Unraveling the effect of sub-cooling temperatures on the kinetic performance of biopolymers for methane hydrate

Abstract

In deep sea plays, where the driving force or sub-cooling temperature for hydrate formation is high, the commercially used kinetic hydrate inhibitors (KHIs) lose their kinetic inhibition performance, additionally they are toxic. Though, biodegradable biopolymers are deliberated as an alternative KHIs. However, the inhibition performance of biopolymers solely for methane hydrate formation at high sub-cooling temperatures has not been evaluated. In current work the kinetic inhibition performance of five biopolymers (Pectin, Sodium- Carboxymethyl cellulose (Na-CMC), Tapioca starch, Dextran and Xanthan gum) on methane hydrate formation is evaluated using isochoric constant cooling method on sapphire hydrate reactor at 95 bar and sub-cooling temperatures of 9 °C and 12 °C. Induction time, hydrate formation rate, amount of methane consumed and percentage relative inhibition power are determined and used as kinetic inhibition indicators. Present data-set reveals that biopolymers efficiently inhibit methane hydrate formation at high sub-cooling temperatures. Among all studied biopolymers Pectin and Na-CMC commendably delayed hydrate nucleation for 78 and 61min respectively. Furthermore, Tapioca starch, Pectin and Na-CMC significantly reduced hydrate formation rate, methane consumption and percentage relative inhibition power. For further analysis on molecular level Conductor like Screening Model for Real Solvents (COSMO-RS) software is used. The interaction energy estimation using COSMO-RS showed that attractive interactions between biopolymers and water molecules are leading to prolonged nucleation. Furthermore, the effect of biopolymer concentrations (0.12 wt% - 1.5 wt%) on kinetic inhibition is elaborated by establishing a relationship between induction time, air-liquid interfacial and electrokinetic properties.