Department of Chemistry and Biochemistry, Florida State University, Tallahassee Florida 32308, United States.
Ion Cyclotron Resonance Program, National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, United States.
Environ Sci Technol. 2020 Aug 18;54(16):9968-9979. doi: 10.1021/acs.est.0c01158. Epub 2020 Aug 4.
Asphaltenes are high-boiling and recalcitrant compounds that are generally minor components of crude oil (∼0.1-15.0 wt %) but dominate the composition of heavily weathered spilled petroleum. These solid residues exhibit a high structural complexity, comprised of polycyclic aromatic hydrocarbons (PAHs) that are a mixture of single-core (island) and multicore (archipelago) structural motifs. The mass fraction of each motif is sample-dependent. Thus, knowledge of a potential structural dependence (single- versus multicore) on the production of water-soluble species from asphaltene samples is key to understanding the contribution of photochemically generated dissolved organic matter from oil spills. In this work, asphaltene samples with enriched mass fractions of either island (single-core) or archipelago (multicore) structural motifs are photo-oxidized on artificial seawater by the use of a solar simulator. Molecular characterization of oil- and water-soluble photoproducts, conducted by Fourier transform ion cyclotron resonance mass spectrometry, reveals that island motifs exhibit very limited production of water-soluble species, and their oil-soluble products reflect the molecular composition of the starting material. Conversely, archipelago motifs yield a water-soluble compositional continuum of O, SO, and NO containing hydrocarbons species that exhibit the typical molecular fingerprint of dissolved organic matter (DOM). The lower carbon number and aromaticity of the archipelago-derived asphaltene photoproducts suggest the occurrence of photofragmentation (or photolysis) reactions. To investigate the possibility of the opposite reaction (photopolymerization), the photo-oxidation of small PAHs isolated from a low-boiling petroleum distillation cut was also performed. It yielded water-soluble compounds with carbon number and aromaticity up to 2-fold higher than the starting material, strongly suggesting that polymerization (addition reactions) occurs. Collectively, the results indicate that the presence of archipelago motifs and the occurrence of cracking/polymerization reactions are central in the production of dissolved organic matter from fossil fuels.
沥青质是高沸点且难处理的化合物，通常是原油的次要成分（约 0.1-15.0wt%），但在严重风化的溢油中占主导地位。这些固体残留物表现出高度的结构复杂性，由多环芳烃（PAHs）组成，这些芳烃是单核（岛）和多核（群岛）结构基序的混合物。每个基序的质量分数取决于样品。因此，了解沥青质样品中从单核到多核结构基序对水溶性物质生成的潜在结构依赖性，对于理解溢油中光化学产生的溶解有机物的贡献至关重要。在这项工作中，使用太阳模拟器在人工海水中对富含单核（岛）或多核（群岛）结构基序的沥青质样品进行光氧化。通过傅里叶变换离子回旋共振质谱对油溶性和水溶性光产物进行分子表征，结果表明，岛基序的水溶性物质生成非常有限，其油溶性产物反映了起始材料的分子组成。相反，群岛基序产生了含有 O、SO 和 NO 的水溶性组成连续体的烃类物质，其具有溶解有机物（DOM）的典型分子指纹。群岛衍生的沥青质光产物的较低碳数和芳香度表明发生了光碎化（或光解）反应。为了研究相反反应（光聚合）的可能性，还对从低沸点石油蒸馏切分物中分离出的小多环芳烃进行了光氧化。它生成了水溶性化合物，其碳数和芳香度比起始材料高 2 倍，这强烈表明聚合（加成反应）发生了。总的来说，结果表明群岛基序的存在和裂化/聚合反应的发生是化石燃料中溶解有机物生成的核心。
