Friederike Stehmann

Decomposition of dimethyl carbonate caused by adsorption onto activated carbon

This contribution addresses the adsorptive cleaning of an exhaust gas released from a Lithium–Ion-battery recycling process. Adsorption in fixed beds is frequently used to clean off gases containing solvents, toxic components, or other contaminates. Well-established short-cut models are available to determine capacity and dynamics of such adsorber beds. However, uncertainties arise if the gas contains unknown trace components or if new components appear due to chemical reaction or decomposition processes. In the present study, the off gas mainly consists of dimethyl carbonate in a nitrogen gas stream. Dimethyl carbonate decomposes when contacted with activated carbon. The decomposition product methanol co-adsorbs together with dimethyl carbonate onto activated carbon and therefore decreases the adsorption capacity for DMC. This paper shows the influences of temperature, residence time, carbon mass and water on the decomposition of dimethyl carbonate. Additionally, first results of fixed-bed experiments including temperature profile and breakthrough curve are discussed to show the effect of decomposition occurring in fixed-bed adsorption.

Separation of the Electrolyte—Thermal Drying

The recycled lithium-ion batteries are shredded to access value components for further processing. The material that has been shredded before must be dried. This is important not only because of the simplified separation of dry material, but also due to safety issues. A material loaded with electrolyte will be surrounded by a gaseous atmosphere loaded with electrolyte. Such a mixture of electrolyte and air has an environmental impact and can build an explosive atmosphere. Therefore, undried material requires gas tight as well as explosion protected equipment. Drying can be achieved by high temperature, low pressure and rinsing with inertization gas. To support process design and optimization, the influence of each parameter and advantageous parameter combinations can be determined with a flow sheet simulation. However, experimental investigations are required to verify simulation data and to identify critical aspects regarding handling of the material. This chapter discusses application and results of a flow sheet simulation as well as experimental investigations on drying.

Off Gas Cleaning by Adsorption

Some process steps in the recycling process containing a significant amount of volatile organic compounds, such as shredding and drying, need to be inertised by flushing with dry nitrogen. Consequently, the off gas of this inertization is loaded with electrolyte or extraction solvents. Due to environmental restrictions, this off gas has to be cleaned before it is released. This chapter addresses the off gas cleaning with adsorption onto activated carbon and gives a basic understanding of the operation mode of a fixed bed adsorber and the database to design an adsorptive off gas cleaning. Relevant data of adsorption equilibria of single as well as binary mixtures of electrolyte components onto activated carbon at temperatures from 20 to 60 °C are presented. Additionally, binary equilibria were calculated with the Ideal Adsorbed Solution Theory and compared to experimental results. Finally, results of the adsorption in a fixed bed are discussed. Breakthrough behavior and temperature profiles of the adsorption process are presented and compared to the adsorption equilibria. Another focus is set onto decomposed electrolyte components that may occur during the lifetime of a battery, the recycling process and the adsorption itself. These decomposition products can affect the adsorption equilibrium and therefore have to be considered.