Water Detection in Dimethyl Ether

What is DME?

DME, or Dimethyl Ether, is an organic compound with the chemical formula CH3OCH3. It is a colourless gas, with many interesting properties. DME can serve as a clean-burning, soot free alternative to propane, and because of this fact it is often used as a cooking fuel in China, and other Asian countries.

Dimethyl Ether has also shown potential as a new form of biodiesel. Traditional diesel engines have demonstrated an ability to burn DME as an alternative type of fuel, needing modifications only to their fuel delivery systems to do so. Dimethyl ether can be manufactured from existing biomass and agricultural waste. Because of this fact, as well as its clean-burning, low emission properties, it shows great promise as a new, eco-friendly fuel source.

Why is water in DME a problem?

Because DME can be burned in standard diesel engines, it is vulnerable to many of the same issues as traditional diesel fuel regarding water contamination. When excess water is introduced into any kind of diesel fuel system a number of problems arise. The first of these is horsepower. When the ratio of water to diesel fuel rises, the amount of available energy in the fuel decreases, resulting in a lower horsepower output.

Another problem that arises due to water contamination in diesel fuel systems is rust. When steel and iron components are exposed to water they can begin to rust. The formation of rust in diesel engines is problematic, because the rust particles that flake off from these components can wreak havoc in a fuel system –clogging filters, and inhibiting the normal functioning of fuel injectors.

Additionally, because much of the testing on DME as a fuel source has been done on shipping trucks in northern Alberta – a cold climate which regularly experiences subzero temperatures – free water freezing inside of fuel systems is a danger as well.

How does DME become contaminated with water?

DME can become contaminated with water in all the same ways as regular diesel fuel. Much like traditional diesel, or any other kind of fuel, DME is vulnerable to water contamination during all stages of the delivery, storage, and transportation phases of the production process.

Although dimethyl ether is generally stored and transported in pressurized containers similar to propane cylinders - rather than in liquid tanks, as is the case with traditional diesel fuel – environmental factors such as condensation, wet weather, and poor housekeeping can easily result in an end product that exceeds acceptable levels of water contamination.

How to dewater DME

Due to DME’s new, experimental role as an alternative fuel source, there have not yet been many methods established for dewatering it. This is especially true because a large portion of this experimentation is being done in wet, snowy climates, where the amount of water being introduced into the fuel delivery system is far above average.

There has been some preliminary success in using industrial desiccants to dewater dimethyl ether in a laboratory setting, but this strategy is still in the early phases of experimentation and optimization.

How is water content in DME being measured?

Water content in DME is currently measured using a Karl Fischer titration device. While these types of devices can be highly accurate and reliable, they carry their own set of challenges. First and foremost is the fact that testing for water content with a Karl Fischer must be done in a laboratory setting, which means that it isn’t an ideal strategy for determining water content in the field, or in a production environment.

Another downside to relying solely on titration is the fact that the test is destructive in nature. Although the quantities of DME required to perform these tests are relatively small, the material being tested is not recoverable. This means that every time a test is done valuable DME is lost, and on a large scale, over hundreds or even thousands of tests, the amount of wasted product starts to become very substantial.

How can capacitive sensing help?

Delta C’s capacitive measurement technology can help to mitigate these problems by offering an on-line, nondestructive alternative to Karl Fischer titration. Established titration methods are still required in order to provide a baseline measurement, but the addition of an on-line solution to the process helps to maximize both time efficiency, and yield.

What’s more, on-line sensors have the ability to be placed into any location in the dimethyl ether supply chain – from the production facility all the way to the fuel delivery systems themselves. Bringing testing capabilities outside of the lab means a much clearer picture of water contamination in the field, as well as greater flexibility and confidence in dealing with the problems it causes.