Investigation on the effect of oxalic acid, succinic acid and aspartic acid on the gas hydrate formation kinetics

Gas hydrate reserves are potential source of clean energy having low molecular weight hydrocarbons trapped in water cages. In this work, we report how organic compounds of different chain lengths and hydrophilicities when used in small concentration may modify hydrate growth and either act as hydrate inhibitors or promoters. Hydrate promoters foster the hydrate growth kinetics and are used in novel applications such as methane storage as solidified natural gas, desalination of sea water and gas separation. On the other hand, gas hydrate inhibitors are used in oil and gas pipelines to alter the rate at which gas hydrate nucleates and grows. Inhibitors such as methanol and ethanol which form strong hydrogen bond with water have been traditionally used as hydrate inhibitors. However, due to relatively high volatility a significant portion of these inhibitors ends up in gas stream and brings further complexity to the safe transportation of natural gas. In this study, organic additives such as oxalic acid, succinic add and L-aspartic acid (all three) having -COOH group(s) with aspartic acid having an additional -NH2 group, are investigated for gas hydrate promotion/inhibition behavior. These compounds are polar in nature and thus have significant solubility in liquid water; the presence of weak acidic and water loving (carboxylic/amine groups) moieties makes these organic acids an excellent candidate for further study. This study would pave ways to identify a novel(read better) promoter/ inhibitor for gas hydrate formation. Suitable thermodynamic conditions were generated in a stirred tank reactor coupled with cooling system; comparison of gas hydrate formation kinetics with and without additives were carried out to identify the effect of these acids on the formation and growth of hydrates. The possible mechanisms by which these additives inhibit or promote the hydrate growth are also discussed. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All tights reserved.