Investigation of oxygen chemisorption during regeneration of a quinhydrone absorbing solution in continuous barbotage layer absorbers

The results of investigations of air oxygen chemisorption during regeneration of a quinhydrone absorbent solution in apparatus with a continuous barbotage layer are given. It is shown that the chemical reaction between chemisorbed O2 and quinhydrone catalyst reducing form is rapid and occurs in a liquid film. Researching results can be used for the choice of mass-exchange equipment for the process.

Equation (3) describes the chemisorption process of the solution regeneration, which consists of two stages -the absorption of air oxygen by the absorbent solution and the interacting of the reducing form of the quinhydrone catalyst with absorbed oxygen. For the regeneration of absorbing solutions with air oxygen in similar industrial processes of gases purification from hydrogen sulfide (Lo-Cat, Stretford, Takahaks, Thylox, Unisulf, etc.), as a rule, use absorbers with a continuous barbotage layer [2]. The effectiveness of the use of this type of apparatus for the quinhydrone method is not established. Therefore, it became necessary to carry out studies on chemisorption of air oxygen by quinhydrone absorbing solution in this type of absorbers.
The aim of the research was to determine the acceleration coefficient of absorption in the process of oxygen chemisorption from the air in apparatus with a continuous barbotage layer.

Experimental part
The research was carried out in a laboratory installation, the main apparatus of which was a glass column (internal diameter of 0.035 and height of 0.5 m) with a built-in bubbler (a porous glass plate with a thickness of 5 and a pore size of 0.2 ... 0.6 mm) in the lower parts of the column.
For investigations of the acceleration coefficient of absorption of air oxygen was carried out the two series of experimental studies, which was differed in the type of absorbing solution -soda (10 kg/m 3 Na2CO3) or quinhydrone (10 kg/m 3 Na2CO3 and 5 kg/m 3 quinhydrone). The other parameters were constant: temperature -17 o C; the height of the solution in the column -0,25 m. Air flow varied within (0.78 ... 1.83) . 10 -6 m 3 /sec. Duration of absorption of oxygen was 480 sec and chemisorption 3600 sec. The dissolved oxygen was stripped from the soda solution by boiling before the investigation. The dissolved oxygen concentration in the solution was determined by Winkler's method. The quinhydrone solution before the studies were saturated with H2S to reach its concentration of 0.85 kg/m 3 . The amount of chemosorbed oxygen was calculated based on analyzes results of the amount of oxidized H2S in the solution.
To calculate the acceleration coefficient of absorption χ [3], the ratio of the multiplication of the liquid phase mass transfer coefficients in the chemisorption (L chem ) and absorption (L аbs ) processes on the surface of the contacting phases (Fi) were used chem chem L i L abs For calculations of the multiplications in these processes, the basic mass transfer equation [3] was used, in which, in view of the results [4], neglected the diffusion resistance of the gas phase.

Results and discussion
Studies and calculations for the two series showed (Table) that, with increasing air flow, the multiplication of the mass transfer coefficient from the liquid phase on the surface of the contacting phases (βL . Fi) increases slightly for both absorption and chemisorption processes. The degree of absorption and chemisorption of the oxygen increases with decreasing of the air flow. However, for the chemisorption process, it is an order of magnitude larger. Calculations have shown that the acceleration coefficient of the absorption χ = 5.10 ... 5.90 (χaver = 5.48), and the parameters [3] M = 9.95 and R = 7.04. The obtained values of МR1 and χ = 5.48 indicate that the reaction between the dissolved oxygen and the reducing form of the catalyst is rapid and ends in a liquid film, and the partial oxygen pressure over a quinhydrone solution which containing chemosorbed H2S, is zero [3].

Conclusion
In an apparatus with a continuous barbotage layer, the diffusion resistance of the liquid film during the oxygen chemisorption is large, which prevents the desired rate of the solution regeneration. Therefore, this type of mass-exchange equipment we do not recommend to regenerate the absorbing solution of the quinhydrone method of gases purification from hydrogen sulfide.