The jet reactor

Measurement of the kinetics of gas-liquid reactions is of great importance in the design of gas absorption equipment. The jet reactor provides a means of determining solubilities and reaction rates for gases which react rapidly with the liquid. A narrow jet of the liquid is passed through a reactive gas into a receiver, from which samples are taken to determine the amount of absorption, Fig. 5.23. 

In a study of the absorption of phosgene in water and aqueous sodium hydroxide [28], the inlet jet diameter was 0.63 mm and the jet length in the range 0.75-7 cm. Contact times were 

When the chemical reaction dominates the absorption rate, this expression becomes Equation 5.15 where D is the diameter of the jet  

This equipment was used to determine the solubility of phosgene in water (0.069 M atm-1 at 25°C). It was also used to measure the first-order rate constant for the hydrolysis of phosgene in water (ki = 6 s 1) and the second-order rate constant for the reaction with hydroxide ion (ki = 1.6 x 104 M 1 s 1), both at 25°C. 

Measurement of the solubility of a material with a half-life of about 100 ms is possible because it is deduced from the physical absorption rate at contact times sufficiently short ( 2 ms) that no chemical reaction occurs, and Equation 5.14 is applicable. 

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In early reaction systems (9,10,31,32) the vaporized hydrocarbon was combined with nitrogen in a reactor and mixed with a nitrogen—fluorine mixture from a preheated source. The jet reactor (11) for low molecular weight fluorocarbons was an important improvement. The process takes place at around 200—300°C, and fluorination is carried out in the vapor state. 

BWRs do not operate with dissolved boron like a PWR but use pure, demineralized water with a continuous water quality control system. The reactivity is controlled by the large number of control rods (>100) containing burnable neutron poisons, and by varying the flow rate through the reactor for normal, fine control. Two recirculation loops using variable speed recirculation pumps inject water into the jet pumps inside of the reactor vessel to increase the flow rate by several times over that in the recirculation loops. The steam bubble formation reduces the moderator density and... 

Fig. 3. The experimental set-up of a double jet reactor for the precipitation of calcium carbonate...

Other reactor types are also used for gas-liquid reactions, but they are not very common in fine chemicals manufacture. Spray towers and jet reactors are used when the liquid phase is to be dispersed. In spray towers the liquid is sprayed at the top of the reactor while the gas is flowing upward. The spray reactor is useful when a solid product, possibly suspended in the liquid, is formed, or if the gas-phase pressure drop must be minimized. In a jet reactor, the liquid is introduced to the reaction zone through a nozzle. The gas flows in, being sucked by the liquid. 

Laboratory reactors for studying gas-liquid processes can be classified as (1) reactors for which the hydrodynamics is well known or can easily be determined, i.e. reactors for which the interfacial area, a, and mass-transfer coefficients, ki and kc, are known (e.g. the laminar jet reactor, wetted wall-column, and rotating drum, see Fig. 5.4-21), and (2) those with a well-defined interfacial area and ill-determined hydrodynamics (e.g. the stirred-cell reactor, see Fig. 5.4-22). Reactors of these two types can be successfully used for studying intrinsic kinetics of gas-liquid processes. They can also be used for studying liquid-liquid and liquid-solid processes. 

The oscillation regime is observed in the oxidation of the iodide ions by the BrCfi ions. The kinetics of this reaction and its mechanism were studied in detail by Citri and Epstein [223]. The process was studied in a jet reactor. The oscillating regime is observed when the concentration of iodide ions changes in an interval of 5 x 10 7 to 4 x 10 2 M (bromate was introduced in excess with respect to the iodide ions). The example of the oscillating kinetic curve can be seen in Figure 10.1. 

This parallel reaction set was used, for example, by Johnson and Prud homme (2003a) to investigate the quality of mixing in a confined impinging-jets reactor. 

The CFD model described above has been used by Liu and Fox (2006) to simulate the experiments of Johnson and Prud homme (2003a) in a confined impinging-jets reactor. In these experiments, two coaxial impinging jets with equal flow rates are used to introduce the two reactant-streams. The jet Reynolds number Re, determines the fluid dynamics in the reactor. Typical CFD results are shown in Fig. 6 9 for a jet Reynolds number of Re, = 400 and a reaction time of tr — 4.8 msec. The latter is controlled by fixing the inlet concentrations of the reactants. Further, details on the reactor geometry and the CFD model can be found in Liu and Fox (2006). 

Fig. 6. Volume fractions px and p2 in the cross-section of the confined impinging-jets reactor.

The importance of chemical-reaction kinetics and the interaction of the latter with transport phenomena is the central theme of the contribution of Fox from Iowa State University. The chapter combines the clarity of a tutorial with the presentation of very recent results. Starting from simple chemistry and singlephase flow the reader is lead towards complex chemistry and two-phase flow. The issue of SGS modeling discussed already in Chapter 2 is now discussed with respect to the concentration fields. A detailed presentation of the joint Probability Density Function (PDF) method is given. The latter allows to account for the interaction between chemistry and physics. Results on impinging jet reactors are shown. When dealing with particulate systems a particle size distribution (PSD) and corresponding population balance equations are intro-... 

Baldyga, J., J. R. Bourne, B. Dubuis, A. W. Etchells, R. V. Gholap, and B. Zimmerman (1995). Jet reactor scale-up for mixing-controlled reactions. Transactions of the Institution of Chemical Engineers 73,497-502. 

In the first step the chlorine from the tail gas and chlorine feed reacts with the caustic in the jet-loop reactor. The advantage of the jet-loop reactor is that it also acts as a suction device for the gas stream. The residence time of the liquid in step one is dependent on the capacity of the hypochlorite production and liquid level in the tank and varies between 1 and 4 h. A heat exchanger in the loop controls the temperatures in steps one and two. The amount of caustic in the feed-tank of step two is the back-up for failure of chlorine liquefaction. 

When the capacity is increased under the same process conditions the caustic concentration is increased on higher dosing. As the quantity of free caustic in the end-product and in the liquid flow of the jet-loop reactor is the same, the percentage of caustic reacting with chlorine increases by roughly 25-60% when the production capacity is increased. Depletion of caustic at the liquid-gas interface can then occur more easily. 

Most of the generated vapour is condensed in spray condensers which are equipped with circulation pumps and an EG cooler. The vapour that is still uncondensed is withdrawn from the gas phase with the help of a vapour jet which is located down-stream behind the spray condenser and generates the necessary vacuum in the reaction zone. The most critical part of the spray condenser system is the end of the pipe leading the vapour from the prepolycondensation reactors and the finishers into the spray condenser. The transition from a hot to a cold environment causes deposition of solid material onto the cold walls which has to be removed manually or by means of a mechanical scraper. 

Process vapours from the esterification reactors and EG from the EG-vapour jet, as well as from the vacuum stages of the spray condensers, are purified in the distillation unit. The distillation unit commonly consists of two or three columns and is designed for continuous operation. The purified EG is condensed at the top of the third vacuum rectification column and returned to the process via a buffer tank. Gaseous acetaldehyde and other non-condensables are vented or burned and high-boiling residues from the bottom of the third column are discharged or also burned. 

The contents of the AHSV are continuously recirculated using the agent hydrolysate transfer pump and are returned to the AHSV through a jet mixer. The vessel contents are agitated and maintained at 194°F. The pH is monitored and controlled at all times to eliminate the possibility of agent reformation. Hydrolysate from the AHSV is supplied to the SCWO reactor units in Area 300 through the agent hydrolysate transfer pump. 

Polycrystalline ZnSe nanoparticles were synthesized from Me2Zn NEts and H2Se gas diluted in H2 [120] using a flexible vapor-phase technique [121]. In a counter-flow jet reactor (CJR) the vapors of Me2Zn NEts and H2Se react to form nanoparticles of ZnSe. This method provides a direct vapor-phase route for nanoparticles preparation. 

Bubble columns and various modifications such as airlift reactors, impinging-jet-reactors, downflow bubble columns are frequently used in lab-scale ozonation experiments. Moderate /qa-values in the range of 0.005-0.01 s l can be achieved in simple bubble columns (Martin et al. 1994 Table 2-4 ). Due to the ease of operation they are mostly operated in a cocurrent mode. Countercurrent mode of operation, up-flow gas and down-flow liquid, has seldom been reported for lab-scale studies, but can easily be achieved by means of applying an internal recycle-flow of the liquid, pumping it from the bottom to the top of the reactor. The advantage is an increased level of the dissolved ozone concentration cL in the reactor (effluent), which is especially important in the case of low contaminant concentrations (c(M)) and/or low reaction rate constants, i. e. typical drinking water applications... 

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