Synthesis and evaluation of poly (N-vinyl caprolactam)–co-tert-butyl acrylate as kinetic hydrate inhibitor

Abstract

• A new KHI PVCap- co -TBA was synthesized and evaluated in different hydrate forming systems. • The relationship between the dosage of KHI and the inhibition performance was analyzed. • PPG was proposed as a good synergist for PVCap- co -TBA with concentration of 1.0 wt%. Low dosage kinetic hydrate inhibitors (KHIs) are a kind of alternative chemical additives to high dosage thermodynamic inhibitors for preventing gas hydrate formation in oil & gas production wells and transportation pipelines. In this paper, a new KHI, poly ( N -vinyl caprolactam)– co - tert -butyl acrylate (PVCap- co -TBA), was successfully synthesized with N -vinyl caprolactam (NVCap) and tert -butyl acrylate. The kinetic inhibition performances of PVCap- co -TBA on the formations of both structure I methane hydrate and structure II natural gas hydrate were investigated by measuring the onset times of hydrate formation under different conditions and compared with commercial KHIs such as PVP, PVCap and inhibex 501. The results indicated that PVCap- co -TBA outperformed these widely applied inhibitors for both structure I and structure II hydrates. At the same dosage of KHI, the maximum tolerable degree of subcooling under which the onset time of hydrate formation exceeded 24 hours for structure I hydrate was much lower than that for structure II hydrate. The inhibition strength increased with the increasing dosage of PVCap- co -TBA; The maximum tolerable degree of subcooling for the natural gas hydrate is more than 10 K when the dosage was higher than 0.5% (mass) while it achieved 12 K when that dosage rose to 0.75% (mass). Additionally, we found polypropylene glycol could be used as synergist at the dosage of 1.0 % (mass) or so, under which the kinetic inhibition performance of PVCap- co -TBA could be improved significantly. All evaluation results demonstrated that PVCap- co -TBA was a very promising KHI and a competitive alternative to the existing commercial KHIs.