• ISSN 1008-505X
  • CN 11-3996/S
向阳, 苗睿, 刘亚青, 赵贵哲. 多聚甲醛与尿素高温缩聚制备脲甲醛缓释肥及其性能研究[J]. 植物营养与肥料学报, 2022, 28(9): 1699-1707. DOI: 10.11674/zwyf.2022203
引用本文: 向阳, 苗睿, 刘亚青, 赵贵哲. 多聚甲醛与尿素高温缩聚制备脲甲醛缓释肥及其性能研究[J]. 植物营养与肥料学报, 2022, 28(9): 1699-1707. DOI: 10.11674/zwyf.2022203
XIANG Yang, MIAO Rui, LIU Ya-qing, ZHAO Gui-zhe. Preparation of and properties of urea-formaldehyde slow-release fertilizer by high-temperature polycondensation of paraformaldehyde and urea[J]. Journal of Plant Nutrition and Fertilizers, 2022, 28(9): 1699-1707. DOI: 10.11674/zwyf.2022203
Citation: XIANG Yang, MIAO Rui, LIU Ya-qing, ZHAO Gui-zhe. Preparation of and properties of urea-formaldehyde slow-release fertilizer by high-temperature polycondensation of paraformaldehyde and urea[J]. Journal of Plant Nutrition and Fertilizers, 2022, 28(9): 1699-1707. DOI: 10.11674/zwyf.2022203

多聚甲醛与尿素高温缩聚制备脲甲醛缓释肥及其性能研究

Preparation of and properties of urea-formaldehyde slow-release fertilizer by high-temperature polycondensation of paraformaldehyde and urea

  • 摘要:
    目的 传统溶液缩聚法制备的脲甲醛缓释肥(SUF)通常含水率较高,产品易于粘结在设备表面,阻碍了反应装置的自动出料,难于实现连续化生产。过高的含水率也增加了后续干燥过程的能耗,因此,本研究改进了制备工艺,以突破这一瓶颈。
    方法 多聚甲醛与尿素高温气固相缩聚工艺制备的脲甲醛缓释肥(HUF),其制备原理是:高温密闭条件下多聚甲醛解聚成甲醛气体,气体甲醛与反应釜中的尿素结合生成脲甲醛和水,少量尿素在高温下会分解产生氨气,氨气与水结合成氨水,促使缩聚反应向正向移动,形成高聚合度的脲甲醛分子链。同时以高温气固相缩聚法和传统溶液浓缩法制备了缓释肥,分别记为HUF和SUF,每个方法均制备了尿素与甲醛摩尔比分别为2、4、6的样品。研究了生成物的干燥时间,并采用亚硫酸盐法、凯氏定氮法、热失重(TWL)、热重(TG)、傅里叶红外光谱(FTIR)、凝胶渗透色谱(GPC)、X射线衍射(XRD)方法表征了脲甲醛的组成与结构。最后,采用浸泡法测试了脲甲醛缓释肥的缓释性能。
    结果 在高温气固相缩聚反应中,反应温度越高,甲醛转化率越高,高于100℃后甲醛转化率升高幅度有限,且高于100℃后尿素分解率也会急剧上升,导致脲甲醛氮含量降低,故将100℃定为高温气固相缩聚工艺的最佳反应温度。高温气固相缩聚工艺显著降低了反应产物的含水率,HUF含水率最高仅为11.72%,干燥时间较SUF至少缩短了1 h。该工艺也提高了原料甲醛的转化率和脲甲醛分子的平均链长,当脲醛比为2∶1时,HUF的甲醛转化率为88.22%,比SUF增加了9.26个百分点;HUF的重均分子量可达4445,而SUF的重均分子量仅为949;HUF的缓释有效氮含量为21.05%,比SUF增加了12.48个百分点;HUF的活性系数为42.33%,比SUF增加了20.48个百分点;HUF的24 h氮释放率为49.6%,比SUF降低了12.1个百分点;HUF的28天氮累积释放率为73.6%,比SUF增加了3.5个百分点。
    结论 采用高温气固相缩聚工艺制备的脲甲醛缓释肥可有效降低产品的含水率,实现设备的连续生产,并不会影响脲甲醛的缓释性能。

     

    Abstract:
    Objectives Urea-formaldehyde slow-release fertilizer prepared by the traditional solution of polycondensation (SUF) usually has a high moisture content, which makes the product adhere strongly to equipment. Consequently, it is difficult to achieve continuous production due lack of automatic discharge from the reactor. Moreover, the high moisture content also increases energy consumption during drying. Therefore, we improved the process technology to overcome this bottleneck.
    Methods Urea-formaldehyde slow-release fertilizer (HUF) was prepared by a high-temperature gas-solid polycondensation process of paraformaldehyde and urea. The principle is that under high temperature and sealing conditions, paraformaldehyde is depolymerized into formaldehyde gas, which combines with urea in the reaction kettle to form urea-formaldehyde and water. A small amount of urea will decompose at a high temperature to produce ammonia gas, which combines with water to form ammonia water and drives the polycondensation reaction to form a urea-formaldehyde molecular chain with a high degree of polymerization. Slow-release fertilizers were prepared by high-temperature gas-solid polycondensation and conventional solution concentration, denoted as HUF and SUF, respectively. Samples with mole ratios of urea to formaldehyde of 2, 4, and 6 were prepared for each method. We studied the drying time of the products and characterized the composition and structure of urea-formaldehyde by the Acetylacetone method, Kjeldahl method, Thermal weight loss (TWL), Thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), Gel permeation chromatography (GPC), and X-ray diffraction (XRD). Furthermore, the performance of urea formaldehyde slow-release fertilizer was tested by immersion method.
    Results In a high-temperature gas-solid polycondensation reaction, the higher the reaction temperature, the higher the formaldehyde conversion rate. The formaldehyde conversion rate slightly increased when the reaction temperature was higher than 100℃. Also, the decomposition rate of urea increased sharply beyond 100℃, leading to the reduction of urea-formaldehyde nitrogen content. Therefore, 100℃ was the best reaction temperature for the high-temperature gas-solid polycondensation process. The high-temperature gas-solid polycondensation process significantly reduced the water content of the reaction product; the highest water content was 11.72%, and the drying time was shortened by at least 1 h compared with SUF. The process also improved the raw formaldehyde conversion rate and the average chain length of urea-formaldehyde molecules. When the mole ratio of urea and formaldehyde was 2∶1, the formaldehyde conversion rate of HUF was 88.22%, which was 9.26 percentage points higher than that of SUF. The average molecular weight of HUF and SUF were 4445 and 949, respectively. HUF's slow-release available nitrogen content was 21.05%, which was 12.48 percentage points higher than SUF. The activity coefficient of HUF was 42.33%, which was 20.48 percentage points higher than SUF. HUF's nitrogen release in 24 h was 49.6%, 12.1 percentage points lower than SUF. The cumulative nitrogen release of HUF in 28 days was 73.6%, which was 3.5 percentage points higher than SUF.
    Conclusions Urea formaldehyde slow-release fertilizer prepared by high-temperature gas-solid polycondensation process can effectively reduce the moisture content of the product and thus achieve continuous production of the equipment, without affecting the slow-release performance.

     

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