Chemical Stability of Sulfur Dioxide in an H_2O-CO_2-SO_2 Fluid at T = 300-400 deg C and P = 500 bar: An Experimental Study and Thermodynamic Modeling

摘要

With the goal of exploring the effect of specific physicochemical properties of carbon dioxide-rich fluids on the chemical stability of solute sulfur dioxide, an experimental study and thermodynamic modeling of the process of SOiaq) conversion in homogeneous water and water-carbon dioxide mixtures were performed. The 4S0z(aq) + 4H2O -H2S(aq) + 3 HSO4 + 3H+ equilibrium was studied in water and water-carbon diox- ide mixtures over the range of temperatures from 300 to 400°C at 500 bar pressure. In support of the known literature, it was established that, in the pure aqueous fluid, the decreasing temperature causes an abrupt shift in the equilibrium to the formation of hydrogen sulfide and sulfate ions. The equilibrium yield of SO2(aq) in percent of the initial SO2(aq) content (0.1m) decreases from 99.5 at 400°C to 18.7% at 300°C. However, it was observed for the first time that carbon dioxide alone induces the chemical stabilization of aqueous sulfur diox- ide: Carbon dioxide additives almost completely suppressed the reaction of SO2(aq) conversion in the water- carbon dioxide fluid even at 300°C when the CO2 mole fraction was 0.2 (corresponding to a 23.4m solution). The experimental and thermodynamic data sets on the apparent constant of the sulfur dioxide conversion in water and water-carbonic fluids are in a satisfactory agreement. This validates the electrostatic approach to the thermodynamic modeling, which takes into account the dielectric constant of a mixture of polar (H2O) and weakly polar (CO2)components.