Sodium Hydroxide-Based CO2 Direct Air Capture for Soda Ash Production─Fundamentals for Process Engineering

Abstract

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 CO2 (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 (KG,CO2), 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 % Na2CO3, 20 °C, and 500 ppm CO2. The effects of NaOH and Na2CO3 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 CO2 DAC process for Na2CO3 production are concluded, in which KG,CO2 decreases with rising temperature while operating at saturated ion concentrations of Na2CO3.