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