Relationship Between the End-Cap Structure of Polyurethanes\nand Their Kinetic Hydrate Inhibition Activity: Effective Hydrate Prevention\nat Low Concentrations

To\naddress the challenges associated with gas hydrate formation\nin deepwater environments, two novel waterborne polyurethanes were\ndeveloped using etidronic acid (EA-WPU) and citric acid (CA-WPU) as\nkinetic hydrate inhibitors. EA-WPU exhibited superior inhibition,\ncompletely preventing sII hydrate formation at a concentration of\n0.5 wt %. CA-WPU also showed strong performance, with subcooling temperature\n(Δ<i>T</i>) values of 13.16 and 11.62 °C at concentrations\nof 0.5 and 0.25 wt %, respectively. These polymers have demonstrated\nhigh efficiency in inhibiting sII gas hydrate formation, even at a\nlow concentration of (0.05 wt %). The inhibition performance against\nsI hydrates varied, with Luvicap EG and CA-WPU demonstrating the strongest\ninhibitory effects. At 0.5 wt %, CA-WPU exhibited a Δ<i>T</i> value of 6.05 °C, comparable to that of Luvicap EG.\nThis study suggests that the specific functional groups present in\nthe end-cap structure of WPUs directly influence their ability to\ninhibit sI and sII hydrates. Carboxylic acid and phosphonate groups\nappear to be more effective for sI and sII hydrates, respectively.\nMoreover, field-specific assessments demonstrated that EA-WPU at 0.25\nwt % achieved a Δ<i>T</i> of 15.5 °C, surpassing\nthe required Δ<i>T</i> of 12 °C to prevent hydrate\nformation at 280 bar and 15 °C. This allowed for a 90-fold reduction\nin inhibitor consumption compared to 23 wt % methanol solution. Additionally,\nthe inhibitor solutions remained transparent and exhibited no clouding\nup to 70 °C at concentrations of 2 and 1 wt %, respectively.\nAlthough clouding occurred at higher concentrations and temperatures,\nboth solutions remained stable without deposition even at a concentration\nof 8 wt % and a temperature of 70 °C. These results highlight\nthe excellent thermal stability of EA-WPU and CA-WPU, making them\nsuitable for high-temperature injection up to 2 wt %. Good inhibition\nperformance at low concentrations and high thermal stability of WPUs\nmake them promising candidates for widespread application in gas hydrate\nmanagement, offering significant operational cost savings and reduced\nenvironmental impact.