Circulating flow reactor

In another kinetics study, Huang and Chen immobilized jack bean urease in the form of a thin film on the surface of a reticulated polyurethane foam. The residual apparent activity of the urease after immobilization was about 50%. The good hydrodynamic properties and flexibility of the support were retained in solution after immobilization. Urea hydrolysis was examined in both a batch squeezer and circulated flow reactor. The results suggest potential for practical applications in various reactors. 

The circulation flow method is applicable for the studies of almost any heterogeneous catalytic reaction. At high pressures steel equipment is used instead of glass. The first circulation flow reactor for high pressures was designed by Sidorov (6) the gas mixture is circulated in this reactor by means of steel bellows that are actuated by a rod introduced into the reactor also through bellows, without any packing. 

The concept of a circulating flow reactor was further developed in the Buss reactor technology (Figure 1.26). Large quantities of reaction gas are introduced via a mixer to create a well dispersed mixture. This mixture is rapidly circulated by a special pump at high gas/liquid ratios throughout the volume of the loop and permits the maximum possible mass transfer rates. A heal exchanger in the external loop allows for independent optimisation of heat transfer. For continuous operation, the product is separated by an in-line cross-flow filter which retains the suspended solid catalyst within the loop. Such a system can operate in batch, semi-continuous and continuous mode. 

Urn. J.. Lee. S.S.. and Ying, J.Y. (2010) Mesoporous silica-supported catalysts for metathesis application to a circulating flow reactor. Chem. Commun., 46,806-808,... 

The principal advance ia technology for SASOL I relative to the German Fischer-Tropsch plants was the development of a fluidized-bed reactor/regenerator system designed by M. W. Kellogg for the synthesis reaction. The reactor consists of an entrained-flow reactor ia series with a fluidized-bed regenerator (Fig. 14). Each fluidized-bed reactor processes 80,000 m /h of feed at a temperature of 320 to 330°C and 2.2 MPa (22 atm), and produces approximately 300 m (2000 barrels) per day of Hquid hydrocarbon product with a catalyst circulation rate of over 6000 t/h (49). 

For technical and safety reasons a number of other parameters must be controlled pressure of circulating gas, reactor pressure, nitrogen flow, temperature of the cooling water for the UV lamps, quantity of circulating gas and of circulating paraffin, extract level, S02 pressure, 02 pressure, S02 flow, 02 flow, off-gas flow, feed paraffin flow, feed water flow, and backwater flow. 

The net flow though the reactor will be small compared with the circulating flow caused by the agitator. The existence of the throughput has little influence on the mixing time so that mixing time correlations for batch vessels can be used for CSTRs as well. 

Figure 11.10(b) can be modeled as a piston flow reactor with recycle. The fluid mechanics of spouting have been examined in detail so that model variables such as pressure drop, gas recycle rate, and solids circulation rate can be estimated. Spouted-bed reactors use relatively large particles. Particles of 1 mm (1000 pm) are typical, compared with 40-100 pm for most fluidizable catalysts. 

In this model, energy balances are set up for the reactor and the separator tube separately, and two equations are obtained. The gas holdup can then be obtained from combining these two equations. Details can be found in Zhang et al. [7]. The comparison between the measured and calculated cross-sectional mean gas holdups is shown in Fig. 5. It can be seen that there is a satisfactory agreement between the experimental and calculated gas holdup in the different operating conditions. Therefore, it is reasonable to conclude that the energy balance model used in this work can describe the circulation flow behavior in the novle internal-loop airlift reactor proposed in this work. 

OS 33] ]R 16h] ]P 25] For the nitration of single-ring aromatics in a capillary-flow reactor, internal circulation, exhibiting an inner downwards and an outer upwards flow, in the aqueous slug of a two-phase flow was simulated [94]. 

Current single-mode continuous-flow microwave reactors allow the processing of comparatively small volumes. Much larger volumes can be processed in continuous-flow reactors that are housed inside a multimode microwave system. In a 2001 publication, Shieh and coworkers described the methylation of phenols, indoles, and benzimidazoles with dimethyl carbonate under continuous-flow microwave conditions using a Milestone ETHOS-CFR reactor (see Fig. 3.11) [104]. In a typical procedure, a solution containing the substrate, dimethyl carbonate, 1,8-diazabicy-clo[5.4.0]undec-7-ene (DBU) base, tetrabutylammonium iodide (TBAI), and a solvent was circulated by a pump through the microwave reactor, which was preheated to 160 °C and 20 bar by microwave irradiation (Scheme 4.31). Under these condi-... 

The major difference between a stirred-tank batch reactor and a stirred-tank flow reactor is that, in the latter, provision must be made for continuous flow of material into and out of the reactor by gravity flow or forced-circulation flow with a pump, together with appropriate block and relief valves. 

In this example, a fluidised biofilm sand bed reactor for nitrification, as investigated by Tanaka et al. (1981), is modelled as three tanks-in-series with a recycle loop (Fig. 1). With continuous operation, ammonium ion is fed to the reactor, and the products nitrite and nitrate exit in the effluent. The bed expands in volume because of the constant circulation flow of liquid upwards through the bed. Oxygen is supplied external to the bed in a well-mixed gas-liquid absorber. 

The catalyst modified with selenium is most suitable for the studies of reaction kinetics since this element, in contrast to chlorine usually used as promoter in the commercial processes, does not volatilize from the surface of silver under the reaction conditions. We studied the kinetics of ethylene oxidation under gradientless conditions (Section II) using a circulation flow system in the experiments at atmospheric pressure (59-61) and a reactor with rotating baskets for the catalyst (5) at elevated pressures (62). 

On the basis of the considered macroscopic flow pattern, the dominant circulation flows (/ c and Fc/2) subdivide the reactor into three parallel levels, where each level is then divided into Nc/3 equally sized compartments of equal volume Vc = Vr/Nc. Every compartment is modeled as a nonstationary ideal continuous stirred tank reactor, with a main inlet and outlet flow, which connects the given compartment with adjacent compartments on the same level, and secondary exchange flow rates accounting for the turbulent mixing with adjacent compartments laying on the upper and/or lower level (Fig. 7.3). 

In addition to the Suzuki-Miyaura reaction, the authors also found the catalyst 136 to be active toward the arylation of olefins with aryl halides as illustrated in Table 20. Again to conduct a reaction, the authors circulated a solution containing 4-iodoacetophenone 138 (1.00 mmol), the alkene (3.00 mmol) under investigation, and tributylamine 139 (3.00 mmol) in anhydrous DMF (3 ml), through the heated reactor (120 °C) at a flow rate of 2 ml min After 24h, the flow reactor was rinsed with DMF and the... 

The principal reactors used are fluidized bed reactors, called Synthol reactors, in which the feed gas entrains an iron catalyst powder in a circulating flow. The suspension enters the bottom of the fluidized bed reaction section, where the Fischer-Tropsch and the gas shift reactions proceed at a temperature of from 315 to 330°C. These reactions are highly exothermic, as described previously, and the large quantity of heat released must be removed. The products in gaseous form together with the catalyst are taken off from the top of the reactor. By decreasing the gas velocity in another section, the catalyst settles out and is returned for reuse. The product gases are then condensed to the liquid products. 

A schematic of the propeller loop reactor is shown in Fig. 37. In this case, the circulation flow of the fluid phases is created by a hydromechanical propeller flow drive. The use of a draft tube often improves the mass and heat transfer efficiency in these reactors (Blenke, 1967). This type of reactor involves complicated construction and leads to operating problems related to the sealing of the shaft. It is not suitable for biosystems due to possible damage to sensitive organisms in the high shear fields at the propeller. However, it is especially suitable for highly viscous polymeric fluids and for medium-size units. 

The issue of multiple time scales is also present in the case of homogeneous tank reactors. As in Fig. 2, a tank reactor consists of several circulating flow loops which exchange material with each other and within which micromixing occurs at the continuum scale. Therefore, there are three physical length scales present in a tank reactor. The size of the reactor is the macroscale. The meso length scale could be anywhere from the size of a circulation loop to the size of an eddy (or cell). The continuum scale is the microscale. The time scales... 

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