Desalination and lignin concentration in a lignin aqueous solution by nano-filtration process: Advanced γ-Al2O3 film-coated porous α-Al2O3 hollow fiber membrane

Abstract

To remove the main barrier for lignin valorization, which is the development of actual lignin separation technology, we studied the ceramic membrane nanofiltration process using a dense, ultra-thin gamma-Al2O3 film-coated porous alpha-Al2O3 hollow fiber (gamma alpha HF) membrane for the simultaneous separation of alkali metals (Na+, K+, etc) and concentration of lignin from an alkaline media like black liquor with success as an advanced wastewater treatment process. The gamma-AlOOH sol was prepared by sol-gel method and coated by dip-coating on alpha-Al2O3 hollow fiber (alpha HF) support. After calcination at high temperature, the mean pore sizes of the alpha HF support and the gamma alpha HF membrane were found to be 0.2 mu m and 1.6 nm. The rejection rate performance for various salts increased in the following order: Na2SO4<MgSO4<NaCl<KCl<CaCl2<MgCl2<AlCl3. Under the best condition, the removal rate of sodium and potassium ions reached about 92% and 85%, respectively, with 19.34% of the lignin being discharged. The gamma alpha HF membrane presents good performance stability during a five day nano-filtration process.