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Sewer gas to hydrogen - a step closer to reality

Tuesday, 14 September 2021

Scientists at Ohio State University have adapted a chemical looping process to produce hydrogen from hydrogen sulphide gas, also known as sewer gas, which would allow the industrial by-product to be converted into a useful energy source and feedstock.

The process, named SULGEN, essentially splits the hydrogen sulphide into its two basic elements, hydrogen gas and sulphur, and is attractive in the sense that energy requirements are low, and the materials required (iron sulphide with traces of molybdenum) are relatively cheap.

"Hydrogen sulphide is one of the most harmful gases in industry and to the environment," said Lang Qin, a co-author on the study and a research associate in chemical and biomolecular engineering at The Ohio State University (OSU). "And because the gas is so harmful, a number of researchers want to turn hydrogen sulphide into something that is not so harmful, preferably valuable."

SULGEN relies on a base process known as chemical looping, which was previously trialled on the conversion of fossil fuels to electricity without direct contact with air, reducing the tendency to form unwanted nitrogen oxides.

Earlier attempts to process hydrogen sulphide used chemically pure iron sulphide. However, the performance was not suitable for large scale industrial applications. The use of small amounts of molybdenum was successful in catalysing the process and improving the conversion.

Opportunities for green hydrogen?

No carbon dioxide is evolved in the SULGEN process; providing that any energy sources used are sustainable, the resulting hydrogen could also be considered green.

Key activities/locations where hydrogen sulphide is emitted include:

  • Sewage gas processing;
  • Geothermal plants; and
  • Natural gas processing.

The latter presents a significant opportunity - some unprocessed natural gas streams can contain up to 30% hydrogen sulphide, and given the scope of natural gas production globally could represent large volumes of hydrogen production.

Currently, the Claus process is the predominant process for desulphurisation of gas streams - hydrogen sulphide is reacted with oxygen to produce elemental sulphur (which can be used for industrial purposes) and water. By comparison, SULGEN gives rise to two useful products; hydrogen, as well as sulphur.

Furthermore, hydrogen can be blended in small amounts with natural gas - this would allow SULGEN hydrogen produced from processing natural gas streams to take advantage of existing infrastructure, namely natural gas pipelines.

However, commercially viable installations are probably in the distant future. Nevertheless, this development by OSU Engineering is worth keeping an eye on.



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