Photochemical reactor immersion-type

Gas-Solid Heterogeneous Reaction Mixtures. Gas-solid heterogeneous reaction mixtures may be advantageously irradiated in annular (immersion-type) photochemical reactors. Again, the content of solid particles is limiting the size and the productivity of the reactor system. This is of particular importance when the solid support is used to specifically adsorb substrates or products of the photochemical reaction the first to enhance specificity of radical substitution reactions [20], the latter to reach better photostability and to ensure optimal purity. 

Figure 6. Block drawing of the pilot installation for the production of trichloromethyl chloroformate by exhaustive photochlorination [39] 1 Dryer for gaseous Cl2 (H2S04 cone.). 2 Safety tank. 3 Thermoregulated immersion-type photochemical reactor. 4 Raschig column. 5 Cl2 detection system (1,2,4-trichlorobenzene). 6 Neutralization tank (20% NaOH). 7 Reservoir of 20% NaOH. 8 Buffer to atmospheric pressure (20% NaOH). 9 Active carbon filter. 10 Reservoir of crude trichloromethyl chloroformate. 11 Buffer to normal atmosphere via CaCl2 filter and direct entry for trichloromethyl chloroformate to be distilled. 12 Distillation flask with Vigreux column. 13 Exit to vacuum pump. 14 Solid NaOH filter before pump. 15 Cooling water alarm linked to power supply of the light source. 16 Medium pressure mercury arc. 17 Heater for distillation apparatus. 18 Magnetic stirrers. /T thermometer /P manometer.

This geometry of irradiation makes the most efficient use of the light emitted by an extended light source. In fact, this geometry is used in all immersion-type photochemical reactors, and most industrial photochemical production units are based on this design. 

In designing modules of mono- or multilamp immersion-type photochemical reactors, again the concept of convergence of light distribution and reactor geometries is followed, and knowledge of light penetration in a suspension of optimal photocatalyst concentration is therefore essential. Optimal thickness of annular irradiated reaction volume is best determined by a spherical probe under conditions where only absorption by the photocatalyst has to be taken into account [12, 78, 98, 99]. The radiant power P = f(r) within the limits of r and rR, respectively, has been simulated by the Monte Carlo method on the basis of... 

Figure 24. Scheme of multilamp immersion-type photochemical installation for the photocatalyzed oxidative degradation of industrial waste water [12]. A Bypass circuit. B Reactor circuit. 1 Gas-liquid mixture and injection. 2 Reservoir. 3 Pump (ceramics). 4 Water pump. 5 Heating circuit. 6 Cooling circuit, hv Medium pressure mercury lamps (Pyrex). T Thermometers. 

Based on the experimental data of Jacob and Dranoff [111], Cerda et al. [113] evaluated the LSSE and ESVE models and found for the latter a much better agreement between experimental and calculated data. However, Tournier et al. state that none of the above mentioned models could be used to interpret all the experimental results obtained from radiant power measurements in an immersion-type photochemical reactor using a lamp jacket equipped with a compartment for filter solutions [78]. 

The simplest photochemical reactors are certainly those of the immersion type, where the lamps are immersed in the reaction medium that they irradiate directly, the gases being injected through perforated tubings at the bottom of the reactor. However, these reactors rapidly get dirty because of by-product deposits and they are difficult to cool and favor the production of chloroalkanes due to higher absorption of chlorine. Residence times range between 2 and 10 h. For example, with a residence time of 2 h and a 34% sulfochlorination rate, the production of sulfochlorides containing ca. 12% di- and polysulfochlorides can reach 80 kg/h m [37]. 

In addition to the most classical simple immersion reactor, three main types of photochemical reactors can be used in plants [32]. Their respective advantages and drawbacks are presented in Table 7.1 [57]. 

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