One cannot imagine a modern laboratory without a rotary evaporator as nowadays evaporation and distillation are still the most frequently used separation methods. To see the commencements of evaporation and separation we have to look back 3500 years into the history of mankind towards the Near East.

The evolution of rotary evaporator

At that time in Persia the ?drop by drop separation” was discovered for the production of rose water. The simplest apparatus design for distillation was based on a clay bowl. When the clay bowl was closed with a cover the vapor formed during heating and condensed at the inner surface of the cover to fine droplets. These droplets were collected from time to time by wiping them off with a feather to process them further. This method was quickly spread from Persia all over Europe, North Africa and Asia.

Due to a coincidence Greek sailors discovered the wool condensator on the high seas more than 2500 years ago. The ship was in distress and the crew had to derive the vital fresh water from salt water. For this purpose they heated sea water and condensed the vapors at wool that was fixed above a pot. The so-called “wool condensator” was widespread from the antiquity until modern times and represented quite a progress compared to the earlier “clay bowl-variant”.

The realization that sea water would become fresh water during evaporation is due to the coincidence, or perhaps the notice, that fog condensed at the sail and fell on the deck of the ship as heavy drops. At this time no specific scientifical experiments were carried out, yet to clarify the connection between fluids and vapors. Not before 350 B.C the basic principle of distillation, evaporation, and condensation was investigated by ARISTOTLE, when he described the vital hydrological cycle in nature. Later, in the 2nd century, distillation apparatuses were developed in Egypt according to the teachings of alchemy. They consisted of the four classical components heating bath, sample flask, helmet and receiving flask. A helmet-shaped cover with an internal drain channel for the condensate was fixed above a kettle. The rising vapor condensated at the walls of the cover, the condensate accumulated in the lower rim and flew through the spout into a collecting vessel. The so-called “alembic” was normally made from copper but also from ceramic or glass. This principle in a modernized style is still used today in the rotary evaporators.

In the 17th and 18th century the apparatuses were continually improved with regard to their distillation power. For this purpose water was used as cooling agent for the first time. As to the choice of material, metal was more and more replaced by the more chemical- resistant glass. In the 17th century the Irish physician Robert Boyle, who intensively studied the vacuum, carried out the first vacuum distillations to clarify the connection between pressure and boiling point. The invention of the pressure controller as well as the improvements of pumps thereupon enabled a more specific use of the vacuum distillation and lead to a more efficient evaporation. At first only bubble apparatuses were used for vacuum distillation. With the emergence of the organic chemistry in the mid of the 19th century a veritable innovation explosion took place and the first rectification columns and multi-step distillations were developed.

In the years 1950 and 1955 the scientists C.C. Draig and M.E. Volk respectively outlined the idea of the rotating flask to improve the mixing and increase the heat input for a product sparing operating procedure. Additionally, they suggested a condenser for the efficient condensation of the vapors.

Walter Buchi took up the idea of C.C. Draig and M.E. Volk together with the chemical industry of Basel and developed the first manufactured rotary evaporator. The first patented instruments were sold 1957 in Basel and introduced to an international public for the first time at the ACHEMA in Frankfurt in 1958. It was a resounding success!

The Rotavapor Model 1957 featured a spark-free operating induction motor and a powerful glass condenser with cooling coil. For the first time it was possible to control the rotation speed of the motor continuously between 0-240 rpm with a simple pre-set potentiometer. The condenser was put on the drive unit by means of a standard joint. Already the first variant of 1957 enabled a continuous feeding of liquids during the distillation with a feeding tube and a cock. A water jet pump was used as vacuum source and a waterbath, into which the rotating flask could be partly immersed, was suggested for heating. For over 20 years the Rotavapor? Model 1957 was popular in countless laboratories. At the ACHEMA 1961 different companies already exhibited rotary evaporators that were obviously copying the B?chi model but could never cope with it. Read more about the progression and success of the B?chi Rotavapor? in the next article on this page.

A vision becomes true: In the year 1957 the first Rotavapor was launched

The year 1957 was a successful year in many respects: The American physician Gordon Gould invented the laser (Light Amplification by Stimulated Emission of Radiation) and the world of music was happy to announce the vinyl record, that in 1958 replaced the shellac record as sound storage medium. The glass blowing factory W. Buchi convinced with the first rotary evaporator called Rotavapor in 1957 and began its triumphant success in laboratories all over the world. This Buchi worldnovelty reached the international clientele quickly and with ground-breaking success. The rotary evaporator literally represented an unfailing and robust workhorse which is meanwhile indispensable in every chemical laboratory.

All-In-One Versions and Other Options Enhance Efficiency and Safety

In 1950, the late biochemist Lyman C. Craig of The Rockefeller University developed a simple rotary evaporator. The first commercial version came from Walter Buchi in 1957. A rotary evaporator is a lab instrument that allows people to do chemical separation or purification by using heat and agitation—or stirring—under vacuum. “You’ll find one in any chemistry lab,” says Jim Dawson, president of Heidolph North America (Elk Grove Village, IL).

As Jeff Reid, product specialist at BUCHI Labortechnik AG (Flawil, Switzerland), points out, “You can use a rotary evaporator to separate a solvent from a compound of interest.” He adds, “Solvent recycling is big as well.” This technology can also be used in other applications, such as crystallizing samples.

Evolving evaporators

“There used to be just a few configurations of rotary evaporators,” says Dawson, “but now there are more options—different configurations to choose from and more manufacturers.”

Enhancing safety is a key trend in this technology. “Many researchers want the ability to safely control a rotary evaporator outside the fume hood or away from the chemistry,” Dawson says. “This doesn’t mean a remote such as a TV remote, but a small wired operating panel that allows the chemist to control the process going on inside the hood at a safe distance.” He adds, “It basically helps to protect the scientist from the chemistry.” Still, chemists often want to watch the process. “Chemists still do lots with their eyes, like visualizing [whether] something is changing,” Dawson explains.

Beyond safety, users want very low maintenance. “All researchers now have to run at higher levels of productivity, and downtime has to be minimized,” Dawson says. “So price isn’t always the game.” He adds, “The keys are the total cost of lifetime ownership and productivity.”

All-in-one control

Beyond controlling a rotary evaporator from outside a hood, some users want additional control with the technology itself. When asked about recent trends, Reid says, “Researchers want a system where you can control all of the components—the chiller, the vacuum pump, and the rotary evaporator itself—together.” He adds, “An all-in-one system can save 75 percent in energy. In such a system, for example, the vacuum pump produces the needed level of vacuum and then holds it, instead of running continuously.”

Users can also build a system from various vendors and run them all from one controller. John Pollard, vice president of sales at BUCHI, says, “Our controller and some of our competitors’ controllers can control other brands, but you lose the green functionality.” When building a system from various components, for instance, the controller might display the vacuum but not turn off the pump when it reaches the desired level. “It’s more automated when it all comes from a single manufacturer,” Pollard says.

An all-in-one system also enhances the simplicity of using a rotary evaporator, which Pollard says is near the top of the list among customer desires. “In an academic market, you could have 100 users of one rotary evaporator.” So that machine needs to be easy to use.

In some cases, the use is easy enough but, as Reid says, “The trick is to find the right parameters.” He adds, “So we provide those for the most common solvents.”

From the field

For a rotary-evaporator customer, two questions should be considered. First, will the rotary evaporator work as the manufacturer says it will? Second, if something goes wrong, will the customer have support to get it running again? “Chemists know things will go wrong,” Dawson says, “because they are using volatile chemicals and acids.”

Alfred Bacher, Ph.D., of the department of biochemistry at the University of California, Los Angeles, teaches lower-division organic laboratory courses and the upper-division inorganic/organometallic laboratory course. He says, “In all of these courses, we use
rotary evaporators very heavily, particularly in the lower-division courses, because the solvents being used are flammable.” Based on working largely with undergraduate students, Bacher would like a range of improvements in rotary evaporators. For one thing, he’d like lower-cost versions because, he says, “The cost of the rotary evaporators is too high to be used in larger numbers in undergraduate laboratory courses.”

In addition, Bacher desires some design improvements. “Overall, the design seems to be very intimidating to many of my undergraduates,” he says. He’d also like the design to “allow for an easier disassembly of the setup for maintenance.” In fact, he’d like less maintenance overall. For example, he says the seals that connect the condenser unit with the motor are “not as robust” as they could be. Maybe, Bacher suggests, a rotary evaporator could include fewer joints in general to reduce the sources of leaks. For example, he says, “While I do understand why the receiving flask is attached with a ball joint, I feel it generates a significant problem as well because most round-bottom flasks used in the lab have normal ground glass joints.” Even adding a simple pressure gauge would be nice, Bacher notes.

Some problems can even be costly. As Bacher says, “The speed of lowering the assembly is too high in some models or a low point cannot be set to avoid the destruction of the vapor duct, which happens frequently in undergraduate laboratories.”

Nonetheless, Bacher realizes that many factors come into play in device design. So he describes his suggestions as “some of them being realistic, others probably not so much.”

Beyond the lab, rotary evaporators also appear in new markets. For example, some chefs use a rotary evaporator to distill liquids that they use over foods, like pouring on a high-tech reduction. The increasing simplicity of using this technology, such as the availability of all-in-one systems, should lead to even wider circles of use.

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