【作者】 韩一松；

【导师】 吴平东；

【作者基本信息】 浙江大学 ， 化学工程与技术， 2007， 博士

【摘要】 EPA和DHA是人体必须的ω-3不饱和脂肪酸，在治疗和防治心脑血管疾病、炎症、抑制肿瘤以及预防老年痴呆等方面具有较好的疗效。但是EPA与DHA的功效不同，有必要将二者分离成纯品，以充分发挥各自的功效。从文献中已经提出的分离方法中，超临界流体色谱（SFC）是比较有前景的。虽然有少数几篇有关的文献，但是内容属于工艺的初步探索。有必要在超临界色谱的理论基础方面（吸附等温线、扩散、传质和色谱动态特性等）作系统的研究，使色谱分离的研发建筑在坚实的工程原理基础上。从学术研究角度来看，至今还没有系统研究上述理论问题的报道，所以这一工作也有学术意义。本论文的具体工作如下。扩散系数测定采用Taylor提出的峰扩展法（CPB）测定了AA-EE、EPA-EE和DHA-EE在308.15 K至338.15 K和8.42 MPa至29.95 MPa条件范围内，在无限稀释条件下的扩散系数。这三种脂肪酸乙酯在超临界CO₂中的扩散系数范围分别为（5.54至13.47）×10^-5cm²·s^-1，（5.54至13.80）×10^-5cm²·s^-1和（5.40至12.80）×10^-5cm²·s^-1。它随CO₂密度的升高和温度的降低而降低，主要受CO₂密度和粘度的影响：在相同的密度条件下，D₁₂／T基本相同。相同的条件下，脂肪酸的扩散系数比其甲酯或乙酯的扩散系数要小。采用预测模型Scheibel、Catchpole-King和He-Yu-Su模型得到的预测结果与实验值相比，平均相对偏差均小于2％。吸附平衡的研究建立了一套可以在线检测的、消耗样品量比较少的静态测定吸附平衡数据装置。并在318.15 K至338.15 K温度范围内和9.98 MPa至21.97MPa压力范围内，研究了超临界CO₂中EPA-EE和DHA-EE在C18键合硅胶上的吸附平衡关系。实验结果表明，超临界CO₂中EPA-EE和DHA-EE在C18键合硅胶上的吸附量随温度的上升和CO₂密度的增大而减少，并且其吸附等温线可用BET方程来描述。实验条件范围内，两种脂肪酸乙酯在C18键合硅胶上的单分子层饱和吸附量范围分别为（0.039至0.048）mmol·g^-1和（0.040至0.063）mmol·g^-1。两种脂肪酸乙酯在C18键合硅胶上的吸附热随着吸附量的增大和密度的增大而减小，直至达到一个最低值(约为10 kJ·mol^-1)。此外，还采用特征点洗脱法（ECP），在319.15 K至340.45 K温度范围内和0.668 g·ml^-1至0.734 g·ml^-1密度范围内研究了超临界CO₂中，两种脂肪酸乙酯在硅胶上的吸附平衡关系。实验结果表明，EPA-EE和DHA-EE在硅胶上的吸附等温线可用Langmuir方程来描述。平衡常数随着密度的增大和温度的上升而减小。在实验条件范围内，两种脂肪酸乙酯在硅胶上的单分子层饱和吸附量范围分别为（0.125至0.144）mmol·g^-1和（0.113至0.131）mmol·g^-1。两种脂肪酸乙酯在单位面积C18键合硅胶和硅胶上的单分子层饱和吸附量相差不大在(2.8x10^-7至3.9×10^-7)mol·m^-2范围内。色谱过程动态特性的模型采用速率模型方程描述EPA-EE和DHA-EE在超临界流体中色谱分离过程。利用流出曲线拟合的方法研究了CO₂流速、温度和压力对EPA-EE和DHA-EE在色谱柱内传质的影响。实验结果表明，N随流速的增大有极大值，k_f先随流速的增大而增大，然后趋于一定值。压力的增大和温度的下降会导致理论塔板数减少，并使总传质系数变小。轴向弥散系数在超临界流体色谱中对理论塔板高度的贡献在3.2％至16.9％之间，并且随着温度的降低和压力的增大而减小。超临界流体色谱法从鱼油中分离提纯EPA-EE和DHA-EE建立了一套适合半制各型超临界流体色谱的馏分收集方法（固相收集法），在固相收集柱内压力为4 MPa至6 MPa时，收集过程的回收率超过95％。采用此方法，研究了不同上载量和CO₂流速下超临界CO₂中EPA-EE和DHA-EE在C18柱（250mm×10mm I．D．）上进行分离时的动态曲线。结果表明，EPA-EE和DHA-EE相互之间的分离很好，原料中硬脂酸乙酯、油酸乙酯和AA-EE与EPA-EE不能分离，AA-EE，二十二碳四烯酸乙酯和二十二碳五烯酸乙酯与DHA-EE不能分离。根据动态曲线，研究了上载量和CO₂流速对生产能力、回收率和流动相消耗的影响。结果表明，产品含量要求为90％时，色谱柱的生产能力随着流速的增大而增大；随载量的增大而增大，但载量过大则生产能力又会减小。回收率随载量的增大而明显减小，CO₂消耗量随载量的变化有最低点，在载量为4.076 mL·L^-1时为最小。适宜载量为7.13 mL·L^-1，流动相流速为3.928 g·min^-1。降低鱼油原料中难分离杂质的含量，并对半制备结果在制备柱（250mm×50mm I．D．）上进行放大。结果表明，采用不同的鱼油原料制备的结果是不同的。反相高效液相色谱分离EPA-EE和DHA-EE研究了甲醇／水配比，流速，柱温对分离的影响。选取甲酵／水（v／v）=88：12作为适宜流动相配比，在制备柱上进行放大。更多还原

【Abstract】 EPA （Eicosapentaenoic acid ） and DHA （Docosahexaeonoic acid） are two ω -3 fatty acids. They are vital for the retina of the human eyes and for the nervous system, and can reduce the risk of cardiovascular disease and inflammatory disease as well. However, the functions of EPA-EE and DHA-EE are different, so it is significant to separate them into their pure compound form. Among the separation techniques in the review, supercritical fluid chromatography（SFC） is regarded as a promising one. Though some investigations on separation of EPA-EE and DHA-EE by SFC have been made, all of them focused mainly on the process itself. Thus, it is necessary to make fundmental researches on supercritical fluid chromatography （such as adsorption equilibria, diffusion and mass transfer） systematically, making the separation process base on a reliable fundamental. To date, there is nearly no systematic research about the above issues, so it is of great value, in a sense of academe, to research the fundamental of separation EPA-EE and DHA-EE by SFC. Some basic researches have been conducted in this work. It includes the following aspects:Diffusion Measurement. The binary diffusion coefficients (D_1,2) of AA-EE, EPA-EE and DHA-EE in supercritical carbon dioxide were studied by Taylor capillary peak broadening （CPB） method at 308.15 K to 338.15 K under 8.42 MPa to 29.95 MPa. The D_1,2s were in the ranges of （5.54 to 13.47）×10^-5cmV, （5.54 to 13.80）× 10^-5 cm²·s^-1 and （5.40 to 12.80）× 10^-5cm²·s^-1 respectively. It decreased with the increasing density of carbon dioxide and temperature. The curves of D_1,2/T vs. density of carbon dioxide almost coincided with each other. The D_1,2s for the esters of the three fatty acids are greater than those of the fatty acids themselves. The Scheibel, Catchpole-King, and He-Yu-Su equations predicted the experimental data quite well with average deviations smaller than 2 %.Adsorption Equilibria Research. A static apparatus which could determinatethe adsorption equilibrium data on-line and cost fewer sample was set up. The adsorption equilibrium of EPA-EE and DHA-EE on C18-bonded silica gel from supercritical carbon dioxide was studied on this set-up. The temperature was in the range of 318.15 K to 338.15 K and the pressure was in the range of 9.98 MPa to 21.97 MPa. The results indicated that the loading of EPA-EE or DHA-EE decreased with increasing temperature and density, and the isotherms were fitted well by BET equations. Under the conditions in this work, the monomolecular saturated capacity of these two fatty acids were （0.039 to 0.048） mmol·g^-1 and （0.040 to 0.063） mmol·g^-1 respectively. The heat of these two fatty acids on C18-bonded silica gel decreased with greater loading and density until it leveled off (at about 10 kJ·mol^-1). The adsorption data of EPA-EE and DHA-EE on silica gel from supercritical carbon dioxide were measured by the method of elution by character point （ECP）. The temperature was in the range of 319.15 K to 340.45 K and the density was in the range of 0.668 g·ml^-1 to 0.734 g·ml^-1. The results showed that the isotherms satisfied the Langmuir equation. The equilibrium constant K decreased with the increasing density and temperature. Under the conditions in this work, the monomolecular saturated capacity of EPA-EE and DHA-EE were in the ranges of （0.125 to 0.144） mmol·g^-1 and （0.113 to 0.131） mmol·g^-1 respectively. The monolayer saturated capacities per square meter for C18-bonded silica gel and silica gel were very close and were in the ranges of 2.8×10^-7 mol·m^-2 to 3.9×10^-7 mol·m^-2.Mass Transfer Research. The lump kinetic model was adopted to describe the chromatographic behavior of EPA-EE and DHA-EE in supercritical carbon dioxide. By fitting the experimental elution curves with the lump kinetic model, the effect of mobile phase flow rate, temperature and pressure on mass transfer kinetic was studied. The results indicated that the theoretical plate number （N） had a maximum value with the increasing flow rate and decreased with greater pressure and lower temperature. The lump mass transfer coefficient （k_f） increased with the increasing flow rate when the flow rate was small and then leveled off when the flow rate was great. Increasing pressure or decreasing temperature makes the theoretical plate number smaller. The contribution of axial dispersion to the theoretical plate height was in the range of 3.2% to 16.9% and decreased with greater pressure and lower temperature.SFC Separate EPA-EE and DHA-EE. An effective fraction collection method （solid trapping） for semi-preparative supercritical fluid chromatography was developed. The recovery exceeded 95 % when the pressure in the collection column was in the range of 4 to 6 MPa. By this method, chromatographic characteristics on a semi-preparative chromatographic column （250mm×10mm I.D.） under various loadings offish oil and flow rate of carbon dioxide were determined. It was found that EPA-EE and DHA-EE were well separated, but other esters of fatty acids presented in the feed could not be separated. By appropriately cutting the effluent, EPA-EE with 90 % content and DHA-EE with 75 % content were obtained. Based on the chromatographic curves, the effect of loading and flow rate of mobile phase on the performance of the column was studied. At EPA-EE content greater than 90 %, recovery of EPA-EE decreased remarkably as the loading increased. The relationship between CO₂ consumption and loading had a minimum consumption at loading of 4.076 ml·l^-1. The optimal loading and flow rate for preparation of 90 % EPA-EE were 7.13 ml·l^-1 and 3.928 g·min^-1 under 12.1 MPa and 55℃. Chromatographic conditions were scaled up directly on a preparative column （250mmx50mm I.D.） loading feed with fewer impurities. The results showed that the component of the feed affected the product greatly.RP-HPLC Separate EPA-EE and DHA-EE, EPA-EE and DHA-EE were separated by reverse-phase HPLC. The effect of ratio of methanol/water, flow rate and column temperature on separation were studied. The optimal ratio is methanol/water （v/v） = 88:12. The chromatographic conditions were scaled up on a preparative column. Economic analyses and comparisons for separation by HPLC and SFC were conducted.更多还原