Hydrates of Acid Gases

The hydrate formation conditions for pure H2S (Carroll, and Mather, 1991 and Glew, 2000) and pure C02 (Yang et al., 2000) are well established. However, a review of the literature revealed that there are no data for acid gas mixtures. Thus we must proceed with some caution. 

Of the components commonly found in natural gas, none forms a hydrate as easily as hydrogen sulfide. 

CSMGem software (Sloan and Koh, 2007). The broken portion of these curves is where the acid gas liquefies and crosses the phase envelope. The steep portion is for the hydrate for the liquefied acid gas. 

1 From figure 5.1 determine whether or not a hydrate will form under the following circumstances. Assume that sufficient water is present. 

Answer For a hydrate to form, the pressure and temperature must be such that the point is above and to the left of the curves in figure 5.1. For case (a) the point is below the hydrate curve and thus a hydrate does not form. For carbon dioxide at 15°C a hydrate will never form regardless of the pressure, so for case (b) a hydrate does not form. For methane at 15°C and 20 MPa, case (c), the point is above the hydrate curve, so a hydrate does form. For H2S at 15°C and 20 MPa, this point is above the hydrate curve and thus a hydrate forms. Finally, for COz at 15°C and 20 MPa, the point is to the right of the hydrate curve and thus a hydrate does not form. 

---