Isolation And Degradation Of Lignosulfonate

Lignosulfonate(LS) is mainly derived from sulfite pulping spent liquor, so it containslots of impurities, and it has a wide molecular weight distribution and complex structure, allof which limit its utilization as a newable resource. LS is still the mixture with divisefractions of different molecular weight after purification by using conventional separationmethod. As LS fraction of different molecular weight contains different contents offunctional groups, it results in a obviously different performances. Therefore, LS fractionwith a high polydispersity index is considered hindering the research on the relationshipbetween structures and performances of LS, and hence preventing its efficient utilization.LS fractions with narrow molecular weight distribution are obtained by using gelchromatography in this work for providing a guidance to the efficent use of LS.In this work, sephacryl S-100was chosen as the stationary phase, and the influence ofisolation condition such as ionic strength, temperature, hydrogen binding, pH value on theseparation effect was studied. The experimental results showed that when0.2mol/L ofNaCl or NaNO3solution with pH5.7was used as the mobile phase, LS fractions withpolydispersity of around1.2can be obtained by using gel column chromatography underroom temperature. Four isolated LS fractions with different molecular weight were chosento analyze its aggregation in aqueous solution by using fluorescence spectroscopy, and theresults show that the critical aggregation concentrations of LS with different molecularweight of4700Da,9800Da,18700Da,26700Da were0.2403g/L,0.1610g/L,0.1563g/Land0.1543g/L respectively. It can be seen that with the increase of molecular weight, LS iseasier to aggregate. However, the CAC of LS changes little when the molecular weight ofLS is more than20000Da.The oxidative degradation of LS assisted by microwave irradiation was also studied.LS can be degraded to get colorless solution when reaction was carried out under theconditions of8of the ratio of30%H2O2to LS,300W of microwave irradiation power at110℃for120min, and the total organic carbon (TOC) of LS can be decreased by70.7%. Under the optimal reaction conditions (reaction was carried out under150℃for15min),LS macromolecule with above10000Da can be degraded into the small molecules of lessthan1000Da. This result may provide a potential pathway to treat the spent pulping liquorafter recovery of LS, and hence completely eliminate pollution of spent pulping liquid.