Continuous operation, comparison with batch

Pressure filters are operated in the range of 30-60 psi and some times up to 100 psi. In contrast to vacuum filters, pressure filters normally operate in batch mode. The rate of cake buildup in batch operation is slow in comparison with continuous drum filters. The time required to dump the cake and clean and reassemble a pressure filter is called dead time. It is a significant element in determining the capacity of a pressure filter. 

Yet, in spite of these benefits linked to PI, there are still significant barriers [7] that hinder changes in chemical industry. One of these, it is now well admitted, is the transposition from batch to continuous operation, which has to be carefully addressed since this generally allows operating under radically different operating conditions in comparison with the those for batch operations, and sometimes under conditions even nonreachable with a fed-batch mode. 

Crystal growth is a layer-by-layer process, and the retention time required in most commercial equipment to produce crystals of the size normally desired is often on the order of 2 to 6 h. Growth rates are usually limited to less than 1 to 2 pm/min. On the other hand, nucle-ation in a supersaturated solution can be generated in a fraction of a second. The influence of any upsets in operating conditions, in terms of the excess nuclei produced, is very short-term in comparison with the total growth period of the product removed from the crystallizer. A worst-case scenario for batch or continuous operation occurs when the explosion of nuclei is so severe that it is impossible to grow an acceptable crystal size distribution, requiring redesolution or washout of the system. In a practical sense, this means that steadiness of operation is much more important in crystallization equipment than it is in many other types of process equipment. 

Mendes et al. (37) studied the use of SC-C02 for vitamin E concentration in deodorizer distillate of soybean oil. Lee et al. (38) applied a SFE method to test the feasibility of tocopherol concentration from soybean sludge with SC-C02. Shishikura et al. (39) separated tocopherols from soybean sludge by SC-C02 and nitrous oxide (SC-N20). Lecithin and other compounds can be concentrated in liquid wastes with continuous/semicontinuous SC-C02 operations production costs will be substantially reduced in comparison with batch operations. 

Typical steady state performance of a continuous SSF membrane process is reported in Figure 7.47. A comparison of continuous SSF to batch SSF shows how performance can be improved with the use of membranes. Enzyme consumption is strongly reduced when the reactor is operated in this way. 

The suitability of the different operating modes can be determined with the aid of programs for modeling batch distillations. The treatment of batch distillations is much more laborious than that for continuous distillations. However, the decision can be simplified by using Equations (2.3.2-29) and (2.3.2-30), which were determined for the different operating modes with the aid of differential equations. The minimum vapor quantity G is used for comparison ... 

Hansenula polymorpha (CBS 4732) was cultivated in a synthetic nutrient medium [113] with glucose, ethanol and methanol as substrates, respectively, in batch and continuous operations. The flotation was performed in batch as well as in continuous mode. A comparison of the performances of batch flotation with continuous flotation indicated that, in the latter, the C values are higher than in the former. For example, at C = 1.5 gl the cell concentration in the... 

If the reaction is to be performed in a continuous setting, two separate sets of equipment are required and must be operated simultaneously. Compositions are then obtained by mixing the necessary streams belonging to each structure in the appropriate proportions. By comparison, if it is desired to perform the same task under batch conditions, an identical outcome may be achieved by two serial operations together with intermediate storage of material used in mixing processes. Hence, it may turn out that a single set of reactive equipment is sufficient to achieve the same result. 

The reports mentioned above provide a systematic coverage of the nonimmobi-lized enzymatic reactors used in biocatalytic reactions under continuous flow operation. Results from microreactor experiments were comparatively higher than conventionally mixed batch reactors in terms of conversion rate and improvement of product yield as demonstrated for hydrolysis [140], dehalogenation [141], oxidation [142], esteriflcation [143], synthesis of isoamyl acetate [144,145], synthesis of cyanohydrins [147,148], synthesis of chiral metabolites [153], reduction [151], and bioluminescent reaction [149]. The small volumes involved and the favorable mass transfer inherent to these devices make them particularly useful for the screening of biocatalysts and rapid characterization of bioconversion systems. The remarkable results of such studies revealed that the product yield could be enhanced significantly in comparison with the conventional batch runs. 

In comparison with a continuously operating system, therefore, the batch operating system would appear to be at a disadvantage. Blow tank systems, however, can operate at very much higher pressures to compensate, and twin arrangements in series can be configured... 

High or ultrahigh product purity is obtained with many of the melt-purification processes. Table 22-1 compares the product quality and product form that are produced from several of these operations. Zone refining can produce very pure material when operated in a batch mode however, other melt ciystallization techniques also provide high purity and become attractive if continuous high-capacity processing is desired. Comparison of the features of melt crystalhza-tion and distillation are shown on Table 22-2. 

This means that as long as a CSTR is used as the first stage reactor and all the recipe ingrediants are fed into the first stage reactor, one cannot have more than 57% of the number of particles produced in a batch reactor with the same recipe as in continuous operation. The validity of these expression is clear from the comparison between the experimental and theoretical values shown in Figure 5. From Figure 5, it is found that the optimum mean residence time of the first stage reactor is about 10 minutes under these reaction conditions. Equation(30) predicts 10.0 minutes, while experimental value is 10.4 minutes where the number of polymer particles is about 60% of that produced in a batch reactor. 

Figure 9.19 shows typical cell concentrations reached in the main industrial bioreactors and a comparison of these values with those found in microbial fermentations. As can be observed, batch and fed-batch cultivations attain dry biomass values comparable to those of continuous cultures of microorganisms, so that mass and heat transfer capacities are not limited for these operation modes. However, high cell density cultivation in heterogeneous bioreactors, such as hollow-fiber devices, reaches dry biomass values similar to the maxima observed in microbial cultures. 

The globules are large, they oscillate with consequent movement of droplets inside the globules and the process is either chemically controlled or limited by the rate of diffusion in the external phase. Since it is also kinetically controlled it can be used in a semi-batch or continuous arrangement. Insufficient data are available at this stage to make a reliable comparison of stirred tanks and spray columns, except that the latter are more suitable for continuous operation. 

Vastly different methods are available for cultivation of biofilms. Basically, these can be described as either batch-mode or continuous mode methods. In batch studies, growth substrata in the form of coupons or glass slides are placed in e.g. Petri-dishes or other holders filled with medium. Under the action of undefined shear forces, investigations in so-called beaker reactors are conducted. A further test system which operates in batch mode and continues to become prominent is the miniaturized test system comprising microtitre plates, in which 96 wells enable the simulation of various experimental conditions simultaneously under static conditions (Geneveaux et al., 1996 O Toole et al., 1999). In general, biocide tests in batch systems are simpler to run, have shorter durations, and are very simple to carry out. Therefore, they are well-suited for initial comparisons or screenings of different biocides, or different concentrations and contact times of a particular biocide. 

In addition, in comparison to conventional batch chromatography, the application of the SMB principle allows the continuous operation of processes, which makes it easier to obtain products of constant purity without analytical controls for each single batch. Even more importantly, a 90% reduction in the overall amoimt of solvents needed for a separation can be achieved [32]. The overloaded conditions make it possible to optimize productivity with regard to the inventory of stationary phases. This optimization requires knowledge of the adsorption isotherms (Eq. 8) and the use of special simulation programs [33]. 

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