Gas reactions

In many cases, cold spots on the reactor shell will result in condensation and high corrosion rates. Sufficient insulation to maintain the shell and appurtenances above the dew point of the reaction gases is necessary. Hot spots can occur where refractory cracks allow heat to permeate to the shell. These can sometimes be repaired by pumping castable refractoiy into the hot area from the outside. 

Hot-Wall Reactors. A hot-wall reactor is essentially an isothermal furnace, which is often heated by resistance elements. The parts to be coated are loaded in the reactor, the temperature is raised to the desired level, and the reaction gases are introduced. Figure 5.6 shows such a furnace which is used for the coating of cutting tools with TiC, TiN, and Ti(CN). These materials can be deposited alternatively under precisely controlled conditions. Such reactors are often large and the coating of hundreds of parts in one operation is possible (see Ch. 18). 

Alten, H., Stjemberg, K., and Lux, B., Influence of Oxygen and Water Traces Contained in the Reaction Gases Used for AI2O3 Deposition by CVD, Proc. 5th. European Conf. on CVD, (J. Carlsson and J. Lindstrom, eds.), pp. 388-393, Univ. of Uppsala, Sweden (1985)... 

A shutter can be placed in front of the substrate to prevent deposition during filament preheating. The reaction gases are injected on the lower-left side of the reactor, and directed towards the reactor wall in order to achieve more homogeneous gas flows. The (unreacted) gas is pumped out at the right side, so the gas flow is perpendicular to the filaments. 

The reaction gases (containing chlorodifluoramine) must be handled at below —5°C to avoid explosion. Ammonium hydrogen fluoride behaves similarly. 

In situ characterization. Catalysts should preferably be investigated under the conditions under which they are active in the reaction. Various reasons exist why this may not be possible, however. For example, lattice vibrations often impede the use of EXAFS, XRD and Mossbauer spectroscopy at reaction temperatures the mean free path of electrons and ions dictates that XPS, SIMS and LEIS are carried out in vacuum, etc. Nevertheless, one should strive to choose the conditions as close as possible to those of the catalytic reaction. This means that the catalyst is kept under reaction gases or inert atmosphere at low temperature to be studied by EXAFS and Mossbauer spectroscopy or that it is transferred to the vacuum spectrometers under conditions preserving the chemical state of the surface. 

The decomposition gases are taken to the sampling valve which, according to the gas to be analyzed and the retarding column used, can be operated at specific intervals. A helium gas stream flushes the reaction gases into the gas chromatograph. 

Contact time between the reactants and the catalyst is about a tenth of a second. The reaction gases—mainly phthalic anhydride, carbon dioxide, and water—are cooled, condensed, and purified in stainless steel facilities. Phthalic anhydride solidifies at 269°Fj so the purified (99.5%) product can be stored in its molten form or cooled and flaked. Minor amounts of by-products, maleic anhydride, phthalic acid, and benzoic acid are also produced. 

The ammoxidacion reaction is carried out at about 800°F and 30 psi. Because it is highly exothermic, heat is removed continuously from the reactor by hear exchangers. The residence time of the reactants is about three seconds. The reaction gases are cooled as they pass by the water-to-steam heat exchanger in the reactor. The effluent is treated for removal of ammonia by scrubbing it with water acidified with sulfuric acid, forming ammonium sulfate, a marketable commodity that can be recovered by crystallization. But that s another story. 

Pfefferle and Lyubovsky executed types of measurements that yielded critical information between active Pd phases for catalytic combustion using pure ot-alumina plates with zero porosity as a support for the catalyst. This procedure uniformly covers the plate with metal particles on the top surface where they are easily available for the reaction gases and optical analysis. This type of experimental procedure has shown that in high-temperature methane oxidation the reduced form of the supported palladium catalyst is more active than the oxidized form. The temperature at which the PdO Pd... 

When R = H, the following mechanism, in which carbonyl sulfide is an intermediate, has been suggested. The presence of carbonyl sulfide in 30% concentration in the reaction gases has been found by infrared spectroscopy when the reaction is run at 150°C [51, 52] (Eq. 36). 

The figures of merit of quadrupole-based ICP-MS, such as the precision of isotope ratio measurements and the detection limits, can be improved significantly, especially for elements which are difficult to determine due to the appearance of isobaric interferences (e.g., by the trace, ultratrace and/or isotope ratio measurements of Ca, Fe, S, As, I or Se).16-22 The occurrence of interference problem can be minimized by the insertion of a collision/reaction cell in ICP-MS as the result of defined collision induced reactions using selected collision/reaction gases or gas mixtures (such as H2, He, NH3, 02, CH4 and others). For each analytical problem, which is different, e.g., for U or... 

A steel autoclave charged with Fe(CO)5 (9.75 g, 46.2 mmol) and pentane (14 mL) was cooled with liquid N2, then perfluoro(2-methyl-l,2-oxazetidine) (10 g, 50.2 mmol) was condensed into it. The autoclave was kept at rt until the pressure reached 20 atm. Reaction gases were then condensed in two cooled traps (—190 and — 78°C). The contents of the — 78nC trap were fractionated to afford the product yield 5.1 g (63%) bp - 10 C/200 Torr. 

The third step in the process involves cooling the reaction gases below their dew point, so that a liquid phase of weak nitric acid is formed. This step effectively promotes the state of oxidation and dimerization (Reactions 3 and 4), and removes water from the gas phase. This in turn increases the partial pressure of the nitrogen peroxide component. 

Cooled reaction gases are absorbed in water/weak acid using a sieve tray-type tower. The bottoms from this tower is a so-called red product acid, the colour resulting from dissolved nitrogen oxide impurities. The red product acid is then bleached in a smaller sieve-tray stripping column. Air is bubbled through the red acid to strip out the dissolved nitrogen oxides. Bottoms from this column is the product nitric acid at 60%(wt.) concentration. 

Waste-heat boiler Cool reaction gases and produce steam. 

Steam superheater Cool reaction gases and superheat steam. 

Tail-gas preheater Cool reaction gases and preheat tail gas. 

Oxidation unit Final oxidation of reaction gases. 

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