Ozonation reactor, performance

Some useful correlations which can be used for a first approximation of the kLa s or c s in laboratory-scale ozone reactors can be found in Dudley (1995) for bubble columns, and Libra (1993) for STRs. Various correlations found in the literature, empirical as well as those based on theoretical or dimensional analysis, have been compared to results from their own experiments. Dudley concluded that correlations based on theoretical support performed better than those developed by curve-fitting. 

The level of ozone affects the reactor volume. The rate of ozonation of NO being fast, NO is consumed almost instantaneously, forming NO2. NO2 concentration decreases due to the formation of N2O5. The residence time required for 99% conversion is 7.4 s. The effect of percentage excess of ozone on reactor performance for 99% conversion of total inlet NOx (NO and NO2) can be easily calculated. 

Van Swaay and Zuiderweg [23] extensively tested the May-van Deemter model as to its ability to scale up the Shell chlorine process (air oxidation of HCl into CI2). To do so they investigated the decomposition of ozone on an FejOs catalyst deposited on sand or silica and carried out gas pulse tracer tests. The bed diameter ranged from 10 to 60 cm, the bed heights from SO to 300 cm. The authors concluded that the van Deemter model adequately describes fluidized bed reactor performance for first-order reactions with a rate coefficient smaller than 2.5 m /kg cat.hr or 1 s" . It follows from their work that with the silica-based catalyst u kj linearly increases from 0.25 m to 0.4 m as u, varies from 6 to 20 cm/s. For fluid beds with a height of up to 1 m, ujkj is proportional to the bed height so that... 

Data generated using the experimental techniques described above are used to formulate hydrodynamic models that may be used to predict reactor performance. In this section, studies that employ chemical reactions to evaluate mass transfer and contacting efficiency are described. Selected references are shown in Table 7. Dry et al. have applied hot air pulses as a reacting tracer [87]. Chemical reactions used to probe gas phase hydrodynamics include thermal decomposition of sodium bicarbonate, ozone decomposition, coal combustion, and FCC coke combustion. 

The process of latex ozonization was performed with the use of pilot laboratory plant comprising of the unit applied for electrosynthesis of ozone and a reactor where interaction of the Indian rubber latex with air-ozone mixture proceeded. This pilot plant permitted to vary ozonoly-sis modes to control and support pH value within the required limits, to control the process temperature, the rate of air-ozone mixture and latex supply, to control ozone concentration in the air flow in front of and after reactor, as well as the time of contact of the air-ozone mixture with latex. 

In an attempt to compare the effectiveness of various two-phase models, Chavarie and Grace (1975) carried out a study of the catalytic decomposition of ozone in a two-dimensional fluidized bed where the reactor performance and the ozone concentration profiles in both phases were measured. They compared the experimental data with those predicted from various two-phase models reviewed above and reported that... 

Experimental studies have been used to predict reactor performance. Frye et al. (1958) used a substitute reaction of ozone decomposition to study hydrocarbon synthesis. The ozone decomposition can be run at low pressures and temperatures and can be rate controlled in the same way and by the same catalyst as the reaction under development. Frye and coworkers used three beds, 2, 8, and 30 inches in diameter to study the size influence. We should interject a caution that the use of pressures and temperatures diflferent from those of the actual reaction may mean that the hydrodynamics of the substitute reaction model will dilfer from the actual application this will be illustrated later in the chapter. Figure 1 shows the apparent reaction rate constant for the different bed diameters at two different bed heights, with the other parameters held constant. Note that the rate constant decreased by roughly a factor of 3 between the 2 inch and 30 inch beds. 

Fig. 3. compares the ammonia conversion for nanostructured vanadia/TiOa catalysts pretreated with O2 and 100 ppm O3/O2 gases. The reactions were conducted at 348 K for 3 h. No N2O and NO byproducts were detected in the reactor outlet. It is clear from the figure that higher vanadium content is beneficial to the reaction and ozone pretreatment yields a more active catalyst. Unlike the current catalysts, which require a reaction temperature of at least 473 K, the new catalyst is able to perform at much lower temperature. Also, unlike these catalysts, complete conversion to nitrogen was achieved with the new catalysts. Table 2 shows that the reaction rate of the new catalysts compared favorably with the established catalysts. 

Water or waste water ozonation - regardless of the scale of equipment - is mostly performed in directly gassed systems, where the ozone containing gas is produced by an electrical discharge ozone generator and is introduced into the reactor by some type of gas diffuser. Since two phases, the gas and the liquid, are required for the oxidation reaction to proceed as it does, they are also called heterogeneous systems. 

Reactors can be operated either in a batch or continuous-flow mode. The combination, batch with respect to the liquid and continuous-flow with respect to the gas, is called semibatch. Often this fine distinction is ignored and it is commonly referred to as batch. The majority of ozonation experiments reported in the literature have been performed in one-stage semi-batch heterogeneous systems, with liquid phase reactor volumes in the range VL = 1-10 L. Most full-scale applications are operated in continuous-flow for both phases. 

Using this approach of a selectivity term SPFR Sunder and Hempel (1996) successfully modeled the oxidation of small concentrations of Tri- and Perchloroethylene (c(M)a = 300-1300 pg D) by ozone and hydrogen peroxide in a synthetic ground water (pH = 7.5-8.5 c(Sj) = 1-3 mmol C03 L"1). In this study an innovative reaction system was used the oxidation was performed in a tube reactor and mass transfer of gaseous ozone to pure water was realized in a separate contactor being located in front of the tube reactor. By this way a homogeneous system was achieved. Since the two model compounds react very slowly with molecular ozone (kD < 0.1 L mol-1 s "1), nearly the complete oxidation was due to the action of hydroxyl radicals, which were produced from the two oxidants (03/H202). With... 

The presence of yeast in beverages, as happens with certain wines, may contribute to the potential incorporation of Hg, a toxic element for humans. Capelo and coworkers [80] developed and investigated the performance of two different reactors for sample ozonization as a previous step to Hg determination in white wines by FI A combined with cold vapor (CV) A AS. The pretreatment with 03 allowed the drastic reduction of the amount of chemical reagents used in the FIA-CV-AAS system. An LoD of 0.5 p,g l-1 was obtained and the Hg content in four analyzed wines varied from 94 + 9 to 101 + 5 jig 1 1-... 

If the reactor walls are involved in the discharge reaction, an increase or decrease in carbon monoxide conversion should be observed. The experiments performed with the packed annulus reactor are compared with those of the open annulus reactor in Figure 6 and the experimental data are given in Table II. Within experimental error, no effect of increased reactor surface can be detected. Thus, it appears that the water-gas shift reaction in an ozonizer discharge proceeds via a purely gas phase mechanism. It appears to be a homogeneous reaction. 

S. Stucki, H. Baumann, H. J. Christen and R. Kotz, Performance of a pressurized electrochemical ozone generator, J. Appl. Electrochem., 1987, 17, 773-778 P. Tatapudi and J.M. Fenton, Synthesis of ozone a proton exchange membrane electrochemical reactor, J. Electrochem. Soc., 1993, 140, 3527-3530. 

We have studied ozonolyzis of cumene catalyzed by Mo-V catalysts. The reactions have been performed at ambient temperature in a glass reactor with a centrifugal pump with 33 ml cumene in the presence of 0.35wt.% mixtures of MoO and V Oj on SiO (Fig. 22) at various ozone concentrations. 

The particle size distribution (PSD) significantly impacts the reactant conversion in a fluidized bed reactor. Sun and Grace (1990) examined the three different particle size distributions, wide, narrow, and bimodal, on the performance of a catalytic fluidized bed reactor using the ozone decomposition reaction. They found that a fluidized bed with particles of wide size distribution yields the highest reactant conversion. Of further interest, the property of particle entrainment and elu-triation is a function of particle size, density, and shape. Both entrainment and elutriation rates increase... 

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