WHAT ARE MERCAPTANS AND WHAT ARE THEY USED FOR?
Original Article: JULY 26, 2021
Mercaptans are organic compounds with a distinct odor. Mercaptans are most commonly found in as an emission from paper or pulp mills, and in coal tar and petroleum distillates. Sometimes, mercaptans can be found naturally in food, including onions, asparagus, and radishes. Mercaptans are also produced by certain marine microorganisms and produce the boggy smell that is associated with marshes. Because mercaptans can be detected by humans at lower concentrations, they can be useful odorants to help individuals detect the presence of other gasses or chemicals.
Examples of Mercaptans
There are several types of mercaptans, several of which have names more familiar to us. Examples include methanethiol, ethanethiol, 2-mercaptoethanol, cysteine, lipoamide, 2-mercaptoindole, and coenzyme A.
What do Mercaptans Smell like?
Mercaptans are effective odorants because they release strong odors that are detectable by the human nose at concentrations as small as 10 parts per billion. Most mercaptans release smells that resemble rotting cabbage or garlic. Others may smell like dirty socks or smelly feet. However, there are exceptions that smell more appealing, such as grapefruit mercaptan, which smells fruitier and more citrusy, like a grapefruit.
Using Mercaptans in Pesticides
Although mercaptans are typically used as an odorant, there are other practical uses as well. For example, methyl mercaptan is used to produce methionine, which is used as an intermediate in the production of pesticides, fungicides, and animal feed additives.
Using Mercaptans in jet fuels and plastics
Methyl mercaptan is not only used to produce pesticides but it is also used as a chemical intermediate to produce jet fuel and various plastics. Again, when used in this setting, the mercaptans is not used so much as an odorant that helps individuals detect the presence of hazardous materials, but instead, it is used to help manufacture these items.
Using Mercaptans in the synthesis of the amino acid methionine
Methionine is a unique amino acid that is found in many proteins in foods we consume. One of the biggest benefits of methionine is that it can be converted into sulfur containing molecules that can protect tissues and maintain proper cell functions in humans and animals. Although methionine is good for you, we are only exposed to it from our diet, and therefore those with a restricted diet, or large animal farms with limited raw plant materials may not be as readily exposed to methionine. However, through complex chemical processes, mercaptans can be used to synthesize methionine and supplement diets to ensure that the body gets sufficient amounts of methionine.
Using Mercaptans for Natural Gas Quality Analysis
Natural gasses often have non-corrosive mercaptans added so that humans can detect the presence of a leak or a spill. Mercaptans are also naturally occurring in some natural wells, which again, can be useful because their strong odor can help individuals detect the presence of the gasses. However, when the concentration of mercaptans is too high, there can be more negative consequences than positive ones. For instance, if the amount of mercaptans is too high, the foul smell may drive away communities. In certain cases, high levels of mercaptans can corrode pipelines, weaken their integrity, and increase the risk of significant leaks or spills. Consequently, natural gas is analyzed for mercaptan as well as other contaminants that decrease the overall quality of the natural gas. Depending on the concentration level, mercaptans may be either removed to decrease the intensity of the smell and protect the infrastructure or added to ensure that the presence of the natural gas is detectable.
How can Mercaptans be removed from Crude Oil to meet pipeline specifications?
The removal of mercaptans from crude oil can be achieved using a few different methods. One method is the use of “scavengers”, or chemical compounds that interact with the mercaptans in a manner that disables their extreme odor or their corrosive properties. Acrolein is a common scavenger because it quickly and efficiently reacts with not only mercaptans, but other harmful sulfides. The downside of using acrolein, however, is that it is extremely toxic and dangerous to use.
Another way that mercaptans are removed from crude oil by adding a substance that oxidizes them. Using a strong reagent, such as hydrogen peroxide or sodium hypochlorite can achieve the desired mercaptan levels. Additionally, adding caustic materials, such as potassium hydroxide or sodium hydroxide, can remove mercaptans. Lastly, various synthesized catalysts can be used to remove the presence of mercaptans in crude oils.
Mercaptan Extraction vs. Sweetening
When it comes to treating mercaptans, there are typically two options: extracting and sweetening. Extracting involves the process of dissolving and removing the mercaptans, typically using a caustic material. On the other hand, sweetening converts the mercaptan to remove the strong odor. The process used typically depends on what product you are trying to remove the mercaptan from. For example, extraction is typically used for lighter products, such as light naphtha, whereas sweetening is the preferred method for heavier products, including gasoline and diesel.
Why are Mercaptans and Other VOCs Important to Wine Making?
Mercaptans and volatile organic compounds (VOCs) are essential in wine making because they greatly impact two important characteristics of the wine, its aroma and its astringency. The subtle differences in these two characteristics lend to the uniqueness and complexity of various wines, giving those wines their own taste and oral sensation. Mercaptans are typically more prominent when wine has undergone the process of reduction, or during reductive winemaking. Reductive winemaking occurs when the winemaker intentionally limits the amount of oxygen the wine is exposed to while it is fermenting. The process of reductive winemaking is designed to preserve fruitiness and freshness, however, if too much oxygen is withheld, you may notice “reduced notes” in your wine, such as a whiff of rotten eggs. Decanting these minor whiffs can typically make them disappear, leaving only the desirable factors from the reductive winemaking process. However, when reductive winemaking is done incorrectly, the presence of the foul smell generated by the mercaptans lingers, and the wine is considered flawed.
How Chem Service can Help in Testing for Mercaptans
With Chem Service’s analytical standards, we help our clients identify the presence of mercaptans in their testing samples. Using our innovative products, Chem Service can help you not only identify the presence of mercaptans but also inform you on the level of concentration. We provide comprehensive testing reports that inform you of the results of our testing samples, which in turn allow you to inform your own clients on the concentration of mercaptans and make suggestions on what steps they should take moving forward. Contact us today to learn more about how Chem Service can help you test for mercaptans.
NIOSH Pocket Guide to Chemical Hazards. “#0425”. National Institute for Occupational Safety and Health (NIOSH).
Committee on Acute Exposure Guideline Levels; Committee on Toxicology; Board on Environmental Studies and Toxicology; Division on Earth and Life Studies; National Research Council. Acute Exposure Guideline Levels for Selected Airborne Chemicals: Volume 15. Washington (DC): National Academies Press (US); 2013 Sep 26. 2. Methyl Mercaptan Acute Exposure Guideline Levels. Available from: https://www.ncbi.nlm.nih.gov/books/NBK201324/
- “Mercaptans and other volatile sulphur compounds in wine”, Article originally appeared in Harpers Wine & Spirit Weekly in 2006. Posted here February 2007. Copyright Jamie Goode, https://www.wineanorak.com/mercaptansinwine.htm
- Formation of Methyl Mercaptan from l-Methionine by Porphyromonas gingivalis
Mamiko Yoshimura, Yoshio Nakano, Yoshihisa Yamashita, Takahiko Oho, Toshiyuki Saito, Toshihiko Koga
Infect Immun. 2000 Dec; 68(12): 6912–6916. doi: 10.1128/iai.68.12.6912-6916.2000 - Sohrab Zendehboudi PhD, Alireza Bahadori PhD, CEng, in Shale Oil and Gas Handbook, 2017
- Jacobi Group, Mercaptan Removal, and Fuel Sweetening,
https://www.jacobi.net/oil-gas/mercaptan-removal-and-fuel-sweetening/
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