Flow tube reactor

The microscopic understanding of tire chemical reactivity of surfaces is of fundamental interest in chemical physics and important for heterogeneous catalysis. Cluster science provides a new approach for tire study of tire microscopic mechanisms of surface chemical reactivity [48]. Surfaces of small clusters possess a very rich variation of chemisoriDtion sites and are ideal models for bulk surfaces. Chemical reactivity of many transition-metal clusters has been investigated [49]. Transition-metal clusters are produced using laser vaporization, and tire chemical reactivity studies are carried out typically in a flow tube reactor in which tire clusters interact witli a reactant gas at a given temperature and pressure for a fixed period of time. Reaction products are measured at various pressures or temperatures and reaction rates are derived. It has been found tliat tire reactivity of small transition-metal clusters witli simple molecules such as H2 and NH can vary dramatically witli cluster size and stmcture [48, 49, M and 52]. 

This class of hybrid components comprises chip micro-reactor devices, as described in Section 4.1.3, connected to conventional tubing. This may be H PLC tubing which sometimes has as small internals as micro channels themselves. The main function of the tubing is to provide longer residence times. Sometimes, flow through the tube produces characteristic flow patterns such as in slug-flow tube reactors. Chip-tube micro reactors are typical examples of multi-scale architecture (assembly of components of hybrid origin). 

Figure 28. (a) Mass spectrum of protonated water clusters H+(H20) (n = 4-45) at 119 K and 0.3 torr He in a flow tube reactor. Note the prominence of H3O+(H2O>20 even under quasi-equilibrium conditions, (b) Mass-spectrometric abundance of OH-(H20)n produced under thermal conditions. Note a magic number at n = 20, though not as prominent as for the case of H30+ hydrates. Taken with permission from ref. 92. 

There are several preparative methods for the production of bare metal clusters including the fast flow reactor (PER), the fast flow tube reactor (FTR), the SIDT (24), the GIB (23), and a supersonic cluster beam source (SCBS) (198). Essentially, all of these methods are similar. The first process is to vaporize the metal sample producing atoms, clusters, and ions. Laser vaporization is generally favored although FAB or FIB may be used. The sample is located in a chamber or a tube and so vaporization generally takes place in a confined environment. An inert gas such as helium may be present in the vaporization source or may be pulsed in after the ionization process. 

Many of the metal cluster anions have been produced by cathode discharge in He doped with Ar and studied in a flow tube reactor. A few clusters have been prepared by laser vaporization using a supersonic cluster beam source and the reac-... 

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. 

The experimental setup and procedures used in this study was described previously in more detail.Briefly, all experiments were carried out in a flow tube reactor... 

Table 4.1 Characteristic behavior of flow tube reactor...

Method 2 use a continuous-flow tube reactor for ozonation to achieve efficiencies and products similar to batch ozonation. 

Method 2 basically addresses the same advantages as Method 1, with the additional consideration that the same favorable reaction rates found in batch ozonation systems can be achieved in a continuous-flow tube reactor (Sunder and Hempel, 1996 Levenspiel, 1972). More work is necessary to see how effective such reactors are for higher loaded (waste) waters, where gaseous ozone must be continuously dosed. 

Wall-coated flow tube reactors have been used to study the uptake coefficients onto liquid and solid surfaces. This method is sensitive over a wide range of y (10" to 10 1). For liquids this method has the advantage that the liquid surface is constantly renewed, however if the uptake rate is fast, the liquid phase becomes saturated with the species and the process is limited by diffusion within the liquid, so that corrections must be applied [70,72,74]. Many experiments were designed to investigate the interaction of atmospheric species on solid surfaces. In this case the walls of the flow tube were cooled and thin films of substrate material were frozen on the wall. Most of the reaction probabilities were obtained from studies on flow tubes coated with water-ice, NAT or frozen sulfate. Droplet train flow tube reactors have used where liquid droplets are generated by means of a vibrating orifice [75]. The uptake of gaseous species in contact with these droplets has been measured by tunable diode laser spectroscopy [41]. 

Keyser, L.F., Moore, S.B., and Leu, M.-T. (1991) Surface reaction and pore diffusion in flow-tube reactors, J. Phys. Chem. 95,5496-5502. 

Cooking extruders have been studied for the liquefaction of starch, but the high temperature inactivation of the enzymes in the extruder demands doses 5—10 times higher than under conditions in a jet cooker (69). For example, continuous nonpressure cooking of wheat for the production of ethanol is carried out at 85°C in two continuous stirred tank reactors (CSTR) connected in series plug-flow tube reactors may be included if only one CSTR is used (70). 

The lowest resistivity silicide film of the four we are considering is the TiSi2 film, so such films have always been of interest. A recent study14 has shown that these films can also be deposited by low-pressure CVD. For these experiments, a cold-wall reactor similar to the parallel-flow tube reactor sketched in Figure 17 of Chapter 1 was used. The wafer was heated by heating the susceptor from below by optical radiation. 

Figure 4.2 The micro-Flow Tube Reactor/Mass Spectrometer instrument. 1 — heated gas inlet/vacuum feedthrough, 2 — hot zone of flow tube, 3 — multiion source block, 4 — ion guide, 5 — quadrupole mass spectrometer, 6 — ion guides, 7 — reaction cell, 8 — quadrupole mass spectrometer, 9 — daly detector...

In another paper, Clyne and Coxon examined the reaction of oxygen atoms with CI2 in their flow tube reactor. The reaction was studied at 1-2 torr total pres-... 

Fig. 14. Flow tube reactor used to study NCl(a) formation and removal kinetics. Note that this apparatus has a two stage prereactor. The first stage is used to generate Cl atoms from F + HCl. The second stage (the first 40 cm of the main reactor tube) is used to generate N3 from the F + HN3 reaction. The inlet for ethane or H2S near the observation window is used for calibration of F or Cl atom concentrations. Reproduced with permission from Ref. 124.

Fickert et al. (1999) examined the production of Br2 and BrCl from the uptake of HOBr onto aqueous salt solutions in a wetted-wall flow tube reactor. The yield of Br2 and BrCl was found to depend on the Cl to Br ratio, with more than 90% yield of Br2 when [Cl ]/[Br ] (in molL ) was less than 1,000. With increasing [Cl ]/[Br ] BrCl was the main product (see Figure 2). They also found a pH dependence of the outgassing of Br2 and BrCl with greater release rates at lower pH. 

Flow systems in use may be classified as heated laminar tubes, or plug flow tube reactors, (PFTR) and burners, or heated turbulent flow reactors and well-stirred reactors, or continuous stirred-tank reactors, (CSTR). 

The decomposition of R3Sb compounds (R = Me, vinyl, isopropyl) in a flow tube reactor has been studied using D2 and He as carrier gases to obtain the deuterium-labelled byproducts and to elucidate the mechanism of the pyrolysis . 

Fig. 1.27. Schematics of the PACIS with flow tube reactor attached to the source nozzle, (a) magnetic valve for buffer gas (He), (b) Macor insulator, (c) electrodes (the cluster material is contained in the cathode), (d) cooling coil, (e) nozzle, (f) source holder, (g) flow tube reactor, (h) reaction gas inlet, (i) pumping chaimels...

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