Breakthrough time determination

Table 4. Index based on breakthrough times determined during constant contact with the test chemical described in European Standard EN 374-3...

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. 

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. 

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. 

The carbon/molecular sieve bed was temperature-controlled at 293 K. The volumetric flow rate was Q = 5.19 dm3 min-1 (1.0 dm3 min 1 cm2), resulting in the linear flow rate vL = 1000 cm min-1. The gas flow was controlled by several flow meters. The outlet concentrations were analyzed in cycles of 3 min with a CP 9001 CHROMPACK gas chromatograph with a flame ionization detector. The breakthrough time was determined at the outlet by a TBB concentration (behind the carbon bed) cx = 10 5 mg dm-3 (cx/c0 = 10 5). To study the water influence on TBB breakthrough, water vapour was added to reach 50% relative humidity (RH) of the air flow. The measurements were performed with dry carbon/molecular sieve beds using dry or wet air. 

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.

Adsorption pH Breakthrough time (in h) determined from TOC analysis Breakthrough time (in h) determined from analysis of UV-absorbing organics... 

For flow through porous media studies, the sandpacks used as porous media were flushed vertically with carbon dioxide for an hour to replace interstitial air. Distilled water was pumped and the pore volume (PV) of the porous medium was determined. By this procedure, the trapped gas bubbles in the porous media can be easily eliminated because carbon dioxide is soluble in water. For determining the absolute permeability of the porous medium, the water was pumped at various flow rates and the pressure drop across the sandpack as a function of flow rate was recorded. After the porous medium was characterized, the mixed surfactant solutions of known surface properties were injected. This was followed by air injection to determine the effect of chain length compatibility on fluid displacement efficiency, breakthrough time and air mobility in porous media. 

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

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

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. 

The amount of exposed Cu may therefore be calculated by static methods, by measuring the fraction of N2 in the final gas mixture,145,146 or using a pulse method to determine the consumption of N20,147 or in a flow method (reactive frontal chromatography) where the breakthrough time for the detection of N2 is measured.34 A check on the amount of oxygen deposited may be made by titrating the adsorbed layer with CO and measuring the... 

To determine the stoichiometric breakthrough time involves integration. Basically, the points 1 through 6 are chosen such that the area of the rectangle 1-2-5-6 equals that above (or below) the curve 1-8-4-6, and likewise the area of the rectangle 2-3-4-S equals that below (or above) the curve... 

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. 

For the adsorption of micro-organics (p-nitrophenol, benzoic acid) in fixed-bed columns, the half breakthrough time increases proportionally with increasing bed depth but decreases inversely proportionally with increasing water flow rate [54,55]. By studying the adsorption of chloroethylenes on activated carhon fibers, Sakoda et al. [56] determined a linear relationship between the overall mass transfer coefficient (Kfu) and the flow rate Uo. The influence of temperature on file dynamic adsorption of phenol on fibrous activated carbon has also been demonstrated [57]. 

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