Understanding Short-Path, Fractional and Pope’s Wiped-Film Molecular Stills
Oftentimes when people are considering distillation equipment for processing hemp and cannabis, there seems to be a lot of confusion and misuse of terminology with short-path stills and Pope’s wiped-film molecular stills. We have explored some of the key points below.
What is Molecular Distillation?
Molecular distillation and short-path distillation are the same things. These both imply the use of high vacuum and a condensing surface in close proximity to a heated evaporation surface. For many applications such as cannabinoids and as well as other compounds with greater molecular weight and boiling points, if the distance is not close enough, the equipment will not work well, if at all.
What does short-path mean?
We discovered some people perceive the term “short-path” to imply a glassware setup involving a basic boiling flask with a neck leading to a condenser and a receiver flask(s), or a similar variation called a KIugelrohr. These are oftentimes also referred to as pot stills, (pot as in a vessel, not in the cannabis sense), and are all considered batch mode apparatus. However, these only refer to one type of short-path, and don’t include the other variations. There are other forms of short-path setups including Pope’s continuous mode Wiped-Film Molecular Still (WFMS).
Is a fractional still the same thing as a short-path still?
Fractional stills are not short-path stills. Fractional distillation equipment implies the utilization of a vertical packed column providing multiple equilibrium stages or “theoretical plates”, requiring the condenser to be further away from the boiling container (reboiler) and reached only after the obstacle of the packed column. While this can be used to increase the purity of a distillate, it is instead a problem for heat-sensitive materials such as cannabinoids. Though Pope does offer fractional distillation equipment, the single theoretical plate of molecular stills is sufficient for most cannabinoid work and offers the least product degradation.
What are the advantages of a wiped-film still compared to a boiling flask short path setup?
Complete Molecular Still Package System with electric band heating (bands removed), external condenser, all utilities, plus optional feed pump.
Now that we have a good understanding of short path, we want to dive into the advantages of Pope’s WFMS over a basic boiling flask type molecular short path still.
One key advantage is that the Pope WFMS is a continuous distillation, rather than a batch mode distillation. This means that with larger flasks, or liquid pumps, they can operate for extended periods of time with any quantity of feed material and with the same consistent product composition over time. The Pope WFMS is also scalable, such that when much larger quantities of material needs to be processed, larger versions of the same type of equipment can be utilized to accommodate the greater throughputs required. Batch mode stills such as the boiling flask short path still can be scaled but lose efficiencies due to heat and mass transfer limitations resulting in extremely long operation times and loss of product to degradation.
In addition to scalability and continuous mode, another advantage is the Pope WFMS offers much less thermal degradation and greater product purity and yield. This is for two reasons. One, there is a very short residence exposure time to a heated surface – only a matter of seconds, compared to many hours in a boiling flask molecular still. And two, the WFMS has a highly efficient dynamic rotating wiped film action providing turbulent moving thin-film mixing compared to the limited, less dynamic liquid/vapor interface of a simple boiling flask apparatus.
Comparison: Pope WFMS vs. Basic Boiling Flask Still
Feature | Pope Wiped-Film Molecular Still (WFMS) | Basic Boiling Flask (Short-Path) |
| Operation Mode | Continuous: Can run indefinitely with feed and discharge pumps. | Batch: Must be stopped, cleaned, and refilled. |
| Thermal Exposure | Seconds: Very short residence time on heated surface. | Hours: Long exposure leads to degradation. |
| Mixing Action | Dynamic: Rotating wipers create turbulent thin-film. | Static: Limited liquid/vapor interface. |
| Scalability | High: Larger units maintain efficiency/throughput. | Low: Larger flasks become inefficient and slow. |
| Product Yield | Superior: Minimal degradation and high purity. | Variable: Subject to heat-induced loss. |
| Consistency | Constant: Same product composition over time. | Declining: Composition changes as the batch depletes. |
Have more questions on terminology or Pope’s Wiped-Film Molecular stills? We are here to help answer your questions. Contact us to learn more or speak with a Pope team member.
Understanding Short-Path, Fractional and Pope’s Wiped-Film Molecular Stills