Effects of a Quaternary Ammonium Salt on the Growth, Wettability, and Agglomeration of Structure II Hydrate Crystals

This work studied the effects of a water-soluble quaternary ammonium salt (called DA 50) on the growth, wettability, and agglomeration of cyclopentane (CP) hydrate crystals and methane (CH4)/propane (C3H8) hydrate crystals. The impact on these properties of adding 4 wt % NaCl to the DA 50 solution was also investigated. The hydrates were formed from water/CP, water/(CP + n-octane (n-C8)), and water/(CP + n-dodecane (n-C12)) mixtures at atmospheric pressure and from a water/n-C8/(CH4 + C3H8) mixture under pressure (about 67 bar). Experiments were performed at a subcooling of 6 °C in the case of the CP hydrates and 9–10 °C in the case of the CH4/C3H8 hydrates. In both hydrate systems, adding NaCl to the surfactant solution of 0.1 or 1 wt % DA 50 led to the formation of individual oil-wettable pyramidal crystals. Without salt, the hydrate formed a water-wettable shell that covered the water/oil interface just as the system without surfactant did. The antiagglomeration performance of the 1 wt % DA 50 solution...