Semibatch reactor semi-batch

Key PFR = Plug Flow Reactor, BSTR = Batch Stirred-Tank Reactor, (S)BSTR = (Semi)Batch Stirred -Tank Reactor, SBSTR = Semibatch Stirred-Tank Reactor, CSTR = Continuous Stirred-Tank Reactor, TBR = Trickle-Bed Reactor. 

Kinetic Model Discrimination. To discriminate between the kinetic models, semibatch reactors were set up for the measurement of reaction rates. The semi-batch terminology is used because hydrogen is fed to a batch reactor to maintain a constant hydrogen pressme. This kind of semi-batch reactor can be treated as a bateh reactor with a constant hydrogen pressme. The governing equations for a bateh reactor, using the product formation rate for three possible scenarios, were derived, as described in reference (12) with the following results ... 

In this chapter, we first consider uses of batch reactors, and their advantages and disadvantages compared with continuous-flow reactors. After considering what the essential features of process design are, we then develop design or performance equations for both isothermal and nonisothermal operation. The latter requires the energy balance, in addition to the material balance. We continue with an example of optimal performance of a batch reactor, and conclude with a discussion of semibatch and semi-continuous operation. We restrict attention to simple systems, deferring treatment of complex systems to Chapter 18. 

Reactors can be operated either in a batch or continuous-flow mode. The combination, batch with respect to the liquid and continuous-flow with respect to the gas, is called semibatch. Often this fine distinction is ignored and it is commonly referred to as batch. The majority of ozonation experiments reported in the literature have been performed in one-stage semi-batch heterogeneous systems, with liquid phase reactor volumes in the range VL = 1-10 L. Most full-scale applications are operated in continuous-flow for both phases. 

You are asked to design a semibatch reactor to be used in the production of specialized polymers (ethylene glycol-ethylene oxide co-polymers). The semi-batch operation is used to improve the molecular-weight distribution. Reactant B (EG) and a fixed amount of homogeneous catalyst are charged initially into the reactor (the proportion is 6.75 moles of catalyst per 1000 moles of Reactant B). Reactant A (EO) is injected at a constant rate during the operation. The polymerization reactions are represented by the following liquid-phase chemical reactions ... 

In a batch reactor, the reactants are initially charged and, after a certain reaction time, the product(s) are recovered batchwise. In the semi-batch (or fed-batch) reactor, the reactants are fed continuously, and the product(s) are recovered batch-wise. In these batch and semibatch reactors, the concentrations of reactants and products change with time. 

Different types of reactors are applied in practice (Figure 1.14). Stirred tank reactors (STR), very often applied for homogeneous, enzymatic and multiphase heterogeneous catalytic reactions, can be operated batchwise (batch reactor, BR), semi-batchwise (semibatch reactor, SBR) or continuously (continuous strirred tank reactor, CSTR)... 

An industrial batch reactor has neither an inflow nor an outflow of reactants or products while the reaction is being carried out. Batch reactions can be carried out in droplet microreactors, where nanoliters of fluid are individually manipulated using techniques such as electrowetting on dielectric (EWOD) and surface tension control. Semibatch reactors are used in cases where a by-product needs to be removed continuously and to carry out exothermic batch reactions where a reactant has to be added slowly. Microfluidics allows precise control of concentration and temperature, which allows batch and semi-batch reactions to be carried out in a continuous manner. Figure 1 shows the general components of a sin5)le industrial-reactor setup, compared with a laboratory-scale setup to carry out a reaction with microfluidic chips. 

Emulsion polymerization studies reported in the scientific literature are usually based on experiments with batch or semibatch reactor systems. Since most workers in the field are familiar with such reactors, the thrust of this discussion will be to compare continuous reactors with batch and semi-batch operations. The particular areas to be reviewed include (i) inhibitor effects, (ii) particle age distributions, (iii) particle nucleation, (iv) copolymerization, (v) particle morphology, (vi) temperature control and heat removal and (vii) polymerization kinetic models. 

FIGURE 13.12 Results of predictive control of for free radical polymerization of Am in semibatch operation. In batch mode, decreases monotonically in time. By computing conditions for isoreactivity (Equation 13.63c) constant during the reaction was achieved. By operating Am flow into the reactor in the flooded regime (Equation 13.63b), a predictable increase in during the semibatch reaction was achieved. Adapted with permission from Kreft T, Reed WF. Predictive control and verification of conversion kinetics and polymer molecular weight in semi-batch free radical homopolymer reactions. Eur Polym J 2009 45 2288-2303. 

Optimization of (semi)batch reactor operation will include considerations of reaction time versus conversion, reaction time versus monomer recovery cosh and the potential for variations in polymerization temperature within a batch to achieve desired product quality, and hence end-use properties. Open-loop trajectories may be determined for the addition of monomers and/or initiators. Temperature programming is often done to develop polymer of unique properties. The semibatch addition of the more reactive monomer in copolymerization is often carried out to develop a product with a uniform or gradient CCD. In pulsion polymerization, programmed addition of monomer, comonomer, initiator. 

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