Phytochemical characterization of selected agro-waste extracts as kinetic inhibitors in methane hydrates formation

Abstract

In this study of gas hydrate inhibition, the bio-active components (phytochemicals) and the influence of functional moieties and chemical structures on selected bio-inhibitors' performance were investigated by advanced analytical techniques. The agro-waste materials of interest are: orange mesocarp (Citrus sinensis (L)) extract (OME), red onion skin (Allium cepa) extract (ROSE), kolanut tesla (Cola acuminata) extract (KTE), coconut coir dusk (Cocos nucifera) extract (CCDE) and peanut skin (Arachis hypogea) extract (PSE). A CO2-enhanced supercritical fluid extraction (SFE) technique was used to extract the bioactive components from their parent materials. After the extraction, advanced analytical techniques including FTIR, NMR and HP-TLC with densitometry were used to identify and isolate functional groups, structurally characterize and quantify the bioactive compounds in the extracts primarily focusing on phenolic acids, flavonoids and tannins. A Bruker 500MZ NMR spectrometer and a CAMAG-semi-automatic HP-TLC system were used for the structural characterization and quantification respectively. Based on the number of anti-oxidants and radicals scavenging characteristics of the individual extracts' polyphenolic and tannin components, the expected hydrates inhibition capacities of the bio-extracts are in the magnitude: CCDE > ROSE > PSE > OME > KTE. The extracts are readily biodegradable and non-toxic and therefore do not pose ecological threat unlike PVP with only 31.50% biodegradation rate and may result in serious ecological risks in offshore environments. Lastly, the numbers of hydroxyl (OH) and meth-oxyl (MeoH) groups are the principal factors that influence the bio-inhibitors performance with hydroxyl group number being more important than that of the meth-oxyl group.