Cleaner soda ash production: A techno-economic assessment of electrochemically-based alternatives to the Solvay process

• Chlor-alkali-based route cuts energy demand and shows economic potential. • Prices of chlor-alkali by-products (H 2 , Cl 2 ) significantly influence costs. • Electrodialysis currently offers no economic advantage. • Direct use of by-products improves viability of electrodialysis-based processes. • Energy demand and CAPEX are the main cost drivers. Although environmentally friendly alternatives to the conventional Solvay process for Na 2 CO 3 production have been known for some time, they have not yet been widely adopted in the industry. A systematic evaluation of their energy demands and costs remains limited. In this work, six electrochemical alternatives to the Solvay process are thoroughly assessed, focusing on their energy efficiency and economic viability. The investigated processes consider an NaOH production step by chlor-alkali electrolysis or electrodialysis with bipolar membranes, a concentration step with mechanical vapor compression, the carbonization of NaOH with CO 2 in a bubble column, the crystallization of NaHCO 3 or Na 2 CO 3 ·H 2 O and finally the calcination of these solids to Na 2 CO 3 . The results indicate a 14 to 45 % lower energy demand for five of the investigated process configurations in comparison to the conventional Solvay process. Apart from that, it has been found that electricity could replace fossil fuels as the main energy source for Soda production. Under the assumptions of a 25-year plant lifetime and a plant capacity of 1,000 t Na 2 CO 3 per day, the processes based on electrolysis could demonstrate economic viability, with net production costs ranging from 0.31 to 0.37 € kg −1 Na 2 CO 3 . The processes involving electrodialysis tend to have much higher production costs under conservative assumptions. However, sensitivity analyses show that economic viability can be achieved under favorable conditions, such as reduced energy costs and valorization of low-concentration by-product hydrochloric acid.