Recycle systems

Figure 1.6 The onion model of process design. A reactor design is needed before the separation ind recycle system can be designed, and so on. (From Smith and Linnhoff, Trans. IChemE, CkERD, 66 195, 1988 reproduced by permission of the Institution of Chemical Engineers.)...

Given the choice of a batch rather than continuous process, does this need a different approach to the synthesis of the reaction and separation and recycle system In fact, a different approach is not needed. We start by assuming the process to be continuous and then, if choosing to use batch operation, replace continuous steps by batch steps. It is simpler to start with continuous process operation... 

The normal boiling points of the materials are given in Table 4.6. Synthesize a continuous reaction, separation, and recycle system for the process, bearing in mind that the process will later become batch. 

Ftgure 4.13 The recycle system for the production of butadiene sulfone. 

In this case, because there are no raw materials losses in the separation and recycle system, the only yield loss is in the reactor, and the process yield equals the reactor selectivity. 

The two inner layers of the onion diagram in Fig. 1.6 (the reaction and separation and recycle systems) produce process waste. The process waste is waste byproducts, purges, etc. 

Separation and recycle systems. Waste is produced from separation and recycle systems through the inadequate recovery and recycling of valuable materials from waste streams. 

Let us now turn our attention to losses from the separation and recycle system. 

Minimization of Waste from the Separation and Recycle System... 

Figure 10.3a shows a simplified fiowsheet for the production of isopropyl alcohol by the direct hydration of propylene. Different reactor technologies are available for the process, and separation and recycle systems vary, but Fig. 10.3a is representative. Propylene... 

The third source of process waste after the reactor and separation and recycle systems is process operations. 

Increasing process yields through feed purification to reduce losses in the reactor and separation and recycle system. 

Methanol Synthesis. AH commercial methanol processes employ a synthesis loop, and Figure 6 shows a typical example as part of the overall process flow sheet. This configuration overcomes equiUbtium conversion limitations at typical catalyst operating conditions as shown in Figure 1. A recycle system that gives high overall conversions is feasible because product methanol and water can be removed from the loop by condensation. 

Recycle and Polymer Collection. Due to the incomplete conversion of monomer to polymer, it is necessary to incorporate a system for the recovery and recycling of the unreacted monomer. Both tubular and autoclave reactors have similar recycle systems (Fig. 1). The high pressure separator partitions most of the polymers from the unreacted monomer. The separator overhead stream, composed of monomer and a trace of low molecular weight polymer, enters a series of coolers and separators where both the reaction heat and waxy polymers are removed. Subsequendy, this stream is combined with fresh as well as recycled monomers from the low pressure separator together they supply feed to the secondary compressor. 

Fig. 5. A suspension perfusion culture process having ceU recycle. System employed at Amgen using CHO cells for production of a recombinant protein.

Many techniques have been developed to accomplish this, for example, the use of a cooled recirculating system in which the chlorine is dissolved in one part and the allyl chloride is dissolved and suspended in another (61). The streams are brought together in the main reaction zone and thence to a separator to remove water-insoluble products. Another method involves maintaining any organic phase present in the reaction zone in a highly dispersed condition (62). A continuous reactor consists of a recycle system in which make-up water and allyl chloride in a volume ratio of 10—50 1 are added... 

Other problems concerning transportation systems, waste processing and recycling systems, nahonal priorities, international economics, employment versus environmental quality, and personal freedoms will continue to surface. The choices will have to be made, ideally by educated citizens and charismatic leaders. 

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