Maximum exchange level

A volume of 100 L of a solution containing 1000 ppm Pb2+ and minor amounts of other ions has to be treated. The desired final concentration is 100 ppm. The available adsorbent is a zeolite with a particle size of 1.3 mm, density of 2 g/cm3, and the REC is QM = 176 mg/g. Suppose that we have efficient agitation and solid diffusion is the controlling mechanism. Solid diffusion is about 6.4 X 10 1° cm2/s. Furthermore, the system obeys a favorable Langmuir isotherm with La = 0.03 and the maximum exchange level is qmm = 106 mg/g. 

As shown in Figure 5, the infrared frequencies for the Rb+ and Cs+ exchanged forms are only slightly different from that of the parent Na+ form. Furthermore, the maximum exchange levels at room temperature are considerably lower than those of other monovalent cations (69% and... 

Additional exchange isotherms Pb (solution) - 2Na (clinoptilolite) were recorded [13, 14] under comparable conditions as in [10]. However, a maximum exchange level of ca. 80% [13, 14] is in contrast to ca. 95% for two different samples [10]. Such discrepancies in the exchange behavior were discussed by Langella et al. [14] concluding that the cation exchange... 

The water-gas-shift reaction (Eqn. 1) has been studied extensively as a basis for improving the yield of hydrogen production. In many applications, including ammonia synthesis or fuel reforming for proton exchange membrane (PEM) fuel cells, the maximum acceptable level of CO in hydrogen is in the parts per million range, therefore the water-gas shift reaction is needed. 

The selectivity for para-products has a slight maximum for a copper content of approximately 1.6 weight% equivalent to an apparent exchange level of 100% (Fig. 3). 

We have recently been investigating the behavior of stilbazolium cations at other anionic interfaces such as Nafion 117 and montmorillonite ciay. Nafion< 117 readily adsorbs the stilbazolium cations with a maximum coverage level (ratio of stilbazolium to exchangeable cations) of 100% and 90% for cations 1 and 2, respectively. 

The experimental results obtained with the different catalysts are summarized in Table 2. In this table, the maximum reduction rate of NO to N2 and the corresponding temperature are given for each catalyst. The temperature range of activity corresponds to the range where the reduction rate is higher than half the maximum rate. In this table Cu-ZSM-5-27.5-100 means that Si/Al = 27.5 and that the Cu exchange level is 100 %. 

ZSM-5 exchanged with both copper and cerium showed a deerease of the reduction rate with a maximum of 20% of reduction at 300°C. The extent of NO reduetion was only 10% at 400°C. Hydroearbons were totally eonverted at 300°C. The performances of the two coexchanged ZSM-5 were very similar whatever the Si/Al ratio and the copper exchange level. It also appears that the activity of a coexchanged ZSM-5 is not close to the sum of the activities of the monoexchanged corresponding materials. 

The catalyst Cu-MCM-22-15.3-56 exhibited only a moderate activity with a maximum extent of reduction of 19% at 350°C. When the exchange level was increased from 56 to 100%, for a similar Si/Al ratio, the maximum extent of NO reduction was not significantly changed but occurred at 300°C instead of 350°C, corresponding to a wider temperature range of activity. 

The catalyst Cu-FAU-3.8-95 exhibited a moderate activity in NO reduction. The maximum extent of reduction was 23% at 300 C. The hydrocarbon conversion was completed at 300°C. The effect of the copper content was also investigated. When the Cu-exchanged level was decreased to 20%, the hydrocarbon conversion was 100% at only 700°C, leading to a drop of the catalytic activity at temperatures less than 400°C. The maximum reduction rate was less than 15% at around 400°C. 

Some of the equipments might have been operated beyond their maximum limits of temperatures (heat exchangers), levels (agitated reactors), and delivery pressures (pumps). 

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