1.
NEUTRALISATION
The efficiency
of Neutralising operation is determined by the least possible
loss of Neutral oil in soap stock. As such, in this operation
the quantity of original oil is reduced by its free fatty acid
content plus quantity of neutral Oil in soap stock plus impurities.
The constitutes refining loss or neutralising loss and is generally
two to two and half times the free fatty acid content of the
oil. After draining of the soap stock the oil which is now free
from fatty acids and impurities is washed repeatedly with hot
water to free it from any caustic soda and soap. These dissolve
in the wash water, which is drained from the bottom after settling.
Neutralisation also removes bulk of the colour of the Crude
Oil and makes it lighter.
2.
GUM CONDITIONING & NEUTRALISATION
The phosphatide
portion of oil is either removed or conditioned in this process
by addition of some additives under specific condition. The
most common additive for this purpose are phosphoric acid and
citric acid. A specified quantity of any one or mix of such
additives is mixed in the oil charge for a specific period and
process parameters. This cause a separation of phosphatides
from oil and are removed after certain settling time. Some times
these separated gums are not directly removed but with soap
stock formed during neutralisation. The oil mass is then neutralised
with Alkali for removal for free fatty acid in the form of soap
stock. This soap stock is removed from oil mass by gravity separation
method. For removal of Alkali traces. Oil is washed with hot
water. The chemical reaction involved in this operation is as
follows: R-COOH+NaOH à RCOONA + H2O
3.
BLEACHING
The neutralised
washed oil is then taken for second step in refining i.e. Bleaching.
In this operation, the oil is taken in Cylindrical vessel provided
with agitator called `Bleacher' and kept under vacuum and heated
upto 90oC with steam. The moisture from oil is thus evaporated
and oil becomes dry. Then dry is treated with Bleaching earth
(fuller's earth) and Carbon. These a outs absorb most of the
residual colour free the oil remaining after Neutralisation.
The mixture of oil and bleaching agents is filtered through
a standard plate and frame press for separation. The clear oil
obtained is bleached oil and is very much lighter in colour
than the neutralised oil. In this operation, the colouring pigments
in oil are adsorbed by certain bleaching agents under specific
conditions. The oil is finally filtered for removal of bleaching
agents. The oil charge is dehydrated under vacuum to avoid any
further detoriation due to oxygen. A specified quantity of bleaching
agents is added that acts as adsorbing material for colouring
matter. This externally added bleaching material is removed
by filtration.
4.
DEODORISATION
The oil after
bleaching is practically pure, but contains minute quantities
of original odoriferous matter. Also the chemicals used during
neutralisation process in a cylindrical vessel called `Deodoriser'.
The Deodoriser is kept under very high vacuum and the bleached
oil is taken in it. The oil then heated at high temeprature
200C with high pressure steam and open steam is passed through
the oil. Under high vacuum and temperature the open steam leaves
the deodoriser is completely bland and free from any odour and
taste. This oil is then cooled and clarified through a Filter
Press to get sparkling oil. The filtered oil is then packed
into standard size tins and sealed. The vitamins `A' and `D'
are added to this filtered oil if necessary before packing.
This step takes care of the odour of the oil. The purpose of
deodorisation is to make oil blend and tasteless. The oil charge
is taken to very high temperature under max attainable vacuum.
The volatile materials are evaporated off with some carrier
(commonly direct steam). In this process the peroxide value
of oil is brought down as minimum as possible. In order to increase
the storage life of refined oil antioxidants may also be added
under specified conditions. This oil is passed through micro
filter to give a crystal clear appearance to the refined oil.
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