Batch versus continuous flow

Most polymers are made in batch reactors, but the relative few that are made continuously dominate total industrial output. There are three factors that dictate the choice of reactor mode  

Economics. Continuous processes are usually cheaper for large volume production. Batch processes are usually cheaper for specialty polymers. 

Product quality. Many polymers are best made in a batch process. For some, converting to a continuous process is difficult or impossible. A few, particularly copolymers, exhibit better properties when made continuously. 

Inertia and conventional wisdom. Most polymer chemists use batch reactors. The decision to change reaction mode is sometimes never made due to technical inertia. Occasionally, an overly eager engineer makes an inappropriate change based on conventional wisdom rather than specific facts. 

Before regarding technical inertia too harshly, it should be noted that a decision to go from batch to continuous operation has strong implications for product development costs. Most polymers companies use general purpose, batch equipment for initial scale-ups. Preliminary product evaluations and even market development studies will use the batch-produced material, and 

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Level 1 Batch versus continuous Level 2 Input—output stmcture of the flow sheet Level 3 Recycle stmcture of the flow sheet Level 4 Separation system specification... 

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. 

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... 

Continuous versus (semi)batch, reaction time, flow rates Materials of construction... 

Manz, A., Bessoth, R, Kopp, M.U., Continuous flow versus batch processing- a few examples. Micro Total Analysis Systems 98, Proceedings pTAS 98 workshop, Banff, Canada, 13-16 Oct. 1998, 235-240. 

Powdered activated carbons offer the advantage of low cost compared to granules in terms of both purchase price and capital expenditure (investment in adsorber units, pumps, etc). The cost of PAC is about 1.00/kg versus 2/kg for GAC [19]. For a system treating 4 million/day the cost is about 0.03/1,000 L [67], A wider range of impurity removal levels can be attained with powdered carbon, where the dose of carbon per batch can be adjusted, depending on the type and concentration of the contaminants [68]. GAC is normally used in continuous flow deep beds and is advantageous when variations in adsorption condi-... 

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. 

Fedotov, P. S., Fitz, W. J., Wermrich, R., Morgenstem, P., and Wenzel, W. W. (2005a). Fractionation of arsenic in soil and sludge samples continuous-flow extraction using rotating coiled columns versus batch sequential extraction. Anal. Chim. Acta 538, 93-98. 

Fmftiermore, a continuous flow-system has been developed using the polymer 82 and overall 23 mmol of a-methylstyrene have been transformed into the corresponding product after 5 consecutive batches. The enantioselectivity did not change between the successive runs (close to 90% ee). The TTN was estimated at 44 or 51 versus the supported Box and copper salt respectively. 

Glasnov, T.N., Findening, S and Kappe, C.O. (2009) Heterogeneous versus homogeneous palladium catalysts for ligandless Mizoroki-Heck reactions a comparison of batch/microwave and continuous-flow processing. Chem. Eur. J., 15 (4), 1001-1010. 

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. 

Figure 17.9. Dialyzed Chemostat Estimated values of specific MAb production rate versus time during the initial batch start-up and subsequent dialyzed continuous operation with a dialysis flow rate of 5 IJd.

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. 

Mass flow and current density Cell voltage and cooling systems Corrosion phenomena Recycling of impurities Continuous versus batch processing Selectivity versus mass yield... 

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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