A Study On Lignin Gradual Separation Methods And Structures&Distribution Of Lignin Fragment

With the development of the society, petroleum resources are less and less, peopleare beginning to realize the importance of biomass resources. In order to solve theproblem, The main content of this paper is that classify lignin and separate lignin fromthe cooking liquid waste, and analyze the chemical structure and molecular weightdistribution of each section lignin samples. On the basis of the experiment, researchdifferent lignin samples, especially the low molecular weight lignin samples, anddevelop it’s high value-added application.Using acid precipitation, adjust the black liquor pH value to2and4respectively,and separate lignin samples from poplar kraft cooking black liquor and Caustic sodaanthraquinone method cooking black liquor respectively. On the basic of acidprecipitation, adjust the black liquor pH value to6,4and2respectively, then separatelignin samples from poplar kraft cooking black liquor and Caustic soda anthraquinonemethod cooking black liquor respectively, and flocculation precipitation, we can getdifferent lignin samples.Total phenolic hydroxyl（Condensed phenolic hydroxyl, Syringyl phenolic hydroxyl,guaiacyl phenolic hydroxyl and p-phenolic hydroxyl）, aliphatic hydroxyl, carboxyl andother functional groups were compared with quantitative analysis by³¹P—NMR. Ligninwas dissolved constantly by decreasing the pH of solution and the amounts of phenolichydroxyl and carboxyl decreased as well.The distribution and change of the molecular mass of dissolved lignin which isobtained from the black liquors of sulfate cooking and soda-AQ pulping can bedeterminate by GPC（Gel Permeation Chromatography）. These findings can providetheoretic and experimental basis for studying the low molecular lignin. Thenumber-average molecular weight（Mw） and molecular weight（Mn） of the dissolvedlignin are both decreasing during the acid-precipitation process.The chemical bonds between the lignin molecules are broken during the cookingand the lignin which has the higher relative molecular mass can be cooked out firstlyfollowed with the lower relative molecular mass of lignin.By comparison of the absorption peak FTIR spectrums and the corresponding assignments of IR bands to understand structural changes of lignin dissolved from black liquids and to estimate the strong and weak of characteristic absorption peak of functional groups which were included in the lignin structures.The changes of the structure of thedissolved lignin can be shown by IR spectral. Characteristic absorption peak of the functional groups was analysed. It comes out that dissolved lignin obtained by theacidulation-precipitation from black liquors mostly consists of Syringyl lignin andguaiacyl lignin.