Steady state conversion

Figure 5.46. A burst of warm feed at 310 K for the first 1400 seconds causes the system to shift into a higher temperature and higher conversion steady state. The fractional conversion curves A and C are for normal startup and B and D are for the startup with a warm feed period.

Figure 6-11 shows a plot of X versus T for this example for =300 K and z = 1 min. It is seen that for this situation a single low conversion steady state exists for low Caoi a single high conversion steady state exists for high Cao multiple steady states can exist for an intermediate range of We will discuss these further in a homework problem. 

Because of the possibility of increased seizure frequency, discontinuance of lamotrigine should be done gradually over a period of 2 weeks. Addition of DVP to lamotrigine therapy reduces lamotrigine clearance and increases steady-state plasma lamotrigine concentrations by 50% (AHFS, 2000). Conversely, steady-state plasma concentrations of lamotrigine are de-... 

The monomer conversion in the tubular reactor was regularly measured during the run, but it did not always reach a steady state value, even after reaction times equivalent to four residence times. At low conversions, steady state was normally obtained. At exit conversions between approximately 30 and 60%, conversion increased to a maximum at two residence... 

Fig. 5.20. Schematic representations of bifurcation diagram appropriate to H2 + O2 system in flow reactor, (a) A low conversion (high [H2]) steady-state exists at low ambient temperature but terminates in an ignition turning point at Ta.cr at which the system must jump to the lower branch of high conversion steady-state. If Ta is subsequently reduced, the system can stay on the lower branch for until the extinction turning point. There is...

Isobutane conversion (Steady-State Approx.) Quantitative scheme of reactions 6 Carbonium ion 3 [7]... 

Baur et al. [17] have compared the EQ and the NEQ models for the MTBE process. They underlined some counter-intuitive features of RD processes. For example, for a methanol feed location yielding a low-conversion steady state, the introduction of mass-transfer resistance (i. e., use of the NEQ model), leads to a conversion higher than that predicted by the EQ model). The introduction of a mass-transfer resistance alleviates a bad situation and has the effect of improving conversion. 

Fig. 9.10 a) Multiple steady states in TAME during the period 860-920 min. The column synthesis. Experimental data on low- and high- shifts from a low steady-state to the higher one. conversion steady states, b) Response of TAME Measurements of Mohl et al. [25] column to injection of pure TAME in the feed... 

The liquid effluent leaving the SO2 scrubber consists of a solution of caustic soda, sodium sulphite, sodium sulphate and traces of active matter. At 98% SO2 SO3 conversion (steady-state running conditions) about 80 kg/h of a 10% sodium sulphite solution will leave the scrubber system, based on a 10(X) kg/hr sulphonation plant (see table 19). The alkaline solution is collected in an acid/caustic-resistant pit. It is common practice to dilute this liquid stream with other effluent streams (ex slurry-making and powder manufacture) and to re-use it in the detergent powder manufacturing plant as dilution water. 

Figure 8.30 represents an initial profile just above the low conversion steady state which crosses the intermediate profile. From this initial condition, the system returns to the low steady state and the behavior is nonuniform. 

In Figure 8.31 an initial profile just below the intermediate steady state returns to the low steady state. The high conversion steady state appears to be locally uniformly asymptotically stable, and that of low conversion possesses nonuniform local asymptotic stability. 

When the initial concentration [A]q is varied, the resulting situation for an adiabatic CSTR is sketched in Figure 1.8b. The number of steady states varies from a single low-conversion steady state at low [A]q to a single high-conversion steady state at high [A]o and MSS in between. 

In the present study we investigate the possibility of enhancing the reactor conversion in the regime of multiple conversions by means of deliberate perturbations of the initial steady state. For all the results reported here, the reactor was initially set to operate at the lowest conversion steady state, and the reactor inlet CO concentration was perturbed by temporarily reducing the CO concentration to a lower value, while maintaining the total flow rate, the reactor pressure, and oxygen concentration essentially unperturbed. Before each pulse, the reactor was cooled down to a temperature well below the hysteresis loop of Fig. 2 and then slowly heated up to a desired temperature to establish the lowest conversion state. 

In order to examine in more detail the conversion enhancement in the multiple conversion regime, we investigated the effects of pulse amplitude and duration at a temperature which falls in the middle of the hysteresis loop in the conversion-temperature plane (see Fig. 2). Fig. 4 shows the observed time variations of CO conversion for various pulse amplitudes at = 212°C. In each case of Fig. 4, a pulse of 3 sec duration was injected at time t = 0 to the reactor which had been previously stabilized at the lowest conversion steady state. As expected, the degree of conversion enhancement was found to increase with increasing pulse amplitudes. Also, it appears that the reactor already attained the highest conversion level (about 40%) with the pulse amplitude of 0.321-0.076-0.321, and thus the even larger pulse amplitude of 0.317-0-0.317 did not provide any further conversion enhancement. 

As expected, a slightly earlier light-off occurs when there are channels with high gas velocity. Conversely, steady state conversions decrease when the velocity is not uniform. For non uniform velocity distributions, at steady state the maximum temperature difference between adjacent channels is about 25 K. Given that the model ignores heat conduction in the solid, the actual temperature difference is probably much smaller except at monolith boundary. 

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