-
University of Nigeria Research Publications
Aut
hor
AKPAN, Udom Mark
PG/M.Sc/04/35487
Title
Temperature Effects on sulphur Catalysed
Dimerisation of melon seed oil (Colocynthis Vulgaris)
Facu
lty
Physical Sciences
Dep
artm
ent
Pure and Industrial Chemistry
Dat
e
February, 2007
Sign
atur
e
-
TEMPERATURE EFFECTS ON SULPHUR CATALYSED DIMERISATION OF MELON
SEED OIL
, (Colocynthis vulgaris)
AKPAN, UDOM MARK PG/M.Sc/04/35487
' DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY UNIVERSITY OF
NIGERIA,NSUICKA.
FEBRUARY, 2007.
-
TEMPERATURE EFFECTS ON SULPHUR CATALYSED DIMERISATION OF MELON
SEED OIL
(Colocynthis vulgaris)
AKPAN, UDOM MARK PGIM. Si$0&13548?
A RESEARCH PROJECT SUBMITTED IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTER OF
SCIENCE IN POLYMERIINDUSTRIAL CHEMISTRY
DEPARTMENT OF PURE AND INDUSTRIAL CHEMISTRY UNIVERSITY OF
NIGERIA, NSUKKA.
FEBRUARY, 2007.
-
APPROVAL PAGE
This research project has been approved by the Department
of Pure and Industrial Chemistry, Faculty of Physical
Sciences,
University of Nigeria, Nsukka.
'DR C.O.B. OKOYE PROF J. A. IBEMESI HEAD OF DEPARTMENT
SUPERVISOR
EXTERNAL EXAMINAR
-
CERTIFICATION
This is to certify that this research work titled: 'Temperature
Effects on
Sulphur Catalysed Dimerisation of Melon Seed Oil (Colocynthis
vulgaris)' was
actually carried out by ~ k ~ a n , Udom Mark (PGIM.SC104135487)
of the Department
of Pure and Industrial Chemistry, University of Nigeria, Nsukka.
The work
embodied in this project report is original and has not been
submitted in part or dull
for any diploma or degree of this or any other university.
> L -------------- 7------ -r------ ,
PROF J. A. lBEMESl SUPERVISOR
-
DEDICATION
To God Almighty and to my beloved mother, Stella Etuk, who in
spite of
difficulties, persevered to see me through my first and'second
degrees.
-
ACKNOWLEDGEMENT
I express my unreserved thanks to my supervisor, Prof
J.A.lbemesi whose
nature is one great thing that ever happened to me. His
diligence, meticulous
nature and critical examination are qualities'l so much
cherished.
My good friends and lecturers in the department mean so much to
me
especially Dr. P. 0. Ukoha who agreed to read through my draft,
Nnamdi Obasi for
his moral advice and encouragement, Asegbolenyin, Ejikeme and
Agbo who are
never tired attending to my needs, Ugwu, Nnagbukwu, Ukwueze, and
Ezema for
their contributions, in no small measure, gave me strength
especially in times of
morale depression.
The department is specially acknowledged for providing some of
the
reagents used for the laboratory work.
My best friend, Etima Akpan and others including my fellow post
graduate '
students are acknowledged. You are all heartily appreciated for
your good nature;
Members of ~ r a d u a t e Students Fellowship and Christ church
Chapel, UNN
are most highly cherished for their persevering prayers.
My unending list of those due for acknowledgement cannot be
exhausted.
To all those I have not mentioned, and those I have, May the
Almighty God bless
and keep you in perfect peace, Amen.
Akpan, Udom Mark February, 2007 .
-
ABSTRACT
Dimer fatty acid was produced from melon seed oil (MSO) using
su1phur.a~
catalyst. The oil was 'dimerised at the temperature values of
300, 310, 320,
330, 34-0, and 350°C, under inert atmosphere of nitrogen using
0.5% sulphur
as catalyst. Ten samples were withdrawn at five minutes interval
each for
every specified temperature and analysed. The analysis of these
dimer fatty
acids (DFA) reveals steady increases in the acid values,
refractive indices,
and the molecular weights. The optimum yield of dimer was
obtained on
dimerisation at 350°C for 30minujes, and the yield under, this
condition was
48.67%. The effectiveness of sulphur catalyst, when compared
with iodine
and NaHS04 used by other researchers under the same methodology
and
laboratory conditions, was adjudged the best of the three types
of catalysts
used for dimerisation. Thermodynamic analysis reveal that the
dimerisation
proceeds in a slow exothermic process and the heat released in
the process
is very appreciable when compared to the enthalpy of
dimerisation catalysed
102,103 by other catalysts
-
viii
LIST OF TABLES '
Table
Fatty acids, their melting points, sources and common names
Percentage fatty acid components of some vegetable oils
Extracting solvents in order of decreasing polarity
lnciease in viscosity with chain length'
Density of some triglycerides
Refractive indices of fatty acids
Classes of oil and their iodine number
Proportions of dimer structures in the feedstock
composition and properties of commercial DFA
Physicochemical properties of MSO
Variation of acid value with time of dimerisation
Acid values produced by different catalysts
Variation of refractive index with time and temperature
Refractive indices produced by different catalysts
Variation of molecular weight with time and temperature
Molecular weights produced by different catalysts
Variation of viscosity of DFA with temperature
Variation of colour with time and 'temperature of DFA
Page
4.10 TLC separation of DFA samples into its components 83
4.1 1 Enthalpy at various times of dimerisation 86
4.1 2 Effect of catalysts on the enthalpy of dimerisation 86
-
LIST OF SCHEMES
Schetnes
1 I A molecule of triglyceride
1.2 Types of triglycerides
I .3 A molecule of tocopherol
1.4 Phosphatide molecules
1.5 Glyceride molecules
1.6 Vegetable oil refining steps
Page
1 .
4
8
9
1.7 Structure of various C36 compounds of DFA 32
1.8 Isomerisation of linoleic acids
I .9 Sequence for thermal polymerization reaction 37
1 .I 0 Diene reaction of two conjugated (9, 1 1 - ) linoleic
acids 38
1 .I 1 Mechanism for sulphur catalysed isomerisation of linoleic
acid 42 .
-
LIST OF EQUATION'S
Equation
1 .I Density
1.2 Refractive index
1.3 %Free fatty acid !
1.4 Saponification value
r1.5 Ploymerisation constant (K)
3.1 Acid value
3.2 Calculation of Normality of Na2S203.5H20
3.3 Iodine value,
3.4 Saponification value calculation from sample
3.5 Relative density
3.6 Molecular weigbt
3.7 Percentage yield of DFA
Page
25
26
28
28
-
LIST OF FIGURES
Figure . Page
4 Plot of acid value against time of dimerisation 66
4.2 Plot of acid value against temperature of dimerisation 67
A
4.3 Plot of acid values against temperature for different
catalysts 69
4.4 Plot of refractive index against time of dimerisation 71
4.5 Plot of refractive index against temperature of dimerisation
72
4.6 Plot of refractive index against temperature for different
catalysts 74
4.7 Plot of molecular weight against time of dimerisation '
76
4.8 Plot of molecular weight against temperature of dimerisation
77 .
4.9 Plot molecular weight against temperature for different
catalysts 79
4.10 Plot of bulk viscosity against temperature 81
4.1 1 Plot of lnAV against 1 /T in Kelvin 85 '
-
TABLE OF CONTENT
Title page
Approval page
Certification
Dedication
Acknowledgement
Abstract
List of Tables
List of Schemes
List of Equations
List of' Fiqures
Table of content
CHAPTER ONE: INTRODUCTION
Chemistry of Fats and Oils
Sources of Fats and Oils
Composition of Vegetable Oils
Extraction of Vegetable Oils
Classification of'vegetable Oils '
Refining of Vegetable Oils
Characterization of Vegetable Oils
Uses of Vegetable Oils
Page
I I
iii
i v
v
vi
vii
viii
i x
x ,
xi
xii
1.9.0 Dimer Fatty Acids (DFA)
-
1.9.1 Properties of DFA
1.9.2 Uses of Dimer Fatty Acids (DFA
'1.10 Thermal polymerization of Drying Oils
1. I 1 Isomerisation and dimerisation catalysts
CHAPTER TWO: LITERATURE REVIEW
2.0 Historical review
2.1 Research Objective
CHAPTER-THREE: EXPERllWlENTAL
3.1 Materials used
3.2 Extraction of Oil from MSO
3.3 Refining of the Crude MSO Extract
3.4 Characterization of the Oil
3.5 Dimerisation of MSO
3.6 Characterisation of the Dimer Fatty Acids (DFA) ,
3.7 Percentage yield of the DFA
CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Extraktion of MSO
4.2 Characterization of MSO
4.3 Characterization of the crude DFA
4.4 Percentage yield of DFA
4.5 Thermodynamics of Dimerisation
Conclusion
Refrences
-
CHAPTER ONE
INTRODUCTION
Fats and oils are water-insoluble substances found in plants and
animals. They
are essential nutrient in both human and animal diets, which
supply twice the amourit
of most concentrated source of energy than that obtained from
equivalent weight of
carbohydrates'. They are 'predominantly glycerides or triesters
of glycerol, which
result from the combination of one unit of glycerol
(OHCH20HCHOHCH2) with three
units of fatty acids.
The fatty acid as the building block of the triglycerides have
its general fortnula thus:
Where R, R,, and R2 represent hydrocarbon chains of fatty
acids.
Scheme 1.1 : A molecule of triglyceride
Oil production from vegetable source was rare, in the
pre-historic times, and
was only known by the ancient Chinos,and the ~ i n d u s ~ .
Since the discovery of this
method by other parts of the world, oils and fats have found
endless use in industrial,
biochemical, and domestic proceses. The knowledge of the
chemical composition.of
fats and oils and their sources are essential in the
understanding of the various
domestic and industrial applications to which different oils may
be put.
-
1 2.0 SOURCES OF FATS AND OlLS
The world report on the supply of fats and oils show that 68.1%,
28.2% and
3.B0/;, come from vegetable, terrestrial animal and marine
sources respectively3. Thus,
plants and animals are the two major sources of fats and
oils.
The dry (hull-covered) row-crop seeds, the kernels of hard-shell
nuts and the
pulpy flesh surrounding seeds make up the possible sites for
oils in plants. Apart from
the above, oils are also found in the roots, stalks, branches,
and leaves of plants but
in' quantities not large enough for commercial purposes. Oils in
seeds are stored in
microscopic globules throughout the cells of dicotyledonous
plants or in the seed
germ or bran in monocotyledonous plants; examples: rice, melon,
corn etc.
Oil content in some fruits and seeds are sometimes as high as
65%, in several
cases 35%. In most cereal, the fats and oils are concentrated in
the seed embryo. The
olive however contains large &mount of fats in the kernel
itself while in the oil palm,
both the pulp and the kernel contain large quantity of oil.
However, the characteristic
of oils from the pulp may differ from those of the kernel.
On the whole, oils from the vegetable sources are referred to as
vegetable oils.
However, both fats and oils are the same substance of different
physical states at
ambient temperature and pressure. At ambient temperature, fat is
solid whereas oil is
liquid.
1.3.0 COMPOSITION OF VEGETABLE OlLS
campbel14 divided the composition of vegetable oils into major
and minor
components.
MAJOR COMPONENTS
The predominant component of vegetable oils is the triglycerides
(scheme 1 .I).
The fatty acid defines the properties of the molecules; and over
one hundred kinds
-
have been
these fatty
fatty acids
isolated from various vegetable and animal sources. The most
abundant of
acids are palmitic, stearic, oleic, and linoleic acids5. The
different types of
are shown in Table 1 .I. They are obtained by the hydrolysis of
oils and
fats, or synthetically by oxidation of petroleum
hydrocarbon.
Within. certain limits of composition, environmental factors can
influence the
fatty acid in the oil seed. chappelow6 reported that the
proportion of unsaturated fatty
acids in the glycerides of linseed, soybean and sunflower oils,
for example, generally '
increase as the climate becomes colder and wetter. Cd to C10
acids are soluble ,in
water and from CIZ and above are insoluble. Therefore, longer
hydrocarbon chains
confer more oiliness, (i.e hydrophobicity), hence less soluble
in water than short chain
fatty acids7. The physical properties of fatty'acids and its
components are largely
determined by the chain length and degree of unsaturation. The ,
non- polar
hydrocarbon chains account for the poor solubility of fatty
acids in water
A simple triglyceride is one with identical fatty acids (R) as
shown in
scheme 1.2 whereas triglycerides with different fatty acids (R,
R,, R2) are referred to
as mixed triglycerides. Tristrearin and distearin are examples
of simple and mixed
triglycerides, respectively.
Naturally occurring triglycerides are mixed and contain only
small percent of
simple triglyceridesO. Thus, no glycerides contain only
saturated or unsaturated acids.
Simple glycerides occur only when one acid occurs in large
amount as in olive oil
(75% oleic acid) and castor oil (87-83% ricinoleic acid) as
shown in Table I .2. Owing
to the natural biosynthesis of fats, most naturally occurring
fatty acids are straight
chains and contain even number of carbon atoms as the molecules
are being built up
from acetate units with two carbon atoms at a time8. This is
evident from Table 1 .I,
-
though lsovaleric acid [(CH3)2CHCH2COOH] is the only odd number
fatty acid isolated
from fats which has an isoprene carbon skeleton.
A triglycetride however can be simple or mixed as illustrated
below:
Mixed triglyccridc Simple triglyccridc
Scheme 1.2: Types of triglycerides
-
, 3 Table 1.1 Fatty acids, their melting points, sources and
common names
1 Common I names
Acetic acid I B&$C acid
.- - - -
Caproic acid
Caprylic
_ __ -1- Caproleic I 9-Decenoic ( 10 1 I db 1 I-_ - Butter
fat
acid C a ~ r i acid
Synthetic names
.
Ethanoic a'zd Butanoic acid ' Hexanoic acid
Octanoic acid
r ~ y r i s t i c I Tetradecanoic 1 14 1: S 1 54.4 1 ,Butter
and
A
Decanoic acid
12 12
No. of
Carb on 2 4 6
8
10
S I db
Palmitic
Ricinoleic 9-hydroxy
Elaidic
Stearic - Oleic
Sources
--
, : 7 -
Butter fat. Butter fat
Coconut oil
No. of bonds
S S S
S
S
44.2 -
9-tetradecanoic Hexadecanoic
9-Hexadecanoic
Melting points
-- - -7.9 -3.4 '
16.7
31.6
Coconut oil Butter fat 1
Octadecanoic 9-octadecanoic
--- Linoleic
Linolenic
Eleostearic
14 16 16
I I Tatiric
18 . 18
(E) 9,12- Qctadeca
-dienoic 9,12,15- octadeca Trienoic 9,11,13-
. - Arachidi Gadoleic
Arachidonic
I d b S
Idb
octadecanoic 9-octadekvnoic
eicosatetraenoic 5,8,11,14,17eico
S Idb
18
18
18
Eicosanoic 9-eicosanoic
5,8,11,14-
sapentaenoic Docosanoic
18.5 62.9
-
69.6 1 :vl;; ;;;; ;;: cd; 1 16.3
18
'20
where: Z and E represent zusameri (cis) amd enfgegen (trans)
forms. S, db, and tb represent single, double, and triple bonds
respectively.
Coconut oil Butter .fat
Most fats and oils Some fish oilslbeeffat
2d bs
3dbs
, 3dbs
20 20 20
22 Erucic'
-
I i ocosahexaenoic 1 Lignoceric Tetracosanoic H-
I tb
5d bs
22 22
13-docosenoic 4,7,10,13,16,19d
Waxlfish oil .
-6.5
-12.8
-
S I db
4d bs
s
Most vegetable oils
Soybeanlcanola oil
-
-
-
I db 6d bs
-
75.4 -
49.5
Some fish oil
80.0
Peanut'oil Some fish oil
Lard
Peanut oil 33.4
- Rape seed
Some fish oil
-
x able 1.2 Percentage fatty acid components of some vegetable
oils'o2
1 - -:c E % FATTY ACID COMPONENTS ~ - ] ~ ~ ~ 1 ( : f l C 1 8 :
~ h 0 0 1- Linseed Linum - - 6.5
1 24 22 54
Oiticia Licania rigida 5 6 - -- -. Rubber Heavea
brasiliensis 2 8 3 J 13 75 1
I tinctorius - - - - -- [ Dehydrated Ricinus castor
Sunflower
i Soybean Glycine max - - 8.3- 4- 22- 51-
-
I Sunflower
Corn 14
communis Helianthus annus
vulgaris . -
Cotton seed Gossypium vars 0.6 - 23- 2-4 24.7 40- - 27 50
Groundnut Arachis hypogaea - - b 4 60 20
-
I )
seed } O l i v e Olea. europea - - 6-14 2-4 ' 64- 7-
-
I--- I Castor Ricinus - 8 7 d-i
-
-
-
3
-
palm (pulp) !-- I P.K.O. ! .
10
Cocus nucifera Fordii aleurites
where : CI2 :0, CI4 :01 CI6 :0, CI8 :O, Cq8 : I , Cj8 :2, CI8 :3
represents Lauric acid, myristic acid, palmitic acid, stearic'
acid, oleic acid, linoleic acid and linolenic acid, respectively.
TOFA = Tung oil fatty acid. a = alpha eleostearic acid; b = licenic
acid; c = Arachidic acid; d = Ricmoleic acid; e = caprylic and
capric acid; f '= saturated acids and rosins; g = saturated acids
and unidentified components ,
7-13
-&bI-T*I
11
Communis Elaeis geneensis
1 ,
I I
! I
44.5 -
85
6
- 48.5
. - -
-
17.5 -
51
- 17
8-1 1 2-6 6-8
- -
38
37.5 8
46 51
- -
e Trac.
5 2
- -
-
8.2' 1.5g
41 43
45 14- 16
3 Trac
e
5.5 1.5
- -
-
8.7e
-
The differences in the propertiek of oils are largely due to
variations in the
structure of fatty acids contained in the oil as well as the
stereochemical conformation
of the unsaturated oils, among other things. Thus, fatty acids
exist in both cis and
trans conformations. The cis conformation lowers the melting
point of the oil%elow its
more stable trans isomer. The degree of unsaturalion and the
relative position of .
double bonds together with the presence of polar groups also
contribute to the .
differences in the properties of oils.
The chain length of the fatty acids, the type of crystal.
present and the number
and location of the cis and trans double bonds on the fatty acid
chains also contribute
to the differences .in the properties of vegetable oils. These
differences in properties I
are due to the fatty acid moiety since only one type of the
glycerol moiety is present i'n
each triglyceride.
A few naturally occurring fatty acids with branch chainsc and
physiological
characteristics include: Hydnocarpic acid (C16H2802),
chaulmoogric acid (C1~H~202)
and Gorlic acid (C18H3002). They contain the cyclopentenyl ring
system with certain
physiological activities and occur as major components of seed
fats of the family
flacourtiaceae.
THE MINOR COMPONENTS
The minor components of vegetable oils are found in small
quantities and
include: sterols, tocopherols, phosphatides, free fatty acids,
pigments, mono-and dl-
glycerides, and vitamins.
(i) STEROLS
These are also referred to as steroid alcohols which belong to
the class of
substances that contain the common steroid nucleus with an 8-10
carbon side chain
and an alcohol group. Sterols occur in fats and oils as free
sterols or esters of the high
-
fatty acids and accounts for 0.5 - 1.5% unsaponifiable
components. They are found
both in vegetable oils and animal fats though with certain
biological differences.
Important steroids derived from squalene (a triterpene) include
cholesterol (an animal
fat sterol) which occurs in trace amount in vegetable oils.
Others are stigmasterol,
sistosterol, catnpesterol and ergosterol which are found in
vegetable oils. The type
and amount of vegetable oil sterols vary with the source of the
oil4. Sterols are
odourless, colourless, and generally inert crystalline alcohols
with 26-30 carbon
atoms.
(ii) TOCOPHEROLS
These serve as important antioxidants in vegetable oils to
retard rancidity and are
also good sources of vitamin E. There are four types of
tocopherols varying in
antioxidation and vitamin E activity. Alpha tocopher~ls have the
highest vitamin E
activity and the lowest antioxidant activity. Naturally
0ccurrin.g tocopherols in most
vegetable fats may be partially removed by pressing and then
added after processing
to improve oxidative stability in finished products. Tocopherols
can be represented
structurally as: c 1-1
HO
' kiO ' 143
~ ~ Q ~ ~ ~ ~ ) ~ - ~ ~ ~ - ~ ~ - ~ ~ CH3 I
'Tocopherol
Scheme 1.3: A molecule of tocopherol
(iii) PHOSPHATIDES
Phosphatides (also known as phospholipids) are a group of
compounds which
like the oils, contain fatty acids. They also contain phosphate
group, usually a
nitrogenous base, and glycerol and are fat soluble. In general,
phosphatides may be
-
considered as triglycerides in which one of the fatty acid
groups has been replaced by
phosphoric acid derivative. Lecithin and cephalin are common'
ph'osphatides found in
edible fats together with inositol phosphatides. They make up
the principal
phosp,holipid compdnents of plants and are almost completely
removed during
vegetable oil refining. The two types of phosphatides can be
represented structurally
as: CH, - OCOR I CH - OCOR I lo- CH2-0-P=O .
~cH~cH~&(cH , )~
LECITHIN (Phosphotidalcholine)
CH2 - OCOR I CH- OCOR I PI-I CHp-0-P=O
I + OCH2CH2N(CH3)2
CEPHALIN , (Phosphotidylethanolamine
Other types of phosphatides are : phosphotidylinositcl and
phosphotidylserine and
can be represented structurally as:
ClH2 - OCOR CI-12 - OC01< I I ~ 1 - I - OCOR ' ! CN-OCOR I $-
I 1 - 0 - - OCH2 - HNH2 F
1-1 0 COOH F 1 0 HO
Phosphatitlyl inositol
Schcmc 1.4 l'hophatide molecules
(iv) FREE FATTY ACIDS
These are fatty acids present in fats and oils. Several percent
fatty acids may
be found in some unrefined oils and the level is reduced during
refi,ning.
(v) PIGMENT
Some co1oure.d n-laterials which occur naturally in vegetable
oils include the oil-
soluble carotenoids, chlorophylls and the xanthophylls
(derivatives of chlorophylls).
They also include the yellow (lutein) in plant leaves, and
zeaxanthin in corn
-
(zea mays). Also, the capsanthins (red pigment in red pepper),
lycopene (red
colouring matter of tomatoes), beta carotene (a yellow-orange
pigment and precursor
of vitamin A) are also found present in the vegetable oils.
Seeds exposed to frost during maturation or immature seeds may
give oils that
contain higher levels of chlorophyll to a level to make the oil
green. These colours are
extracted along with the oils and dissolve in them to give the
range of colour from
yellow to deep red.' The pigment level in vegetable oils is
reduced during ,processing
of the extracted oils to 'improve the market value of the
oil.
(vi) MONO- AND Dl-GLYCERIDES
These are used frequently as emulsifiers. They are mono- and
di-esters of fatty
acids and glycerols. They occur naturally in very minor amounts
in both animal fats
and vegetable oils. They include alpha and beta monoglycerides
as well as 1,2 - and
1,3 - diglycerides. Strl;cturally, they are represented as
follows: I
CH2 -01-1 CI-12 - CO(]R2 C'kI? - C(lOR2 C:II2 - ClOOR I I I I CM
- COOR CH - COORl CI-I - 01-1 C'H - 011 I I I I CH2 - OH CH2 - 01.1
CI-I2 - COORI ' (21-12 - 01-1
Alpha-monoglyceride Beta-monoglyceride 1,2- diglycericlc 1,3 -
diglyceride
Scheme 1.5: Glyceride molecules
(vii) VITAMINS
Vegetable oils are good sources of vitamin k. The vitamin is
present in small
quantity and owes its reactivity to the tocopherol content of
the oil. Oils also
serve as good carriers of the fat soluble vitamin A (retinal; a
colo~rless
compound considered to result from cleavage of beta carotene)
and vitamin D3
(cholecalciferol, a steroid) and vitamin K which include
menadione and its
derivatives.
-
(vii) OTHER MINOR COMPONENTS
Some vegetable oils may contain traces of proteins and
carbohydrates which
are almost completely removed during refining. Pesticide
residues and metals
(examples, iron, copper, lead, arsenic, cadmium, and mercury),
are also found i
present in the oil" as a consequence of crop treatment and
environmental influences',
Polycyclic aromatic hydrocarbons are also found in some
vegetable oils. In rape seed,
for example, sulphur in the form of elemental sulphur;
isothiocynates also occurs. All
of these undesirable contaminants are reduced to negligible
level during refining.
EXTRACTION OF VEGETABLE OILS: 1.4.0
Obtaining oils from vegetable sources is of ancient origin. The
,native in the
tropical region of the globe have long been removing these oils
from various nuts after
drying them in the sun". The vegetable oil extraction techndogy
has evolved in
various phases which include extraction by pressing and solvent
extraction processes
amongst other methods.
1.4.1 THE PRESSING PROCESS
The pressing method of oil extraction is in two forms: First,
the meal is preheated
to coagulate the protein matter which is largely responsible for
the extremely fine state
of division of the oil inethe cells. Secondly, pressing, which
is attributed to edible oils,
removes more oils and greater quantity of non-glyceride
impurities such as
phospholipids, coloured bodies, and unsaponifiable matter.
Heating in the first form
enables the very small oil droplets to coalesce, wl'ile the low
viscosity facilitates the
flow from the material to the press. However, oils expressed
without pre-heating
contain the least amount of impurities and is often of edible
quality. Such oils are
known as cold drawn, cold-pressed or virgin oilq3.
-
I . L Z ' SOLVENT EXTRAC,TION PROCESS (SEP)
The method of extraction that is increasingly used for seed oil
extraction is the
SEP. In this process, low boiling petroleum fraction is used for
the extraction. The
boiling point of the solvent must however be optimal to minimize
solvent loss at
complete re-distillation of the solvent from the oi! without
employing unduly high .
temperatures. The Extractability of the oil has been foundto
,depend on the nature of
the oil, solvent, flake thickness and the pre-treatment
condition of the oil seeds16.
Different factors determihe the choice of solvent for oil
e~traction'~. These are:
Solvent extractive capacity
Effect of solvent on oil properties ,
Process safety
Solvent volatility '
Stability and
Economic factor.
Ideally, solvents used for extraction should dissolve only
glycerides but
not undesirable components such as colouring matter, gums, and
phospholipids. For
health concerns, commercial oil extraction is done almost
exclusively with normal
hexane. Ethyl and isopropyl alcohols areattracting the most
attention as alternative
extracting solvent^'^. Table 1.3 shows the boiling points1
ranges of common extracting
-
Table 1.3: Extracting solvents in order of decreasing
polarity
Acetic acid CH3COOH 1 v: / Acetonitrile * C H X N
1 Ethyl acetate I CH3COOC2H5 I 1 Dichloromethane CH7C17
Methanol Ethanol
CH30H C2H50H
- - I- ~hi0r0~~i-i~~ Carbon tetrachloride
MECHANISM OF SOLVENT EXTRACTION
65 ' 78
6 1 76
Benzene C6Hs Toluene . C6H5CH3
- - -
C5H12 - C6H14
N - heptane c7H16 , CyAohexane, ' C6H12 .
Solvent extraction of oil has been shown to be temperature
dependent. The study
80 11 1
90 - 100 - 40 - 60160-80
36 69 94 8 1
on the effect of temperature on the extraction of rubber and
melon seed oils shows
that; the yield increases with increase in temperature.' It
reaches its maximum value at
the boiling point of the solvent16. The extraction involves
several mechanisms, viz'":
(i) Freshly harvested seeds are cleaned of trash, foreign weeds,
and stones which
may hirbour moisture that could accelerate the formation of free
fatty acids. It is then
dried before storage. If this was not done before storage, it
must be done before
extraction.
(ii) Removing hulls by cracking, aspirating or screening
operation.
(iii) Cracking or roughrgrhding the kernels.
(iv) Steaming (tempering or cooking) of the meats or pre-pressed
cake.
-
(v) Extraction of oil with suitable solvent.
(vi) Removing the solvent from the miscella (oil-solvept
solution).
(vii) Filtration of the oil to remove solid particles which
found their way into the
solution during extraction.
1.4 3 USE OF CARBON DIOXIDE
The latest technique of extraction is a high-pressure critical
state extraction with
carbon dioxide. This is mainly applied to high value products
such as essential oils, I
hops, and instant coffee1'.
1 5.0 CLASSIFICATION OF VEGETABLE OILS
Two classes of oil exist and these include: those of the mineral
and those of
plant and animal origins1'. Oils from the plant and animal
origins contain: Carbon,
Hydrogen and Oxygen as the major constituent elements and are
known as natural
oils. Natural oils are further classified as volatile
(essential) oils ands non-volatile
(fixed oils). Oils from the mineral origin are classified into
petroleum, shale oils, and
coal tar; hence, are referred to as synthetic oils. Synthetic
oils are complex mixture of
hydrocarbons with varying amount of Oxygen, Nitrogen, and
Sulphur compounds
togeiher with ~ ~ d r o ~ e n and Carbon.
1.5.1 . VOLATILE (ESSENTIAL) OlLS
Volatile oils are the odourous substances found in various plant
parts and are
also referred to as essential oils. They evaporate easily when
exposed to air at
ordinary temperature. They vary from colourless to yellow or
brown due to oxidation
and rancidification when exposed to air for sometime. To avoid
darkening, volatile oils
are stored in a cool, dry place (in tightly stoppered amber
glass c~ntainbrs)~. Example
of volatile oils include certain phenols and the/r esters such
as Eugenol (oils of
-
15
Cloves),.Soeugenol (oils of nutmeg), Anetbole (oil of aniseed),
Vanillin (oil of vanilla
bean), thymol (oil of thyme and mint) ', etc.
Volatile oils are used as flavouring and fragrance in various
applications,.
blending these oils (example, mint and cinnamon for toothpaste,
mouthwash, etc) also
make possible some fragranced products such as room fresheners,
paper, printing
ink, paint, candle, soap, condiment, floor polish'g.
1.5 .2 NON - VOLATILE (FIXED) OILS
Fixed oils are obtained from either plants or animals. Their
basic characteristic
is food storage such as essential ingredient like vitamins,
proteins, etc which aid
growth and development. Fixed oils and fats are important
products which are used, as
pharmaceutical components because of their emollient properties.
Thus, it becomes
the principal constituent of many drugsq8.
Their composition differs from essential oils since they contain
mainly
glycerides (fatty acid esters of glycerol). The degree of
unsaturation of the fatty acids
involved affects the melting 'point of the ester. The more
unsaturated acids give esters ,
with low melting points; as a result, non-volatile oils can be
classified into fatty oils and
the fats". Fatty oils refer to those that are liquid at room
temperature whereas fats are
those that are solid or semi-solid at ordinary temperature.
The classification of vegetable oils can also be based on their
ability to absorb
oxygen from the air.On. this basis, fixed oils are classified as
drying, semi-drying'and
non-drying oilsz0.
(i) Drying oil
These are oils dch in the glycerides of the unsaturated fatty
acids particularly,
linoleic acid with few co,mpounds of oleic acid. On exposure to
air, they absorb oxygen
and form a tough elastic but water resistant film. The value of
drying oils depends on
-
their ability to polymerize or dry upon application onto a
surface to form tough,
adherent, in~pervious and abrasion-resistant film. They are used
as important solvents .
in paints, artificial rubbers, linoleums and varnish
industriesz0. Examples are linseed,
tung (China wood) oil, castor oil, oiticia oil and tall oils
amongst others; which provides
fatty acids for use in non-yellowing alkyds and find its primary
Use,in the industries.
(ii) Semi - drying oil
' The intermediate between drying and non-drying oils is the
semi-drying oil.
They are slow drying when compared to drying oils and their
fatty acids are valuable
components for making non-yellowing alkyds. Large amounts of
linoleic and other
saturated acids are" present but no linolenic acid. When exposed
to the atmosphere,
they thicken but do not form a hard, dry film. The film remains
sticky (tacky), and
absorbs atmospheric oxygen slowly producing a soft film after
prolonged exposure to
air. Examples of'semi-drying oils include: tobacco oil, corn
oil, melon oil, soybean oil,
etc. However, paints of lower grades could be made by mixing
full-drying with semi-
drying oils.
(iii) Non-drying oil
Non-drying oils remain liquid at normal temperature and are
incapable of
forming elastic film after long exposure to air. They are
important sources of fatty
acids used in non-drying alkyds. Castor 'oil and coconut oil are
best known examples.
Others include groundnut oil, palm oil and olive oils. They are
occasionally used as
plasticizers for spirit and lacquersz'. Also, they .enter into
soaps and cleanse'rs,
cosmetics, lubricants, leather dressing, and candles.
The drying rate of. oils can be determined as the rate at which
a thin film of oil
exposed to air changes to a solid non-tacking skin. The rate
m,ay be accelerated when
a small quantity of metallic compound called drier such as
linoleate acids, and
-
naphthanates of lead, manganese and cobalt is introduced into
the oil. The driers
therefore act as oxygen carriers to the sensitive centers in the
oil molecules.
I 5 3 OTHER CLASSIFICATION
Oils can also be classified as being edible and non-edible.
Various edible oils
such as soybean, corn, cotton seed, melon seed oils etc are
basically employed for
cooking purposes, salad dressing and other table uses.
Hydrogenated fats for cooking
and baking may include a wide variety of vegetable oils such as
cotton seed, palm oil,
and soybean oil. The hydrogenating process improves the odour or
flavour of the
original crude product as well as its keeping factor.
The non-edible oils on the other hand are oils used for soap
making and those
found useful in paints and varnish industries etc. ,Some of the
oils are slightly
hydrogenated to make them suitable for use. Drying oil
industries 'consumes a large
percentage of non-edible oils. These drying oils are essentially
unsaturated and
produce film or coating upon oxidation. They are also employed
with synthetic resins
and cellulose derivatives to give special types of films.
1.6.0 REFINING OF VEGETABLE OIL
Extracted oils are 'crude' as they contain small quantities of
compound other
; than triacylglycerol esters22.. Crude fats and oils contain
variable amounts of non-
glyceride impurities such as sterols, phosphatides, free fatty
acids, certain pigments
(carotenoids, chlorophyll, xanthophylls, etc), metals etc which
are susceptible to
foaming and smoking on heating and liable to precipitation of
solid materials when the
oil is heated during processing operations.
There are three basic objectives for refining and processing
crude fats and
oils. These are:
(i) to remove free fatty acids (FFA); phospholipids (gums),
pigments and off
-
flavour/odour compounds and toxic substances to produce
light-coloured .
products with long shelf lives.
(ii) to obtain a mixture of triacylglycerol with the desired
solid content profiles over
the range of products use.
(iii) to prepare and store semi-solid products with desired
textures17.
There are various nlethods of refining and the one chosen is
dictated by the end
use of the oil. The solid contaminants however are removed by
filtration or
decantation. The classical oil refining procedure consists of
degumming,
deacidification, decolouration, dewaxing, deodourization and
acid wash.
1.6.1 DEMUNlFlCATlON OR DEGUMMING
This process involves the removal of phospholipids, which may
have been
extracted alongside the oil, to avoid darkening the oil during
high temperature
deodourisation. The process generally involves treatin,g the
extracted oil with a limited
amount of water to hydrate the phosphatides and make them
separable by
centrifugation. Super degumming step is that where citric acid,
glycerin, or phosphoric
acid is. added to remove phospholipids that are not hydrated by
water alone.
Sometimes the degumming is done to recover and further process
the phospholipid to
yield a variety of lecithin products which are good emulsifying
agents. The degumming
temperature is between 50-70°C above which there is increased
solubility of the
phosphatides in the bi~. 'At.temperatures below 50°C, the high
viscosity of the oil ' ,
makes separation of the phosphatides more difficult.
1.6.2 DEACIDIFICATION
The degummed crude vegetable oil is then neutralized with alkali
to form sodium
salts of fatty acids which are removed (as soap stock) by
continuous centrifugationz3.
Large amounts of these free fatty acids in oils are not
desirable because:
-
(0
(ii)
(iii)
The unsaturated free fatty acids are more sensitfve to oxidation
than the
corresponding glycerides and this can reduce the shelf life of
the oil.
Free fatty acids interfere with hydrogenation by being
selectively adsorbed '
on the surface of the catalyst through either of the carbonyl
groups. This
hinders the hydrogenation process of the glycerides.
Low acidity in oils favour fast bodying and good colour in
bodied oils and
vanishess.
The soap stock also occludes some phosphatides, colour and
flavour compounds on
each percent free fatty acids (%FFA) present.
This process is also referred to as ALKALI REFINING and can be
carried out
either with dilute or concentrated solutions. Concentrated
solution of the alkali has a
more powerful demunification action than the dilute solution. It
is good for
undegummed vegetable. oils because it causes greater
saponification of the
glycerides than the dilute solution. Foots (soap stock) after
separation may be used
for soap production. Thus, calcium chloride may be added
directly to the soapstock for
prompt separation of the calcium soap (by precipitation) from a
relatively pure saline
(NaCI) solution. Calcium, soaps are useful industrial
ingredients for instance, as
demoulding agents22.
1.6.3 DECOLOURISATION
Bleaching is the heating of the oil with adsorbent (bleaching
earth -example,
activated carbon, fuller's earth or acid activated
montmorillonite clays) which ensures
an almost complete elimination of colouring matters in the
vegetable oil. During
bleachirlg, phospholipids,'soaps, peroxides, aldehydes and other
polar compounds
are also adsorbed alongside the pigment. The spent adsorbent is
then recovered
-
through filtration although it is plagued with disposal
problemad. The process of
decolourisation involves three basic methods:
(i)
(ii)
(iii)
Oxidative bleaching: this is mostly applicable to saturated
oils. It has to do with
the blowing of air into the oil at an elevated temperature
(about 1 10°C). Some
quantities of cobalt, manganese and iron salts are used to
accelerate the
process8.
Adsorptive bleaching: ,bleaching earths are used which, due to
its large
surface area, largely removes the pigment type molecules without
damage to
the oil itself. It'is the method used for bleaching edible oils
and oils for the
surface coating industries. :
Heat bleaching: oils are heated t~ high temperature under high
vacuum with
the addition of stripping steam to enable some pigments like
carotenes become
colourless. This method leaves the pigments in the oil which may
have adverse
effect on the quality of the oil.
There are indications that the earths in adsorptive bleaching,
also adsorb
polymers probably polar o ~ ~ ~ o l ~ m e r s ~ ~ . Adsorptive
bleaching has been applied in
bleaching a number of oils including palm oil, melon and' ~ i l
b e a n ~ ~ , although colouring
matter in soybean, linseed and rapese'ed oils resist this
treatment.
Bleaching earth is by far the most widely used adsorbent
ma'terial though in
many cases, the bleaching effect obtained with the carbon is
greater and it adsorbs
various other substances that have objectionable taste or
odour.
To minimize the loss of oil during adsorptive bleaching, solvent
(e.g. hexane) is
added to increase the adsorptive capacity of the bleaching
earthZ6 and the colour of
the bleached oil decreases linearly with increasing dilutions in
the solvent27. The oil . '
-
. 21
remaining in the filtered cake may be up to 20-40% and can
partly be recovered by
any or a combination of the following processes:
Blowing steam on the cake
Circulating hot water, and or hexane through the cake in the
filter.
Mixing the cake with oilseed and passing it through the
extraction process.
Extraction of the cake with hexane and
Boiling the cake in water containing soda and salt.
DEODOURISATION
Superheated steam is blown through the oil at hydrogenation
temperature to
remove volatile odouriferous component present in the oil. These
include: volatile
pesticides, aldehydes, tocophens-like natural antioxidants, and
residual amount of
free fatty acidsz8. The natural antioxidants may be recovered
from the deodourised
condensate and the final refined, bleached, and deodourised
product is called RBD
oils (Scheme 1.6).
Deodourisation is conveniently carried out at pressure 1.5 -
9mmHg and
temperature 175 - 270°C. Removal of pesticides from the oil
requires a
deodourisation temperature greater than 240°C; but in some
cases, example in the
cocoa butter processing, it is essential to use low temperature
preferably less than
180'~. A small amount of concentrated citric acid solution is
normally added during
deodourisation to scavenge any metal present in the oil.
In scheme 1.6, the degummed oil may be subjected to minor
bleaching and
then physically refined using a high temperaturelvacuum process
that strips away the
compounds normally removed in the deodouriser plus the free
fatty acids2'. The major
advantage of physical refining is reduction of oil loss that
occur by occlusion. On the
-
whole, deodourisation may not be done in oils for paint
industries, but a must for
edible fats and oils.
' CRUDE VEGETABLE OIL
1 Water -+ Degumn-ring -, Cmde I ,xithin 1
1 Alkali + Alkali Refining -, Soap stock
1 REFINED OIL
1 Activated -, Bleaching - Spent Earth Earth 1.
BLEACHED OIL 1 +
Deodourization -+ Deodousized Condensate Bleaching and Physical
Refining
RBI)
Where RHD represent: Refining, Bleaching, and Deodourization
Schcn~e 1.6 Vegetable Oil Refining Steps
This is applicable only to a few oils like the su~;;lower oil,
maize oil, and linseed , I
oils which contain some wax from the seed shells that makes the
oil cloudy at low
solubility. The quantity of wax in crude oil varies from a few
hundred to over 2000ppm.
Wax content in the oil has to be reduced to a level of about
10ppm (by dewaxing) to
enhance sufficient cold stability of the oil3'.
All materials that will solidify-out at ; refrigeration
temperatures are removed
during dewaxing and this is accom&hed by cooling to 5OC and
filtering-out any
solidified material. It can be'carried out on the micelle from a
seed extraction plant or ' .
in combination with neutralization. The traditional method of
dewaxing as applied to
the refined oil is similar to fractional crystallization
(Winterisation).
-
' 1.7.0 CHARACTERISATION OF VEGETABLE OIL
Proper identification and assessment of quality and purity of
vegetable oil is achieved
by characterization using a number of physical and chemical
constants. Whereas the
physical constants include: melting point, density, refractive
'index, viscosity, colour,
solubility etc., the chemical constant include: iodine value,
saponification value,.acid
value, and volatile fatty acid contents. 1
1.7.1 PHYSICAL CONSTANTS
(A) MELTING POINT
Oils generally,represent the melting points of their constituent
fatty acids which
define its properties. Melting point increases with chain length
and where only one '
double bond exists (e.g Clo : I ) , the melting point is lower
if the double bond is located
after an odd number carbon than even number carbon . Also, the
melting point is
lower if the double bond is located near the middle df the chain
as compared to one
located at either ends. The melting points of mixed
triglycerides (whether animal or
vegetable sources) consisting primarily of 16 to 18 carbon fatty
acids generally rises
smoothly with increased'content of higher melting fats.
Geometric isomers reveal that ,
trans fatty acids always have higher melting points than their
cis counterparts for any
chain length3'.
However, the same sample of pure or mixed fatty acid
triglyceride may show as
; many as five different melting points depending on its heating
and cooling history".
Thus, tristearin has an amorphic (non-crystalline) solid form
and three crystalline
forms with melting points at 54.7'C, 63.2OC, and 73.5OC.
Therefore, different methods exist1' for the determination of
,the melting points of
triglycerides. These are:
(i) Capillary method: ahis determines the temperature at which a
sample of I
-
(ii)
(iii)
(iv)
2 4
fat in a closed capillary becomes completely clear and
liquid.
By matter dropping point : the method determines the temperature
at which a
sample becomes sufficiently fluid to flow in a specified
apparatus.
By open tube-softening point: this determines the temperature at
which a
solidified fat, in an open capillary tube, softens sufficiently
to slip and rise to the
top of the heating bath. It is applicable to fats such as
coconut oils, stearin,
hydrogenated fats and hard tallows. The results, 'sometimes, are
reported as
'melting slip points'
Wiley method: determines the temperature at which a sample disc
of solidified
fat assumes a spherical shape while suspended in a heating bath
with an
alcohol water density gradient.
Factors that affect melting'points of different samples
include:
(i) the types of the fatty acids present in the triglycerides
and their locations
(ii) chain length of the fatty acids
(iii) number and location of cis and trans double bonds on the
fatty acid chains.
(iv) type of crystal present.
(B) VISCOSITY
Oils owe their relatively high viscosity to the intermolecular
attraction between
their fatty acid chains, which has to do with the rate of flow
of the molecules against
one another. Measurement of viscosity is important in the study
of the polymerization
of drying oils and also i r connection with the technical
properties of polymerized oils
for the paint industry. Solution viscosity of oils has been used
to elucidate the mode of
network formation in drying oils32. Generally, viscosity tends
to increase slightly with
increasing chain length. The linear relationship between log
viscosity and temperature
is seen in the increase of the viscosity of oils in prolonged
heating due, to the
-
formation of dimeric and oligomeric fatty acid groups. Table 1.4
gives the viscosities 'of
some faky acids as a function of chain length.
Table 1.4: Increase in viscosity with chain length
[ ~ r y ~ ~ ~ w - k - - Tricaproin --
Tricaprylin 8.8 --
NO.CARBON ATOMS (MPa.S)
1 Tristearin 18 23.4 -1 Trimyristin . 1 14 I Tri~almitin 16
DENSITY
17.6 20:5
This is a measure of the mass to volume ratio of the oil. It
decreases with
increasing molecular weight, degree of unsaturation and free
fatty acid contents., It
can be calculated using the formula in equation 1 .16
Density = 0.8475 + 0.0003*saponification value + 0.00014*iodine
value 1.1
Oxidation generally leads to higher densities. High free fatty
acid content tends
to decrease the density of crude vegetable oil. Up to 260°C, the
density decreases by
about ~0.00064~lcrn~ per temperature increase of I0C. For most
fats and oils, the
specific gravity lies between 0.90 and 0.94 at 20°C.
Table 1.5: Density of some triglycerides TRIGLYCERIDES NO. OF
DENSITY
CARBON ATOMS
Trica rin Trilaurin
Trimvristin
Trilinolein 18:2 Trilinolenin 18:3
G / c ~ ~ At 15OC
1- Tripahitin Tristearin
10 12 : I 4
0.891 3 0.8801 0.8722
16 18:O
0.8663 0.8632
-
(D) REFRACTIVE INDEX
The refractive index generally increases with the degree of
unsaturation,
average molecular weight of the oil (chain length), and the
extent of conjugation of the
double bonds. It is one of the most important aids for
classifying fatty acids since it is
closely related to the nature of the product (molecular weight
and degree of
unsaturation) and can be determined quickly with great
accuracy8. Table 1.6 gives
refractive indices of different fatty acids as it increases with
chain length and
unsaturation. Prolonged. heating leads to increase in refractive
index due to the
introduction of polar groups into the fatty acid chain. Equation
1.2 gives the
relationship between refractive index for fresh,
non-hydrogenated oils and fats and
other oil parameters states thus:
Saponification value (S.V)
Table I .6: Refractive indices of fatty acids.
FATTY ACl DS
Tricaprin Trilaurin
Trimvristin
I ,
Tripalmitin Tristearin
(E) COLOUR
10 12 14
Triolein Trilinolein
The colour of crude vegetable ,oil is determined by the nature
of oilseed being
1.4370 1.4402 1.4428
16 18:O
extracted and the power of the solvent used for the extraction.
The colour is important
1.4452 1.4471
L
18:l 18:2
in judging quality and determining the degree of bleaching. In
some oilseeds, the
colour disappears campletely after bleaching.
1.4645 1.4645
-
(F) SOLUBILITY AND MISCIBILITY
The solubility of fats and oils in organic solvents decreases
with increasing
molar mass and increases with degree of unsaturation. It plays a
part .in determining
the immiscibility curves of oil or fat in various solvents and
may be used to check the
purity of the oil. Nearly all fats and fatty acids are easily
miscible in common organic
solvents such as hydrocarbons, chlorinated hydrocarbons, ether
and acetone. The
difference in solubility enables categories of glycerides to be
separated by fractional
crystallization although complete separation is rarely achieved
because of mutual
solubility effects. The solubility of oils in water is low. It
decreases with increase in
chain length and increases with temperature.
1.7.2 CHEMICAL CONSTANTS
(A) Iodine value (Number)
The iodine value is used'to determine the degree of unsaturation
by measuring
the number of milligram of iodine absorbed per gramme of an ,oil
sample. The extent
of rancidity is also indicated by the amount of iodine
consumed33 since iodine is added
across €he double bonds of the fatty acids. The higher the
iodine number, the greater
is the unsaturated fatty acid content. The Wij's method is most
commonly used for its
determination though; it can be inaccurate with conjugated
systems. The effect .of
temperature on unsaturation could be expressed by the iodine
number of the
triglyceride34. However, the importance of determining the
iodine value is to classify
the oil according to its drying ability as indicated in table
1.7.
Table 1.7: Classes of oil and their iodine numbers
I IODINE I CLASS OF OIL I I NUMBER I I
>I 30 Drvina oil I
. t'0%0A30 Semi-drying oil Non-drying oil
-
(B) ACIDVALUE
The acid value is used to express the degree of acidity of the
oil. It is defined as
the number of milligramme of potassium hydroxide (KOH) required
to neutralize the
free acids in I g of the sample. The importance of acid value
lies in the fact that it
measures the free fatty acid content in the oillfat. It is
especially important for judging
the quality of raw oils and for determining the quantity of
alkali required for alkali .
refining of oil at minimal saponification. Solvent selectivity
towards phosphatides
affects the acid value of fatty acids and the presence of 1 O/O
phosphatide.increases the
acid value by 0.30 - 0.35 M ~ K O H ~ ~ . Different extraction
solvents often give different
acid values for the same oils8. One unit acid value is
equivalent to 0.503% free fatty
acideg .That is:
%FFA = 0.503 * acid value 1.3
(C) SAPONIFICATION VALUE
Saponification value gives the number of miiligramme of
potassium hydroxide
(KOH) required to neutralize the fatty acids resulting from
complete hydrolysis of l g of
fatloil. It indicates the average molecular weight of fatty acid
present and is related to
the molecular weight by the expression:
where M.W is the average molecular weight, S.V is the
saponification value of the oil .
and A.V is the acid value.
Saponification value does not change appreciably by
polymerization, but
increases with oxidation. Low molecular weight glycerides have
high saponification
value (example coconut with S.V = 260.267) which reflects ,the
presence of high
percentage of fatty acid with CIZ or less carbon atoms. A high
molecular weight
-
glycerides have low saponification value (example, soyabean with
S.V = 189 - 195)
which reflects a large percentage of C16 and C18 carbon atoms of
fatty acid35.
(0') Reichert-Meissle, ~olenske and Kirschner Value
The amount of steam-volatile fatty acid which can be recovered
from oils under
standard conditions is measured by Reichert-Meissle Polenske and
Kirschner values.
The acids involved include: butyric-C4, caproic-C6, caprylic-C8,
capric-Clo, lauric-Cq2
Butyric and caproic acids are water- soluble while caprylic and
lauric acids are water-
insolubleA. The water-soluble and water-insoluble acids are
measured by ~eichert
value and Polenske value, respectively. The Kirschner value
measures butyric acid 6y
separati6n from caproic acid precipitating the'later as a silver
salt.
1.8.0 USES OF VEGETABLE OILS
The report from Food and Agricultural Organisation in
collaboration with the
World Health ~ r ~ a n i s a t i o ' n ~ ~ shows that fats and
oils have both domestic and
industrial applications. As such there are both edible and
non-edible uses of vegetable
oils,
1.8.1 EDIBLE USES OF OIL
Oil and fat products used for edible purposes can be divided
into liquid oils and
plastic fats. The liquid oils include peanut oil, soya bean
oils, sunflower oils, olive oils,
etc. the plastic fats include butter, lard, shortening, and
margarine. The primary use of
fatty oils is closely related to man's desire for food. As
earlier stated, fats and oils are,
the most concentrated saurces of energy in the diet and they are
dlso important
sources of oil-soluble vitamins like vitamins A and D. They are
also good sources of
vitamin E which is present in tocopherols.
-
Researches carried out by food scientists and biologists reveal
that; of the two
dozen fatty acids availa'ble, two cannot be synthesized within
the animal's body.
These include linoleic and linolenic acids and are referred to
as essential fatty acids
(EFA). These are said to govern every life process in the body
and also include
prevention of distinct heart and vascular diseases. This,
therefore, promotes the
production and application of vegetable oils with high linoleic
acid content such as
melon, soybean, and sunflower oils.
Generally, most seeds are grown specifically for processing to
oils and protein
meals and short chain fatty acids are mostly desirable for foods
and feed uses.
Hence, the principal consumer of vegetable oils and fats is the
edible oil industries.
1.8.2NON-EDIBLE USES OF OIL
The non-edible uses of vegetable oils include the various
industrial applications
of oils. In these applications, the level of unsaturation of the
oil becomes important. As
indicated earlier, oils are classified as drying, semi-drying
and non-drying (Table 1.7).
The drying and the semi-drying oils are mostly employed for the
production of paints, .
soaps, and cosmetics. Only recently, have the non-drying oils
been found useful in the
formation of plasticizers in paints and vanish industries aswel
l as in the cosmetics
industries where they are mostly used as emulsions. The
non-edible use of oil
employs the long chain fatty acid which has been in demand for
production of
lubricants and polymers. On this note, linseed oil, soybean and
castor oils can be
used as lubricants. Castor oil can also be used as a hydraulic
fluid.
Hydroxyl fatty acids are used for thickening greases and
improving the pliability
of plastic covering materials. Epoxy fatty acids are useda in
the production of plastics
and coatings.
-
Fatty acids with conjugated unsaturation are often desired as
chemical
intermediates in industrial products e.g. tung oil. Conjugated
unsaturation can be
obtained by alkali isomerisation of soybean and linseed fatty
acids. Novel sources of
conjugated unsaturation in vegetable oils include: valeriana
officinalis (40%
unsati~ration at positions 9, 11, and 13), candendula
officinalis oils (55% unsaturation '
at positions 8, 10, and 12), centranthus macrosiphon oil (65%
unsaturation at
positions 9, 11, and 13), and impatiens edgeworthii oil (60%
unsaturation at positions
9, 11, 13, and 15).
The following authorities have studied other uses of vegetable
oils for non-
edible purposes: peterson3', who studied 'vegetable oils as
diesel ,fuel' and
~aufmann~' , studied 'field evaluation of sunflower gilldiesel
fuel blends in diesel
engines'. Others are ~ o n w e r ~ ' and schwab4' who studied
'liquid fuels from Mesua
ferrea linseed oil' and 'diesel fuel thermal decomposition of
soybean oil', respectively.
1.9.0 DlMER FATTY ACIDS (DFA)
The term dimer fatty acids is applied to the dicarboxylic acids
formed as a product
of thermal polymerization of two or more CI8 unsaturated fatty
acids such as oleic and
linoleic acids. Commercial DFA products are mixtures of C36
dibasic acids containing
some trimers (C54) and hlgher oligomers. Small amounts of
monomer acids (CI8 and
saturated, unsaturated and structurally modified fatty acids)42
are also present in the
product. The main constituent is substituted cyclohexanes, which
arise through Diels
Alder reactions. DFA is used to synthesize a fatiy polyamide by
reacting with
ethylenediamine to produce either solid or liquid polymers. The
solid polymers are
largely linear products obtained by reacting dimer acids with
diamines, while the liquid
polyme;s are highly branched products of tower molecular weight,
which result from
the reaction of dimer acids and polyamines containing three or
more amino groups43.
-
1 I, 1 PROPERTIES OF DFA
Dimers from fatty acids having 18 or more carbon atoms are a
mixture of 36-
carbon atoms dibasic acids, 54-carbon atom tribasic acid (trimer
acid), 18-carbon
atotn monomer and structurally modified monobasic fatty acids.
The mixture is
characterized by increase in the acid number of the polymerized
oil. These dimer
acids have the unique advantages of being hydrophobic, with high
molecular weight,
and generally having sdme degree of unsaturation and are
dibasic. Both the
unsaturation and the acid functionality provide sites at which
further chemical
tnodification may be undertaken. The degree of unsaturation of
the dimer acid may be
reduced by hydrogenation to enhance its stability.
The formation of a conjugated system in the fatty acids' leads
to a rise in the
refractive index. The physical and chemical properties of the
dimers of trienoic acid
suggest the formation of a bicyclic structure by an
intra-molecular ring closure which
follows the 1,4-diene addition reaction. Thermal polymerization
can also lead to the
formation of acyclic dimers which occurs predominantly by the
free radical
mechanism. A bicyclic dimer could also be formed as shown in
scheme 1 .I 1
CH3(CH2)8CH(CH2)7COOH I
CH3(CH2)7C = CH(CH2)7COOH
C143(CH2)3CH=C'I I Acyclic Dimer Acid
Monocyclic Dimer Acid
Scheme 1.7 Structure of various C36 compounds of DFA
-
The relative proportion of each of these structu'res in the
feedstock of
d i rner i~at ion~~ is as stated in Table 1.8.
Table 1.8: Proportions of dimer structures in the feed
stock..
ACYCLIC / Oleic and 40
Linoleic acid
---A-
MER STRUCTURES,
Apart from the structures above, many other structures including
aromatics
\ have been found among the products of d imer i~at ion~~. Von ~
i k u s h ~ ' stated that the ,
logarithm of viscosity plotted against time for dehydrated
castor and linseed oils
undergoing dimerisation, approaches a straight line; the slope
gives a measure of the
polymerization rate. cannegieteaO showed that the polymerization
rate constant K is
given by the expression:
where Vq and Vl = viscosities at times Tq and TI, respectively,
for samples removed
during the progress of any one cook at a constant temperature.
It is howev,er
impossible to obtain reliable polymerization rate data in open
kettle laboratory cooks,
especially with smaller quantity of oil. Generally, the
composition of a dimer influences
its properties as shown in Table 1.9.
-
Table 1.9: Composition and properties of commercial DFA.
I PROPERTIES , I
Dirner content (%) 'Trimer content (%)
I I Unsaponifiable
matter(%mass 1 0; " 1 1 .o ! L--- ! Colour (Gardner max) 9
. I . Monobasic acid '(%) , i Acid number (MgKOHIg) I
1 Saponificationvalue 1 (MaKOHla)
.-
TYP€ OF DlMER FATTY ACID
~.T 1.5 r--i I 190,- I98 -- 190 - 197- 189 - 197 -- 195 - 201
191 - 199 191 - 199,
Higher dimer 87 13
: . - .-. - Viscosity - .- (at 23OC) Cst I S~ecific aravitv (1
00/25°C) k 0.91
1.9.2 USES OF DlMER FATTY: ACIDS (DF.A) !
0.91 , . Density ( K g l ~ ' L ~efractiv%-hdex (at k ° C )
DFAs are used in adhesives, ink and surface coating formulation,
reactive and
Intermediate &h trimer
non-reactive polyamides, corrosion inhibitors (basically,
trimers), and metal working
83 -- 15.3
952.4
~ubr icants~~. When incorporated into adhesives, dimerised fatty
acids offer the
following benefits:
PA-
75 - 23.5
I --
(i) better bond stability due to flexibility that comes with the
dimer building
block which allows the absorption of mechanical stress, even at
very low
1.484 353.6
temperature.
953.6
(ii) better adhesion due to the improved flow behaviour between
the adhesive.'
i Pour point (OC) 1 - 1 0 -4 -4 1.481
(iii) Durability of the adhesive bond is improved due to dimer's
intrinsic water .
1.484
repellant, and its inertness towards dxygen and heat.
DFAs are widely used in polyamide hotmelt adhesives as
conventional
polyamide tends to have too high a melting point to be of
practical value as hotmelt
adhesives. The incorporation of DFA allows the synthesis of
polyamides within a
practical range of melting points.
-
They are also used to manufacture improved biomedical apparatus
which $are
essentially intended to be affixed, or adhered in any manner to
a patient's skin such
as: electrode bandages,. iontophoresis devices, surgical tapes,
transcutaneous
electronic nerve stimulation (TENS) devices, and ostomy
appliances. These
adhesives have advantageous skin compatible properties56. These
biomedical
adhesives are pressure sensitive and are inherently tacky,
hydrophobic, skin
compatible, adhesive composition.
The fatty dimer acids are also used in the production- of dimer
soaps (ie dimer
acid salts), dimer esters, dimer amides, dimer glycols, dimer
diisocyahates or
essentially any other acid derivative which is sufficiantly
reactive5". The dimeric
product of sesame oil has curative properties on skin lesions
such as chronic
dermatitis, eczema, and tenia57.
1 . I 0 THERMAL POLYMERIZA~ION OF DRYING OILS
Drying oils in general are mixed glyceryl esters of oleic,
linoleic, linolenic, and
eleostearic acid as well as related saturated and unsaturated
acids. The process &
thermal polymerization involves heating drying oils in a n inert
atmosphe.re to
temperatures in the range of 300°C and above. The amount of
unsaturation
decreases rapidly, and their density and viscosity increase44.
Under this condition, the
polyunsaturated CI8 fatty acids present in the oil is dimerized
to form mixtures'of C36
dibasic acids with some trimers (CS4) and higher oligomers.
Small amounts of
monomeric fatty acids which include Cqa saturated, unsaturated
and structurally
modified fatty acids are alsc present.
Although catalysts are not necessary, their use is to lower the
temperature and
time necessary for the dimerisation to occur. The reaction
passes through the process
of isomerisation ,of the double bonds in the polyunsaturated
fatty acids. Scheme 1.7
-
shows a typical alkaline isomerisation process of linoleic acids
which gives a mixture
of 9, 11 and 10, 12 di,enes with many minor components. This is
produced
commercially for use as conjugated linoleic acid (CLA).
CI-I~ ( C I I - I ~ ) ~ C I I = CH - CI-I = CH - CI I ~ ( C ' I
1 , )~( '001 I 10,13- Octadccadienoic acid
CI I3 (CI-12)jCI-I = CI-I - CH2 - CI-I= CI-I(C1 12)7C001-I . f
9, 12- Octaclecadienoic acid (Starting ma~erial)
( C H ~ ) ~ C I I~ - CH = CI-I - CH = CH - ( C I - I ~ ) ~ C ~ O
I - I 9,11- Ocladecadienoic acid
Sclicnlc 1.8 Isomeriation of Lholeic Acid
The dimerisation process is predominantly a bimolecular additive
reaction of
the unsaturated fatty acid radical where one double bond of a
thermally generated
conjugated form reacts directly with one or more other
non-conjugated double bonds
in a Diels-Alder type of reaction. This is shown in schemes 1.8
and 1.9for gylcerides
45 ' containing linoleic acid group. The sequence of reaction
for the thermal
polymerization of methyl linoleate in the bulk has shown that
the isomerisation stage is
the rate controlling stage in'the thermal polymerization of
drying oils. The sequence of
reactions is given in scheme 1.8.
The observations that can be made of the change that take place
during dimerisation,
when treated under the above conditions may be summarized in the
following
manner:
(i) a relatively slow rearrangement of pentadiene group to
conjugated diene
groups.
-
(vii)
the rapid reaction of the conjugated diehes with another
linoleic group in
the same triglyceride, the product containing two double bonds
for two
octadecadienoic acid groups.
with the rapid decline of linoleic radical content, formation of
another
product by the union of a conjugated diene with a single
ethenoic group not a
part of a pentadiene system and containing one double bond, for
each 18-
carbon radical.
migration of a hydrogen atom from a methylene'group, wI3ich is
between two
double bonds or adjacent to a single double bond, to 'a carbon
atom in a
conjugated diene, thus, linking two 18-carbon units by a
carbon-carbon
crosslink.
completion of chemical changes in unsaturated molecules at the
stage the
viscosity is about 20 poises, followed by a slow, but steady
decrease in linoleic
acid content. This is accompanied by a small increase in
monoethenoic
unsaturated compounds. Finally, a rapid increase in viscosity
with little change
in the constitution of acid groups occurs.
formation of new dimeric groups between different triglycerides
or linkage of
dimeric groups within a triglyceride molecule to similar groups
in other
N - C Relatively slow N+N-D
Minor reactions N+D-T
where N = Non- conjugated linoleate, C = Conjugated linoleate, D
= dime!., T = Trimer
Scheme 1.9 Sequcnce of thermal polynierisation
-
=it1 \ Non-conjugated Iinoleic acid
Scheme 1 .I 0: Diene reaction'of two Conjugated (9 , 11)
linoleic Acids
1.1 1 ISOMERISATION AND DlMERlSATlON CATALYSTS
The faster rate at ,which conjugated esters are polymerized
compared to the
, non-conjugated esters led to the search for means of
introducing conjugation into
dryinglsemi-drying oils. This process is referred to as
isomerisation and is facilitated
by the introduction of certain catalysts into the thermally
polymerized oil. It is evident
that, isomerisation of the double bonds, from the na:urally
occurring cis- to the
conjugated trans- configurations of fatty acids, precedes
dimerisation. By so doing,
the process time and temperature of dimerisation is highly
reduced and the crude'
product, which usually contains about 60 - ?o% dimmer, is
formed46. The dimer
content can be enriched to obtain products up to 97% by standard
separation
technique such as vacuum distillation, recrystallization, urea
adduction, liquid and size '
-
exclusion .chromatography .etc. However, only the distillation
method has wide
commercial application. The rest are used for laboratory
analytical purposes.
Useful isomerisation catalysts claimed by various patents
include nickel,
aluminium, alkalis, phosphoric acid (H3PO4), dioxonitrate ,
sulphur (iv) oxide,
nnthraquinone, phenanthre~e, silicon, selenium, montmorillonite
clay, boron triflouride
(9F3). Anyaogu ( 2 0 0 3 ) ~ ~ reported the following as useful
isomerisation catalysts:
iodine, sulphur, bromine, hydrogen fluoride (HF), sodium
hydrogen sulphate
(NaHS04), etc. They are used to effect isomerisation ,in the
polyunsaturated, non-
conjugated fatty acid, to its conjugated form and to lower the
temperature and time,of
dimerisation. The neutral clay and water mixture, for example,
is reported to reduce
process cbnditions to 230 - 260°C at 2 - 4 hours when conducted
under pressure47v
In another case, S U Z U ~ ~ ~ ~ , employed synthetic
silica-alumina to catalyze
dimerisation, and reported a process' condition of 290 - 310°C
at 1 - 2 hours of
dimerisation. ~imerisation, catalysed by iodine appears to be
highly efficient with
respect to time reduction4'. Wang and ~ a o ~ ' reported that by
the addition of just
about 0.0025% of iodine crystal, it is possible to optimally
effect the dimerisation of
soya bean oil at 350°C in just 20 minutes under argon
atmosphere. chappelow6
states that if selenium or oxides of nitrogen and sulphur are
used in the cis - trans
isomerkation (elaidization) of oleic acid, there is virtually,
no positional isomerisation.
However, cis-trans isomerisation of linoleic acid and linolenic
acid leads to conjugated
double bonds.
1 .I 1 .I SULPHUR AS AN ISOMERISATION AND DlMERlSATlON
CATALYST
Cyclooctasulphur is, the most stable form of sulphur at standard
temperature
and pressure (STP). The molecules are in the solid, liquid and
gaseous phases. The
cyclooctasulphur can crystallize in several different lattices
to display the structure of
-
three solid allotropes to include: orthorhombic (a - sulphur),
monoclinic (P - sulphur).
and y - monoclinic suphur.
The orthorhombic a - sulphur is the STP form of cyclooctasulphur
whereasthe
monoclinic p - sulphur is formed at 94.4OC from a - sulphur and
it contains six Sa I
molecules i.e. 48 atoms in a unit cell with a melting point of
119.6°C . The y -
monoclinic suphur is an allotrope which can be obtained from
solutions of cycloocta-S,
and from its melt.
The monoclinic P - sulphur is a yellow crystalline solid with
boiling point
(1 19.6OC), it is in equilibrium with a liquid mixture of
unknown composition. Around
159.4OC, almost all properties of liquid sulphur (e.g cycloocta
- S, P - sulphur) suffer a
discontinuity for example, the change in density and most
importantly, viscosity
amongst other physical properties. At 250°C, sulphur is still
yellow, but the absorption
is now due to separation of the spectrum of SF, with that of
plastic sulphur (polymeric
sulphur) which is dark yellow. Solid polymgric sulphur, obtained
by quenching a thin
film of liquid sulphur at 200°C in liquid nitrogen, remains
yellow. The absence of deep '
dark colour in solid and liquid polymeric sulphur at 160 and
200°C remains a puzzle,
because the free-radical chains, according to all known theories
should be deeply
co~ou red~~ . At higher temperature, above 250°C, the viscosity
of liquid sulphur
decreases rapidly, and almost black. Simultaneously, it becomes
extremely reactive.
Thus in all, ,except the most pure sulphur (99.999+ %), the
colour effect is
obscured by irreversible darkening due to reaction of organic
impurities. The critical
properties indicate that liquid sulphur, as well as the
vapour,.con~ist essentially of S2,
S3, and S4, with very little S5, S6, S7 where S8 and S p being
the most stable form sf the
small sulphur molecules whose ground sthte depicts that of 02.
The sulphur atoms (Si
and S3), have their physical and chemical properties similar to
those of oxygen (02)
-
and ozone (03) respectively. Their excited electronic levels
also correspond to those
of oxygen and ozone.
In non-polar liquids, cyclooctaslphur and other rings dissolve
,at room
temperature without decomposition. However, it should be noted
that.above 150°C,
thermal dissociation of the ring by homolytic scission induces
free radical reactions,
recognizable by the colour change. With H2S, Sulphur forms
reactive system, as it
does with Iodine, Chlorine, Arsenic, etc. From the above, the
mechanism for the
isomerisation and polymerization of drying oils catalysed by
sulphur can be seen to
follow a free radical process of hydrogen abstraction by sulphur
radical after
undergoing homolytic scission. This is represented in scheme 1 .
I 0 (i, ii and iii).
The isomerisation reaction below (scheme 1.10) is likely to
occur at the
temperature range of 160-200°C after the formation of sulphur
free radicals. The
rationalization of the dienoic radicals and thermal
decomposition of the fa'tty acids
occur simultaneously in the system and lead to the formation of
free acids. The 9,lO-
and 10,12- isomers of octadecalinoleic acids amongst other fatty
acids (oleic) are the
products of isomerisation which is followed by a deep colour
change in the mixture at
the temperature range as proposed by eat^'.:
The conjugated linoleic acids produced therefore undergo
dimerisation through
different mechanisms. These are: the Diels-Alder mechanism as
shown in scheme 1.8
and 1.9 above, the free radical mechanism'occasioned by the
numerous free radicals
produced by the catalysts' (sulphur) during isomerisation, which
take part in the
dimerisation reaction. Owing to the high temperature employed in
the process, free
radicals are generated through hydrogen abstraction and C - C
scission especially at
the very high temperature of dimerisation. These mechanism (as
shown in scheme
-
1.8 above) therefore enhances the formation of a mixture of
mono-cyclic, bicyclic and
acyclic dimer fatty acid products as in scheme 1 .I 1.
There is catalyst regeneration, insitu, in the reaction mixture
which can be
recovered by purification using either gel permeation
chromatography or distillation
methods.
( i ) SS A 4S2 Formation of liquid hlotloclinic Liquid sulphur '
sulphur ~~-slllpllll~
> 1 50°C ( i i ) S 2 - 2s:': I-Iomolytic scission 01'
Sulplir~r ' Sulphur radical liquid sulphur
(iii) Hydrogen abstraction by sulphur radical and
isomerisation:
Migration of the hydrogen atom during isomerisation occurs
predominantly at
the methylenegroup53. Thus:
(CI 12)7 -COOH I I 2-H
/I CH CH
9, 1 1 -0ctadecalinolei'c acid 10, 12-Octadecalinoleic acid
Scheme 1.11 : Mechanism of Sulphur catalysed isomerisation of
linoleic acid moiety
-
CHAPTER TWO I
LITERATURE REVIEW
2.0 HISTORICAL REVIEW
Thermal polymeriation of drying oils co when luld be dated prior
to 1940
~ i n o ( 1 936)65, ~ a ~ ~ e l m i e r ( 1 933)6! Steger and
Van ~oon (1 934)67 Brod, France, and
~vans(1940)~' gave definite evidence that the methyl or ethyl
esters of drying oil acids
polymerized when heated, to form polymer which appeared to be
largely dimer. A
more detailed study of the polymerization product of the methyl
esters from olive,
dehydrated castor, soybean, linseed, and tung oils was carried
out in 1940 by Bradely
and ~ohnson~'. Their work exposed the fact that the predominant
reaction of thermal
polymerization is dimerisation leading to.dibasic acid esters.
The esters of conjugated
acids dimerised much more rapidly than those of the
non-conjugated acids. The
dimers of dienoic acid esters are similar in physical and
chemical constants, whether
from conjugated or non-conjugated acids. Their physical and
chemical constants
support earlier conclusion that the dimerisation is a 1,4-diene
addition, resulting in a
monocyclic cyclohexene structure. These constants also support
the Scheiber theory
that isomerisation from the non-conjugated double bonds to the
conjugated form
precedes polymerization (cheiber, 1946)~'. Bradely's work also
stated that the dimers
of trienoic acid esters are similar to one another, whether from
conjugated or non-
conjugated acids. Their ~hysical and chemical constants suggest
a bicyclic structure I
formed by an intramolecular ring closure which follows the diene
reactions.
During dimerisation, side reactions occur, creating unsaturated
hydrocarbons
and esters of low molecular weight. ~ h e s e ' fragments may
unite with monomers to
form polymer intermediate whose molecular weight is between
normal monomer and
dimer. Besides, Bradely and ~ohnson(1940)~~ reported that
trienoic acid esters '
-
polymerization have low iodine values and high densities
indicating a possible cyclic
structure.
In 1941, pure dimer of methyl linoleate was isolated by
fractional molecular
distillation of the heat polymerized methyl esters of dehydrated
castor oil acids by '
Bradely and ~ohnson~' . In spite of confirming the general
nature of the str,ucture, the
possibility of various isomers of the proposed cyclohexane
structures was recognized.
It was shown that a certain proportion of trimer was also
formed'in the process ,
Drying fat was polymerized under the influence of sulphur
monochloride by
Kaufman et al (1 9861~' and was discovered that the action of
sulphur monochloride on
drying or semi-drying oils brought about increases in molecular
weight, probably by
the mechanism of formation of dithrane rings. Also, in 1938,
Kappelmeier polymerjzed
linseed and perilla oils, which contain glycerides of linoleic
and linolenic acids with no
conjugated double bonds. I t was shown that a higher temperature
or a longer time
was required for their polymerization to be completed.
The isomerisation of linseed oil was studied by Bradely and'
Richardson
(1942)~~ on heating them for 2- 3.5 hours at 25OC with 37.5 -
50% aqueous sodium
hydroxide (NaOH). It was found that linseed oil acids gave 41%
of doubly unsaturated
and 8.2% of triply unsaturated conjugated acids. It was
concluded in the study that
large excess of alkali, slightly increased the rate of
isomerisation and that the amount
of conjugation was decreased by long heating of the drying
oil.
Blekkingh (1957')~~ studied the effect of catalysts on double
bonds migration
and found that migration of the double bond during isomerisation
occurred
predominantly at the methyl group when nickel catalyst is used.
He stated that no a
migration was observed with elaidinization catalysts (SO2, Se,
N2, and 03) or with .
alkali isomerisation.
-
The effect of temperature on the polymerization and
isomerisation of
dehydrated castor oil was studied by Chowdhury and Mukherji
(1951)73 to regulate the
polymerization during bodying and to enrich the product with
conjugated isome'rs.
They dbselved that at' 250°C and abbve, polymerization
predominates over
isomerisation and the optimum temperature for the formation of
9,11 - linoleic acid at
the expense of 9,12 - linoleic acid was 200°C.
~ i l v e r s t o n e ~ ~ studied the dimerisation and
polymerization of unsaturated fatty
acids by heating a mixture of dehydrated castor oil fatty acids
in the presence of
0.0001 - O.lwt% iodine at 250 - 350°C to give dimer-polymer
mixtures. Using
0.0005wt0h iodine and heating the mixture for 2hours at 280°C he
obtained a product
of 34.6% yield with a dimerl polymer ratio of 4.1.
Den offer ( 1 9 7 0 ) ~ ~ carried out dimerisation of oleic acid
with a montmorillonite
catalyst, to examine sor~ie important process parameters e.g.
amount of catalyst, I
water content, stirring intensity, reaction time and pH. A yield
limit of approximately
60% (dimers and trimers) was obtained; the remaining 40% of the
product consisted
of cis-and trans mono-Unsaturated fatty acids. lnfra red (IR)
spectra of these
monomers showed the presence of small amounts of stearolactone
groups which
probably resulted from skeletal isomerisation. These results
indicate that a fairly large
amount of saturated fatty acids is formed probably by hydrogen
transfer; in which
case, dienoic acids could be formed which are readily dimerized
to cyclic dimers.
Dimethyl esters of dimeric fatty acid was studied by ~uj ihana
and Masayoshi
(1971)'~ by continuous addition of methyl hydroxide to
unsaturated fatty acid methyl
esters (safflower fatty &id) having two or more double bonds
at 120 - 320°C. Thus,
the safflower fatty acid containing 76.3% methyl
dimerized in the presence of 150g terra alba for 2
linoleate (acid value 0.3) was
hours at 220°C with continuoQs
-
addition of 642g of 9g0/0 methyl hydroxide to give 1450g dimeric
fatty acid dimethyl
esters (acid value 1.6, saponification value, 195.2).
Dsouza Cletus and' Ramaiah ( 1 9 7 6 ) ~ ~ studied the
polymerization of sesame oil
in the presence of Pb3O4. The dimeric products upon topical
application had curative
properties on skin lesions such as chronic dermatitis, eczema,
and tenia.
Studies on the dimerisation of castor fatty acids and their
methyl esters as well