Isolation Of Lignosulfonate By Using Column Chromatography

Lignin is the renewable natural polymer with the characteristic of abundant, cheap, innoxious and complicated structure. Lignosulfonate is a kind of anionic surfactant which has been widely used in various industrial fields. However, the utilization of lignosulfonate has been limited due to its wide molecular weight distribution and complex structure. There are great differences in the structure and performance of lignosulfonate with different molecular weight. It is of very significance to obtain lignosulfonate with low polydispersity index for investigating its characteristics and hence providing the theonetical basis for the efficient utilization of lignosulfonate.In this work, the column chromatography was used to purify lignosulfonate, and the process variables of column isolation of lignosulfonate were investigated. The results show that the sephadex LH-20 column exhibits a good isolate effect to the lignosufonate with the molecular weight less than 6000 Da, and the polydispersity of around 1.1 of isolated products. The monodispersity lignosufonate, as low as 1.042, can be obtained by two-step purification with sephadex LH-20 column system. Sephacryl S-100 shows a good isolation effect to the lignosulfonate with wide molecular distribution. Lignosufonate fraction with polydipersity of around 1.2 can be obtained by using sephacryl S-100 column system. The optimal process variables for small sephacryl S-100 column are as follows: mobile phase is 0.2 mol/L NaCl, elution rate is 0.6 mL/min and injection volume is 2mL. The optimal lignosufonate isolating conditions for big sephacryl S-100 column are as follow, mobile phase is 0.2 mol/L NaCl, elution rate is 5 mL/min and injection volume is 15mL.The structural characterizations of isolated lignosulfonate show that there is relative higher syringyl unit content and lower guawyl unit in the lignosulfonate with lower molecular weight. The content of S element decreases with the increase of molecular weight of lignosulfonate. The content of sulfonic group of samples LS1 is 1.52 times to that of LS5. There are more content of ether linkages and aromatic groups and lower content of methyoxyl group in the lignosulfonate with higher molecular weight. TG-DSC results show that the thermal stability of lignosufonate enhance with the increase in molecular weight of lignosulfonate fraction, sample LS5 presents the best stability. Lignosulfonate with low molecular weight show poor dispersibility to pesticide suspension, and the dispersity and stability effects of lignosulfonate to pesticide suspension increased with the increase in molecular weight. However the disperxive effects became poor when the molecular weight of lignosulfonate is more than 30,000 Da Dynamic scattering results show that Rg value measured of lignosulfonate changs with the change of scattering angles. Form-factor fitting results indicate that lignosulfonate present the association behaviors of polydisperse coil in solution with the concentration of 0.2050 to 0.8070 g/L.