Multiple-tube reactors

The limitation to the size of the reactor with light conductors is the UV transparency of fhe maferial and the light distribution to the catalyst particle. The critical and probably the most intricate factor is the distribution of fhe available lighf in fhe conductors to the catalyst particles and to ensure that each particle receives at least the minimum amoimt of light necessary 

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Multiple tube reactor, tube light reactor TiOj-UV-A Laboratory Mukherjee and Ray (1999)... 

During the development of this new concept of photocatalytic reactor based on multiple hollow tubes [multiple tube reactor (MTR)], we developed a unique new lamp design. These are extremely narrow diameter fluorescent tube lamps of low wattage emitting lights in the wavelength of our interest (A<365nm). These new lamps address many of the solutions to the... 

Figure 10 Schematic diagram of multiple tube reactor (MTR) (Ray, 1999).

Tube light reactor Multiple-tube reactor Rotating tube raector... 

In typical fixed photocatalytic reactors, the photocatalyst can be coated or anchored on the reactor walls around the light source casing or attached to a solid matrix. Since Ti02 is not present in the water or air streams at any time, these reactors have the intrinsic advantage of not requiring a catalyst recovery operation. Relevant examples of this type of reactor are the coated fiber optic cable reactor and the multiple tube reactor (Peill and Hoffmann, 1995, 1996, 1997, 1998, Ray and Beenackers, 1998a). 

FIGURE 2.5. Schematic representation of a multiple tube reactor (Reprinted from Catal. Today, 40(1), A.K. Ray and A. Beenackers, Development of a New Photocatalytic Reactor for water purification, 73-83, Copyright 1998, with pemiission from Elsevier). 

In order to control heat removal and therefore the catalyst temperature, multiple-tube reactors (Lurgi process) or quench reactors with several catalyst layers and introduction of cold gas (ICI process) are mainly used. Catalyst performance in modern larger reactors is 1.3-1.5 kg of methanol per liter per hour, and large-scale plants have capacities of up to 10 fra, which reflects the position of methanol as a key product of Ci chemistry. 

Fig. 22. Schematics of chemical vapor deposition epitaxial reactors (a) horizontal reactor, (b) vertical pedestal reactor, (c) multisubstrate rotating disk reactor, (d) barrel reactor, (e) pancake reactor, and multiple wafer-in-tube reactor (38).

Exothermic processes, with cooling through heat transfer surfaces or cold shots. In use are sheU-and-tube reactors with smaU-diameter tubes, or towers with internal recirculation of gases, or multiple stages with intercoohng. Chlorination of methane and other hydrocarbons results in a mixture of products whose relative amounts... 

The chemical reactivity of cobalt cluster anions, Co (n = 2-8), toward 02, N2, and CO have been investigated using a flow tube reactor (226). The reactivity was found to be in the order 02 > CO > N2 the least reactive ligand N2 only reacted with C07 and Cog. The primary reaction of oxygen was the removal of one or two cobalt atoms from the cluster. Carbon monoxide reacts by multiple additions giving saturation limits shown in Table V. 

It is important to attain as high an area as possible for a membrane reactor. Configurations with multilayer planar membranes, coiled membranes, or as multiple tubes also can be used for similar processes with potentially very high surface areas, as sketched in Figure 12-6. 

A further improvement was the development of the reactor type unit using multiple tube-and-shell reactors for better temperature control (25). This type of reactor proved useful in larger installations and for selective polymerization of either C3 or C4 olefins only. The larger reactor type units are so arranged that the steam produced in the reactor shell by the exothermic reaction is used to preheat the feed to the proper inlet temperature. The tubes usually are from 2 to 6 inches in diameter. 

There is also a wider variety of reactor and system types for tubular reactors. Many operate adiabatically, while others are heated or cooled. Multiple tubular reactors in series with intermediate heating or cooling are quite common. The most common industrial use of tubular reactors is in systems where a solid catalyst is required. The catalyst is installed in beds or inside tubes in the shell of the reactor vessel, and the process reacting fluid (gas or liquid) flows through the fixed catalyst. 

The packed bed reactor is used to contact fluids with solids. It is one of the most widely used industrial reactors and may or may not be catalytic. The bed is usually a column with the actual dimensions influenced by temperature and pressure drop in addition to the reaction kinetics. Heat limitations may require a small diameter tube, in which case total through-put requirements are maintained by the use of multiple tubes. This reduces the effect of hot spots in the reactor. For catalytic packed beds, regeneration is a problem for continuous operation. If a catalyst with a short life is required, then shifting between two columns may be necessary to maintain continuous operation. 

Chemical reactors basically come in the form of tanks, such as for batch reactors or back-mix flow reactors, large cylinders, such as for fluidized-bed or plug-flow reactors, or multiple tubes inside a cylindrical container, such as for plug-flow reactors when special needs exist for temperature control. High pressure and extremes of temperature as well as corrosive action of the materials involved can introduce complications in the design which must be handled by the design engineer. 

In the following we present a detailed model of the commercial, multiple-wafer-in-tube reactor illustrated in Figure 2. We have selected the LPCVD as an example because of its central role in the microelectronics industry and because it nicely demonstrates the analogies to heterogeneous catalytic reactors, in particular the fixed bed reactor. 

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