麦秸秆与黑龙江褐煤共热氧化法制备腐植酸及其结构分析

Preparation and structural analysis of humic acid by co-thermal oxidation of wheat straw and Heilongjiang lignite

结合矿源腐植酸(HA)产率高及生化HA活性高的特点,本研究提出将低阶煤与生物质共热氧化制备复合型HA(MIXHA)的想法。将黑龙江褐煤(HL)及麦秸秆(WS)的混合物(MIX)在10%的HNO_(3)溶液中进行了共热氧化,制备了MIXHA。通过SEM、FT-IR、^(13)C NMR等分析,重点从HA的宏观形貌及微观结构对比了MIXHA与HL、WS分别单独制备的矿源HA、生化HA,分析HL与WS在共热氧化过程的协同作用。结果表明,MIXHA含量高于理论值,HNO_(3)分子的分解产生的活性氧原子、氮氧化物进攻HL与WS的分子结构,由于氢键重排、糖苷键断裂、交联等作用,WS纤维素与半纤维素产生的大量烷基自由基结合在HL缩合芳环上被氧化产生的醌基、羧基的邻对位,从而将芳香环上的质子碳转化为脂肪取代碳。得到的MIXHA含氧官能团丰富、活性高,FT-IR谱图具有明显的特征峰。本研究为低阶煤与农林废弃物的分级、资源化利用提供了一种新思路。

Combining with the characteristics of high yield of mineral humic acid(HA)and high activity of biochemical HA,co-thermal oxidation of low rank coal and biomass to produce complex HA(MIXHA)was newly proposed.The mixture(MIX)of Heilongjiang lignite(HL)and wheat straw(WS)was co-thermally oxidized in 10%HNO_(3) solution to prepare MIXHA.This work focused on comparison of the macro morphology and microstructure of MIXHA between HLHA and WSHA by SEM,FT-IR and _(13)C NMR analyses,and explored the synergistic effect between HL and WS during the co-thermal oxidation process.The results show that MIXHA content is higher than the theoretical value.Decomposition of HNO_(3) molecular produces active oxygen atoms and nitrogen oxides to attack the molecular structure of WS and HL.Due to hydrogen bond rearrangement,glycosidic bond rupture,and crosslinking,plenty of alkyl radicals generated in WS are combined with the condensation aromatic ring in HL.Thus,the protonated aromatic carbon is changed into aliphatic substituted aromatic carbon.The obtained MIXHA is rich in oxygen-containing functional groups,and has high activity.Obvious characteristic peaks are observed in FTIR spectra of MIXHA.This work would provide a new idea for classification and resource utilization of low-rank coal and agricultural and forestry wastes.