Nader Vahdat

Estimation of permeation rate of chemicals through Elastometric materials

Elastometric materials are used as barriers to protect workers against exposure to chemicals. The effectiveness of a polymer as a chemical protective material therefore depends on the rate of the permeation of chemicals through it. The permeation rate depends on the solubility and the diffusion coefficient of chemicals in the materials. The diffusion coefficient itself is a strong function of concentration of the chemicals in the polymeric material. Permeation rates can be measured directly using a permeation cell or they can be calculated from the solubility and the diffusion coefficient data. Sorption/desorption experiments can be used to determine solubility and an expression for the diffusion coefficient in terms of concentration. Experiments were conducted for the sorption and desorption of ethyl acetate in three glove (one butyl and two neoprene materials) and two garment (neoprene and chlorinated polyethylene) materials. The data collected were used to estimate the steady-state permeation rates of ethyl acetate through the materials. The results of the experiments show that the solubility of ethyl acetate in butyl rubber is 0.795 g/cm3, and the steady-state permeation rate is 0.32 μg cm−2 s−1. The solubility of the chemical through the three neoprene materials is in the range of 2.25–5.31 g/cm3, and the steady-state permeation rates vary from 27 to 43 μg cm−2 s−1. The solubility of ethyl acetate in the chlorinated polyethylene is 7.14 g/cm3, and the steady-state permeation rate is 62.43 μg cm−2 s−1. The experimental method is very simple to use and it requires a small sample of the material (less than 1 cm2) and only a few milliliters of the chemical. Sorption/desorption experiments can also provide information on the amount of additives extracted from an elastomeric material during contact with a chemical.

Adsorption Capacity and Thermal Desorption Efficiency of Selected Adsorbents

Four solid adsorbents (Tenax GR, Carbotrap, Carboxen 569, and Carbosieve S-III) were evaluated for possible use in a long-term, personal chemical-exposure monitor. Adsorption/thermal desorption and breakthrough experiments were performed to determine the efficiencies and the adsorption capacity of these adsorbent/organic vapor pairs. Different amounts of organic vapors (toluene, n-hexane, methylene chloride, and methyl ethyl ketone) were collected on adsorbent tubes at various flow rates, followed by thermal desorption and analysis using gas chromatography. The concentrations sampled ranged from 0.01 to 0.1 µg/mL, and the flow rate through the tubes ranged from 20 to 117 mL/min. The adsorbent tubes were spiked with 2 mL of a solvent solution containing 5mg/L of deuterated benzene, which served as an internal standard. The average recoveries for n-hexane, methylene chloride, and methyl ethyl ketone ranged from 95 to 107%; the recovery for toluene was about 85%. In the breakthrough experiments, known concen...

Theoretical study of the performance of activated carbon in the presence of binary vapor mixtures

The performance of activated carbons in an environment containing two contaminants was evaluated theoretically. A mathematical model developed earlier was used to determine the effect of different parameters on the breakthrough curves of binary mixtures through activated carbon. Due to the difference between the adsorption capacity of carbon for the two components of a binary mixture, one of the compounds travels faster in the carbon bed and has a shorter breakthrough time. The results of this study show that under certain conditions, changing the concentration of the compounds can cause the more strongly adsorbed component to become less strongly adsorbed and travel faster in the bed. A database containing Langmuir constants for adsorption isotherms of many compounds for eleven different types of activated carbon was generated. The data base can be used to predict breakthrough times of pure or binary mixtures through activated carbons.

Fire-extinguishing effectiveness of new binary agents

Abstract The search for a new fire-extinguishing agent with all the desirable properties of halon 1301 has not been successful. During the last few years, several chemical groups with very low extinguishing concentrations have been identified. Most of these compounds have high boiling points and are not suitable replacements for halon 1301. However, mixtures of these chemicals in an inert gas could produce fire-extinguishing agents with many of the desirable properties of halon 1301. To study binary fire suppressants, one has to determine the extinguishing concentrations for several compositions of a given chemical in an inert gas. This process is expensive and time consuming. A method to estimate the extinguishing concentrations would be helpful in reducing the number of experiments needed for any binary system. In this study, a method based on adiabatic flame temperature calculations and the dependence of the rate of fire suppression of chemical agents on temperature was used to estimate the extinguishing concentration of binary mixtures. The method was tested for five organic compound/nitrogen mixtures. Five compounds that have been shown to have very low extinguishing concentrations and very short atmospheric lifetime were selected for this study. Cup burner experiments were conducted for several concentrations of each chemical in nitrogen. All the five binary systems showed synergism. As expected, the degree of synergism was highest at low concentrations of the chemical. For each binary system, extinguishing concentrations of the pure compounds and one binary data were used to predict the extinguishing concentrations for the entire range of binary composition. The predicted values are very close to experimental data.

Adsorption Prediction of Binary Mixtures on Adsorbents Used in Respirator Cartridges and Air-Sampling Monitors

A mathematical method was developed for predicting the performance of respirator cartridges and air-sampling monitors in the presence of binary mixtures. This method uses only data for pure-component adsorption equilibrium to calculate the breakthrough curves of the two components in a binary vapor mixture. The Ideal Adsorbed Solution Theory was used to calculate the adsorption equilibria for the components in a binary mixture. The adsorption capacities were then used in expressions similar to the modified Wheeler equation for pure compounds to determine the breakthrough curves for the binary mixture. This technique applies to a wide variety of binary mixture/adsorbent systems. In the present study it was successfully applied to the adsorption of four binary mixtures of acetone and m–xylene on activated carbon, three binary mixtures of acetone and styrene on activated carbon, and a binary mixture of carbon dioxide and water vapor on a molecular sieve. The predicted breakthrough curves were in agreement wi...

Decontamination of Chemical Protective Clothing

This study explored decontamination procedures for removing some organic solvents from protective clothing. The permeation experiments were performed on new and decontaminated specimens in seven polymer/chemical pairs. The decontamination methods investigated were thermal decontamination and air drying at room temperatures followed by detergent washing. Breakthrough time and steady-state permeation rate were determined by two different methods for new and decontaminated materials. The results showed that unless the contamination is limited to the outside surface of an elastomer (a material found in most barrier fabrics used in chemical protective clothing) or the chemical has a very large diffusion coefficient in the material, aeration and washing with detergent may not be an effective decontamination procedure for the type of solvent studied. On the other hand, thermal decontamination was shown to be effective in removing the contaminant from the matrix of the elastomers, and the decontaminated materials had permeation parameters similar to the new materials.

Permeation of Polymeric Materials by Toluene

The permeation of toluene through butyl, butyl-coated nomex, neoprene, and polyvinyl alcohol was tested at 25°C and 45°C with the use of ASTM method F-739. Butyl exhibited breakthrough of 18 min at 25°C and 11 min at 45°C. Butyl nomex exhibited breakthrough times of 11 min and 25°C and 6 min at 45°C. PV A showed no breakthrough in 20 hr. The steady-state permeation rates and the diffusion coefficients were determined.

Fire extinguishing ability of 1-bromo-1-propane and 1-methoxynonafluorobutane evaluated by cup burner method

Abstract The fire extinguishing ability of 1-bromo-1-propane/nitrogen (the molecular formula of 1-bromo-1-propane: CH 3 –CH 2 CH 2 Br) and 1-methoxynonafluorobutane/nitrogen gas mixtures (the molecular formula of 1-methoxynonafluorobutane: CF 3 CF 2 CF 2 CF 2 OCH 3 ) as total flooding agents were evaluated by a cup burner method. It was shown that addition of small amounts of 1-bromo-1-propane and 1-methoxynonafluorobutane to nitrogen can enhance the extinguishing ability of the inert gas by 47.1 and 31.5%, respectively, and the relative of the extinguishing concentration to the concentration of 1-bromo-1-propane or 1-methoxynonafluorobutane in the flooding agents is: Y=5.18866+26.72165 e −X/11.07715 or Y=5.96301+23.59368 e −X/22.46021 . Meanwhile, an arrangement for mixing organic compounds with inert gases (N 2 ) before applying to fire was proposed.

Permeation of chemicals through glove-box glove materials

Abstract A study of the resistance of two commercially available glove box gloves to 20 chemicals used in glove boxes has been carried out. The chemicals tested are members of seven classes of organic and inorganic compounds, namely, inorganic acids, bases, organic acids, alcohols, glycols, chlorinated hydrocarbons, and oils. Hypalon provides protection against all the chemicals except trichloroethylene and carbon tetrachloride. Trichloroethylene permeated through hypalon at an extremely high rate after only a few minutes of exposure. With carbon tetrachloride, breakthrough occurred in 57 minutes. The rate of permeation increased rapidly to an alarming rate a few minutes after breakthrough. Acetic acid permeated through neoprene with a breakthrough time of 6:28 hours and a steady-state permeation rate of 33.7 μg/cm2 min. With ethanol, breakthrough occurred in 3:28 hours and the steady-state permeation rate was 2.68 μg/cm2 min. Neoprene showed no protection against trichloroethylene and carbon tetrachlorid...

Permeation of protective clothing materials by methylene chloride and perchloroethylene.

The permeation of methylene chloride and perchloroethylene through seven protective clothing materials was studied to determine the permeation parameters, and to investigate the effect of solubility (polymer weight gain) and material thickness on the permeation parameters. The materials tested were two different nitrile rubbers, neoprene, Combination (a blend of natural rubber, neoprene and nitrile), two different polyvinyl chlorides, and polyvinyl alcohol. Methylene chloride permeated through all materials, except PVA, with breakthrough times in the range of 2 to 8 min, and permeation rates in the range of 1250-5800 micrograms/cm2 X min. PVA and unsupported nitrile offered good protection against perchloroethylene with breakthrough time occurring after 2 hr. Perchloroethylene permeated through the other materials with breakthrough times in the range of 8 to 36 min and permeation rates in the range of 200 to 1600 micrograms/cm2 X min. It was shown that for both chemicals, there is a correlation between the solubility (weight gain) and the ratio of permeation rate to breakthrough time (PR/BT). For all material/chemical pairs, an increase in solubility, increased (PR/BT). The change in material thickness had an effect on breakthrough time and permeation rate, but no effect on normalized breakthrough time. An increase in thickness reduced permeation rate and increased breakthrough time.