Assessing the Biological Stability of a Terpene-Based Advanced Biofuel and Its Relationship to the Corrosion of Carbon Steel

Abstract

Energy-dense terpene biofuels have recently been recognized as renewable alternatives for high-density petroleum-derived fuels. While the physicochemical properties of terpene dimer fuel (TDF) have been well-documented, the propensity of these mixtures to undergo biodegradation and exacerbate the corrosion of the fuel infrastructure remains unknown. Coastal seawater/sediment incubations were amended with TDF or a blend of petroleum-derived hydrocarbons and incubated under strict anaerobic conditions. In some incubations, a model hydrocarbon-degrading sulfate-reducing bacterium (Desulfoglaeba alkanexedens, strain ALDC) was inoculated as a positive control. No increase in sulfate reduction or corrosion was observed in long-term experiments (300 days) relative to TDF-free controls when only seawater/sediment served as the inoculum. However, inoculation with the positive control organism and a mixture of C6–C12 n-alkanes increased both the sulfate reduction rate (95.2 ± 5.2 μM/day) and general corrosion, as determined by both coupon weight loss (27.9 ± 1.6 mg) and the number of pits (495 ± 62). The ratio of manganese (Mn)/weight loss (0.34) in incubations exhibiting coupon pitting was lower than those (0.53–0.68) showing only generalized coupon corrosion. Despite no indication for TDF biodegradation under all test conditions, the detection of a suite of alkylsuccinate metabolites attested to the anaerobic metabolism of the suite of n-alkanes when strain ALDC and the hydrocarbons served as amendments. These findings suggest that TDF is resistant to biodegradation and will not exacerbate the corrosion of carbon steel. If used in combination with petroleum hydrocarbons, the degree of metal corrosion would be that expected as a result of labile fuel components. However, the relatively recalcitrant nature of TDF might pose other risks if released to the environment and, thus, warrants further study.