Leonard A. Jonas

The Effect of Moisture on the Adsorption of Chloroform by Activated Carbon

The effect of moisture on the ability of a granular activated carbon to adsorb chloroform vapor from a flowing airstream was studied under three test conditions: (1) chloroform and water vapor were introduced concurrently into a dry carbon bed; (2) dry chloroform was introduced into a humidified carbon bed; (3) humidified chloroform was introduced into a carbon bed at the same relative humidity. The criterion for bed performance was the time when the downstream chloroform concentration was 1% of that in the inlet stream. Chloroform concentration was essentially constant at 108 +/- 2 micrograms/cm3; relative humidities (RH) varied from 0 to 97%. No RH effect on the adsorption of chloroform by the carbon was observed in test (1); tests (2) and (3) showed monotonic decreases in chloroform adsorption for RH greater than 40%. These results indicated that, for a dry carbon bed, the 1% breakthrough time for chloroform adsorbed from atmospheres of RH from 13% to 95% was essentially the same as that when RH = 0%. For humidified carbon beds, no change in 1% breakthrough time for chloroform was observed until RH was greater than 40%.

Prediction of adsorption rate constants of activated carbon for various vapors

Abstract In the past decade, a theoretical calculation of the adsorption properties of activated carbon has successfully been used to predict the adsorption capacity for untested vapors after initial characterization of the carbon with a reference vapor. However, using this theoretical approach, it has not been possible to predict the second fundamental property of carbons, namely its adsorption rate constant, and therefore only a family of curves for adsorption performance could be calculated. A new extension of the present theory is proposed which would permit prediction of the adsorption rate constant of vapors, after initial characterization of the carbon with a reference vapor, so that a curve of adsorption performance can be calculated for any vapor needed.

Prediction of activated carbon performance for carcinogenic vapors

After an activated carbon was characterized with a reference vapor (CCl4), gas adsorption kinetic equations were used to predict carbon performance for 31 carcinogenic vapors. Previous work has shown that predicted and experimental values will correspond within a range of about ±15%.

Prediction of Activated Carbon Performance for Binary Vapor Mixtures

The adsorption characteristics of a packed bed of carbon granules were determined under dynamic flow conditions for individual vapors and binary vapor mixtures of various compositions and concentrations. Carbon tetrachloride, chloroform, and benzene and binary mixtures of these vapors, with wide variations in the mole fraction of each vapor, were used. We found that the adsorption space occupied by each vapor was proportional to its mole fraction in the mixture; that is, the vapors adsorption space was reduced from the adsorption space it would have occupied at the same relative pressure if the carbon bed had been exposed to each vapor separately. The diminished effectiveness of the carbon for one vapor due to the presence of another was quantitatively predicted for binary mixtures by applying this finding to previously established adsorption relationships.

Residual adsorption capacity of carbon beds

Abstract The retention time of a small (0.3 cm 3 ) ethane pulse, to which various dry weights (1–3 g) of activated carbon were exposed, was studied as a nondestructive method of determining the residual adsorption capacity of the bed. Carbon beds, partially saturated with CCl 4 or water, adsorbed the ethane from and then desorbed the ethane into the nitrogen carrier gas stream. At a fixed flowrate and fractional carbon saturation the retention time in the bed varied linearly with carbon weight. A critical bed weight existed, below which the retention time of ethane in the bed was zero. The logarithm of a dimensionless time parameter, normalized with respect to the effective bed weight (total weight minus critical weight), was a linear function of the percentage carbon saturation (or the percentage residual adsorption capacity) of the bed. This approach constitutes a nondestructive, in situ method for determining the residual adsorption capacity of an activated carbon bed that is independent of bed weight.

Resistance of protective clothing materials to permeation by solvent “splash”☆

Abstract One hundred microliters of solvent was applied to protective clothing materials to estimate the extent of permeation when a garment is splashed with a liquid. Various thicknesses of butyl rubber, natural rubber, neoprene, neoprene plus natural rubber, nitrile, and polyvinyl chloride were exposed to benzene or carbon tetrachloride at ambient temperature. Permeating solvent was trapped in 5°C n-octane and its concentration was measured continually. Breakthrough time was defined as the time at which 0.1% of the applied solvent permeated. From the data obtained, two conclusions were drawn: permeation of a small quantity of liquid (a 100-μl “splash”) more closely resembles permeation of liquid than permeation of low vapor concentrations in continuous contact with a garment, and a garment thickness can be defined which is sufficient to provide a known degree of protection for a particular solvent.

Prediction of activated carbon performance for sequential adsorbates.

A packed bed of carbon granules was exposed to benzene and carbon tetrachloride sequentially to determine the adsorption characteristics of the bed under dynamic flow conditions. We found that the total adsorption space of the carbon was invariant at a fixed relative pressure and temperature. This finding allowed us to predict carbon performance for adsorbates introduced concurrently and/or sequentially.

The effect of exposure to daylight and dark storage on protective clothing material permeability

To estimate the effects of daylight and dark storage on permeability, samples of protective clothing materials were placed in a window facing east at 39°2′ N. latitude or in a closed cabinet for 0, 1, 2, and 3 months. At the end of the storage period the permeability of the sample was determined after 60-minute exposure to each of two solvents. Test data were normalized to account for differences in sample material thickness. Statistical analysis of the data showed that no significant differences in permeability occurred as a result of dark storage; small differences in 3 of 12 cases were observed following daylight storage.