The processes and factors controlling air filtration by impregnated activated carbon and its application in environmental pollution

[摘要] ENGLISH SUMMARY: Environmental issues are attracting ever-increasing attention at local, national andinternational levels. Part of the problem facing society and government alike is thechoice of strategies that maintain a safe environment without excessive regulationnd cost. One of the cost-saving exercises is to provide a universal personalprotective device that protects the worker against any contamination. The objectof this study was to determine the time for which a worker would be protected byan impregnated activated-carbon filter against an organic gas and an inorganic gas,both simply and as a mixture. It was found that the effectiveness of the filter wasreduced when the gas mixture companied two or more gases.The degree of protection afforded by a gas mask filter against a mixture of gasesis an important criterion because workers will most probably work inenvironments in which more than one contaminant is present. Two types offiltration mechanisms are possible with activated carbon namely, physicaladsorption and chemisorption.The filtration of carbon tetrachloride (CCI4) depends on physical adsorptionwhereas filtration of hydrogen cyanide (HCN) depends on chemisorption.Exposure simultaneous to an organic and an inorganic substance has not beenreported in the literature to date. In this study the influence was investigated ofsimultaneous exposure on the capacity and, therefore, on the protection timeafforded by the impregnated carbon.The capacity of impregnated carbon is also affected by other variables, and theinfluence of a number of different variables on the capacity of the carbon wasstudied. These variables included the carbon base material, the challengeconcentration, the relative humidity, the carbon weight and the exposure of thecarbon to mixtures of gases. The capacities were measured experimentally andcalculated by means of the Wheeler equation. The Wheeler equation was alsoused to determine the reaction- rate constant. In addition to the protection timesand the capacities, the active surface and pore volume distribution weremeasured. The influence of the different variables on the capacities was compared in orderto determine the percentage variance between the results obtained. The resultshave shown that the influence of the simultaneous exposure of the impregnated carbon simultaneous to gas mixture has a signiificant impact on the capacity of thecarbon with respect to the CCI4. The protection time and therefore the capacity for HCN were not affected significantly.The reason for the large reduction, in the capacity for the' physical adsorptiondependent vapour was due to the partial masking effect of the micropores by thereaction products of the chemisorption process. This was proved by the changein active surface, micropore volume and capacity. This reduction has directimplications for the application of the gas mask filters and cartridges in industry.

[发布机构] Stellenbosch University