Black Liquor Lignin Extraction And Antioxidant Activity,

Lignin,one of the main recalcitrant substances in pulping black liquor,is only second to cellulose among the largest natural polymers and has been widely used in agricultural,industrial and pharmaceutical areas.In recent years more attentions have been paid to lignin's bioactivity.Lignin exhibits effective free radical scavenging and antioxidant activity,anti-cancer activity and anti-mutagenic activity at some circumstances,and can improve the utilization of protein in vivo for certain animals. This study focused on lignin extraction from pulping black liquor and the corresponding variations of lignin antioxidant activity.The author firstly tried to investigate the requirements needed for a better antioxidant activity of lignin obtained, and explore a new way for its reclamation.In this paper,the best extraction conditions obtained were pH 2.50,temperature 55℃and extraction time of 3h,under which 16kg/m³ of lignin could be extracted from black liquor with COD removal being 77.30%.Besides,the impacts of extraction conditions on lignin antioxidant activity were investigated in order to obtain the highest antioxidant activity of lignin.The results showed that lignin exhibited the highest antioxidant activity under the extraction conditions of pH 3.50,temperature 55℃and extraction time of 5h,and the highest antioxidant activity was 31635U/g-lignin.These conditions can be realized in ordinary acidification processes of lignin extraction equipments.The results of FTIR analysis indicated that hydroxyls contributed a lot to lignin antioxidant activity.It was also found that the antioxidant activity of lignin could be increased to 87440U/g-lignin after modification with 50%sulfuric acid under 60℃conditions, but alkaline H₂O₂ modification did obviously have opposite impact on the antioxidant activity of lignin.The results of actual chemical consumption and related cost analysis showed that 1kg of lignin extracted from black liquor in laboratory cost about 155 RMB,and the chemical cost was about 755-887 RMB for 1kg of lignin antioxidant.