Batch versus Continuous Reactors

Batch versus Continuous Fermentation A process can be run in batch or continuous mode. In continuous mode, there is a constant flow of fermented sugar out of the reactor that is equal to a continuous flow of fermentation medium into the reactor. During batch fermentation, there can be an inflow of medium, but there is no outflow [58]. Batch fermentation needs to be inoculated with a starter culture every time, whereas this is not needed in a continuous fermentation setup. However, in case of problems, the continuous fermentation needs to be restarted, so an infrastructure for starter cultures is needed anyway. A high volumetric production rate can be achieved when combining continuous... 

Another major decision on scale-up is batch versus continuous. If something is to be manufactured in a batch reaction, starting materials are added, the reaction is performed, and the product purified and isolated. If more is needed, then a second run or a second batch is performed. Often batch manufacturing processes run one batch after another around the clock. Another option is to run chemical reactions on a continuous basis. In a continuous process, starting materials are continuously fed to the reactor and product continuously purified and isolated. 

Both batch and continuous reactors are used in industrial vinyl polymerization processes. Agitated kettles, tower reactors, and linear flow reactors are just a few examples of industrially used polymerization reactors. The choice of reactor type depends on the nature of polymerization systems, (homogeneous versus heterogeneous), the quality of product, and the amount of polymer to be produced. Sometimes, multiple reactors are used and operated at different reaction conditions. Whichever reactor system is used, it is always necessary to maximize the process productivity by reducing the reaction time (batch time or residence time) while obtaining desired polymer properties consistently. 

Back-mix reactor design, 721, 728 Baffles in heat exchangers, 595, 610-612 pressure drop over, 599-602, 605-606 Bailee s liahihty, 263 Balance sheet, 140-142 Barometric-leg pumps, 523 Batch operation versus continuous, 35-36 Batch-reactor design, 721-727 Battery-limit additions, definition of, 167 Berl saddles, 688-690 cost of 710... 

Form of enzyme and concentration of substrate influence the yield and type of lOS produced, however another study by Yun et al. [277] used whole cells of Escherichia coli HB101 whereby the gene for an endo-inulinase from Pseudomonas sp was expressed. In a batch reactor the production of lOS using the recombinant enzyme was compared to that of the native and there were differences in the DP distribution of the products formed although the yield of lOS was comparable. The native form produced less inulobiose and more DP4 and > DP4 products compared to the recombinant. Additionally Yun et al. [277] studied the effect of different reactor conditions batch processing versus continuous using immobilized recombinant cells but no differences in product composition were observed. 

The authors found that the model-predicted As concentration is close to the leachate concentrations from the column packed with dust from the continuous reactor (1 120 H.gL-1 versus 1 330 xgL-1), when the solubility product of scorodite from Robins (1990) and the triple layer model is used. Only 11% As in the system was sorbed onto hydrous ferric oxide surfaces. Arsenic concentrations in the leachate are largely controlled by scorodite solubility. It should also be pointed out that simulations using solubility only and without including surface adsorption resulted in a closer match (1 270 n-gL-1 versus 1330 piglA1). For the simulation of the column experiments using wastes from the batch-reactor, the triple layer model predicted too low an As concentration (33 jigL-1 versus 120 pigL-1). 

A second stream can also be used in RBatch by attaching it to the blue arrow on the side of the reactor called Continuous Feed (optional) (see Fig. 4.21). As the name implies, this stream is used if fed-batch operation is desired. This stream is a real flowing stream, whose flow-versus-time profile can be specified, as we will illustrate later. 

Comparative tests have been performed in the semi-batch reactor system to evaluate the Ru/Ti02 cataly versus a more conventional nickel-based catalyst. These tests show that rutlienium at only 3% metal loading has about the same activity as nickel at S0% metal loading. This comparison is only for short-term activity of the catalyst. As demonstrated in the continuous flow tests, the nickel catalyst loses activity readily in tlie first hours on stream, while the ruthenium maintains its activity. 

Free enzyme versus immobilized enzyme can influence the yield of lOS, additionally an immobilized system would be favorable economically as the biocatalyst can be reused, enables continuous production and the end product is free of contamination. Kim et al. [275] intended to make a comparison between the reaction kinetics of free and immobilized endo-inulinases in a batch reactor however significant differences were observed in the reaction behavior and product composition due to the form of enzyme used and the initial concentration of substrate. Yun et al. [276] investigated the effect of inulin concentration on the production of lOS by free and immobilized endo-inulinase from Pseudomonas sp. Their findings corroborate those of Kim et al. [275] whereby different products are formed depending on the form of enzyme a soluble enzyme yielded inulobiose and DP3 products, whereby the immobilized form predominantly produced inulobiose. As the concentration of inulin increased the yield of lOS did not increase in the soluble system and in the immobilized the yield remained the same. Although the enzyme was derived from Pseudomonas the immobilized form required a differ-... 

Compare these results to those of Equation 2.22 for the same reactions in a batch reactor. The CSTR solutions do not require special forms when some of the rate constants are equal. Intermediate components B and C will exhibit maximum concentration at particular values of t, and a plot of outlet concentrations versus t is qualitatively similar to the behavior shown in Figure 2.2. However, the value for t that gives a maximum in a CSTR will be different than the value of t that gives a maximum in a PFR. For the normal case of bi = 0, the value of t that maximizes bojn is a root mean, fniax = 1/V a s > rather than the log mean of Equation 2.23. The best possible yield of B is lower in a CSTR than in a PFR or batch reactor. Continuous flow stirred tank reactors are almost always worse in terms of selectivity because the entire reactor operates under conditions that favor production of undesired byproducts. 

Fig. 2.6 The three ideal types of chemical reactor and their characteristic concentration versus time or concentration versus distance behaviour for the reactant and product, (a) Simple-batch reactor, (b) Plug flow reactor (PFR). (c) Continuously stirred tank reactor (CSTR).

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