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Degumming of Feedstocks – Part 2
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You are here: Home / Biodiesel / Degumming of Feedstocks – Part 2
Degumming of Feedstocks – Part 2
08/16/2018 By R.C. Costello
1.
Overview
The Degumming of biodiesel feedstocks process is necessary prior to the esterification and
transesterification processes. Typical crude degummed oils have had their Hydratable Phospholipids
(HPLs) removed by a simple water wash process. We typically accomplish this at the crushers facility.
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Degumming of Feedstocks – Part 2
However, a typical soybean oil contains both hydratable and non-hydratable phospholipids (NPL’s). The
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water
wash process
does not remove
theseUS
NPLs and they remain in the oil. The typical concentration of
NPLs in water degummed oil is 200 ppm.
The presence of these NPLs in the oil feed to the Transesterification may potentially cause two problems.
First, the finished biodiesel may not pass the ASTM specification for phosphorous. Secondly, the
phospholipids act as emulsifiers, and their presence can lead to an inefficient phase separation. This is turn
leads to lost product in the glycerin phase, and excess soaps and glycerin in the biodiesel phase. For these
reasons, a Degumming unit can be installed at the biodiesel plant.
2.
Acid Degumming Section
Oil is pumped through a plate and frame heat exchanger where the temperature is heated up In the outlet
piping, a mixture of 85% phosphoric acid/15% water is added to the oil. The acid concentration is to be 500
ppm. The acid and oil are mixed in a high shear mixer. Upon exiting the mixer deionized water may be
added if necessary to maintain a good water balance. After the water addition, the oil flows to an agitated
mix tank. There the residence time allows the acid to react with the NPLs, converting them to HPLs. Citric
acid may also be used.
A very small quantity of 20% caustic solution is added to the oil through a static mixer. The caustic will
assist in hydrolyzing the phospholipids. A very slight excess, approximately 50 ppm, is added just to be
sure enough caustic has been added. This caustic will convert an equivalent amount of FFAs to soap.
This mixture flows to a surge drum for the centrifuge. In the centrifuge the water, gums and HPLs are
removed as the heavy phase and the oil comes out as the light phase. The heavy phase flows into a
collection tank and is pumped to the wastewater system. The oil undergoes further processing. At this
point, the phosphorous level had been reduced from 200 ppm to 50 ppm.
3.
Absorbent
An absorbent is added to the oil. The absorbent contains approximately 65% water. Remaining water must
be removed before the absorbent is removed in a filter. Therefore, the oil flows to a vacuum dehydration oil
drying system. This will reduce the water level from 2 – 3% to approximately 500 ppm.
The oil and absorbent is pumped to a vertical frame pressure filter. The phosphorous level in the finished oil
is below 10 ppm. Solids from the filter are dumped into a hopper and can be land filled.
An alternative to the absorbent is a bleaching clay. However, the absorbent does not retain oil and does not
become a flammable solid as with bleaching clays.
4.
Safety System Considerations
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Degumming of Feedstocks – Part 2
The elimination of bleaching clays for purifying the oil results in a much safer materials handling operation.
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US autooxidation occurs since the bleaching clays retain oil.
There
have been
numerous landfillCONTACT
fires where
Don’t forget to check in with us next week for Part
3 on ESTERIFICATION!
COSTELLO implements one-of-a-kind process
engineering with exceptional knowledge and
experience, process safety support and superior
customer service.
Contact us today for your biodiesel project needs!
Filed Under: Biodiesel
Tagged With: biodiesel, ChemCad, chemical engineering, chemistry, Costello, degumming, engineering solutions
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