Effects of structural properties of alcohol molecules on decomposition of natural gas hydrates: A molecular dynamics study

Abstract

Natural gas hydrates, which are mainly distributed at the sea floor and in permafrost regions, are expected as a future but untapped energy resource. Design of effective chemicals for promotion of the gas hydrate decomposition is one solution of achieving sustained and steady exploitation of natural gas hydrate. Among possible additives, alcohols are commonly used. However, the effectiveness is limited and few studies have been conducted to understand the effects of molecular structure of alcohols on the hydrate decomposition. Here, with the aid of molecular dynamic simulations, we systematically investigate the effects of chain length, hydroxyl position and hydroxyl number of alcohols on the decomposition of methane hydrates. Combining variations of potential energy, radial distribution functions, and mean square displacement, the influences of alcohol structural properties on the hydrate decomposition are evaluated. Simulation results show that 1-pentanol, 2-pentanol and 3-pentanol are added, methane hydrates decompose completely at 1420 ps, 1300 ps and 1500 ps respectively. Alcohol with short branched chains is conducive to promoting the decomposition of methane hydrate. However, adding methanol, ethanol, 1-propanol, 1,2-propanediol and glycerol, methane hydrates decompose completely at 1530 ps, 1650 ps,1700 ps, 1500 ps and 900 ps respectively and methane hydrate can’t completely decompose at 2000 ps adding 1-butanol. The result indicates that shortening the chain length of alcohols and increasing the hydroxyl number of alcohols are beneficial to improving the promotion effect on methane hydrate decomposition. Our results thus provide useful guidelines for future design of alcohol-based molecules for promoting gas hydrate decomposition.