Study on the phase separation characteristics of HI–I2–H2SO4–H2O mixture at 20 °C

The phase separation of the Bunsen products mixture containing HI, I2, H2SO4, and H2O is an essential subsection of the iodine–sulfur hydrogen production process (I–S process). It is also the pre-condition of the continuous operation of the I–S process. This experimental study was conducted at 20 °C using jacketed glass vessels to clarify the characteristics of the phase separation of the quaternary mixture. The critical conditions of the phase separation, iodine solubility in the mixture, and intermiscibility of the constituents in the solution were investigated. The favorable concentration range of each component in the Bunsen products mixture was illustrated using a tetrahedron diagram. Within the concentration range, the solution separates spontaneously into two liquid phases without iodine precipitation. In addition, a computer program was developed to easily ascertain the phase state of the quaternary mixture with a given composition.

► We investigate the phase separation characteristics of the HI–I2–H2SO4–H2O mixture.
► Effects of the molar ratios of I2 to HI and H2SO4 to HI on phase separation are analyzed.
► Solubility of iodine in the quaternary mixture is demonstrated.
► A tetrahedron coordinate diagram is made to illustrate the phase state of the mixture.
► A computer program is developed to easily judge the phase state of the mixture.