The effect of ethanol added to the natural gas stream on the top of line corrosion: An approach on vapor phase condensation and carbonic acid generation yield

Abstract

This study investigates the side effect of ethanol, added to the natural gas stream as hydrate inhibitor, on vapor condensation and top of line corrosion (TLC). The methodology presented allowed the measurements of both condensation and TLC rates under 1 barg and 8 barg CO2 partial pressures. Tests were performed without any hydrate inhibitor and with ethanol or monoethylene glycol (MEG) for comparison. Ethanol greatly reduced TLC rates, providing TLC rate inhibition efficiencies of at least 80% in the absence of acetic acid (HAc) and above 42% when HAc is present. Simulated data indicates ethanol concentration of 70% w/w in the condensates, indirectly reducing the conversion degrees of dissolved CO2 into H2CO3 (for instance, 0.01 instead of 0.12 at 8 barg in the absence of HAc). Also, the presence of ethanol reduces the dissociation of HAc into free H+ and Ac− when compared with other condensates. Therefore, indirectly, ethanol reduces the cathodic reactions’ rates and, hence, the anodic reaction rate. Additionally, ethanol changed the condensation mode from dropwise to Marangoni, which proved to be convenient since it probably provided low water concentration at the solid-liquid interface. These observations bring up the benefit of adding ethanol to the natural gas stream not only as hydrate inhibitor but also as a support for consolidated TLC prevention techniques.