New data on sulfonated castor oil reveals potential in gas hydrate formation

A new paper appeared in Fuel.

"Gas hydrates are solid crystalline substances resembling ice and consisting of gas and water molecules. Under conditions of high pressure and low temperature, gas molecules are contained within the cavities of the frameworks formed by water molecules. One volume of hydrate can hold about 160 volumes of gas. A promising method of storing and transporting natural gas is to convert it into gas hydrates," explains Mikhail Varfolomeev, Chair of the Department of Petroleum Engineering.

Natural gas, according to the researcher, can be converted to hydrate 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 extracted from the hydrate by simply heating or depressurizing it for further use as a fuel. At the same time, the water formed by "melting" the hydrate can be reused.

The advantages of the hydrate method of gas transportation and storage are moderate temperature and pressure conditions, as well as enviornmental and general safety.

"For Russia, gas hydrate technology is relevant from the point of view of developing small and medium-sized fields for which it is impossible or unprofitable to use traditional methods of storage and transportation. At the same time, gas hydrates can be used to reduce flaring of associated petroleum gas at the fields, as well as to gasify small settlements. Low temperatures, which are typical for the Russian north, are an advantage in this case when implementing hydrate technology. The main disadvantage of hydrate technology, which hampers its widespread implementation, is the low rate of hydrate formation and growth. To solve this problem, so-called promoter agents capable of accelerating the process of hydrate formation are used, such as chemical agents-promoters, nanoparticles, or porous media. Our team is searching for such promoter systems," continues Dr. Varfolomeev.

Earlier, a group of researchers from KFU developed a reagent based on sulfated castor oil, which proved to be a good promoter of hydrate formation, compared to the well-known commercial reagent—sodium dodecyl sulfate. In addition, the new reagent does not form foam and is biodegradable.

"Since there are few data on the joint effect of different types of promoting agents in the scientific literature, we decided to study the synergism of promoter-surfactants and porous medium. Our research is important for understanding the behavior of natural gas hydrates, on the one hand, and, on the other hand, for their practical application in the processes of transportation and storage," says Yulia Chirkova, Junior Research Associate of the Laboratory of Hydrate Technologies of Utilization and Storage of Greenhouse Gases.

Using the method of differential scanning calorimetry, the scientists investigated the effect of sulfonated castor oil and sodium dodecyl sulfate additives on the formation of methane hydrates and methane-propane gas mixture in a porous medium, which was quartz sand.

"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 increasing sand-to-solution weight ratio, in contrast to the pure water system. This is probably due to the fact that the promoters increase hydrate growth on the reactor walls. This effect is not observed for gas mixture hydrates, indicating differences in the promotion of hydrates with sI (methane hydrate) and sII (natural gas hydrate) structures. Kinetic calculations using the Avrami equation showed that both reagents (sulfated castor oil and sodium dodecyl sulfate) increase the rate of hydrate formation, but the reagent created at KFU allows to do it under milder conditions," adds Chirkova.

The study has shown that sulfonated castor oil has a higher synergistic effect with porous media and is a promising reagent for solving the problem of slow hydrate formation in natural gas storage and transportation. The conversion of gas to hydrate when sand and castor oil are used together increases by 25 percent compared to the use of castor oil alone, namely from 70 to 95 percent.

More information:
Synergistic effect of sulfonated castor oil and porous medium on kinetics of gas hydrates formation
www.sciencedirect.com/science/ … ii/S0016236122039631

Provided by Kazan Federal University