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摘要: 聚甲氧基二甲醚（H3CO（CH2O）nCH3，PODEn或DMMn，n ≥ 2）具有独特的物理化学性质；作为一种柴油添加剂，可以有效提高油品燃烧效率并达到节能减排的目的。首先合成了一系列聚合度n为2、3、4和5单一组分的聚甲氧基二甲醚，采用NMR、FT-IR、Raman和DFT计算等手段对每个聚甲氧基二甲醚单体的化学结构进行表征，并对其在298.15-323.15K温度的密度和黏度进行了测试。结果表明，聚甲氧基二甲醚的密度和黏度随着温度的升高而逐渐降低，随着聚合度的增加而逐渐升高。同时，聚甲氧基二甲醚PODEn（n =2-5）的闪点和倾点以及溶解热和凝固热均随着聚合度的增加而提高。Abstract: Polyoxymethylene dimethyl ethers (H3CO(CH2O)nCH3, PODEn or DMMn, n ≥ 2) with unique physical and chemical properties are a potential additive for diesel fuels, which can effectively enhance the combustion efficiency and reduce the emission of pollutants. In this work, a series of pure PODEn components (n=2-5) were synthesized from methylal and trioxymethylene and obtained with high purity through collaborative separation; their structure and properties were characterized by NMR, FT-IR, Raman, and DFT calculation and a detailed assignment of the expressions in the spectrogram to the various groups was performed. The density and viscosity of PODEn were measured at 298.15-323.15 K. The results indicate that the density and viscosity of PODEn decrease gradually with the increase of temperature. Meanwhile, with the increase in the number of -CH2O-units (n) from 2 to 5, the density, viscosity, flash point, pour point, and the heat of fusion and solidification of PODEn are all increased. These results are valuable for the practical synthesis and application of PODEn.
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Figure 4 Temperature dependence of density for PODEn
■: PODE2; ●: PODE3; ▲: PODE4; ▼: PODE5
Figure 5 Temperature dependence of viscosity for PODEn
■: PODE2; ●: PODE3; ▲: PODE4; ▼: PODE5
Table 1 Comparison of the experimental and calculated vibration wave number and the assignment of various radicals in PODEn
Table 2 Density of PODEn under different temperatures
Table 3 Viscosity of PODEn under different temperatures
Table 4 Flash point and pour point of PODEn
Table 5 Thermal characteristics of PODEn
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