The Bunsen reaction in the presence of organic solvent in H2S splitting cycle

Abstract

This research project is a part of our endeavor to developing a new hydrogen sulfide (H2S) splitting cycle for hydrogen production. In view of that the Bunsen reaction is the key step for the overall efficiency, the objective of this research is to develop an effective and efficient process to carry out the Bunsen reaction in the presence of organic solvents. Organic solvents can help dissolve iodine crystal, lower the reaction temperature and reduce the corrosiveness accompanying the reaction. Through screening of the ordinary organic solvents, aromatic hydrocarbons stood out and toluene was used in this project.

In order to study the Bunsen reaction rate in the presence of toluene, the iodine solubility in HI solution was extensively explored at room temperature. Although the iodine solubility in water is small (0.3404g/L at 25℃), it was found that the iodine solubility in HI solution increases greatly as the [HI] increases. At lower [HI] (0~0.238 M), the iodine solubility is linear to [HI] with a relationship of [iodine solubility] = 0.57[HI] + 0.0030; at higher [HI] (0.238 ~7.6 M), the relationship of the iodine solubility and [HI] conforms to [iodine solubility]/[HI] = 0.190[HI] + 0.58.

In the second part, the iodine distribution behavior between HI solution and toluene phase was studied at room temperature. It was determined that the iodine distribution coefficient (D = [I2]HI solution/[I2]toluene) increases as the increase of [HI]. At lower [HI] (0~1.89 M), the distribution coefficient has a quadratic relationship with [HI] as D = 1.4027[HI]2 + 0.8638[HI] + 0.0088; at higher [HI] (1.89~7.54 M) the distribution coefficient is linear to [HI] with a relationship of D=5.5937[HI]-3.5632.

On the basis of the above work, in a semi-batch reactor, the Bunsen reaction rate in the presence of toluene was measured. In a mixture of toluene and water, iodine prefers to stay in toluene phase. The Bunsen reaction was readily initiated by feeding SO2 into water phase. Experimental results indicated that the rate of the Bunsen reaction in the presence of toluene is equal to the molar flow rate of feeding SO2 when the iodine concentration is higher than a certain value. This specific value depends on the reaction conditions, such as the interface area between water and toluene phase, the dispersion efficiency and the flow rate of SO2.