Study On Quantitative Determination Of Phenol Hydroxy Structure Of Spruce Lignin By Nuclear Magnetic Resonance Technology

With the shortage of energy supply and demand in the world and the increasingly serious problem of environmental pollution,the key to solve the problem of energy and environment is to find a clean and stable renewable biomass energy with abundant raw materials.In the near future,the bio refining industry based on lignocellulosic biomass will gradually replace the petrochemical industry based on fossil energy.However,the use of natural plant resources?such as lignocellulose?to produce bioethanol and energy will produce a large number of by-products,namely lignin.In addition,lignin is also considered as a by-product in the pulping industry.Therefore,lignin exists in lignocellulose as primary lignin,and a large amount of industrial lignin is produced every day in the world.However,the low purity,complex structure and low reactivity of industrial lignin limit its further application,so most industrial lignin is burned to generate energy.Therefore,in addition to the conversion of cellulose into valuable products,the conversion of lignin into other value-added products has also attracted the attention of researchers.The depolymerization and separation of lignin is one of the important challenges to improve the utilization of lignin.Therefore,accurate determination of phenolic hydroxyl content in lignin samples will help to improve the high value utilization of lignin,and provide theoretical basis for the structure,reaction performance and degradation mechanism of lignin.Based on this,this paper uses spruce as raw material,through ball milling/acetone pretreatment,enzymatic hydrolysis method to separate and extract lignin from ground wood,enzymatic hydrolysis lignin and enzymatic hydrolysis residue lignin,and uses cooking method to prepare sulfate lignin.The main content of this paper is to quantitatively determine the phenolic hydroxyl content of ground lignin,enzymatic lignin and sulfate lignin of spruce by ³¹P NMR,¹³C NMR and ¹H NMR.The main conclusions of this paper are as follows:1?Through the analysis of the 5-5`structure of lignin,it was found that the integral change of the 124.34-126.4 ppm region in the quantitative carbon spectrum of non acetylated and acetylated NMR was the phenol hydroxyl content of 5-5`structure.The content of 5-5`structural phenolic hydroxyl group in milled lignin,enzymatic lignin and sulfate lignin was determined by <sup>13</sup>C NMR.The values were 6%,6%and 20%,respectively.2?In this paper,<sup>13</sup>C NMR decrement method and <sup>13</sup>C NMR increment method are proposed for the determination of phenol hydroxyl content in lignin samples.The results are close to those of <sup>1</sup>H NMR and <sup>31</sup>P NMR,which proves the feasibility of the two methods.In addition,it was further verified that the <sup>13</sup>C NMR method was more reasonable for the determination of phenolic hydroxyl in lignin samples.3?In this paper,the test conditions of <sup>1</sup>H NMR are optimized,and a method is proposed to calculate the internal standard content?5.8-7.9 ppm?of <sup>1</sup>H NMR accurately.In addition,the content of phenolic hydroxyl group in?-?`structure can be determined by ¹H NMR.