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5. H₂S REMOVAL FROM GAS WITH IRON OXIDE (GROBREINIGUNG)

The removal of H₂S from gases from gases by iron oxide mixtures is well known in the United States in the manufactured gas industry and no new information was obtained on this process.  Briefly, the process is to pass the raw gas at low pressure and at atmospheric temperature through a vessel containing beds of wood shavings covered with crude iron oxide, beds of pelleted crude iron oxide or iron oxide mixtures.  The H₂S reacts with the iron oxide to form iron sulfide and water.  The Germans ordinarily add air to the inlet gas in an amount sufficient to supply about half of the theoretical oxygen to convert the iron sulfide back to the oxide and to precipitate the elemental sulfur in the bed.  When the H₂S has been previously reduced by Alkzid or other process to 0.1% or loss in the gas entering the oxide box, this air usually amounts to 4-6 m³/per 1000 m³ of gas.  The hydrogen sulfide in the outlet gas is nil, the organic sulfur is not diminished.  When a gas with a high sulfur content is sent to the oxide boxes, the removal may be less complete and the life of the mass is naturally proportionately shorter.  The outlet sulfur is, rarely over 1 gram per 1000m³, because three to four boxes are usually operated in series, with the freshest mass in the last box.

Under proper operating conditions the mass will hold 40-55% of its dry weight in sulphur before excessive H₂S break through or excessive pressure drop occur.  Most plants use a continuous addition of 0.1% to 0.2% oxygen to the inlet gas to react and precipitate the sulfur, but batch regeneration by circulating inert gas with 1% to 4% O₂ has been carried out by some concerns.  When the maximum sulfur loading is attained the catalyst is removed, the sulfur burned for recovery of SO₂ and the residue is discarded.

The purifying agent is usually bought under the trade name Luxmasse which is the iron oxide residue from the refining of aluminum ore, or a mixture of Luxmasse and the bog iron ore.  A newer agent is called Lauta-masse, which is the same general type of material containing 3-4% alkali as NaOH, Na₂CO₃ and/or NaHCO₃.  A typical analysis of Lauta-masse is as follows:

To conserve iron oxide, used Feinreinigung mass containing about 5-10% sulfur and 30% Na₂CO₃ is sometimes mixed with the fresh charge.  It was stated that if too much of this material is mixed in, trouble is experienced with fusing of the carbonate due to the wet operating condition.

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