Natural gas storage using clathrate technology : Enhanced formation at High temperature

Abstract

Solidified natural gas (SNG) by storing natural gas in the hydrate form, which is safe and easy to recover stored gas compared to other methods. However, to make this technology competitive, storing natural gas at a higher temperature, lower pressure with faster formation is needed. Tetrahydrofuran (THF) is a well-known thermodynamic promoter used to increase the hydrate formation temperature. However, increasing the hydrate formation temperature has a drawback on decreasing the formation rate. Nonpolar amino acids have been used as a secondary promoter, which increases the hydrate formation kinetics. This work used 5.56 mol% THF cooperated with different concentrations of nonpolar amino acids (leucine, valine, and methionine) at 20 °C 8 MPa in the unstirred reactor configuration. The experiment was investigated for the effects of these co-promoters in both kinetics and morphology studies. Results showed that the nonpolar amino acids affected the hydrate kinetics by increasing the hydrate formation rate up to 5 times, and certain nonpolar amino acids did not show the muti-step hydrate formation, which resulted in the low methane uptake. However, the methane uptake in the presence of leucine and methionine was as high as that 5.56 mol% THF. The morphology showed different hydrate growth patterns with the investigated solutions. The hydrate formation morphology in the 5.56 mol% THF was similar to leaflike stack up. However, that behavior was not observed when the amino acids were added for the hydrate formation. In addition, the formation morphology among the solutions with the amino acids was also different. Moreover, the presence of the amino acids did not result in the foam formation as surfactants during the hydrate dissociation. When the formation temperature was increased to 25 °C, the formation pressure at 8 MPa or even at 9 MPa was not enough to form the hydrates. To induce the hydrate formation, the hybrid reactor configuration was installed. The results showed the need of amino acid to maintain the high methane uptake and the formation kinetics was not promoted by the amino acids but rather by the hybrid reactor at this condition.