Coating reactor

Figure 3.12 Residence time distribution in a micro reactor which is tightened by different means. ( ) Glued reactor without catalyst coating (X) glued reactor with catalyst coating ( ) reactor with graphite joints. Calculated curves for tubular reactors with the Bodenstein number Bo = 33 (solid line) and Bo = 70 (dashed line).

Jackson, T. and Clark, J.H. and Macquarrie, D.J. and Brophy, J. H. (2004). Base catalysts immobilised on silica coated reactor walls for use in continuous flow systems. Green Chem., 6, 193-195. 

Concern about fission-product release from coated reactor fuel particles and fission-product sorption by fallout particles has provided stimulus to understand diffusion. In a fallout program mathematics of diffusion with simple boundary conditions have been used as a basis for (1) an experimental method of determining diffusion coefficients of volatile solutes and (2) a calculational method for estimating diffusion profiles with time dependent sources and. time dependent diffusion coefficients. The latter method has been used to estimate the distribution of fission products in fallout. In a fission-product release program, a numerical model which calculates diffusion profiles in multi-coated spherical particles has been programmed, and a parametric study based on coating and kernel properties has provided an understanding of fission product release. 

Figure 35.6 shows pictures of the inner tube coating reactor. The reactor is a dual-vacuum system. The top of a sample tube is connected to the monomer feed-in system and the bottom is connected to a pumping system, which constitutes one vacuum system. The majority of the tube is rolled on a spool in the bottom section (not shown). The outside of the tube (within a quartz tube) is pumped by another pump system. The monomer flows from top to bottom, and the tube is pulled from bottom to top. In this counterflow mode, the deposition occurs on the uncoated portion of the tube. The coating thickness is controlled by the WjFM and the pulling speed, which is controlled by a surface speed control device, of the tube that determines the resident time of a section of surface in the glow. 

Figure 35.6 Inner tube coating reactor with dual vacuum systems, dye tested coated tube samples are compared with that of uncoated control T top, M middle, B bottom of Im long...

Along with the inclusion of heterogeneous metal catalysts in continuous flow reactors, numerous authors have evaluated the advantages associated with the incorporation of acid and base catalysts in these reaction systems, using a range of packed beds, monoliths, and wall-coated reactors. 

Figure 14.3 Residence time distribution in different microreactors , glued reactor without coating X, glued reactorwith coating , reactor with graphite joints. Theoretical RTD curves for tubular reactors with (solid line) Bo = 33 and (dotted line)...

Y. S. S. Wan, A. Gavriilidis, J. L. H. Chau, K. L. Yeung, 1-Pentene epoxidation has been successfully conducted in a microfabricated TS-1 coated reactor, Chem. Commun. 2002, 878-879... 

Flushing a coke-coated reactor with either helium or nitrogen for about 30 minutes was found on several occasions to acti> vate the reactor in the subsequent run. Certain hydrocarbons were desorbed during the flushing as will be discussed in more detail later. 

Fuel-rich H2/air hetero-Zhomogeneous combustion was less studied than its fuel-lean counterpart. Maestri et al. (2007, 2008) investigated fuel-rich H2Zair combustion on Rh-based catalysts at atmospheric pressure in a nearly isothermal annular reactor with channel gap of 2.1 mm. Fundamental homogeneous ignition studies were reported only recently (Schultze et al., 2013) in the Pt-coated reactor of Fig. 3.2, at pressures up to 5 bar, nonpreheated fuel-rich H2Zair mixtures, and surface temperatures 760 K< T < 1200 K. Fig. 3.10 provides comparisons between LIF-measured and -predicted OH distributions at two different pressures. Simulations were performed with the hetero-Zhomogeneous reactions schemes from Deutschmann et al. (2000) and Li et al. (2004). Raman measurements further attested a nearly transport-Umited conversion of the deficient O2 reactant, which was captured by the numerical model (Schultze et al.. 

Consumers know PTFE because it is used as a coating material in non-stick cookware. The excellent chemical resistance makes it suitable for coating reactors and piping that are exposed to aggressive chemicals. The extremely low coefficient of friction makes it usefiil for bearings and gears. Specialty bullets are coated with PTFE to reduce wear on a rifle barrel. 

Aluminum alkyls and related aluminum compounds are well-knovra catalysts for the oligomerization of ethylene. The catalytic potential is a consequence of the readiness with which a trivalent aluminum atom forms electron-deficient or so-called half, bonds. The kinetics of the homogeneous oligomerization of ethylene into 1-butene catalyzed by triethyl aluminum in the gas phase has been studied in Teflon-coated reactors at temperatures ranging between 160 and 230°C [17]. The catalyst is recovered quantitatively from the product mixture. The homogeneous reaction mechanism is summarized in the following reactions ... 

There are two main ways to incorporate the catalyst in a microreactor as a packed bed [57] or as a coating [58]. The advantage of the second method is that industrial catalysts direct in the desired sieve group can be used. Also, the accessible catalyst contents are much higher than those in catalytic wall reactors. Because of the high-pressure loss in the microchannel and a less efficient heat removal as in coated reactors, the packed-bed microreactors can play only a minor role [19]. 

To prevent wall fouling, the following approaches can be taken [63] prevent the deformation of the monomer droplet prevent the adhesion of the polymer particles to a reactor surface prevent the adsorption of monomer to a reactor surface and the polymerization either at the wall or in the aqueous solution. For example, the fouling at the reactor walls can be reduced by using glass-coated reactors, reactor internals with smooth surfaces, fouling suppressants, correct choice of initiator, buffer, and pH. A reflux condenser may be installed to aid the reactor s heat removal capacity. After polymerization, the polymer is steam-stripped to remove residual monomer... 

Classification of the many different encapsulation processes is usehil. Previous schemes employing the categories chemical or physical are unsatisfactory because many so-called chemical processes involve exclusively physical phenomena, whereas so-called physical processes can utilize chemical phenomena. An alternative approach is to classify all encapsulation processes as either Type A or Type B processes. Type A processes are defined as those in which capsule formation occurs entirely in a Hquid-filled stirred tank or tubular reactor. Emulsion and dispersion stabiUty play a key role in determining the success of such processes. Type B processes are processes in which capsule formation occurs because a coating is sprayed or deposited in some manner onto the surface of a Hquid or soHd core material dispersed in a gas phase or vacuum. This category also includes processes in which Hquid droplets containing core material are sprayed into a gas phase and subsequentiy solidified to produce microcapsules. Emulsion and dispersion stabilization can play a key role in the success of Type B processes also. 

Commercially, sulfonation is carried out by the classic method with sulfuric acid. Modem reactors are glass-lined older equipment was made from cast iron or coated with enamel Processes often use chlorosulfonic acid or sulfur trioxide to minimi2e the need of excess sulfuric acid. Improved analytical methods have contributed to the success of process optimi2ation (9—12). 

Fig. 2. Fuel for high temperature gas-cooled reactor. Fissile material is coated with carbon and siHcon carbide, fertile material with carbon. Particles mixed...

The catalyst combines two essential ingredients found in eadier catalysts, vanadium oxide and titanium dioxide, which are coated on an inert, nonporous carrier in a layer 0.02- to 2.0-mm thick (13,16). Other elements such as phosphoms are also used. Ring-shaped supports are used instead of spherical supports to give longer catalyst life, less pressure drop though the reactor, and higher yields (17,18). Half rings are even better and allow more catalyst to be loaded (18). 

Qua.driva.Ient, Zirconium tetrafluoride is prepared by fluorination of zirconium metal, but this is hampered by the low volatility of the tetrafluoride which coats the surface of the metal. An effective method is the halogen exchange between flowing hydrogen fluoride gas and zirconium tetrachloride at 300°C. Large volumes are produced by the addition of concentrated hydrofluoric acid to a concentrated nitric acid solution of zirconium zirconium tetrafluoride monohydrate [14956-11-3] precipitates (69). The recovered crystals ate dried and treated with hydrogen fluoride gas at 450°C in a fluid-bed reactor. The thermal dissociation of fluorozirconates also yields zirconium tetrafluoride. 

In the CVD coating process, the tools are heated in a sealed reactor with gaseous hydrogen at atmospheric or lower pressure volatile compounds are added to the hydrogen to supply the metallic and nonmetaUic constituents of the coating. For example, TiC coatings are produced by reaction of TiCl vapors with methane (CH and hydrogen (H2) at 900 to 1100°C. The reaction is... 

The Tj-carbides are not specifically synthesized, but are of technical importance, occurring in alloy steels, stelUtes, or as embrittling phases in cemented carbides. Other complex carbides in the form of precipitates may form in multicomponent alloys or in high temperature reactor fuels by reaction between the fission products and the moderator graphite, ie, pyrographite-coated fuel kernels. 

SiHcon carbide s relatively low neutron cross section and good resistance to radiation damage make it useful in some of its new forms in nuclear reactors (qv). SiHcon carbide temperature-sensing devices and stmctural shapes fabricated from the new dense types are expected to have increased stabiHty. SiHcon carbide coatings (qv) may be appHed to nuclear fuel elements, especially those of pebble-bed reactors, or siHcon carbide may be incorporated as a matrix in these elements (153,154). 

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