Simultaneous CO₂ mineralization and organic acid purification via diffusion dialysis process

Organic acids (OA), such as lactic acid and gluconic acids, are the key building blocks in the biorefinery industry, analogous to olefins in the petrochemical refinery process. OAs, produced via fermentation or chemical synthesis, often exist in low-value conjugate base form ion-paired with excess potassium (e.g., potassium lactate and gluconate). In this work, we propose a two-step diffusion dialysis (DD) process — DD-CCU (carbon capture and utilization) and DD-SA (strong acid) — employing a cation exchange membrane (CEM) to selectively exchange K⁺ and H⁺ ions and yield high-value OAs. We screened various CEMs with different backbone structures and concluded that sulfonated polyarylene ether sulfone (SPAES) membranes demonstrate a good balance between backbone rigidity and ion exchange capacity with optimal permselectivity. Moreover, we implemented the DD-CCU strategy for the first time, where CO₂ reacts with K⁺ (from the feed side), exchanged with H⁺ (from the dialysate side), forming KHCO₃ minerals in the dialysate stream, enabling 62.4% protonation of the organic acid in the feed. For the subsequent DD-SA process, the required amount of strong acid (H₂SO₄) was significantly reduced by 80% to achieve quantitative OA protonation. Interestingly, we observed a unique K⁺ transport behavior during the DD-SA operation, where K⁺ migrated against its concentration gradient (low to high K⁺ concentration) without an external electrical potential. Such a peculiar transport mechanism could be explained using the coupled ion-transport mechanism. A thorough techno-economic analysis (TEA) showed that the process profitability heavily depends on the downstream evaporative unit operations, and carbon credit revenue generated from the DD-CCU was marginal with the current carbon price, but we envisage its contribution to expand in the future.