Comparative Studies On Formation Of Organic Acid In Extracting Aspen And Reed With Ethanol-water At High Temperature

The high-yield pulps of aspen or reed was obtained in the high-temperature ethanol/water extraction system,becaused it has removed selectively lignin and hemicellulose.Therefore,the formed organic acid played a decisive role on lignin crushing into pulp and liquor recycling components.However,slurry temperature of aspen and reed materials was varied greatly in the ethanol/water solvents system.190²05?of aspen,and only 170¹80?of reed.At present,there is few reports that the organic acid generated and effected to system in the ethanol/water extractionin.In this study,organic acid generation and its affect on pH of system were researched using model compound of lignin,based on the characteristics of aspen and reed was extracted with ethanol/water solvent.Firstly,the extraction of aspen and reed was researched in the ethanol/water system.The result that the lignin removal curves of aspen and reed have similarities,there are relatively stable and rapid removal stage.However,the variation of yield of aspen was relatively gental compared reed.Simultaneously,the ethanol consumption of aspen and reed of 22.22%and14.95%,respectively.Secondly,the affection of organic acid on ethanol/water extraction of aspen and reed were compared.Meanwhile,the composition and contents of organic acid were analyzed qualitatively using UPLC.The result that three kinds of low molecular organic acids,including formic acid,acetic acid and acetyl acid,were found in aspen and reed extracts.However,the content of three kinds of organic acids in aspen and reed were different,and the contents order of three kinds of organic acids in aspen is acetic acid,formic acid and levulic acid,but that of reed is formic acid,acetic acid and levulic acid.Simulstanously,the variation of pH of extraction liquor was researched by distillation and dilution of extraction liquor.The result that the phenomenon of first down and then up was found when the extraction liquor was diluted.Therefore,the mainly influence of pH variation was investigated by adding the fractions of different components,such as oxalic acid,glucose or xylose.The conclusion is that the soluble sugar of system,such as glucose and xylose etc.,had inhibitory effect on the ionization of H⁺on organic acid.And then,the FTIR,NMR?2D and HSQC?were used to characterize the structure of lignin obtained from ethanol/water extraction,and the molecular weight was characterized by GPC.The result that lignin of aspen and reed were GSH type.However,reed lignin contained more G type structure unit compared with aspen lignin,the mainly link is?-O-4,?-?and?-5.And the molecular weight of both gradually decreased with the extraction time is extended,but reed is faster than aspen.At the same time,the degradation of reed lignin in ethanol/water system more easily.Finally,lignin degradation as organic acids and their interactions were studied by lignin model of HL.The result that the degradation rate of 60%of reed was higher that of 45%of aspen.However,the molecular weigth of both was similar to that of 4536g·mol^-1 and4432g·mol^-1,respectively.The main degradation of aspen is formic acid and levulic acid,but that of reed is formic acid,acetic acid and levulic acid.Simulatanously,the levulic acid is instability will occur further degradation,formic acid and acetic acid are stable and mainly derived from side chain of lignin.