Extraction,Fractionation And Characterization Of Fulvic Acid From Qujing Lignite

The study on the extraction of fulvic acid from lignite is of great significance for utilization of lignite.In this paper,Yunnan lignite was used as the experimental coal sample,and the fulvic acid was obtained by Chemical oxygenolysis method,high purity fulvic acid is obtained after purification by sulfuric acid ethanol method.The purified fulvic acid is classified into different molecular weights,and the chemical analysis,instrumental analysis and physiological activity application experiments were carried out on various fractions in order to obtain the chemical and physiological differences of different fractions,which provides new ideas for the deeper researches and applications of coal-based fulvic acid.Hydrogen peroxide was used as an oxidant to study the oxygenation of lignite to extract fulvic acid under microwave heating conditions.The optimum process parameters for extracting fulvic acid by orthogonal experimental study were as follows:Reaction time is 10 min,microwave power is 650 watts,hydrogen peroxide concentration is 25%,the ratio of oxidant and coal is 6.Under the optimal conditions,the extraction rate of fulvic acid reached 35.16%.The above factors have significant impact on the experimental results,especially the hydrogen peroxide concentration.According to the design principle of the central composite design experimental program,a quadratic regression model between the purification yield of fulvic acid and various factors was obtained.The decisive coefficient of the model reached0.9758,and the missing item is 0.4800,which means the model fit well.The optimum process parameters for the purification of fulvic acid from the model were as follows:the ratio of acid and fulvic acid is 0.09,purification time is 51.28 min,theratio of alcohol and fulvic acid is 14.4,purification temperature is 39.42°C.Under the optimum conditions,the average purification yield was 85.64%.The significant factors of affecting the purification yield were purification time,liquid-solid ratio and reaction temperature,there are significant interactions between the two in three factors.In addition,excessive acid will affect the quality of high-purity fulvic acid,which product will be sticky and difficult to dry.The purified fulvic acid was fractionated to obtain four fractions with different molecular weight ranges:FA₁?Mr<500?,FA₂?500<Mr<1000?,FA₃?1000<Mr<3500?and FA₄?Mr>3500?.The ratios of the four fractions were 72.92%,18.07%,2.18%,and 3.55%.Experiments have shown that the fraction with small molecular weight has lighter color,higher water absorption property,more oxygenated acidic functional groups and better solubility under strong acid.The elemental analysis,UV-visible spectroscopy and infrared spectroscop were used to analyze different fractions of fulvic acid.The results show that different fractions contain certain oxygen-containing groups such as alcoholic hydroxyl group,phenolic hydroxyl group,carbonyl group,ester group,carboxylic acid and acid anhydride.However,the fraction with higher molecular mass has a lower relative content of oxygen-containing functional groups,less types of substitution occurring on the benzene ring,higher degree of aromaticity and condensation.Different fulvic acids have a high characteristic peak in the range of 200-230 nm,and the hyperchromic effect of the high molecular weight fraction is more obvious,and accompanied by red shift phenomenon in UV-visible spectroscopy.As the main component of fulvic acid,FA₁ has the lowest degree of aromatization and carbonyl condensation,the E₄/E₆ value reaches 30,Besides,FA₁ contains more ester structure than other fractions.The structure of FA₄ has the least oxygen-containing functional groups,and there is a distinct saturated fat structure absorption peak in the infrared spectrum analysis.The physiological application experiments of fulvic acid showed that the application effects of different fractions were quite different.The fulvic acid with lower relative molecular mass is more obvious in breaking seed dormancy and promoting germination,and the optimal use concentration of different fractions is quite different.In addition,FA₁ can significantly improve the photosynthesis ability of seedlings.Compared to FA₁,FA₂ is more effective in reducing cell membrane permeability and the self-protection ability and survival rate of seedlings under adversity are significantly improved.FA₃ can significantly promote the longitudinal growth of seedlings.In addition to FA₁,other fractions have a significant effect on reducing the degree of stomatal opening,plants have higher relative water content,which has a better promoting effect on growth and development.