ABSTRACT
This
research work gives the description of how the saponification value of some
selected natural oil can be determined. A definite amount of each sample of oil
was reflexed in a given volume of standard ethanolic potassium hydroxide
solution for 45 minutes. On completing the saponification reaction, the
ethanolic KOH was titrated against a standard HCL solution.
From
the obtained result, palm kernel oil had the highest saponification value and
would therefore be the best natural oil for soap – making. The value obtained
for palm oil was below expectation. This might be due to lack of proper
purification during its preparation.
TABLE OF CONTENT
Title page
Certification
Dedication
Acknowledgement
Abstract
Table of content
CHAPTER ONE
Introduction
Types of oil
Occurrence and extraction
General physical characteristics
General chemical characteristics
Analysis of fats and oils
Fats as food
Uses of oils and fats
Aim of the project
CHAPTER TWO
Experimental
CHAPTER THREE
Results and Calculations
CHAPTER FOUR
Discussion
REFERENCES
CHAPTER ONE
INTRODUCTION
Saponification
is a routine laboratory and industrial reaction of particular interest as most
soaps are being manufacture by the saponification of animal fats.
Saponification
is an alkaline – catalysed chemical reaction in which an ester splits to form
an alcohol and a salt of carboxylic acid. The term arose from the alkaline
hydrolysis of fat to yield soaps, hence soaps are potassium or sodium salts of
long chain carboxylic acid. (William,
1976).
Saponification
is made effected by boiling the ester in an aqueous alkali (KOH or NaOH)
solution. The free carboxylic acid can be recovered by neutralizing the mixture
via mineral acid.
O O
R – C – OR1 +
Na+ OH-+ H2O R –
C – O – Na+ + R1
- OH
ester Alkali carboxylate Alcohol
the
insoluble carboxylic acid in solution, can be separated from the solution. The
glycerol or other alcohol is separated from the water by distillation.
(Fernandez, 1980).
Types of oil
Naturally,
there are four types of oily substances
1)
Natural oils and fats: the commonly called oils and fats
are the ester of glycerol, known as glyceries and are with higher fatty acids.
they are the glycerides of stearic, palmittic and oleic acids. The acid usually
have normal chain and even number of carbon atoms. In butter fat, a few ester
if acids with odd number of carbon atoms and with branched chains are also
present. Glyceride are contained in chaulmoogra oil with cyclic structures.
2)
Mineral oils: these are the mixture of various
hydrocarbon, occurring inderneathe the earth surface. Some important ones are petrol, gas oil,
paraffin oil and petroleum which we obtain kerosene. They generally possess unpleasant odour.
3)
Essential Oils: They are liquids, possessed with
pleasant smell and they occur in plants. e.g. kiltus oil, rose oil, lemon oil,
olive oil, turpentine etc. The main constituents are the turpenes with the
groups of aldehyde, ketone, alcohol, esters etc.
4)
Waxes: These are examples of simple
lipids. They are esters of higher fatty acids with monohydric alcohol of high
molecular weight.
They are
insoluble in water and difficult to hydrolyse; these properties explain their
value as protective layer on leaves, stems, fruits, on fur of animal and the
integument of insects (Cutidle). They
differ from paraffin wax which is a mixture of alkanes, they dissolve readily in benzene, carbon
disulphide and light petroleum.
The major
difference between oils and fats is that oils are liquids at ordinary
temperature, as fats are solids at ordinary temperature. The incorporation into glycerides of low
molecular weight fatty acids and high molecular weight acid, containing
unsaturated groupings, result in fats with low melting point, hence the
incorporation of saturated, high molecular weight fatty acids produce
triglycerides which are semi – solids or solids at room temperature. Examples of fats are oleic acid (C27H31COOH),
Linolenic (C18H29COOH) acid while fats can be exemplified
as; (C11H23COOH) lauric acid, (C13H27COOH)
myristic acid etc.
The system
for naming is based upon the constituents of the fatty acid e.g. glycerol
tristerene contains three stearic acids and Oleodiesterene contains one oleic
acid and 2 stearic acids.
In stearic
and palmittic acids, the glyceride of unsaturated oleic acid is a liquid
(TEWARI, 1980). Usually, the same
glyceride may contain more than one acid residue. Such a glycerode is a ‘mixed glyceride’.
These are present in naturally occurring oils and fats. Examples are Oleo – palmito – stearic,
palmito distearin which are in lard, the fat obtained from pig.
CH2O.CO.C17H38 CH2O.OCO.C17H35
CH.O.CO.C17H31 CH.O.CO.C17H35
CH2O.CO.C17H35 CH2.O.CO.C15H31
Oleo
palmito – stearin Palmito
– distearin.
Occurrence and Extraction
Oils and fats are mainly found in
seeds of plant while they are present under the skin in tissues and muscles of
animals.
Extraction:
The following processes are generally used for extracting fats and oils from
the parent materials. (TWEARI, 1980).
i.
Pressing: In this, vegetable fats and oils –
containing seeds are crushed by rollers and pressed in hydraulic press or
continuous expellers. The oil separates
leaving behind the ‘oil cake’ which is used as cattle feed. The produced pressed cake is heated and
further pressed to give second grade oil which contains undesirable components
and a strong odour.
ii.
Rendering: This is the usual process for
extracting animal fats. The animal
tissues are chapped off and boiled with water or steam. The fats melt and float on the surface whence
it is withdrawn.
iii.
Solvent Extraction: This usually follows the pressing
process. The hot – press cake is crushed
and extracted with organic solvents such as carbon tetrachloride, benzene,
petroleum ether etc to obtain the remaining oil.
Refining: The
fat or crude oil undergoes treatment with a little alkali to neutralize free
acid and for coagulation of any colloidal impurities present. Warming follows at 70 – 80OC with
animal charcoal or plaster of paris.
This is called bleaching. Half an
hour later, the decolorized oil is filtered, superheated steam will then be
passed through it. The oil is quickly
cooled and withdrawn.
General Physical Characteristics
Oils
and fats are colourless liquids or solids, lighter than water and immiscible
with it, but due to impurities, they may yellow or brown. They are freely
soluble in organic solvents such as benzene, petroleum, ethyl ether e.t.c. they
are non-volatile but decompose on strongly heating which produces irritating
odour of acrolein. Their agitation with water in the presence of soap results
in emulsions. Instead of soap, gelatin or ther emulsifiers may be used.
Animal
fats contain cholesterol, an unsaturated alcohol, likewise vegetable fats
contain phylosterol (TEWARI 1967).
General Chemical Characteristics
1.
Drying: certain oils, containing glycerides
of unsaturated acids with two or three double bonds such as linolenic (3 double
bonds) and linoleic acids (2 double bonds), have the properly of slow
absorption of oxygen from air and polymerizing to form a hard transparent coating
which are used in making paints and oil cloth. This is known as drying and the
oils are drying oils.
Drying takes
place much more readily, as compared to glycerides containing non-conjugated
double bondsif the acid contains conjugated system of double bonds e.g
eleostearic acid present in tung oil.
2.
Rancidification: this is another property (chemical)
which explains its nature on long storage. When it is in contact with air and
moisture, oils and fats undergo slow decomposition and develop unpleasant smell.
This process is called rancidification. Rancidification is believed to take
place with the accompany of the following chemical changes.
a) Enzymatic
Hydrolysis: hydrolysis of lower fats and oils take place producing bad
smelling lower fatty acids when there are actions of micro-organism and enzyme.
b) Aerial oxidation of unsaturated acid is
produced during hydrolysis, forming aldehydes and ketones with unpleasant
odour.
c) Oxidation of saturated acids produced as
a result of hydrolysis, followed by decarboxylation forming ketones possessing
unpleasant flavour (Jane, 1979) .
3.
Hydrolysis: dilute acids hydrolse fats and oils into glycerol
and fatty acids. Hydrolysis may also be brought about by alkalis or superheated
steam or enzymes e.g lipase.
O
CH2O C R1 CH2 OH O
CHO C R2 + 3H2O H+
OH- CH2 OH + 3RCOOH
lipase (fatty
acid) O
CH2O C R3 CH2 OH
(glycerol)
The
hydrolysis of oils and fats by alkalis is known as saponification, the result
being formation of soaps and glycerol.
4.
Hydrogenation: Fats contains less of unsaturated
glycerides than oils and so are solid or semi solids at ordinary temperature. Under pressure, if hydrogen is passed through
them in the presence of suitable catalyst, usually finely divided nickel or
Roney Nickel, the unsaturated glycerides are converted into saturated
glycerides and the oil attain a solid or
semi – solict form. It can then be known
as vegetable ghee or margarine.
CH2O.CO.C17H33 CH2O.CO.C17H35
CHO.CO.C17H33 3H2
CHO.CO.C17H35
Ni/175 – 190OC
CH2O.CO.C17H33 CH2O.CO.C17H35
Olein (m.p = 17OC) sterim (m.p = 71OC)
Hydrogenation is
mentioned in improvement of colour, odour, taste. Hydrogenated oils are used as ‘vegetable’ or
‘vanaspat ghee’ and also for the manufacture of margarine, candles and soaps.
In some
developed countries, large quantities of ‘vanaspat ghee’ are prepared from
cotton seed. ‘Vanaspat ghee’ with melting
point below 73OC is dutable for human consumption, as it is easily
assimilated in the digestive system, but those with melting point 37O
and above are unfit for use as they remain unmelted in the stomach and cause a
number of intestinal disorders.
