Cyclic steady state

Fig. 9-3. Concentration versus time in the extract for SMBS at cyclic steady state. — more retained component — less retained component.

Fig. 9-4. Cyclic steady state internal concentration profiles of the more retained component during a switch time interval (start, 25 %, 50 %, 75 %, and at the end of a switch time interval) for SMBS.

The cyclic steady state SMB performance is characterized by four parameters purity, recovery, solvent consumption, and adsorbent productivity. Extract (raffinate) purity is the ratio between the concentration of the more retained component (less retained) and the total concentration of the two species in the extract (raffinate). The recovery is the amount of the target species obtained in the desired product stream per total amount of the same species fed into the system. Solvent consumption is the total amount of solvent used (in eluent and feed) per unit of racemic amount treated. Productivity is the amount of racemic mixture treated per volume of adsorbent bed and per unit of time. 

A run was carried out with an extract flow rate of = 8.64 niL min (and a raffinate flow rate of = 4.72 niL min ). Raffinate purity close to 100 % (PUR = 99.6 %) was obtained, but the extract purity was lower (PUX = 97.5 %). The internal concentration profiles were evaluated at cyclic steady state (after 20 full cycles of continuous operation). Also evaluated were the average concentrations of both species in both extract and raffinate during a full cycle. 

The steady state TMB package was used to compare the theoretical and experimental internal concentration profiles in Fig. 9-19. Figure 9-20 shows the transient evolution on the concentration of both species in the raffinate. Average concentrations over a full cycle were evaluated experimentally for cycles 3, 6, 9, 12, 15, and 18. Also shown are the corresponding SMB model predictions. The agreement between them is good and the cyclic steady-state, in terms of raffinate concentrations, is obtained after 10 full cycles. 

CO concentration at the outlet of each zone was continuously measured using a CO analyzer (Shimadzu CGT-7000). To evaluate the performance of the reactors, the conversion of CO for the PBR (Xco) with 4g of catalyst and the time-average conversion of CO for the SCMBR (Tea) with 2g of catalyst in each zone were calculated and compared. It should be noted that the CO concentration wave used for Eq. (1) was obtained whrai the system is at cyclic steady state (after 30 min of operation). 

Fig. 4 Concentration waves of CO observed at the reactor outlet after reaching cyclic steady state...

We shall see later how such linking affects many flow systems where elements or compounds, here water, circulate. In fact, this is a way of reaching a controlled cyclic steady state, a central thermodynamic objective in the Earth s ecosystem evolution, but we must be aware that the cycles of one element or compound, here water, are not independent of the changes in cycles of others. These considerations are fundamental for the appreciation of ecosystems (see Chapter 3). 

The case is unusual and not quite correct, as no energy has been put into it since its initial creation, so that it is not in a true cyclic steady state. Friction, no matter how small, will cause the flow to stop it must produce some thermal entropy. Unlike a true cyclic system it is not truly time-independent and would require energy input to be so. We treat next a physical system where energy input is clear. 

Optimal Rates of Energy Conversion and Optimal Retention of Energy in Cyclic Steady States Content of a System... 

Looking back at Table 4.4 the anaerobic cyclic steady state is from the first product of C0(C02) reduction, formaldehyde (HCHO), to [CH2OH] . This step requires a kinetic pathway in redox potential from -0.2 to -0.6 V versus the H2/H+ potential at pH 7, where sulfur is the oxidised waste ... 

As the oxygen partial pressure increased above one-tenth of its present level the effect of the incoming UV radiation from the Sun upon it created an increasing ozone layer. This layer then became an approximately cyclic steady state 302 20, some 500 million years ago (see Chapter 3). It may well be that... 

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