Applied Energy, Vol.249, 190-203, 2019
Clathrate hydrate formation of CO2/CH4 mixture at room temperature: Application to direct transport of CO2-containing natural gas
CO2 is one of the major contaminants in natural gas produced from the reservoir. Many gas fields are not monetized due to the presence of high levels of CO2 in the natural gas reservoir (in some locations, as high as 80%). SNG (solidified natural gas) technology provides a potential method to directly transport CO2-containing natural gas in the form of gas hydrates. We examined the performance of hydrate formation for 24% CO2/76% CH4 mixture in the presence of stoichiometric tetrahydrofuran (THF, 5.56 mol%) in an unstirred tank reactor (UTR). The presence of 24% CO2 exhibited two contrasting kinetic behaviors for CO2/CH4/THF hydrate formation. Considering only the high-kinetics cases, the hydrate formation kinetics was significantly enhanced by increasing the experimental pressure from 3.0 MPa to 7.0 MPa at 283.2 K. The increase of experimental temperature from 283.2 K to 293.2 K at 7.0 MPa reduced the gas uptake by around 40%. We observed different morphology patterns during hydrate formation under different temperatures. By the addition of a kinetic promoter, 100 ppm sodium dodecyl sulfate (SDS), and applying a hybrid formation method involving a very short period of stirring at the beginning and unstirred operation during the hydrate growth stage, we achieved rapid hydrate formation of 75.40 +/- 2.62 mmol/mol within 2 h with extremely short induction time (11.3 +/- 4.79 min) at room temperature (298.2 K) and 9.1 MPa. The simplicity of this process and the enhanced kinetic performance at room temperature could result in an overall cost reduction making it feasible to develop an economical transport method for CO2-containing natural gas.