Slurry reactors batch time

Soil slurry-sequencing batch reactor (SS-SBR) is a technology for the biological treatment of organic contaminants in soil. The technology has been evaluated in full-scale field tests but is not commercially available. The SS-SBR system consists of a set of tanks operated on a fill-and-draw basis. Each tank is filled during a discrete period of time and operated as a batch reactor. According to the vendor, reaction times are on the order of days. 

According to the vendor, the estimated price of remediation using a soil slurry-sequencing batch reactor system was 50 to 110/m of waste treated in 1995. Costs are usually 1.5 to 2 times less than excavation and inceration. The quantity of waste and initial contaminant concentration were cited as the most significant factors effecting price (D10036N, p. 15 D15328G, p. 7). 

Emulsion polymerization is usually carried out isothermally in batch or continuous stirred-tank reactors. Temperature control is much easier than for bulk or solution polymerization because the small ( 0.5 fim) polymer particles, which are the locus of the reaction, are suspended in a continuous aqueous medium. This complex, multiphase reactor also shows multiple steady states under isothermal conditions. In industrial practice, such a reactor often shows sustained oscillations. Solid-catalyzed olefin polymerization in a slurry batch reactor is a classic example of a slurry reactor where the solid particles change size and characteristics with time during the reaction process. 

In a batch slurry reactor, the liquid-solid mass-transfer coefficient can be measured by dissolving a sparingly soluble solid in liquid. The concentration of dissolved solid in liquid (Bt) can be measured as a function of time, preferably by a continuous analytical device. Systems such as the dissolution of benzoic acid, jS-naphthol, naphthalene, or KMn04 in water can be used. A plot of B( as a function of time and the slope of such plot at time t = 0 can give ks as... 

It is assnmed that the gas is completely backmixed. Gas-side resistance for mass transfer is neglected. The reaction is performed under isothermal conditions. Initially, a slurry of Ca(OH)2 in water is prepared and the liqnid is saturated with Ca(OH)2. Then CO2 gas is sparged to the reactor. It is assnmed that the number of reacting Ca(OH)2 particles per nnit volnme of the reactor is constant (no breakage or agglomeration) until the particles are completely consnmed. The instantaneous rate of reaction is integrated with respect to time until all the Ca(OH)2 is consumed. Thus, the batch time is obtained ... 

Both batch and continuous reactor operation were studied. The latter was utilized, as although, fine chemicals are usually produced in batch-wise operating slurry reactors, continuous reactors offer several benefits, e.g. minimization of the time between batches, exclusion of catalyst separation and abrasion problems. 

Gas-solid batch microreactor, initial outgassing of the catalyst for 2 h at 5(X) °C under vacuum (2) gas-liquid-solid slurry reactor, n-heptane liquid phase, 6 °C, 100 % conversion of ethylene, run time 34 h... 

If the simplifying assumptions above also hold for a slurry reactor, one should be able to obtain values for the rate constant k in an autoclave experiment. One would measure changes in concentration with time (i.e., batch reactor procedure) rather than changes with position as in a trickle bed, but the two measures should be proportional to each other. For the slurry reactor. 

The reaction progress is monitored ofF-Une by HPLC. Flow rates, residence times and initial concentrations of 4-chlorophenol are varied and kinetic parameters are calculated from the data obtained. It can be shown that the photocatalytic reaction is governed by Langmuir-Hinshelwood kinetics. The calculation of Damkohler numbers shows that no mass transfer limitation exists in the microreactor, hence the calculated kinetic data really represent the intrinsic kinetics of the reaction. Photonic efficiencies in the microreactor are still somewhat lower than in batch-type slurry reactors. This finding is indicative of the need to improve the catalytic activity of the deposited photocatalyst in comparison with commercially available catalysts such as Degussa P25 and Sachtleben Hombikat UV 100. The illuminated specific surface area in the microchannel reactor surpasses that of conventional photocatalytic reactors by a factor of 4-400 depending on the particular conventional reactor type. 

All photocatalytic reactions are carried out with an immobilized heterogeneous photocatalyst. Slurries are difficult to handle in microstructures and often lead to clogging problems. Immobilized catalysts in microstructures, however, have the advantage that no separation from the reaction mixture in an additional costly and time-intensive separation step is required as for conventional slurry-type batch reactors. In contrast to conventional immobilized systems, a high interfacial irradiated surface area of the catalyst can be maintained despite its immobilization due to the large surface-to-volume ratio of the microchannels. 

Hydrogenation of xylose to xylitol is an important process in the production of sweeteners, and the sponge nickel catalyst (often called Raney-Ni) deactivates in the slurry reactor. In successive batches, the catalyst activity declines, and it has to be removed after a few batches and replaced by a new one. However, by applying in situ ultrasound treatment, the catalyst deactivation was considerably suppressed as illustrated in Figure 9.32. In this way, the catalyst life time can be considerably prolonged [23]. 

Continuous reactors in the pharmaceutical and specialty chemical industries may not only be needed for high productivity as in other segments of the chemical industry, but additionally to solve specific reactor design problems caused by limitations in batch operation. These limitations include heat transfer, mass transfer, and mixing. Continuous reactors are also used to minimize the reacting volume of thermally potent and/or noxious reactions and to decrease the potential and exposure for catastrophic failure of a vessel. Chemical industry reactor standards such as packed bed, fluid bed, and trickle bed reactors And limited utility since this type of phase contacting can usually be achieved in a slurry reactor, where residence time distribution variations, which can lead to changes in product distributions, are eliminated. Continuous stirred tank reactor operation is used only... 

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. 

There are several practical scaleup lessons with heterogeneous catalysts in batch slurry reactions. One often uses four times the catalyst concentration in the lab to achieve the same results in the plant reactor. Plant charge is 1 wt. part for 1000 wt. part, where as in the lab one uses 5 grams or more per 1000 grams. A common error is the confusion between wet (gross) weight and dry weight (net)... 

The esterification reactor is usually not emptied completely after a batch is finished and a small amount of prepolymer is retained in the reactor. The reason for this is the solubility of TPA in EG and BHET, as discussed earlier in Section 3.1. During operation, the batch-wise prepared slurry is fed continuously into the esterification reactor while the esterification is already proceeding. For a significant part of the process time, the batch esterification reactor is operating semi-continuously. 

In a slurry-batch reactor the hydrogen and the liquid are mixed intensively together with the solid catalyst. The catalyst concentration is normally a few wt%. The reaction time is typically a few hours. This means that the productivity becomes in the range of 100 - 1 000 kgproduct/m3reactorh. The transport resistance between the liquid and the catalyst ( C in Fig. 9.3-2) is normally the restricting factor. 

Except for continuous weighing, control of the flow of solids is less precise than that of fluids. Several devices used for control of feed rates are shown schematically in Figure 3.7. They all employ variable speed drives and are individually calibrated to relate speed and flow rate. Ordinarily these devices are in effect manually set, but if the solid material is being fed to a reactor, some property of the mixture could be used for feed back control. The continuous belt weigher is capable ordinarily of 1% accuracy and even 0.1% when necessary. For processes such as neutralizations with lime, addition of the solid to process in slurry form is acceptable. The slurry is prepared as a batch of definite concentration and charged with a pump under flow control, often with a diaphragm pump whose stroke can be put under feedback control. For some applications it is adequate or necessary to feed weighed amounts of solids to a process on a timed basis. 

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