Solubility of Elemental Sulfur in Dense Phase Carbon Dioxide from T = 324 to 424 K and p = 10 and 20 MPa

Abstract Both H2S and CO2 (acid gases) are removed during natural gas treatment and, if purified, CO2 fluids can be marketed as a high-pressure product, thereby adding a secondary value to hydrocarbon production. If high-pressure cryogenic separation techniques are used to separate the acid gas components, the CO2 fluid will require further processing before sale. In exploring high-pressure oxidation of H2S in CO2, we first required the solubility of elemental sulfur, S8, within CO2 and a model to calculate the sulfur fugacities over a range of temperatures and pressures. Solubility information allows one to (a) define sulfur dew point conditions within high-pressure recovery processes and (b) provide for fugacity coefficients necessary to calculate high-pressure recovery limits. In this work, the solubilities of elemental sulfur in dense phase CO2 were measured from T = 323.75 to 424.05 K and at p = 10 and 20 MPa. The measured solubilities of elemental sulfur increased with increasing temperature as well as increasing pressure. Two thermodynamic models were tested to correlate the experimental solubility: (i) a previous Virial Equation Model and (ii) a Fluctuation Solution Theory correlation. Both models are self-consistent with the reference vapor pressure at low pressure. Through the comparison of the calculated results, the Fluctuation Solution Theory correlation was found to best fit the experimental data.