Breakthrough plot

Fig. 20. Typical C02/CH4 breakthrough plot for CFCMS monolith sample 21-11 (9% bum-off) at 25° C...

A typical HjS/H, breakthrough plot is shown in Fig. 21 for a gas composition of 5.4% HjS, 14% Ar, with the balance bemg Hj. The Hj (not shown in Fig. 21) is not adsorbed, whereas the HjS is held on the carbon, producing a HjS free H, stream for approximately 18 minutes. In Fig. 21 the HiS concentration can be seen to increase sharply after breakthrough is completed The concentration mcrease... 

Fig. 21. A typical HjS breakthrough plot for a CFCMS monolith 21-2B (18% burn-off) at 25 C...

Fig. 22. CO2/CH4 breakthrough plots for CFCMS sample 21-lF (10% bum-off) showing the benefit of eleetrically enhanced desorption A. 1 volt, He purge 04 sipm B 1 volt, He purge 0.06 slpm, and C. 0 volt. He purge 0.06 slpm...

Figure 3. Breakthrough plots of TBB (dry or wet airstream) on different carbons after different treatments such as freezing-thawing with water adsorbed in different media or pre-adsorbed water, oxidizing (labelled Ox) and reduction (Re).

Abstract. Activated carbon Norit R 08 Extra, and molecular sieve type 4A, were investigated using dynamic (tert-butylbenzene (TBB), cyclohexane (CHX) and water vapour) adsorption methods. The TBB, CHX and water breakthrough plots for fixed activated carbon - molecular sieve beds were analyzed. It was found that the type of bed composition with mechanically mixed activated carbon with molecular sieve, or separated activated carbon and molecular sieve layers, affects the dynamic adsorption characteristics. 

Figure 1. Log-scaled TBB breakthrough plots vs. time for mixed M and separated S beds of activated carbon and molecular sieve without water vapour (RH = 0 %).

Comparing the log-scaled TBB breakthrough plots vs time for mixed M and separated S beds of activated carbon and molecular sieve without or with water vapour, it can be affirmed that separated activated carbon/molecular sieve bed ( S ) is more effective than mixed ( M ). In the case of cyclohexane breakthrough a negative effect caused by mixing of activated carbon with molecular sieve is observed. This effect is probably caused by the different linear flow rates for TBB and CHX on the breakthrough experiments. 

Low inorganic salt amounts (5 wt.% or smaller) on the carbon surface lead to small changes in the TBB breakthrough plots at RH = 0%. However, for polar DMMP, addition of NaCl (even 5 wt.%) strongly lowers the breakthrough time (more than two times) and the effective overall adsorption rate coefficient at RH = 0 % (Table 1). 

The sulfuric acid tends to desorb slowly from the carbon surface, and if the acid occupies all the active sites for SO2 oxidation and hydration, the carbon becomes inactive for further adsorption of SO2, as illustrated in Fig. 12. When a gas stream containing SO2 is passed through a bed of activated carbon, there is complete removal of SO2 for a period, during which the SO2 is removed by both physical and chemical adsorption (Zone I). At the breakthrough point, the SO2 concentration downstream of the adsorber unit begins to rise, as all the physical adsorption sites are occupied and only chemical adsorption and reaction to produce H2SO4 are available for SO2 removal (Zone II). The SO2 removal may further decrease due to the production of acid, which occupies some of the active sites and can lead to catalyst deactivation (Zone III) as the carbon surface becomes saturated. If there is almost no acid desorption. Zone III hardly exists, and the breakthrough plots go directly from 0 to 100%. 

FIG. 12 Typical breakthrough plot for the SO. adsorption over activated carbon in the presence of oxygen and humidity. 

At constant NR and increasing r (decreasing K), the breakthrough curves become more shallow. At constant Np and Nf as r increases, NR will also decrease because of the behavior of b this intensifies the diminution in slope. Figure 10 gives a family of breakthrough plots for Np = 20 and Nf = 20 at several r values, as calculated from the equivalent reaction-kinetic curves, and indicates a very great effect of equilibrium upon the concentration history. 

Most of the industrial processes of adsorption with activated carbon operate in adsorption columns where a continuous fluid stream crosses the column and an adsorbate is removed by the stationaiy fixed carbon bed. As the adsorption process proceeds, the adsorption capacity of the activated carbon diminishes due to the fact that the adsorbate molecules are filling the pores. Finally, when the adsorption capacity of the activated carbon is exhausted, the adsorbate concentration level at the outlet begins to rise until it reaches the inlet level (breakthrough plot), the carbon adsorbent becoming unsuitable for further use so that it must be replaced by fresh activated carbon. 

The breakthrough plots (Figure 5.8) for a PAN-based ACF sample using a simulated flue stream containing 1000 ppm of SO2, 5% O2, and 10% H2O at different... 

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