氢化油脂英文PPThydrogenation

Hydrogenation
Definition : To treat oil with H2 and catalyst to decrease double bonds and increase saturated bonds.
Reaction Result Saturation of double bonds Migration of double bonds Trans-fatty acid formation
.
C H
C H
.
C H
R2
-H
8 9
.
-H
-H
.
10 11
.
8 9 10 11
-H
.
8 9 10 11
R1
H H H C C C C H H H (D)
H R2 R1 R1 R2 C H C H C H C H C
H C
H C
(E)
C
R2
H
H
H
H
(F)
H
Conjugated Fatty Acids Formation
Isooleic acid
Selectivity
Preferential hydrogenation of more unsaturated acids with minimum formation of completely saturated fatty acids. Linoleic acid : Oleic acid Very selective hydrogenation 50 : 1 Non-selective hydrogenation 4 : 1 Selectivity can be expressed as the ratio KLO/KO ; the relative rate of hydrogenation of linoleate to that of oleate.
Why does selectivity important in hydrogenation?
Selectivity
How can we increase the linoleic acid selectivity ratio? When the affinities of oleic and linoleic acids to catalyst are the same, what are the selectivity ratios of both acids?
Partial hydrogenation
Complete Hydrogenation
?
Hydrogenation Reaction Rate
• Nature of the substance to be hydrogenate
(Oleic acid vs Linoleic acicd)
• The nature and concentration of the catalyst • Pressure (reaction) – the concentration of hydrogen • The reaction temperature • The degree of agitation
C C C R2 H H H
.
.
R2
(B)
(C)
R
Formation of Double Bond Migration and Transisomers during Hydrogenation
8 9 10 11 H H H H R1 C H C (B) 8 9 10 11 H H H H R2 R1 C H C H (C) C
Double-bond migration to form conjugated trans-fatty acids.
9 10 C C 11 12 C C 13 14 15 16 C C C C
9 11 (A) C C C C
C
OR
15 C C Cቤተ መጻሕፍቲ ባይዱ
From the hydrogenation of A; 9, 15 and 11, 15 From the hydrogenation of B; 10,15 and 12, 15 From the hydrogenation of C; 9, 12 and 9, 14 From the hydrogenation of D; 9, 13 and 9, 15
H C3 H
C1 H
C2
C3
+
Schematic Diagram of Hydrogenation
Catalysis
Oil + Catalyst Oil-Catalyst Complex
Oil-Catalyst Complex + H2 Hydrogenated Oil + Catalyst
HYDROGENATION
Vegetable oil
Seventy five (75) % of world edible oil is vegetable oil
•Shortening •Margarine •Mayonnaise •Confectionary fat •Less desirable for salad and frying oil, Why?
Advantages of Hydrogenation
Making fat suitable for manufacture of margarine, shortening, coating fats, cooking oil and salad dressing oil.
Hydrogenation
9 10 11 12 13 14 15 16 C C C C C C C C
9 11 C C C C
C OR
15 C C
C
10 12 C C C C
C
15 C C
C
OR
9 C C 12 C C 14 C C C OR 9 C C C 13 15 C C C C C C
Adsorption
Adsorption of the reactants on the catalyst surface is
Selectivity for Hydrogenation
Oleic acid Linoleic Acid
?
Polar or nonpolar catalyst surface
The affinity of unsaturated fatty acids to catalyst through hydrogen bond. Geometric configuration and chemical and physical characteristics of catalyst will determine the selectivity of catalyst will determine the selectivity ration of different fatty acids.
* The unsaturated trans fatty acids is 42% of total unsaturated fatty acids
Hydrogenation Scheme
Linoleic acid Oleic acid
Linolenic acid
Stearic acid
Isolinoleic acid
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.
Formation of Double Bond Migration and Transisomers during Hydrogenation
8 R1 9 10 11 R2
H H H H C C C C H H (A) +H
+H
8 C 9
.
.
10 11 R1
H H H H R1
R
8 9 10 11 H H H H C C C C H H H
Hydrogenation Steps of Oils
• Transfer and/or diffusion
• Adsorption
• Hydrogenation/isomerization
• Desorption
• Transfer
Transfer and Diffusion
Transfer and adsorption steps are critical steps in controlling the degree of isomerization and selectivity of reactions.
Hydrogenation of Soybean Oil
Catalysts
Nickel Catalyst: Nickel on various supports Copper Catalyst: • • • Copper-Chromium (CUO 50% + Cr2O3 40% + BaO 10%) High selectivity for linolenic acid (KLn / KLO = 10) Almost infinite selectivity for linoleate