Researchers transform ‘sewer gas’ into clean hydrogen fuel

Rotten-egg gas might one day help power your world—and clean it at the same time. Researchers at The Ohio State University have found a way to turn hydrogen sulfide, a highly toxic and foul-smelling gas, into hydrogen fuel. If scaled up, their approach could offer a low-cost, energy-efficient solution to a growing industrial waste problem while delivering a clean-burning energy source.

Hydrogen sulfide is better known as "sewer gas." It leaks from manure piles, sewers, and is a major byproduct of oil refining, paper production, and mining. While common, it’s also dangerous. Even low levels of exposure can corrode metal equipment and pose serious health risks.

“Hydrogen sulfide is one of the most harmful gases in industry and to the environment,” said Lang Qin, a co-author of the new study and a research associate in chemical and biomolecular engineering.

Current industry practices use the Claus process to remove hydrogen sulfide from waste streams. This process burns the gas to recover elemental sulfur and steam, but it wastes hydrogen and requires large amounts of energy. It's costly, inefficient, and doesn't recover hydrogen as a fuel. Alternative strategies, like selective oxidation and reactive adsorption using metal oxides, can capture more sulfur but still destroy the hydrogen content.

A better way would be to keep the hydrogen and transform it into usable fuel. That’s where the new process—nonoxidative decomposition of hydrogen sulfide—comes in. Instead of burning the gas, this method splits it directly into hydrogen and sulfur. However, there's a catch. The chemical reaction needed is highly endothermic, meaning it demands a lot of heat. Worse, the reaction tends to reverse itself before much hydrogen is made.

The research team tackled this problem using a clever reactor design. They developed a one-reactor system based on sulfur looping—a concept where the decomposition is split into two stages: sulfidation and regeneration. In the first step, a metal absorbs sulfur from hydrogen sulfide while releasing hydrogen gas. In the second step, the sulfur-laden metal is regenerated by heating it in an inert atmosphere to release solid sulfur, readying it for another round.

This two-step cycle helps push the chemical equilibrium toward hydrogen production, bypassing the limitations of direct decomposition. Past attempts at sulfur looping needed two separate reactors with high mass circulation and energy needs. This new setup does it all in one reactor with alternating gas feeds, making it far more efficient and scalable for industry.

To make this design work, the choice of material acting as the sulfur carrier is crucial. The scientists chose iron sulfide, a low-cost, non-toxic compound that’s widely available and stable at high temperatures. However, on its own, iron sulfide doesn’t react quickly enough with hydrogen sulfide to make the system practical. That’s where chemistry comes into play.

To improve iron sulfide’s performance, the researchers added a small amount—just 2%—of molybdenum. This trace metal is already known for its strong catalytic activity in removing sulfur during fuel processing. Its atomic size is nearly identical to that of iron, making it a suitable addition without disrupting the iron sulfide's crystal structure.

The results were clear. The molybdenum-doped iron sulfide absorbed 24% more sulfur than its undoped counterpart. It also performed better across multiple cycles, maintaining reactivity and structural integrity.

Computational modeling using density functional theory supported the findings. The models showed that the main barrier in the reaction was the diffusion of hydrogen atoms across the surface. Molybdenum helped speed up this step by changing the material’s surface chemistry, making hydrogen atoms move more freely. This improvement increased the overall reaction rate and hydrogen yield.

“These results demonstrate a novel strategy for high-yielding hydrogen sulfide removal,” said the researchers. Their findings also lay the groundwork for developing more effective materials by tweaking the atomic composition of sulfur carriers.

While the results are promising, the work is still in the lab stage. The team, led by Liang-Shih Fan, a professor of chemical and biomolecular engineering at Ohio State, tested the process in a controlled setup. Scaling it to industrial levels remains a challenge, but the foundation is strong.

The process evolved from an earlier system the group developed called SULGEN. That method applied chemical looping to hydrogen sulfide using iron-based particles, but didn’t deliver the results needed for commercial use. By doping iron sulfide with molybdenum, the researchers found a way to make the reaction more viable.

“Our goal is to solve the harmful gas issue,” said Qin. “And here, we have found a way to do it in the lab that creates this value-added hydrogen fuel.”

Lead author Kalyani Jangam, a graduate student in Ohio State’s Clean Energy Research Laboratory, added, “It is too soon to tell if our research can replace any of the hydrogen fuel production technologies that are out there. But what we are doing is adjusting this decomposition process and making a valuable product from that.”

Because the new system uses cheap, earth-abundant materials and requires less energy than traditional methods, it could one day become a greener, more cost-effective option for dealing with hydrogen sulfide emissions—especially from oil and gas refining.

If proven successful on a larger scale, it may also help reduce the world’s dependence on fossil fuels. Hydrogen gas, when used in fuel cells, generates only water as a byproduct. That makes it one of the cleanest forms of energy available today.

The study, published in ACS Sustainable Chemical Engineering, not only advances the science of chemical looping but also points toward a future where pollution becomes part of the solution.

Note: The article above provided above by The Brighter Side of News.

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