Preparation of humic acid from sugarcane leaf biomass using a hydrolysis-oxidation method
Humic acid was prepared from sugarcane leaves by simulating the chemical reactions used to form mineral derived humic acid.A study of the comparative efficacy of humic acid preparation from mineral substrates and lignin was performed.Acid hydrolysis,in which cellulose and hemicellulose were hydrolyzed into soluble sugars and lignin was converted into an insoluble humic acid precursor was conducted first,followed by solid-liquid separation.An oxidant was then used to oxidize the humic acid precursor,and the hydrophilic carboxyl group was regenerated to complete the preparation of humic acid.Based on our results,when the solid-liquid ratio was fixed at 20∶50(g∶mL)during hydrolysis,the best reaction conditions were:150℃for 3 h,10%sulfuric acid,and 1%nitric acid.The best oxidation step reaction conditions were:humic acid precursor reacted with 3.5%nitric acid at a solid-liquid ratio of 1∶13(g∶mL)for 2 h at 80℃.A series of analytical methods including elemental analysis,acid group analysis,UV,IR,and NMR confirmed that the humic acid prepared from sugarcane leaf exhibited a high degree of humification and aromatization,and its various indicators were close to those of mineral source humic acid.This method can successfully prepare humic acid,and utilizing the generated hydrolyzed sugars also has potential within various existing biomass industries to solve the problem of hydrolyzed residues.
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