氢化和交酯 油脂专业课程-江南大学.pptVIP

Chapter 8 Hydrogenation Definition To treat oil with H2 and catalyst to decrease double bonds and increase saturated bonds Reaction Results Saturation of double bonds Migration of double bonds Trans-fatty acid formation Advantages of Hydrogenation Making fat suitable for manufacture of margarine, shortening, coating fats, cooking oil and salad dressing oil Stabilize and improve oxidative stability for oils Bleaching and removal of off—flavor Diversity，such as CBE Steps in Partial Hydrogenation Transfer and/or diffusion Adsorption Hydrogenation/isomerization Desorption Diffusion Transfer and adsorption Transfer and adsorption steps are critical steps in controlling the degree of isomerization and selectivity of reactions. Transfer Transfer of reactants and products to and from the bulk of the liquid oil phase and outside surface of the catalyst. Diffusion Diffusion of reactant into the pores of the catalyst. Diffusion of products out of the pores of catalyst. Postulated Schematic Diagram of Hydrogenation Formation of Double Bond Migration and Transisomers during Hydrogenation Trans-fatty acid formation Unsaturated Fatty Acid Composition of Partially Hydrogenated Oleic Acid Trans-fatty acid formation Conjugated Fatty Acids Formation Hydrogenation Scheme Hydrogenation Reaction Rate Preferential hydrogenation of more unsaturated acids with minimum formation of completely saturated fatty acids k＝Aexp(－Ea/RT) A＝2×6.02×1023d2(πRT/M)0.5 dlnk/dT＝Ea/RT2 lnk2/k1＝Ea/R(1/T1－1/T2) 习题 油脂的氢化是一个放热反应，即ΔH＜0，升高温度，对化学平衡转化率和反应速度各有什么影响，请给出定量表达式。如何理解放热反应在平衡转化率和反应速度上存在的这种矛盾。在实际生产中，如何提高产物的得率 Selectivity the relative rate of hydrogenation of unsaturated acids SR2＝K1÷K2，亚麻酸选择性 SR1＝K2÷K3，亚油酸选择性 异构化比，Si＝加氢生成的反式异构体数／双键被饱和数 脂肪酸位置的选择性，Sp，甘油三酯１，３位和２位上脂肪酸的氢化选择性 甘油三酯选择性，ST，氢越以随机的方式与油脂中的各个甘油三酯分子发生氢化反应，ST越大 随机化的结果：单烯酸被氢化为饱和酸的概率是均匀地发生在所有的甘油甘油三酯分子上，即氢化均匀，三饱和甘油酯比例少 催化剂的选择性，S，催化反应伴随着副反应，催化剂对主反应起加速作用的性能称为催化剂的选择性，高选择性的催化剂可以节省原料，减少副反应及其后处理工序 S＝消耗于目的产物的原料／原料总的转化率 Nature of the substance to