• ISSN 1008-505X
  • CN 11-3996/S

葡萄糖改性尿素的反应特征及其对尿素转化率的影响

Reaction characteristics of glucose-modified urea and its effects on the urea conversion rate

    摘要
  • 摘要:
    目的 利用葡萄糖对尿素改性可延缓尿素水解，提高尿素氮肥利用率。从葡萄糖与尿素的反应特征、产物结构方面，研究其作用机理及葡萄糖添加量对尿素分解的影响。
    方法 将葡萄糖按10%的比例加入到熔融尿素中获得葡萄糖改性尿素，利用傅里叶变换红外光谱(FTIR)、X射线光电子能谱(XPS)和液相色谱–质谱联用(LC-MS)分析葡萄糖改性尿素的化学结构、物质组成和相对分子质量。将葡萄糖按照0.2%、0.5%和1.0%的比例添加到熔融尿素中制备出3种比例的葡萄糖改性尿素，在3个样品分别加入脲酶溶液(1 U/mg)，于(25±2)℃恒温箱中培养30 min后，用比色法测定剩余尿素的含量，计算尿素的分解率。
    结果 1)葡萄糖与尿素反应后，FTIR位于1599 cm−1处伯酰胺NH2变角振动消失，3441 cm−1处伯胺NH2反对称伸缩振动强度减弱，推测葡萄糖与尿素胺基发生反应，XPS C 1s和N 1s图谱分别出现未知形态的碳结构(―CX)和氮结构(―NX)，醛基碳(―CHO)消失，O 1s图谱发现醛基的C=O化学键发生断裂，证明葡萄糖的醛基与尿素的胺基反应生成了新的产物。依据LC-MS分析，葡萄糖中的醛基与尿素的胺基发生亲核加成反应，生成了含有C=N结构的物质。2)与普通尿素的分解率(20.16%)相比，添加0.2%、0.5%和1.0%比例的葡萄糖改性尿素的转化率分别为15.5%、3.3%、11.0%，其中葡萄糖添加比例为0.5%的改性尿素处理降幅高达16.9个百分点。
    结论 尿素熔融条件下加入葡萄糖，葡萄糖的C=O化学键断裂，碳原子与尿素中的氮原子结合形成C=N键。C=N键结构的存在延缓了尿素的水解，进而显著降低了脲酶对其分解率。葡萄糖添加量对葡萄糖改性尿素的分解率影响显著，以葡萄糖添加比例为0.5%的处理效果最佳。

     

    Abstract:
    Objectives Glucose-modified urea (GMurea) has high fertilizer use efficiency but low decomposition. We investigated the mechanism responsible for decreasing the conversion rate of glucose-modified urea from its structural perspective under various glucose addition rate.
    Methods Glucose (10%) was added to molten urea to produce glucose-modified urea. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and liquid chromatography-mass spectrometry (LC-MS) were employed to characterize the chemical structure, material composition and relative molecular mass of the glucose-modified urea. Glucose-modified urea containing 0.2%, 0.5% and 1.0% of glucose were prepared, then urease solution (1 U/mg) was added and incubated at (25±2)℃ for 30 min. The remaining urea was tested using spectrophotometer.
    Results 1) In the mixture of glucose and melted urea, the FTIR at 1599 cm–1, the primary amide NH2 variable angle vibration disappeared, and the primary amine NH2 at 3441 cm–1 weakened the asymmetric stretching vibration intensity. It was speculated that glucose reacted with the urea amine group. In addition, XPS C 1s and N 1s spectra showed unknown carbon structure (―CX) and nitrogen structure (―NX), and aldehyde-based carbon (―CHO) disappeared, and the O 1s spectrum showed that the C=O chemical bond of the aldehyde group was broken, indicating that the aldehyde group of glucose reacted with the amine group of urea to form a new product. The aldehyde group in glucose underwent a nucleophilic addition reaction with the amine group of urea to produce a substance containing a C=N structure through LC-MS analysis. 2) All the three ratios of glucose-modified urea reduced the decomposition rate of urea. The decomposition rate of urea and GMurea containing 0.2%, 0.5% and 1.0% glucose were significantly different vis – 20.16%, 15.5%, 3.3%, and 11.0%, respectively. Reduction in the rate of urea decomposition was markedly higher by 0.5% modification treatment, with 16.9 percentage points lower than that of ordinary urea.
    Conclusions The formation of C=N bond between glucose and urea slowed down the decomposition of urea by urease. The glucose addition ratio has significant impact on the decomposition of glucose-modified urea, with an optimal glucose addition of 0.5%.

     

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