Spinning Disk Reactor Reveals Potential

Smaller reactor could increase the safety of chemical production processes

By Seán Ottewell, Editor at Large

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Spinning disk reactor (SDR) technology and its variations have been discussed on and off for many years now.

For example, the May 27, 2000, issue of Industrial and Engineering Chemical Research contained an article that evaluated SDR technology for the manufacture of pharmaceuticals. Co-authored by engineers from SmithKline Beecham Pharmaceuticals R&D, Tonbridge, U.K., and the Centre for Process Intensification and Innovation, University of Newcastle upon Tyne, U.K., the article states that a continuously operating SDR displayed distinct advantages over batch processing techniques used in commercially relevant processes for pharmaceutical manufacturing.

New reactor shows promise for processes where conversion and selectivity are important.

The engineers described very encouraging results for a reaction to prepare a drug intermediate and for recrystallization of an active pharmaceutical ingredient. In comparison to batch processes in use at the time, the drug intermediate reaction enjoyed a 99.9% reduced reaction time, 99% reduced inventory and 93% reduced impurity level (see Industrial and Engineering Chemical Research 2000, 39 (7), pp 2175–2182).

Since then, others have tried variations on the SDR — for example, the spinning tube in a tube (STT) reactor mentioned in "Tiny Reactors Aim for Big Role."

Now, SDR technology gets another boost with a novel version developed by researcher Marco Meeuwse of Eindhoven University of Technology (TU/e), The Netherlands.

Meeuwse's technology features a cylinder containing a rotor that increases the safety and efficiency of chemical production processes involving gases, liquids and solids through its very high mass-transfer rate. This new reactor is particularly beneficial for the pharmaceutical and fine chemical industries.

The idea came from Meeuwse's co-supervisor, assistant professor John van der Schaaf. Based on his observations of an earlier research project, Van der Schaaf thought combining the rotating disc with a nearby wall would create high shear stress and rapid turbulence, leading to higher efficiency. He asked doctoral candidate Meeuwse to investigate whether this was true.

Four years later, Meeuwse can state without hesitation that the newly developed reactor does exactly what was expected of it. "In fact it does even more," says Meeuwse. "We were sure it would perform better than the conventional reactors, but we didn't expect it to be so much better."

Gas is fed into the reactor through the floor of the cylinder, with the rotating disc located just above it. The high-speed flow of rotating liquid shears off the gas bubbles as they pass through.

"The higher the rotational speed, the smaller the bubbles and the larger the surface area," explains Meeuwse. "That translates into a higher rate of reaction and mass transfer. That was confirmed every time by analyses of the images of the gas/liquid flow and the mass transfer measurements."

Meeuwse scaled-up the principle using a series of rotating discs. Three discs each with a diameter of 13 cm were mounted on a shared spindle in a cylinder. "If each unit does the same thing, the total mass transfer of the three discs in series should also be three times as great. Our measurements clearly showed that this reasoning was true, providing the proof that we can scale the system up."

Because the reactor is much smaller than conventional ones, it's considered to be much safer — a big advantage in processes using hazardous substances.

Further development of the reactor currently is in full swing, and a number of related PhD projects are in progress at TU/e. A major equipment manufacturer has become involved, and several chemical and pharmaceutical companies also have shown interest.

Meeuwse explains: "We know that this reactor is better than the conventional types. We have measured improvements by factors ranging from two to ten, but we haven't yet been able to identify the full potential of the new concept."

Is there a big market for this new type of reactor? "It is definitely usable for processes in which conversion and selectivity are important factors, such as in the pharmaceutical industry," says Meeuwse. "The raw materials for medicines are very costly, so the less you need to purify the products afterwards, and the less waste you throw away, the more rewarding it will be to use our reactor. In terms of volume it may not be a big market, but on the other hand the processes concerned have a high added value."

Seán Ottewell is Chemical Processing's Editor at Large. You can e-mail him at sottewell@putman.net.

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