Method Development for the Quantitative Analysis of Hydrocarbon Impurities in Amine-Based Desulfurization Solvents

The antifoaming performance of natural gas desulfurization solvents is critical for maintaining product gas quality and ensuring the safe operation of processing units. Hydrocarbon impurities can enter amine solutions through feed-gas entrainment, wellhead flowback carryover, and leakage of equipment lubricants. These contaminants may gradually accumulate in the solvent system and become a significant contributor to foaming. To address the industrial demand for rapid quantitative determination of hydrocarbon contaminants in desulfurization solvents, this study investigates in-service UDS-series solvents and representative samples collected from a natural gas purification plant in western Sichuan. NMR spectroscopy and GC-MS analyses reveal that the impurities are predominantly n-alkanes in the C13-C18 range, based on which a corresponding reference standard oil was prepared. COSMO-RS calculations combined with molecular interaction analysis identify n-hexane as the optimal extraction solvent. The ultraviolet spectrophotometric method commonly used to determine hydrocarbons in environmental water samples shows limited sensitivity to long-chain n-alkanes and requires strong acid pretreatment that disrupts the amine solvent matrix, rendering it unsuitable for UDS solvents. In contrast, the n-hexane extraction-GC-FID method showed good linearity, precision, and accuracy, meeting engineering analytical requirements for monitoring hydrocarbon contamination in MDEA-based UDS desulfurization solvents.