Diffusion and adsorption of volatile organic solvents in various gypsum samples

In this study, diffusion and adsorption behaviour of volatile organic compounds (VOC) in various gypsum sample pellets were investigated by single pellet moment technique. Experimental studies were conducted in a one-sided single pellet Wicke Kallenbach type diffusion/adsorption cell under isobaric conditions. In the experiments; perlite plaster, thermal isolation plate plaster, construction, machine and polish gypsums were used as building materials. Nitrogen gas used as a carrier while toluene, methanol and acetone were used as tracer compounds. Dry environment experiments were carried out using different gas flow rates between 50-175 ml/min. and at the temperature range between 25 and 60°C. In order to determine the effect of relative humudity on VOC diffusion and adsorption, the experiments were conducted at 25-40°C and with %20 and %40 relative humidity. The samples analysises were carried out using gas chromatography. Adsorption mechanism, adsorption equilibrium constant and effective diffusion coefficient were calculated by the analysis of response peaks obtained from GC detector. From the analysis of zeroth moments, it was observed that all tracer compounds were adsorbed reversibly in all gypsum pellets studied. Adsorption equilibrium constants and effective diffusion coefficients of volatile organic compounds in all gypsum pellets were calculated with the evaluation of first absolute and second central moments. It was observed that adsorption coefficients of tracers studied were decreased with the increasing of temperature. Highest adsorption occured on machine and building gypsum and lowest on thermal isolation plaster. Effective diffusion coefficients of tracers in all gypsum pellets were increased with temperature. The experimental results show that adsorption equilibrium constants and effective diffusion coefficients of all tracers were decreased with an increase in relative humidity. Key Words: Gypsum, Volatile Organic Compound, Adsorption, Effective Diffusion Coefficient, Dynamic Method.