Hydrogenation of Edible Oils

Overview Edible Oils – Intro Oils & Fats (Triglycerides) Hydrogen Concentration Selectivity Effects of changing Temperature & Pressure Impurities that affect the catalyst Filtration

Edible Oils

Global production of oils and fats 113 million metric ton / year (MMT/yr)

Average consumption is about 15kg (30lbs) /person • lower in some countries e.g. 7kg (15lbs) in Sudan

& Bangladesh • higher in some countries e.g. 40kg (88lbs) in USA

• Palm Oil (PO)- Primarily derived from the palm oil plantations in Malaysia and Indonesia is the major feedstock in Asia.

• Sunflower - Predominantly grown in Eastern Europe.

• Fish oil (FH) - Predominantly used in Chile/Peru. Was popular in UK, Norway, Japan.

• Canola/Rapeseed - Predominantly grown in Canada and northern Europe. Typically has higher poisons than soya.

• Soyabean Oil (SO)- Primarily derived from the major soya states in the US, Brazil and Argentina.

• Tallow - animal fat, usually a by-product of rendering. Lard from pigs also used.

Where do edible oils come from?

Hydrogenation Process Crushing Refining

Filtration

Blending/ Packaging/Delivery

Ni catalyst in

Ni catalyst out

Oil Seeds

Hydrogenation

Product

Post bleaching/

Deodorization

Where the hydrogenated oils go….

What is an oil / fat?

Fat (triglyceride) molecule • 3 chains of carbon (C) atoms (green) • Hydrogen (H) atoms attached to carbon (white) • C atoms joined by glycerol “backbone” (red OH groups)

How much hydrogen attached is related to “saturation” of fat

Oil / fat types Notation CX:Y (e.g. C18:2)

• X = number of carbon atoms in chain (18) • Y = number of double bonds in chain (2)

Cis double bond (same side)

…-C-C-C C-C-C-…

C=C

• Trans double bond (opposite side)

…-C-C-C

C-C-C-… C=C

Oleochemicals Can “split” the chain off the glycerol backbone

to get glycerin and fatty acids Fatty acids main building block of the

oleochemical industry Form components of:

• soaps & shampoos • rubber tires

• Cosmetic cremes

• fabric softeners

• detergents

• lubricants

Why Hydrogenate?

Main objectives of hydrogenation • improve flavor stability

• adjust melting characteristics

Hydrogenation reaction

Simple reaction - chemically:

Oil + H2 “hardened” Oil Ni

• Physically difficult 3 components, 3 phases

-Oil Liquid -H2 Gas -Ni Solid

The “Art” of Hydrogenation…. ….is getting all 3 components in the same place at

the same time!

Key parameters Catalyst

• type (e.g. VULCAN VIG Series) • dosage

Hydrogen concentration

• Pressure • Temperature • Mixing/Agitation

Reaction requires: 1 1 In reactor: 1000 1 Not enough hydrogen!

Why is H concentration important?

Hydrogen Concentration

Why is H concentration important?

Melting Point Pressure

Temperature

Catalyst Dosage

SFI curve

Stability

Trans Content

At given RI / IV

Reaction Time

Pressure = Driving force for H2 diff.

In general, as pressure increases the more H2 available at the catalyst surface for reaction.

In actual fact solubility of H2 is the driving force but this is proportional to pressure.

H2 gas H2 liquid

Pressure = Driving force for H2 diff.

In general, as pressure increases the more H2 available at the catalyst surface for reaction.

gas H2 H2

liquid

Temperature affects rate of reaction

In general, as temperature increases the less H2 available at the catalyst surface for reaction.

Hardened Oil H2 liquid Oil +

k

Mixing - replaces reacted H2

Mixing is often over-looked and is the limiting factor in the hydrogenation reaction in many cases.

H2 H2

oil phase

Nickel surface

Hydrogenation reactions occur at Nickel surface

The amount of nickel is not as important as how it is distributed - Nickel Surface area is more relevant than nickel

mass!

adsorbed molecules

C=C R R

H H

1 2

H H

R R

H H

1

2

C C H

R R H H

1 2

C C

R R H H

1 2 C C

H H

cis- unsaturated

trans- unsaturated saturated

C=C R H

H

3

R 4

H H

Selectivity in EO Hydrogenation

How to influence product properties

C18:2 C18:1cis C18:0

C18:1 trans

Many chemical reaction - including TG hydrogenation - have intermediate products and side products:

“Selectivity” means the ability of capturing (desired) intermediate products ( + , -- )

Selectivity Definition

Selectivity in edible oil hydrogenation

polyene selectivity

trans selectivity

Polyene selectivity

More selective • Reacts C18:3 to C18:2 without reacting too much

C18:1 to C18:0 • Gives good color and oxidative stability without

raising the melting point too much • Not as much tailing (due to too much C18:0) in SFC

curve

Less Selective • Hydrogenates any double bonds • Some C18:3 remain while C18:0 increase and m.p.

increases • gives flatter SFC curves

C18:3 C18:2 C18:1 C18:0

Polyene Selectivity Catalyst choice has a large influence

• Should use a selective catalyst when a very selective reaction is required

Hydrogen concentration has a large influence • lower hydrogen concentration gives better

selectivity • higher hydrogen concentration gives worse

selectivity but this can be overcome by using a selective catalyst (e.g. VULCAN VIG)

Stability Resistance to Oxidation

Oxidation rates are directly linked to unsaturation:

C18:0 C18:1 C18:2 C18:3

= = = =

1 10

100 200

• Oils / fats with higher C18:3 will go rancid and color quicker • Oils / fats with lower C18:3 can be kept or used for longer

"Trans selectivity": (trans-) isomerisation vs. hydrogenation

adsorbed molecules

C=C R R

H H

1 2

H H

R R

H H

1

2

C C H

R R H H

1 2

C C

R R H H

1 2 C C

H H

cis- unsaturated

trans- unsaturated saturated

C=C R H

H

3

R 4

H H

Nickel surface

oil phase

The desired intermediate products are trans isomers

Melting Temperatures Triglycerides

°C C 12:0 30 C 16:0 65 C 18:0 73 (163F) C 18:1 cis 5,5 (41.9F) C 18:1 trans 42 (108F) C 18:2 cis -13 C 18:3 cis -24

Solid Fat Content Curve

A typical SFC curve at certain conditions

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Temperature (C)

Solid

Fat

Con

tent

(%)

Solid Fat Content Curve

Areas of influence

Solid Fat Content Curve

If H2 concentration decreased OR if Sulfided Ni catalyst used

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Temperature (C)

Solid

Fat

Con

tent

(%)

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50

Temperature (C)

Solid

Fat

Con

tent

(%)

Solid Fat Content Curve

If H2 concentration increased OR If less selective catalyst used

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60

Temperature (C)

Solid

Fat

Con

tent

(%)

“Tailing”

If polyene selectivity poor, tailing will occur

Trans Selectivity Hydrogen concentration is one of the main

factors in trans selectivity

Use of a sulfurized catalyst greatly increases trans selectivity • High trans products (low H concentration

or sulfurized catalyst) have steep melting curves and are often

used in candy or bakery products

• Low trans products (high H concentration) Used for “healthier” oils low trans products also have less solid

content at room temperature

Effects of increasing pressure There is a higher hydrogen concentration in the oil

• lowers trans selectivity less trans, less solids due to trans, less steep SFC

curve

• reduces polyene selectivity more C18:0 and related solids, less stable for

given IV, more tailing on SFC curve

• speeds up reaction

Reducing the pressure will have opposite effects

Effects of increasing temperature

There is a lower hydrogen concentration in the oil • increases trans selectivity more trans, more solids due to trans, steeper SFC

curve

• increases polyene selectivity more stable for given IV, less tailing on SFC

curve, lower formation of C18:0 at given IV

• speeds up reaction

Reducing the temperature will have opposite effects

Effect of process changes on hydrogen concentration and subsequent effects

*In general, the lower the hydrogen concentration at the catalyst surface the greater the probability of forming trans. However, there is also a time effect - longer reaction generate more trans. This column only is considering the hydrogen effect.

** This refers to agitation “improving”, i.e. a better gas liquid mass transfer and a better dispersion of hydrogen into the liquid.

Process parameter Hydrogenconcentration

at catalystsurface

Probability ofmore transforming*

Hydrogenationtime

Pressure ⇑ ⇑ ⇓ ⇓

Temperature ⇑ ⇓ ⇑ ⇓

Agitation ⇑** ⇑ ⇓ ⇓

Catalyst dosage ⇑ ⇓ ⇑ ⇓

Catalyst activity ⇑ ⇓ ⇑ ⇓

Sulphur promotion, re-usingcatalyst ⇑ ⇓⇓ ⇑⇑ ⇑

Summary of Catalysis (EO) Need to get Oil, H2 and Ni at same place! Different catalysts for different needs Hydrogen concentration is often limiting

factor in reaction Hydrogen concentration influences

selectivity Hydrogen concentration determined by:

• Pressure • Temperature • Mixing • Catalyst activity & dosage

Impurities to consider and effect on catalyst

Sulfur • occurs in the plant and varies seasonally • can also occur as a result of pre-processing (e.g.

copra) • “sits” on Ni surface and blocks the active sites. • Can deactivate catalyst and promotes trans

formation

Phosphorous • occurs in oils as lecithin and other phosphotides • “gums” up the catalyst pores, thereby

deactivating it. • Can also “gum up” the filter causing blockages.

Impurities ….. FFA

• is present in crude oil (hence neutralization or steam stripping step)

• being an acid, it will begin to dissolve nickel metal, thereby deactivating some of the catalyst if the FFA level is high.

Water • oil can become contaminated with water in

pretreatments and transport and storage • it affects the nickel surface area and

lowers the activity of the catalyst • if water is present the TG can be split in a

hydrolysis reaction, and form FFAs.

Impurities ….. Soap

• ion exchange with Ni can occur • Na+ can block Ni surface area too

Pigment

• Chlorophyll, gossypol (in cottonseed oil), can impart colours to the oil and this colour can change after hydrogenation

Oxidized fat • Oil can oxidise in storage and this deactivates

catalyst

Filtration Reactor mix is filtered to remove the catalyst There is usually a maximum allowed residual

nickel content in the product 2 types of residual nickel

• (a) Particulate nickel - small black particles • (b) Dissolved nickel - soluble nickel soaps,

salts, etc Identifying which type:

• Can check if it is (a) by using a filter paper check and particle analysis

• If no black dots on filter paper and still Ni in ICP reading it is probably dissolved nickel

Removal of Residual Nickel (a) Particulate Nickel removed with

• Improved filter system • use of filteraid • stronger catalyst particles

(b) Dissolved Nickel removed with • post bleaching with citric or phosphoric acid • use of bleaching earth • reduction in FFAs and/or water in feed oil • reduction in contact time without hydrogen

Glossary of terms C = carbon double bond = a C=C bond where there are two

links between two C atoms H = hydrogen kLa = gas-liquid mass transfer coefficient; a

measure of the agitation in the reactor lauric = C12:0 LEL = lower explosive limit linoleic = C18:2 linolenic = C18:3 mono-unsaturates = triglyceride with just one

double bond e.g. C18:1 myristic = C14:0 Ni = nickel O = oxygen oleic = C18:1 oleochemical = a chemical or material derived

from a triglyceride generally

Glossary of terms P = Pressure palmitic = C16:0 polyene selectivity = the ability to

hydrogeante the higher unsaturated compunds first

poly-unsaturates = triglycerides with more than one double bond e.g. C18:2, C18:3

saturated bond = a C-C bond where there is only one link between the two C atoms

saturates= triglycerides with no double bonds e.g. C18:0

stearic = C18:0

Glossary of terms T = temperature t = time trans selectivity = the ability to

increase the trans isomerisation effect and end trans level

trans-fatty acid (TFA) = a fatty acid chain with trans double bond, one where the chain links are on opposite sides of the double bond

triglyceride = a molecule of part of a fat or oil

UEL = upper explosive limit unsaturated bond = double bond