Isothermal crystallization kinetics of refined palm oil
Isothermal crystallization kinetics of refined palm oil
复制标题
DOI：
10.1007/s11746-002-0496-4
复制
发表时间：
2002-04-01
影响因子：
2
通讯作者：
Chong, CL
中科院分区：
文献类型：
--
作者：
Chen, CW;Lai, OM;Chong, CL
采用粘度法研究了精炼、漂白和精炼棕榈油在等温条件下从熔体中结晶的诱导时间。在低于295 K的温度下，观察到棕榈油的结晶发生在两个阶段的过程中。这两个阶段的过程是由棕榈油的分馏，最有可能成为硬脂和油精馏分。在高于295 K的温度下，仅观察到单阶段结晶过程。如在偏振光显微镜下所见，球形晶体最初在287至293 K的温度下由第一级分形成。这些球形晶体的直径随着温度的升高而减小。之后，由第二级分形成针状晶体，并从这些球形晶体的表面继续生长，直到球形晶体完全封闭，即，观察到两种多晶型物的共结晶。在高于293 K的温度下，从两个馏分的混合物形成的针状晶体被发现是唯一的多晶型物开发与结晶的开始。X射线衍射结果表明，在低于295 K的温度下，第一级分形成的球形晶体为α晶型，而第二级分后来成核的针状晶体为β晶型。β ′晶体是在295 K以上温度下形成的唯一多晶型物。所得结果与诱导时间-温度曲线中观察到的不连续性吻合良好。根据Fisher-Turnbull方程计算各种多晶型的成核活化自由能。观察到粘度是表征整个结晶过程的灵敏方法。该技术适用于棕榈油结晶的诱导时间研究，特别是在较低温度和粘性油的情况下。
The induction times for the crystallization, under isothermal conditions, of refined, bleached, and deodorized palm oil from the melt were studied by viscometry. At temperatures below 295 K, the crystallization of palm oil was observed to occur in a two-stage process. This two-stage process was caused by the fractionation of palm oil, most probably into the stearin and olein fractions. At temperatures higher than 295 K, only a single-stage crystallization process was observed. As seen under polarized light microscopy, spherical crystals were initially formed from the first fraction at temperatures from 287 to 293 K. The diameters of these spherical crystals decreased as the temperature increased. After that, needle-shaped crystals were formed from the second fraction and continued to grow from the surface of these spherical crystals until the spherical crystals were fully enclosed, i.e., the cocrystallization of two polymorphs was observed. At temperatures higher than 293 K, the needle-shaped crystals formed from a mixture of the two fractions were found to be the only polymorphs developed with the onset of crystallization. X-ray diffraction results showed that for temperatures below 295 K, the spherical crystals formed from the first fraction were in alpha form, whereas the needle-like crystals that nucleated later from the second fraction were in beta' form. beta' crystals were the only polymorphs formed for temperatures above 295 K. The results obtained were in good agreement with the discontinuity observed in the induction time vs. temperature curve. Activation free energies for nucleation were calculated according to the Fisher-Turnbull equation for the various polymorphic forms. Viscometry was observed to be a sensitive method for characterizing the overall crystallization process. This technique is suitable for induction time studies of palm oil crystallization, especially at lower temperatures and with viscous oil.