Rotary Evaporators: An Innovative Approach to Their Design

Electronic devices have substantially altered chemistry. Just as home kitchens now include machines like multicookers and electric kettles that make food preparation more convenient, modern laboratory benches have also begun to employ dedicated labor-saving devices.

The rotary evaporator is one of the most commonly seen and regularly used pieces of equipment in many laboratories, particularly those working with organic chemistry. Next-generation, electronic rotary evaporators are starting to provide significant, tangible performance benefits.

Commonly referred to as a rotovap, these workhorses can remove the solvent at the end of practically any synthetic chemistry procedure, and again the following chromatography to leave the pure end product.

In most organic chemistry and pharmaceutical labs, rotovaps are used so frequently that each lab member will often have their own machine. Because they are so heavily used and relied upon, any innovation resulting in faster, more energy-efficient, or more convenient rotovaps will likely have major payoffs for both lab productivity and environmental sustainability.

Rotovap Basics

At some point during the majority of experimental chemical procedures, solvents in the reaction vessel or those introduced during purification must be removed. For many solvents, their comparatively low boiling points can be utilized to evaporate off the solvent, leaving behind reaction products.

For a long time, chemists have sought new means of accelerating solvent removal. These have historically including warming the vessel or the application of a vacuum to lower the solvent’s boiling point. Rotovaps do both, while also spinning the sample to minimize what is known as “bumping” – a problem where superheated solvent leaks out of the reaction flask, carrying with it some of the precious reaction product.

Solvent vapor may contain hazardous substances, so this cannot be simply vented into the environment. The rotovap includes a condenser unit responsible for cooling the solvent vapor and condensing it back into a liquid to be collected. This captured, liquid solvent then drips into a receiving flask for safe disposal.

Until recently, the cornerstones of rotovap design and operation had not changed much since the release of the first commercial machine in 1957, by Swiss company Büchi. These first-generation rotovaps were heavy consumers of water, as is often noted by those chemists who may recall using them just a decade ago.

“When I did my PhD, we used water aspirators and water running through the rotovap to cool the solvent distillate,” says Richmond Sarpong, professor of organic chemistry at the University of California, Berkeley, who began his graduate education in 1995. Water aspirators were attached to a fast-running tap, generating the vacuum. The user would also need to continually run tap water through the condenser to enable cooling, and all that water ultimately went directly down the drain.

Ecodyst’s rotary evaporators

Ecodyst’s rotary evaporators incorporate condenser coils that are made from a polymer-coated metal rather than the traditional glass. Combining condenser and chiller into a single unit has proven to be a scalable approach.

One of the initial steps in the emerging laboratory sustainability movement, which began in the early 2000s, was the recognizition that rotovaps’ level of water consumption was unsustainable and that alternatives had to be introduced.

Kathryn Ramirez-Aguilar, who started the Green Labs program at the University of Colorado Boulder 10 years ago, elaborates, “Prior to Green Labs, one of my supervisors worked with the chemistry labs on rotovaps,” she says. Single-pass water condensers and water aspirators were replaced with vacuum pumps and recirculating chillers, which work by pumping an antifreeze solution through the rotovap condenser’s glass coils within a closed-loop system.

Other companies, universities and research institutions chose to replace liquid coil condensers with “cold finger” attachments that were filled with dry ice, but each of these options has its drawbacks, outlines George Adjabeng, co-founder and CEO of the instrument company Ecodyst founded in 2014. Adjabeng spent several years working in chemistry labs, including a decade at a major pharmaceutical company where he used rotovaps almost every day.

I grew frustrated with looking for dry ice. Chillers were not an option, for two reasons. One, they are heavy and bulky—we couldn’t fit them in our fume hood. And second, they are very inefficient. It takes about 45 minutes to get the condenser down to –10 °C.

George Adjabeng, Co-Founder and CEO, Ecodyst

These frustrations very much fed into Adjabeng’s work to develop a new type of rotovap.

Frustration-Free Technology

Adjabeng’s prototype merged the condenser and chillers into a single, compact and efficient unit. “In 2015, I put our first condenser unit in a University of California, Berkeley, lab,” he explains. “That machine never came back; they liked it so much they bought it.”

In traditional rotovap chillers, refrigerant is used to cool a water-antifreeze mixture, which is pumped to the rotovap condenser’s glass coils. The primary advance made by Adjabeng - which now underpins all of Ecodyst’s innovations in the rotovap sphere - was to not only to combine the chiller and condenser but also to completely reassess the material used to manufacture the condenser coil.

Everybody assumed glass is the only material chemically resistant enough to use in a rotovap. Nobody thought of making metallic coils and coating them with a chemically resistant polyfluoromer.

George Adjabeng, Co-Founder and CEO, Ecodyst

The strong carbon-fluorine bonds in fluorine-rich polymers, like Teflon, are also sufficiently resistant to chemical attack.

The condenser’s protective polymer coating has been proven to be robust. “We have had units in industry for almost 5 years now, and they have not had any issues with corrosion,” he says. “I think we have established this is a better alternative to glass.”

The cannabis industry is driving the transition toward stationary-flask rotovaps that have higher capacity than traditional rotating flask designs.

The cannabis industry is driving the transition toward stationary-flask rotovaps that have higher capacity than traditional rotating flask designs.

Academic Research Sustainability

Most universities now prioritize environmental sustainability, with discussions around the sustainability of university lab space beginning in around 2005, at a time when universities began to track and record their greenhouse gas emissions.

“When those first greenhouse gas inventories were published, the footprint of research labs was a shock,” points out Allen Doyle, a lab sustainability consultant in Atlanta who, up until 2018, was the Green Labs program manager at the University of California, Davis. “The lab space at a major research university will typically account for 25-30% of the university’s square footage but 60-70% of their energy budget,” he notes.

Electricity usage by devices plugged into electrical sockets in the lab are often a significant factor in overall laboratory energy consumption,

Anything that involves heating is the biggest energy user, then freezing, then vacuum pumps. Electric motors in labs are a small draw.

Allen Doyle, Lab Sustainability Consultant, Atlanta

As well as their direct impact on electricity consumption, appliances tend to heat up during use, and this may place additional strain on building cooling in spaces where airflow is not sufficient. The more electricity a device uses, the more heat it will radiate into the room.

Because scientists only intermittently work with rotovaps during the day, the instrument’s impact on a lab’s energy consumption might be considered to be small. However, when Ramirez-Aguilar installed electricity meters on rotovap equipment across the university, the results were a surprise.

“We metered two chillers that were used for condensers on rotovaps,” Ramirez- Aguilar says. These chillers used 8.9 kW h/day and 9.6 kW h/day. This is around one-third of the daily electricity consumption of an average US home. “That’s not a small amount of energy,” she highlights.

The chillers used so much electricity because they were left running all the time. “The scientists found they had to keep the chillers turned on to reach the temperatures that they need,” Ramirez- Aguilar says. Green Labs installed timers to automatically turn chillers off at night and restart them in the morning, but even then a chiller would still be running for hours despite the rotovap not being actively used. “A condenser that gets down to temperature within a few minutes would be great,” Ramirez-Aguilar says. Thankfully, Ecodyst’s 1-minute cooldown successfully eliminates this problem.

Rather than using chillers, in Sarpong’s lab, the majority of his research group’s 30 members cool their rotovap condensers using a cold finger attachment, which requires dry ice to run. This approach also has drawbacks, however, as Sarpong points out, “Dry ice prices are rising through the roof, and the supply is not fully reliable, especially on holidays and weekends when the dry ice delivery company cannot access our buildings.”

The inability to run a rotovap is a substantial bottleneck in any synthetic organic chemistry lab because the reaction solvent consistently needs to be removed in order to move from one synthetic step to the next.

Self-cooling units have the potential to be highly beneficial in these instances. Sarpong’s team members employ Ecodyst’s stand-alone EcoChyll condenser, which can be attached to any rotovap instead of a cold finger attachment and glass coil condenser. The new condensers have proven to be a well-liked addition to the lab, according to Sarpong, who says, “The fact it cools down very quickly after you turn it on is definitely a convenience.”

The all-in-one rotovap could replace traditional benchtop rotovaps.

The all-in-one rotovap could replace traditional benchtop rotovaps.

Thinking Big

A research laboratory may have different needs for an industry laboratory, but rotovaps are equally common in both these settings. The nascent cannabis industry has a distinct need for efficient extractions, with cannabis processors using solvent extraction to isolate bioactive compounds from plant material, before using rotovaps to obtain the purified oil.

People setting up small cannabis extraction facilities find that having to deal with dry ice or consume substantial volumes of water to chill a conventional rotovap is not financially viable. However, as the cannabis industry continues to grow, standard rotovap systems are actually becoming a bottleneck when scaling up operations.

A lot of chemists in industry and academia have had issues when scaling up a reaction, finding that they have to evaporate off a considerably larger volume of solvent than their rotovap was designed to accommodate.

Since Ecodyst introduced its first product - the  EcoChyll condenser-chiller - the company has rapidly expanded its range of product offerings, focusing on addressing the aforementioned issue of scale. “We designed our cooling technology to be very scalable,” says Adjabeng. By 2017, the company had introduced 22, 50, 72, and 100 L systems.

The multistep organic syntheses conducted in Sarpong’s lab involve bringing starting materials through the first few steps of synthesis and running large scale reactions, often at 100 g or more. Using a benchtop rotovap to evaporate off the solvent at the end of these kinds of reactions is often a slow, inefficient process. Furthermore, the weight of a solvent-filled flask may compromise the glass piece that fits into the rotovap, resulting in leaks.

The demand for larger capacity rotovaps has been particularly noticeable in the rapidly expanding cannabis industry. For example, Tikun Olam is a large Israeli medicinal cannabis company that launched 15 years ago and now operates subsidiaries in Australia and the US.

Like many cannabis companies, until very recently Tikum Olam was utilizing standard industrial-scale, 20 L rotovaps to evaporate off ethanol used to extract cannabis oils from plant material.

This formed a considerable production bottleneck, even when their rotovaps were run 24 hours a day according to Oded Lahmish, who heads the company’s wet-production facility in Israel as well as handling all R&D related to production. “We realized the cannabis industry needed larger industrial-scale machines,” Adjabeng adds.

Alongside its innovative choices in combining the condenser and chiller into a single unit, while switching to a metal condenser material, Ecodyst has also been a pioneer with its larger-scale machines. “We realized that there is no need to rotate the flask,” Adjabeng says. Flasks sit vertical and remain stationary inside a heating mantle while high-speed overhead stirrers are used to minimize bumping.

The flask itself can be filled to capacity since it is upright, whereas a traditional, 20 L rotovap can only be filled halfway because it tilts the rotating flask on an angle.

Thar Process is a tolling company that relies on Ecodyst’s large capacity machines to successfully convert customers’ cannabis plant biomass into cannabis oil. “Since we do very large-scale extractions, typically 1000 kg/day of hemp biomass, we require the largest solutions available,” says Jason Lupoi, a project manager in Thar’s chemistry department.

Meanwhile, Patrick Healy, extraction lab manager at North Carolina hemp extraction company Innovative AgriProducts says his company is heading in the same direction Healy can fit a complete extraction batch into each individual 72 L Ecodyst machine, which he says possesses a comparatively compact footprint due to its integrated design. “They fit within our building without a whole lot of building modifications or drilling holes in walls for chillers and heaters.”

The removal of ethanol to isolate extracted oil is usually the biggest bottleneck during cannabis processing. “It’s not just the evaporation but unloading the product out of the machine at the end,” that slows the process, Healy says. Raw cannabis oil has a consistency similar to that of thick molasses, so removing this oil from the system is often a messy and time-consuming process resulting in unwanted machine downtime.

Ecodyst’s larger units are fitted with valves at the bottom of the flask to speed up this process. “With these larger models, we can just drain [the oil] out of the bottom,” Healy explains. Ecodyst has worked closely with the Innovative AgriProducts team to refine numerous aspects of the machine’s design, including this valve.

Tikun Olam says that its 50 L Ecodyst machine is already paying dividends. Rather than the 3-4 L/h evaporation rate provided by a 20 L standard rotovap, the Ecodyst machine is efficiently removing 9-12 L/h. “In our protocol, it shortened a 4-day process to 1.5 days,” says Lahmish.

The system also offers energy savings, with Ecodyst’s 100 L machine consuming 10 kW of power. This is around the same power consumption as a traditional, 20 L rotovap, but Ecodyst’s machine has 10 times the capacity due to the angled flask positioning on the 20 L rotovap.

Ecodyst’s large-scale machines have already gained attention from researchers in other chemistry-related industries, bringing Adjabeng back full circle to the pharmaceutical industry where he has previously worked.

“We recently set up a 100 L machine for a pharma company,” he points out. Previously, when working with large volumes of solvent, the pharma company’s scientists would split this between four 20 L rotovaps. “Then they would wait and wait,” Adjabeng adds. “On a conventional 20 L machine, for a solvent like an ethyl acetate, they were removing 10 L an hour if they were lucky. In our system, they were getting 50 L an hour.”

Two key factors are responsible for this enhanced speed, Adjabeng says. With Ecodyst’s highly efficient metal condensers filled directly with refrigerant, researchers are able to increase the heat on the sample to evaporate solvent vapors faster, with no risk of the condenser overheating.

Ecodyst’s stationary systems are especially suited for use with liquid products because they include drain valves at the bottom, designed to collect the product after the process is completed. The system can also accommodate solid products.

For convenient product isolation, chemists may prefer to employ the 100 L machine to rapidly reduce solvent volume down to a manageable 10 L before switching to a conventional rotovap to complete the task.

The environmental and productivity benefits of this new generation of rotovaps continue to grow when they are employed at scale. However big they are, rotovaps remain the labor-saving electronic device of choice for most bench chemists.

This information has been sourced, reviewed and adapted from materials provided by Ecodyst.

For more information on this source, please visit Ecodyst.

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