【作者】 刘元法；

【导师】 王兴国；

【作者基本信息】 江南大学 ， 粮食、油脂及植物蛋白， 2007， 博士

【摘要】 随着食用油脂工业的发展和人民生活水平的提高,食用油脂与人体健康之间的关系越来越成为人们关注的焦点之一,油脂加工品质的研究与控制日显重要。脱色是油脂精炼必不可少的过程,探明油脂脱色过程中的作用机理及其对油品品质的影响水平,对于保证食用油脂风味和营养,明确油脂加工工艺和吸附剂对油脂品质的影响,保障人民健康,提高油脂加工水平都具有重要的意义。采用DSC-TGA、FT-IR、SEM、XRD、能谱分析、孔径分析和酸性点分析等方法对凹凸棒石矿物特性和改性机理进行了系统研究,首次对凹凸棒石油脂脱色吸附剂工业制备过程的改性机理进行研究,提出在凹凸棒石改性过程属于低酸改性,纤维束的解聚、八面体阳离子的部分萃取、中温处理使孔道和破键更多暴露是其改性的主导变化。酸处理过程和中温活化过程构成了对凹凸棒石结构改变的主要因素,改性过程中虽没有改变凹凸棒石原有的晶体结构,但促进了晶体结构的有序性,促进了蒙脱石水化分解过渡产物的转化和再结晶,同时对凹凸棒石表面性质和孔道结构产生了明显影响。研究表明,油脂脱色体系符合Freundlich吸附等温模型,结合吸附热力学参数(△G、△H、△S)求解,明确了凹凸棒石油脂脱色体系为放热过程,吸附过程是孔道填充、范德华力和氢键力共同作用下的物理吸附过程,凹凸棒石所特有的二八面体晶体结构、丰富的纳米孔道、表面破键形成的酸性位点是其吸附本质所在,改性后凹凸棒石的孔道结构变化在脱色过程中起到了至关重要。选用非均匀表面吸附的Bangham动力学方程,采用无量纲变量法对凹凸棒石在单吸附质吸附体系、多吸附质吸附体系的吸附动力学进行了研究和比较,明确了凹凸棒石油脂脱色为竞争吸附过程,分为快速传质、扩散、吸附的快速吸附过程和慢速吸附过程两个阶段,明确了凹凸棒石油脱色体系中不同物质吸附速率符合叶绿素>类胡萝卜素>FFA>磷脂的竞争关系。采用FT-IR、SPME-GC-MS等方法分析了脱色过程油脂品质的变化,首次发现凹凸棒石催化一级氧化反应效果不明显,凹凸棒石在吸附过程中对氢过氧化物的吸附作用大于催化作用。凹凸棒石表面酸性点的存在对极性化合物尤其是呋喃类化合物的生成具有明显的催化作用,而对于其它物质的生成来说催化效果不明显。脂肪酸异构化反应是在温度和凹凸棒石共同作用的结果,其中前者对反式酸的形成起到了关键作用,而后者起到了催化作用。更多还原

【Abstract】 The role of edible oils in human health, along with the development of the edible oils industry and improvement of human being’s living standards, has gained increasing attention. Hence, the investigation of oil processing procedures are of rising importance for oil quality control.. Bleaching is one of the crucial steps in oil refining. Elucidation of the oil bleaching procedure with respect to its mechanism of action and influence on oil quality have, therefore, paramount value in maintaining oil flavor and nutrition, understanding the effects of oil processing technology and adsorbents on oil quality, guaranteeing human health, and upgrading oil processing technolgy.An extensive study was performed on the mineral characteristics and modification mechanism of attapulgite in terms of thermal properties (DSC-TGA), chemical composition (FT-IR spectroscopy), morphology (SEM), specific surface area (BET method), pore size distribution (gas adsorption method), basal spacing (XRD), elemental composition (XPS), and acidic points distribution (NH3-TPD method). The mechanism of attapulgite modification in preparing oil bleaching agents was first established to be a low acidic process with the following major changes involved: acid treatment induced deaggregation of the fasciculi,and partial substitution of the cation in the octahedral crystal structure, and medium temperature activation enhanced exposure of broken bonds. Acid treatment and medium temperature activation, therefore, constitute the predominant factors in modifying the structure of attapulgite.,The crystal structure of attapulgite was not changed, but it became more ordered; the conversion and re-crystalization of hydration decomposed transitional products of montmorillonite was stimulated; and the surface characteristics and pore structure of attaplgite was remarkable affected.Oil bleaching tests showed an adsorption curve fittable to the Freundlich isotherm. The calculated thermodynamic parameters (△G,△H,△S) indicated that the the oil bleaching process was exothermic. The adsorption was a physical process composed of pore filling, Van der Waals’forces and H-bonding forces. The adsorption capacity was closely related to the dioctahedral crystal structure of the attapulgite, large amounts of nanoscale channels, and surface modification formed acidic sites, The changes in the channel structure played a key role in improving the oil bleaching performance of the modified attapulgite. The Bangham equation for nonhomogeneous surface absorption systems was used to compare the adsorption kinetics of single- and multi- sorbate on attapulgite using unitless variables. Oil bleaching with attapulgite was shown to be a competetive adsorption process consisting of two steps: one of rapid mass tranfer, diffusion and adsorption followed by the other of relatively slower adsorption. The adsorption rate of the components in the oil bleaching system followed the sequence: chlorophyll > carotinoids>free fatty acids (FFAs) > phospholipids. Analyses of the adsorption process by FT-IR and SPME-GC-MS indicated that the modified attapulgite has remarkable catalytic activities towards a series of reactions including hydrolysis of triglycerides, decomposition of hydrogen peroxides, and oxidization, isomerization and polymerization of fatty acids.Analyses of the adsorption process by FT-IR and SPME-GC-MS indicated that the modified attapulgite has unremarkable catalytic activities towards primary oxidative reactions, and has adsorptive activity stronger than catalytic activity towards hydrogen peroxide. Acidic sites on the surface of attapulgite has significant catalytic activity towards the formation of polar compounds, especially furanoids, but has unremarkable catalytic activities towards the formation of other substances. The isomerization of fatty acids was caused by the heating and attapulgite combined, with the former playing a key role in producing trans fatty acids and the latter in providing catalytic activity.更多还原