Comparative Study of Solid-Phase Extraction of Dissolved Organic Matter from Oilfield-Produced Brine by Different Sorbents

摘要

Dissolved organic matter (DOM) has been widely studied in streams, lakes, and oceans due to its role in biogeochemical processes, allowing it to act as a sunscreen, food source, trace metal chelator, and photosensitizer. Few studies have examined DOM in oilfield-produced water. In this study, three major types of solid-phase extraction (SPE) sorbents, a silica-based sorbent (ENVI-18), an active carbon (ENVI-Carb), and polymer-based sorbents (PPL, XAD resins, and HLB), were used to isolate DOM from oilfield-produced brine. Isolated SPE DOM samples were analyzed using dissolved organic carbon (DOC), Fourier transform infrared spectroscopy, and pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS). Results showed that the oilfield-produced brine DOM sample was dominated by aliphatic hydrocarbons and aromatic compounds. Nitrogen-containing compounds and carbohydrates were also observed; however, polycyclic aromatic hydrocarbons, fatty acids, and sulfur-containing compounds were relatively absent. Under acidic conditions, extraction efficiencies of DOM from oilfield-produced brine were enhanced for different SPE sorbents as follows from high to low: XAD-8/4 tandem, HLB, PPL, ENVI-18, and ENVI-Carb. DOM samples isolated by different sorbents exhibited different properties. ENVI-18 and XAD-4 DOM isolates were enriched in aliphatic hydrocarbons but devoid of aromatic compounds, XAD-8, HLB, and PPL samples contained relatively higher levels of aromatics, and HLB and PPL samples showed a high retention capacity for carbohydrates, while ENVI-Carb and HLB DOM isolates contained more nitrogen compounds than those obtained using other sorbents. In addition, XAD-8 and PPL extracts were characterized by higher concentrations of sulfur-containing compounds. This is the first study of its type to study oilfield-produced brine DOM, and the results will help us better understand their structures and properties.