Relationship Between the End-Cap Structure of Polyurethanes and Their Kinetic Hydrate Inhibition Activity: Effective Hydrate Prevention at Low Concentrations

To address the challenges associated with gas hydrate formation in deepwater environments, two novel waterborne polyurethanes were developed using etidronic acid (EA-WPU) and citric acid (CA-WPU) as kinetic hydrate inhibitors. EA-WPU exhibited superior inhibition, completely preventing sII hydrate formation at a concentration of 0.5 wt %. CA-WPU also showed strong performance, with subcooling temperature (ΔT) values of 13.16 and 11.62 °C at concentrations of 0.5 and 0.25 wt %, respectively. These polymers have demonstrated high efficiency in inhibiting sII gas hydrate formation, even at a low concentration of (0.05 wt %). The inhibition performance against sI hydrates varied, with Luvicap EG and CA-WPU demonstrating the strongest inhibitory effects. At 0.5 wt %, CA-WPU exhibited a ΔT value of 6.05 °C, comparable to that of Luvicap EG. This study suggests that the specific functional groups present in the end-cap structure of WPUs directly influence their ability to inhibit sI and sII hydrates. Carboxylic acid and phosphonate groups appear to be more effective for sI and sII hydrates, respectively. Moreover, field-specific assessments demonstrated that EA-WPU at 0.25 wt % achieved a ΔT of 15.5 °C, surpassing the required ΔT of 12 °C to prevent hydrate formation at 280 bar and 15 °C. This allowed for a 90-fold reduction in inhibitor consumption compared to 23 wt % methanol solution. Additionally, the inhibitor solutions remained transparent and exhibited no clouding up to 70 °C at concentrations of 2 and 1 wt %, respectively. Although clouding occurred at higher concentrations and temperatures, both solutions remained stable without deposition even at a concentration of 8 wt % and a temperature of 70 °C. These results highlight the excellent thermal stability of EA-WPU and CA-WPU, making them suitable for high-temperature injection up to 2 wt %. Good inhibition performance at low concentrations and high thermal stability of WPUs make them promising candidates for widespread application in gas hydrate management, offering significant operational cost savings and reduced environmental impact.