Effects of cyclic structure inhibitors on the morphology and growth of tetrahydrofuran hydrate crystals

Abstract

Morphology and growth of hydrate crystals with cyclic structure inhibitors at a hydrate–liquid interface were directly observed through a microscopic manipulating apparatus. Tetrahydrofuran (THF) hydrate was employed as an objective. The effects of four kind of cyclic structure inhibitors, polyvinylpyrrolidone (PVP), poly(N-vinyl-2-pyrrolidone-co-2-vinyl pyridine) (PVPP), poly(2-vinyl pyridine-co-N-vinylcaprolactam) (PVPC) and poly(N-vinylcaprolactam) (PVCap), were investigated. Morphological patterns between each hydrate crystal growth from hydrate–liquid interface into droplet were found differ significantly. Lamellar structure growth of hydrate crystal was observed without inhibitor, while with PVP was featheriness-like, PVPP was like long dendritic crystal, PVPC was Mimosa pudica leaf-like and PVCap was like weeds. The growth rate of hydrate crystal without inhibitor was 0.00498mm3/s, while with PVPP, PVPC and PVCap, were 0.00339mm3/s, 0.00350mm3/s, 0.00386mm3/s and 0.00426mm3/s, respectively. Cyclic structure inhibitors can decrease the growth rate, degree of reduction in growth rate of hydrate crystals decrease with the increase of cylinder number.