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?

Melting Point

•

Slip Melting Point

Official

AOCS (1989)

Method Cc

3-25. A

column of fat

was

tempered at

10

C for

16

h in an open capillary tube. The tube was then heated slowly in a water bath until the fat column started to rise due to hydrostatic pressure. The temperature at which this occurs was determined as SMP using averaging of four replicates.

•

Solid Fat Content (Nuclear Magnetic Resonance, NMR)

Hydrogenation

Definition : To treat oil with H 2 and catalyst to decrease double bonds and increase saturated bonds.

Reaction Result 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.

Hydrogenation

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

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.

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.

Schematic Diagram of Hydrogenation H H H 2 + Catalyst Surface H H C 1 C 2 C 3 H H H C 1 C 2 C 3 H

Schematic Diagram of Hydrogenation H H C 1 C 2 C 3 H H H H C 1 C 2 C 3 H H H C 1 H C 2 C 3 H H C 1 C 2 C 3 H + H H

Schematic Diagram of Hydrogenation Catalysis Oil + Catalyst  Oil-Catalyst Complex Oil-Catalyst Complex + H 2  Hydrogenated Oil + Catalyst

Formation of Double Bond Migration and Transisomers during Hydrogenation +H .

R 1 8 9 10 11 H H H H C H C C C H (A) R 2 +H .

R

R 1 8 9 10 11 H C H H C .

(B) H C H H C H R 2 R 1 8 9 10 11 H H H C C H C .

H H C H (C) R 2

R

Formation of Double Bond Migration and Transisomers during Hydrogenation R 1 R 1 - H .

8 9 10 11 H H H C H C C H C H (D) 8 9 10 11 H H H H C H C .

C H C H (B) R 2 - H .

R 1 R 2 R 1 8 9 10 11 H H H H C C C .

H H C H (C) R 2 H 8 9 10 11 H H H C H C C C H (F) - H .

- H .

R 2 R 1 8 9 10 11 H C H H C H H C ( E) C H R 2

Conjugated Fatty Acids Formation 9 10 11 12 13 14 15 16 C C C C C C C C 9 11 15 C C C C C C C C OR C 10 12 15 C C C C C C C OR C 9 12 14 C C C C C C C OR C 9 13 15 C C C C C C C

Adsorption

Adsorption of the reactants on the catalyst surface is important in controlling the selectivity and isomerization during hydrogenation.

Fatty Acid Compositions of Partially Hydrogenated Oleic Acid __________________________________________________________________ Double bond Total unsaturated Trans unsaturated % Positional isomer (Position) fatty acide (%) fatty acids (%)*

trans

form __________________________________________________________________ 11 . . . . . . . 7.0 10 . . . . . . . 15.7 9 . . . . . . . 54.5 8 . . . . . . . 15.8 4.7

9.8 13.4

9.8

67.2

62.5

24.6

62.0

7 . . . . . . . 7.0 4.7

67.2

__________________________________________________________________ * The unsaturated trans fatty acids is 42% of total unsaturated fatty acids

Hydrogenation Scheme

Linoleic acid Oleic 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 K LO /K O ; the relative rate of hydrogenation of linoleate to that of oleate.

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.

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?

Hydrogenation of Soybean Oil

Catalysts

Nickel Catalyst: Nickel on various supports Copper Catalyst: • Copper-Chromium (CUO 50% + Cr 2 O 3 40% + BaO 10%) • High selectivity for linolenic acid (K Ln / K L O = 10) • Almost infinite selectivity for linoleate

Double-bond migration to form conjugated

trans

-fatty acids. C 9 10 11 12 13 14 15 16 C C C C C C C (A) 9 11 15 C C C C C C C C OR (B) C 10 12 15 C C C C C C C OR (C) C 9 12 14 C C C C C C C OR (D) 9 13 15 C C C C C C C C 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

Triglyceride Stereospecificity

Hydrogenation of fatty acids in triglyceride is not a function of their location

Catalyst Activity

Defined as iodine value decrease per unit of time during a hydrogenation under a specific set of conditions.

American Oil Chemists’ Society method Comparison of the time to hydrogenate soybean oil to iodine value to 80 from 120 at 350F, 20 psig, 0.05 % your catalyst to the time used by standard catalyst from AOCS The life of catalyst – how long a catalyst will remain active and useful.

Production of Simulated Olive Oil from Soybean Oil by Chromium Carbonyl Iodine Value Hydrogenated Soybean Oil 95 Olive Oil 77-94 Palmitate (%) Stearate (%) Other Saturates (%) 10.3

4.3

0.0

7-16 1-3 0.1-2 Monoene (%) Diene (%) 60.7

23.9

65-85 4-15 Triene (%) 0.8

Trans

-Acids (%) 6.8

_____________________________________________________________

Production of Simulated Cocoa Butter from Hydrogenated Cottonseed Oil by Chromium Carbonyl _____________________________________________________________ Hydrogenated CSO Cocoa Butter Palmitate (%) Stearate (%) 58.0

1.0

24.4

35.4

Monoene (%) Diene (%) 37.6

3.4

38.1

2.1

Trans

-Acids (%) Iodine Value Melting Range (  C) 7.2

38.0

30-40 36.7

24-35 _____________________________________________________________

FACTORS AFFECTING HYDROGENATION Independent Variables Pressure Temperature Agitation Catalyst concentration Dependent Variables Trans fatty acids Selectivity ratio Hydrogenation rate

Effects of Pressure and Temperature on

Trans

Unsaturation at 80 I.V. Soybean Oil As pressure 3 Psi 35 Psi at 180C, trans fatty acids decrease from 40 to 35%

Effects of Pressure and Temperature on

Trans

Unsaturation at 80 I.V. Soybean Oil As temperature 210 235C at 30 Psi, trans fatty acids increase from 40 to 45 %

Effects of Pressure, Temperature, and Catalyst on Selectivity Ratio What does selectivity 40 mean?

As pressure 14 34 Psi at 180C, 0.02% catalyst, selectivity rate decrease from 40 to 20

Effects of Pressure, Temperature, and Catalyst on Selectivity Ratio As temperature 130C 160Cat 0.08 % and 25 Psi, Selectivity rate increases from 20 to 40

Effects of Pressure, Temperature, and Catalyst on Selectivity Ratio As catalyst 0.02 0.08 % at 25 Psi and 165 C, selectivity rate increases from 20 to 40

Effects of Agitation and Catalyst Concentration on Selectivity Ratio As catalyst 0.03 0.07% at 1330 RPM, selectivity rate increases from 28 to 36.

Effects of Agitation and Catalyst Concentration on Selectivity Ratio As agitation 1300 1700 RPM at 0.06 %, selectivity rate decreases from 36 to 28.

Effects of Pressure and Temperature on Selectivity Rate As pressure 20 35 Psi at 170C, selectivity rate increases from 20 to 28

Effects of Pressure and Temperature on SR As temperature 140 190 at 20 Psi, selectivity increases from 20 to 36

Effects of Agitation and Catalyst Concentration on Hydrogenation Rate As agitation 800 1000ppm at 0.06 % Ni, hydrogenation rate increase from 2.5 to 3.2 IV/min.

Effects of Agitation and Catalyst Concentration on Hydrogenation Rate As catalyst 0.06 0.10% at 1000rpm hydrogenation rate increases from 3.3 to 3.8 IV/min.

Factors Affecting Hydrogenation

The Relationship between Process Conditions and their Effects on Selectivity Ratio,

Trans

-Contents, and the Rates of Reaction Selectivity Ratio Content Reaction Rate Temperature Pressure Agitation Catalyst