Dichloromethane (DCM) is a non-flammable, volatile chemical that is widely used as an organic solvent. Also knows as methylene chloride, it has many industrial applications because of its high volatility and ability to dissolve compounds. But what is it used for exactly?
Dichloromethane is commonly used in aerosol products like spray paint. This is because it acts as a:
- Strong Solvent
- Flammability Suppressant
- Vapour Pressure Depressant
- Viscosity Thinner
Because DCM is a non-flammable solvent, it is ideal in aerosols as it provides protection against, and reduces risk of combustion. As well as this, its low boiling point (40°C) gives it fast-drying properties which are great for adhesive aerosols.
DCM’s ability to vaporise at room temperature also makes it perfect for aerosol propellants. By having a low boiling temperature, DCM vapour exists in equilibrium with its bulk liquid when inside the pressurised can. This is because, while its pressure is higher than atmospheric pressure, it isn’t dangerously high.
However, there are dangers associated with aerosol products due to their dichloromethane concentrations. Considered a highly toxic substance and carcinogen, DCM is dangerous in large quantities. Inhalation is the most common form of exposure and can cause a variety of health risks, from dizziness to carbon monoxide poisoning. In extreme circumstances, dichloromethane exposure can be fatal.
Find out more about the dangers of dichloromethane in our previous post.
The Drinking Bird
Although DCM has a sinister side, it still brightens people’s day in the form of a popular Chinese toy. The drinking bird is known for its ability to continually dip its beak into a cup of water, and is often mistaken as an example of perpetual motion.
The drinking bird is actually a heat engine, and operates because of a thermodynamic cycle. This means that it uses temperature difference as an energy source, exploiting the shifting temperature gradients between head and body by converting them into continuous mechanical work. Dichloromethane plays a huge role in the drinking bird’s process.
The drinking bird is constructed by connecting 2 light bulbs with a tube – these components represent the head, neck, and abdomen. While the head is covered in absorbent material that will later be made wet, DCM is kept in the abdomen. It is used because of its low boiling point, which means it can evaporate at room temperature. This is vital when it comes to thermodynamics.
- Dichloromethane vapour begins to gather in the head. This is because DCM evaporates at room temperature. The vapour travels up the tube and into the higher light bulb.
- The material on the head is soaked in water. As this evaporates, it cools the head because evaporation lowers temperature. This decrease in temperature also condenses the vapour in the head.
- Vapour pressure in the head is now lower than vapour pressure in the abdomen. This means that the abdomen is warmer, and this difference forces DCM fluid to travel up the tube and into the head. This makes the bird top-heavy, and it tips forward.
- Warm vapour bubbles travel up the tube. With the liquid in the head, the bottom of the tube is no longer submerged. This means that warm vapour bubbles are released into the head.
- The vapour bubbles displace the liquid in the head. This causes the DCM to go back down the tube and into the abdomen. The bird become bottom-heavy, and the process continues.
Dichloromethane’s high volatility makes it suited to a variety of applications besides the drinking bird, and is part of the reason it makes an ideal solvent.
DCMs high volatility allows it to dissolve a wide range of organic compounds. Therefore, it is the ideal solvent to use in many chemical processes.
Perhaps the most common application of DCM is paint stripping. Its aggressive solvency allows it to penetrate the layers of the paint, which causes them to swell. This increases volume and creates internal strains. Not only does this weaken the paint’s adhesion to the underlying surface, it also allows DCM to completely break the bond between them.
DCM is also proficient at removing oil, grease, and other contaminants from most surfaces. Its low boiling point also makes it ideal for degreasing temperature sensitive parts.
Parts cleaning is an essential process in many industries. This is why dichloromethane is widely used as an industrial solvent in order to ensure equipment is stripped of contaminants. Dichloromethane has excellent dissolving properties which make it well suited to this.
For a cleaner, more thorough result, DCM can be used in vapour degreasing. This is where the solvent is boiled so that it vaporises and condenses on the desired work piece. DCM can then dissolve the leftover contaminants that standard parts cleaning couldn’t eradicate. It does this by trapping the impurities in its liquid beads, which then drip off.
Dichloromethane was the favoured solvent to use when separating an organic compound, like caffeine, from a mixture of compounds. This is because the solubility of caffeine in DCM is 140mg/ml, which is more than six times greater than its solubility in water.
To decaffeinate coffee, the unroasted beans would be repeatedly rinsed in dichloromethane after being steamed. During this process, the caffeine would become extremely soluble with the DCM, allowing the solvent to extract it from the beans. The dichloromethane would then be drained away, leaving behind decaffeinated coffee beans.
While DCM was the preferred solvent in this extraction process for many years, its status as a hazardous substance and potential carcinogen meant that it was eventually replaced with a non-toxic alternative.
In the electronics industry, dichloromethane is used to produce printed circuit boards.
Before the photoresist layer is added onto the board, DCM is used to degrease the foil surface of the substrate. It is also used later on to strip the photoresist layer from the board. This exposes the copper foil between the printed circuit patterns.
Another process that takes advantage of dichloromethane’s flexible properties is the manufacturing of photographic films.
Cellulose triacetate (CTA) is used to create safety films in photography. Dichloromethane is used as a solvent in the production of CTA, which is created when cellulose reacts with acetic acid. The cellulose acetate is then dissolved in DCM, which eventually begins to evaporate. As it does, the fibre of pure triacetate is left behind.
From the drinking bird to caffeine extraction, and every chemical process in between, dichloromethane is perhaps the most widely used organic solvent. It is also the most sweet-smelling: a deceptive guise for its sinister undertones.
At ReAgent, we sell three varieties of dichloromethane that are sure to suit the needs of your business. We also offer a wide range of pack sizes, from 25L screw cap bottles to 25,000L tankers. There’s something for everyone at ReAgent – how can we help you today?