A reactor with a good energy balance

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Reactions in the chemical industry typically consume large amounts of energy. That may soon be about to change. With the help of Evonik scientists, one group of researchers has developed a new method that makes a major, large-scale reaction up to 70 percent more efficient.

TEXTNADINE NÖSLER

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Up to now it has been accepted as a virtual law of the chemical industry: if you’re running a catalytic reaction, you have to choose between homogeneous and heterogeneous catalysts. Unlike their heterogeneous counterparts, homogeneous catalysts are dissolved in the reaction medium, which is why their reactions are more active and selective, and why they work at relatively low temperatures. The problem? After the reaction is complete, they have to undergo a second, highly energy-intensive step to separate and recover them from the resulting product. This is why, despite the advantages of homogeneous catalysis, researchers prefer to use a heterogeneous alternative wherever possible—a solid catalyst, in other words, that does not mix with the reactant. The reason is that the lower amount of energy required for separating the catalyst from the solvent outweighs the demonstrable benefits of homogeneous catalysis.

Now, however, a research group led by Evonik expert Dr. Robert Franke has solved this problem and united the best of both catalysis worlds—by developing a new concept for a reactor that merges reaction and separation of the catalyst within a single process step. The result is something of a 2-in-1 reactor made exceptionally energy efficient thanks to the use of a membrane.

The team of researchers hopes that the reactor will allow them to revolutionize the hydroformylation process. Hydroformylation is an industrial-scale reaction that combines olefins and syngas to form aldehydes, which then serve as precursors for compounds such as the alcohols used in pharmaceuticals, detergents, surfactants, and plasticizers. The process generates roughly 12 million metric tons of products each year.

Dr. Robert Franke (l.) is the project manager for ROMEO and leads the hydroformylation research in Evonik’s Performance Intermediates Business Line.

INTERNATIONAL COLLABORATION

Nine partners from science and industry have come together to develop their competencies as part of ROMEO, an EU-sponsored project whose name stands for Reactor Optimization by Membrane-Enhanced Operation. In the new membrane reactor, the desired product is continuously discharged from the reaction mixture. What makes this possible is an external membrane attached to a monolith—a cylinder of sorts whose interior surface is coated with catalyst. This setup keeps the catalyst on the monolith, while the reaction product is removed through the membrane, thus eliminating the need for the energy-intensive process of separating the reaction product in a distillation column.

While the principle sounds tantalizingly simple, there are a number of complications—beginning with the properties of the carrier, catalyst, and membrane, and extending to the modular structure of the reactor, which allows researchers to scale up the system quickly so that it can be implemented, for example, in an industrial production plant. “Overcoming these challenges meant having to merge a number of technologies,” explains Franke, who heads hydroformylation research in Evonik’s Performance Intermediates Business Line . “That made it important for us to find experts from various fields dealing with chemical reactions and reactor technologies and bring them together for a joint project.”

Two of these experts are Dr. Rasmus Fehrmann, a professor at the Technical University of Denmark, and Dr. Peter Wasserscheid, the chair of Chemical Reaction Engineering at the University of Erlangen/Nuremberg (Germany). Under Fehrmann’s direction and in collaboration with other researchers, these scientists were the first to demonstrate, back in 2003, how hydroformylation can succeed using a specialized catalyst—one that does not dissolve in the product—in what is called a fixed-bed reactor. Known as supported ionic liquid phase (SILP) catalysts, these homogeneous catalysts are dissolved, applied on a carrier, and then used in reactions in this solid format. The method “immobilizes” the highly selective, homogeneous catalyst, in other words turning it into a heterogeneous catalyst.

“It was clear to me that I needed to bring Fehrmann on board to improve hydroformylation,” Franke recalls. The Danish researcher was excited when Franke reached out to him: “While we pursue basic research at the Technical University, we also want our work to effect change in industry,” says Fehrmann. “But in order to study and ultimately demonstrate that our findings can be implemented on a large scale, we still need a powerful partner in the industry.”

The monolith is a sort of a cylinder whose interior surface is coated with a catalyst.

DEMONSTRATING BROAD INDUSTRIAL APPLICATIONS

Taking SILP catalysts from the lab to an industrial plant required additional, extensive research. The team had to find a suitable carrier, for instance, and monoliths from the Danish firm LiqTech lent themselves well to this purpose. “So more and more partners kept coming together. And we were all sure of one thing: this is an area where we can pull off a mini-revolution in chemical process engineering and take a major step toward more sustainable processes,” Franke explains.

In order to move forward with their research, the scientists applied to the EU’s Horizon 2020 research and innovation program. And they succeeded: the project immediately landed among the top 15 percent of all of those submitted—and received €6 million in funding. “That inspired us even more,” says Franke.

Once the team had successfully combined membrane, catalyst, and carrier material in a laboratory-scale reactor module, the Evonik researchers conducted a long-term study (lasting over 5000 hours) at the hydroformylation miniplant in Marl. The findings from the study included proof that the catalyst does not lose its reactivity after downtimes. That was a major milestone on the road to industrial-scale application. “We were able to demonstrate here that our concept can reduce energy consumption in hydroformylation reactions by up to 70 percent,” says Franke. “We finally made the breakthrough.” He also assumes that the membrane reactor is capable of saving even more energy: “Right now we’re focusing on developing the technology further. Our goal is to use the new technology regularly in our production.”

In order to transfer the reactor concept to an industrial scale, the researchers are designing a reactor with 100 monoliths—instead of the seven used in the pilot plant. If this step is successful, then the concept could also conceivably be applied in other catalytic reactions as well.