Providing CO2 by pressure-swing chemical absorption: Ionic liquid-based CO2 separation technology

Introduction
CO2 separation from gases with the aim of further utilization (carbon dioxide capture and utilization, CCU) is a vivid field of research where also the use of ionic liquids (IL) as solvents has been discussed. State-of-the-art processes for chemical absorption of CO2 mainly use aqueous solutions of amines. However, these processes generally suffer from the high thermal energy demand for CO2 desorption at elevated temperature. Recently, we have presented a new absorption process based on IL, which allows for efficient separation of CO2 in biogas upgrading. Contrary to other approaches, key feature of this process is the regeneration of the solvent at reduced pressure. Owing to the negligible vapour pressure of IL, evaporative loss of solvent is avoided. The quasi-isothermal process design results in a distinctly reduced energy demand (ca. 50 %) compared to conventional chemical scrubbing systems.
Results
In this contribution, we give an overview over physico-chemical characterization data of different ILs relevant for CO2 absorption. To test promising IL candidates under realistic, i. e. continuous conditions, a mini-plant was developed. ... mehrWe will present details of the mini-plant design and results of its operation under quasi-isothermal conditions. Absorption and desorption were carried out at a constant temperature of only 80 °C while pressure was reduced in the desorption step from ambient pressure to typically 40 to 100 mbar. Promising results from an experimental campaign at a German biogas plant illustrate that the system achieves constant performance over more than 100 h under real gas conditions. The versatility of the approach is demonstrated in the light of two recent research projects. In the framework of the European research project RECODE (“Recycling carbon dioxide in the cement industry to produce added-value additives”), integration of the technology in a pilot plant is currently prepared to provide CO2 from flue gases for further chemical utilization on-site [https://recodeh2020.eu/]. Here, upscale of the system to pilot scale with the target amount of treated flue gas of 50 m3/h is planned.