Controlling water dynamics for kinetic inhibition of clathrate hydrate

Abstract

Subsea natural gas drilling and gas transport is challenged by the catastrophic formation of gas clathrate hydrate in production lines. Polymer inhibitors are vital to mitigate this technical problem in subsea gas drilling operation. However, physico- chemical factors affecting their performance are not yet completely known. Herein, we report that the activities of synthetic kinetic inhibitors of clathrate hydrates are correlated to the surrounding water dynamics. Two types of linear polyamide inhibitors are found to be capable of producing immobilized nonfreezable water molecules with fast transverse relaxation in sub-millisecond to millisecond time-scale as revealed by NMR relaxometry. Such a unique state of water can be construed as a form of nonfreezable bound water measured by differential scanning calorimetry. The quantity of such water species can be tuned by the size of the hydrophobic groups introduced to the polyamides and result in longer inhibition time before the rapid growth of the hydrate crystals. Addition of a single hydroxyl side group in the polymer structural unit can also affect the dependence of the kinetic inhibition time on the amount of the supercooled water. Both the hydrophobic and hydrophilic groups in the polymer inhibitors exert coordinated influence on the dynamic properties of the bound water, which are responsible for the early recognition and inhibition of the clathrate hydrate clusters.