Iron compounds, particularly iron hydroxide and iron(III) oxide, are not only significant in the metal industry or construction but also in biogas production. In this context, they are essential primarily for the desulfurization of biogas.

Basic Chemistry

Iron Hydroxide:

The general formula for iron hydroxide is Fe(OH)_n, where n represents the valence of the iron. There are two commonly occurring forms:

• Fe(OH)₂: Iron(II) Hydroxide or green rust
• Fe(OH)₃: Iron(III) Hydroxide

Iron Oxides:

There are several iron oxides, of which the most common are:

• FeO: Iron(II) oxide or wüstite
• Fe₂O₃: Iron(III) oxide or hematite
• Fe₃O₄: Iron(II,III) oxide or magnetite

Application in Biogas Plants

Desulfurization of Biogas:

Biogas typically contains hydrogen sulfide (H₂S), which is converted to sulfur dioxide (SO₂) upon combustion. This can lead to environmental pollution and corrosion of machinery. Desulfurization is therefore an essential step to avoid these issues.

Internal Desulfurization in the Fermenter:

Iron hydroxide is added directly to the fermenter. There, it reacts with hydrogen sulfide to form insoluble iron(II) sulfide, which settles at the bottom of the fermenter. This process is particularly efficient, as it significantly reduces the concentration of H₂S in biogas.

Benefits of Using Iron Hydroxide

• Efficiency: Iron hydroxide can absorb large amounts of H₂S, increasing the efficiency of desulfurization.
• Cost: Compared to other desulfurization methods, iron hydroxide is relatively cost-effective.
• Simplicity: Adding iron hydroxide directly to the fermenter is a straightforward and direct process.
• Environmentally Friendly: The solids produced in the reaction are non-toxic and can be safely disposed of.

Drawbacks

• Continuous Dosing: When the iron hydroxide is fully saturated with H₂S, it must be continually dosed.
• Waste Products: The formation of insoluble iron(II) sulfide requires regular cleaning of the fermenter.

Conclusion

Iron hydroxide provides an efficient and cost-effective method for desulfurizing biogas. Its use minimizes the negative effects of hydrogen sulfide in biogas, enabling more environmentally friendly biogas production. Especially for biogas plants looking for a simple and effective solution to the H₂S problem, iron hydroxide is the best choice.

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