Petroleum scientists continue studies of castor oil in gas hydrate formation
A new paper on the topic was published in Fuel.
Head of the Department of Petroleum Engineering Mikhail Varfolomeev explains, “Gas hydrates are solid crystalline substances which look like ice and consist of gas and water molecules. Gas molecules under conditions of high pressures and low temperatures are contained inside the framework cavities formed by water molecules. In this case, one volume of hydrate can contain about 160 volumes of gas. One promising method for storing and transporting natural gas is its conversion into gas hydrates.”
Natural gas, according to the researcher, can be converted into a hydrated form at high pressure and low temperature using water and a small amount of promoter additives for transportation or storage, after which it can be easily removed from the hydrate by simply heating or depressurizing for further use as fuel. In this case, the water formed during the melting of the hydrate can be reused.
“In Russia, gas hydrate technology is relevant for small and medium-sized deposits, for which it is impossible or unprofitable to use traditional methods of storage and transportation. At the same time, with the help of gas hydrates, it is possible to reduce the burning of associated petroleum gas in the fields, as well as gasify small settlements. The low temperatures typical for the Russian north are in this case an advantage when introducing hydrate technology. The main disadvantage of the hydrate technology, which hinders its widespread implementation, is the low rate of formation and growth of hydrates. To solve this problem, the so-called promoting agents are used, which are capable of accelerating the process of hydrate formation, for example, chemical promoters, nanoparticles, and porous media. Our team is looking for such promotional systems,” continues Varfolomeev.
Recently, the team offered a new reagent based on sulfonated castor oil; it has shown good effectiveness for hydrate formation in comparison with now widely used sodium dodecyl sulfate. Additionally, the KFU-made compound is non-foamy and biodegrradable.
“We decided to study the synergy of two surfactants – the castor oil and the sodium dodecyl sulfate – in porous media,” continues Junior Research Associate of the Laboratory of Hydrate Technologies of Utilization and Storage of Greenhouse Gases Yulia Chirkova.
In this case, quartz sand served as the porous medium, and the studies hydrate of methane and of methane-propane mix.
“We have shown that in the case of methane hydrate, when promoters are added to the system at a concentration of 0.5 percent, the amount of hydrate in the system increases with an increase in the ratio of mass of sand to solution, in contrast to the system with pure water. This is probably due to the fact that promoters increase the growth of hydrates on the walls of the reactor. This effect is not observed for hydrates of the gas mixture, which indicates differences in the promotion of hydrates with the structure sI (methane hydrate) and sII (natural gas hydrate). Kinetic calculations using the Avrami equation showed that both reagents (sulfonated castor oil and sodium dodecyl sulfate) increase the rate of hydrate formation, but the reagent created at KFU allows this to be done under milder conditions,” concludes Chirkova.