Kinetic Hydrate Inhibition Performance of Poly(vinyl caprolactam) Modified with Corrosion Inhibitor Groups

Abstract

Multifunctional polymers were designed and synthesized that contain both a kinetic hydrate inhibitor and corrosion inhibitor groups. This was achieved by modifying a copolymer of vinyl caprolactam and acrylic acid (PVCap-co-AA) where the acid groups were converted to known corrosion inhibitor groups including imidazole (APIM) and quaternary ammonium (ATCH) moieties. Therefore, all of the resulting polymers had the same molecular weight, end groups, and overall composition which allowed for accurate determination of the performance of these inhibitors. Their performance as kinetic hydrate inhibitors was evaluated by determining the hydrate onset time, growth rate, and resistance to flow using a high pressure autoclave. The experimental results show that both PVCap-co-APIM and PVCap-co-ATCH were able to delay hydrate nucleation; however, PVCap-co-APIM was better than PVCap-co-ATCH. The performance of new KHICIs was evaluated and compared with that of a commercial KHI, Luvicap, with three different cooling rates: for high and medium cooling rates, Luvicap delayed hydrate nucleation for a longer time compared to the new KHICIs. At low cooling rate, one of the KHICIs (PVCap-co-APIM) showed better performance than Luvicap. PVCap-co-APIM also performed better than Luvicap and PVCap-co-ATCH in decreasing the hydrate growth rate. Hydrate growth rate and resistance to flow were also studied during the hydrate formation to investigate the effect of the inhibitors on the growth of hydrate particles in the liquid phase. PVCap-co-APIM successfully suppressed hydrate growth in the early stage of hydrate formation, whereas PVCap-co-ATCH resulted in fast growth of the hydrate phase. For all of the studied cooling rates, PVCap-co-APIM showed stable resistance to flow even with increasing hydrate fraction in the liquid phase; however, PVCap-co-ATCH showed a torque surge in the early stage of hydrate formation when a fast cooling rate was used, which suggests that the ATCH group has a negative effect on the hydrate inhibition performance. These results provide a proof-of-concept that the modified PVCap-co-APIM, or related structures, that contain both kinetic hydrate inhibitor and corrosion inhibitor groups can be used as multifunctional inhibitors for offshore oil and gas fields.