Introduction
Chemical refining
usually refer to a neutralization process where alkali reacts with the free
fatty acid (FFA) in the crude oil to form oil insoluble soap and water. Usually,
seed oil with high FFA might need to go through this neutralization process
before going for physical refining. This process can give almost complete
removal of FFA and some of the impurities. Neutralization plant is a small
plant but it may be the most complicated plant in vegetable oil refinery
complex. This is because there are lots of parameters that must be control
properly in order to get the neutralized oil quality and minimize the oil
loss.
In recent year, researches have
showed that phospholipase are able to perform the degumming process. Enzymatic
degumming offers advantages of lower oil loss, eco friendly process. However,
the expensive production cost is main concern.
Process Description
In general, the
crude soft oils will be going through a degumming process before going to
chemical refining. The crude soft oil will be mixed with phosphorous acid in a shear
mixer at 80 – 100 OC to convert the non-hydratable phospholipids to
hydratable phospholipids. After this, the crude degummed oil is sent to the
caustic neutralization process where a base is added in to neutralize the FFA
in the crude oil. In most cases, caustic soda (NaOH) is used as the
neutralizing agent. This is because it is much more effective compared to other
weaker alkali. However, it has a disadvantage of saponifying the neutral oil. Saponification
process is the reaction of a metallic alkali (base) with a fat or oil to form
soap. Equation below shows the chemical
reaction of neutralization process.
RCOOH + NaOH à
RCOONa + H2O
There
are two common technologies in neutralization process namely short mix and long
mix process. Long mix process is usually
used in United State while short mix process used widely in Europe and many
other areas worldwide. Long mix process usually applied to good quality crude oil
with low FFA which allows the neutralization process to occur at a much lower
temperature, lower caustic dosage and longer retention time. Long mix process
will reduce the caustic consumption but will give higher oil lost to
soponification if the caustic dosage is not control properly. This is because
of the longer contact time. On the other hand, Short mix process requires a
higher concentration of caustic, higher temperature and shorter resident time.
In return, short mix process gives advantages of eliminating the potential of
large losses and suitable for poor quality crude oil with high FFA.
The mixture with neutralized oil,
gum and soap stock is sent to a separation process consists of centrifugation
and water washing. First, the mixture is sent to a centrifuge to separate soap
stock (heavy phase) from neutralized oil (light phase). Hot water is added in
to the light phase to further reduce the soap in oil content. The neutralized
oil is fed into the vacuum drier for drying the moisture level to 0.05-0.1 %
before sending to storage. After neutralization process, NSBO, NRSO will be send
to physical refinery while NMZO and NSFO will go through a dewaxing process
before send to physical refinery.
The soap stock from the
centrifugation process will go through acidulation process. The soap stock is
mixed with sulfuric acid in a splitting tank and agitated with steam or air.
After this, the mixture is left for cooling and separation. Acid oil will be
collected at the top while acid water is collected fro the bottom of each
splitting tank. Acid water will be sent to effluent plant.
RCOONa + H2SO4 à RCOOOH + NaSO4 
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