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

Barnardt, Cornelius Andries (1998-01)

Dissertation (PhD)--University of Stellenbosch, 1998.

Thesis

ENGLISH SUMMARY: Environmental issues are attracting ever-increasing attention at local, national and international levels. Part of the problem facing society and government alike is the choice of strategies that maintain a safe environment without excessive regulation nd cost. One of the cost-saving exercises is to provide a universal personal protective device that protects the worker against any contamination. The object of this study was to determine the time for which a worker would be protected by an 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 was reduced when the gas mixture companied two or more gases. The degree of protection afforded by a gas mask filter against a mixture of gases is an important criterion because workers will most probably work in environments in which more than one contaminant is present. Two types of filtration mechanisms are possible with activated carbon namely, physical adsorption and chemisorption. The filtration of carbon tetrachloride (CCI4) depends on physical adsorption whereas filtration of hydrogen cyanide (HCN) depends on chemisorption. Exposure simultaneous to an organic and an inorganic substance has not been reported in the literature to date. In this study the influence was investigated of simultaneous exposure on the capacity and, therefore, on the protection time afforded by the impregnated carbon. The capacity of impregnated carbon is also affected by other variables, and the influence of a number of different variables on the capacity of the carbon was studied. These variables included the carbon base material, the challenge concentration, the relative humidity, the carbon weight and the exposure of the carbon to mixtures of gases. The capacities were measured experimentally and calculated by means of the Wheeler equation. The Wheeler equation was also used to determine the reaction- rate constant. In addition to the protection times and the capacities, the active surface and pore volume distribution were measured. The influence of the different variables on the capacities was compared in order to determine the percentage variance between the results obtained. The results have shown that the influence of the simultaneous exposure of the impregnated carbon simultaneous to gas mixture has a signiificant impact on the capacity of the carbon 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 adsorption dependent vapour was due to the partial masking effect of the micropores by the reaction products of the chemisorption process. This was proved by the change in active surface, micropore volume and capacity. This reduction has direct implications for the application of the gas mask filters and cartridges in industry.

AFRIKAANSE OPSOMMING: Die aaridag van die plaaslike, nasionaleen internasionale gemeenskap word meer en meer gevestig op omgewingsake. Deel van die probleem wat die gemeenskap en die regering in die gesig staar, is die keuse van 'n strategie wat sonder oormatige wetgewing en kostes 'n veilige omgewing handhaaf. Universele persoonlike beskermingstoerusting vir die werker vir beskerming teen enige vorm van kontaminasie is een van die kostebesparings. Hierdie studie is gedoen om die beskermingstyd van 'n geimpregneerde koolstof filter te bepaal indien dit aan 'n organiese en anorganiese gas onderskeidelik en gelyktydig as 'n mengsel blootgestel word. Daar is gevind dat gelyktydige blootstelling van 'n filteraan twee of meer gasse die filterkapasiteit verlaag. Die beskerming van n gasmaskerfilter teen 'n mengsel van gasse is 'n belangrike aspek aangesien werkers heel waarskynlik in omgewings werk waar meer as een kontaminant teenwoordig is. Twee tipes filtrasiemeganismes is moontlik met geaktiveerde koolstof, naamlik fisiese adsorpsie en chemiese adsorpsie. Die filtrasie van koolstoftetrachloried (CCI4 ) is afhanklik van fisiese adsorpsie terwyl waterstofsianied (HCN) deur middel van chemiese adsorpsie gefiltreer word. Gelyktydige blootstelling aan 'n organiese en anorganiese kontaminant is nog nie in die literatuur gerapporteer nie. Hierdie studie is gedoen om die invloed van gelyktige blootstelling op die kapasiteit en derhalwe die beskermingstyd van geimpregneerde koolstof vas te stel. Aangesien die kapasiteit van geimpregneerde koolstof ook deur ander veranderlikes beinvloed word, was dit belangrik om die invloed van die verskillende veranderlikes op die kapasiteit van die koolstof te bepaal. Veranderlikes wat by hierdie studie ingesluit is, is die koolstof roumateriaal, die blootstellingskonsentrasie, die relatiewe humiditeit, die koolstofmassa en die gelyktydige blootstelling van die koolstof. Die kapasiteite is eksperimenteel en teoreties met behulp van die Wheeler vergelyking bereken. Die Wheeler vergelyking is ook gebruik om die adsorpsiesnelheidskonstante te bereken. Behalwe vir die beskermingstye en die kapasiteite is die aktiewe oppervlakte en die porievolumeverspreiding ook bereken. Die invloed van die verskillende veranderlikes op die kapasiteite is vergelyk om die persentasie variasie tussen die resultate te bepaal. Dit is duidelik vanuit die resultate dat diegelyktydige blootstelling van die geimpregneerde koolstof 'n beduidende impak op die kapasiteit van koolstof vir CCI4 het. Die beskermingstyd en kapasiteit van HCN is nie beduidend geaffekteer nie. Die rede vir die groot afname in kapasiteit vir die fisiese adsorpsie-afhahklike kontaminant kan aan gedeeltelike afskerming van die mikroporiee deur die reaksieprodukte van die chemisorpsie proses toegeskryf word. Dit is deur die verandering in die aktiewe oppervlakte, mikroporievolume en kapasiteitsmetings bewys. Die gevolg van hierdie afname hat direk betrekking op die toepassing en gebruik van gasmaskerfilters in die industrie.

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