What is Methyl Mercaptan?
Methyl Mercaptan, also known as Methanethiol, is a volatile organic compound known as an organosulfur, because it contains sulfur. Methyl mercaptan is a member of a series of compounds, in which there can be chains of up to 20 carbon-atoms attached to sulfur. The chemical formula for methanethiol is CH3SH; it is classified as a thiol. It is colorless, highly flammable, and has a strong rotten-cabbage-like odor. It is a colorless, low-boiling liquid, that is denser than water. When inhaled, Methyl Mercaptan is very toxic, and the dangerous gas is often overlooked when in low concentrations. It can undergo steam reforming to hydrogen-rich gas over cerium oxide-coated rhodium or aluminum oxide catalyst via the solid-gas reaction, under certain operating conditions. This process has potential use in toxic-waste treatment, such as removal of methanethiol present in industrial-waste off-gas. Because it is derived from decaying organic matter, Methyl Mercaptan is a weak acid, and is reactive with dissolved metals, in aqueous solutions.
Where is Methyl Mercaptan found?
Methyl Mercaptan is an organic compound that naturally exists within the blood, brain, and tissues of living things, including plants, animals, and humans. It can also be found in certain foods, such as nuts, and cheeses, as well as asparagus. Methyl mercaptan is actually the substance that causes the foul odor in urine after ingesting asparagus. Interestingly, this was once believed to be a genetic tendency, but recent research indicates that the odor is simply the release of the methanethiol, and happens in everyone. It is also responsible for the putrid odor in in feces, as well as flatulence. This odor causing gas is also one of the chemicals off-puts from decomposing organic matter, like a dead body, that creates the infamous “dead body” smell, after time.
In sea water, methanethiol is the primary breakdown-product of the algal metabolite, dimethyl-sulfonio-propionate, or DMSP. It is believed that marine bacteria obtain most of the sulfur in their proteins by the breakdown of DMSP, and incorporation of methanethiol, despite the fact that methanethiol is present in sea water at much lower concentrations than sulfate. Bacteria in environments both with, and without oxygen, can convert methanethiol to dimethyl sulfide, or DSM; most DMS in sea water is produced by a separate pathway. Dimethyl sulfide is an important trace gas, with roles in sulfur cycling, signaling to higher organisms, and in atmospheric chemistry. DMS and methanethiol can be used by some microbes, as substrates for methanogenesis in some anaerobic-soils. Significant amounts of DMS are also generated from terrestrial or soil environments, like peat bog. Methyl mercaptan naturally occurs in marshes, which helps with the formation of DSM. These gases release the unpleasant odor associated with bogs and marshland, and make up a large portion of the natural gases in regions where they occur.
What is Methyl mercaptan used for?
On an industrial level, methyl mercaptan can be found in many different area. Its most common application is as a means to produce methionine, which is used predominately as a dietary supplement for poultry, and animal feed. Methionine is an amino acid, which are the building blocks that human beings use to make proteins. Methionine is found in meat, fish, and dairy products, as it plays an important role in many cell functions in living things. Methionine is also used to prevent liver damage in acetaminophen (Tylenol) poisoning, on a medical level.
Methanethiol is also used in the plastic industry, as a moderator for free-radical polymerizations, and as a precursor in the manufacturing of fungicides and pesticides. As a pesticide, it is most widely used as a weed killer for cereal crops, such as wheat, corn, and rice.
Why is Methyl Mercaptan a concern?
Methyl Mercaptan is on the Hazardous Substance List. It is highly toxic, and incredibly flammable. High levels of methyl mercaptan can cause loss of consciousness, breathing difficulties, and even death. It can cause damage to the liver, and the kidneys, and is believed to affect red blood cells, causing anemia. It is a strong irritant to soft tissue in living things, like the eyes and sinus passage. In an extreme case, a plant worked was exposed to high levels of methyl mercaptan, and slipped into a coma. He developed internal bleeding, and sadly, he died less than a month after the initial exposure incident.
Beyond the health risks associated with Methyl Mercaptan, it is one of the most flammable gases on the planet. When high concentrations are condensed into small spaced, they become explosive, and volatile. There are several incidents on record where plant explosions were linked to improper storage or handling of methyl mercaptan.
How do we treat methyl mercaptan?
Treating methyl mercaptan is a 2-part process.
Part 1: A thermal oxidizer is the is the first piece of equipment used to abate methyl mercaptan. A Thermal Oxidizer (also known as thermal oxidiser, or thermal incinerator and often referred to as a direct fired oxidizer or afterburner) is a process unit for air pollution control, that decomposes hazardous gases, like methyl mercaptan, at a high temperature, and releases heat (which can be recovered), water vapor, and carbon dioxide into the atmosphere. Any type of thermal oxidizer would work for this process, but with different results; Direct Fired Thermal Oxidizers, Regenerative Thermal Oxidizers (RTOs), Thermal Recuperative Oxidizers, Aqueous RTO, Catalytic Oxidizers, Catalytic Recuperative Oxidizers, Regenerative Catalytic Oxidizers (RCO), and Vapor Combustion Units (VCUs). The method of reduction of methyl mercaptan in a Thermal Oxidizer revolves around thermal destruction. The chemical process of thermal oxidation is quite simple; the exhaust stream temperature is raised to a point that the chemical bonds that hold the molecules together are broken. The VOCs in the process exhaust stream are converted to various combinations of carbon dioxide (CO2), water (H2O), and thermal energy by the high temperature of the combustion chamber. There are several types of thermal oxidizers, and any type would be a good fit for the abatement of methyl mercaptan.
Part 2: The second step in the methyl mercaptan abatement process is the use of a wet scrubber. Alone, a scrubber is not the best option for treating methyl mercaptan, but works well in conjunction with a thermal oxidizer, to treat the formed SO2 from the Thermal Oxidizer. Wet scrubbers are designed to remove pollutants, like sulfur dioxide, from a gaseous stream with a scrubbing liquid, often sodium hydroxide. In a single-stage, vertical packed scrubber, the tower contains randomly dispersed packing to improve contact between the gas and liquid phases. The polluted stream of sulfur dioxide flows upwards through the bottom of the packed tower, counter currently to the flow of a scrubbing liquid. The cleaned gas then passes through a mist eliminator to remove any entrained liquids. One of the many products offered by GCES is a vertically packed bed scrubber. A packed bed scrubber is a wet scrubber that removes soluble chemicals, fumes, and odors. The sulfur dioxide flows through a specially designed packing media that is wetted with recirculated liquid. The liquid solvent absorbs the sulfur dioxide by physical, or chemical reactions. A liquid blow-down from the tank or sump section of the packed bed scrubber removes contaminant products before they precipitate.
Gulf Coast Environmental Systems offers multiple design solutions to best fit the operational parameters of its customers. In some cases, the desire is for a lower capital investment for a higher operating cost for those systems that do not need to run continuously, or the need may be for a slightly higher capital investment with a lower operating cost for those systems that do need to run continuously. The designs include single-stage solutions as well as multi-stage solutions. GCES also offers complete integrated solutions with other air purification systems such as thermal oxidizers, carbon adsorption systems, filtration packages, etc. Gulf Coast Environmental Systems is a single source solution for highly durable and efficient air pollution control equipment.
Part 2: Chlorine Abatement
Part 6: SOx, the compounds of sulfur and oxygen molecules including Sulfur Monoxide, Sulfur Dioxide and Sulfur Trioxide
Part 11: Sulfuric Acid – H2SO4
Part 12: Ethylene Oxide – EtO