Continuous operation reactors

The model is able to predict the influence of mixing on particle properties and kinetic rates on different scales for a continuously operated reactor and a semibatch reactor with different types of impellers and under a wide range of operational conditions. From laboratory-scale experiments, the precipitation kinetics for nucleation, growth, agglomeration and disruption have to be determined (Zauner and Jones, 2000a). The fluid dynamic parameters, i.e. the local specific energy dissipation around the feed point, can be obtained either from CFD or from FDA measurements. In the compartmental SFM, the population balance is solved and the particle properties of the final product are predicted. As the model contains only physical and no phenomenological parameters, it can be used for scale-up. 

The productivity of continuously operated reactors at steady state is... 

The accumulation can be either positive or negative, depending on the relative magnitudes of the input and output. It should be zero with a continuously operated reactor mentioned in the previous section. 

All hydroformylation experiments were performed in a continuously operated reactor. The concentration of the catalyst was varied from 0.1 to 0.4 wt % to keep olefin conversion at the same level (80-90% ) for all reaction temperatures. The total pressure for all experiments was 280 atm, and n-octene was used as typical straight chain olefin of medium chain length. 

A more promising approach for the synthesis of hydrophobic substances with ADHs is published by Kruse et al. [159, 238], They use a continuously operating reactor where the enzyme containing water phase is separated from the hydrophobic substrate-containing organic phase by a membrane. The hydrophobic product is extracted continuously via a hydrophobic membrane into an hexane phase, whereas the coenzyme is regenerated in a separate cycle, that consists of a hydrophilic buffer system. This method decouples advantageously the residence time of the cofactor from the residence time of the substrate. Several hydrophobic alcohols were prepared in this way with (S)-ADH from Rhodococcus erythropolis (Table 16). 

The integral selectivity of a desired component D, So, is related to the corresponding consumption of a reactant A. Considering molar fluxes of components at the inlet and outlet of a continuously operated reactor, Sd is defined as follows ... 

High pressure continuously operated reactor. The design of the continuously operated apparatus is shown in Figure 2. An air operated high pressure pump delivered CO2 in the system. The gaseous fluid was dried when passing through columns packed with molecular sieves. The flow rate of C02 was 1.0 L per min. Equimolar solution of substrates (oleic acid and oleyl alcohol) was pumped into the system with an HPLC pump. Carbon dioxide and substrates were equilibrated in the saturation column. The reaction was performed in a... 

Tbe conversion ratio, X, of the char is defined by (6). It is simple to determine the conversion ratio in a batch process but quite complicated to determine in a continuously operated reactor where non-converted char (X = 0) is introduced and the char later on are transported downwards during the gasification. 

Needless to say, what has been described for the continuously operating ROSEN-LEW reactor also applies to the continuously operating reactor of QUAKER OATS. It, too, generated significant quantities of diacetyl. By contrast, in the continuous SUPRATHERM process, where the air of the raw material is eliminated in the slurry preparation, diacetyl is... 

As shown above, the formation of diacetyl in furfural reactors requires oxygen as supplied by the air introduced by the feed mechanisms of continuously operating reactors (shutters in the case of the ROSENLEW and ESCHER WYSS reactors, augers in the continuous QUAKER OATS process). By implication, this means that hatch reactors. 

To derive the overall kinetics of a gas/liquid-phase reaction it is required to consider a volume element at the gas/liquid interface and to set up mass balances including the mass transport processes and the catalytic reaction. These balances are either differential in time (batch reactor) or in location (continuous operation). By making suitable assumptions on the hydrodynamics and, hence, the interfacial mass transfer rates, in both phases the concentration of the reactants and products can be calculated by integration of the respective differential equations either as a function of reaction time (batch reactor) or of location (continuously operated reactor). In continuous operation, certain simplifications in setting up the balances are possible if one or all of the phases are well mixed, as in continuously stirred tank reactor, hereby the mathematical treatment is significantly simplified. 

For some of them, the use of membrane reactors for their recovery or application in continuously operated reactors has been demonstrated. Examples include the use of dendrimer-bound nickel catalysts for the Kharasch addition [54, 59] and dendritic palladium catalysts for an allylic substitution [73, 60]. The membrane reactor concept has also been transferred to reactions at higher pressure, as shown for the hydrovinylation of styrene (cf. Section 3.3.3) [75]. Modem ultra-and nanofiltration membranes allow an effective recovery of the homogeneously soluble catalyst. However, in some cases the long-term stability of the catalyst under operating conditions has to be improved. 

Despite the experience with batch reactors it may be worthwhile to operate continuous reactors also for fine chemicals. Continuously operated reactors only demand for one start-up and one shut-down during the production series for one product. This increases the operating time efficiency and prevents the deactivation of dry catalysts this implies that the reactor volume can be much smaller than for batch reactors. As to the reactor type for three phase systems an agitated slurry tank reactor [5,6] is not advisable, because of the good mixing characteristics. Specially for consecutive reaction systems the yields to desired products and selectivities will be considerably lower than in plug flow type reactor. The cocurrent down flow trickle flow reactor... 

We also discussed the choice of the reactor. A batch reactor has a much larger volume per unit of reaction product and tank like pressure vessels are much more expensive than cylindrical vessels. This combined with the difficulties of handling catalyst slurries and above all of preventing losses of the often rather expensive catalysts made us consider continuously operating reactors with fixed catalyst beds too. We eventually chose for the packed bubble column as a well suited reactor. 

Plotted in Figure 4.6-9 is the copolymer mole fraction Fma versus the monomer mole fraction /ma for E-MA copolymerizations carried out in a continuously operated reactor [46] at 2000 bar and temperatures of 220, 250, and 290 °C. Total monomer conversion in these reactions is very small, mostly below 1 %. As can be seen from the figure, copolymerization leads to a significant increase in MA content (in going from die monomer mixture to the polymer). From pairs of Fma and /ma values measured at identical pressure and temperature, the two reactivity ratios, rg and Tma. are obtained via eq (4.6-14). 

In order to model a continuously operating reactor a feed and a removal term with a volumetric flow of V m s are added to Eq. (3.6). It is supposed that the volume of the reactor contents does not change. Differences in composition are expressed via the concentrations Cj,in and Cj in mol m . In line with the assumption of an ideally stirred reactor, the composition of the substances flowing out of the reactor is the same as that inside the reactor. We obtain... 

It is important to emphasize the fact that even for first order reactions the density change influences the performance of continuously operated reactors in contrary to batch reactors. In Figure 2.8 the influence of the expansion factor on the conversion of first order reactions is demonstrated. 

For separate feed to a continuously operated reactor, the volume fraction corresponds to the volumetric flow containing referred to the total inlet flow. 

Reproducible processes in continuously operated reactors depend on, in addition to pressure and temperature measurements, precise control of the mass throughput of chemicals. To meet these demands, metering devices in modern microreaction... 

Heated or cooled chemicals can be sent to reactors that are designed to combine chemicals and form new products. Reactors come in a variety of shapes and designs, such as stirred, fluidized, fixed-bed, and tubular (Figure 10-1). Reaction technology can be described as batch, semi-batch, or continuous operation. Reactors are vessels designed to allow a reaction to occur as two or more... 

Figure 9.1 Reactor types for continuous-flow operation with immobiiized/retained biocatalysts [33]. Continuously operated reactors with plug-flow behavior [feed one (S) or more (S. ..) substrates outflow one (P) or more (P. ..) products] (a) Continuous stirred-tank reactor (CSTR) (b) packed-bed reactor (PBR) (c) fluidized-bed reactor (FBR) (d) continuously operated membrane...

---