Circulation apparatus

Specimens were placed in a silica reactor that was equipped with two side tubes for XPS and ESR measurements and connected to a circulation apparatus, described elsewhere [25, 26]. The catalysts, dried at 383 K, were characterized as prepared (a.p.), after heating in dry oxygen at 773 K (s.o.), or after reduction with CO. In some experiments, as specified, samples were exposed to NO, NH3, or various mixtures NO-O2-NH3. Electrons per V atom (e/V) were determined from the CO consumed. The average oxidation number of vanadium was calculated as 5 - eA/. 

With appropriate precautions, condensation and addition polymerization reactions can be carried out in the same apparatus as customarily used for organic preparative work (see Sects. 4.1 and 4.2). In order to obtain high molecular weights by polycondensation in solution, a special circulation apparatus can be advantageously used with advantage (Fig. 2.4). 

Fig. 2.4. Circulation apparatus for preparation of polyesters. A water separator, B drying tube...

Using the circulating apparatus it was found that only traces of hydrogen chloride were evolved during the initial stages of autoxidation thus, at 2 mole % oxidation the mole ratio of oxygen absorbed to hydrogen chloride evolved was 435. 

Temperature-controlled immersion water circulator Apparatus to hold viscometer vertically in water bath Thermometer... 

Figure 9.3 Schematic of circulation apparatus for upward-flow gel chromatography.

An alternate method that is quite similar to the circulation method and is described in the literature (Myerson 1977 Myerson and Kirwan 1977) is shown in Figure 2.37. In this method, solution is pumped past a crystal that is suspended from a rod in a chamber. The flow rate can be directly measured by a rotameter, which is not possible in the circulation apparatus. As previously mentioned, the mass or change in dimension of the crystal can be measured at the beginning and end of the experiment or can be directly observed by using a microscope. This method is more difficult to use for several reasons. First, pumping of the solution tends to increase the chance of nucleation as does the presence of the various tubing and connections. Second, the lines must be kept at the desired temperature or material will crystallize in the lines. 

Apparatus equipped with a Cottrell pump has also proved suitable for systems with relatively high volatilities AKp. > 100°C) [H5]. The improved Labodest circulating apparatus makes use of a Cottrell pump and electromagnetic valves with Teflon cones for sample withdrawal [112]. Its microscale construction is designed along the same lines and requires only 100 ml charge (Fig. 50). The sources of error... 

Kumarkrishna Rao et al. [119] used the equipment shown in Fig. 52 for measurements on the systems benzene-n-hexane and benzene-cyclohexane at pressures up to 18 atm. It is also possible, however, to place an ordinary glass apparatus inside a pressure vessel. Jost et al. [120] buUt a circulating apparatus of glass with an adiabatic jacket into a 20-litre autoclave. 

The kinetics of oxidation of isotactic polypropylene was investigated in circulating apparatus with freeze-volatile products of oxidation at the temperature of liquid nitrogen. When the film thickness is less than 60 microns maximum rate of oxidation of the sample is proportional to its thickness. Consequently, at a thickness of less than 60 microns ( 1<60 mcm) kinetic regime is realized, i.e. diffusion of oxygen is a rapid process and does not affect the rate of oxidation. On the contrary, for 1 > 200 microns oxidation occurs in the diffusion regime and the maximum speed calculated for 1 cm the surface is practically independent of the thickness. 

Fig. 1-1. Circulation apparatus for vapor-liquid equilibrium measurements.

The photocatalytic water decomposition was performed in a closed gas-circulating apparatus equipped with a quartz reaction cell. About 250 mg photocatalyst was placed in ion exchanged and distilled water in the quartz reaction cell. The reaction system was filled with 1.33 kPa of Ar gas that was circulated with... 

The increase in the amount of 1,3-disilapropanes in the pyrolysis products of Me2SiH2 can be satisfactorily explained. Because the storage flask in the circulation apparatus had to be cooled to —45 ""C to maintain an appropriate partial pressure of Me2SiH2, the 1,3-disilapropanes were trapped and could not participate in further... 

The observed pyrolysis products are formed through very complicated and still not sufficiently elucidated reaction pathways. This uncertainty is caused mostly by the fact that all initially formed compounds of low molecular weight in the continually-working gas circulation apparatus will participate according to their partial pressures in the overall reaction, in addition to the starting methylsilane. 

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