Lignin purification from poplar hydrolysis rest: A sub-product from a bioethanol pilot plant

Within the European H2020 project REHAP, lignin has been purified from a solid poplar hydrolysis rest obtained from BIOCHEMTEX after their improved pilot production of bioethanol. The aim in the project is to develop an industrial scalable process, to obtain lignin for further transformation into a high value product, such as cement superplasticizer. As the main sub-product is the solid residue enriched in cellulose, that will be hydrolyzed to glucose and tested for the fermentability. The optimized simple and mild lignin extraction method used 1M NaOH at 90°C for three hours to solubilize most of the lignin content in the hydrolysis rest. Thereafter, sulfuric acid was added to acidify the solution to pH 1.5, then the reaction was heated to 70°C and kept at that temperature for 1h. During all the procedure the stirring was maintained giving a flocculated lignin product, easy to filter and wash with water. After drying in a ventilated oven at 80°C a free flowable light brown powder was obtained. The dry weight yield of purified lignin was 54.5% when starting with 69.3% initial Klason lignin content and 30% yield was obtained when the starting material Klason lignin was 53%. The purified lignin was characterized by GPC, ATR-FTIR and 31P-NMR. Further upscaling of the method is planned at the project partner's site Bio Based Europe Pilot Plant in Belgium.