Batch mode production

For smaller production quantities (mle of thumb 10 000 t/a) and/or frequent product changes, it has advantages over the tubular reactor. Very long residence times can readily be achieved, and reaction conditions such as temperature, pH value, and catalyst concentration can be changed and optimized during the reaction time. In batch mode, product quality is subject to certain variations, and hence continuous process control is necessary. 

The ion-exclusion process for sucrose purification has been practiced commercially by Firm Sugar (104). This process operates in a cycHc-batch mode and provides a sucrose product that does not contain the highly molassogenic salt impurities and thus can be recycled to the crystallizers for additional sucrose recovery. 

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. 

The alternative to batch mode operation is continuous operation. In the continuous mode there is a continuous flow of medium into the fermentor and of product stream out of the fermentor. Continuous bioprocesses often use homogenously mixed whole cell suspensions. However, immobilised cell or enzyme processes generally operate in continuous plug flow reactors, without mixing (see Figure 2.1, packed-bed reactors). 

In many cases, problems cannot be overcome by biological means. This is especially true for those related to inhibition by substrate or product. There may, however, be technical solutions to these problems. Nowadays, complicated feed strategies with different substrates can be achieved through the use of flow injection analysis, on-line sensors, mass flow meters and sophisticated computer control. Such control coupled to a fed-batch mode of operation (Figure 2.5) can often eleviate problems caused by substrate inhibition. For some processes, continuous product removal can avoid the problems associated with product inhibition the various options include ... 

Most industrial bioprocesses are now operated in a batch mode. Batch processing is the method of choice for small-scale production,... 

Many industrial reactors operate in the fed-batch mode. It is also called the semibatch mode. In this mode of operation, reactants are charged to the system at various times, and products are removed at various times. Occasionally, a heel of material from a previous batch is retained to start the new batch. 

On an industrial level, the reaction is carried out in semi-batch mode with a yield of 70% [61, 62,127]. First steps towards continuous production with a mixer and a cooler increased the yield to 80-85% however, the reaction occurred partly in the mixer, thereby increasing the temperature in this unit The reaction is quenched by dilution with water, also having a cooling function. 

Crameri et al. (1997) have reported an asymmetric hydrogenation constituting an important step in the production of a new calcium antagonist, Mibefradil (POSICOR) (of Hoffmann-LaRoche). Pilot-scale synthesis of (S)-2-(4-flurophenyl)-3-methylbutanoic acid by the asymmetric hydrogenation of 2-(4-fluorophenyl)-3-methyl but-2-enoic acid with a [Ru (/ )-MeOBIPHEP)(OAc)2]-catalyst has been described. The hydrogenation was performed in a continuous mode in a cascade stirred-tank reactor system at a pressure of 270 bar. A large reduction in total reactor volume compared to the batch mode was realized. 

The facility considered in the industrial case study is a pharmaceuticals production plant, which produces a wide variety of consumer products, e.g. shampoos and creams, and female sanitary products. The plant was chosen due to the fact that production was carried out in batch mode. In a year the plant uses on average 90000 m3 of water, with approximately 60-70% of this discarded as effluent. An on-site treatment facility pre-treats wastewater produced from the site to a level where the water can be discharged into the municipal water system. 

The catalytic ethylene oligomerization was performed in a 0.3 L well-mixed three-phase reactor operating in semi-batch mode, at constant temperature (70 or 150 °C) and pressure (4 MPa of ethylene) in 68 g of n-heptane (solvent). Prior to each experiment, the catalyst was successively pretreated, firstly in a tubular electrical furnace (550 °C, 8 h) and then in the oligomerization autoclave (200 °C, 3 h), under nitrogen flow at atmospheric pressure. After 30 min of reaction, the autoclave was cooled at -20 °C and the products were collected, weighted and analyzed by GC (FID, DB-1 60 m capillary column). 

Birhanli E, Yesilada O (2006) Increased production of laccase by pellets of Funalia trogii ATCC 200800 and Trametes versicolor ATCC 200801 in repeated-batch mode. Enzyme Microb Technol 39 1286-1293... 

The real-word case study considered here is the production of expandable polystyrene (EPS). Ten types of EPS are produced according to ten different recipes on a multiproduct plant which is essentially operated in batch mode. In this section, the multiproduct plant, the production process and the scheduling problem are presented. 

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