Tips for a Successful Distillation
The most frequent thing we are asked is what people can do to get better at distillation with an SPD. Simple answer is: do more runs and learn from your mistakes… Fail better! But aside from understanding from visual cues – it really does help tremendously to have the right instruments to work with. Give yourself the competitive advantage by having measurable variables to compare every time you run a batch! Below you will find the most essential gadgets you should be outfitting your system in order to be successful. We’ve put together a little excel log so you can keep track of your run progress – this will help you to see the changing variables in a more organized manner and if your still lost – you can show more experienced distillers (like us) your data to get tips for next time. Download it at the bottom of this article.
Monitoring System Temperature:
Get yourself some good temperature probes! (preferably some digital ones)
Where they need to be:
- Inside the boiling flask to measure the temperature of the starting material as it progresses through the various fractions. This probe is usually connected to the boiling flask heating element which you can set accordingly.
- Inside each distillation head to measure the vapor temperature of the fractions discharging into the condenser(s).
Even temperature distribution is very important in the boiling flask when you are trying to coax fractions out at deep vacuum levels. As the various compounds travel up the distillation head in either vapor or liquid form, the energy of the reaction will cause temperatures to rise through the column thus allowing for other compounds to “Carry Over” Its important to keep progressing through the various fractions and not allow for steep temperature fluctuations within the head. Therefore, an accurate bottom mantle along with an insulation method or a heated top mantle are highly recommended. Keeping a record of the rising temperatures in the distillation head is also a must – therefore a high-accuracy digital probe to measure and record vapor temps is by far the best investment you can make as both a novice and an expert SPD operator.
Let’s look at some common equipment used for heating and insulating:
Types of mantles:
Bottom heated (pic)
Top and Bottom Heated (pic)
Oil Jacketed *Not typically used for SPD, this is a common method to heat other large cauldron-style vessels such as reactors and also the outside bodies of WFE distillation Systems (pic)
Glass Stove Rope (pic)
Electric Heat rope (Pic)
Silvering (For Glass)
Vacuum Insulation (Glass/SS)
Monitoring system vacuum:
Vacuum Gauges (Digital)
Having a few good vacuum gauges plumbed into the system and specific points will be a huge timesaver and will help you understand what is going on in the system and which stage of the process you are at. Using this data along with the readouts from the temperature probes allows us to develop our run methodology, create SOP’s, and control our variables.
In a typical SPD system, you will find one vacuum gauge affixed to read vacuum inside the distillation system – the location varies depending on which glass manufacturer you are using. Some vacuum ports are located at the head condenser discharge (pic). Some are located further away, but prior to the last cold trap before the vacuum pump manifold. There is nothing wrong with having more than two points of vacuum being read, the more data we have the more we can learn about what’s happening inside the system! The last vacuum gauge is typically located directly on the Vacuum pump manifold – it should be set-up in such a way to be able to isolate from the rest of the system and tell you what your pump’s ultimate vacuum is when its not pulling vapors. We typically recommend no more than 20 micron or 0.020 torr as the ultimate vac from your main deep-vacuum pump.
The best way to ensure a proper vacuum seal is to use a good vacuum grease. There are two types of grease we recommend you should look at. The first is Dow Corning – which is a standard food-grade safe vacuum grease which is popular. I would personally recommend this for any glass joints which will ever come in contact with final product such as the receiving flask or product pathway glass. It has some limitation though – it doesn’t like temperatures above 200C and is soluble in alcohol. This could be a potential issue as we often do push our first pass beyond 200C on the mantle so another solution is needed for this.
Apizion 501 is the other product we use – it is an ultra high vacuum grease that is rated to 13 scale vacuum – used in scientific laboratories and at NASA. This product is very expensive compared to Dow Corning so use it sparingly. It has a high temperature threshold and can handle temps well above 200C so its great for use on or near the boiling flask joints.
What we like to do is use both at the same time. We grease the outer portion of the glass joint with Apizion 501 to ensure a tight seal. The inside (potentially distillate touching side) we apply a bit of Dow Corning lubricant. Its important to slowly “massage” the joints back and fourth after putting your system together and also when applying vacuum to ensure even distribution and to work out any potential air bubbles.
Keep and eye on your in-system vacuum gauge when massaging the joints back and fourth to ensure the fluctuations are progressively moving towards a deeper vacuum.
Recording your Progress:
Keep a log of the entire run on a spreadsheet for reference:
There are numerous techniques for logging your SPD runs – and doing so will allow you to compare data from all the various instruments such as temperature, vacuum levels, and event visual ques. You will notice subtle changes which will help you determine how to proceed.
The number one reason distillate comes out discolored or with an odor is because the operator rushed through the fractions due to a lack of understanding when to raise mantle temperatures. By having these vital instruments installed and recording the data, you will be be able to spot an increase in vacuum depth and slight decrease in head vapor temperature as a signal that the current fraction is depleting and that it is time to ramp up the mantle.
We’ve created a basic excel spreadsheet to allow you to log your run progress. Get to know your system and refine your process by doing it the old-fashioned way. The good news is that there are products we will soon feature which will allow you to not only automatically log all this data, but to automate your process too! Stay tuned.