Course: BFM 202 Biodiesel Production

Lecture

Biodiesel Production Processes and Separation
Credits
BFM 202 Biodiesel Production Unit 3 Lecture has been adapted from "ENGY 131 Unit 3 Transestrification Made Simple" by Southeastern Illinois College.

ENGY 131 Biodiesel Production course content by Southeastern Illinois College is licensed under a Creative Commons Attribution 3.0 Unported License. Except where indicated otherwise.

Biodiesel Production Processes and Separation

Biodiesel producers come in many sizes. There's the home-brewed biodiesel
for those who prefer self-sufficiency, and then there are the world's largest
producers that include:
- Neste Oil in Singapore produces 800,000 metric tons per year from
vegetable oil, meat fats, and food industry waste products.

- In Houston, TX, Dynoil LLC is building the largest biodiesel refinery in the
world with an output capability of 1.5 billion gallons of biodiesel annually.

- In Brazil, Eco Energia uses soybeans to produce 225 million gallons of
biodiesel per year.

- Dominion Energy Services, LLC is building their Canadian plant in Alberta to
produce 100 million gallons of biodiesel per year from wheat and canola oil.

- In Chesapeake, Virginia, the SE Energy plant is capable of producing 320
million gallons of biodiesel per year.

In order to understand the production process, it is necessary to
understand the various types of plants. Please see also these resources:

Additional Resources
Reactors for Biodiesel Production
by Drs. Brian He & Jon Van Gerpen, University of Idaho
National Biodiesel Education Program

Biodiesel Reaction and Separation Technology
by Christina Borgese and Marc Privitera
PreProcess, Inc.

Batch Reactors

In smaller biodiesel plants, batch reactors are used to produce single batches.
The batch reactor is a tank with an agitator where the alcohol, oil and catalyst
are mixed. These plants are used for small-scale biodiesel production yields
and do not allow for more than one tank at time to be processed.

Continuous, Large-scale Production

Larger biodiesel plants are considered to have an output of greater than
4 million liters per year and use a continuous-stirred tank reactor (CSTR) or
plug-flow reactors. Larger facilities employing either the continuous stirred-tank
reactor or plug-flow reactor, use low temperatures and atmospheric pressure
which requires longer reaction times. Additional equipment can be installed to
accelerate the reaction by increasing the temperatures and pressure, however
it is normally cost prohibitive to do so.

The reaction begins by combining an alkali-based catalyst, approximately
80% of the total alcohol used, and a highly-refined soybean oil, canola oil,
or high grade restaurant-waste oil. This mixture is agitated for about 1 hour at
60 degrees C. Using the continuous process, the mixture then flows into a
second reactor vessel where the remaining 20% of the alcohol is added and
the reaction is completed. CSTR requires sophisticated process monitoring
and controls while employing in-line quality control measures to ensure
ASTM specifications are met.

This reaction is known as transesterification and produces methyl esters,
glycerin, and water.

Glycerin

Gravity pulls the heavy glycerol to the bottom of the settling tank and a
centrifuge may be used to speed the process and remove the excess methanol.
Excess methanol is removed since it causes the reaction to stabilize, therefore
it is removed before it slows or reverses the reaction.

Next, water washing the biodiesel removes the remaining catalytic material,
salts, methanol, soap, and free glycerol. However, free fatty acids (FFA)
remains in the biodiesel.

Oil and methanol can react without a catalyst and eliminates the water
washing step however this process uses significantly higher temperatures
and large quantities of methanol with large investments in additional equipment.

Upon separation of the glycerol, the biodiesel (methyl esters) is neutralized
and passed through a falling film evaporator or vacuum flash to strip out the
remaining methanol. Both of these technologies will be covered more completely
in a later lesson. The remaining catalyst in the biodiesel is neutralized by adding
acid which results in water-soluble soaps and free fatty acids. This neutralization
step reduces the amount of water needed for the process and limits the
formation of emulsions.

The glycerol leaving the separator is made up of 50% glycerol with methanol,
most of the original catalyst, and soap. Glycerol has no value in this form,
disposal is difficult and, due to the methanol content, must be treated as
hazardous waste material.  The glycerin by-product still contains soap and
catalytic material which is neutralized with an acid to a purification level of
about 80-85%.

This crude glycerin is then sold to refineries for use in pharmaceuticals,
cosmetics, printer's inks, cake and candy, antifreeze, soaps, and plastics.

It also used as an emulsifier in mayonnaise, butter, margarine, and cigarettes.