Efficient extraction of lignin from black liquor via a novel membrane-assisted electrochemical approach

摘要

A novel membrane-assisted electrochemical approach for the precipitation of lignin from black liquor has been developed. Without the addition of acid or CO_2, the pH in the black liquor solution was lowered to 4.7 due to water electrolysis, leading to pH-dependent lignin precipitation. Simultaneously, Na~+ ions traversed the membrane to the cathode compartment to balance the OH~- that was generated in the cathodic reaction, facilitating caustic recovery. Owing to lignin precipitation and oxidation, greater than 70% of the chemical oxygen demand (COD) was removed, which surpasses the efficacy of COD reduction via conventional acidic precipitation. In addition, it has been demonstrated that the pH change was significantly influenced by the electrolyte condition in the system. With decreasing cation concentration in the cathode compartment, Na~+ transport through the membrane was facilitated, which inhibited competitive H~+ transport and improved the performance of the electrochemical cell. This novel approach may serve as a promising alternative for the cost-effective extraction of lignin and recovery of NaOH from the black liquor with modulation feasibility.