Dimethyl sulfide (DMS), also known as methylthiomethane, is an organosulfur compound. It is a methyl sulfide, in which the sulfur atom is substituted by two methyl groups, with the chemical formula of (CH3)2S. It is a highly flammable straw-colored liquid, with a boiling point of 37 degrees Celsius, or 99 degrees Fahrenheit. This is a compound that is easily recognized by its foul odor, that is often described as “cabbage like”. Unlike many other organosulfur compounds, this disagreeable odor is present in even low concentrations of DMS. Dimethyl sulfide is the product of dimethylsulfoniopropionate (DMSP) breakdown, and is also the result of bacterial metabolism of methanethiol.
Where is Dimethyl Sulfide Found?
The primary source of dimethyl sulfide is from DMSP. DMSP is a zwitterionic metabolite, found in marine algae, seaweed, and phytoplankton. Dimethyl sulfide is the most common and abundant organo-sulfide emitted into the atmosphere from plankton in the oceans. When oxidized, DMS is converted into sulfur dioxide, dimethyl sulfoxide, dimethyl sulfone, methanesulfonic acid and sulfuric acid. Some of these compounds have the potential to create new aerosols, and aid in the formation of clouds. Because of it’s role in the formation of clouds, dimethyl sulfide plays a huge roll in regulating the earth’s climate, and may even play a role in the overall balance of life on this planet.
Another notable source of dimethyl sulfide is as an odor, produced by certain meats and vegetables, when cooked. Shrimp, cabbage, brussels sprouts, beets, and corn, all produce a strong odor when being cooked; dimethyl sulfide is one of the compounds responsible for these less than pleasant smells.
Industrial applications that produce dimethyl sulfide include kraft pulping. Also known as sulfide pulping, this is a process that converts wood, into wood pulp. Wood pulp consists of nearly 100% cellulose fibers, which are the primary component of paper. This process creates a strong odor, that must be abated, per most regulatory agencies.
It should also be noted that dimethyl sulfide is found in very low concentrations in the healthy human body; predominantly in the blood, urine, and expired breath. Dimethyl sulfide can become dangerous, in high concentrations, causing a condition called dimethylsulfidemia. This condition is characterized by a strong, unpleasant odor of the breath, or halitosis.
Why is Dimethylsulfidemia a Concern?
The most immediate risk with dimethyl sulfide is that is an incredibly flammable compound, that must be handled with extreme care because of its combustibility.
Dimethyl sulfide can be detrimental to human health because it is very irritating to the membranes. The most dangerous aspect of exposure is respiratory irritation. When inhaled long term, in even small concentrations, dimethyl sulfide can cause inflammation and chronic cough. In high concentrations, DMS can be acutely dangerous. It can cause hypoxemia and loss of consciousness, and possible long-term inflammation issues. DMS is also considered a moderate eye irritant, and eye washing stations should be kept on-site, whenever dimethyl sulfide is being handled.
The largest concern associated with dimethyl sulfide is the odor. Although this is not necessarily a health risk, it is something that is regulated through governing agencies and bodies. Not complying with regulations can incur high regulatory fines, and eventually, even plant shut-downs. The odor of DMS is incredibly strong, even in very low concentrations. The scent is known to make people light headed and nauseous from its overwhelming strength.
The most widely used method of abatement for dimethyl sulfide is a wet scrubber. A wet scrubber is a common piece of pollution control equipment that uses a scrubbing liquid – typically water – to remove VOCs like DMS from industrial exhaust streams. Contaminated gas flows through a specially designed packing media that is wetted with recirculated liquid. The liquid solvent absorbs the gas pollutant 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.
DMS can also be treated in a 2-part process, especially if other Hazardous Air Pollutants (HAPS) and VOCs are present with the dimethyl sulfide.
Part 1: A thermal oxidizer is the is the first piece of equipment used to abate dimethyl sulfide and other volatile organic compounds. 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 dimethyl sulfide, 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 dimethyl sulfide 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 dimethyl sulfide.
Part 2: The second step in the dimethyl sulfide abatement process is the use of a wet scrubber. 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 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.
The tail gas to be cleaned is carefully analyzed to determine the optimum design parameters and to allow for the best operating solution for each installation. After thorough analysis, GCES offers several options of fume or exhaust scrubber equipment packages based on plant equipment, local air regulations, plant locations, and other factors. Our experience in designing scrubbers for many different chemicals shall provide each customer with the assurance that the plant’s air quality will have a minimal impact on the environment.
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 multistage options. GCES also offers complete integrated solutions with other air purification systems such as carbon adsorption systems or filtration packages.
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 – EOX