate. Microstructures were introduced later [40] for catalytic gas-phase reactions. The authors also demonstrated [41] the rapid screening of reaction conditions on a chip-like reactor for two immiscible liquids on a silicon wafer (Fig. 4.8). Process conditions, like residence time and temperature profile, were adjustable. A third reactant could be added to enable a two-step reaction as well as a heat transfer fluid which was used as a mean to quench the products. 

Some of these criteria help to explain the greater success of chromatographic reactors over adsorptive reactors for the gas phase reactions described here. They also point to a niche (if somewhat trivial) application of adsorptive reactors in end-of-pipe environmental processes, in which low concentrations of a gas-borne pollutant are adsorbed from waste gas over a long period before being destroyed by catalytic oxidation in a high-temperature regeneration step utilizing the heat liberated by combustion by means of a gas recycle. 

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 7. Schematic representation of a membrane reactor for rapid gas-phase catalytic reactions (adapted from Ref. 64).

The attrition of solid particles is an unavoidable consequence of the intensive solids motion resulting from the presence of bubbles in the fluidized bed. The attrition problem is especially critical in processes where the bed material needs to remain unaltered for the longest possible time, as in fluidized-bed reactors for heterogeneous catalytic gas-phase reactions. Catalyst attrition is important in the economics of such processes and may even become the critical factor. 

In this section the industrial uses of fluidized-bed reactors for heterogeneous catalytic gas-phase reactions and the polymerization of alkenes are presented. The most important applications are listed and a few typical examples are analyzed in more detail. Complete descriptions of industrial uses of the fluidized-bed reactor can also be found in Refs 2, 6, 12 and 13. 

The fluidized-bed reactor offers the following principal advantages over the fixed-bed reactor for heterogeneous catalytic gas-phase reactions ... 

Zwahlen A. G., Agnew J. Modification of an Internal Recycle Reactor of the Berty Type for Low-Pressure High Temperature Catalytic Gas-Phase Reaction CHEMECA 1987, I, 50.1-50.7, Melbourne, Australia. 

Example 7.4 Design a packed-bed reactor for the gas-phase, heterogeneous catalytic cracking reaction... 

Ktifner, R. and Hofmann, H., 1990. Implementation of Radial Porosity and Velocity Distribution in a Reactor Model for Heterogeneous Catalytic Gas-Phase Reactions (Torus-Model). Chemical Engineering Science, 45(8) 2141-2146. 

Tubular reactors with both axial and radial temperature gradients In many exothermic processes the reactor temperature has to be controlled within much narrower limits. This is particularly true for many catalytic gas phase reactions. The reasons are usu y that undesired side reactions have to be avoided, or that the catalyst has to be protected against sintering. There are two reactor types for solid/gas-reactions that make good temperature control possible ... 

Giitlhuber, F. (2002). Reactor Arrangement for Carrying Out Catalytic Gas Phase Reactions, Especially to Obtain Phthalic Anhydride, W02003022418, issued in Germany. 

Recent research development of hydrodynamics and heat and mass transfer in inverse and circulating three-phase fluidized beds for waste water treatment is summarized. The three-phase (gas-liquid-solid) fluidized bed can be utilized for catalytic and photo-catalytic gas-liquid reactions such as chemical, biochemical, biofilm and electrode reactions. For the more effective treatment of wastewater, recently, new processing modes such as the inverse and circulation fluidization have been developed and adopted to circumvent the conventional three-phase fluidized bed reactors [1-6]. 

Basket-type reactor (CSTR) for gas-phase reactions) High temperature, high pressure catalytic processes High transport rates, easy variation of parameters Limited particle size, high equipment cost, difficult to operate under a wide range of conditions without creating flow maldistribution... 

Single-phase catalytic fixed bed reactors are the main reactor type used for large-scale heterogeneously catalyzed gas-phase reactions. Frequently, multitubular... 

In a fixed-bed catalytic reactor for a fluid-solid reaction, the solid catalyst is present as a bed of relatively small individual particles, randomly oriented and fixed in position. The fluid moves by convective flow through the spaces between the particles. There may also be diffusive flow or transport within the particles, as described in Chapter 8. The relevant kinetics of such reactions are treated in Section 8.5. The fluid may be either a gas or liquid, but we concentrate primarily on catalyzed gas-phase reactions, more common in this situation. We also focus on steady-state operation, thus ignoring any implications of catalyst deactivation with time (Section 8.6). The importance of fixed-bed catalytic reactors can be appreciated from their use in the manufacture of such large-tonnage products as sulfuric acid, ammonia, and methanol (see Figures 1.4,11.5, and 11.6, respectively). 

Various types of reactor configuration may be employed to effect non-catalytic gas—solid reactions. Events occurring during such reactions (see Sect. 5) are complex and industrial equipment for particular applications has evolved with operating experience rather than as a result of analytical design. Those factors which influence the course of the reaction are the reaction kinetics (as observed for a single particle), the size distribution of the solid reactant feed and the flow pattern of both solid and gas phases through the reactor. An excellent account of gas—solid reactions and... 

Catalytic test. The catalytic behavior was evaluated for the gas phase isobutene trimerization reaction using a fixed bed reactor, with dimensions of 2 cm of diameter and 55 cm of length respectively. The operation conditions and evaluation procedure were as follows the catalyst was activated at 400°C in flowing air (1 ml/s) during 8 hours. After the activation treatment, temperature was lowered to 40°C and a mixture of isobutane/isobutene 72 28 w/w was feed. The GHSV value was varied to 8, 16, 32 and 64 h respectively. The average time of reaction was 11 h. The time of reactor stabilization after the beginning of the catalytic evaluation was 2 h. 

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