Abstract

Calcium carbonate is one of the most abundant minerals precipitating during gas production. This work is focused on precipitation of CaCO3 in presence of Monoethylene glycol (MEG), used as hydrate inhibitor. MEG is known to affect the thermodynamics of calcium carbonate and this study shows that it has a large impact on the precipitation kinetics. The whole precipitation process has been investigated including polymorphism, induction times, nucleation rates and growth rates. Growth rate is emphasized as it has a large impact on both induction time and transformation rate from metastable polymorphs to stable calcite. The experiments were performed at 25-800C with MEG concentration up to 90 wt%.

MEG prolongs the induction period for precipitation as its presence decreases both nucleation rates and growth rates. The growth rates of all three polymorphs are reduced in presence of MEG, but calcite is most inhibited. The slow growth of calcite at high MEG concentrations result in a very slow transformation from initially mixed metastable polymorphs.

Ferrous ions (Fe2+) affect the polymorphism of CaCO3. The growth of vaterite and aragonite is retarded to different extent. Vaterite growth is most inhibited resulting in aragonite being the most abundant polymorph in a larger MEG and temperature range. The effect depends strongly on Fe2+ concentration relative to solid surface area.

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