Chlorine (Cl₂) is one of the most important base chemicals in the world and is used industrially for the production of numerous materials such as polymers, drugs and agrochemicals. To meet the global demand for chlorine, it is produced worldwide at a rate of over 90 million tons per year. In Germany, about 5.5 million tons of chlorine are produced, mainly by chlor-alkali electrolysis. This consumes about 2.5% of the German electricity (about 7% in NRW) per year.

Currently, the production of chlorine by chlor-alkali electrolysis is highly dependent on base-load electricity. Although chlor-alkali electrolysis is in principle adaptable to electricity fluctuations, most downstream processes that use chlorine are not. To produce chlorine with renewable energy, intermediate storage of the chlorine is useful. Usually chlorine is stored by pressure liquefaction, which is problematic and energy consuming and therefore mostly avoided. Another problem is the transport of pressure-liquefied chlorine, e.g. by rail, especially if this leads through heavily populated areas.

In recent years, the AG Riedel has developed a new type of chlorine storage based on so-called polychlorides, which, in contrast to the usual pressure liquefaction of chlorine, offers a better safety profile. With this new storage material, the current restrictions on the storage and transport of chlorine could be overcome, so that renewable energies can be used more efficiently and a flexibilization of the chlorine industry can be achieved.

Newspaper: Tagesspiegel article about Chlorine-Chemistry Oktober 2023.

Wikipedia pages for polychlorides

[NEt₃Me][Cl₃]

[NEt₄][Cl₃]

Publications and Patents

• The Rise of Trichlorides Enabling an Improved Chlorine Technology - M. Kleoff, P. Voßnacker, S. Riedel Angew. Chem. Int. Ed. 2023 e202216586

• Alkyl Ammonium Chloride Salts for Efficient Chlorine Storage at Ambient Conditions - P. Voßnacker, N. Schwarze, T. Keilhack, M. Kleoff, S. Steinhauer, Y. Schiesser, M. Paven, S. Yogendra, R. Weber, S. Riedel ACS Sustainable Chemistry & Engineering, 2022, 10, 9525.

• Novel Synthetic Pathway for the Production of Phosgene - P. Voßnacker, A. Wüst, T. Keilhack, C. Müller, S. Steinhauer, H. Beckers, S. Yogendra, Y. Schiesser, R. Weber, M. Reimann, R. Müller, M. Kaupp, S. Riedel Science Advances 2021, 7, 40: eabj5186

• Storage medium and a method of separating, storage and transportation of chlorine derived from chlorine-containing gases; Paven, Maxime; Schiesser, Yuliya; Weber, Rainer; Langstein, Gerhard; Trieu, Vinh; Hasenstab-Riedel, Sebastian; Schwarze, Nico; Steinhauer, Simon PCT Int. Appl (2018), WO 2019215037 A1. (Patent)

• Method for releasing chlorine gas from polychloride-based storage media by means of chlorine-releasing agents and use in chemical reactions; Paven, Maxime; Schiesser, Yuliya; Weber, Rainer; Bramer-Weger, Elmar; Yogendra, Sivathmeehan; Hasenstab-Riedel, Sebastian; Steinhauer, Simon; Keilhack, Thomas PCT Int. Appl. (2021), WO 2021069757 (Patent)
  

• Verfahren zur Herstellung von Phosgen durch Umsetzung von Polychlor-Anionen und Kohlenstoffmonoxid (2020), EP20213933.3 (Patent)

• Phosgensynthese durch Umsetzung eines Chlor und Kohlenstoffmonoxid enthaltenden Gasgemisches an organischem, Chloranion-haltigen Katalysator (2020), EP20213938. (Patent)

Further Publikations on Polychlorides and Applications

• Synthesis of a Hexachloro Sulfate(IV) Dianion Enabled by Polychloride Chemistry - Patrick Voßnacker, Alisa Wüst, Carsten Müller, Merlin Kleoff, Sebastian Riedel Angew. Chem. Int. Ed. 2022 e202209684, VIP Paper

• From Missing Links to New Records: A Series of Novel Polychlorine Anions - Patrick Voßnacker, Thomas Keilhack, Nico Schwarze, Karsten Sonnenberg, Konrad Seppelt, Moritz Malischewski, Sebastian Riedel Eur. J. Inorg. Chem. 2021, 1034, VIP Paper

• Insights in the topology and the formation of a genuine ppσ bond: Experimental and computed electron densities in mono anionic trichlorine [Cl3]− - Helena Keil, Karsten Sonnenberg, Carsten Müller, Regine Herbst-Irmer, Helmut Beckers, Dietmar Stalke, Sebastian Riedel, Angew. Chem. Int Ed. 2021, 60, 2569

• Conductivity and Standard Potentials of the Ionic Liquid Trihalogen Monoanions, [X3]– and [XY2]–, [BrF4]–, X = Cl, Br, I and Y = Cl, Br - Tyler A. Gully, Patrick Voßnacker, Jonas R. Schmid, Sebastian Riedel, ChemistryOpen 2021, 10, 255

• Poly- and Interhalogen Anions from Fluorine to Iodine Karsten Sonnenberg, Lisa Mann, Frenio A. Redeker, Benjamin Schmidt, Sebastian Riedel, Angew. Chem. Int. Ed. 2020, 59, 5464 (Review)

• Beyond the limit: Investigation of large polychloride anions [Cl₁₁]⁻, [Cl₁₂]²⁻ and [Cl₁₃]⁻ - Karsten Sonnenberg, Patrick Pröhm, Nico Schwarze, Carsten Müller, Helmut Beckers, Sebastian Riedel, Angew. Chem. Int. Ed. 2018, 9136

• Matrix-Isolation and Comparative Far-IR Investigation of Free Linear [Cl₃]⁻ and the Series of the Alkali Trichlorides - Frenio A. Redeker, Helmut Beckers, Sebastian Riedel, Chem. Comm., 2017, 53, 12958

• Structural Proof for the First Dianion of a Polychloride: Investigation of [Cl₈]²⁻ - Robin Brückner, Patrick Pröhm, Anja Wiesner, Simon Steinhauer, Carsten Müller, Sebastian Riedel, Angew. Chem. Int. Ed, 2016, 55, 10904

• A 2D Polychloride Network Glued by Halogen-Halogen Interaction - Robin Brückner, Heike Haller, Simon Steinhauer, Carsten Müller, Sebastian Riedel Angew. Chem. Int. Ed. 2015, 54, 15579

• Recent discoveries of polyhalogen anions – from bromine to fluorine - Heike Haller, Sebastian Riedel Z. Anorg. Allg. Chem. 2014, 640, 1281 (Review)