Sometimes, people describe a technique as more art than science.  Sometimes it is unclear what that means, but I want to explore that idea in this post. I’m a chemist. That means that while I am a scientist, I still have a little bit of art left in me.  I’m not an engineer.  I still have a soul.

Any series that discussed common applications of wiped film stills would be incomplete without mentioned their use in the cannabis industry. 

Wiped film still manufacturers experienced an extremely large increase in sales when the 2018 Farm bill reclassified hemp as an agricultural commodity. Today, the industry has shrunk some, with many cannabis companies out of business and profits dropping compared to the early days.  However, this industry is still an important part of any wiped film still companies customers.  In THC legal states, the stills are also used to purify marijuana.

The topic for today is the use of wiped film stills in wax purification.

Wiped film stills are used in the production of both natural and industrial waxes.  The stills are chosen because the short residence time prevents burning  or degrading of sensitive waxes.

There are several different processes that the stills are used for. 

Many times, a manufacturer will target a particular product for an application.  These oils are used in food, cosmetics and animal care.  In order to produce a specific product, the manufacturer will take a pure fatty acid and run a reaction with glycerin to produce the desired polyglyceride mix.  The manufacturer could be targeting the monoglyceride, the diglyceride or the triglyceride.  Glycerin has three locations where a fatty acid can add, so all three molecules are made when the reaction is run. 

A process known as “folding” is often done to distill the D-limonene away from the rest of the compounds.  The D-limonene is often used as an industrial cleaning agent, solvent, insecticide, and cosmetic.  Then the sesquiterpenes are distilled away from the waxes to be used in the flavor and fragrance industry.   Finally, the residual tars are often distilled further to target high value compounds like nootkatone and sinensal.  All of these distillations are performed on wiped film stills. 

This week I would like to discuss some of the common applications of wiped film stills.  For starters, let’s talk about polymers. A technical discussion of wiped film still usage in the world of polymers would fill much more than a short post.  A book could be written on all of the various ways a wiped film still can be used in polymer production.  This post will be a brief overview of the topic.  If you have a specific application you would like to discuss, please reach out.

Wiped film still depends on the ability of the feed material to flow down the walls of the still.  Therefore, the feed material must be a liquid, or it must be handled under conditions that make it a liquid.  In addition, it must be a relatively thin liquid. 

Wiped film stills are a simple distillation device, meaning they consist of a single theoretical plate.  When used to perform separations, they are capable of purifying mixtures whose components are far apart from each other.  If the boiling points are too close, the still is not capable of producing pure components.  Instead, the best that can be achieved is enrichment in one component.

Reason three to consider wiped film distillation: Larger Molecule

Wiped film distillation makes distilling larger molecules easy. 

I am using the word “large” relatively.  For example, in traditional equipment like reactors and rotovaps, it is often a challenge to distill higher boiling solvents like dimethylformamide or dimethyl sulfoxide.  Chemists often avoid these solvents because of the difficulty in removing them by distillation.

Sometimes it is necessary to distill volatiles out of a mixture, leaving behind the desired product.  Some common examples of materials that are often devolatilized are food products, oils, polymers and nutraceuticals.  Many times the volatile component is water or a solvent and just needs to be lowered to less than 1%.  Other times the volatile compound may be a starting material from the reaction and has to be removed as low as 20 ppm prior to proceeding with the process. 

Wiped film distillation is widely considered the best option for distillations of heat sensitive materials.  The reason for this is wiped film distillation is a continuous process.  The feed material enters the cylindrical still body and flows down the inside wall of the cylinder. 

Sometimes you know that this product is made using a wiped film still, but you just aren’t getting the results you need.  In these cases, please reach out.  I can provide a quick, free review of your process and give a straight answer about feasibility.  I should be able to tell if the desired separation will be straightforward, impossible or challenging.

When dialing in a wiped film still, users focus on the big three levers of Feed Rate, Vacuum and Temperature. 

This is the correct approach as these three controls have the majority of the power when controlling a wiped film distillation.

However, it is critical to remember the wipers as well. 

A material may run perfectly one time, and then the next time it gives you all kinds of trouble. These distillations can be finicky, even for the experienced practitioner.

When working well, wiped film distillation is low maintenance and easy to run.  Wiped film stills can quickly distill large volumes of material.  They offer low residence times and minimal heat exposure, so even the most sensitive distillations can be processed quickly and well.

When not working well, wiped film distillations can make you pull out your hair.