A group of chemical engineering scientists have developed a clean and efficient way to transform toxic untreated sewer water into a source of clean hydrogen fuel.
Anyone who has lived in an urban environment is – unfortunately -- familiar with the noxious smell of untreated sewer water.
That smell, which we normally associated with rotten eggs, is hydrogen sulfide gas. It is one of the most dangerous gases to occur in urban habitats, with high risk to anyone exposed to it even in small amounts.
Hydrogen sulfide is generated as a normal byproduct of chemical, agricultural, and industrial processing activities which are a part of daily life. The gas is released during oil refining, from mineral separation and cleansing operations, paper processing, tanneries, coke manufacturing, and other industrial operations. It is also released from decomposing manure accumulated from cattle, pigs, chickens, and other livestock in agricultural pens.
In the wild, hydrogen sulfide is also released from saline marshes where sea grasses and other plants decompose and underground formations.
Exposure to high levels of hydrogen sulfide – 100 ppm or more – can cause breathing difficulty, shock, convulsions, and death. It is also a highly corrosive substance, damaging not just living tissues but also containment pipes and transport of sewer and other wastewater.
Thanks to discoveries just now disclosed by scientists at Ohio State University (OSU), more of that hydrogen sulfide in wastewater may be recoverable – and something able to be transformed – into clean hydrogen fuel.
“Hydrogen sulfide is one of the most harmful gases in industry and to the environment,” said Lang Qin in commenting about the just-released research on this topic. “And because the gas is so harmful, a number of researchers want to turn hydrogen sulfide into something that is not so harmful, preferably valuable.”
Lang Qin is a co-author on the study and a research associate in biomolecular engineering at OSU.
The new research explores new means of using a process called chemical looping. That process works by mixing particles of metal oxides into fuels. By selecting the right metal oxides, it is possible to burn those fuels without ever having air and the fuels contact each other directly.
The research team had previously explored chemical looping with coal and shale gas, using iron oxide as the metal particle substance injected into the mix. By putting these together, they were able to generate electricity directly without carbon ever being released into the atmosphere.
The scientists then reworked their innovation to apply the same idea – using iron oxide as the metal particle addition – to the processing of hydrogen sulfide into hydrogen. While doing so they ended up created the important SULGEN process, using iron oxide to assist as a catalyst in the chemical transformation involved.
While the iron-oxide-based process using iron oxide worked on a small scale and did produce reliable hydrogen yields, it proved inefficient hard to control when scaled up to what would be required for a full production facility.
The researchers then looked at what other metals could be added to the process. Their experiments eventually led them to the introduction of trace amounts of molybdenum. Molybdenum is already commonly used in modern oil refining both because of its relatively low cost and because it is resistant to sulfur absorption, also known as sulfur “poisoning.” So it was a logical choice although it had not been attempted before.
What the scientists found was that added just tiny amounts of molybdenum to the iron oxide allowed not just an efficient reaction in small quantities, but also one that appears to scale up reliably. They also discovered the presence of the molybdenum improves the efficiency of the breakdown of hydrogen sulfide into hydrogen fuel and sulfur.
While this is still just as the scientific research stage, the innovation developed here could provide a means of transforming what used to be just toxic wastewater in sewers, in agricultural runoff, in industrial processing, and even in marshes around the world. That transformation would enable a new form of “carbon capture” without the need for complex industrial baffles and filtration systems.
And it would also provide a potentially endless, natural, and renewable supply of clean hydrogen to fuel a portion of the globe’s future power needs.
More details on the chemical engineering processes and experiments conducted are available in the paper, “Mo-Doped FeS Mediated H2 Production from H2S via an In Situ Cyclic Sulfur Looping Scheme,” by Kalyani Jangam, Yu-Yen Chen, Lang Qin, and Liang-Shi Fan. It was published in the August 12, 2021 issue of the American Chemical Society’s peer-reviewed journal, ACS Sustainable Chemical Engineering, in its August 12, 2021 issue.