Tips for Homogenizing Volatile Samples
What is a volatile sample?
Before we provide tips for homogenizing volatile samples it’s good to understand what these are. Three key terms apply:
- Volatility denotes rapid evaporation, that is evaporating rapidly in the form of a vapor.
- Flash point is the temperature at which particular organic compounds give off sufficient vapor to ignite in air.
- Flammability is the ability of a substance to burn or ignite, causing fire or combustion.
Volatility generally applies to a liquid. Not all liquids are volatile when evaporating, boiling water being a great example. But acetone and IPA certainly are.
On the other hand, flash points and flammability apply more generally. Heat something like wood or upholstery hot enough and it can burst into flame, thereby being flammable.
A flammable liquid is a liquid with a flash point that does not exceed 100⁰F while a combustible liquid is one whose flash point is 100⁰F or higher.
The Division of Organic Chemistry of the American Chemical Society has published a table of properties for common organic substances that includes flash points.
Now back to the topic of this post.
Homogenizing Volatile Samples
Homogenizing exercises include rapid mixing of liquids some of which may give off vapors that can cause a fire or explosion and also expose personnel to dangerous fumes. Exercises such as this create what the National Fire Protection Association (NFPA) terms a hazardous area. Special precautions apply that include securing authorization from local public safety authorities.
To handle this, specially designed lab homogenizers are available that disperse immiscible samples such as oil, toluene, and diesel fuel in water in a totally enclosed area. These processes then can be scaled up to commercial production. The process employed uses what is termed a flow-through chamber.
How a Flow-Through Chamber Works
A flow-through chamber is a specially designed vessel attached to a lab homogenizer drive motor. While standard homogenizing rotor-stator generators are immersed in test tubes, flasks or beakers, the flow through generators are encased in chambers such as the DK30 or DK40 flow-through chambers offered by CAT Scientific.
The DK30 model is attached to a drive motor by standard length stainless steel shafts and operates in the vertical position. The DK40 is mounted horizontally and uses a short length shaft.
Unlike standard homogenizer shaft configurations there are no ports that allow samples to circulate and cool the rotor shaft. This avoids potential damage to the assembly by the media being processed. These shafts are fitted with a two-part slip ring seal along with other components not found in standard shafts.
The chambers usually operate by drawing samples from container A, homogenizing them and discharging them into container B. An option is a closed-loop system. Homogenizing time in the chamber can be adjusted by the speed of the drive motor, the size of the shaft and by restricting the discharge flow to extend dwell time in the chamber.
Applying Flow-Through Chamber Design for Volatile Samples
Flow-through chamber design, then, creates what in effect is a sealed system due to the absence of cooling ports and the presence of shaft seals. These features support processing volatile samples.
Container modifications are called for to handle volatile vapors given off by the samples. For lab and pilot plant operations sealed containers are required. A representative configuration has both chambers fitted with two tubes. One set of tubes carries the sample into and out of the flow-through chamber and the other set vents the containers to a standards-compliant air handling and filtration system.
Other safety precautions should be in place when working with volatile substances. For example you should install code-approved ventilation such as a fume hood over the processing site to draw off vapors and protect personnel should tubes become disconnected. This also applies and when containers are unsealed to add new or remove processed samples.
All electrical fixtures in proximity to the homogenizing operation must meet explosion-proof standards, and operating personnel should not carry cell phones or other electronic devices that could cause a spark.
You may think this is “overkill” but there is no substitute for common sense and strong safety measures if your homogenizing operations involve dangerous chemicals.