Immersion type

Immersion-type extractors have been made continuous through the inclusion of screw conveyors to transport the soHds. The Hildebrandt immersion extractor (18) employs a sequence of separate screw conveyors to move soHds through three parts of a U-shaped extraction vessel. The helix surface is perforated so that solvent can pass through the unit in the direction countercurrent to the flow of soHds. The screw conveyors rotate at different speeds so that the soHds are compacted as they travel toward the discharge end of the unit. Alternative designs using fewer screws are also available. 

Air-eooled dry type and oil-immersed type This will depend upon the size of the reactor and the design of the manufacturer. The latest practice is to use aircooled dry type, which call for lesser maintenance and are free from any fire hazards. 

Electrical resistance boilers use banks of fixed, immersion-type, resistance heating elements (typically sheathed in seamless copper, Incoloy 800, or 316SS) to provide an energy source that is contained within a carbon-steel pressure vessel. The vessel is provided with a sight glass and all normal boiler controls, valves, and regulators necessary for automatic operation. The vessel is generally well insulated and housed within an enameled metal cabinet. Various electrical supply options are available. 

Phenylmethyldichlorosilane (Petrarch) was distilled prior to use and dried over CaH2- Toluene was distilled from CaH2 and dried over CaH2- The known amounts of sodium were placed in a flask filled with toluene and purged with dry argon. This flask was placed in the ultrasonic bath (75-1970 Ultramet II Sonic Cleaner, Buehler Ltd.) until stable dispersion of sodium was formed. In some experiments an immersion-type ultrasonic... 

We have observed a dependence of the yield, polymerization degree, and polydispersity of polysilanes on temperature and also on the power of ultrasonication. In the ultrasonication bath the simplest test of the efficiency of cavitation is the stability of the formed dispersion. It must be remembered that the ultrasonic energy received in the reaction flask placed in the bath depends on the position of the flask in the bath (it is not the same in each bath), on the level of liquid in the bath, on temperature, on the amount of solvent, etc. When an immersion probe is used the cavitation depends on the level of the meniscus in the flask as well. The power is usually adjusted close to 50% of the output level but it varies with the reaction volume, flask shape, and other rection conditions. The immersion-type probe is especially convenient at lower temperatures. 

Probe systems, also called as the ultrasonic horn are being most frequently used for the sonochemical research at laboratory scale of operation. A typical schematic representation of the setup of probe systems has been given in Fig. 2.5. These are typically immersion type of transducers and the most important advantage of using... 

Immersion types of transducers are poorest, when scale-up possibilities are considered, though very high intensities (pressures of the order of few thousands atmosphere) are observed very near to the horn. The intensity decreases exponentially as one moves away from hom and vanishes at a distance of 1-3 cm both in axial as well as radial directions depending on the maximum power input to the equipment and also on the operating frequency [11,32]. 

Actually, this is not that difficult to understand. We all know that the more stable form of diesters between fumarate and maleate is the fumarate due to the trans configuration, which minimizes the crowdedness of the esters. In the case of phthalic esters, the aromatic esters cannot possibly rotate to any trans forms and are therefore in a state with a high strain energy. In order to release this energy, these esters would rather prefer to kick-off the esters. This is why they are so prone to attack by hydrolysis, and is why GP resins will fail in any water-immersion type of test, especially under elevated temperature. 

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 sensitized or photocatalyzed reactions, conditions of total or constant absorbance can easily be controlled by the concentration of the sensitizer or photocatalyst added. In addition, experience has shown that the concept of spatial separation between the light source and the reaction mixture is in general not required. Dragoco uses immersion-type annular reactor geometries [2, 3, 69, 70] for the production of ( —)-rose oxide by rose bengal sensitized oxidation of (— )-citronellol (Eqs. 45-48, Figure 23). 

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 commercially used reference electrode—salt bridge combination usually is of ihe immersion type. Some provision is made to allow a slow leakage of the bridge solution out of the tip of the electrode to establish the liquid junction with (he lest solution. 

Total immersion type low temperature pentane thermometers (Kessler) were used to measure the temperature in the partial immersion mode. The readings are usually 7-8°C higher compared to the actual temperature under our reaction conditions. The temperatures reported here are all corrected by subtracting 7°C from the thermometer readings. The checkers used a Delta MC-20R digital thermometer (Sato Keiryoki Co., Japan). Temperature control is very important to obtain a satisfactory yield. 

The recrystallized a-oxoamide 1 (100-300 mg) was sandwiched between a pair of Pyrex plates (diickness 2 mm) and put into a polyethylene envelope. The envelope was sealed and placed in a cold medium (water, ice-water, or dry ice-methanol) and irradiated with a high-pressure mercury lamp (100 W) for 1-10 h. The lamp was used with a vessel for immersion type irradiation which contained dry air. The products were isolated by column chromatography on silica gel. 

Notes The reaction was carried out in toluene with an immersion-type probe and the following conditions [M]o = 0.32 mol/L [Na]o/[SiCl]o = 1.2 and temperature = 60 °C. Polymerization was exothermic and was completed just after the addition of monomer (15 min). Polysilane separated from the reaction mixture and sonicated in the presence of 0.2 equivalent of Na was degraded in a similar way. 

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