Total Aromatic Content in Petroleum Solvents Modifies Headspace Benzene Vapor Concentrations: Implications for Exposure Assessments
2013
Richter, Richard O. | Kerger, Brent D. | Hoyt, Steven | Fedoruk, Marion J.
This study evaluates how equilibrium vapor concentrations above petroleum solvent mixtures are affected by total aromatic content and the implications for estimating benzene vapor exposures. Headspace vapor concentrations over mixtures with liquid benzene content ranging from 0.001 to 1.0% and varying percentages of 1,2,4-trimethylbenzene and n-nonane were studied using a direct-injection gas chromatography/flame ionization detection method that showed good precision. The measured values were compared to predictions based on Raoult's Law, with and without non-ideality corrections using activity coefficients. Ratios of vapor to liquid benzene concentrations decreased with increasing total aromatic content; that is, mixtures with 10% to 20% trimethylbenzene simulating non-hydrotreated mineral spirits had much lower ratios compared to the ≥99% aliphatic mixtures that simulate hydrotreated mineral spirits. Positive deviations from Raoult's Law were greatest at liquid benzene concentrations less than 0.1%, particularly in the predominantly aliphatic mixtures. Correcting for non-ideality using activity coefficients resulted in predicted vapor concentrations that were closer to measured values. The data indicate that higher aromatic content and higher liquid benzene content suppress benzene vapor concentrations due to benzene's greater affinity for similar aromatic molecules in solution. Benzene exposure reconstructions should consider actual composition of the historic material with respect to aromatic content.
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