【作者】 刘云；

【导师】 丁霄霖；

【作者基本信息】 江南大学 ， 食品科学， 2004， 博士

【摘要】 天然VE具有许多对人体非常有益的生理功能,同时又是一种天然抗氧化剂,附加值高,国内外市场前景看好,因此提取浓缩天然VE就成为广大科技工作者和众多企业研究开发的热点。我国是一个油脂生产和油脂消费大国,可用于提取天然VE的脱臭馏出物原料逐年增加。从植物油脂脱臭馏出物中提取浓缩天然VE这种高附加值的产品,不仅会带来较高的经济效益,而且还可解决由于馏出物的排放所造成的环境污染。利用超临界CO2技术从油脂脱臭馏出物中提取浓缩天然VE已有不少的报道,基于前人研究的成果和研究过程中存在的诸如相平衡数据等的不足,本文在相平衡测定与溶解度计算和关联等方面作了较为全面深入的基础研究,最后还比较了超临界CO2萃馏浓缩天然VE的三种工艺方案,并对双柱逆流萃取浓缩天然VE工艺进行了初步探讨。全文主要研究内容和结果如下:利用气液交替循环装置耦合重量法,在313.15K~343.15K、10MPa~20MPa范围内分别测定了生育酚、油酸甲酯在超临界CO2中的气液相平衡,根据气相中CO2的P-V-T关系计算了生育酚和油酸甲酯在超临界CO2中的溶解度和分配系数,并将溶解度实验值与相同条件下文献报道值进行了比较。结果表明:油酸甲酯与CO2的互溶程度比生育酚与CO2的互溶程度高,生育酚在超临界CO2中的溶解度比油酸甲酯低。从测定的溶解度数据中可以看出,在温度为313.15K、压力低于10MPa以及323.15K和343.15K、压力低于15MPa下,生育酚在超临界CO2中的溶解度很低,此时用重量法几乎检测不到生育酚的存在。随着温度的提高,油酸甲酯在超临界CO2中的会溶压力也升高。313.15K、323.15K、343.15K条件下,油酸甲酯在超临界CO2中的会溶压力分别为13MPa、15MPa、20MPa。从生育酚和油酸甲酯二者在超临界CO2中溶解度与分配系数大小可知,用超临界CO2分离生育酚和油酸甲酯是可行的。通过对不同类型植物油脂在超临界CO2中的溶解度比较得出,大豆油脱臭馏出物经甲酯化处理后,其在超临界CO2中的溶解度增加;如再经甲醇解处理后,溶解度将进一步加大。因此利用超临界CO2萃馏技术从大豆油脱臭馏出物中浓缩天然VE时,甲酯化和甲醇解等预处理步骤相当重要。文中指出,del Valle and Aguilera模型不适合于用来关联大豆油脱臭馏出物预处理产物在超临界CO2中的溶解度。利用气液交替循环装置耦合GC分析法,在313.15K~333.15K、9MPa~17MPa范围内等温、等压和等密度条件下分别测定了大豆油脱臭馏出物预处理产物中主要脂肪酸甲酯在超临界CO2中的气液相平衡,根据P-V-T关系分别计算了主要脂肪酸甲酯在超临界CO2中的溶解度、分配系数和相对分离因子。结果表明:大豆油脱臭馏出物预处理产物中油酸甲酯在超临界CO2中的溶解度与油酸甲酯/CO2二元系相比较变化不大,说明了混合物中有比油酸甲酯更难溶性成分的增加,并不能明显地影响易溶性成分油酸甲酯在超临界CO2中的溶解度。预处理产物中主要脂肪酸甲酯在气液两相中的分配系数在同温度下,棕榈酸甲酯的分配系数随压力的升高而增大,其他主要脂肪酸甲酯的分配系数则随压力的升高而减少;在同密度下,所有七种主要脂肪酸甲酯的分配系数则随温度的升高而增大。总体而言,碳链越短的脂肪酸甲酯对超临界CO2的气相亲和力越强;相同碳链的脂<WP=10>肪酸甲酯如C18,双键数目越多其与超临界CO2气相亲和力越差。利用气液交替循环装置耦合HPLC分析法,在313.15K~333.15K、9MPa~17MPa范围内等温、等压和等密度条件下分别测定了大豆油脱臭馏出物预处理产物中天然VE各异构体在超临界CO2中的高压相行为。结果表明:大豆油脱臭馏出物预处理产物中天然VE在超临界CO2中的溶解度比生育酚/CO2二元系中生育酚的溶解度要高11倍多,这说明了在超临界CO2萃馏技术的实践应用中,溶质间的协同作用不容忽视。由此可见,用生育酚/CO2二元体系的相平衡数据来指导工业生产实践,将会产生工艺操作参数选取的偏差。天然VE各异构体在气液两相中的分配系数以α-VE的分配系数最大,约为0.75~0.9;δ-VE的分配系数次之,约为0.6~0.8;γ-和β-VE最小,约为0.5~0.65,且这两种异构体的分配系数相当接近。从天然VE各异构体的相对分离因子来看,α-VE相对于β-、γ-、δ-VE的分离因子在1.09~1.51之间。因此,只利用超临界CO2萃馏技术,在现有的设备上从大豆油脱臭馏出物中萃取浓缩高d-α-VE是很困难的。如果把脱臭馏出物预处理产物人为地分为三类,即易挥发性的脂肪酯甲酯、中等挥发性的天然VE和难溶性油渣。通过计算可以得到脂肪酸甲酯与天然VE、脂肪酸甲酯与油渣、天然VE与油渣的相对分离因子,它们分别在2.1、10和2.5以上。因此用超临界CO2双柱萃馏技术分离脂肪酸甲酯、天然VE和油渣是完全可行的。由于脂肪酸甲酯和天然VE在超临界CO2中的溶解行为与它们的质量含量有关系,所以连续稳态操作方式尤为重要。利用改进型BP人工神经网络(BPANN)模型分别计算了二元系、多元系中溶质在超临界CO2中溶解度和相平衡数据,并对模型中影响计算误差的各参数进行了较详细的讨论。所有溶解度和相平衡计算值与实验值之间的平均相对误差在4%以内,结果是令人满意的。从而说明改进型BP神经网络模型是一种简便有效的关联与预测天然VE在超临界CO2中的溶解度模型。以大豆油脱臭馏出物甲酯化产物为原?更多还原

【Abstract】 Having many benefits, being a very strong antioxidant, and being a high-value natural product, extracting and concentrating natural vitamin E becomes a hotspot research for many scientists and industrial technologists. In our country, there are lots of oil deodorizer distillates (in short as ‘DOD’) from which concentrating this high-value material---- natural vitamin E can not only bring higher economical benefits, but also decrease the environment pollution causing by deserting oil DOD.Although the technology of supercritical carbon dioxide (in short as ‘SC-CO2’) has been widely applied to extract and concentrate natural vitamin E from DOD, and many achievements have also been reported, there are some drawbacks such as the absence of phase equilibrium for pretreatment of DOD/CO2 system. Therefore, this paper comprehensively investigates the determination of phase equilibrium including binary and multi-compound systems; the calculation and correlation of solubilities of vitamin E are also discussed; finally three different extraction technologies are compared using SC-CO2, and the two-column countercurrent extraction and fractionation (in short as ‘TCCCEF’) technology is primarily studied in this paper. Main research contents and results are as follows:Gas-liquid equilibrium data are reported for tocopherol/CO2 and methyl oleate/CO2 two binary systems at 313.15K, 323.15K and 343.15K, respectively. A new gas and liquid phase circulation apparatus coupled with gravimetric method is employed for solubility measurement. The quantity of dissolved solute per 100 gram CO2 and distribution coefficients of solutes are calculated from the P-V-T relationship for CO2 in gas phase. All experimental results are compared with values reported in the literatures under the similar conditions. The results show that the solubility of methyl oleate is much higher than that of tocopherol. From the data of solubilities, there is too little tocopherol in SC-CO2 to be determined by gravimetric method under the conditions of 313.15K, below 10MPa, 323.15K and 343.15K below 15MPa. Critical pressure of methyl oleate in SC-CO2 increases with pressure, for example 313.15K-13MPa, 323.15K-15MPa, and 343.15K-20MPa respectively. Based on the solubilities and distribution coefficients between tocopherol and methyl oleate in SC-CO2, It is feasible to isolate and separate tocopherol from these two compounds mixture.It is concluded that the solubility of DOD alcoholysate in SC-CO2 is much higher than these of DOD esterification, DOD, and plant oil, therefore, it is very <WP=12>important to esterify and alcoholism DOD from which concentrating natural vitamin E by SC-CO2 fractionation method. This paper presents that del valle and Aguilera model is not suitable to correlate the solubility of soybean oil DOD alcoholysate in SC-CO2.Gas-liquid equilibrium data are determined for SC-CO2 and fatty acid methyl ester (FAME) in soybean oil DOD pretreatment under isothermal, isobaric and isochoric conditions of pressure ranging from 9MPa~17MPa and temperature from 313.15K~333.15K. Gas Chromatography (GC) analyzes samples from liquid and gas phases. The solubilities, distribution coefficients and relative separation factors for seven main FAME are calculated. The results show that the solubilities of methyl oleate are no influential variance between in pretreatment of DOD/CO2 and in methyl oleate/CO2 systems, which testifies that the solubilities of more soluble components in mixture are not obviously affected by the presence of less soluble components. At isotherm, the distribution coefficient of palmitic acid methyl ester increases with pressure, but others decrease with pressure. At isochoric, the distribution coefficients of all seven main fatty acid methyl esters increase with temperature. All in all, for a family of linear long-chain saturated methyl esters, the smaller chain length, the higher the solubility of the methyl ester in the gas phase; for the equal-chain methyl esters (here, C18), the larger the unsaturation, the lower the solubili更多还原