Kinetic Hydrate Inhibition by Lambda-Carrageenan and Its Synergistic Compositions with Ethylene Glycol, 4-Methyl-1-Pentanol, Polyvinylpyrrolidone, and Polyvinylcaprolactam

Abstract

For the oil and gas industry to function smoothly, it is essential to have a continuous flow of oil and gas in pipelines without interruptions caused by hydrate blockages. Kinetic hydrate inhibitors (KHIs) are becoming popular as they offer safe and effective hydrate inhibition at low dosages (0.5–2 wt % of the water content). The current commercial KHIs are synthetic and poorly biodegradable, which causes disposal concerns for environmental regulators. The lack of natural, sustainable, and biodegradable KHIs opens the scope to develop natural and biodegradable KHI alternatives. This study investigates the use of a natural and biodegradable polysaccharide, lambda carrageenan (λ-crgn), as a standalone KHI and its combinations with biodegradable solvents mono ethylene glycol and 4-methyl-1-pentanol and commercial KHI polymers (PVP and PVCap) for improved biodegradability and performance. λ-crgn is an environmentally friendly polysaccharide derived and cultivated from red seaweeds. Two variants of λ-crgn, one with a smaller mean size and a lower viscosity (LV) and one with a larger mean size and a higher viscosity (HV), are tested for hydrate inhibition. The lower molecular size/viscosity variant, λ-crgn (LV), showed similar induction times and lower hydrate growth rates compared to PVP when used as a standalone KHI. However, the high-viscosity variant did not perform as well as PVP. λ-crgn (HV or LV), when blended with commercial KHIs (PVP and PVCap), synergized and led to an increase in induction times by up to 63% and a decrease in the hydrate growth rates by 73% compared to when only the commercial KHIs were used at the exact total dosages. When λ-crgn (HV or LV) was blended with solvents 4-methyl-1-pentanol or MEG, again a significant synergy was observed, leading to the hydrate inhibition performance that was found to be at par or better than the commercial KHIs (PVP and PVCap) at the exact total dosages.