Loop reactor comparison

Table 37.1 Comparison of the loop reactor and the stirred autoclave.

Because of the difficulties of stabilizing the pH at the pH optimum of 6.0 owing to liberation of C02, a loop reactor was developed which keeps the C02 dissolved at lObar and thus helps to stabilize the pH. Co-immobilization of E. coli and Ps. dacunhae cells for direct production of L-alanine from fumaric acid was not successful because E. coli cells work best at a pH of 8.5, in comparison with a pH of 6.0 for Ps. dacunhae cells and the decarboxylase. The sequential process has been run since 1982. The high enantioselectivity of L-aspartate-/kdecarboxylase (ADC) led to a process, in 1989, in which inexpensive DL-aspartate was converted to L-alanine and D-aspartate [Eq. (7.1)] the latter commands interest for synthetic penicillins ... 

S. Becker, A. Sokolichin, G. Eigenberger, Gas-liquid flow in bubble column and loop reactors. Part II. Comparison of detailed experiments and flow simulations, Chem. Eng. Sci. 49 (1994) 5747-5762. 

Becker, S., Sokolichin, A., and Eigenbeiger, G., Gas-liquid flow in bubble columns and loop reactors Part n Comparison of detailed experiments and flow simulation. Chem. Eng. Set, 49,5747 (1994). 

The granulate-filled sandwich structure described in Section II.B permits continuously operated loop systems to be developed as replacements for batch processes. Loop reactors so equipped also exhibit advantages by comparison to conventional fixed-bed reactors better exploitation of the catalytically active component due to smaller granulate size, lower pressure drop, and better gas-liquid mass transfer. 

Becker S, Sokolichin A, Eigenberger G (1994) Gas-Liquid Flow in Bubble Columns and Loop Reactors Part II. Comparison of Detailed Experiments and Flow Simulations. Chem Eng Sci 49(24B) 5747-5762. 

A direct comparison with pilot plant scales is ongoing at the time of writing, but a point raised by a number of authors is that true pilot plant or production comparison must probably be made on a case-by-case basis. - One such example quoted in the literature is for the synthesis of the cosmetic Laurydone (presumably a high-value product), which used a batch-loop reactor where an energy savings of 40% had been claimed. However, the original comparison has now been identified as flawed, and the reactor setup dismantled. ... 

Aside from process comparisons, the main contrast between the systems is that of size, weight, and cost, especially for pressurized systems. Construction of batch reactors for use with ethylene at pressures of 1000 psi (70 atm) and upward has to be massive. The simple construction of the Loop process just pumps and pipework blends itself to use at high pressures. Apart from cost and weight, the small volume of the Loop reactor has obvious safety advantages. Despite these attractions, the Loop reactor system has so far been used successfully only for low-pressure systems such as poly(vinyl acetate) homopolymer for adhesives and copolymers for paint. Large-scale production of ethylene-vinyl acetate copolymers has yet to be demonstrated. 

A comparison of stirred tan)c reactors (1.1.1) with tower reactors (1.1.2) and tower loop reactors (1.1.3) indicate that all of them behave similar if cell-free feed is used at nonlimiting growth there is no stable steady state. 

Table 4.Comparison of single-stage concurrent tower loop reactors by employing H.polymorpha, ethanol and glucose as substrate.Biological parameters of the investigated systems...

ADVANTAGES OF THE VENTURI LOOP REACTOR A DETAILED COMPARISON... 

Table 8.2 gives a semiquantitative comparison of venturi loop reactor with stirred tank reactor. 

TABLE 8.2 Comparison of Venturi Loop Reactor with Stirred Tank Reactor... 

Table 3. Comparison of the loop Reactor and the Stirred Autoclave...

In order to see how these advantages could be realized in practice, the performance of a loop reactor was compared with that of a conventionally-built integral reactor.In this comparison the capability to handle actual industrial catalysts, the settling time of changing experimental conditions, the difficulty of the mathematical evaluation of the measured data were considered. The accuracy of the datas for scale up problems was checked in a pilot plant. For the reaction, the oxidation of o-xylene with a vanadiumpentoxide catalyst, an industrially important process, was chosen. 

The styrene conversion versus reaction time results for runs in the laminar flow regime are plotted in Figure 8. Both the rate of polymerization and the styrene conversion increase with increasing flow rate as noted previously (7). The conversion profile for the batch experimental run (B-3) is presented as a dashed line for comparison. It can be seen that the polymerization rates for runs with (Nj e e 2850 are greater than the corresponding batch polymerization with a conversion plateau being reached after about thirty minutes of reaction. This behavior is similar to the results obtained in a closed loop tubular reactor (7J) and is probably due to an excessively rapid consumption of initiator in a... 

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. 

The output temperature is given by the ambient temperature of the waste-heat loop and can be taken to be 30°C for purposes of estimation. The input temperature of the steam is limited by physical constraints on the reactor primary cooling loop to be about 300°C. Therefore, the maximum Carnot efficiency is approximately carnot = (573 K-303 K)/573 K = 0.47, whereas the actual efficiency is typically 8dec = 0.35 when measured as electrical power outside the plant to total thermal power in the core. For comparison, a coal-powered plant might have values of carnot = 0.65, 8eiec = 0.5 due to higher steam temperatures... 

The feed to the reactor element within the loop is amix. The flow rate entering the reactor element is Qin + q and the exit concentration is aout. The relationship between amix and aout can be calculated without direct consideration of the external recycle. In the general case, this single-pass solution must be obtained numerically. Then the overall solution is iterative. One guesses amix and solves numerically for aout. Equation (4.21) is then used to calculate amix for comparison with the original guess. Any good root finder will work. The function to be zeroed is... 

Figure 17.19b presents a direct comparison of all alternatives with respect of impurity L. It may be seen that the effect depends on the recycle structure deflation for the base-case and inflation in alternatives A and C, while in the alternative B the steady state effect is almost negligible. The explanation can be found in the negative feedback effect of reactor Rl, where L is destroyed in heavies. In alternatives, by suppressing the back flow from S4 to Rl, the converted L diminishes and the accumulation becomes positive. The effect is maximum in alternative C and minimum in the alternative B, corresponding to differences in the path of the recycle loops. 

Table 17.5 Comparison of loop slurry reactor performance with mechanically agitated reactor (MASK) performance under corresponding conditions (adapted from Leuteritz, 1973)...

Blazej, M., Annus, J., andMarkos, J. (2004a), Comparison of gassing-out and pressure-step dynamic methods for kja measurement in an airlift reactor with internal loop, Chemical Engineering Research and Design, 82(10) 1375-1382. 

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