Structural changes of rice straw during the preparation of bio-chemical potassium humate
Bio-humic acid is a new non-coal humic acid resource,which was obtained from crop straw,wood chips,bagasse and other agricultural wastes by chemical or microbial fermentation process.It is an important resource of green fertilizer and an important way to solve the comprehensive utilization of agricultural wastes.Bio-chemical fulvic acid(FA)and bio-chemical potassium humate(HA-K)were prepared and extracted after nitrification and alkali extraction with rice straw(RS)as raw material and HN03 as oxidant in this study.The structural changes of RS before and after extraction were studied by three major components'contents analysis,thermogravimetric analysis and soild carbon nuclear magetic resonance(13C NMR)analysis.Results showed that after nitrification and alkali extraction,the proportion of cellulose in the residue(ER)reached as high as 91.26％-96.78％.The main weight loss temperature was concentrated at 350-420℃,which belonged to cellulose cracking range,accounting for 75.49％.In the 13C NMR spectrogram of ER-10％60 min,the carboxyl and carbonyl carbon(N° 1)contributed by the carbonyl group in the acetoxy group of lignin and the carboxyl group in hemicellulose and the aromatic carbon(N° 2-6)contributed by the aromatic structure of lignin disappeared.These phenomena reflected that the hydrogen bond and ester bond connecting the three major components were broken during nitrification and extraction.The carbonyl and carboxyl functional groups(N° 1)in lignin and hemicellulose and the aromatic structure(N° 2-6)in lignin entered FA and HA-K,and cellulose was left as the main component in ER.
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