Reactors continuous flow

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

Batch reactors often are used to develop continuous processes because of their suitabiUty and convenient use in laboratory experimentation. Industrial practice generally favors processing continuously rather than in single batches, because overall investment and operating costs usually are less. Data obtained in batch reactors, except for very rapid reactions, can be well defined and used to predict performance of larger scale, continuous-flow reactors. Almost all batch reactors are well stirred thus, ideally, compositions are uniform throughout and residence times of all contained reactants are constant. 

Mixing of product and feed (backmixing) in laboratory continuous flow reactors can only be avoided at very high length-to-diameter (aspect) ratios. This was observed by Bodenstein and Wohlgast (1908). Besides noticing this, the authors also derived the mathematical expression for reaction rate for the case of complete mixing. 

Both kinetic and equilibrium experimental methods are used to characterize and compare adsorption of aqueous pollutants in active carbons. In the simplest kinetic method, the uptake of a pollutant from a static, isothermal solution is measured as a function of time. This approach may also yield equilibrium adsorption data, i.e., amounts adsorbed for different solution concentrations in the limit t —> qo. A more practical kinetic method is a continuous flow reactor, as illustrated in Fig. 5. 

Fig. 5. Schematic continuous flow reactor for characterizing the effectiveness of active carbons for purifying water.

Fig. 6. Breakthrough curves for aqueous acetone (10 mg 1" in feed) flowing through exnutshell granular active carbon, GAC, and PAN-based active carbon fibers, ACF, in a continuous flow reactor (see Fig. 5) at 10 ml min" and 293 K [64]. C/Cq is the outlet concentration relative to the feed concentration. Reprinted from Ind. Eng. Chem. Res., Volume 34, Lin, S. H. and Hsu, F. M., Liquid phase adsorption of organic compounds by granular activated carbon and activated carbon fibers, pp. 2110-2116, Copyright 1995, with permission from the American Chemical Society.

Harada, M., Arima, K., Eguchi, W. and Nagata, S., 1962. Micromixing in a continuous flow reactor. Memoir of the Faculty of Engineering, Kyoto University, Japan, 24, 431. 

Cyclization via continuous flow reactor (380 °C, 45 s loop) and decarboxylation have been described neat. The change in selectivity of cyclization is notable and will be addressed later (compare conversion of 51-52 with 56-57). 

Molecular Weight Distribution Control in Continuous-Flow Reactors... 

Continuous-flow reactors are usually preferred for long production runs of high-volume chemicals. They tend to be easier to scaleup, they are easier to control, the product is more uniform, materials handling problems are lessened, and the capital cost for the same annual capacity is lower. 

There are two important types of ideal, continuous-flow reactors the piston flow reactor or PFR, and the continuous-flow stirred tank reactor or CSTR. They behave very diflerently with respect to conversion and selectivity. The piston flow reactor behaves exactly like a batch reactor. It is usually visualized as a long tube as illustrated in Figure 1.3. Suppose a small clump of material enters the reactor at time t = 0 and flows from the inlet to the outlet. We suppose that there is no mixing between this particular clump and other clumps that entered at different times. The clump stays together and ages and reacts as it flows down the tube. After it has been in the piston flow reactor for t seconds, the clump will have the same composition as if it had been in a batch reactor for t seconds. The composition of a batch reactor varies with time. The composition of a small clump flowing through a piston flow reactor varies with time in the same way. It also varies with position down the tube. The relationship between time and position is... 

The decolorization of crystal violet dye by reaction with sodium hydroxide is a convenient means for studying mixing effects in continuous-flow reactors. The reaction is... 

The use of glutaric dialdehyde as a coupling agent bound the enzymes trypsin or glucose-6-phosphate dehydrogenase to the surface. A large part of the enzymic activity was retained (Fig. 4), and the activity was such that the particle-enzyme conjugate could be used in laboratory scale continuous-flow reactors. 

Probably the first non-covalent immobilization of a chiral complex with diazaligands was the adsorption of a rhodium-diphenylethylenediamine complex on different supports [71]. These solids were used for the hydride-transfer reduction of prochiral ketones (Scheme 2) in a continuous flow reactor. The inorganic support plays a crucial role. The chiral complex was easily... 

In the present work CWPO of dyehouse effluent was carried out in a batch reactor with IL capacity and in a pilot plant scale continuous flow reactor with 5ra /day treatment capacity. Cu/Al203 and Copper plate were used as the catalysts. 

Figure 1. Pilot plant scale continuous flow reactor for wet oxidation of dyehouse effluent.

Girguis PR, AE Cozen, EF Delong (2005) Growth and population dynamics of anaerobic methane-oxidizing archaea and sulfate-reducing bacteria in a continuous-flow reactor. Appl Environ Microbiol 71 3725-3733. 

The information flow diagram, for a non-isothermal, continuous-flow reactor, in Fig. 1.19, shown previously in Sec. 1.2.5, illustrates the close interlinking and highly interactive nature of the total mass balance, component mass balance, energy balance, rate equation, Arrhenius equation and flow effects F. This close interrelationship often brings about highly complex dynamic behaviour in chemical reactors. 

The reductive alkylation of DAP with acetone led to high conversions and selectivity to the dialkylated product over Al, Bl, and BS2 catalysts. The ASl catalyst, which typically has lower activity than the Al or Pt-based catalysts showed greater formation of heterocycles. These results indicate that a more active catalyst, a shorter reaction time, a higher operating temperature, or sterically hindered amines/ketones will help minimize the formation of the heterocycles. Similar high selectivities were obtained with DAP-MIBK reaction over BSl and BS2 catalysts with no heterocycles being formed. However, over Al, the undesired heterocyclic compound was over 15%. This indicates that the reaction between diamines and ketones has a significant potential to form heterocyclic compounds unless the interaction between these is kept to a minimum by the use of a continuous flow reactor as proposed by Speranza et al. (16) or by other methods. 

The first few experiments in the continuous flow reactor yielded inconsistent octene conversions (Figure 28.3). The experiment ran for 218 hours. Initially the conversion was consistent at 3-4% for several hours, then improved significantly to 16% and then rapidly dropped off to less than 2% (Figure 28.3). The selectivity was also very good for this ran, with an average normal to branch isomer ratio of 7 1. 

Competitive adsorption on carbon was also studied. The results are shown in Figure 34.8. The product PG competitively adsorbs to carbon more readily than the starting material. This can have implications in reaching full conversion and on product stability. The impact of the relative adsorption is alleviated under continuous flow reactor conditions where we are able to achieve high conversion and high yield. A full accounting of the adsorption work will be the subject of a later publication. 

Catalytic tests were performed in a gas-phase continuous-flow reactor. The outlet flow of the reactor was either sampled for the analysis of the gaseous components, or condensed in a dry frozen trap, for the analysis of the solid and liquid products. Two liquid layers formed an organic layer containing the unconverted n-hexane, and an aqueous layer, some products dissolved preferentially in the organic layer, others in the aqueous one. Both layers were analyzed by gas chromatography. 

Catalytic Testing for NMP Synthesis - Continuous Flow Reactor... 

Table 4 Hydrolysis of continuous flow reactor product solution.

About one half of the coal samples used in the above study (61) have been investigated by workers in Gulf Research and Development Company, using a continuous flow reactor (63). The throughput was about 1 kg./h of coal/solvent slurry, the solvent was a partly hydrogenated anthracene oil, temperatures of 440 and 455°C were used, and the system was pressurized with hydrogen to 20.69 MPa. 

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