Breakthrough charcoal

A recovery of 5% of the total sample from the back-up section of charcoal in a sample tube was defined as the breakthrough point 50% of this value is shown as the recommended maximum tube loading, to allow for high humidity or the presence of other substances which reduce the normal tube capacity. 

These compounds migrate rapidly to the back-up section of the charcoal tube. A 400 mg tube should be used for sample collection with a second 100 mg tube in series behind the large tube to determine breakthrough. 

Various forms of carbon are used to sample those analytes whose breakthrough volume is too low on Tenax for sufficient preconcentration [8,395-399]. Charcoal, graphitized carbon blacks, and ceurbosieves with wface areas from 5 to 900 w /g are commercially availablJ Bhe high surface area sorbents are used... 

With chromatography on graphite, higher amounts of toluene in the hexane-toluene mixture can be used to improve solubility [199, 200]. The major breakthrough, however, allowing the use of pure toluene as mobile phase was achieved by chromatography on mixtures of charcoal and silica gel [201, 202]. This is the most inexpensive and efficient method for a fast separation of Cjq. A flash... 

In some cases it was necessary to use a large charcoal tube, a low flow rate and a limited sample size to avoid losses due to breakthrough. 

Other solid sorbents have been found more suitable than charcoal for a number of compounds. Silica gel and alumina have been used as a complement to charcoal when sampling polar compounds, but water vapor is strongly adsorbed on these sorbents which leads to deactivation of the sorbent and breakthrough of the compounds by frontal elution. Difficulties also arise with compounds that hydrolyze easily. Alternative sorbents for the collection of polar organic compounds which are sensitive to hydrolysis are porous polymers such as the Chromosorb porous polymer series, Porapak porous polymer series, Tenax-GC and Amberlite XAD sorbent series. 

Charcoal does have limitations that can affect its performance. Humidity may reduce the capacity of the charcoal tube, or interfering substances may displace the substance of interest. Frequent periods of high level exposure may exceed the breakthrough volume for very volatile materials. 

Activated Charcoal. The original intent of the research was to develop a sampling technique that used coconut-shell charcoal to collect vinyl acetate vapors from air samples. Therefore, the breakthrough volume and desorption efficiency of vinyl acetate on coconut-shell charcoal were studied. 

The results of the breakthrough studies, summarized in Table I, indicate that charcoal has a high affinity for vinyl acetate. 

The use of charcoal tubes for the collection of solvent vapors is recommended in the NIOSH method. The charcoal tubes presently used contain 150 milligrams (mg) of coconut charcoal. Figure 1 illustrates the charcoal tube subdivided into two sections of 100 mg and 50 mg of charcoal. The front portion of 100 mg is used to collect the solvent vapors while the 50 mg backup section is intended to determine if solvent breakthrough occurred on the front portion. This is a built-in quality control check. (6)(14)... 

EXPERIMENTAL The sampling and analytical method employed in determining the various solvent vapor concentrations in air are described in detail by White etal (A)and NIOSH (2), Four Bendix National Environmental Instruments Model BDX 30 Personal Samplers were used daily (one in each laboratory) with large size charcoal tubes (SKC cat no. 226-09-100) which contained two sections of activated charcoal per tube (a 400 milligram section followed by a 200 mg backup section to indicate when "breakthrough" of the main section has occurred). The sampling pumps were operated at a rate of one liter per minute and were calibrated by means of an Environmental Compliance Corporation Model 302 Universal Pump Calibrator (a device that generates a thin film of soap which is carefully timed as it traverses a very... 

If a respirator contains 100 g of this charcoal and breakthrough occurs when 82 percent of the adsorbent is saturated, how long can the respirator be used in a dichloropropane concentration of 750 ppm when the temperature is 80°F Assume that the flow rate of contaminated air through the adsorbent is 45 I/min. The molar volume of the dichloropropane may be assumed to be 100 cm3/g mole. 

A respirator cartridge contains 80 g of the above blend of charcoal, and tests have shown that breakthrough (when A starts to be emitted from the cartridge) will occur when 80% of the charcoal is saturated. How long will this cartridge be effective if the ambient concentration of substance A is 700 ppm and the temperature is 30°C Assume that the breathing rate of a normal person is 45 L/min (45,000 cm /min). 

The /z-transf orm method was also applied to the calculation of the breakthrough curve for the separation of a binary mixture on a charcoal bed by Tien et al. [36]. By using the li-transform, the course of the separation can be calculated by transforming the concentration variable via the /i-transform into a coordinate system in which algebraic equations describe the process for any number of components. 

Figure 16.1 Comparison between the experimental breakthrough curves obtained with benzene ( ) and toluene (o) vapors on activated charcoal and the prediction of constant pattern. Reproduced with permission from W.J. Thomas and ].L. Lombardi, Trans. Chem. Eng., 49 (1971) 240 (Fig. 23).

Figure 16.21 Left Binary breakthrough curve of glucose and maltose in water on a 1 x 15 cm column packed with activated charcoal. Left Ternary breakthrough curve of sucrose, maltose, and lactose on the same column. Reproduced with permission from f.-W. Lee, T.-O. Kwon, I.-S. Moon, Carbon 42 (2004) 371 (Figs. 8 and 9).

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