Research On The Law Of Lignin Adsorption On Fiber Surface During The Aspen Alcell Pulping And Washing Process

Alcell pulping existed a phenomenon that during the washing process, when the volume fraction of ethanol was reduced or washing temperature was lower, there would be a substantial of ethanol lignin adsorb on the surface of the fiber. It leaded to that the extract of lignin content was reduced and the amount of subsequent bleaching drugs was increased. General approach on this issue was washing the pulp by ethanol solution in high temperature (the temperature at about 60℃). Because ethanol is easy to evaporate and flammable, so Alcell pulping requires high washing equipment. It also increases the burden of ethanol recovery. If we could understood from the mechanism of ethanol lignin adsorption, it would provide a theoretical basis for the control and prevention of ethanol lignin adsorption.This paper conducted some experiments explore about determining the content and structure of the fiber surface adsorbed lignin effected by different washing methods of aspen ethanol pulping and simulating lignin adsorption on the surface of analog substrate in the black liquor. The purpose of this paper is to provide some data to support the lignin adsorption mechanism, prevention of lignin adsorption and washing theory of aspen Alcell pulping.Conducted washing condition optimization experiments of the fiber surface adsorbed lignin of Alcell pulping, obtained the more excellent alkali extraction condition and the better ethanol washing condition. Determined the difference of content and structural of the fiber surface adsorbed lignin be washed under different washing methods, and explore the influence of different washing methods on the washing conditions of fiber surface adsorbed lignin. The ultraviolet test results showed that the ethanol washing and alkali extraction methods both can wash off the fiber surface adsorbed lignin, lignin wash-out rate is high, and the washing effect of the tow methods were close. The results of EDS test and UV determination of the lignin content of the fiber surface adsorbed lignin were consistent.IR and 1H-NMR analysis about the structures of fiber surface adsorbed lignin obtained by different washing methods and black liquor lignin show that the difference between the two kinds of structures is that the surface adsorbed lignin contained more guaiacyl structural unit and more hydroxyl groups on the aliphatic side chain, which indicates that the fiber surface adsorbed lignin have a selectivity in the structure.Using slurry as the substrate simulated adsorption experiments in the black liquor to simulate different holding time, different holding temperatures and different substrate adsorbed lignin during the cooking process. The UV spectra tests showed holding time had no significant impact on the content of lignin adsorbed on the surface of the substrate, the content of lignin adsorbed on the surface of the substrate is low under lower holding temperature, the content of lignin adsorbed on the surface of the substrate increased significantly under higher holding temperature, due to the lignin have high activity at high temperatures. IR and 1H-NMR analysis showed that with the holding time and holding temperature increasing, the fiber surface adsorbed lignin had a certain selectivity in the structure. The structural differences between analog substrate adsorbed lignin and the original aspen Alcell pulping slurry adsorbed lignin is that the analog substrate adsorbed lignin contained more guaiacyl and syringyl structural units than the original aspen Alcell pulping slurry adsorbed lignin. Bleaching substrates adsorbed lignin contained most syringyl structural unit than the aspen slurry analog substrate and original aspen Alcell pulping slurry adsorbed lignin. The structure of fiber surface adsorption lignin affected by the chemical properties of the analog substrates.