Scrubbing Hydrogen Sulfide with Hydrogen Peroxide
Air pollution control is one of the problems facing plant operators and designers today. Hydrogen peroxide has been shown to be a convenient way to eliminating oxidizable pollutants from air or other gases. This data sheet describes a scrubbing system using hydrogen peroxide, a simple means of completely eliminating such obnoxious materials as hydrogen sulfide.
The scrubbing solution consists of dilute sodium hydroxide to which enough hydrogen peroxide is added to react with the hydrogen sulfide according to the equation:
|4H2O2 + H2S → H2SO4 + 4H2O|
The equation shows, that 4 parts of hydrogen peroxide by weight are needed for each part of H2S present in the gas to be cleaned. Enough sodium hydroxide must be present to neutralize the sulfuric acid formed according to the equation:
|2NaOH + H2SO4 → Na2SO4 + 2H2O|
This indicates that for each weight part of hydrogen sulfide, approximately 2-1/2 weight parts of sodium hydroxide are needed. To accelerate the oxidation reaction small amounts of iron salts may be added, but they are not essential. The recommended quantities are 10-100 mg/l of Fe, added either as FeSO4 or the EDTA complex.
The simplest and most reliable type of scrubber for this purpose is a packed-bed tower operated counter-currently; the gas is moved upwards and liquid flows downward.
Conventional scrubber design can be used. The packing is loaded by wet dumping on a support plate. A distributor is used for even distribution of liquid. Because of the short column length no redistributors are needed. A collecting reservoir at the bottom of the scrubber is recommended. Here the reaction can go to completion within a few minutes.
For all the equipment alkali and hydrogen peroxide resistant materials of construction must be used, i.e., 316 stainless steel, ceramic, glass. For service below boiling point of water, polypropylene is acceptable.
Approximate size and performance parameters for such a tower are shown here. The example describes a scrubber which can handle a gas flow of 50 m3/min (1800 cu ft/min). Several choices of tower diameter and height combinations are given in the table. The packing chosen is 1" Intalox saddles (Norton Company). Two sets of values are given: One for removal of H2S originally present in an amount of 200 ppm, the other for treatment of gas originally containing 20 ppm H2S.
|Diameter of Column||Liquid Flow||Height of Column and Minimum Blower HP|
|200 ppm H2S||20 ppm H2S|
The hydrogen peroxide consumption for gas containing 200 ppm H2S will be 56 g/min (7.5 lbs/hour) calculated as 100% material. The consumption of NaOH will be 35 g/min (4.5 lbs/hour).
For other gas flow rates the height of packing will remain the same. The column diameter will change proportionally to the square root of the gas flow. The liquid flow and needed HP for blowers will change in direct proportion to the gas flow. It should be noted, that the HP values refer to what is needed to overcome scrubber pressure drop when the blower is working at maximum efficiency.
The controls necessary for the most effective and efficient operation are a pH controller to keep the liquid at the bottom of the column at a pH of 9 or higher. A sulfide monitor is desirable to make certain that the effluent is free from sulfide, an indication that enough hydrogen peroxide has been added to complete the oxidation. Although a continuous potentiometric monitor (i.e., Orion 1000) is preferred, periodic tests with field kits (i.e., Hach kits or Drager tubes) may be used.
---FMC Technical Data, Pollution Control Release No. 8
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