Semi-continuous operation

The design techniques used include both stagewise and continuous-contac ting methods and can be applied to batch, continuous, and semi-continuous operations. 

Additionally, the influence of the life time of the micro-structured devices as well as the expenditure of the peripheral equipment was estimated in order to obtain insight into the ecological hot-spots of the system. A conventional macro-scaled semi-continuously operated batch process was chosen as a reference process. The comparison of both technological systems was performed by means of the two-step synthesis of m-anisaldehyde serving as model reaction. 

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. 

Laboratory studies of the rearrangement process began with semi-continuous operation in a single, 200-mL, glass reactor, feeding 1 as a liquid and simultaneous distillation of 2,5-DHF, crotonaldehyde and unreacted 1. Catalyst recovery was performed as needed in a separatory funnel with n-octane as the extraction solvent. Further laboratory development was performed with one or more 1000-mL continuous reactors in series and catalyst recovery used a laboratory-scale, reciprocating-plate, counter-current, continuous extractor (Karr extractor). Final scale-up was to a semiworks plant (capacity ca. 4500 kg/day) using three, stainless steel, continuous stirred tank reactors (CSTR). 

Bacterial inactivation is achieved by CO2 absorption in the liquid phase, even though the reason why it happens is still not clear. In this respect, batch- and semi-continuous operating modes are substantially different. In the batch system the residence time, i.e., the time of contact between gas- and liquid phase, must be sufficient to allow the diffusion of CO2 in the liquid, and is therefore a fundamental parameter to assure a desired efficiency. In the semi-continuous system the contact between the phases is localized in the surface of the moving micro-bubbles. In this second case, the efficiency of the process is influenced by temperature, pressure, gas flux, bubble diameter, and other parameters that modify the value of the mass-transfer coefficient. Therefore, it is not correct to use the residence time as a key parameter in the semi-continuous process. In fact, a remarkable microbial inactivation is reached even with an exposure time of 0 min (i.e., pressurizing and immediately depressurizing the system) these two steps are sufficient to allow CO2 to diffuse through the liquid phase. 

A commercial rotary, resistance-heated vertical reactor system for semi-continuous operation (Rotox-60) is sold by Unicorp, Inc., CA. It features premixed gas input through four tubes inside the conical deposition chamber for uniform distribution, and has separate stations on a carrier disk for wafer loading/unloading, preheating, deposition, and cool-down. As many as seven 5 cm wafers can be accommodated per station. The maximum oxide deposition rate is 1,700 A/min, with a conservatively estimated overall uniformity of 5% (Kern, 1975). 

The design of SMBR processes has to take into account the requirements of different types of reactions. Therefore, different types of flowsheets and operating modes can be chosen. As with a semi-continuous operation, a process without section IV (regeneration of the solvent), a five-section process or a four section process without recycle of the eluent may be advantageous. Relevant design criteria for the SMBR are discussed in Section 8.4. 

Cooking.—Starch is completely pastified by cooking under pressure. In order to maintain semi-continuous operation this is accomplished in three cookers used cyclically at intervals of an hour. That is, cooking of each distinct batch consumes three hours, but each hour another cooker in rotation has completed its batch and commences with a fresh one. A scheme of this operation is shown in Figure 32, p. 125. 

The fourth model of an ideal reactor can be described as a sort of combination of CSTR and BR. It is the semi-continuously operated, ideally mixed, stirred batch reactor, SBR. This is operated by charging one or more components and auxiliary materials initially and feeding at least a second reactant, with or without further auxiliary materials, at a constant rate over a certain period. 

Even in the case of a semi-continuous operation this loss in cooling capacity cannot be compensated by the increase of the wetted heat transfer area. Under these operating conditions a decrease of the heat removal power to 1/3 of its original value, again, is not uncommon. 

Degradation of organopollutants by fungal cultures has been carried out successfully at bench and pilot scale, preferentially in batch or semi-continuous operations (Alleman et al. 1995 Fujita et al. 2002 Mielgo et al. 2002). Continuous treatment systems are desirable alternatives to increase process efficiency. A modified conventional configuration (fixed-bed bioreactor) coupled with a pulsation system has... 

Most industrial precipitation units are simple in construction. The prime aim is usually to mix reacting fluids rapidly and to allow them to develop a precipitate of the desired physical and chemical characteristics. Batch operation is more often favoured for industrial precipitation than is the truly continuous mode, although the merits of semi-continuous operation deserve serious consideration, i.e. a continuous reactant mixing step from which the product stream passes to batch-operated agitated hold-up tanks to permit equilibration, phase transformation, ripening, etc. The hold-up tanks may be arranged in a sequenced battery or in a continuous cascade system (see section 9.1.2). 

In contrast to the pultrusion process, the production speed and the maximum size of the profile are not limited by the required pulling forces. Due to the use of release films, there is no adhesion between the polymer and the surface of the mold. Furthermore, the friction between the release film and the tool is minimized because of the semi-continuous operating principle of the CCM process. 

One of the recent developments in this filter category is the vertical recessed plate automatic press shown schematically in Figure 12.4. While the conventional filter press usually has the plates hanging down and linked in a horizontal direction, this type has the plates in a horizontal plane and placed one upon another. This design offers semi-continuous operation, savings in floor space and easy cleaning of the cloth, but it allows only the lower face of each chamber to be used for filtration. The filter usually has an endless cloth. 

Yan Q, Hu RX, Tan RX, Wu J (2005) Efficient production and recovery of diterpenoid tanshinones in Salvia miltiorrhiza hairy root cultures with in situ adsorption, elicitation and semi-continuous operation. J Biotechnol 119 416... 

Standard fed-batch operation is not economically viable due to solvent toxicity, so the system can be coupled with an in situ recovery process (Lee et al. 2008 Ezeji et al. 2004a, b). Fed-batch fermentation is used principally in laboratories, but it cannot be applied without in situ product removal due to its strong cell inhibition. Semi-continuous operation is also used in industrial practice in order to avoid strain degeneracy (Branduardi et al. 2014 Xue et al. 2013a). 

S.R. Son, S.D. Kim, Semi-continuous operation of chemical looping combustion with metal oxides supported on bentonite in an annular fluidized bed reactor, in Proceedings of the Asian Conference on Fluidized Bed and Three Phase Reactors (2006)... 

This chapter focuses on key features to understand the emulsion copolymerisation kinetics and on the influence of operation on the copolymer composition of the final latex products. Focus is on batch and semi-batch or semi-continuous operation, see Figure 4.1. Only the free-radical emulsion copolymerisation of two monomers is considered but the concepts can be directly applied for formulations containing more than two monomers. The reacting monomers usually having different reactivities, polymerise simultaneously. The reactivities and the individual concentrations of the monomers at the locus of polymerisation, that is, the particle phase, govern the built-in ratio into the polymer chains at a certain time. 

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