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