Determination of breakthrough time

The linear velocity, u, of the mobile phase is needed for calculating permeability. Information on theoretical plates is not strictly correct without involving , as the plate height is a function of flow-rate (see Fig. 2.7). Thus u is calculated as follows  

Note u AF/dc iT as the stationary phase matrix takes up a specific amount of column volume. The true equation is m = AFor, with c = 0.65  

Porosity can be used to verify the breakthrough time. The total porosity, c, of a column is the volume fraction taken up by the mobile phase  

If columns filled with a bonded phase packing (e.g. Cig phase) have an = 0.65, then the calculated breakthrough time is correct if 1, then the components in question do not migrate at the same rate as the mobile phase but are effectively retained by the stationary phase and eluted later if 0.5, then the components are excluded from the pores of the stationary phase (cf. size-exclusion chromatography) and migrate faster than the breakthrough time would indicate. 

In the last two cases, the test substance used is unsuitable for the determination of breakthrough time. 

The breakthrough time, to, therefore must be known, (to is also needed for the 

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The problems of the determination of breakthrough time were discussed by C.A. Rimmer, C.R. Simmons... 

Example 13 Estimation of Breakthrough Time With reference to Example 9, determine the 10 percent breakthrough time and the column dynamic binding capacity if the column is 20 cm long. 

Schematic of device employed to determine long-term diffusion of dyes through hair. A similar set-up could be used for measurement of drugs employing radioactive tracers by placing the drug in the lower chamber. Removing aloquots from the top at regular intervals and measuring the radioactivity would then determine the breakthrough time.

Two macroscopic methods to design adsorption columns are the scale-up and kinetic approaches. Both methods rely on breakthrough data obtained from pilot columns. The scale-up method is very simple, but the kinetic method takes into account the rate of adsorption (determined by the kinetics of surface diffusion to the inside of the adsorbent pore). The scale-up approach is useful for determining the breakthrough time and volume (time elapsed and volume treated before the maximum allowable effluent concentration is achieved) of an existing column, while the kinetic approach will determine the size requirements of a column based on a known breakthrough volume. 

In view of the above limitations the potential use of an annular bed for adsorption was initially assessed by conducting preliminary experiments in a small unit at room temperature and determining the breakthrough time. The obtained results demonstrated that breakthrough did not take place immediately and were thus encouraging. 

Determination of breakthrough volume at concentrations of 2 times exposure guideline and relative humidity of 85 %. 

Sensitive analytic procedures enable detection and measurement of very low tracer levels. In tracer studies, an identifiable tracer material is injected through one or more injection wells into the reservoir being studied. Water or other fluid is then injected to push the tracer to one or more recovery wells in the reservoir. The output of the recovery wells is monitored to determine tracer breakthrough and flow through the recovery wells. Analysis of the breakthrough times and the flows yields important information regarding how to perform the secondary or enhanced recovery processes. 

The determination of the breakthrough time and the rate at which the particular PCB of this study permeated the various garment materials was performed by placing 110 mL of PCB (T=25°C) in the organic phase side of the permeation cell with the test material in place and with 120 mL of water and 40 mL of n-heptane atop the water in the cells aqueous phase side. The aqueous phase was stirred vigorously to allow the heptane to continuously extract the PCB from the water. This procedure was necessary because of the limited solubility of PCB constituents in water. 

Each of the above is of value for determining the relative efficacy of a given material in protecting the worker against exposure to the particular chemical being studied. The breakthrough time (Tg) gives the "bottom line for.the particular materials included in this study. 

As shown in Box 18.5, D,eff determines the speed at which a pollutant penetrates a porous media. The so-called breakthrough time indicates how long it takes until a pollutant has crossed a porous layer of a given thickness. In contrast, once both the fluid and sorbed concentrations have reached steady-state, the flux is solely controlled by Dipm and thus independent of sorption (independent offif). Illustrative Example 18.4 demonstrates the latter while the role of D,eff is shown in Illustrative Example 18.5. 

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