Evonik is driving forward the green transformation with electrodialysis

Electrochemical process converts salts into valuable raw materials

24-Sep-2024

With the help of electrodialysis, salts that are produced in many chemical processes can be separated and converted back into their valuable raw materials, using electricity. The technology is being tested in the pilot plant at Evonik's Hanau site.

Evonik Industries AG

Evonik is researching to make electrodialysis available on an industrial scale for the green transformation of the chemical industry. Scientists anticipate improved access to key raw materials on a circular basis and simpler and more efficient processes that require fewer raw materials. With the aid of electrodialysis, salts that occur in many chemical processes can be separated and reprocessed into valuable starting products. Evonik is currently expanding its activities in the field of electrochemistry. In the next five years, the company will be investing an amount in the low double-digit millions of euros in its electrochemical processes & products platform. Around 20 employees are working on this in Hanau (Germany) and Shanghai (China).

Patrik Stenner, an Evonik expert for electrochemical processes and products, sees enormous potential. “We estimate that electrodialysis can help us make around 20 percent of our processes more efficient and environment-friendly.” That includes reduced energy consumption, reduced use of raw materials, less CO2 emissions, and lower environmental impact, for example, by salt loads. At the same time, Stenner sees specific economic benefits: “Depending on raw material and electricity prices, recovering raw materials from salt loads makes financial sense.”

Salts are produced, for example, when adjusting the pH, a key step in many chemical processes. The pH describes how acid or alkaline a solution is and can be adjusted by adding alkaline solutions or acid.

Using electrodialysis, raw materials such as caustic soda and sulfuric acid can now be recovered from the resulting salts, such as sodium sulfate, even in highly dilute solutions. Initial estimates based on life cycle analyses show that the carbon footprint of caustic soda recovered in this way is about two-thirds lower than that of conventionally produced caustic soda. A further significant improvement is achieved by using green electricity for electrodialysis. Evonik’s engineers are taking this a step further: In the future, they want to completely avoid the use of alkaline solutions and acids to set the pH; instead, they aim to set the pH directly via electrodialysis.

Electrodialysis has already been used in the food industry for about 20 years to regulate the acid content of juices and wine. Its mode of action has been known for a long time. An electric current in an electrolysis cell causes migration of the salt ions dissolved in water. In the case of sodium sulfate, for example, the positively charged sodium cation migrates to the negatively charged cathode. The negatively charged sulfate anion is attracted to the positively charged anode. Thanks to a sequence of bipolar ion exchange membranes, the cations and anions can now be separated and concentrated. At the same time, the electric current splits the water into protons (H+) and hydroxide ions (OH-), which can then also be separated with the aid of the bipolar ion exchange membrane. In this way, sodium sulfate and water can produce caustic soda and sulfuric acid.

“The challenge for us is industrial-scale realization of electrodialysis,” explains Stenner, a process engineer who is a group leader in the Process Technology unit. Stenner: “A standard process for the chemical industry is still a long way off. There are not yet any off-the-peg plants.” The technology needs to be aligned to each application and the substance to be separated. Another challenge according to Stenner is the membrane itself and its service life.

Evonik’s process technology experts are working on industrial-scale realization and driving forward solutions for specific production processes. Here is an example: One process step in the production of isophorone diamine, which is used in wind turbines, generates ammonium sulfate. In the future, electrodialysis could be used to recover the ammonia and sulfuric acid. Initial trials in a pilot facility are promising.

Another example is the production of precipitated silica, which is used in energy-saving tires. Some of the acids and sodium-containing lyes and salts used in this process could be used in a closed cycle with the aid of electrodialysis. Evonik is examining whether this technology could be used in a demonstration plant next year. This would allow the generation of the data needed to scale up the process for production. The aim is repeated use of raw materials that have a significant carbon footprint, which would help customers in the tire industry achieve their sustainability targets.

Evonik has bundled its group-wide expertise in electrochemical processes in a technology platform. In addition to electrodialysis, scientists are working, for example, to produce carboxylic acids from bio-based materials. They are also developing materials to enhance the efficiency of electrochemical methods such as the electrolysis of water to produce green hydrogen. Stenner: “The platform for electrochemical processes & products brings together key technology that is driving forward the transformation of the chemical industry towards climate neutrality and increased sustainability.”

https://www.chemeurope.com/en/news/1184500/evonik-is-driving-forward-the-green-transformation-with-electrodialysis.html