Continuous operated stirred tank reactor

Biocatalysts in nature tend to be optimized to perform best in aqueous environments, at neutral pH, temperatures below 40 °C, and at low osmotic pressure. These conditions are sometimes in conflict with the need of the chemist or process engineer to optimize a reaction with respect to space-time yield or high product concentration in order to facilitate downstream processing. Furthermore, enzymes and whole cells are often inhibited by products or substrates. This might be overcome by the use of continuously operated stirred tank reactors, fed-batch reactors, or reactors with in situ product removal [14, 15]. The addition of organic solvents to increase the solubility of substrates and/or products is a common practice [16]. 

The continuously operated stirred-tank reactor with continuous extraction of the unconverted enantiomer yields an enantiomeric excess of 95%. Afterwards, the unconverted enantiomer is racemized and reused in the synthesis process carried out by Coca Cola. 

Due to the behavior of the membrane reactor as a continuously operated stirred tank reactor (CSTR) [2], it can be used effectively to suppress side-reactions, for example the noncatalyzed reduction yielding the racemate in the oxazaborolidine reaction [11]. 

CSTR continuously operated stirred tank reactor... 

The continuously operated stirred tank reactor is fed with reactants at the same time as the products are removed by an overflow or a level control system (Figure 8.1). This ensures a constant volume and, consequently with a constant volume flow rate of the feed, a constant space hme. We further assume the reactor contents... 

The use of membrane reactors is favorable not only with respect to an increase in the total turnover number. In certain cases the selectivity can also be increased by applying high concentrations of the soluble catalyst together with making use of the behavior of a continuously operated stirred-tank reactor. Basically, this is also possible with a catalyst coupled to an insoluble support, but here the maximum volumetric activity is limited by the number of active sites per mass unit of the catalyst. This has been shown for the enantioselective reduction of ketones (eq. (2)) such as acetophenone 5 with borane 6 in the presence of polymer-enlarged oxazaborolidines 8 and 9 [65-67]. 

The N-acetyl-D,L-amino acid precursors are conveniently accessible through either acetylation of D,L-amino acids with acetyl chloride or acetic anhydride in a Schotten-Baumann reaction or via amidocarbonylation I801. For the acylase reaction, Co2+ as metal effector is added to yield an increased operational stability of the enzyme. The unconverted acetyl-D-methionine is racemized by acetic anhydride in alkali, and the racemic acetyl-D,L-methionine is reused. The racemization can also be carried out in a molten bath or by an acetyl amino acid racemase. Product recovery of L-methionine is achieved by crystallization, because L-methionine is much less soluble than the acetyl substrate. The production is carried out in a continuously operated stirred tank reactor. A polyamide ultrafiltration membrane with a cutoff of 10 kDa retains the enzyme, thus decoupling the residence times of catalyst and reactants. L-methionine is produced with an ee > 99.5 % and a yield of 80% with a capacity of > 3001 a-1. At Degussa, several proteinogenic and non-proteinogenic amino acids are produced in the same way e.g. L-alanine, L-phenylalanine, a-amino butyric acid, L-valine, l-norvaline and L-homophenylalanine. 

A continuously operated stirred tank reactor (CSTR) for use up to 3 kbar and 300"C is shown in Fig. 4.10. The reactor is equipped with a fairly large sapphire window (visual observation and spectroscopic analysis. Spectroscopic studies may be conducted using a reflectance technique developed by Franck and Roth probing light enters the cell, passes through a sample layer with a precisely known thickness, and is reflected from a mirror which is positioned inside the fluid under investiga-... 

The calculation of a continuously operating stirred tank reactor used for polymerisation is based on the solution of the equation of material balance for the monomer [1] ... 

Ideal Continuously Operated Stirred Tank Reactor (CSTR)... 

In Figures 3.4 and 3.5, the RTDs of ideal reactors are presented together with the RTD of a real reactor. The ideal, continuously operated stirred tank reactor (CSTR) has the broadest RTD between all reactor types. The most probable residence time for an entering volume element is t = 0. After a mean residence time t = t), 37% of the tracer injected at time t = 0 is still present in the reactor. After five mean residence times, a residue of about 1% still remains in the reactor. This means that at least five mean residence times must pass after a change in the inlet conditions before the CSTR effectively reaches its new stationary state. 

The cascade consists of a series of ideal continuously operated stirred tank reactors, CSTR, connected one after the other. The outlet function of one CSTR is... 

In order to quantify the influence of the gas flow rate on the residence time of the particles a simple model can be used that represents the horizontal apparatus by a series of continuously operated stirred tank reactors (CSTRs). The principle of this model is illustrated in Fig. 7.40. The size (length) and number of the tanks express the intensity of back-mixing (mixing in the direction of solids transport). They are flctitious for an open process chamber (as in Fig. 7.38), but may correspond to... 

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