Permeation of BTEX compounds through polyethylene pipe

Abstract

Equilibrium sorption test, microscopic visualization test, and pipe-bottle permeation test were conducted to study the permeation of various organic solvents through polyvinyl chloride (PVC) and polyethylene (PE) pipes. Five PVC pipes from different manufacturers were used and all five pipes gave similar sorption results of trichloroethylene and toluene using the equilibrium sorption test. Sorption was rapid and reached equilibrium within 7-11 days. When different types of gasoline was used, PVC pipes sorbed less than 1.5% of gasoline after 100 days indicating the PVC can resist permeation of gasoline. It was noted that PVC pipes sorbed more premium gasoline than regular- and 10% ethanol gasoline about 0.85% gain in weight after 90 days. The visualization test confirmed the permeation of the premium gasoline where a moving front of 0.3 mm was observed at 120 days while there was no moving front detected in regular- and 10% ethanol gasoline. The results suggested that percent gain in weight of gasoline may be directly proportional to concentration of BTEX (benzene, toluene, ethylbenzene, xylene) in gasoline. In the presence of a solvent such as TCE or toluene, permeation of gasoline through PVC pipes may be enhanced. For PE pipe exposed to pure gasoline and aqueous solution saturated with gasoline, breakthrough of BTEX compounds occurred after 7 and 10 days of exposure. Concentration of individual BTEX compounds in pipe water at stationary state of permeation was over their MCL for both PE pipe exposed to gasoline and aqueous solution saturated with gasoline. Diffusion coefficients were strongly dependent on the concentration of individual BTEX compounds at the outer surface of the pipe wall