Two processes were developed in the joint project "Improving the efficiency of chlorine production" that reduce both the energy demand and the CO2 emissions of chlorine production. Consumption of the noble metal ruthenium is also decreased with the help of new catalysts.
Chlorine is a key element in the chemical industry and is used directly or indirectly to produce about 65 percent of all chemical products. Approximately 95 percent of the chlorine required is produced via the energy-intensive electrolysis of aqueous solutions of sodium chloride, also partly via the electrolysis of hydrochloric acid (aqueous hydrogen chloride solution). The more energy-efficient alternative of hydrochloride oxidation has not been used extensively up to now (Deacon process).
Catalysts containing noble metals, mainly ruthenium, are needed in both processes. Ruthenium is one of the platinum group of metals and features on the EU’s list of critical raw materials that are subject to particular supply risks. One objective of the project was to develop catalysts which contain either no ruthenium at all or only small amounts in order to become more independent of this rare raw material. The catalysts developed by the group make it possible to significantly reduce or even substitute ruthenium.
Approximately 0.35 tonnes of noble metals (especially ruthenium) are currently used in Germany as catalysts to produce chlorine via the electrolysis of sodium chloride. This demand can be lowered to about 0.08 tonnes due to the new catalysts. Using the Deacon process, it is possible to lower the ruthenium demand by 50 percent. A high-temperature catalyst that does not contain a noble metal was also piloted for this process. In total, the Deacon process can reduce the use of noble metals by 70 to 80 percent, which corresponds to about 0.045 tonnes of ruthenium each year.
The new catalysts additionally reduce the electrical cell voltage by about 50 millivolts during electrolysis, which could result in annual savings of about 250 million kilowatt hours and 0.16 million tonnes of CO2 if these were used throughout Germany. In addition, if all the plants using hydrogen chloride electrolysis were converted to hydrochloride oxidation (Deacon process), around 400 million kilowatt hours of electricity and 0.3 million tonnes of CO2 could be saved.