Study On The Treatment Of Hydrogen Sulfide Waste Gas By The Method Of Two-step Direct Electrolysis

Hydrogen sulfide is a noxious industrial gas. Recovering hydrogen sulfide from industrial waste gas can not only protect the environment but also provide cleaning energy - hydrogen and sulfur. In this dissertation, the alkaline absorption of hydrogen sulfide in industrial waste gas is taken as the object of study. In order to solve the problem of anode passivation in direct electrolysis and the coexisting of hydrogen sulfide and carbon dioxide in the waste gas, a new process named two- step direct electrolysis is suggested. The main principle of the new process is: firstly , hydrogen sulfide ion is oxidized to polysulfide and hydrogen is released simultaneously at the same time; secondly , the polysulfide containing anode electrolyte is used to absorb hydrogen sulfide in industrial waste gas. The polysulfide would decompose to form sulfur when the anode electrolyte is acidified. The solution, which has absorbed hydrogen sulfide and been separated of sulfur, would be feed back to electrolytic cell. The main research is as follows:1)The electrochemical measure method together with XRD, SEM were employed to investigate the mechanism of anode reaction and passivation. It has been shown that the oxidation process of alkaline sulfide includes two stages: at the first stage, the oxidation of hydrosulfide ion is dominated , rhomboherdral which is easy to form polysulfide with hydrosulfide is produced at this stage, and the auto-catalytic effect of polysulfide will accelerate the oxidation of hydrosulfide ; at the second stage, the oxidation of polysulfide is dominated with the product of polymer sulfur--111a - S8 .The point of demarcation of two stages is that the number of dissociate hydrosulfide is equal to the that of sulfur in solution. The reason of passivation is that the polymer sulfur- a - S8 is difficult to be transmitted and dissolved so that it is formed and accumulated continuously on the anode. The AC impedance experiments show that the impedance of absorbed intermediate of 0.5M Na2S solution increases 10 times when half of hydrosulfide is converted to sulfur. Therefore, it is difficult to solve the polymer sulfur within the solution. The only method to avoid passivation of anode is removing the sulfur from anolyte. This is the basis principle of twostep direct electrolysis to produce hydrogen and sulfur.2)The principle of electrolysis on the solution of alkaline sulfide has been summarized systematically. The effect of process condition on electrolytic reaction was studied, the results showed that the electrolytic reaction is influenced by current, temperature, concentration of hydroxide and hydrosulfide, velocity of flow and so on, with current and temperature the most violent. Therefor the key of gaining more sulfurs from sulfide is the strict controlling of the temperature and current. Experimental results show that current efficiency of this process is high and ions can keep equilibrium during the circulate process.3)As the absorbent of two-step direct electrolysis, aqueous sodium carbonate solution was firstly used. The thermodynamic analysis of absorption was carried out. Research on the selective absorption of H2S from mixture gas shows that it can be achieved using sodium carbonate solution selective absorption of H2S through the controlling of process condition. The anolyte was acidified by the source gas. The effect of temperature, feed concentration of H2S and CO2. and gas and liquid flow rates were investigated. It was found that the content of sulfur and concentration of sulfide in solution were increased at higher H2S concentration and higher gas and liquid flow...