Polycyclic aromatic hydrocarbons from asphalt binder: extraction and characterization

Article J. Braz. Chem. Soc., Vol. 20, No. 2, 222-228, 2009. Printed in Brazil - ©2009 Sociedade Brasileira de Química 0103 - 5053 $6.00+0.00 Polycyclic Aromatic Hydrocarbons from Asphalt Binder: Extraction and Characterization Lucidalva S. Pinheiro,*,a Paulo R. N. Fernandes,b Rivelino M. Cavalcante,b,c,# Ronaldo F. Nascimento,c Jorge B. Soares,d Sandra A. Soaresb and José A. K. Freire†,a a Departamento de Física, Universidade Federal do Ceará, Campus do Pici, CP 6030, 60455-900 Fortaleza-CE, Brazil b Departamento de Química Orgânica e Inorgânica, Universidade Federal do Ceará, Campus do Pici, CP 12200, 60455-760 Fortaleza-CE, Brazil c Departamento de Química Analítica e Físico Química, Universidade Federal do Ceará, Bloco 940, Campus do Pici, 60451-970 Fortaleza-CE, Brazil d Departamento de Engenharia de Transportes, Universidade Federal do Ceará, Campus do Pici, CP 6001, 60455-760 Fortaleza-CE, Brazil O ligante asfáltico de petróleo é comumente empregado na pavimentação de ruas e estradas de rodagem. Esse material contém hidrocarbonetos policíclicos aromáticos (HPAs) e diversos outros componentes alifáticos e aromáticos. Os HPAs são compostos poluentes que podem induzir problemas de saúde. Este trabalho tem como objetivo extrair e caracterizar os HPAs presentes no ligante asfáltico e suas concentrações. Dispersão de Matriz em Fase Sólida foi utilizada como técnica para a extração dos HPAs. Para análise e caracterização foram utilizadas as técnicas de Cromatografia Gasosa e Microscopia de Tunelamento. Quinze dos HPAs prioritários listados pela USEPA (United States Environmental Protection Agency) e também coroneno foram encontrados nas amostras analisadas. The asphalt binder, derived from petroleum, commonly employed in road paving contains PAHs (Polycyclic Aromatic Hydrocarbons) and a variety of other aliphatic and aromatic compounds. PAHs are pollutants that can induce health problems. This work aims to extract and characterize the PAHs in samples of asphalt binder and its concentration. Matrix solid phase dispersion was used as a technique for extraction of the PAHs. Characterization was performed employing gas chromatography and scanning tunneling microscopy. Fifteen of the priority PAHs listed by USEPA (United States Environmental Protection Agency), as well as coronene, were found in the binder samples. Keywords: chromatography, PAH, recognition, self-assembly, STM Introduction Asphalt binder is one of the products of the distillation of crude oil, which is an extremely complex mixture containing a large number of organic compounds. It has been widely used as a binder for aggregation in road pavement and to manufacture asphalt concrete due to its good adhesion, impermeability and viscoelastic properties.1 Unfortunately, fumes released from asphalt binders during road paving, especially in the production of hot mixtures, present a large number of substances that can be hazardous to *e-mail: † In memorian # Present address: Universidade Federal do Ceará, Av. Abolição, 3207 – Meireles, 60165-081 Fortaleza-CE, Brazil human health. Long time exposure to these fumes can lead to diseases caused by inhalation or skin contact with substances that are carcinogenic and mutagenic, such as the polycyclic aromatic hydrocarbons (PAHs) found in this material.2 PAHs are a class of organic elements formed by two to seven benzene rings, whose origin can be natural or anthropogenic. The petroleum industry and the fossil fuel combustion are the main sources of PAH production.2 Statistical data reveal that there is evidence of cancer risk, and there is some relation between carcinogenesis and the molecular structure of PAHs.2 This implies adequate procedures to detect PAHs in asphalt and the correct use of the material in such a way to avoid environmental and human contamination.3 There are few consistent studies devoted to analyze PAHs contents from asphalt binder. Vol. 20, No. 2, 2009 Pinheiro et al. Therefore, it is of great interest to develop an efficient method that can aid in evaluating the real contribution of the asphalt industry to the PAHs. This study was performed by employing matrix solid phase dispersion (MSPD) as an analytical method for extraction and analysis of the 16 PAHs classified by USEPA. The performance of MSPD was tested in this work as a method to provide fast and reliable separation of these compounds, which allowed the simultaneous extraction and clean-up of analytes from solid samples.3 MSPD has been mainly used for the extraction of organic environmental pollutants in food and biological matrices.3 To the best of our knowledge, it is the first time that MSPD was used to isolate PAHs from asphalt binder. A mixed extract of PAHs obtained from the MSPD was analyzed by gas-chromatography (GC), which was employed to separate and quantify the aromatic compounds.4 The extract was later analyzed by Scanning Tunneling Microscopy (STM). The STM experiments aimed to characterize the size of the components of the asphalt binder extracted by MSPD. It would complement the assignment proposed by the characterization through GC. Gold samples modified with a thiol layer were employed to recognize the PAHs contained in the extract. The thiol employed was 5-(4-pyridinyl)-1,3,4-oxadiazole thiol (HPYT). This molecule forms a stable layer on the gold with a well-known structure, the √3x√3 R30°.5 This lattice is also observed for the adsorption of other aromatic and alkyl thiols.6,7 Thus, a different lattice from the thiol layer would be readily identified in the STM image as due to molecules from the PAH extract. This study is important in molecular sensing since it has potential applications in several fields of chemistry and biochemistry. The analysis by STM and Atomic Force Microscopy (AFM) of the PAHs extracted from the binder are relevant because these techniques have been employed to characterize asphalt binder morphology and its constituents in just a few reports.8 Experimental Materials The asphalt binder penetration grade 50/70 was from the State of Espirito Santo in the Southeast of Brazil, and processed by Lubnor/Petrobrás located in the State of Ceará, northeast of Brazil. Standard PAHs solutions were from Supelco. Internal standard 2-fluoro-biphenyl and the surrogate standards: acenaphthene-d10, phenanthrene-d10, Chrisene-d12 and Perylene-d12 were from Aldrich. The solvents n-hexane, toluene, ethyl acetate (P.A. grade) were distilled twice before being employed in the analysis. 223 Methods PAH extraction by MSPD Asphalt binder is made of two main constituents, the maltenic and the asphaltene fraction. The maltenic fraction was firstly isolated from the asphaltenes and then it was separated in its constituents, such as aliphatics and aromatics. The PAHs were extracted from a sample of 0.3 g of asphalt binder (in triplicate) spiked with 20 µL of surrogate standards (acenaphthene-d10; phenanthrene-d10, chrysene-d12, and perylene-d12) 10 ppm plus n-h (...truncated)