Sodium Hydroxide-Based CO<sub>2</sub> Direct Air Capture for Soda Ash Production─Fundamentals for Process Engineering
Somayyeh Ghaffari, María Fernanda Gutiérrez, Andreas Seidel-Morgenstern, Heike Lorenz, Peter Schulze
Abstract
High Resolution Image Download MS PowerPoint Slide This work introduces the principles and supplies the first key parameters for replacing the conventional ammonia-soda (Solvay) process with a new environmentally friendly and sustainable process. For this, the absorption of diluted CO 2 (0.0153–1.2 vol %) in carbonated NaOH solutions was experimentally studied in a temperature range relevant for direct air capture (DAC) in the middle Europe (5–20 °C). A dynamic process model was formulated and solved based on the literature parameters. It was found that by refitting the parameters, the average error was reduced from 9.49 to 7.8%. The absorption performance was evaluated using the mass transfer coefficient ( K G,CO 2 ), which is considered as a useful parameter for the future process design. The mass transfer coefficient reaches a maximum amount of about 3 mm/s at around 6 wt % NaOH, 0 wt % Na 2 CO 3, 20 °C, and 500 ppm CO 2 . The effects of NaOH and Na 2 CO 3 concentrations and temperature on the mass transfer coefficient were experimentally and theoretically studied. Considering all effects simultaneously, the design aspects for an efficient NaOH-based CO 2 DAC process for Na 2 CO 3 production are concluded, in which K G,CO 2 decreases with rising temperature while operating at saturated ion concentrations of Na 2 CO 3 .