Continuous Production of High-Purity NaHCO3 via Carbonation of NaOH: Thermodynamic Analysis and Two-Stage Reactor Design

Abstract This study established a high-purity continuous production system for NaHCO3 via NaOH carbonation. Using simulated flue gas containing CO2 and NaOH solutions, the reaction mechanism was elucidated through real-time monitoring of pH and electrical conductivity, revealing four distinct reaction stages. Evaluation of reaction parameters and thermodynamic analysis using the Na2CO3–NaHCO3–H2O ternary phase diagram revealed that NaOH concentrations of 20 wt % and above induce metastable byproducts such as Trona and Na2CO3, thereby degrading the purity of the NaHCO3 product. Conversely, a concentration range of 10–15 wt % was identified as the favorable regime for selectively precipitating pure NaHCO3. Based on these findings, a continuous production system consisting of two reactors in series was designed to address the kinetic disparity between the rapid carbonate formation (Stage 1) and the slower bicarbonate formation and crystallization (Stages 2–4). Under the selected conditions of 15 wt % NaOH at 25 °C, the continuous process achieved stable steady-state operation, yielding high-purity NaHCO3 with a production capacity of 0.72 kg h–1 corresponding to a volumetric productivity of 0.36 kg L–1 h–1 based on the total 2 L liquid volume of the two-stage reactor system. This study not only provides theoretical insights into the byproduct formation mechanism but also demonstrates the feasibility of industrial-scale utilization of CO2 for producing high-value carbonate minerals.