The waste problem in the chemical industry requires new, environmentally friendly solutions. The combination of mechanochemistry with continuous extrusion represents a promising approach.
The increasing problems with waste disposal in the chemical industry call for sustainable solutions. One particularly promising strategy is mechanochemistry, a process that has proven effective in a wide range of chemical applications. Mechanochemical reactions are environmentally friendly, as they often do not require solvents, achieve high yields, and enable short reaction times. Currently, mechanical energy is mostly supplied by ball milling, which is an established process but is limited to small production volumes. Scaling up to industrial levels has been a challenge so far. To overcome this bottleneck, continuous reactive extrusion is increasingly coming into focus. It offers the potential to transfer mechanochemical processes into industrial practice in an efficient, continuous, and resource-saving manner.
Viviene Chantrain is conducting research on this topic as part of Prof. Dr. Borchardt's team at Ruhr University in Bochum: «We are convinced that mechanochemistry will make an important contribution to the further development of the chemical industry toward the sustainable use of resources and energy. However, since the production capacities of most ball mills are limited for safety reasons, the extruder offers an easily scalable and continuous method.»
Using a Three-Tec ZE 12 extruder with an L/D ratio of 40:1, Viviene Chantrain and her team developed the first direct mechanocatalytic reaction protocol for the Suzuki-Miyaura reaction* in an extruder. By coating the screws or cylinder of the extruder with a thin layer of palladium, they were able to carry out cross-coupling reactions continuously, without solvents and without the addition of molecular or powdered catalysts.
The study highlights the delicate interplay of key process parameters such as temperature, mechanical energy input, residence time, rheology, and catalyst contact time. Targeted optimization of these parameters resulted in product yields of 36% % and 75% %, respectively, with longer reaction times. The extruder and the support provided by Three-Tec impressed Viviene Chantrain in her work: «For me, the Three-Tec extruder stands out in particular for its user-friendly and flexible design, as this allows us to use many different synthesis methods or run cascade reactions. When using it, you can clearly see how well thought-out the design of the extruder is, especially in the details. Three-Tec was always helpful when we had problems or questions. Even with our unusual special parts and very specific problems, we were always taken seriously and given competent and friendly advice.»
The results of the research make a significant contribution to the further development of mechanocatalysis into a continuous, scalable, and industrially viable process. Looking to the future, the aim is to make mechanochemistry more attractive for industrial production. In particular, this will be achieved through further ball mill protocols that are adapted for the extruder based on the trends shown (e.g., amide bond formation, Buchwald-Hartwig coupling, Dakin reaction, Michael addition, Heck reaction, or Friedel–Crafts reaction). At the same time, geometric scale-up to larger extruders/screws for the required reaction mixtures and their sometimes unfavorable rheology, as well as the exact influences of the various kneading elements and their number, should also be further investigated.
Here You can find the complete paper «Continuous Direct Mechanocatalytic Suzuki-Miyaura Coupling via Twin-Screw Extrusion.».
| Viviene Chantrain wrote her master's thesis on «Mechanochemical synthesis by extrusion.» She is currently a doctoral student at Ruhr University in Bochum, where she continues to conduct research on «Scalability and sustainability of mechanochemical processes.». |
* The Suzuki-Miyaura reaction is a chemical reaction that allows two organic molecules to be linked together by a C-C bond. The reaction connects a molecule containing a boron atom to another molecule containing a halogen atom such as bromine or iodine. A palladium catalyst is necessary for this coupling to proceed efficiently. It accelerates the reaction and enables the connection under mild conditions. In addition, a base is added, which is necessary for the catalysis cycle. The result is a new, often more complex molecule in which two carbon groups are directly linked to each other. The Suzuki-Miyaura reaction is one of the most important methods in modern organic chemistry due to its reliability and versatility. It is frequently used in pharmaceutical research, in the manufacture of active ingredients, and in materials science.