THE DIRECT ROUTE

But back then Jaeger had not come up with a practical approach to a solution, so he merely left a note about his project in the in-house database. In this memory bank of ideas, Evonik researchers save suggestions for which they don’t yet see a possible technical implementation, but which they hope will someday be found by someone.

While Wiederhold, a chemist, was reading Jaeger’s note, he suddenly realized how this chemical synthesis could work. “That was the starting point of HYPROSYN™,” he says. The project for developing the cost-effective and sustainable direct synthesis of propylene glycol has been conducted by the Active Oxygens Business Line in the laboratories of process technology since 2013.

The demand for propylene glycol is huge, and it’s growing by 2.5 percent annually. This compound is used in antifreeze, lubricants, fiberglass-reinforced plastics, cleaning and washing products, and latex wall paints. It’s also indispensable for the food industry. It gives chewing gum the right consistency, makes baked goods soft, and keeps packaged foods moist. Livestock farmers use it to treat metabolic disorders of their dairy cows. “Propylene glycol has developed into an all-round bestseller,” says Thomas Bode, who is responsible for HYPROSYN™ technology at Evonik. Today about two million tons of propylene glycol are processed annually worldwide. In order to meet the growing demand, developers have been working for years to find new solutions.

At Evonik, a core team of four colleagues set out to develop a new process for synthesizing propylene glycol. “In order to refine this process, we needed the support of additional colleagues from a whole range of different areas,” explains Wiederhold. Many colleagues from all over the Group contributed their know-how to this development process.

Previously, the first step in the production of propylene glycol had often been the production of propylene oxide. In order to manufacture this precursor product, Evonik cooperated with thyssenkrupp from 2000 on to develop the HPPO process. This acronym stands for “Hydrogen Peroxide to Propylene Oxide.” In 2008 this process was licensed for the first time for a production plant in South Korea, which today is turning out more than 130,000 tons of propylene oxide annually. By contrast to traditional synthesis methods, which require substances such as chlorine or benzene, this process requires only propylene and H2O2, which is supplied by Evonik. The only byproduct of the process is water.

The intermediate product propylene oxide is in high demand. One fifth of the total production volume is used to synthesize propylene glycol. Two thirds of the total production volume are processed into polyether polyols, which are then processed via intermediate steps into polyurethane (PU) products such as construction foams and paint bases. The remaining propylene oxide is used as a starting material for producing other valuable chemicals. The demand for propylene oxide has recently grown even faster than that for propylene glycol, by about four percent to approximately 11 million tons.

One way to continue meeting this demand in the future would be to build additional propylene oxide production plants. However, each of these plants would cost hundreds of millions of euros. Alternatively, researchers could search for innovative solutions that simultaneously open up new applications for environmentally friendly hydrogen peroxide. “We considered the second alternative much more attractive,” says Wiederhold, who headed the project.

The key to success, which helped Wiederhold achieve a breakthrough, was a newly developed catalyst system. Thanks to this, it is now possible to generate propylene glycol in a single reaction between propylene and hydrogen peroxide—without the intermediate step of propylene oxide. In general, a catalyst system makes a chemical reaction easier and faster. The special charm of this particular solution is that some of the components of the new catalyst were already used in other chemical processes at Evonik. “The combination of different input materials, together with special technical processes, ensures that the catalyst remains stable over a long period of time,” says Wiederhold. “In addition, it transforms the basic materials propylene and hydrogen peroxide in a process that is especially efficient and energy-conserving.”