Hydrothermal transformation of Chinese privet seed biomass to gas-phase and semi-volatile products

Hydrothermal (HT) treatment of seeds from Chinese privet (Ligustrum sinense), a non-native and invasive species in the southeastern United States, was examined with respect to the generation of gas-phase and semi-volatile organic chemicals of industrial importance from a lipid-rich biomass resource. Aqueous seed slurries were transformed into biphasic liquid systems comprised of a milky aqueous phase overlain by a black organic layer. Present in the headspace were elevated levels of CO2 and acetic acid. Analysis of the semi-volatiles by GC–MS showed the formation of alkyl substituted benzenes, oxygenated cyclic alkenes, phenol, substituted phenolics, and alkyl substituted pyridines. Compared to immature seeds, mature seeds gave high relative amounts of oxygenated cyclic alkenes (cyclopentenones) and alkyl pyridines. The presence of fatty acids in the HT products likely resulted from both lipid hydrolysis reactions and the inherent stability of fatty acids under HT treatment conditions. Estimates of lignin and protein contents showed no definite trend that could be linked to the HT data. The proportion of aromatic HT products appeared to derive primarily from the proportion of extractives. Thus, variations in extractives yields impact HT product yields and thereby demonstrate the importance of timing in feedstock collection to favor targeted HT products.