Inhibition effects of polysaccharides for gas hydrate formation in methane-water system

Water-soluble polymers such as polyvinylpyrrolidone (PVP), PVCap, and Gaffix VC-713 are predominantly used as kinetic hydrate inhibitors (KHIs) in the petroleum and natural gas industry to control the formation of hydrates. However, very few of them exhibit good biodegradability. Therefore, developing environment-friendly, biodegradable inhibitors is necessary. In this study, five natural polysaccharides, gum Arabic, sodium alginate, guar gum, carboxymethyl chitosan, and starch, were screened as potential green inhibitors. Their hydrate inhibition performances were investigated using a high-pressure stainless steel cell and methane gas and were compared with that of a typical KHI, PVP K90. The impact of the polysaccharides on the hydrate microstructure was investigated using powder X-ray diffraction and Raman spectroscopy. All polysaccharides increased the maximum subcooling of hydrate formation and inhibited the hydrate growth well below their respective maximum subcooling. Guar gum exhibited the best performance, most probably owing to the presence of the side anhydroglucose group in its skeleton. Remarkably, it lowered the gas uptake by similar to 30% as compared with that of pure water. The next best performance was shown by sodium alginate. Starch and carboxymethyl chitosan also performed well until the subcooling exceeded the respective maximum subcooling. In contrast, gum Arabic showed weak hydrate inhibition at low subcooling and rather started to promote hydrate formation when the subcooling was increased to 6 degrees C. Moreover, its hydrate promotion activity improved as the subcooling was further increased. Finally, the hydrate inhibition mechanism of the polysaccharides is discussed. (C) 2019 Elsevier B.V. All rights reserved