Mark P. Cal

Removal of VOCs from humidified gas streams using activated carbon cloth

This research investigates the effects of relative humidity (RH) on the adsorption of soluble (acetone) and insoluble (benzene) volatile organic compounds (VOCs) with activated carbon cloths (ACC). A gravimetric balance was used in conjunction with a gas chromatograph/mass spectrophotometer to determine the individual amounts of water and VOC adsorbed on an ACC sample. RH values from 0 to 90% and organic concentrations from 350 to 1000 ppmv were examined. The presence of water vapor in the gas-stream along with acetone (350 and 500 ppmv) had little effect on the adsorption capacity of acetone even at 90% RH. Water vapor in the gas stream had little effect on the adsorption capacity of benzene (500 ppmv) until about 65% RH, when a rapid decrease resulted in the adsorption capacity of benzene with increasing RH. This RH was also about where capillary condensation of water vapor occurs within ACC pores. Water vapor condenses within the ACC pores, making them unavailable for benzene adsorption. Increasing benzene concentration can have a significant effect on the amount of water vapor adsorbed. At 86% RH and 500 ppmv, 284 mg/g water was adsorbed, while at 86% RH and 1000 ppmv, only 165 mg/g water was adsorbed. Water vapor was more inhibitory for benzene adsorption as benzene concentration in the gas stream decreased.

Chemically treated activated carbon cloths for removal of volatile organic carbons from gas streams : evidence for enhanced physical adsorption

The micropore surfaces of activated carbon cloths (ACCs) have been chemically modified by introducing controlled amounts of nitrogen, oxygen, or chlorine on the surface of the micropores. The treatments with ammonia, oxidative reagents, or chlorine produce surfaces that are basic, acidic, and polar, respectively. The modified ACCs were evaluated for removal of several different volatile organic compounds (VOCs) in the 10-1000 ppmv concentration range. VOCs examined included acetaldehyde, acetone, and benzene. Acetaldehyde adsorption capacity increased by 500% with oxidized ACC surfaces as compared to untreated ACC surfaces. Acetone adsorption was also enhanced by 350% on oxidized surfaces. The level of benzene uptake was high with most all of the treated surfaces. Thermal regeneration of the ACCs at 100 °C was sufficient to desorb each of the three VOCs without any decrease in the adsorption capacity of the treated ACCs.

Laboratory data and model comparisons of the transport of chemical signatures from buried land mines/UXO

Sensing the chemical signature emitted from the main charge explosives from buried landmines and unexploded ordnance (UXO) is being considered for field applications with advanced sensors of increased sensitivity and specificity. The chemical signature, however, may undergo many interactions with the soil system, altering the signal strength at the ground surface by many orders of magnitude. The chemidynamic processes are fairly well understood from many years of agricultural and industrial pollution soil physics research. Due to the unique aspects of the surface soil environment, computational simulation is being used to examen the breadth of conditions that impact chemical signature transport, from the buried location to a ground surface release. To provide confidence in the information provided by simulation modeling, laboratory experiments have been conducted to provide validation of the model under well-constrained laboratory testing conditions. A soil column was constructed with soil moisture monitoring ports, a bottom porous plate to regulate the soil moisture content, and a top plenum to collect the surface flux of explosive chemicals. The humidity of the air flowing through the plenum was set at about 50 percent RH to generate an upward flux of soil moisture. A regulated flux of aqueous phase 2,4-DNT was injected into the soil at about ten percent of the upward water flux. Chemical flux was measured by sampling with solid phase microextraction devices and analysis by gas chromatography/electron capture detection. Data was compared to model results from the T2TNT code, specifically developed to evaluate the buried landmine chemical transport issues. Data and model results compare exceptionally well providing additional confidence in the simulation tool.

Predicting humidity effect on adsorption capacity of activated carbon for water-immiscible organic vapors

Abstract This paper presents a simple numerical solution to the method of Manes (Proceedings of the Engineering Foundation Conference Bavaria, West Germany, 1984: 335) developed from the Polanyi adsorption potential theory to predict the effect of water humidity on the adsorption capacity of activated carbon for a water-immiscible organic vapor. The input parameters for the solution are the pure vapor adsorption isotherms quantified using the Qi, Hay and Rood (QHR) equation in Qi et al. (J. Environ. Eng., 124(11);1998:1130) for water, and the Dubinin–Radushkevich equation in Dubinin (Progress in Surface and Membrane Science, vol. 9, 1975, Academic Press) for the organic chemical. The solution employs a simple algorithm of decrement search and requires the least possible number of iterations in calculation. Predicted results compare favorably with the adsorption data for benzene in the relative humidity range 0–90%. This numerical approach is straightforward and better suited than the original graphical technique for use in dynamic simulation of activated carbon adsorbers.

Effect of soil wetting and drying on DNT vapor flux: laboratory data and T2TNT model comparisons

Sensing the chemical signature emitted from the main charge explosives from buried landmines is being considered for field applications with advanced sensors of increased sensitivity and specificity. The chemical signature, however, may undergo many interactions with the soil system, altering the signal strength at the ground surface by many orders of magnitude. A simulation code named T2TNT was developed specifically to evaluate buried landmine chemical transport issues. A vapor-solid partitioning parameter that is strongly dependent on soil moisture content is included in T2TNT. Laboratory soil vapor flux experiments were conducted to provide data to validate the T2TNT model under well-constrained laboratory testing conditions. The landmine source release, soil transport and surface flux was simulated by aqueous phase injection of DNT, evaporation induced upward water flux and solid phase microextraction sampling of headspace vapor in an air flowing plenum. The surface soil moisture content was reduced by suction removal of soil water followed by artificial rain to evaluate the soil-vapor partitioning function in T2TNT. The data showed the dramatic decline in DNT vapor concentrations expected as the surface soil moisture declined; and, then rebounded upon wetting. This phenomenon was modeled with T2TNT and showed excellent correlation.