H2S – Hydrogen Sulfide

Although H2S (or hydrogen sulfide) might not be familiar to the average consumer, millions of tonnes of this gas are generated each and every year. H2S is a common byproduct of processes such as petroleum production, the breakdown of organic materials and the treatment of wastewater.^[1] However, hydrogen sulfide gas is dangerous to humans and many efforts have been devoted to its removal from the environment.

This is why it is interesting to note that H2S could very well prove to be quite useful to a certain degree. Some feel that this substance may serve as a viable form of electrical energy. There are still many issues to address if we hope to gain a better understanding of H2S gas as well as why such an unappealing substance might be more beneficial than it initially appears.

This article will cover several topics. We will first discuss some of the main characteristics of this gas before moving on to highlight a handful of possible hazards. A final portion will be devoted to current and potential future applications in relation to the generation of renewable energy.

What is H2S?

H2S has been referred to by such terms as "swamp gas", "sewer gas" and "sour damp". This gas may also be known by the chemical names dihydrogen monosulfide and/or dihydrogen sulfide. Note that all are technically correct. It is colourless and many individuals will immediately notice its presence due to the characteristic hydrogen sulfide smell of rotten eggs.

"As already mentioned, H2S is often a byproduct of many manmade technological processes; specifically those associated with certain manufacturing and refining sectors. Still, H2S can be produced by a number of completely natural scenarios. Many of these occur when bacteria begin to break down organic waste products.^[2] Some examples include:"

The release of H2S from an underground concentration of oil or natural gas.
H2S is sometimes naturally present in well water.
Volcanoes produce H2S alongside a host of other gases.

It is therefore clear to see that H2S is a relatively common gas. The only issue is that this substance is also highly toxic to humans; leading into the next main section of our article.

How Toxic is H2S?

Contrary to popular belief, H2S is not the deadliest gas. This position is actually awarded to nitrogen (N2). When found in large concentrations, nitrogen is extremely lethal to humans as well as the majority of life on earth. Nitrogen asphyxiation occurs when ambient levels of oxygen fall by as little as two per cent. The issue here is that as nitrogen is odorless, most victims are unaware of their predicament until it is too late.^[3]

On the opposite, the presence of H2S is normally detected by its foul smell. It is nonetheless an extremely dangerous gas. Part of this is due to the fact that H2S is heavier than air. It will therefore sink and remain within low-lying environments for extended periods of time. This also allows it to accumulate and become highly concentrated.

"To put these observations into perspective, the Occupational Health and Safety Board of the United States observes that any H2S concentrations of over 100 ppm (parts per million) are immediately dangerous to life and health.^[4] This is why workers who may be potentially exposed are required to take various safety measures including:"

The use of instrumentation that can detect the presence of H2S.
Wearing a self-contained breathing apparatus (SCBA).
Adhering to the “two-man rule” when working in hazardous locations where the gas may be present.

Even H2S levels below 100 parts per million need to be taken seriously, as long-term health effects can still occur (such as damage to the lungs and eyes). Another issue is that some symptoms may take time to develop; heightening the chances of falling seriously ill.

Additional Safety Measures and Potential Symptoms of Exposure

In fact, there are now many personal detectors that workers who may be exposed to this gas are required to wear at all times. Most detectors will emit a beeping sound if this gas is present above a specific concentration; enabling individuals to take the proper steps in order to avoid the associated hazards.

It should still be mentioned that H2S cannot be absorbed through the skin on normal occasions. It instead directly impacts the respiratory system. Some common symptoms that can appear if an individual has been exposed to dangerous levels include:

Eye and throat irritation
Nausea and dizziness
Headache
Irritability and/or confusion (within extremely high concentrations)
Convulsions
Coma
Frostbite (if handled in its liquid form)

One of the issues here is that this gas can sometimes be present alongside other hazardous airborne agents such as carbon monoxide, hydrogen cyanide or argon. This is once again the main reason why appropriate safety protocols need to be in place at all times.^[2]

What Might Cause H2S to Combust?

Yet another problem with this gas is that under some conditions, it is highly flammable. Although H2S will not explode in and of itself, it can easily combust when mixed with air. This obviously depends on whether or not there are any nearby sources of ignition (such as a pilot light or a welding torch). In the event that airborne H2S ignites, one of the byproducts of its combustion is sulfur dioxide; another extremely toxic gas that can easily kill a human being.^[5]

Now that we have begun to appreciate the hazards associated with H2S, are there any practical applications of this gas? Some of these have been known for decades and others are only just beginning to emerge. You might be surprised to learn the answers to why this gas could possibly impact the generation of electrical energy in the not-so-distant future.

What Can H2S be Used For?

Interestingly enough, H2S has been found to serve a number of purposes over the years. Many of these are associated with the manufacturing and industrial sectors. Here are some well-known examples:

The production of sulfur and sulfuric acid.
Manufacturing pharmaceutical products.
Creating different types of pesticides.
When transformed into hydrogen sulfide, the production of heavy water that is used in some nuclear power plants.

Other byproducts such as sodium hydrosulfide are often required when manufacturing paper and when removing hair from animal hides during the tanning process. We should still stress that workers will need to take various precautions in order to reduce the chances of personal injury when handling this gas.^[6]

What About H2S in Relation to Fuel Cells?

It should be noted that some research involving H2S in relation to fuel cell technology is ongoing. There are still several issues to be overcome and perhaps the most challenging is that H2S can actually "poison" typical fuel cells and lead to long-lasting damage. Not only are we referring to physical degradation, but high concentrations of H2S can lead to a severe drop in voltage output.^[7]

Notwithstanding the concerns mentioned above, some believe that H2S may eventually be used as an alternative energy carrier for hydrogen fuel cell. Scientists state that several practical modifications such as the presence of composite catalysts and a thermally stable environment could lead to more practical applications within fuel cells. Furthermore, the only byproducts are steam and elemental sulfur.^[8]

Conclusion

We have already seen that H2S is an extremely toxic and dangerous gas. This is one of the reasons why other well-known methods of generating power such as the breakdown of hydrogen and DMFC (direct methanol fuel cells) technology both represent much more viable and safe solutions, than the same power generation out of H2S.

However, the fact of the matter is that one of the core components of H2S is hydrogen. As scientists already know how to use this gas as fuel to generate electricity, it is not unrealistic to assume that H2S may become a viable option in the not-so-distant future.